There is a wave: look to the sky

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There is a wave: look to the sky
There is a wave: look to the sky
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Physicists announced the discovery of gravitational waves - perturbations of space-time predicted by Einstein. This discovery can take science to a new level of understanding the history of the Universe.

Higgs boson

An article from the journal Naked Science (# 13, May-June 2014).

It has only been a year since the Higgs boson was confirmed. But physicists studying the structure and origin of the Universe have already presented the world with another discovery, comparable in importance to the discovery of a "particle of God." This time, astronomers managed to record the "gravitational echo" of the Big Bang, which most likely confirms one of the theories of the origin of the Universe. According to this theory, in the first fractions of a second after the Big Bang, the universe expanded at a speed much higher than the speed of light, after which the expansion slowed down, but continues to this day. Confirmation of such a model is the most important step in understanding the most basic properties of the Universe: quantum mechanics, gravity, the nature of space and time. It is expected that the researchers of the "gravitational echo" will receive a Nobel Prize.

An international team of researchers used in their work the BICEP2 radio telescope located in Antarctica near the South Pole. Using this instrument, scientists for two years "listened" to cosmic microwave background radiation and analyzed its properties. The unprecedented accuracy of the data allowed scientists to identify in it traces of undulating fluctuations in the gravitational field caused by the Big Bang 13.8 billion years ago.

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The very existence of gravitational waves is the most important physical discovery. Unlike electromagnetic waves propagating in four-dimensional space-time, gravitational waves themselves are perturbations of the rectilinear structure of space-time. They were predicted by Einstein's General Theory of Relativity. But detecting gravitational waves is very difficult: it took scientists a hundred years. However, even now this was not done directly (scientists cannot yet “catch” the gravitational wave itself), but indirectly - by analyzing their influence on the relic radiation.

But the main thing in the new discovery is not the discovered properties of the relict radiation (the so-called B-mode of its polarization), and even the existence of gravitational waves that does not follow from them. Scientists are primarily interested in the second corollary from the BICEP2 data: they make it possible to quite confidently assert what happened in the first moments of the existence of the Universe.

In the beginning was math

Like gravitational waves, electromagnetic waves were theoretically predicted long before they were experimentally detected. In 1832, Michael Faraday wrote a secret letter to the secretary of the Royal Society in London. In this letter, which lay unopened until 1937, Faraday predicted that magnetic and electrical forces propagate in space and time "like vibrations on the surface of disturbed water." Faraday wanted to stake out the title of the discoverer of these waves in case they were actually discovered

However, thirty years later, in the 1860s, James Maxwell proposed a much more detailed mathematical justification for the existence of electromagnetic waves. It was even possible to calculate the speed of these waves from Maxwell's equations: it turned out to be strikingly close to the speed of light established experimentally. It is Maxwell who is usually credited with the final unification of electricity with magnetism and the prediction of the existence of electromagnetic waves, experimentally discovered in 1888 by Heinrich Hertz

Naked Science spoke with Stanford University astrophysicist Walt Ogburn, a BICEP2 contributor. More accurate measurements of the interaction between gravitational waves and relic radiation are planned in the coming years, he said, including at the next stage of the project, BICEP3. This will provide an even clearer picture of the origin of our world. In addition, several scientific groups in the foreseeable future can indirectly confirm the discoveries of BICEP2 by studying gravitational waves from other sources (such as black hole mergers) and other methods, without using the relic radiation.

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Relict radiation

It all began in 1964, when young astronomers Arno Penzias and Robert Wilson studied radio signals received from the constellation Cassiopeia using an antenna that was supersensitive at that time. To the scientists' annoyance, they could not get rid of the interference in the devices. This noise seemed to arise from everywhere, which is why Penzias and Wilson reasonably concluded that the matter was in the antenna itself. When they found bird droppings in the detector, they breathed a sigh of relief. But cleaning the antenna, like all other attempts to fix the devices, did not lead to anything: the noise continued to intrusively interfere with the measurements.

Today we know that birds had nothing to do with interference - however, they were not interference at all.

Penzias and Wilson literally stumbled upon radiation from the "creation of the world."

