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cosmic soup

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jnrvjebr

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I'm blue, da ba dee daba die, da ba dee daba die, da ba dee daba die

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In a three dimensional universe how does the concept of a two dimensional fabric of space-time apply? Does the fabric have more dimensions? If so, how does the fabric work and what is the impact of gravitational waves of this fabric on matter?

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Are individual particles themselves stretched/compressed by gravity waves or is the space between them changed? If the space is changed how can the space in between photons be changed?

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How does gravity affect photons (that is, bend light) if photons have no mass?

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How does gravity affect photons (that is, bend light) if photons have no mass?

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Light has no mass but we see it bend when around sources with high masses due to gravity

This is because the object with the high mass (ex. Black hole) warps the space time through which the photons (light particles) travel

The mass does not pull on the photon directly

The concept of space-time warping because of high mass sources can be thought of as a bowling ball on a mattress. The ball acts as a high mass object like the sun and the mattress represents space-time. (space-time is 4d but it's harder to imagine that)

When you place the ball on the mattress, it creates a sort-of dip, deforming the surface of the mattress. The same is true when a high mass object (a star for example) is sitting in space time. The star deforms the space time around it.

If grid lines were drawn on the mattress, the grid lines would deform around the ball. The lines would no longer be straight, they would curve toward the ball. The same is true for a star in space-time. Space time would curve toward the ball

Imagine if a marble (representing photon/light) was rolled along the mattress in a straight line and it came too close to the bowling ball. The marble will curve because the mattress is deformed. The same is true when light is traveling through space-time.When light comes too close to a huge object, it encounters warped space-time and curves because of that. It does not curve because it's being pulled by gravity.

Gravity affects the path photons are traveling on, not the photon directly

All objects with mass warp space-time around them.

Objects with smaller masses have an effect on space-time, just not enough for it to be noticeable

Objects with larger masses, the more pronounced the warping of space-time is

To answer the question: photons are affected by gravity, just not directly. Individual light particles (photons) are not stretched or compressed but instead, space-time is. The movement of photons are affected by space-time, and space-time can be warped by gravity, therefore light/photons are affected by gravity

Next Question: How and why does gravity warp/deform space-time?

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While it is true that photons have no mass, it is also true that we see light bend around sources with high mass due to gravity. This is not because the mass pulls on the photons directly, but instead because the mass warps the space-time through which the photons travel.

Imagine a bowling ball on a mattress. The ball is a massive object - say, the Sun - and the mattress represents space-time, in which it sits. (Of course, space-time is four-dimensional, but it's a bit harder to imagine that!) When you place the bowling ball on the mattress, it deforms the surface. If a grid were drawn on the mattress, you would see the grid deform, so the straight lines of the boxes were no longer straight. The same is true for a star sitting in space-time - the star deforms space-time around it, causing it to curve toward the star.

Bringing the universe to your door. We're excited to announce Astronomy magazine's new Space and Beyond subscription box - a quarterly adventure, curated with an astronomy-themed collection in every box. Learn More >>.

Now imagine a marble; this represents a photon. If you roll the marble in a straight line on the mattress and it comes too close to the bowling ball, the marble will curve because the mattress it's traveling on dips and curves around the bowling ball. This is what happens to light traveling through space: When it comes too close to a massive object, it encounters warped space-time and curves not because it's being pulled by gravity, but because the space-time it's traveling through is curved, so its "straight" path becomes a curved, bent one.

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How does gravity affect photons (that is, bend light) if photons have no mass? | Astronomy.com

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LIGO Experiment Explains Differences in Effects of Gravity Waves on Light & Baryonic Matter

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LIGO Experiment Explains Differences in Effects of Gravity Waves on Light & Baryonic Matter

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Gravity waves stretch/compress wavelength of light, but very small

Light stretch/compress factor has little to no impact on experiment conducted → beams will travel different distances varied by the gravitational waves; LIGO only cares about these distances that the light travels

During LIGO Experiment:

Design: Two 90 degree arms have exact same distance for laser to travel → Laser should take same time to travel said distance → Total Destructive Interference, no light emerges; Proves Gravity waves are not real and Universe is quiet

Experiment: Gravitational waves interfere by changing the distances of the arms in an alternating pattern; As one arm elongates while the other contracts, vice-versa → Oscillation persists until the gravitational wave dissipates

Laser beams pass interferometer regardless of distance to travel; As opposed to canceling out constantly, lasers sometimes interfere to produce a brighter light

Result: Laser interference varies between Total Constructive and Total Destructive during gravitational waves; Flickers of light appear out of interferometer

Varying patterns produced by the misaligned lasers shows 2 things:

Change in length of arms during light’s journey

Frequency at which the arms changed lengths

Experiment proves that any effects of wavelengths of lasers is miniscule compared to the change in the arms → so much so that it can be ignored in calculations altogether

Experiment also proves that gravity waves stretch/compress the spaces in between particles → stretch/compress wavelength of light changing its period → Lengths of arm changes but the physical mass of the arm is the same → Only the volume changes

Next Question:

How do Gravitational Waves interact with other forms of energy or matter in the universe such as dark matter? Why do some forms of energy or matter have a bigger stretch/compression factor than others?

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Below are answers to some of the most frequently asked questions about LIGO.
Why did you build LIGO in Washington and Louisiana?
Since LIGO was planned as a 2-site observatory, we had to find two locations about 3000 km apart that shared many characteristics. Their separation alone limited the possible places where the interferometers could be located in the continental United States. Other factors considered when looking for pairs of sites included:

Finding places that could accommodate such enormous instruments. Effectively, LIGO would require several square kilometers of open land.

The land had to be flat to reduce the amount of ground leveling required to build the 4km long arms to keep construction costs reasonable.

The sites had to be seismically quiet and stable so they wouldn't be constantly shaken up by nearby earthquakes.

The sites needed to be relatively far from big metropolitan areas, but not so far that all of LIGO's infrastructure (water, electricity, access roads, etc.) had to be built from scratch, and importantly, not so far that it would be hard to find housing or to find people who wanted to live in the area (about 40 people work full-time at each location).

The sites had to have easy access to an airport, so visiting scientists and engineers could easily access the sites, and so staff would have easy access for travel to other LIGO facilities (like MIT or Caltech).

There were other factors, but these were among the biggest and the most challenging to find in pairs. Ultimately, twelve sites were selected in 11 states, and 7 different pairings considered (including considering optimal placement should a third LIGO detector be build in Europe). After two years of study and evaluation, in 1992 the Washington and Louisiana sites were selected as the homes for LIGO's detectors.
If a gravitational wave stretches the distance between the LIGO mirrors, doesn't it also stretch the wavelength of the laser light?
While it's true that a gravitational wave does stretch and compress the wavelength of the light in the arms ever so slightly, it does NOT affect the fact that the beams will travel different distances as the wave changes each arm's length. And the only thing that matters to LIGO is how far the beams travel in each arm before being merged once again.

LIGO is designed so that as long as the distance the laser beams travel is exactly the same in both arms, they will make their trips in exactly the same time. When recombined, the beams totally destructively interfere with each other. In other words, they cancel each other out and no light emerges from the instrument. When this is occurring, we know the interferometer and its components are stable and the Universe is quiet.

Suddenly, a gravitational wave passes! What happens?

A gravitational wave causes each of LIGO's arms to change length in an opposite fashion, i.e., when one arm gets longer, the other gets shorter. Then they switch--the longer arm becomes the shorter arm and the shorter arm becomes the longer arm. This opposite oscillation in length occurs for as long as the waves pass, one getting longer while the other shorter, then vice versa, and so on, until the waves dissipate.

As this is happening, the laser beams are making their way through the interferometer unaware of the fact that the distance they have to travel before meeting up again is changing. A beam traveling through a longer arm, therefore, takes a little longer to return to the merger point than the beam in the shorter arm, which means, when they do meet up again, their waves won't necessarily just cancel each other out. Instead, they pass through each other, sometimes canceling out, but other times adding together to make a brighter light. Back and forth the waves pass through (*interfere with*) each other as the arms themselves change length, causing light interference that ranges fully between totally destructive to totally constructive. In other words, instead of nothing coming out of the interferometer, a flicker of light appears.

While this sounds like a mess, it's not. In fact, during a gravitational wave's passage, the resulting interference pattern itself changes in-step with the changing lengths of the arms. Looking at the changing interference pattern, LIGO computers decipher exactly how the arms of the interferometer itself must have changed over the time of the wave's passage to create the patterns that emerge. In this elegant way, the changing times of arrival of the laser beams from each arm cause a changing interference pattern that betrays changes in the lengths of the arms caused by the gravitational wave!

This varying pattern of misaligned laser beams observed and recorded over the time it takes for the gravitational wave to pass tells us two things: 1. How much the arms changed length during the light-beams' journeys and, 2. the frequency at which, or how quickly the arms changed lengths (longer then shorter then longer, etc.) in response to the gravitational wave. This information can tell us what generated the gravitational wave in the first place.

This is why the wavelengths of light have no bearing on the all-important interference pattern. The effects of the length changes in the arms far outweigh any change in the wavelength of the laser, so we can virtually ignore it altogether.
How will LIGO know that a signal in the data really came from an event in space? Can you ever be 100% certain, even when multiple labs measure the same vibration?
LIGO uses several techniques to sift through the din of vibrational noise to confirm a gravitational wave detection. Some of these are:

Measuring all known noise sources (e.g., earthquakes, winds, ocean waves, traffic, farming activities, even molecular vibrations in LIGO's mirrors) with seismometers, magnetometers, microphones, and gamma ray detectors, and then filtering out the vibrations caused by these sources from our data.

Looking for identical, simultaneous signals from multiple detectors world-wide (LIGO, Virgo, GEO600). This rules out noise sources which are local to a given detector. The more detectors that feel the same vibration at "the same time" (accounting for travel-time between detectors), the more certain we are that the source of the vibration was not local.

Constantly comparing the signals coming out of the interferometers with theorized patterns of gravitational waves generated by known phenomena (these patterns are derived directly from the equations of general relativity).

Comparing the time of arrival of a possible gravitational wave event with an electromagnetic (EM) event seen by EM observatories.

These methods have proven hugely successful. Perhaps most significantly, the last technique mentioned above was first used in August, 2017 when LIGO detected its first pair of merging neutron stars. The arrival time of the gravitational waves coincided with a short gamma ray burst detected by an orbiting observatory. Within tens of minutes, data from LIGO, Virgo, and the gamma ray detectors were combined and the source of the event localized to a very small patch of sky. Within just a few hours, astronomers, systematically imaging the galaxies in that patch of sky, spotted a new star-like object in a galaxy 130-million light years away, marking the first time a gravitational wave event was also observed by electromagnetic astronomers.

As further test of LIGO's abilities, LIGO's estimate of the distance to this event (information also encoded in the interference pattern) was in near-perfect agreement with estimates independently-acquired by EM astronomers. This provided irrefutable evidence that LIGO is truly detecting gravitational waves from distant regions of the Universe. Our confidence will only increase with our numbers of detections, especially as more are also observed by our electromagnetic partners.

All that being said, it bears noting that no measuring device is 100% accurate. At LIGO, we like to be more than 99.9999% sure that a signal wasn't just caused by some Earthly noise before we announce a true detection to the world.
Why do you need to create a vacuum to get accurate data?
There are two main reasons why LIGO needs to operate in a pristine vacuum:

1. To reduce sound vibrations. Sound waves are vibrations of molecules which, when they bounce off of obstacles, cause other things to vibrate (like your eardrum). Because the signals that LIGO needs to feel are so unimaginably delicate, even a few molecules bouncing off of LIGO's mirrors could cause vibrations that could mimic or mask a gravitational wave signal. This is why so much effort goes into getting rid of as much air as possible with LIGO's vacuum system. Since sound cannot travel in a vacuum (no molecules means no sound), LIGO's vacuum environment prevents sound waves from inducing vibrations in the mirrors. The vacuum provides a super quiet, nearly molecule-free environment in which the detector can operate and 'listen' for gravitational waves.

2. To reduce light scattering. LIGO uses lasers to measure the distance between the hanging mirrors (we call them "test masses"). Unfortunately, laser light can be scattered, refracted, and (potentially) absorbed by molecules. Even a few oxygen or nitrogen molecules in the path of one of LIGO's laser beams could cause the beam to scatter and create a 'flicker' that could mimic a gravitational wave signal. Think of twinkling stars. Stars twinkle because the light from the star gets bounced around as it encounters pockets of air of varying density in our atmosphere (caused by different temperatures and humidity levels). The photons themselves get scattered, reflected, and refracted as they travel to your eye, which perceives the effect as twinkling. In the vacuum of space, stars don't twinkle because there's no atmosphere to impede the photons. So if LIGO's beam tubes had air in them, the photons in the laser beams would bounce around (in essence, twinkle), making it impossible for us to distinguish a gravitational wave flicker from just some scattered light. To eliminate this problem, LIGO's vacuum tubes have 8 to 10 times fewer atoms and molecules than the vacuum of space! This ensures that any observed vibrations in the laser light are not caused by scattering by atoms or molecules in the beam tube.
How do you prevent the mirrors from detecting vibrations of the Earth?
LIGO uses two basic strategies to shield the detectors from Earthly vibrations. They are referred to as "Passive" and "Active" vibration isolation systems. Each one has many components, but the basics are pretty simple.

Passive Vibration Isolation
LIGO's Passive Vibration Isolation system prevents vibrations from reaching the mirrors ("test masses") that reflect the laser beam, which tells us whether or not a gravitational wave has passed. It does this using some fairly basic physics concepts: principles of pendulums, and the Law of Inertia.

