The rebound of the universe: the opposite of the Big Bang
People have always been fascinated by two main theories about the origin of the universe. "In one of them there is a universe in a single moment of creation (as in the Judeo-Christian cosmogony and Brazilian)," wrote Mario Novello cosmologists and Santiago Perez-Bergliffa in 2008. Another - "The universe is eternal and consists of an infinite series of cycles (as in the cosmogony of the Babylonians and Egyptians)." Separation in modern cosmology "somehow echoing cosmological myths," wrote cosmologists.
it may seem that much confrontation was not in the last few decades. The Big Bang Theory, a standard topic in textbooks and television programs, enjoys strong support in modern cosmology. Picture of an eternal universe was preferable to a hundred years ago, but lost support when astronomers saw that the cosmos is expanding and that it was small and simple 14 billion years ago. The most popular modern version of the theory of the Big Bang started with the so-called "cosmic inflation" - burst of exponential expansion, in which an infinitesimal piece of space-time has ballooned into a huge, flat, macroscopic space, which has since continued to grow.
Today, using one source ingredient (inflaton field), inflationary models reproduce many well-known parts of the cosmos. But as the history of the origin of inflation theory is losing much: it is not clear what preceded it, and it was up to. Many theorists believe that inflaton field should naturally fit into a more complete, though it is not known theory of the origin of time.
In the last few years more and more cosmologists began to carefully review the alternatives. They say that the Big Bang could be ... Big Bounce. Some cosmologists prefer to see the big picture, in which the universe expands and contracts like a cyclic light, bouncing off each time shrinks to a certain size; others suggest that the cosmos bounced only once - and that it is compressed to a rebound for an infinitely long time, and will expand indefinitely thereafter. At any time, the model continues to flow into the past and the future without end. With modern science there is hope to solve this ancient debate. In coming years, the telescopes have to find conclusive evidence of cosmic inflation. During the first violent growth - if it was - quantum ripples in the space-time fabric was stretched and printed in the form of small eddies in the polarization of the ancient world - the cosmic microwave background. Experiments involving current and future telescopes look for these twists. If they do not find in the next few decades, it also will not mean that the inflation theory is wrong (after all, these twists are too dim), but strengthen the position of the rebound cosmology, according to which these vortices should not be.
Several groups of scientists have made remarkable progress at the same time. In the past, physicists have identified two new options for a possible rebound. One of the models described in the paper, which appeared in the Journal of Cosmology and Astroparticle Physics, was represented by Anna Iddzhas of Columbia University, in continuation of its previous work in conjunction with the cosmologist Paul Steinhardt. Suddenly, yet another new solution to the rebound, accepted for publication in Physical Review D, was proposed by Peter Graham, David Kaplan and Surdzhitom Rahendranom, the well-known trio of scientists who were engaged in any more questions in particle physics and had no relation to the community of cosmologists rebound.
Generally, this issue has taken on new meaning in 2001 when Steinhardt and three cosmologist said that the period of slow compression in the history of the universe can be explained by its exceptional smoothness and the plane that we see today, even after the bounce - without having to connect the inflation.
Perfect simplicity of the universe, the fact that not a single area of the sky contains more matter than any other, and that space is so flat, as can be seen telescopes - all of this is surprising and inexplicable. That space was so homogeneous as it is, experts believe that when the cosmos was a centimeter across, he had to have the same density everywhere within one part per 100 000. But with the growth of the small size, matter and energy were immediately komkovatsya and distort space-time. Why did our telescopes can not see the universe destroyed by gravity? "Inflation came out of the idea that the smoothness and the plane of the universe - that's crazy," says cosmologist Neil Turok, Director of the Institute for Theoretical Physics Perimeter in Waterloo, Ontario, and co-operation in 2001 on space compression theme, written by Steinhardt, Justin Khoury and Bert Ovrutom . According to the scenario of inflation, the size of a centimeter region came in the course of inflationary expansion in the region even less - a small speck no bigger than a trillionth of a trillionth of a centimeter. Stretching in a flat and smooth inflaton field, this spot should not have to pass through the space and time of strong fluctuations and dragged into a large and smooth universe like ours. Raman Sundrum, a theoretical physicist at the University of Maryland, said that the inflation he likes "built-in fault tolerance." If during the phase of explosive growth and was the accumulation of power that distorts space-time in a certain place, the concentration was rapidly expanding.