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Approximately 379 thousand years after the Big Bang, the young Universe cooled so much that protons began to combine with electrons, forming atoms and emitting light at the same time. But at the same time, space itself continued to expand as a result of the Big Bang. As a result, by the time the planet Earth appeared with astronomers inhabiting it, the waves of that ancient radiation turned out to be strongly "stretched" - today they reach us in the form of microwave radio emission (microwaves are actually "stretched" light). They were stumbled upon by Penzias and Wilson, who in 1978 received the Nobel Prize for their discovery. Microwave radiation, discovered by astronomers, was called relict, that is, ancient. The entire modern theory of the origin of the Universe is based on its properties.

Ambulance stars

"Stretching" of light in space is one of the key discoveries of astrophysics at the beginning of the 20th century. The works of Vesto Slipher, Edwin Hubble and others have shown that the light of distant stars, viewed from Earth, "shifts" towards the red part of the spectrum, that is, "stretches" during its flight through space. This is explained by the Doppler effect and relativistic time dilation: if the wave source moves away from the observer at a high speed, then the wave itself comes to the observer longer. Such "stretching" makes light (waves of electromagnetic field vibrations) redder, and, for example, sound (waves of air vibrations) - lower. Typically, the Doppler effect is illustrated by an ambulance siren: its tone is heard changing as a car rushes by quickly. The discovery of the redshift of the radiation of celestial bodies allowed physicists to conclude that all distant stars are constantly moving away from us - which means that the Universe is in a state of expansion

Ever since the battles of Penzias and Wilson with bird droppings, it has been known that the relic radiation is remarkably uniform. Whichever direction the researchers pointed their instruments in, the microwave interference turned out to be exactly the same. The noise did not depend on the angle at which the detector was placed. It did not differ day and night, that is, from different sides of the Earth. It turned out that the microwave "echo" of the Big Bang is practically uniform in any visible point of the Universe.

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This uniformity is more mysterious than it might seem. It applies not only to the relict radiation itself.As far as we can tell, on the largest scales, the Universe is also homogeneous: there are no regions densely packed with galaxies, but there are no completely empty regions.

Mathematical calculation shows: if the Big Bang looked like an ordinary one, in which energy and matter are randomly scattered in all directions, then today there should be much more heterogeneities. Otherwise, one would have to assume that the initial configuration of the explosion, by some miracle, turned out to be exactly the same to ensure homogeneity. Are we just lucky?

Big Bang and Big Roulette

In principle, luck is possible. If we assume that a homogeneous Universe is for some reason the only form of the universe suitable for life, then the anthropic principle comes into play. This is a concept that asserts that the world exists exactly in this form, not because it is so convenient for us, but because if it were different, we simply would not exist.

The anthropic principle is a very serious way of explaining many physical phenomena. But a real scientist is difficult to satisfy with an abstract philosophical concept. He wants something more material and definite.

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In the 1980s, American physicist Alan Guth proposed a model that could explain the uniformity of the universe and a number of its other strange properties without resorting to the "just lucky" hypothesis. According to Guth's theory, the first fractions of a second after the Big Bang resembled not so much an explosion as a very rapid inflation of a crumpled balloon. This analogy was suggested by Stephen Hawking in his classic popular science work A Brief History of Time.

To simplify greatly, Guth's theory can be reduced to the fact that in the first moments after the Big Bang, the Universe was heterogeneous, but the heterogeneities expanded, grew at an increased rate and eventually “straightened out”.

Immediately after the Big Bang, matter in the usual sense did not yet exist - the physical interactions that are required to form atoms were a single force. But with the cooling and expansion of the Universe, this combined force quickly "disintegrated" into separate independent interactions known today: electromagnetic, strong and weak (the fourth force - gravitational - was separated even earlier). This disintegration was a bit like a game of roulette: at high speed the ball runs along the edge, but when it slows down, it “selects” one of the cells.

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Theoretically, the separated interactions can be combined "forcibly": for this you need to concentrate the right amount of energy in the right particle. High energies can be achieved by accelerating particles to enormous speeds and pushing them together - this is precisely the task of colliders. For example, electromagnetic and weak interactions combine at energies of the order of 100 GeV. This energy was achieved back in the 1980s with the help of the Proton Super Synchrotron, the predecessor of the current Large Hadron Collider. Having gained access to particles of the required energy, scientists proved the existence of a single electroweak interaction.