Pendulums are excellent vibration isolators. Try this at home: Using the image at left as a guide, tie four heavy washers together in a line, each one separated by an equal length of string (this is analogous to LIGO's 4-segment or "quad" suspension). Hold the string at the top and rapidly shake it back and forth by a small amount to simulate a vibrtation from the environment around LIGO. This mimics a high-frequency environmental vibration. Notice that the lowest mass (in LIGO this is the test mass) moves very little, if at all, compared to the top one. This is because each segment in the pendulum absorbs the vibration it 'feels' from above and prevents it from being transmitted to the segment below. In this way, this system "isolates" the bottom mass from all the "noise" you created above it. If you swing the pendulum more slowly, the lower mass does move, however. This menas that LIGO is more susceptible to lower-frequency environmental noise, which can drown out low-frequency gravitational waves.

But there's another factor that can affect how still the bottom mass remains as you shake the top: the weights of the things you tied together in your pendulum. This is where the Law of Inertia comes into play. The Law of Inertia states that the heavier something is, the more energy it takes to move it and also to stop it from moving (a big truck accelerates and slows more slowly than a compact car.) To take advantage of inertia, each 'node' in LIGO's quad suspension chain (or the bolt or washer in your homemade suspension system) is a hefty mass in itself; possessing a lot of inertia that makes it resist forces like environmental vibrations. In this way, each mass in the chain of masses absorbs some of the vibrations coming from above and isolates them from the mass immediately below. A little may leak through to the next mass, but then its inertia absorbs a little more, isolating them from the next one, and so on. The result is that each subsequent mass in the chain senses fewer and fewer external vibrations that started at the top.

How effective can this really be? In LIGO's suspensions, this process reduces any vibrations present at the top of the suspension by 100-million times by the time they reach the test mass! Yes, there are other ways within the quad suspension that LIGO engineers have found to reduce vibrations. But in large part, it is achieved through the processes described above.
Active Vibration Isolation
As good as it is, on its own, the passive isolation system is still not good enough to enable LIGO to detect gravitational waves. To get to that level, the passive system is itself contained within an active vibration isolation system. In "active" isolation, a number of sensors in and near LIGO's interferometers detect vibrations from the environment (wind, earthquakes, traffic, etc.) and send feedback signals to actuators that physically move the entire passive isolation suspension system around to counteract those vibrations before they can reach the top level of the quad suspension. It is the same basic principle by which noise-cancelling headphones operate. This active system cannot remove all vibrations, however, and what little makes it to the quad suspension is taken care of by the passive isolation system, which further reduces those vibrations by 100 million times!

Working together, the Active and Passive Isolation Systems keep LIGO's mirrors perfectly still and primed to detect gravitational waves. Impressively, all of this effort has made LIGO's interferometers the most sensitive measuring devices ever built.

For more about how these isolation systems work, read Vibration Isolation.
How does LIGO use the data that it collects?
In 1916, Albert Einstein predicted the existence of gravitational waves in his theory of general relativity. Mathematically, these waves were inferred for the first time in 1974 when Russell Hulse and Joseph Taylor Jr., of the University of Massachusetts, discovered the first binary pulsar system. when Hulse and Taylor measured the rate of orbital decay between these two objects, it perfectly matched what was predicted by general relativity. This was a beautiful confirmation of the existance of gravitational radiation, and the work won Hulse and Taylor the Nobel Prize in Physics in 1993. Nevertheless, direct sensing of the waves eluded us. That changed in 2015 when LIGO became the first scientific instrument to physically sense the passage of a gravitational wave from the depths of space. The more detections LIGO makes, the more questions we will answer about physics and the Universe in general. Since each source of gravitational waves plays a unique "tune", by styding the form of each wave as it passes through the detectors, we can undersand what generated the wave. The known possibilities are:

Merging (coalescing) black-holes, or neutron stars, or a neutron star merging with a black hole
The gravitational waves detected by LIGO on September 14, 2015 were generated by the merger of two massive black holes. Less than two years later, on August 17, 2017, LIGO detected colliding neutron stars. These two events in particular, made scientific history. To date, LIGO has confirmed the detection of 83 binary black hole mergers, two binary neutron star mergers, three neutron star/black hole mergers, and 2 mystery mergers, where one object was a black hole and the other had a mass placing it in the so-called 'mass gap' between the masses of known neutron stars and the masses of known black holes. This object was either the heaviest neutron star ever detected or the lightest black hole ever detected. Unfortunately, there's no way to know definitively which it was. But LIGO likes mysteries.

The rotation of a bumpy neutron star - if a neutron star is not a perfectly smooth sphere, it too will emit a regular pulse of gravitational waves. These are expected to be exceedingly weak and very difficult to detect, but we are looking nonetheless.

The explosion of a lumpy star (if a star isn't perfectly spherical when it explodes), called a supernova

Motions of matter and energy that occurred right after the Big Bang

Of course, there's always a chance we'll detect something we can't yet explain. This would occur if our detectors (and our partners around the world) detect a signal that doesn't look like anything scientists have predicted or previously modeled in simulations.

LIGO's results will greatly augment the knowledge-base of astronomers who observe in the electromagnetic spectrum (e.g., radio waves, infra-red, X-rays, gamma rays). In some cases, LIGO's data may contain key pieces of information needed to answer these big questions:

How many neutron stars and black holes reside in a typical galaxy?

What happens when a massive star collapses?

How do compact binary stars form and evolve, and what can they tell us about the history of star formation rates in the Universe?

How are binary systems containing these objects created in the first place, and how often do they collide?

Are these systems the source of the observed but mysterious short gamma ray bursts we often see? (LIGO's detection of colliding neutron stars in August 2017 provided clear evidence that at least some short gamma ray bursts are, in fact, caused by colliding neutron stars.)

How "lumpy" are supernova explosions and neutron stars?

Do black holes really affect space and time in the way Einstein's theory predicts?

Can gravitational waves tell us anything about the first instants after the Big Bang?

In addition, although LIGO will be looking for gravitational waves caused by astronomical phenomena, LIGO's data will also contribute to the broader physics and engineering communities and will help to answer fundamental questions of physics, such as:

What are the properties of gravitational waves?

Is general relativity the correct theory of gravity?

Is general relativity still valid under extremely strong gravity conditions?

Are nature's black holes the black holes of general relativity?

How does matter behave under extremes of density and pressures

Last, but not least, LIGO is already making contributions outside of astronomy and astrophysics by advancing knowledge in the following fields:

Quantum measurement/high-precision spacetime metrology

Optics/quantum optics/laser systems

Geology and seismicity

Materials science and technology

Cryogenics and cryo-electronics

Computing

Ultrahigh vacuum technology

System engineering and project management for high-technology science

Chemistry (LIGO's detection of colliding neutron stars resulted in a completely new understanding of the origins of heavy elements in the periodic table, answering a long-standing question about how such elements were formed in the quantities we observe in the Universe at large.)

Although LIGO was designed to listen for one elusive, almost undetectable phenomenon, its broader impact on science has already been significant. Read more about LIGO's impact on technology in LIGO's Impact on Science and Technology
How often do gravitational waves that LIGO can detect pass by the Earth?
Nobody really knows yet. Strong gravitational waves are believed to occur rarely enough that LIGO did not detect any in its first years of operation between 2002 and 2010. However, after a major upgrade that took 4 years to complete, LIGO detected its first gravitational wave on September 14, 2015, within days of turning on the new and improved detector. In other words, in a few days, LIGO accomplished something that was not achieved in 8 years of previous operation! That bodes well for future detections.

On average, over its first three observing runs and a total of 25 months of active observing, LIGO's detections have been made at a rate of 3.6 per month. The 90 confirmed detections made so far suggest that these kinds of events are relatively common. Once LIGO's detectors reach their maximum sensitivity, they could be detecting gravitational waves at a rate of more than one per week. The only way to refine the estimates of how often detectable gravitational waves pass, is to keep making detections!

To that end, it is expected that within 10 years, five gravitational wave detectors like (and including) LIGO will be operating around the world. When that happens, we should be ready to detect gravitational waves 24 hours a day, 7 days a week, 365 days a year. Who knows what multitude of wonders await!
If current estimates say that merging neutron stars generate gravitational waves in a galaxy once per 10,000 years, how many events could we currently detect per year?
LIGO detected its first neutron-star merger on August 17, 2017 in an event that was also observed around the world by electromagnetic astronomers. Once LIGO reaches its most sensitive state, about 40 merging neutron stars per year may be detected.

You might now ask, "how is this possible if such events are so rare in our galaxy?"

If LIGO couldn't sense events happening outside of our own galaxy (beyond about 80,000 light years), we would probably have to wait a very long time to detect a gravitational wave from a binary neutron star (BNS) merger. But LIGO's advanced detectors can sense thousands of times farther away than this, and are primed to detect gravitational waves originating in galaxies as far as 200 million light years away (the August 2017 BNS event occurred in a galaxy 130 million light years away).

In its first three observing runs, LIGO, working alongside its international partner, Virgo in Italy, confirmed 90 gravitational wave detections. Of those, 83 were black hole mergers, and only five were confirmed to involve neutron stars (two BNS mergers and three neutron star/black hole mergers). Two more involved the merger between a black hole and a mystery object that was either an unusually massive neutron star or an unusually light black hole (we can't say for sure).

What's really important to LIGO is the v olume of space it 'samples'. LIGO and Virgo (and hopefully also KAGRA in Japan) ultimately hope to be able to detect merging neutron stars out to ~600-million light years from Earth (180 megaparsecs*). This translates into a volume of space of over one-BILLION cubic light years! A volume of one-billion cubic light years centered on our own galaxy contains about one-million Milky Way type galaxies. So with a million entire galaxies to probe, we expect to detect (on average) about 40 neutron-star mergers per year. Whatever the outcome, the numbers of detections will tell us a lot about the population of binary neutron star systems in the universe.

* A parsec is a unit of distance equivalent to 3.26 light years. A megaparsec is one-million parsecs.
If gravitational waves exert such tiny changes on Earth, why are they important?
Gravitational waves probably won't be useful in helping us understand processes on the Earth, but they will help us understand processes that occur in outer space, such as the collisions of pairs of black holes. We've already learned a lot:
From our first detection of merging black holes we learned:
(a) binary black holes actually exist (they were only theorized before), and

(b) black holes with masses about 30 times that of the Sun also exist (astronomers are working to understand how to make such black holes)

Neither of these facts were known before LIGO's historic first detection.
From our first detection of merging neutron stars we learned:
(a) that at least one source of short gamma ray bursts is merging neutron stars, and

(b) that merging neutron stars are, in fact, responsible for generating the quantities of heavy elements that we observe throughout the Universe. This single detection resulted in revealing the origin stories of many elements in the periodic table. (To learn more about this amazing result, check out this news story.)

The knowledge that astronomers gain from measuring gravitational waves could also improve our understanding of space, time, matter, energy, and their interactions. In so doing, we could revolutionize humanity's knowledge and understanding of the nature of existence itself. Also, LIGO's impact on science in general will reach far beyond just the fields of astronomy and astrophysics. For more on that topic, visit Why Detect Them? in Learn More.
What kinds of information can gravitational waves provide?
Fundamentally, and directly, GW contain information that reveals the masses and properties of things like black holes, neutron stars, and their binary systems.

More esoterically, gravitational waves will provide a test of Einstein's theory of general relativity under extreme conditions of gravity where it has never before been tested. They will also give us more information about the unimaginably dense form of matter that makes up neutron stars. Neutron stars contain more matter than our Sun packed into a sphere the size of a city--about 10 km (6 mi.) across. These objects are so dense and their gravity so immense that a person weighing 150 lbs. (68 kg) on Earth would weigh 21,000,000,000,000 lbs. (9,545,000,000,000 kg) on a neutron star! Packed so closely and densely together, the matter that makes up a neutron star is called " degenerate matter", which is not well understood. LIGO will help improve our understanding of degenerate matter.

Gravitational waves will also tell us about how many objects like black holes and neutron stars exist in the Universe. They will give us insight into what happens during some of the Universe's most violent explosions. Someday, gravitational waves might even allow us to understand what was happening in the earliest moments of the Universe when it was so dense and hot that no light could move around. Any photons emitted during that time were long ago absorbed by a plasma of hot ions, but gravitational waves from that era could travel directly to Earth with little interference from the matter in the Universe.
What discoveries does LIGO hope to make?
LIGO's historic 2015 detection of two colliding black holes, and its paradigm-shifting detection of colliding neutron stars in 2017 has opened up a new field of astrophysics. Whether gravitational waves are detected from colliding black holes, supernovae, remnant radiation from the Big Bang, or even just the tiniest imperfections on rapidly spinning ultra-dense neutron stars, the amount of potentially new fundamental knowledge of the extreme Universe that we stand to gain is enormous. Even better, as with any science, the best rewards come from discovering things we never knew about, could never have imagined, or simply do not understand. As with every other time we've looked up at the sky in a different way, be it through infrared, X-ray, or gamma-ray goggles, we will almost certainly be inspired and intrigued by what we didn't expect to find.

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If so, how does the fabric of spacetime work and what is the impact of gravitational waves of this fabric on matter?

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If so, how does the fabric of spacetime work and what is the impact of gravitational waves of this fabric on matter?

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Sources

1. Gravitational wave astrophysics at UBC - https://gravitational-waves.phas.ubc.ca/research/

2. A Spacetime Surprise: Time Isn’t Just Another Dimension - https://www.forbes.com/sites/startswithabang/2020/08/12/a-spacetime-surprise-time-isnt-just-another-dimension/?sh=6430bc947dc8

Content:

The model of spacetime being 2D or 3D is generally used for common understanding. In reality it is 4D. 3 spatial dimensions, and 1 chronal.

The four dimensional fabric of spacetime works in a very weird way, leaving the spatial dimensions all interacting with each other easily, and the chronal dimension needing a conversion to go from one to the other.

