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Why is the expansion of the universe speeding up?

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Doesn't really explain but introduces other topics

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(Image: © NASA, ESA, Adam Riess, and Palomar Digitized Sky Survey)

The universe is expanding faster than expected, suggesting that astronomers may have to incorporate some new physics into their theories of how the cosmos works, a new study reports.

The revised expansion rate is about 10% faster than that predicted by observations of the universe's trajectory shortly after the , according to the new research. The study also significantly reduces the probability that this disparity is a coincidence, from 1 in 3,000 to just 1 in 100,000.

"This mismatch has been growing and has now reached a point that is really impossible to dismiss as a fluke," study lead author Adam Riess, a professor of physics and astronomy at The Johns Hopkins University in Baltimore, said in a statement.

"This is not what we expected," said Riess, who won the Nobel Prize for physics in 2011 (along with Brian Schmidt and Saul Perlmutter) for showing, in the late 1990s, that the universe's expansion is accelerating. It's unclear what's driving this surprising acceleration, but many astronomers invoke a mysterious, repulsive force called dark energy.
Related:

(Image credit: NASA, ESA, and A. Feild (STScI))

The Universe: Big Bang to Now in 10 Easy Steps
In the new study, Riess and his colleagues used the Hubble Space Telescope to study 70 Cepheid variable stars in the Large Magellanic Cloud (LMC), one of the Milky Way's satellite galaxies. Cepheid variables dim and brighten at predictable rates and are therefore "standard candles" that allow astronomers to calculate distances.

(Another kind of standard candle, the star explosions known as Type 1a supernovae, enables scientists to measure distances even farther out into space. Riess, Schmidt and Perlmutter's studies of Type 1a supernovae led to their Nobel-winning discovery.)

Riess and his team also incorporated observations made by the Araucaria Project, a collaboration involving researchers in the United States, Europe and Chile, who studied various LMC binary star systems, noting the dimming that occurred when one star passed in front of its neighbor. This work provided additional distance measurements, helping the study team to improve their understanding of the Cepheids' intrinsic brightness.

The researchers used all of this information to calculate the universe's present-day expansion rate, a value known as the Hubble constant, after American astronomer Edwin Hubble. The new number is about 46.0 miles (74.03 kilometers) per second per megaparsec; one megaparsec is roughly 3.26 million light-years.

The uncertainty attached to this number is just 1.9%, the researchers said. That's the lowest uncertainty value to date that has been calculated using this approach - down from about 10% in 2001 and 5% in 2009.

The "expected" expansion rate, by contrast, is about 41.9 miles (67.4 km) per second per megaparsec. This projected rate is based on observations that Europe's Planck satellite made of the cosmic microwave background - the light left over from the Big Bang that created the universe 13.82 billion years ago.

"This is not just two experiments disagreeing. We are measuring something fundamentally different," Riess said.

"One is a measurement of how fast the universe is expanding today, as we see it. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding," he added. "If these values don't agree, there becomes a very strong likelihood that we're missing something in the cosmological model that connects the two eras."

The new study was published today (April 25) in The Astrophysical Journal. You can read it for free at the online preprint site .

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The Universe Is Expanding So Fast We Might Need New Physics to Explain It

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(Image: © NASA, ESA, Adam Riess, and Palomar Digitized Sky Survey) The universe is expanding faster than expected, suggesting that astronomers may have to incorporate some new physics into their theories of how the cosmos works, a new study reports.

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So dark energy may be related to expansion

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So dark energy may be related to expansion

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Dark Energy, Dark Matter | Science Mission Directorate

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What is dark energy? More is unknown than is known — we know how much there is, and we know some of its properties; other than that, dark energy is a mystery — but an important one. Roughly 70% of the Universe is made of dark energy. Dark matter makes up about 25%. The rest - everything on Earth, ev…

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The universe is around 68% dark energy, 27% dark matter, and 5% normal matter.

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As the universe expands, more dark energy is created, which goes against gravity ( pulling the universe onto itself) and eventually overpowering it, causing the universe to expand quicker.

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(Image: © NASA, ESA, M. Postman and D. Coe (STScI), and the CLASH Team)

The Hubble Constant is the unit of measurement used to describe the expansion of the universe. The cosmos has been getting bigger since the Big Bang kick-started the growth about 13.82 billion years ago. The universe, in fact, is getting faster in its acceleration as it gets bigger.

What's interesting about the expansion is not only the rate, but also the implications, according to NASA. If the expansion begins to slow down, that implies that there is something in the universe that is making the growth slow down - perhaps dark matter, which can't be sensed with conventional instruments. If the growth gets faster, though, it's possible that dark energy is pushing the expansion faster.

As of January 2018, measurements from multiple telescopes showed that the rate of expansion of the universe is different depending on where you look. The nearby universe (measured by the Hubble Space Telescope and Gaia space telescope) has a rate of expansion of 45.6 miles per second (73.5 kilometers per second) per megaparsec, while the more distant background universe (measured by the Planck telescope) is a bit slower, expanding at 41.6 miles per second (67 km per second) per megaparsec. A megaparsec is a million parsecs, or about 3.3 million light-years, so this is almost unimaginably fast.

Discovery by Hubble

The constant was first proposed by Edwin Hubble (the namesake for the Hubble Space Telescope). Hubble was an American astronomer who studied galaxies, particularly those that are far away from us.

In 1929 - based on a realization from astronomer Harlow Shapley that galaxies appear to be moving away from the Milky Way - Hubble found that the farther these galaxies are from Earth, the faster they appear to be moving, according to NASA.

