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Le quattro forze fondamentali della fisica

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Le quattro forze fondamentali della fisica

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o interazioni fondamentali.
Scelto con Federica Sortiero.

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Scelto con Letizia Boselli.

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(Image credit: Shutterstock)

Gravity is one of the four fundamental forces in the universe, alongside electromagnetism and the strong and weak nuclear forces. Despite being all-pervasive and important for keeping our feet from flying off the Earth, gravity remains, in large part, a puzzle to scientists.

Ancient scholars trying to describe the world came up with their own explanations for why things fall toward the ground. The Greek philosopher Aristotle maintained that objects have a natural tendency to move toward the center of the universe, which he believed to be the middle of the Earth, according to physicist Richard Fitzpatrick from the University of Texas.

But later luminaries dislodged our planet from its primary position in the cosmos. The Polish polymath Nicolas Copernicus realized that the paths of the planets in the sky make much more sense if the sun is the center of the solar system. The British mathematician and physicist Isaac Newton extended Copernicus' insights and reasoned that, as the sun tugs on the planets, all objects exert a force of attraction on one another.

In his famous 1687 treatise " Philosophiae naturalis principia mathematica," Newton described what is now called his law of universal gravitation. It is usually written as:

Where F is the force of gravity, m1 and m2 are the masses of two objects and r is the distance between them. G, the gravitational constant, is a fundamental constant whose value has to be discovered through experiment.

(Image credit: marekuliasz (opens in new tab) Shutterstock (opens in new tab))

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Gravity is powerful, but not that powerful

Gravity is the weakest of the fundamental forces. A bar magnet will electromagnetically pull a paper clip upward, overcoming the gravitational force of the entire Earth on the piece of office equipment. Physicists have calculated that gravity is 10^40 (that's the number 1 followed by 40 zeros) times weaker than electromagnetism, according to PBS's Nova.

While gravity's effects can clearly be seen on the scale of things like planets, stars and galaxies, the force of gravity between everyday objects is extremely difficult to measure. In 1798, British physicist Henry Cavendish conducted one of the world's first high precision experiments to try to precisely determine the value of G, the gravitational constant, as reported in the Proceedings of the National Academy of Science's Front Matter.

Cavendish built what's known as a torsion balance, attaching two small lead balls to the ends of a beam suspended horizontally by a thin wire. Near each of the small balls, he placed a large, spherical lead weight. The small lead balls were gravitationally attracted to the heavy lead weights, causing the wire to twist just a tiny bit and allowing him to calculate G.

Remarkably, Cavendish's estimation for G was only 1% off from its modern-day accepted value of 6.674 × 10^−11 m^3/kg^1 * s^2. Most other universal constants are known to far higher precision but because gravity is so weak, scientists must design incredibly sensitive equipment to try to measure its effects. Thus far, a more precise value of G has eluded their instrumentation.

The German-American physicist Albert Einstein brought about the next revolution in our understanding of gravity. His theory of general relativity showed that gravity arises from the curvature of space-time, meaning that even rays of light, which must follow this curvature, are bent by extremely massive objects.

Einstein's theories were used to speculate about the existence of black holes - celestial entities with so much mass that not even light can escape from their surfaces. In the vicinity of a black hole, Newton's law of universal gravitation no longer accurately describes how objects move, but rather Einstein's tensor field equations take precedence.

Astronomers have since discovered real-life black holes out in space, even managing to snap a detailed photo of the colossal one that lives at the center of our galaxy. Other telescopes have seen black holes' effects all over the universe.

The application of Newton's gravitational law to extremely light objects, like people, cells and atoms, remains a bit of an unstudied frontier, according to Minute Physics. Researchers assume that such entities attract one another using the same gravitational rules as planets and stars, but because gravity is so weak, it is difficult to know for sure.

Perhaps, atoms attract one another gravitationally at a rate of one over their distance cubed instead of squared - our current instruments have no way of telling. Novel hidden aspects of reality might be accessible if only we could measure such minute gravitational forces.

A perpetual force of mystery

Gravity perplexes scientists in other ways, too. The Standard Model of particle physics, which describes the actions of almost all known particles and forces, leaves out gravity. While light is carried by a particle called a photon, physicists have no idea if there is an equivalent particle for gravity, which would be called a graviton.

Bringing gravity together in a theoretical framework with quantum mechanics, the other major discovery of the 20th-century physics community, remains an unfinished task. Such a theory of everything, as it's known, might never be realized.

But gravity has still been used to uncover monumental findings. In the 1960s and 70s, astronomers Vera Rubin and Kent Ford showed that stars at the edges of galaxies were orbiting faster than should be possible. It was almost as if some unseen mass was tugging on them gravitationally, bringing to light a material that we now call dark matter.