Essentially you have time using one set of units and space using another set of units, to get from time to space you need to convert from the units that mean space, (m, in, etc.) to units that mean time (c, s, ms, etc)

The impact of a gravitational wave is fundamentally the increasing or decreasing of gravity in a localized area (or the stretching/compression of spacetime) If a gravitational wave were to pass over earth, essentially it would squeeze and stretch the areas that align with peaks or valleys of the wave.

Follow Up:

What dimensional axis does spacetime change in when a gravitational wave passes through it (Spatial, Chronal, both or neither)

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In a three dimensional universe how does the concept of a two dimensional fabric of space-time apply?

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In a three dimensional universe how does the concept of a two dimensional fabric of space-time apply?

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Einstein’s theory of relativity disproved the Newtonian fixed space and time.

The picture of masses bending spacetime of fabric is not wholly accurate yet is the most common depiction of it

Spacetime appears to be bent towards the source of gravity and experiments over the last 100 years confirm that spacetime is truly bending, but from pictures it is unconfirmed as to how spacetime is bending

In the common image of a fabric of spacetime being pushed away from the masses, it neglects the fact that gravity attracts things towards it instead of pushing things away

Also, what invisible force is causing the fabric to bend away from the masses - a problem with the image

Gravity is how the general relativity equations are defined in nature and are shaped in geometric ways

Since the experiments back up Einstein’s theory of relativity and are consistent with the equations, the theory must be right but the depictions of it and graphics must be wrong

The author suggests that we imagine space as a massless 3-dimensional grid that curves towards an object in it in set patterns and the curve of space changes when the object moves through it

If the mass of an object increases, the magnitude of the curve of spacetime towards it also increases

Therefore larger masses curve space more than smaller masses and the curved space created by them tells the smaller objects how to move within it

As the universe expands, the wavelength of radiation gets longer

When the universe expands, the distance between any pair of points in space changes according to general relativity theory

Equations that describe the universe are simply equations, they are qualitative, and describe things that people can see

We cannot measure space because we cannot see it but measure the matter and radiation within it to come to conclusions

The three dimensional model of the universe is flawed and is not completely accurate, the best we can do is to visualize the universe in the best possible way

Next question:

How should we think about spacetime? What is the difference between spacetime and space?

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Gravity might have been the first fundamental force ever discovered, but in many ways, it remains the least-well understood. We know that it's always attractive, and that any two masses in the Universe, no matter where they are, will experience its force. When Einstein concocted his general theory of relativity, one of the great advances was to recognize that space and time were combined into a single entity: spacetime. Another was that the presence of matter and energy curved the very fabric of this spacetime, and that curved spacetime, in turn, dictated how matter moved. But is this picture right? Mariusz Wroblewski is skeptical, asking:

I'd like somebody to finally acknowledge and admit that showing balls on a bed sheet doesn't cut it as a picture of reality.

I freely acknowledge and admit it. As ubiquitous as pictures of bent sheets or coordinate systems are, they aren't exactly reflective of the reality we inhabit.

If you've ever seen a picture of a bent, two-dimensional grid with masses on it representing space, you'll know this type of illustration is extremely common. It appears to depict the fabric of space as being curved by the presence of mass, and therefore, any other particle traveling along this fabric will have its path bent towards this gravitational source. The larger the mass and the closer you get to it, the larger the curvature, and therefore, the larger the bending.

This appears to line up, at least intuitively, with the experiments and observations that have taken place to verify and validate General Relativity over the past nearly 100 years. From the bending of background starlight during a total solar eclipse to the effect of gravitational lensing today, at least qualitatively, the picture appears to agree.

But what would such a picture actually imply? If space is like a fabric, how does mass curve it?

It appears as though a mass somehow gets pulled "down" onto the fabric, and then the other particles traveling through that space are pulled "down" by some unseen, mysterious force as well. Clearly, this can't be right, because there's no external gravitation at play at all! Additionally, the grid lines curve away from, rather than towards, the mass, which also can't be right, especially if gravity is attractive.

Gravity simply is, and it's merely that the equations that describe General Relativity are geometric in nature. The idea that mass-and-energy curves space can be right, even though this naive visualization must be wrong.

Instead, we can do better by going to the correct number of spatial dimensions: three.

Imagine, to start, that we have completely empty space. There are no masses nearby; there's no radiation; there's no dark matter, dark energy, neutrinos, or anything else that might cause this space to curve. There's also no intrinsic curvature.

Instead, just imagine that space is flat, static, and empty. If we insisted on drawing a grid, like a mathematical overlay, atop space itself, here's what it would look like.

Now, let's put a mass down in this spacetime. The mass has got to curve spacetime, but it isn't actually a fabric: it's simply the nothingness that makes up the empty Universe itself. The equations of General Relativity tell us how this curvature works, geometrically, but they don't tell us how to visualize it.

One brilliant way to do so, however, is to draw your grid lines as though they represent the force experienced by a negligibly-massed, pressure-free dust particle that's at rest with respect to the new mass. The greater the force that particle would experience, the greater the spacetime curvature. If we were to draw that out, we'd arrive at a very different, potentially more useful picture.

The biggest problem with this picture is that it's difficult to draw!

Thankfully, with the advent of computer animation, we can visualize how space itself curves even with objects in motion. Remember, it isn't actually a fabric, but rather takes up the entirety of the Universe. Spacetime simply is: it's what's left over when we take everything in the Universe away that we're capable of taking away. When we put things like masses down in the Universe, spacetime is still there, too, but its properties are altered by whatever it is that's inside it. The larger a mass you put inside it, the more that spacetime gets curved.

This is true even of a single mass that we simply move around. It could move in a straight line or along a curved path; it could move naturally (because of the motion of other masses) or artificially (because an external force moved it). Either way, it doesn't make much of a difference. The real issue is that as masses move through space, the geometry describing spacetime changes.

As a result, the objects residing in that space, whether they're massive or massless, will change their motion in response to the presence and properties of all the matter and energy within it. John Wheeler's explanation, that mass tells space how to curve, while curved space tells matter how to move, still holds.

You can talk about space as a fabric, but if you do, be aware that what you're doing is implicitly reducing your perspective down to a two-dimensional analogy. Space in our Universe is three dimensional, and when you combine it with time, you get a four dimensional quantity. When it comes to the notion of spacetime curvature, this is what General Relativity refers to.

But under no circumstances should you conceive of space as though it's a material, physical thing; it isn't. This is only a mathematical structure that we can write down equations to describe: the equations of Einstein's General Relativity. The fact that matter and radiation respond to that curvature in the exact ways that the equations predict validates this theory, but it doesn't mean that space is actually a fabric.

We also talk about the expanding Universe in the context that 'the fabric of space is stretching,' even though there is no fabric and it isn't really stretching, or for that matter, changing in any way. What's happening is simply that the distance between any two points in the Universe is changing according to a particular set of rules in the context of General Relativity. Galaxies, like raisins embedded in a loaf of baking bread, expand away from one another. The wavelength of radiation gets longer too, as though the length of the wave crests and troughs expanded away from one another too.

But in reality, there isn't any fabric causing the expansion. In the raisin/bread analogy, the raisins (galaxies) are physically real, but the bread (fabric of space) is just a visualization.

One of the most paradoxical ideas to wrap your head around in all of physics is that the equations that describe the Universe are just that: equations describing things we can physically observe. We can no more observe the 'fabric of space' than we can observe the nothingness of empty spacetime; it simply exists. Any visualization we attempt to assign to it, whether it's a 2D fabric, a 3D grid, or a baking ball of dough, is just that: a human-inspired creation. The theory itself doesn't demand it.

What we can observe, however, are the physical objects - the matter and radiation - present within that space. Those are the entities we can measure, and it is the predictions for the behavior of those objects that enables us to test theories like Einstein's General Relativity. We don't do very well at accepting mathematics for what it is, so we choose to make analogies to help us picture what's happening with the Universe. The success of General Relativity rises and falls with observations and measurements. We can observe the measurable consequences of this theory, but not the actual structure of spacetime, even if it's predicted by underlying theory itself.

All analogies, in this regard, have limitations and flaws. We can choose a visualization that's less wrong, perhaps, than a 2D picture of a bent fabric, but there is no correct answer. General Relativity tells us what the Universe does given matter and energy distributed in a specific way, and our observations are consistent with it. We can choose to visualize it in whatever way makes the most sense to us, but all visualizations are inherently flawed. The best we can do is try to comprehend the Universe, as puzzling as it may be, as it actually is.

Send in your Ask Ethan questions to startswithabang at gmail dot com!

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Ask Ethan: Is Spacetime Really A Fabric?

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In General Relativity, even space and time themselves aren't what they seem.

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How and why does mass warp/deform space-time?

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How and why does mass warp/deform space-time?

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How mass warps spacetime is one question, why is another question entirely.

HOW

To sum up how mass warps spacetime, every particle has a mass, that mass curves spacetime around itself, when you add up a bunch of particles, the curvature also adds up. Essentially you end up with a "gravity well"

As said in the NASA article and also your answer, this can be visualized in a simply way by placing a heavy object on a mattress or a rubber sheet, and then adding another object, they seem to "Attract each other" (gravity isn't an attractive force but something a little more interesting)

This "gravity well" is an area of high curvature, although the typical images of a ball on a grid help to understand, in reality the curve occurs across all axes, creating more of a gravity bubble, really hard to imagine.

WHY

To save everybody's time, we don't know. I spent about 2 or 3 hours trying a bunch of different search terms and even went to ChatGPT to try and get some help. The conclusion is that we know that gravity curves spacetime, we don't know what causes it, the reasons that ChatGPT provided were that it may be due to "string theory" or "quantum gravity" (don't bother, they're a bunch of hodgepodge) but this is the limit of our current understanding.

(My source is not ChatGPT, I was just desperate to see the tool could help me narrow my search, it helped me realize there's literally nothing)

FOLLOW UP QUESTION:

Our best analogy of how gravity works due to spacetime curvature is with the bowling ball on rubber sheet analogy, but in that case, the smaller ball is being pushed by the normal force exerted on it by the rubber sheet

How can less massive objects seemingly accelerate into gravity wells given there's no force pushing it in (Very hard question, start by looking up "geodesics in spacetime" and "can anything completely stop moving")

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I n 1916, Einstein addressed these two contradictions (the instant propogation problem and the equivalence of gravity and acceleration) by reconstructing the theory of gravity. Einstein presented the world with a new understanding of the world- his theory of general relativity. In this theory, space is not an empty void, but an invisible structure called spacetime. Nor is space simply a three-dimensional grid through which matter and energy moves. It is a four-dimensional structure whose shape is determined by the presence of matter and energy. Around any mass (or energy), spacetime is curved. The presence of planets, stars and galaxies deform the fabric of spacetime like a large ball deforms a bedsheet. (This deformation occurs in four dimensions, so the two-dimensional bedsheet is a limited model. Try visualizing these depressions on all sides of a planet to build a more accurate image of this concept.)

When a smaller mass passes near a larger mass, it curves toward the larger mass because spacetime itself is curved toward the larger mass. The smaller mass is not "attracted" to the larger mass by any force. The smaller mass simply follows the structure of curved spacetime near the larger mass. For example,the massive Sun curves spacetime around it, a curvature that reaches out to the edges of the solar system and beyond. The planets orbiting the Sun are not being pulled by the Sun; they are following the curved spacetime deformed by the Sun.

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B. A New Understanding: Curved Spacetime

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I n 1916, Einstein addressed these two contradictions (the instant propogation problem and the equivalence of gravity and acceleration) by reconstructing the theory of gravity. Einstein presented the world with a new understanding of the world- his theory of general relativity. In this theory, space is not an empty void, but an invisible structure called spacetime.

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Newtonian Physics - Space & Time are independent identities

Theory of Relativity disputes Newtonian physics, claiming spacetime exists and separating those was human convention

Relativity is hard to understand → unifies space and time into single entity challenging our current concepts and viewpoints

James Clerk Maxwell → unified electricity and magnetism into theory of electromagnetism(1860s); theory explained light to be an oscillating wave in electromagnetic fields → speed of this wave is significant leading scientists to wonder what particle was moving in a lightwave

To find this particle and support this theory → evidence of why it is undetectable is needed

Albert Einstein suggested that this was due to a misconception of space and time → theory is known as special relativity (fixed, flat spacetime)

Proposed speed of light is the constant at the absolute speed limit → no matter how you are moving or are positioned light will maintain the same speed

Einstein eventually incorporated force of gravity, stating spacetime is dynamic and curved, said curvature being gravity → theory is known as general relativity(dynamic, flexible spacetime)

Relativity → events in spacetime are specified by both space and time coordinates

Duration between two events is not absolute; instead, there are two notions of time

One is a coordinate on spacetime, akin to "6 p.m." and "7 p.m

Another is proper time, measured by a clock carried along the journey between events → depends on path taken, similar to distance

Concept challenges the absolute nature of time in classical physics, highlighting the relativistic nature of time measurement

Major Difference:

Space: straight line is shortest distance between two points

Spacetime: straight path is longest elapsed time between two events; flip from shortest distance to longest time is difference between time and space

Next Question:

What experimental evidence supports the concept of gravity bending spacetime, as predicted by Einstein's general theory of relativity?

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How to Think About Relativity’s Concept of Space-Time | Quanta Magazine

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Albert Einstein’s ideas about space-time aren’t exactly intuitive, and they aren’t exactly Einstein’s, either.