While scientists then understood the phenomenon to be galaxies moving away from each other, today astronomers know that what is actually being observed is the expansion of the universe. No matter where you are located in the cosmos, you would see the same phenomenon happening at the same speed.

Hubble's initial calculations have been refined over the years, as more and more sensitive telescopes have been used to make the measurements, including Hubble and Gaia (which examined a kind of variable star called Cepheid variables) and other telescopes that extrapolated the constant based on measurements of the cosmic microwave background - a constant background temperature in the universe that is sometimes called the "afterglow" of the Big Bang. [Infographic: Cosmic Microwave Background Explained]

(Image credit: NASA/JPL-Caltech/Carnegie )

Cepheid variables

There are many kinds of variable stars, but the one that is most useful for measuring the Hubble constant is called a Cepheid variable. These are stars that regularly change their luminosity on a scale that usually ranges between 1 and 100 days (Polaris is among the most famous members of this group). Astronomers take distance measurements of these stars by measuring the variability of their luminosity.

The brighter the Cepheid appears from Earth, the easier it is to measure it. Some Cepheids can be seen from the ground, but for more accurate measurements, going into space is the best bet.

While Edwin Hubble was able to measure Cepheids about 900,000 light-years away - an astonishing distance for the time - within the universe that is still relatively close to Earth. Farther in space, the Cepheids are fainter and recede more quickly, which is where the Hubble Space Telescope was able to help in the 1990s after its launch. In 2013, the Gaia space telescope launched to accurately map the positions and luminosities of approximately 1 billion stars. Its data releases have also helped with refining the Hubble Constant.

Cepheids, however, are not perfect for measuring cosmic distances. Among other difficulties, they are often located in dusty areas (which obscure some wavelengths in photographs) and the more distant ones are hard to spot because they are so faint from our perspective.

Other techniques arose to supplement Cepheid measurements, such as the Tully-Fisher relation, which is a correlation between the luminosity of a spiral galaxy and its rotational velocity, according to Shoko Sakai, a research associate at the National Optical Astronomical Observatory. "The idea is that the bigger the galaxy is, faster it is rotating," he wrote. "That means that if you know the rotation velocity of the spiral galaxy, you can tell by using this Tully-Fisher relation its intrinsic brightness (that is, how bright that galaxy really is). By comparing the intrinsic brightness with the apparent magnitude (what you actually observe -- because the further the galaxy, the dimmer it "appears"), you can calculate its distance."

Telescopes that measure the cosmic microwave background - such as Planck - used another technique that examines fluctuations in the cosmic microwave background to determine the constant.

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(Image: © NASA, ESA, M. Postman and D. Coe (STScI), and the CLASH Team) The Hubble Constant is the unit of measurement used to describe the expansion of the universe. The cosmos has been getting bigger since the Big Bang kick-started the growth about 13.82 billion years ago.

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How Do We Know The Universe Is ACCELERATING?

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If the universe is expanding, then the universe can't be infinite, and if it’s not infinite, what’s outside the boundaries of space?

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A newer idea is that the universe's expansion is fluctuating, never staying in the same place. so in some parts it's growing, and in others it's shrinking, but overall it's still expanding at the same rate.

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Unbeknownst to most of us, our universe is constantly expanding. Cosmologists-scientists that study the development of the universe-can determine how it changes over time by visualizing very distant radiation left over from the Big Bang that occurred 13.8 billion years ago. Because light travels at a constant speed, viewing distant objects in space allows them to be seen as they were when the universe first began. Using this technique, cosmologists predict that while the universe first expanded quite quickly after the Big Bang, this expansion later slowed due to the appearance of the mysterious force known as dark matter.

Using a new technique, cosmologists from the University of California, Davis have now determined that the universe is expanding faster than the original models predicted. In their study, the researchers utilized the Keck Observatory telescope in Hawaii, which is equipped with special lenses that measure the way light gets distorted by space objects as it travels towards Earth. After pointing it at three very active galaxies deep in space, the telescope collected multiple distorted images of the galaxies that corresponded to different points in time. By comparing these images, the cosmologists determined that the universe is expanding approximately 9% faster than the rate predicted by conventional models.

Although it is not uncommon for experimental data to challenge theoretical models, scientists must carefully rule out possible causes of error before accepting provocative conclusions. This study is strengthened by the fact that the results corroborate those obtained from the Hubble Space Telescope, a widely trusted instrument in the cosmology field. The unique optical properties of the Keck Observatory telescope now open up the possibility of using additional lens to generate even more accurate data. If future results hold up, cosmologists will be tasked with unraveling why the discrepancy between the theoretical and experimental data exists. Some have suggested that this study may usher in an era of 'new physics', as a currently unidentified energy or particle may be behind the rapid expansion of the universe.

Managing Correspondent: Benjamin Andreone

News Article: A crisis in cosmology: New data suggests the universe expanding more rapidly than believed. Phys.org

Original Article: A SHARP view of H0LiCOW: H ₀ from three time-delay gravitational lens systems with adaptive optics imaging. Monthly Notices of the Royal Astronomical Society

Image Credit: Pixabay

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The Universe is Expanding Faster than Scientists Thought - Science in the News

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Unbeknownst to most of us, our universe is constantly expanding. Cosmologists-scientists that study the development of the universe-can determine how it changes over time by visualizing very distant radiation left over from the Big Bang that occurred 13.8 billion years ago.

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This isn't completely related but it's still interesting

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This isn't completely related but it's still interesting