However, accelerating the particles to the unification of all four forces is unlikely to work in the near future. Even the Large Hadron Collider - the most powerful particle accelerator in history - can achieve energies of the order of 4 TeV (40 times more than is needed to combine electromagnetic and weak interactions), but, according to mathematical calculations, it takes about 1016 TeV to combine all interactions. A collider reaching such energies would be the size of the solar system!

Based on Guth's theory, the disintegration of a single force and the formation of matter were uneven. "Lumps" of space, where physical forces were separated, existed parallel to the areas where they continued to exist in their original, united form.In different parts of the young Universe (we are talking about 10–32 seconds after the Big Bang), different physical laws operated.

The universe was not homogeneous. But in those areas where the forces did not disintegrate, a special "anti-gravity" energy arose, due to which the space expanded faster. As a result, the "folds" of the Universe, like the folds of a balloon when inflated, straightened, and it gradually became homogeneous and homogeneous.

So luck has nothing to do with the homogeneity of the universe, according to Guth. It's just that the very existence of heterogeneities causes a force that helps to eliminate them.

This "antigravitational" energy is the basis of the accelerated, "superfast" expansion, or inflation of the universe in the first fractions of a second after the Big Bang.

This model has a number of implications. One of them is the presence of gravitational waves, which, together with the electromagnetic relict radiation, should constitute the “echo” of the Big Bang, the echo of which can be caught to this day.

As BICEP2 project participant Walt Ogburn explains, initially gravitational waves were quantum fluctuations - microscopic fluctuations of the gravitational field on the scale of elementary particles, that is, incomparably smaller than a hydrogen atom. But over billions of years, these waves have stretched out to enormous sizes: from the point of view of a telescope on the Earth's surface, they are several times larger than the full moon! Other than inflation, this stretching is very difficult to explain. Although it is not yet possible to detect gravitational waves directly, their existence can be proved by the effect on microwave radiation - the second component of the "echo", the same one that American astronomers in 1965 attributed to bird droppings. This is what the researchers working with the BICEP2 telescope did.

The discovery caused a rather violent reaction in scientific circles. Stephen Hawking, for example, announced that he had won an old argument with cosmologist Neil Turok. What the Canadian scientist betrayed Hawking is not reported.

All for one

According to the most common hypothesis today, immediately after the Big Bang, four fundamental interactions - gravitational, strong, weak, and electromagnetic - were indistinguishable from each other and represented one force. This became possible due to the monstrous concentration of energy in a very small universe

It is believed that such a combination lasted only 10–43 seconds. With a decrease in the energy density (that is, with the slowing down of particles, or the cooling of the Universe - all this is approximately the same), the forces gradually "split off" from each other. First, gravity separated, then a strong interaction, which allowed the formation of protons and neutrons. Electromagnetic and weak interactions were the last to disperse

Parallel Worlds

The new discovery has another interesting consequence. Amid the excitement around gravitational waves, amateurs to fantasize about parallel universes, as well as their ideological opponents, have sharply intensified.

Although many scientists are skeptical about parallel worlds, astrophysics and cosmology have a solid set of open questions that fundamentally allow their existence. Having confirmed (at least with high probability) the inflationary model of the Big Bang, scientists opened a Pandora's box.

Inflation in the universe implies that in the early stages there were areas within which the laws of physics operated in different ways. In the thickness of the "primordial chaos", "bubbles" of normal (in our understanding) physics were formed. The space between the bubbles expanded like an avalanche and very quickly - faster than the speed of light.

The basic model assumes that as a result, the entire space has become one large homogeneous "bubble". But what if the process never finished? It is possible that the Universe we see is just one of the “bubbles”.Others may be inaccessible to us: within our "subuniverse" nothing can move faster than light, so we, with all our desire, will not be able to "catch up" with the parallel universes receding from us.