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The commonly used visualization of a two dimensional fabric is incorrect and does not accurately represent our universe

Space cannot be conceived as a physical fabric on which matter resides because space is the absence of matter

Furthermore, this model of the fabric makes it appear as if the mass somehow gets pulled downwards onto the fabric it is bending

This must be wrong because there is no such force pulling every mass in the universe downwards, furthermore, the fabric seems to curve away from the middle of the mass and towards the bottom, which does not account for the masses in all directions (up, down, left, right, forward, back)

To better imagine the space-time fabric, we must account for all 3 dimensions

Instead of a 2d flat grid like we’re used to seeing, the grid would look like an endless mesh of rubix cube- like grids

If a mass was placed in this grid, it would bend the lines from each dimension towards the center of its mass. The greater the mass, the greater the curvature of the lines

Space-time isn’t actually a fabric, it is what's left when we take away everything in the universe like mass, energy and light. It is what makes up the base of the universe

However, an issue arises when masses move through space, the geometry that depicts must be changed to accurately describe what happens

Because of this, the motion of all the objects in that space will change because of the effect of this mass

When we talk about the universe expanding or the space-time ‘fabric’ stretching, nothing is actually expanding, rather the distance between two points in the universe is changing

Even though we can use theories like general relativity to predict what happens in the universe and use the success of these predictions to know which theories are accurate, we still cannot know for certain the true nature of spacetime

Next question:

How is the physics of moving masses different from stationary masses?

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Gravity might have been the first fundamental force ever discovered, but in many ways, it remains the least-well understood. We know that it's always attractive, and that any two masses in the Universe, no matter where they are, will experience its force. When Einstein concocted his general theory of relativity, one of the great advances was to recognize that space and time were combined into a single entity: spacetime. Another was that the presence of matter and energy curved the very fabric of this spacetime, and that curved spacetime, in turn, dictated how matter moved. But is this picture right? Mariusz Wroblewski is skeptical, asking:

I'd like somebody to finally acknowledge and admit that showing balls on a bed sheet doesn't cut it as a picture of reality.

I freely acknowledge and admit it. As ubiquitous as pictures of bent sheets or coordinate systems are, they aren't exactly reflective of the reality we inhabit.

If you've ever seen a picture of a bent, two-dimensional grid with masses on it representing space, you'll know this type of illustration is extremely common. It appears to depict the fabric of space as being curved by the presence of mass, and therefore, any other particle traveling along this fabric will have its path bent towards this gravitational source. The larger the mass and the closer you get to it, the larger the curvature, and therefore, the larger the bending.

This appears to line up, at least intuitively, with the experiments and observations that have taken place to verify and validate General Relativity over the past nearly 100 years. From the bending of background starlight during a total solar eclipse to the effect of gravitational lensing today, at least qualitatively, the picture appears to agree.

But what would such a picture actually imply? If space is like a fabric, how does mass curve it?

It appears as though a mass somehow gets pulled "down" onto the fabric, and then the other particles traveling through that space are pulled "down" by some unseen, mysterious force as well. Clearly, this can't be right, because there's no external gravitation at play at all! Additionally, the grid lines curve away from, rather than towards, the mass, which also can't be right, especially if gravity is attractive.

Gravity simply is, and it's merely that the equations that describe General Relativity are geometric in nature. The idea that mass-and-energy curves space can be right, even though this naive visualization must be wrong.

Instead, we can do better by going to the correct number of spatial dimensions: three.

Imagine, to start, that we have completely empty space. There are no masses nearby; there's no radiation; there's no dark matter, dark energy, neutrinos, or anything else that might cause this space to curve. There's also no intrinsic curvature.

Instead, just imagine that space is flat, static, and empty. If we insisted on drawing a grid, like a mathematical overlay, atop space itself, here's what it would look like.

Now, let's put a mass down in this spacetime. The mass has got to curve spacetime, but it isn't actually a fabric: it's simply the nothingness that makes up the empty Universe itself. The equations of General Relativity tell us how this curvature works, geometrically, but they don't tell us how to visualize it.

One brilliant way to do so, however, is to draw your grid lines as though they represent the force experienced by a negligibly-massed, pressure-free dust particle that's at rest with respect to the new mass. The greater the force that particle would experience, the greater the spacetime curvature. If we were to draw that out, we'd arrive at a very different, potentially more useful picture.

The biggest problem with this picture is that it's difficult to draw!

Thankfully, with the advent of computer animation, we can visualize how space itself curves even with objects in motion. Remember, it isn't actually a fabric, but rather takes up the entirety of the Universe. Spacetime simply is: it's what's left over when we take everything in the Universe away that we're capable of taking away. When we put things like masses down in the Universe, spacetime is still there, too, but its properties are altered by whatever it is that's inside it. The larger a mass you put inside it, the more that spacetime gets curved.

This is true even of a single mass that we simply move around. It could move in a straight line or along a curved path; it could move naturally (because of the motion of other masses) or artificially (because an external force moved it). Either way, it doesn't make much of a difference. The real issue is that as masses move through space, the geometry describing spacetime changes.

As a result, the objects residing in that space, whether they're massive or massless, will change their motion in response to the presence and properties of all the matter and energy within it. John Wheeler's explanation, that mass tells space how to curve, while curved space tells matter how to move, still holds.

You can talk about space as a fabric, but if you do, be aware that what you're doing is implicitly reducing your perspective down to a two-dimensional analogy. Space in our Universe is three dimensional, and when you combine it with time, you get a four dimensional quantity. When it comes to the notion of spacetime curvature, this is what General Relativity refers to.

But under no circumstances should you conceive of space as though it's a material, physical thing; it isn't. This is only a mathematical structure that we can write down equations to describe: the equations of Einstein's General Relativity. The fact that matter and radiation respond to that curvature in the exact ways that the equations predict validates this theory, but it doesn't mean that space is actually a fabric.

We also talk about the expanding Universe in the context that 'the fabric of space is stretching,' even though there is no fabric and it isn't really stretching, or for that matter, changing in any way. What's happening is simply that the distance between any two points in the Universe is changing according to a particular set of rules in the context of General Relativity. Galaxies, like raisins embedded in a loaf of baking bread, expand away from one another. The wavelength of radiation gets longer too, as though the length of the wave crests and troughs expanded away from one another too.

But in reality, there isn't any fabric causing the expansion. In the raisin/bread analogy, the raisins (galaxies) are physically real, but the bread (fabric of space) is just a visualization.

One of the most paradoxical ideas to wrap your head around in all of physics is that the equations that describe the Universe are just that: equations describing things we can physically observe. We can no more observe the 'fabric of space' than we can observe the nothingness of empty spacetime; it simply exists. Any visualization we attempt to assign to it, whether it's a 2D fabric, a 3D grid, or a baking ball of dough, is just that: a human-inspired creation. The theory itself doesn't demand it.

What we can observe, however, are the physical objects - the matter and radiation - present within that space. Those are the entities we can measure, and it is the predictions for the behavior of those objects that enables us to test theories like Einstein's General Relativity. We don't do very well at accepting mathematics for what it is, so we choose to make analogies to help us picture what's happening with the Universe. The success of General Relativity rises and falls with observations and measurements. We can observe the measurable consequences of this theory, but not the actual structure of spacetime, even if it's predicted by underlying theory itself.

All analogies, in this regard, have limitations and flaws. We can choose a visualization that's less wrong, perhaps, than a 2D picture of a bent fabric, but there is no correct answer. General Relativity tells us what the Universe does given matter and energy distributed in a specific way, and our observations are consistent with it. We can choose to visualize it in whatever way makes the most sense to us, but all visualizations are inherently flawed. The best we can do is try to comprehend the Universe, as puzzling as it may be, as it actually is.

Send in your Ask Ethan questions to startswithabang at gmail dot com!

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Ask Ethan: Is Spacetime Really A Fabric?

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In General Relativity, even space and time themselves aren't what they seem.

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What truly is dark matter and how is it affected by gravity?

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What truly is dark matter and how is it affected by gravity?

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What is dark matter?

Creates gravity, not affected by electromagnetic forces (gravity is a weak electromagnetic force)

Dark matter is invisible, inferred matter that does not interact with electromagnetic waves/forces

This means it does not emit, reflect, absorb, or bend when light hits it which makes it hard to spot (we do not have the techno

Scientists believe that the dark matter is the extra mass which generates extra gravity to hold the universe together

We need more experimentation with dark matter to determine more of its properties, our best bet is to run experiments in the world’s largest particle accelerator, the Large Hadron Collider

One theory is that dark matter contains “supersymmetric particles”, ones that are partners to known standard model particles, hypothetically

Many theories describe that dark matter would be light enough to be created in the particle accelerator and escape undetected. If this happened, the missing momentum and the missing energy could be inferred to be dark matter

Seems to outweigh visible matter 6:1 and makes up roughly 27% of the universe

The matter known to mankind makes up roughly 5% of the universe

What is dark energy?

Dark energy is thought to be related to the vacuum in space and makes up 68% of the universe

Throughout the entire universe, dark energy is spread equally through space and time, which means that as the universe expands it is not diluted

Has a global effect on gravity of the universe and not in a specific area due to it’s even distribution

Leads to a repulsive force which seems to quicken the rate of expansion of the universe

Using Hubble law, we can calculate the rate change

Along with other scientific data, Hubble law calculations have confirmed the existence of dark energy in the universe

TL:DR - Gravity has no effect on dark matter for some reason (did not discover it because more experimentation needs to be done to discover the properties of dark matter)

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Remember that light exerts a force so it must have a mass, a force of ~10^-9 Newtons

Therefore light has a mass as well since Newton’s second law states fnet = ma

Gravity affects all masses equally

In the LIGO experiment the photons sent to the end of the 4-km tunnel cancel out with the shrinking of the tunnel and there is total interference initially

New photons are sent out to the end of the tunnel with the mirror and the interference between this new laser and the original laser is measured to find the effect that the gravity wave has on the oscillations of the tunnels in the experiment

If the gravitational wave frequency was too rapid so that the travel time of the second laser could not make it, then the experiment would not work, but the limit has not been reached, making the experiment helpful

Next question:

Does the magnitude of mass of impacted objects increase the effect of gravity's stretch/compression?

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Most recent answer: 02/13/2011

Gravity affects light, yes? Then how come the sun(or stars for that matter) gives out light? it has a very strong gravitational force. shouldn't the light be bent or something? light reaches perfectly to our eyes even if the stars were billions of lightyears away. consequently, does light(or waves) have force?
- Farhan (age 14)
Brunei

Dear Fahran,

You have asked some very interesting questions!

1) Gravity does indeed affect light. All light in the presence of a gravitational source either "bends" or shifts its frequency, but unless the gravitational field is extremely strong it's difficult or impossible to detect with the naked eye. Using precise instruments, we can measure the light from a star and determine this effect, which gives us information about the star's gravitational field.

2) Stars, including our sun, are extremely massive but not massive enough to trap light in its gravitational field. That doesn't mean they do not bend light. Some stars actually bend light so much that, were they not millions and billions of lightyears away, we would definitely notice something funky going on. Neutron stars are the densest stars that we are aware of, and if you were a reasonable distance away from one you would be able to see more than half of the star at any time!

(Source: Freehand!)
That's hopefully a better visual explanation of why you would be able to see more than half of a neutron star. From a "head on" perspective, a neutron star would look like this:

(Source: )

3) There are objects in the universe, however, which have a strong enough gravitational field that no light can escape from a certain region around its center! These objects are known as Black Holes.

4) Light does exert force on other objects, too! That is to say, when you shine a flashlight or a laser on a wall, the light pushes on the wall! Don't get too worried, though. The force is usually very small--powerful lasers exert a force around ~10^-9 Newtons (about the weight of a grain of sand).

I hope this answers some of your questions! You're doing some great thinking.

Sincerely,

John
(published on 02/13/2011)

Follow-Up #1: Gravitational waves and LIGO detection

When a gravity wave affects distance, why doesn't the laser light's path distance in wavelengths become equally affected? In other words, why doesn't the LIGO experiment "cancel itself out" ? Thanks in advance
- Chloe Quayle (age 57)
Southport, UK

Hello Chloe,

A gravity wave, like an electromagnetic wave, has only transverse components. It does not affect distances in the direction of its travel. So if a gravity wave strikes the earth perpendicularly to the earth's surface then the north-south and east-west components will alternatively shrink and expand. The vertical component is not affected. Since the arms of the LIGO detector are aligned in the NS-EW directions they will see oscillations in their differences.

Lee H

On the great question of why the scale changes of the apparatus and the light waves don't just cancel, here's a nice article: http://scitation.aip.org/content/aapt/journal/ajp/65/6/10.1119/1.18578. The basic idea is that if you had a gravitational wave affecting both the apparatus and the pre-existing light-waves in it, the effects would initially cancel, just as you suspected. In the actual set-ups, the light waves are replaced with new ones generated from the lasers, and these new waves are not stretched by the gravitational wave. So the number of wavelengths of these new light waves that fit in the apparatus does change. It turns out that in between the initial effect (light and apparatus change together, so no phase shift) and the final effect (new light waves, full phase shift) there's a gradual onset of the phase shift due to the increased travel time of the waves inside the stretched arm. That has an interesting implication. A LIGO-type detector would not work for high-freqency gravity waves, ones for which the travel time inside the apparatus is small compared to the wave period. The highest frequencies of the recently observed chirps, however, were below that limit. Mike W.
(published on 03/04/2016)

Follow-Up #2: LIGO and gravity wave detection

Background: Detection of gravity waves is done by syncing the interference pattern of two laser beams received at a detector -- the laser beams are reflected off two mirrors set at 90 degrees angle. Gravity waves shorten the path of one laser beam resulting in an out-of sync interference. The amount of out-of sync is then related to the strength of the gravity wave. My question is: Does the out-of sync happen momentarily as the gravity wave hits one of the mirrors, or does it happen continuously as the wave travels the (space) path between the mirror and the detector and, due to contraction of space at the gravity wave front shorten the path until the gravity wave has passed?
- Lee

It's actually kind of the reverse. The wave does nothing to the relative position of a wave crest just reaching a mirror. They stay at the same place as each other. It's later crests that weren't near the mirrors that then have to travel farther in one arm than the other arm and thus don't arrive quite in phase with each other.