In recent years, scientists have also managed to capture another consequence of Einstein's relativity - gravitational waves emitted when massive objects like neutron stars and black holes rotate around one another. Since 2017, the Laser Interferometer Gravitational-Wave Observatory (LIGO) has opened up a new window to the universe by detecting the exceedingly faint signal of such events.
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(Image credit: Shutterstock) Gravity is one of the four fundamental forces in the universe, alongside electromagnetism and the strong and weak nuclear forces. Despite being all-pervasive and important for keeping our feet from flying off the Earth, gravity remains, in large part, a puzzle to scientists.

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Scelto con Letizia Boselli.

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Scelto con Federica Sortiero.

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Electromagnetic force definition at Dictionary.com, a free online dictionary with pronunciation, synonyms and translation. Look it up now!

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Scelto con Letizia Boselli.

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What hold a nucleus together? Why does it not just fall apart. In this video I discuss the Strong Nuclear Force, in simple terms that holds the atom together. This concept is essential to explain radioactive decay, fission and fusion. Follow me on facebook - www.facebook.com/HighSchoolPhysicsExplained

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Weak Interaction: The Four Fundamental Forces of Physics #2

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di Roberto Servi.
Scelto con Letizia Boselli.

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Nei laboratori dell'Institute for Advanced Study di Princeton, la giovane ricercatrice Mary Costello si imbatte, al termine di una simulazione al computer sui sistemi complessi, in una sorprendente scoperta relativa alla Teoria del Caos, dalle ripercussioni immani e potenzialmente distruttive.Per lei sarà l'inizio di una serie imprevedibile di conseguenze, che

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Per un pubblico infantile.
Scelto con Federica Sortiero.

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An explanation of the Four Fundamental Forces by Mike Jones and Kaitlin Snapp. We do not own any of the music from the video.

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Were the four fundamental forces of nature unified at the big bang?

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Answer (1 of 2): Yes they were indeed. Temperature is the factor that plays major role over here. Even though in day today life gravitational force is the weakest one and strong force is the strongest force, as temperature of system (in this case universe) increases, it is observed that these for...

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Scelto con Letizia Boselli.

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In the beginning, the universe was in a very hot state and so the forces were much alike each other. However, after sometime, the temperature of the universe decreased and the effects of the different forces became more and more observable. This phenomenon is much like the game of roulette, in the beginning when the wheel has just been spun, the ball rolls over all the numbers(all the forces are alike) but as the ball loses energy(temperature of the universe decreases) the ball falls onto a certain number (effects of the forces are observable, eg. strong nuclear force binds the nucleus).

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Why did the four fundamental forces differentiate after the Big Bang, instead of remaining as one unified force?

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Answer (1 of 2): In the beginning, the universe was in a very hot state and so the forces were much alike each other. However, after sometime, the temperature of the universe decreased and the effects of the different forces became more and more observable. This phenomenon is much like the game o...

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Scelto con Federica Sortiero.

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Please refine your question. I assume you're talking about particle physics and you want to know whether the weak and strong forces we have discovered have always existed. If that is what you are asking, by using "always" you have placed into consideration the concepts of "before" and "after" the Big Bang.

However, if nothing existed before the Big Bang, and if time was created at the instant of the Big Bang, the forces you refer to only came into existence at the time, or the moment of the Big Bang. The concept "nothing" is problematic; that is to say we poor humans cannot visualize or image with our limited brains, nothing. It's not empty space nor is it a void.

There is an assumption here that requires us to accept the proposition that "something came out of nothing" but we cannot visualize nothing, just as we cannot visualize the face of God. (If we could, we would try to manipulate and anticipate what God will do - if anything).The concept of nothing is completely counter intuitive. The question is, is it possible? For Moslems and Christians and Jews, the answer is "yes" because with Allah (God) all things are possible. Our human notions of always" implies a timeline extending backwards or forwards from the Big Bang to infinity.

We get to the concept of infinity through the imagination. "Infinity" can't exist, or can it? We again believe that time can extend forward always. The question is whether time bends to the right or to the left or up and down. If time can be curved it may loop around and make a circle. This is mere conjecture on my part and I cannot back it up with mathematical certainty, but it is something to think about and consider. "Infinity" is a very useful concept in mathematics. But, as Einstein said: "as far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality." Enjoy.

We use "infinity" like a magician uses "abracadabra". We get to the concept of infinity through the imagination. "Infinity" can't exist, or can it? We know that time can extend forward always. The question is whether time bends to the right or to the left or up and down. If time can be curved it may loop around and make a circle. This is mere conjecture on my part and I cannot back it up with mathematical certainty, but it is something to think about and consider. "Infinity" is a very useful concept in mathematics. But, as Einstein said: "as far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality." Enjoy.

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Have any of the four forces come into existence since the Big Bang, or were they always there?

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Answer (1 of 6): I'm not sure what you mean by "materialize", but it's possible for a single force to split into two forces that seem completely separate at low energies. At high energies, the two low-energy forces will recombine again. Understanding how this works is kind of complicated, but t...