That is why many scientists do not want to discuss the existence of such a Multiverse: if parallel worlds, even theoretically, cannot influence us in any way, then from our position this is equivalent to the fact that they do not exist. In addition, one of the generally accepted criteria for scientific truth is its falsifiability, that is, the fundamental possibility of refutation. The theory of the Multiverse cannot be proved or disproved - at least not in the form in which it is currently being discussed. Therefore, the participants in the BICEP2 project themselves are not too concerned about the problem of parallel worlds, as Walt Ogburn told Naked Science.

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But according to Alan Guth - the one who "invented" cosmic inflation in the 1980s, it is rather difficult to imagine an inflationary theory without the Multiverse.

In addition, the idea of ​​“bubbles” of parallel worlds is a good way to reinforce the vague anthropic principle (that is, the concept of “we were lucky with the universe, and those who were unlucky were simply not born”) with a real theoretical basis. On the scale of the Multiverse, "bubbles of the worlds" can form randomly and have different physical laws. But we are able to exist - and wonder about our own existence - only in that one where all the laws are exactly what we have.

The mass of an electron, for example, cannot be deduced from any other quantities - as far as we can judge, it is determined completely by chance. But the slightest deviation from this mass would lead to the complete collapse of the Universe as we know it. Atoms would not be able to form, there would be no planets, stars and galaxies, chemical reactions - and therefore life - would not be able to arise.

One of the main theorists of the Multiverse, a professor at Stanford University, Andrei Linde, back in 2002, described the potential connection between cosmic inflation, "bubbles" of universes and the anthropic principle. In his opinion, the existence of other worlds with different physical laws is a perfectly reasonable explanation of the properties of our own "subuniverse", even if this explanation cannot be proved.

But Linde's opponents are in no hurry to recognize the evidence of the existence of parallel worlds behind the discoveries of the BICEP2 project. For example, mathematician Peter Woit points out in his blog that the multiverse can exist in two ways. The first arises if the physical laws of all "bubbles" are the same. The second type involves the random formation of these laws, for different universes separately. Voight argues: inflationary theory, which is presented in the media almost as proof of the existence of parallel worlds, in fact admits (but in no way proves) only a type 1 multiverse (in which all the "bubbles" are the same). This, of course, is not bad, but, firstly, it is much more boring than the "diverse" multiverse, and, secondly, it does not help in any way to "strengthen" the anthropic principle - if all the bubbles are the same, then it is still not clear why the electron weighs exactly that much, How much does it weigh.

What will the discovery open?

As all serious commentators and almost none of the journalists note, it is too early to consider cosmic inflation to be unequivocally proven. The data on gravitational waves must be verified by independent experts and confirmed in further experiments. Researchers are currently preparing for the BICEP3 project, which will use a new generation detector.

As is almost always the case in modern science, what the press calls "discovery" is not really Archimedean's "Eureka!"But the fact that scientists have decided to present their results now is encouraging.

But even if the existence of gravitational waves is finally confirmed and proven, this result will not put an end to the studies of the Big Bang and the origin of the Universe. On the contrary, in cosmology there are many more questions than answers. Scientists, for example, still do not know how to reconcile the two central pillars of modern physics - quantum mechanics and General Relativity.

Quantum mechanics describes the behavior of very small objects that have both particle and wave properties. In contrast, general relativity is used to describe space, time, and gravity on very large astronomical scales. Therefore, in practice, they rarely meet each other. But in the situation of the Big Bang, both theories are applicable: from an initially infinitely small volume, an infinitely large Universe emerged. How exactly quantum effects interact with gravitational ones is one of the most difficult questions of modern physics.

Understanding the details of the origin of the universe is not just a ground for pseudo-scientific fantasies. The more we understand about the history of the world, the more opportunities we open up for the physics of the future. According to Walt Ogburn, understanding physics at the level of unifying fundamental interactions in the future may lead to the creation of technologies that today cannot even be imagined. Without the theory of relativity, there would be no GPS navigators, and without quantum mechanics, there would be no lasers or modern computers. What doors will open the disclosure of the secrets of the Big Bang, today no one knows. Perhaps, in another hundred years, the discoveries of BICEP2 will be the starting point of a new era, as it once became the reference point for noise in antennas directed to the constellation Cassiopeia.

* An article from the journal Naked Science (# 13, May-June 2014).

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