We found this question hard until we read this nice link: http://scitation.aip.org/content/aapt/journal/ajp/65/6/10.1119/1.18578.

Mike W.
(published on 04/20/2016)

Follow-Up #3: clarifying LIGO

I checked the link; it was not clear to me -- above my pay grade! Also I could not understand your explanation "... The wave does nothing to the relative position of a wave crest just reaching a mirror. They stay at the same place as each other. It's later crests..." It seems you are talking about two different waves. Are they both gw's (gravitation waves) or laser beam waves? Let me expand on your depiction of the situation (if I understand it correctly): You have a SINGLE gw crest that reaches a mirror and then travels the length of the mirror-detector arm; and you have CONTINUOUS laser beam that is traveling from the detector to the mirror and back to the detector. The gw crest shortens (or lengthens?) the space it occupies. The laser beam is passing through the same crest-space as the gw crest, and at the same speed c as gw, hence it never clears the crest-space. Well, all of these get too complicated to draw a clear picture. Could you respond possibly with several diagrams (as you did earlier in this thread) and show what happens to laser beam as it hits a moving gw crest. The way I see is that the laser beam is affected only when it travels opposite gw. The laser beam traveling in the same direction as gw stays at the same speed (c). Of course the picture is even more complicated since, more than likely, the laser beam and gw travel at some angle with respect to each other -- not along or exactly opposite, the assumptions which I made to keep things simple and to get to the gist of question. Also, even for the laser beam in the opposite direction as gw, doesn't the crest-space contraction and time dilation cancel each other's effect, i.e., slow clock measuring a short path? Here are the root questions: Does the gw-crest contract / dilate the space? How does the laser beam going through this crest get affected? How does the mass (mirror) react to the gw-crest? I know this is a grab bag of questions and possibly requires detailed explanation and may be even some relativistic computations. But then you folks may come up with some commonsensical answer.
- Anonymous

The wave crests we were discussing were those of the light.

As I understand it, the gravitational wave affects (to lowest order) only the spatial coordinates, not the time coordinates. So one arm of the interferometer becomes shorter and the other becomes longer- and so do the light waves initially within those arms. What do we mean by changing "length" in a case where meter sticks change along with everything else? What we mean here is essentially the length of time that it would take a light wave to travel back and forth through that arm. That's what changes. The gravity wave makes it take longer for the light waves to travel along one arm than the other. So if the two light waves are initially exactly out of phase at the detector, the different travel times cause them to get a little bit in phase there. That's why the gravity wave causes some light to be detected.

Mike W.
(published on 04/21/2016)

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How is the physics of moving masses different from stationary masses?

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How is the physics of moving masses different from stationary masses?

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When you are moving at a constant velocity, it is impossible to distinguish from stationary position

This is why we don’t feel how we are traveling through space (around the sun and galaxy)

Since the speed of light is constant at about 3x10^8 m/s, we can construct a really accurate clock by placing two mirrors parallel to each other and measure the time it takes for the light to bounce of one mirror to the other

If we place one of these clocks on a spaceship traveling past earth and another on earth, observing each clock independently, they would seem to tick at the same speed, however if we observe the space ship’s ‘clock’ from earth, we would see the light traveling in a diagonal zigzag shape rather than straight up and down, which would take a longer time to reach the other side causing the clock seem to tick slower for the observer on earth

This effect is called time-dilation it means that the after you travel through space, the slower you travel through time

Therefore rather than thinking of the universe as having 3 dimensions and a separate dimension of time, we can better think of the universe as having a fourth dimension of time

Another way to imagine gravity is like acceleration, if you were accelerating upwards in a spaceship at the same speed as gravity, you would weight the same on a scale meaning you experience the same amount of force

Based on this fact, einstein theorized that acceleration also causes the same kind of warp in space time as gravity does

Next question:

Would an accelerating mass have a greater force of gravity than another identical mass that is stationary?

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Understanding gravity-warps and ripples in space and time - Curious

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Essentials

Isaac Newton described the effects of gravity, but didn't propose a mechanism for how it worked

Albert Einstein proposed that massive objects warp and curve the universe, resulting in other objects moving on or orbiting along those curves-and that this is what we experience as gravity

This theory, general relativity, has led to a number of predictions that have held up to experimental testing

One prediction of this theory is that 'gravitational waves' ripple through the universe, but Einstein thought they would be too small to detect

In February 2016 the direct measurement of gravitational waves was announced. This provides us with a new method for exploring the universe

In its current form, general relativity is incompatible with quantum mechanics-signalling that a shift in our understanding may be on the horizon

Take a moment to observe the effects of gravity. Lift your arm and feel how you are compelled to drop it again. Gravity is always there-it's stable, it's permanent, it's unchanging. Or is it?

For hundreds of years we've been able to predict the effects of gravity. But we had no idea how it worked until Einstein stepped in, painting a strange and unintuitive picture. In Einstein's view, gravity is far from a static, unchanging force-it is a fundamental part of the structure of the universe, which curves and twists and ripples as objects move and rotate and jostle about.

The predictions of Einstein's theories have been validated time and time again. And now, 100 years after the formulation of his theory of gravity, another one of its predictions-gravitational waves-has been directly measured, despite Einstein's belief that we'd never be able to do this.

Let's begin by looking at why Newton's laws didn't provide a complete picture of gravity.

Isaac Newton (1642-1726) and Albert Einstein (1879-1955) were pivotal in advancing our understanding of gravity. Image source: Wikimedia Commons (Newton / Einstein).

Newton and the laws of gravity

Newton published one of the most celebrated works of science, the Principia, in 1687. In it, he described that the force that pulls objects towards the ground is the very same force that underlies the motion of the planets and stars.

To come to this conclusion, Newton imagined taking an object far from the surface of Earth, and throwing it. If you throw it with too little momentum, it will fall towards Earth, captured by gravity like we are ourselves. If you throw it with too much momentum, it will speed away from the planet, beginning its journey into the reaches of space. But with exactly the right momentum, you can throw it so that it falls continuously around Earth, around and around in an eternal tug-of-war. The object tries to continue in the path you threw it, but gravity keeps on pulling it back in. With the right balance, the object is now in orbit around Earth-just like the moon, or like Earth around the sun.

Newton realised that gravity was responsible for objects falling to the ground and for the orbit of celestial objects.

Newton formulated this insight into a mathematical equation, known today as the law of universal gravitation. When combined with knowledge of geometry and Newton's other equations of motion, we can use it to make predictions about the movement of the planets, or the paths of comets, or how much force is needed to get a rocket to the moon.

We acknowledge Newton not just because of his idea, but because he formulated that idea into an equation that made predictions with greater accuracy than ever before. But it wasn't perfect-Newton's equations produced some incorrect predictions, and, more importantly, he didn't describe how gravity works the way it does. Newton was well aware of this when he said,

Gravity must be caused by an agent acting constantly according to certain laws; but whether this agent be material or immaterial, I have left to the consideration of my readers. Isaac Newton

Distortions in space and time

More than 200 years after the Principia was published, the world was still without an understanding of gravity's mechanism. Enter Albert Einstein-a man who was to change the world in so many ways. But before we get to his work, we'll have to take one more detour.

You can't tell if you're moving (at a constant rate)

In 1632, even before Newton published his now-famous work, Galileo Galilei wrote about the relative motion of objects familiar in his time: ships.

If you are in a closed room on a ship sailing at a constant speed and the ride is perfectly smooth, objects behave as they would on land. There's no physical experiment you could conduct to tell whether you're moving or stationary (assuming you're not peeking out of a porthole). This is the core idea behind relativity, and is the same reason why we don't feel our planet's movement around the sun, or our solar system's movement through the galaxy.

Experiments in a smooth-moving vehicle yield the same results as experiments conducted on land.

Space and time are linked

Almost 300 years after Galileo, Einstein pondered the consequences of relativity in the context of an important factor: the speed of light. He wasn't the only person who was pondering these topics-other physicists at the time were aware that there were unanswered questions on this front. But it was Einstein who formulated a theory-his theory of -to explain existing phenomena and create new predictions. At first, special relativity may not seem to have much to do with gravity, but it was an essential stepping stone for Einstein for understanding gravity.

Moving clocks tick more slowly

Experiments during Einstein's time had shown that the speed of light appeared to be constant. No matter how fast you try and catch up, light always appears to zip away from you at almost 300,000,000 metres per second.

Why is this important? Well, let's imagine constructing a clock out of light itself. Two mirrors are placed opposite each other, and a "tick" of the clock is the time it takes for a particle of light to travel from one side to the other and back.

Now let's imagine that your friend, who's on a spaceship zipping past Earth, has one of these clocks. For your friend, the clock seems to be working normally-the particles of light travel up and down, as expected, and time proceeds in its usual fashion. But from your perspective, watching the ship pass by, the light is moving both up and down and to the side, with the ship. The light travels a longer distance with each tick.

(in slow motion)

As seen from inside the spaceship

As seen by a stationary observer

So if, for the space traveller, light travels at 300,000,000 m/s but only has to travel up and down; and to the Earthbound observer, light travels at 300,000,000 m/s, but must travel a longer, diagonal distance; then for the Earthbound observer, the clock takes longer to "tick".

Perspective matters

But whose time is really slowed down? Is it the person on Earth, watching his friend zip past in her spaceship? Or the astronaut, who argues she's staying still while the Earth flies by?

Moving clocks tick more slowly, but perspective matters.

Strangely enough, both viewpoints are valid-but only while both are in constant motion.

The effects are only noticeable if they were travelling really, really fast-but it's still true to say that when today's astronauts and fighter pilots return from a high-speed mission, they will have aged a teeny-tiny bit less than the rest of us did during that mission.

The four dimensions of spacetime

Following from this, rather than thinking of three dimensions of space and one separate dimension of time, we can consider them as four dimensions of "spacetime". The faster you travel through space, the slower you travel through time, and vice versa.

Moving objects contract in space

Another consequence of special relativity is that fast-moving objects appear to contract in size, in the direction of their motion. (And again, this gets flipped around depending on whose perspective you're looking from.)

Those moving faster than you appear to contract in size (in the direction of their motion).

This follows from the distortion of time-after all, you can measure the length of something by the amount of space something travels through time(e.g. light-years, light-seconds). And while it's tricky to imagine measuring the length of a moving object from someone else's perspective, length contraction is a real, physical effect, and not just an outcome of imprecise measurements.

Unlike the age differences that can arise from time dilation, there are no residual effects due to length contraction once the moving object and the observer are reunited.

Understanding gravity

Einstein's description of gravity leads to situations just as bizarre as special relativity-time travel included!

Acceleration and gravity can be indistinguishable

Imagine waking up in a spaceship, accelerating through space. Just as you're pushed back in the seat of an accelerating car, the accelerating spaceship pushes you to the side opposite the one it's accelerating towards. At a certain rate of acceleration, a set of scales could tell you that you weigh exactly the same as you do when you're at home on Earth.

In deep space, away from gravity, you could stand in an accelerating spaceship and weigh the same as you would on Earth.

Einstein realised that the effects of acceleration and gravity are indistinguishable.

Space warps under accelerated motion

Once Einstein had formulated the equivalence principle, gravity became less mysterious. He could apply his knowledge of acceleration to better understand gravity.

You may know that acceleration doesn't always mean a change in speed, like when you speed up in a car, pushing you to the back of your seat. It can also mean a change in direction, like when you go round a roundabout, causing you to lean towards the side of the car.

To extend this further, let's imagine a cylindrical carnival ride where you and your fellow passengers are pinned to the outer surface. The cylinder is rotated faster and faster until the acceleration eases and the movement stays constant. But even once the speed is constant, you still feel the accelerated motion-you feel yourself being pinned to the outer edge of the ride.

In an object spinning at a constant rate, you still feel the accelerated motion pinning you to the outer edge.

If this spinning ride was large enough and moving at a fast enough rate, you'd start to notice some bizarre effects inside the ride itself, not just from the point of view of someone standing outside it.

With every rotation, those at the edge of the ride travel the full circumference of the cylinder-while at the very centre, there's hardly any movement at all. So if someone stood in the very centre of the ride (perhaps held by a brace, stopping them from falling to the edge), they would notice all those weird effects we saw under special relativity-that those on the edge will contract in length, and their clocks will tick at a slower rate.

Gravity is the curvature of spacetime

The equivalence principle tells us that the effects of gravity and acceleration are indistinguishable. In thinking about the example of the cylindrical ride, we see that accelerated motion can warp space and time. It is here that Einstein connected the dots to suggest that gravity is the warping of space and time. Gravity is the curvature of the universe, caused by massive bodies, which determines the path that objects travel. That curvature is dynamical, moving as those objects move.

In Einstein's view of the world, gravity is the curvature of spacetime caused by massive objects. Image source: T. Pyle / Caltech / MIT / LIGO Lab.

Spacetime grips mass, telling it how to move... Mass grips spacetime, telling it how to curve Physicist John Wheeler

The success of general relativity

Just as Newton's formulation of the laws of gravity were valuable because of their predictive power, the same goes for those of Einstein. To date, his predictions-as strange as they may sound-have all stood the test of time.

Evidence of Einstein's theory of gravity includes the bending of starlight (or, in this case, the light of entire galaxies) around massive objects. Image source: ESA / Hubble & NASA / Wikimedia Commons.

Gravitational waves

Echoes of cataclysm from far away

Imagine two very massive objects, such as black holes. If those objects were to collide, they could potentially create an extreme disturbance in the fabric of spacetime, moving outwards like the ripples in a pond. But how far away could such waves be felt? Einstein predicted that gravitational waves existed, but believed they would be too small to detect by the time they reached us here on Earth.

So it was with great excitement that on February 11 2016, the scientific community was abuzz with the announcement that a had been detected. We needed instruments capable of detecting a signal one-ten-thousandth the diameter of a proton (10⁻¹⁹ meter). That's exactly what the Laser Interferometer Gravitational-Wave Observatory (LIGO) equipment, operated by the California Institute of Technology and the Massachusetts Institute of Technology, can do.

The LIGO experiment

In the LIGO experiment, a laser is directed into a large tunnel structure. The laser beam is split so that half of it travels down one of the 4-kilometre-long 'arms', and the other half travels down the other 4-kilometre arm at the exact same time. At the end of each arm, a mirror reflects the light from the laser back to where it came from, and the two beams merge back into one.

Normally, the laser beams should recombine at exactly the same time. But if a gravitational wave comes rippling through space while the detectors are switched on, that ripple will stretch one arm of the L-shaped structure before stretching the other. The gravitational wave distorts the passage of the light, resulting in a particular kind of interference light pattern detected at the end.

A technician inspecting LIGO's equipment before it is sealed up. Image source: Matt Heintze / Caltech / MIT / LIGO Lab.

On 11 February 2016, the LIGO teams announced the direct discovery of a gravitational wave matching the signal predicted from the collision of two black holes.

Gravitational wave astronomy

The successful LIGO experiment has ushered in a new era of astronomy. Before now, astronomers have largely focused on the study of the electromagnetic spectrum (including light and radio waves). We've been able to discover a huge amount about our universe through that work, but now we have a brand new way to study the universe.

The discovery of gravitational waves gives astronomers a new 'sense' with which to explore the universe, and so there will almost certainly be surprises ahead. What we do know is that this technique will allow us to better understand the most massive objects in the universe such as black holes, neutron stars, and supernovae; and it will provide us with a new window to study how the universe formed.

Is our understanding complete?

While Einstein's theory of gravity has been validated by experiment after experiment, this does not mean our understanding is complete. In fact, we know that something's not quite right.

Whether or not Einstein's theory of gravity will remain unchanged is not known. But it has produced many unexpected, unintuitive predictions that have been confirmed again and again for over a hundred years. That's the sign of a great scientific theory-it makes predictions that may not be able to be proven at the time, but stand up to rigorous testing. This has been one of the greatest journeys in the history of science, involving not just Newton and Einstein, but thinkers and doers all around the world who have worked to put these theories to the test.

Even so, the schism between relativity and quantum mechanics remains. As for what's next, no one knows with certainty. However, there are a few theories-stringy, loopy, multi-dimensional theories-unproven but with promise of becoming the next milestone in understanding our cosmos.

Topics on quantum mechanics and the search for a theory of everything will be published on Nova soon.

The dark stuff of our universe

Exploring the unknown with the Square Kilometre Array

Is Earth safe from asteroids and comets?

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Understanding gravity-warps and ripples in space and time

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Understanding gravity-warps and ripples in space and time - Curious Javascript must be enabled for the correct page display Essentials Isaac Newton described the effects of gravity, but didn't propose a mechanism for how it worked Albert Einstein proposed that massive objects warp and curve the universe, resulting in other

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Would an accelerating mass have a greater force of gravity than another identical mass that is stationary?

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Would an accelerating mass have a greater force of gravity than another identical mass that is stationary?

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Sources:

1. Why do Objects increase in mass as they get faster? - https://futurism.com/why-do-objects-increase-in-mass-as-they-get-faster-2

2. What is the difference between the inertial and gravitational mass? - https://www.physlink.com/education/askexperts/ae305.cfm

Content:

Objects fundamentally have something called a rest mass, this is what its mass is when it's relativistically at rest.

When you increase the speed, you increase the energy of that object, thereby increasing its mass when you look at E = mc^2

When you increase the energy (in this case kinetic) you must increase the mass, thereby increasing how much it has an effect on spacetime.

One caveat is that there are two types of mass, inertial mass and gravitational mass. Rather, there is one kind of mass expressed and measured in two different ways.

However in the second article linked, we can see that throughout all of our experiments, they are numerically the same. Meaning that it would also have an effect on the gravitational mass, thereby influencing how much it warps spacetime.

As we know that gravity is essentially the magnitude of how much spacetime is warped. So the answer is yes, the apparent force of gravity on a relativistically stationary object will be weaker than that of an accelerating object.

Follow-up Question:

How do we know if an object is accelerating or decelerating (going against the velocity that we are already traveling in), does this affect whether or not its mass increases or decreases. And if this is the case could we not use this information to find our objective velocity.

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What causes the force of gravity to change?

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What causes the force of gravity to change?

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Since the effect of gravity originates from the core of the earth and curves spacetime around it so objects accelerate towards it, the effect of gravity weakens the further that you move away from the centre of the earth

The stronger gravity curves spacetime more, which happens closer to the earth which makes time progress slower

Sensitive machines can notice the nanosecond difference of time between 3 and 4 meters, but humans can not

Again, the observer in weaker gravity observes that the time at their height runs normally and the clock at the other height runs slow when closer to the earth, and vise-versa

Very accurate atomic clocks can measure the difference in time at different altitudes and are used by the US National Institute of Standards and Technology

GPS satellites are so high into orbit that they must adjust their internal clocks to that it matches the time of the GPS receivers on the ground to determine their position

The force of gravity changes when an object moves closer to (stronger) or further away from (weaker) the source because of the curving of spacetime being more severe closer to the centre of the mass. Did not touch on accelerating masses.

Next Question:

How do planets collapse to form black holes and how is time affected? What is the difference in time at the outskirts of a black hole compared to the inner core? Is it even possible to find out?

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Science Questions with Surprising Answers

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Yes, time goes faster the farther away you are from the earth's surface compared to the time on the surface of the earth. This effect is known as "gravitational time dilation". It is predicted by Einstein's theory of General Relativity and has by verified multiple times by experiments. Gravitational time dilation occurs because objects with a lot of mass create a strong gravitational field. The gravitational field is really a curving of space and time. The stronger the gravity, the more spacetime curves, and the slower time itself proceeds. We should note here, however, that an observer in the strong gravity experiences his time as running normal. It is only relative to a reference frame with weaker gravity that his time runs slow. A person in strong gravity therefore sees his clock run normal and sees the clock in weak gravity run fast, while the person in weak gravity sees his clock run normal and the other clock run slow. There is nothing wrong with the clocks. Time itself is slowing down and speeding up because of the relativistic way in which mass warps space and time.

Gravitational time dilation occurs whenever there is difference in the strength of gravity, no matter how small that difference is. The earth has lots of mass, and therefore lots of gravity, so it bends space and time enough to be measured. As a person gets farther away from the surface of the earth - even just a few meters - the gravitational force on that person gets weaker. We don't notice it much as humans, but even going from the first floor of a building to the second floor of a building moves you away from the earth and therefore slightly weakens the gravitational force that you feel. The difference in gravity between that felt at three meters above the surface of the earth and that felt at four meteres is too small to notice with our human senses, but the difference is large enough for sensitive machines to pick up.

Because the strength of gravity is weakening with every step you take up a flight of stairs, the rate at which time proceeds is also speeding up with every step. People who work on the bottom floor of a skyscraper are literally time traveling into the future compared to the people who work on the top floor. But the effect is very small. So small, in fact, that you will never notice the time difference in everyday life. People who live and work farther away from the surface of the earth are only fractions of a nanosecond ahead per year compared to those close to the surface. Though small, the time rate difference between different altitudes is real and has been measured experimentally using very accurate atomic clocks. The U.S. National Institute of Standards and Technology (NIST) has measured such small time rate differences and published its findings. NIST was able to measure the small time rate difference between a point on the earth and a point half a meter higher, by simply raising their experimental table a half of a meter. Their findings matched well the time dilation predicted by Einstein's relativity. The time dilation due to earth's gravity is significant enough that the GPS satellites, which orbit high above the earth, must adjust their internal clocks in order to take into account their faster time and therefore accurately determine the location of GPS receivers on the ground.

If you liked my explanation, then you'll love my new book: The Top 50 Science Questions with Surprising Answers. Check it out! This book has been years in the making, but it's finally available. It contains detailed, highly accurate, surprising answers to science questions like this one that you just read. It includes a substantial amount of original content that can only be found in the book.

Topics: general relativity, gravity, relativity, spacetime, time, time dilation, time travel

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Does time go faster at the top of a building compared to the bottom?

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Yes, time goes faster the farther away you are from the earths surface compared to the time on the surface of the earth. This effect is known as gr...

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Black Holes - Object of large mass → Large gravity → Nothing can espace; theorized since 1700s but modern science is founded from Einstein's theory of gravity in 1917

Principles suggest - Any object if squeezed to small enough volume → become a black hole → Object collapses under its own weight → zero size, but mass and gravity remain as extreme distortion of spacetime → Said distortion is the black hole

Nature shows - Only stars several times larger than our Sun (or other celestial objects of similar size) from black holes at the end of their lives → Resulting black hole → only a few miles across → Shaped spherical

Black Holes → darkest black in universe → Light is swallowed by the hole

Black Hole is a true hole in space → any object that crosses the horizon of the hold is swallowed forever → Suggests black holes are possibly one-way exit doors from our universe (nothing inside a black hole can ever communicate with our universe again, even in principle)

Closer to a black hole → Flow of time slows down relative to flow of time further from black hole

Einstein's theory → All massive body produce similar effects, but even Earth’s gravity is so weak slowing of time → not noticeable; effect has been confirmed through sensitive instruments

Sea level = one-billionth of a second less every year than the top of Mt. Everest

Near a black hole, the slowing of time is extreme; Observer outside black hole, time stops

Objects falling into the hole appear frozen in time at the edge of the hole

Einstein's theory → time and space, in a way, trade places inside the hole

Flow of time itself draws falling objects into the center of the black hole → No force can stop (due to no force being able to stop time)

Center → predicts that time is destroyed → comes to an abrupt end; "reverse of creation”

Einstein's theory of gravity does not apply at this center

Next Question:

How does Stephen Hawking's theory collide and intersect Einstein's theory? What similarities and differences do they share and why is that the case?

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The idea of a black hole - an object so massive that nothing could escape the grasp of its gravity - dates back to the 1700s. But the modern story of black holes really starts with Einstein's revolutionary theory of gravity, completed in 1917. Over the past century, scientists have used Einstein's theory of gravity to develop a picture of what black holes must be like. Here are some of the amazing properties of black holes that they have predicted.

In principle, any object - even a rock - can be made into a black hole, by squeezing it into a tiny enough volume. Under these conditions, the object continues to collapse under its own weight, crushing itself down to zero size. However, according to Einstein's theory, the object's mass and gravity remain behind, in the form of an extreme distortion of the space and time around it. This distortion of space and time is the black hole.

In nature, the only objects that can form a black hole on their own are large stars - stars several times more massive than our own Sun. At the end of their lives, these stars collapse under their own weight, forming a black hole. While the original star might be millions of miles wide, the resulting black hole is just a few miles across. The hole itself is shaped like a beach ball - spherical.

The resulting black hole is the darkest black in the universe: No matter how powerful a light you shine on it, no light ever bounces back, because the light is swallowed by the hole. A black hole is a true "hole" in space: Anything that crosses the edge of the hole - called the "horizon" of the hole - is swallowed forever. For this reason, black holes are considered an edge of space, a one-way exit door from our universe; nothing inside a black hole can ever communicate with our universe again, even in principle.

However black holes are even stranger than that. As you get closer to a black hole, the flow of time slows down, compared to flow of time far from the hole. (According to Einstein's theory, any massive body, including the Earth, produces this effect. Earth's gravity is so weak that the slowing of time is not noticeable, but the effect has been confirmed using sensitive instruments. For example, at sea level you age one-billionth of a second less every year than you would if you lived on top of Mt. Everest.) Near a black hole, the slowing of time is extreme. From the viewpoint of an observer outside the black hole, time stops. For example, an object falling into the hole would appear frozen in time at the edge of the hole.

Inside a black hole is where the real mystery lies. According to Einstein's theory, time and space, in a way, trade places inside the hole. Inside the black hole, the flow of time itself draws falling objects into the center of the black hole. No force in the universe can stop this fall, any more than we can stop the flow of time.

At the very center of the black hole is where our understanding breaks down. Einstein's theory of gravity seems to predict that time itself is destroyed at the center of the hole: time comes to an abrupt end there. For this reason, a black hole is sometimes described as the "reverse of creation." But no one knows how or why time could come to an abrupt end, any more than we know how time was created in the first place. Einstein's theory of gravity no longer applies at these tiniest scales of distance, and new laws of nature must be found that describe what happens at the center of a black hole.

Does the inside of a black hole lead to another universe, as some scientists have claimed? The truth is, no one really knows. We cannot do a direct experiment to find out, even in principle, since no information or evidence can ever get back out of a black hole. That's what makes it so important to find and study black holes from the outside, while at the same time developing theories that can more confidently predict what might happen on the inside of the black hole.
It is one thing to predict what black holes should be like. It is quite another to hunt for them in nature. Do black holes really exist? If so, what are they like? Explore the evidence for black holes in the next section >

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--Universe Forum--Black Holes--What are they?

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The idea of a black hole - an object so massive that nothing could escape the grasp of its gravity - dates back to the 1700s. But the modern story of black holes really starts with Einstein's revolutionary theory of gravity, completed in 1917.

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Experimental Evidence for General Relativity

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Experimental Evidence for General Relativity

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English astronomer Arthur Eddington considered Einstein’s prediction that light rays are bent near a massive body → realized it can be tested → star positions during solar eclipse(pictures) compared to star positions when sun was in different position of the sky

Hyades star cluster → target for this experiment as it was in the vicinity of a long total solar eclipse

Comparing photographs from expeditions with reference photographs of the Hyades → Starlight was deflected about 1.75 seconds of arc → as predicted by General relativity

This same effect produces gravitational lensing → massive celestial object focuses light from another object → produces a distorted/magnified image

Gravitational lenses (discovered in 1979) gave additional support for general relativity

More evidence from Mercury → Mercury doesn’t return to same spot after every orbit → ellipse rotates slowly →  each orbit the perihelion(the point of closest approach to the Sun) moves to a slightly different angle

Newton’s law of gravity could not explain this perihelion shift →  general relativity gave the correct orbit

Time dilates in a gravitational field → clocked run slower while approaching large mass’s gravity field

Measured directly and by gravitational redshift of light

Light vibrates at lower frequency within a gravity field due to slowing of time → Light shifts to a longer wavelength → Towards the red side of electromagnetic spectrum

Measurements verified the equivalence principle →  inertial mass = gravitational mass

Gravitational Waves - predicted by General relativity → Proven through LIGO experiment (Laser interference oscillates during a gravity wave)

Next Question:

Are there any phenomena to explain why General Relativity is not a complete picture of the universe? If not, why is General Relativity still a theory with so much evidence to back it up?

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Soon after the theory of general relativity was published in 1915, the English astronomer Arthur Eddington considered Einstein's prediction that light rays are bent near a massive body, and he realized that it could be verified by carefully comparing star positions in images of the Sun taken during a solar eclipse with images of the same region of space taken when the Sun was in a different portion of the sky. Verification was delayed by World War I, but in 1919 an excellent opportunity presented itself with an especially long total solar eclipse, in the vicinity of the bright Hyades star cluster, that was visible from northern Brazil to the African coast. Eddington led one expedition to Príncipe, an island off the African coast, and Andrew Crommelin of the Royal Greenwich Observatory led a second expedition to Sobral, Brazil. After carefully comparing photographs from both expeditions with reference photographs of the Hyades, Eddington declared that the starlight had been deflected about 1.75 seconds of arc, as predicted by general relativity. (The same effect produces gravitational lensing, where a massive cosmic object focuses light from another object beyond it to produce a distorted or magnified image. The astronomical discovery of gravitational lenses in 1979 gave additional support for general relativity.)

Further evidence came from the planet Mercury. In the 19th century, it was found that Mercury does not return to exactly the same spot every time it completes its elliptical orbit. Instead, the ellipse rotates slowly in space, so that on each orbit the perihelion-the point of closest approach to the Sun-moves to a slightly different angle. Newton's law of gravity could not explain this perihelion shift, but general relativity gave the correct orbit.

Another confirmed prediction of general relativity is that time dilates in a gravitational field, meaning that clocks run slower as they approach the mass that is producing the field. This has been measured directly and also through the gravitational redshift of light. Time dilation causes light to vibrate at a lower frequency within a gravitational field; thus, the light is shifted toward a longer wavelength-that is, toward the red. Other measurements have verified the equivalence principle by showing that inertial and gravitational mass are precisely the same.

The most striking prediction of general relativity is that of gravitational waves. Electromagnetic waves are caused by accelerated electrical charges and are detected when they put other charges into motion. Similarly, gravitational waves would be caused by masses in motion and are detected when they initiate motion in other masses. However, gravity is very weak compared with electromagnetism. Only a huge cosmic event, such as the collision of two stars, can generate detectable gravitational waves. Efforts to sense gravitational waves began in the 1960s, and such waves were first detected in 2015 when LIGO observed two black holes 1.3 million light-years away spiralling into each other.

Applications of relativistic ideas

Although relativistic effects are negligible in ordinary life, relativistic ideas appear in a range of areas from fundamental science to civilian and military technology.

The relationship E = m c ² is essential in the study of subatomic particles. It determines the energy required to create particles or to convert one type into another and the energy released when a particle is annihilated. For example, two photons, each of energy E, can collide to form two particles, each with mass m = E/ c ². This pair-production process is one step in the early evolution of the universe, as described in the big-bang model.

Knowledge of elementary particles comes primarily from particle accelerators. These machines raise subatomic particles, usually electrons or protons, to nearly the speed of light. When these energetic bullets smash into selected targets, they elucidate how subatomic particles interact and often produce new species of elementary particles.

Particle accelerators could not be properly designed without special relativity. In the type called an electron synchrotron, for instance, electrons gain energy as they traverse a huge circular raceway. At barely below the speed of light, their mass is thousands of times larger than their rest mass. As a result, the magnetic field used to hold the electrons in circular orbits must be thousands of times stronger than if the mass did not change.

Fission and fusion: bombs and stellar processes

Energy is released in two kinds of nuclear processes. In nuclear fission a heavy nucleus, such as uranium, splits into two lighter nuclei; in nuclear fusion two light nuclei combine into a heavier one. In each process the total final mass is less than the starting mass. The difference appears as energy according to the relation E = Δ m c ², where Δ m is the mass deficit.

Fission is used in atomic bombs and in reactors that produce power for civilian and military applications. The fusion of hydrogen into helium is the energy source in stars and provides the power of a hydrogen bomb. Efforts are now under way to develop controllable hydrogen fusion as a clean, abundant power source.

The global positioning system (GPS) depends on relativistic principles. A GPS receiver determines its location on Earth's surface by processing radio signals from four or more satellites. The distance to each satellite is calculated as the product of the speed of light and the time lag between transmission and reception of the signal. However, Earth's gravitational field and the motion of the satellites cause time-dilation effects, and Earth's rotation also has relativistic implications. Hence, GPS technology includes relativistic corrections that enable positions to be calculated to within several centimetres.

Cosmology, the study of the structure and origin of the universe, is intimately connected with gravity, which determines the macroscopic behaviour of all matter. General relativity has played a role in cosmology since the early calculations of Einstein and Friedmann. Since then, the theory has provided a framework for accommodating observational results, such as Hubble's discovery of the expanding universe in 1929, as well as the big-bang model, which is the generally accepted explanation of the origin of the universe.

The latest solutions of Einstein's field equations depend on specific parameters that characterize the fate and shape of the universe. One is Hubble's constant, which defines how rapidly the universe is expanding; the other is the density of matter in the universe, which determines the strength of gravity. Below a certain critical density, gravity would be weak enough that the universe would expand forever, so that space would be unlimited. Above that value, gravity would be strong enough to make the universe shrink back to its original minute size after a finite period of expansion, a process called the "big crunch." In this case, space would be limited or bounded like the surface of a sphere. Current efforts in observational cosmology focus on measuring the most accurate possible values of Hubble's constant and of critical density.

Relativity, quantum theory, and unified theories

Cosmic behaviour on the biggest scale is described by general relativity. Behaviour on the subatomic scale is described by quantum mechanics, which began with the work of the German physicist Max Planck in 1900 and treats energy and other physical quantities in discrete units called quanta. A central goal of physics has been to combine relativity theory and quantum theory into an overarching "theory of everything" describing all physical phenomena. Quantum theory explains electromagnetism and the strong and weak forces, but a quantum description of the remaining fundamental force of gravity has not been achieved.

After Einstein developed relativity, he unsuccessfully sought a so-called unified field theory with a space-time geometry that would encompass all the fundamental forces. Other theorists have attempted to merge general relativity with quantum theory, but the two approaches treat forces in fundamentally different ways. In quantum theory, forces arise from the interchange of certain elementary particles, not from the shape of space-time. Furthermore, quantum effects are thought to cause a serious distortion of space-time at an extremely small scale called the Planck length, which is much smaller than the size of elementary particles. This suggests that quantum gravity cannot be understood without treating space-time at unheard-of scales.

Although the connection between general relativity and quantum mechanics remains elusive, some progress has been made toward a fully unified theory. In the 1960s, the electroweak theory provided partial unification, showing a common basis for electromagnetism and the weak force within quantum theory. Recent research suggests that superstring theory, in which elementary particles are represented not as mathematical points but as extremely small strings vibrating in 10 or more dimensions, shows promise for supporting complete unification, including gravitation. However, until confirmed by experimental results, superstring theory will remain an untested hypothesis.

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Relativity - Gravitational Waves, Spacetime, Tests

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Relativity - Gravitational Waves, Spacetime, Tests: Soon after the theory of general relativity was published in 1915, the English astronomer Arthur Eddington considered Einstein's prediction that light rays are bent near a massive body, and he realized that it could be verified by carefully comparing star positions in images of the Sun taken during a solar eclipse with images of the same region of space taken when the Sun was in a different portion of the sky.

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Since general relativity does not relate well with einstein’s theory of relativity, scientists have been trying to connect the two with another theory to make a potential ‘theory of everything’

One of the possible theories that can be classified as the ‘theory of everything’ is string theory

This theory essentially states that everything is made of tiny strings that vibrates at different frequencies

For example the string of a quark would vibrates differently than an electron’s string

However, this theory cannot exist without the existence of dimensions greater than the 4 we know of(3 physical + time)

This theory states that rather than a wave, gravity is caused by a particle called the ‘graviton’ which like photons would be without mass and charge

It would be very difficult to detect gravitons because according to this theory they can travel across dimensions and created gravitons would rapidly disappear into other dimensions that we cannot detect

This means gravity exists in all dimensions

String theory also states that there are two types of strings, closed and open

Closed strings are like a circle and can travel through dimensions

Open strings have ends and are therefore confined to the dimensions in which they exist

Gravitons are closed strings and photons are open

This theory explains why gravity is the weakest of the four fundamental forces since it would leak into other dimensions only leaving a fraction for us to feel

This theory also offers a solution to dark matter, it could be gravitons from other dimensions leaking into our 3 dimensions

Next question:

Is gravity a combination of gravitons and the warping of space-time? Do the gravitons cause the warping of space time?

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How do planets collapse to form black holes and how is time affected?

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How do planets collapse to form black holes and how is time affected?

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Sources

1. The Silent Black Hole - https://www.science.org/content/article/silent-black-hole#:~:text=According%20to%20theory%2C%20a%20black,into%20an%20infinitely%20dense%20speck.

2. The Effect Density Has on the Speed of Light, Time, and the Dimensions of the Multiverse - https://www.scirp.org/journal/paperinformation?paperid=120196#:~:text=As%20density%20increases%2C%20gravity%20increases,same%20factor%20that%20dt%20increases.

Content

First note is that black holes cannot be formed from a planet. The reason that stars are able to not implode is because they have constant nuclear fusion going on in the core of the star. This is the only force preventing it from turning into a black hole.

It's essentially a MASSIVE fusion reactor going on at all times, and fusion in of itself is even stronger that what we use to generate massive amounts of energy with small quantities, which is nuclear fission.

The fusion is like constant nuclear bombs being exploded inside of the star and it pushes the mass outwards. Heavier stars do rely on this force to prevent themselves from being imploded, lighter stars like our sun will simply shrink when it dies, it simply does not have enough mass to overcome its structure.

To summarize, the bigger celestial objects will always try to collapse, the thing holding it in balance is the fusion going on inside the star

In terms of how time is affected, we can look at the second paper linked, citing that as the density of an object increases, its effect on spacetime also increases, thereby forcing time to run slower.

This would mean that before the collapse and after the collapse (assuming no matter and energy is lost which it typically is) there would be a shift in how much time is dilated. Rather, an increase.

Follow up

Given the relationship between density and time dilation, how might this be applied to a singularity? Given its supposed infinite density, would it not cause time to completely stop, in this case, how would any matter reach it. Does the progressively approach a complete stop? Or is our assumption of infinite density simply erroneous.

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Context:

Anything that crosses the apparent horizon of a black hole will never escape the black hole

As you approach the horizon the flow of time progressively slows down compared to the flow of time far away from the black hole

This effect of time distortion is true for any massive object in the universe including earth

Using very accurate clocks we observed this effect her on earth

However near black holes the fabric of space-time is distorted to such a magnitude that one would be able to see visible changes in the flow of time

What happens to time near black holes?

To someone observing the black hole, the time would seem to stop for a supposed object falling into the black hole, making it appear frozen in time

According to Einstein’s theory of relativity, inside the black hole, space-time is so heavily distorted that time and space switch places

Inside the black hole, the flow of time would act as the primary dimension through which an object would fall

Instead of falling through space, it would fall through time towards the singularity

No force in the universe would be able to stop this fall because all forces act in the three spatial dimensions, there is no force that can affect time

What happens at the singularity (centre of the black hole)?

Our understanding of black holes does not extend beyond this point, at the singularity nobody knows what would happen

Einstein’s theory of gravity no longer applies at these very small scales in the singularity

Einstein theorised that time would be destroyed in the singularity

Other scientists have theorised that the singularity leads to a new universe

We cannot conduct direct experiments on black holes because anything that enters the black hole would never be able to communicate with the outside universe, and no information can ever escape the black hole

New research must me done on the laws of the universe to devise more accurate theories of what may happen in the centre of a black hole

Next question:

Similar to black holes, neutron stars(the second densest objects in the universe after black holes) also cause extreme distortions in space time that even light bends around the star. Could research be conducted on these stars to improve our understanding of black holes and how they affect time?

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The idea of a black hole - an object so massive that nothing could escape the grasp of its gravity - dates back to the 1700s. But the modern story of black holes really starts with Einstein's revolutionary theory of gravity, completed in 1917. Over the past century, scientists have used Einstein's theory of gravity to develop a picture of what black holes must be like. Here are some of the amazing properties of black holes that they have predicted.

In principle, any object - even a rock - can be made into a black hole, by squeezing it into a tiny enough volume. Under these conditions, the object continues to collapse under its own weight, crushing itself down to zero size. However, according to Einstein's theory, the object's mass and gravity remain behind, in the form of an extreme distortion of the space and time around it. This distortion of space and time is the black hole.

In nature, the only objects that can form a black hole on their own are large stars - stars several times more massive than our own Sun. At the end of their lives, these stars collapse under their own weight, forming a black hole. While the original star might be millions of miles wide, the resulting black hole is just a few miles across. The hole itself is shaped like a beach ball - spherical.

The resulting black hole is the darkest black in the universe: No matter how powerful a light you shine on it, no light ever bounces back, because the light is swallowed by the hole. A black hole is a true "hole" in space: Anything that crosses the edge of the hole - called the "horizon" of the hole - is swallowed forever. For this reason, black holes are considered an edge of space, a one-way exit door from our universe; nothing inside a black hole can ever communicate with our universe again, even in principle.

However black holes are even stranger than that. As you get closer to a black hole, the flow of time slows down, compared to flow of time far from the hole. (According to Einstein's theory, any massive body, including the Earth, produces this effect. Earth's gravity is so weak that the slowing of time is not noticeable, but the effect has been confirmed using sensitive instruments. For example, at sea level you age one-billionth of a second less every year than you would if you lived on top of Mt. Everest.) Near a black hole, the slowing of time is extreme. From the viewpoint of an observer outside the black hole, time stops. For example, an object falling into the hole would appear frozen in time at the edge of the hole.

Inside a black hole is where the real mystery lies. According to Einstein's theory, time and space, in a way, trade places inside the hole. Inside the black hole, the flow of time itself draws falling objects into the center of the black hole. No force in the universe can stop this fall, any more than we can stop the flow of time.

At the very center of the black hole is where our understanding breaks down. Einstein's theory of gravity seems to predict that time itself is destroyed at the center of the hole: time comes to an abrupt end there. For this reason, a black hole is sometimes described as the "reverse of creation." But no one knows how or why time could come to an abrupt end, any more than we know how time was created in the first place. Einstein's theory of gravity no longer applies at these tiniest scales of distance, and new laws of nature must be found that describe what happens at the center of a black hole.

Does the inside of a black hole lead to another universe, as some scientists have claimed? The truth is, no one really knows. We cannot do a direct experiment to find out, even in principle, since no information or evidence can ever get back out of a black hole. That's what makes it so important to find and study black holes from the outside, while at the same time developing theories that can more confidently predict what might happen on the inside of the black hole.
It is one thing to predict what black holes should be like. It is quite another to hunt for them in nature. Do black holes really exist? If so, what are they like? Explore the evidence for black holes in the next section >

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--Universe Forum--Black Holes--What are they?

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The idea of a black hole - an object so massive that nothing could escape the grasp of its gravity - dates back to the 1700s. But the modern story of black holes really starts with Einstein's revolutionary theory of gravity, completed in 1917.

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 Does the Magnitude of  mass of impacted objects increase the effect of gravity's stretch/compression?

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 Does the Magnitude of  mass of impacted objects increase the effect of gravity's stretch/compression?

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The Warping Of Space Time

Albert Einstein discovered that time is not constant -> it will not go in the same speed at different spots in the universe

Einstein proved that gravity and acceleration are able to change the way which time travels

because of the warping of time due to gravity, people who are on the international space station are actually aging slower than people on earth

this is because of the idea of general relativity

the theory of general relativity is the idea that instead of objects beings connected to each other by an invisible force, they are connected by gravity curving and warping space

the more massive the object, the more it warps space around it. This also changes the way time warps

gravity is formed by any massive object in the universe

Every planet makes its own gravity. The planet pulls space towards itself, making it accelerate at increasing speeds

Every object in the universe has a gravitational field

For example, a pencil has a gravitational field, but the pull of that gravitational field is so small that it basically affects nothing surrounding it. It's so small that it also cannot be measured by modern technology

Next Question: What is the relationship between acceleration and the warping of space-time?

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Most people think that time is constant. They think that time will tick at the same speed wherever they go in the universe. According to Albert Einstein, this is false. Einstein proved that gravity and acceleration are actually able to change the way in which time travels. For example, with the warping of time due to gravity, people who are on the space station are actually aging slower than everyone else on Earth! This is due to the idea of general relativity.

In simple terms, the theory of general relativity is the basic idea that, instead of being an invisible force that attracts objects to one another, gravity is a curving or warping of space. The more massive an object, the more it warps the space around it. This is able to change the way in which time warps as well. To explain further, one needs to understand relativity and how time works.

To start off, one needs to understand the effects of gravity on objects. Gravity is the reason humans are stuck to the face of the Earth and it is the force preventing us from floating away into the abyss of space. Gravity isn't something that just exists either. Gravity is formed by any massive object in the universe. For example, every planet makes its own gravity. The planet pulls space in towards itself, getting it to accelerate at ever increasing speeds. It also depends on the mass of the object. For example, a pencil will create its own gravitational field, but the gravitational pull will be so miniscule and small that it simply could not be detected with modern technology. On the other hand, the acceleration of gravity on the surface of the Earth (at sea level) is -9.8m/s/s. As one gets farther and farther from the center of mass of the object, the gravity decreases more and more. To put this in perspective, if one were to go to the beach and weigh themselves and then go weigh themselves on top of mount Everest, they would be slightly less heavy on the top of Everest. This is because they are farther from the center of gravity. It is also important to note that gravity only affects weight, not mass. Mass is how much matter something is composed of, and weight is how much gravity affects the mass.

The next concept is that acceleration and gravity are essentially the same thing. This is dubbed the equivalence principle. Consider someone weighing themselves on a scale at the beach and they weigh 80kg. Then consider someone in outer space riding a spaceship accelerating at 9.8m/s/s. (remember the acceleration of gravity at sea level is -9.8m/s/s) Would the person weigh the same amount on the spaceship in outer space as they would on Earth? The answer is yes, and only because the acceleration of the rocket matches the acceleration of the gravity on Earth. This proves that acceleration and gravity can act in replacement of one another.

Let's relate these concepts to a physical example, like light in an elevator. If a person were to stand in an elevator and shine a laser at the wall opposing them parallel to the floor of the elevator, the laser and the laser's point on the wall should be at the same height. Now let's assume the elevator is accelerating upwards extremely fast. In this scenario, the laser and its corresponding mark would be at different heights. The mark on the wall of the elevator would actually be lower!

One of the common principles in the universe is that light will always take the straightest path, or the shortest path. In the stationary elevator, this path is straight across from the laser onto the wall. In the moving elevator, the path is not actually a straight line. This is confusing because physicists had always figured that the straight line was the shortest path. This idea can further be visualised by thinking about the fastest way to get from the north pole to the south pole. The true fastest way would be through the core of the Earth in a straight line, but that isn't possible. Since humans cannot go through the core of the Earth, they go around the curve of the Earth. This is an example of how the shortest possible path isn't always the straightest one.

Time follows the same pattern as light does in this scenario. As the gravity warps the fabric of space around a massive body, time warps as well. To explain this, it is important to know that light has been proven to travel at the same speed in the presence of gravity and in the absence of gravity. Now remember that the shortest path for light to travel isn't always a straight line. With this information we can use the formula for speed (s=d/t) to determine how time warps. Consider light traveling from point A to point B with a set distance. The speed of light is always constant, and the distance is fixed, so time equals distance divided by speed. Now consider light traveling from point C to point D but in a curved line due to gravity. The speed is constant, but the distance is longer than before. This means that the numerator is bigger than the previous equation. With a bigger numerator, this means that the time it takes for the light to travel the exact same distance is longer. Therefore time has just been warped.

To sum it all up: gravity affects the accelerations that the universe is subject to. The accelerations are responsible for the compression and decompression of space and that affects the distance at which light travels. Since light travels at a constant speed, the difference in distance outputs a change in time. That's all there is to it!

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Most people think that time is constant. They think that time will tick at the same speed wherever they go in the universe. According to Albert Einstein, this is false. Einstein proved that gravity and acceleration are actually able to change the way in which time travels.

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The universe is expanding at rate that is accelerating rate

this fact contradicts what researchers understand about the effect of gravity on the universe

The universe's expansion accelerating can be compared to throwing an apple in the air and it continuing and accelerating upwards

The cause of the acceleration of the universe is a result of dark matter. The logistics behind this phenomena is still a mystery

The universe's accelerating expansion contradicts the current understanding we have of gravity's effect on the universe

It hints that the understanding we have of gravity at the universal level is incomplete

This potential misunderstanding may help scientists explain dark matter

Einstein's theory of general relativity has up until this point been able to accurately describe gravity (has been able to predict things like the orbit of mercury and the existence of black holes) until this point.

The theory cannot explain dark energy however, so some scientists have argued that they may need to modify some equations or add new components to the theory

To find out whether or not the theory needs modifications, scientists would have to look for evidence that the strength of gravity has varied throughout the history of the universe or over cosmic distances

So far, the research scientists have conducted has shown that Einstein's theory of general relativity still works. This means that there is no explanation for dark energy yet

Most of the matter in our universe is dark matter which is matter that does not reflect, emit or absorb light (this makes it really hard for us to observe or determine what it's made of)

We know it exists because gravity gives it away

Large masses of dark matter warp space itself. When light travels through space, it encounters these portions of warped space. These cause images of distant galaxies to appear curved or smeared to us, which is something that proves the existence of dark matter

The strength of gravity determines the size and distribution of dark matter structures and then those dark matter structures determine the warping of light and how distant galaxies appear to us

The subtle distortions due to dark matter bending space are called weak gravitational lensing

Next Question: Why does the strength of gravity affect the size and structures of dark matter?

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The universe is expanding at an accelerating rate, and scientists don't know why. This phenomenon seems to contradict everything researchers understand about gravity's effect on the cosmos: It's as if you threw an apple in the air and it continued upward, faster and faster. The cause of the acceleration, dubbed dark energy, remains a mystery.

A new study from the international Dark Energy Survey, using the Victor M. Blanco 4-meter Telescope in Chile, marks the latest effort to determine whether this is all simply a misunderstanding: that expectations for how gravity works at the scale of the entire universe are flawed or incomplete. This potential misunderstanding might help scientists explain dark energy. But the study - one of the most precise tests yet of Albert Einstein's theory of gravity at cosmic scales - finds that the current understanding still appears to be correct.

The results, authored by a group of scientists that includes some from NASA's Jet Propulsion Laboratory, were presented Wednesday, Aug. 23, at the International Conference on Particle Physics and Cosmology (COSMO'22) in Rio de Janeiro. The work helps set the stage for two upcoming space telescopes that will probe our understanding of gravity with even higher precision than the new study and perhaps finally solve the mystery.

More than a century ago, Albert Einstein developed his Theory of General Relativity to describe gravity, and so far it has accurately predicted everything from the orbit of Mercury to the existence of black holes. But if this theory can't explain dark energy, some scientists have argued, then maybe they need to modify some of its equations or add new components.

To find out if that's the case, members of the Dark Energy Survey looked for evidence that gravity's strength has varied throughout the universe's history or over cosmic distances. A positive finding would indicate that Einstein's theory is incomplete, which might help explain the universe's accelerating expansion. They also examined data from other telescopes in addition to Blanco, including the ESA (European Space Agency) Planck satellite, and reached the same conclusion.

The study finds Einstein's theory still works. So no explanation for dark energy yet. But this research will feed into two upcoming missions: ESA's Euclid mission, slated for launch no earlier than 2023, which has contributions from NASA; and NASA's Nancy Grace Roman Space Telescope, targeted for launch no later than May 2027. Both telescopes will search for changes in the strength of gravity over time or distance.

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NASA Scientists Help Probe Dark Energy by Testing Gravity

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Could one of the biggest puzzles in astrophysics be solved by reworking Albert Einstein's theory of gravity? A new study co-authored by NASA scientists says not yet.

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How do gravitons affect gravity and the warping of space time?

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How do gravitons affect gravity and the warping of space time?

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Graviton, the particle that we think can carry gravity, has been something that researchers have been searching for decades

They have never been detected in space but a graviton-like particle has been seen in a semiconductor

Einstein's theory of general relativity and the quantum theory (describes the subatomic world) have contradictions with each other

Each theory takes radically different view of the force of gravity

Einstein theorized that matter distorts the fabric of space time around it -> creating the effect of a force field

The quantum theory describes all forces in terms of -exchange particles' that move around from place to place (in the case of the force of gravity, those particles are known as gravitons)

The existence of gravitons would be the bridge between the differences in these to theories

The main reason theorists believe gravitions must exist is because quantum theory has successfully explained every other force in nature.

Proving gravitons exist would unify the quantum theory with the theory of general relativity

Not scientists agree with gravitons existing; this is because no theory that claims to unify the quantum theory with GR has ever been successfully proven -> this has caused suspicions that maybe gravity does not exist like all other forces. In that case gravitons may not exist

Even if gravitons exist, finding them and actually roving they exist is very hard to do.

Quantum theory predicts that gravity essentially has an infinite range. This means the graviton must have an extremely low mass

Studies that came from gravitational waves from colliding black holes suggest that the mass of a graviton should be approximately a billion, billion, billion times lighter than a electron

A graviton detector has to be extremely massive and has to be placed near a source with a ton of gravitons to

Even a detector the size of jupiter placed near a neutron star (good source of gravitons) would have a hard time finding anything

To answer the question: graviton is a particle of gravity. Since the warping of spacetime occurs because of gravity, and gravity is made up of gravitons, therefore gravitons cause warping of gravity. The higher the density of gravitons, the more warping of spacetime occurs

Next Question: How does the quantum theory affect gravity and explain the warping of space-time?

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What are gravitons, and do they really exist?