But where exactly it is incredibly small spot and why it was so smooth and flat, no one knows. Theorists have found many options include inflaton field in string theory, on which they can be established quantum theory of gravity. But so far there is no evidence either for or against these ideas.
Cosmic inflation also has a controversial effect. The theory presented in 1980 by Alan Guth, Andrei Linde, Alexei Starobinski and Steinhardt, almost automatically leads to the hypothesis that our universe - this is a random bubble in an infinite multiverse sea. Once inflation starts, calculations show that it will last forever and only stop in places, in the "pockets", which will then flourish universes of our type. The possibility of ever-expanding process of inflation suggests the multiverse, what exactly is our bubble may remain forever unknown, as everything possible was happening in the multiverse infinite number of times. Of course, this conclusion is retching experts. It is difficult to imagine that our universe may be just one of many. Steinhardt himself called the idea "nonsense". This attitude is partly motivated him and other researchers do rebound. "In the model, there is a rebound period of inflation," said Turk. Instead, they added compression period before the Big Bang, which explains our homogeneous universe. "As the gas in your room completely uniform, because air molecules collided and mixed, and the universe was large and slowly shrank, which gave her time to smooth out."
While the first model of a contracting universe were confused and imprecise, many scientists were convinced of the basic idea: that the slow compression can explain many features of our expanding universe. "And then a narrow bottleneck began to rebound. People agreed that the move in the compression phase is very interesting, but not if you can not go into the expansion phase. "
Rebound - it's not easy. In the 1960s, British physicists Roger Penrose and Stephen Hawking have proved a set of so-called "theory of the singularity," shows that in very general terms of compression of matter and energy will inevitably turn infinitely dense point - a singularity. These theorems can hardly accommodate representation as a contracting universe, in which matter, space, time and energy to fold inwards avoids collapse to a singularity - in which the classical theory of gravity and space-time Albert Einstein ceases to function and which are beginning to work the rules of quantum gravity . Why shrinking universe can escape the fate of a massive star that dies, shrinking to the point, and becomes a black hole?
Both models use the suggested rebound gaps in the theorems on singularities - those who for many years seemed a dead end. Cosmologists rebound long recognized that the rebound may be possible, if the universe contains matter with negative energy (or other sources of negative pressure) that would counteract gravity and would be repelled by it. Scientists have tried to use this loophole since the early 2000s, but have always come to the fact that the addition of ingredients with negative energy makes them unstable model of the universe, because quantum fluctuations of positive and negative energy can spontaneously born in the vacuum of space with zero energy. In 2016, a Russian cosmologist Valery Rubakov and his colleagues have even proved the theorem, which excluded large class rebound mechanisms. Then Iddzhas found rebound mechanism that can get around and this is an exception. A key ingredient in its model - a simple substance, "scalar field", which, in theory, could come into play when the universe was compressed and energy is becoming highly concentrated. Scalar field could hide itself in a gravitational field so as to have a negative pressure on the earth, preventing the compression and stretching space-time. Iddzhas work - "the best attempt to rein in all the possible instability and create a really stable model with this special type of matter," says Jean-Luc Leyners, theoretical cosmologist at the Institute for Gravitational Physics Max Planck in Germany, who also worked on variations rebound.
Graham, Kaplan and Rahendran presented their idea of a non-singular rebound in the preprint on arxiv.org site in September 2017. His work, they began with the question of how could the previous compression phase in the history of the universe to explain the value of the cosmological constant - is strikingly small number, which determines the amount of dark energy, sewn in the fabric of spacetime, energy that is pushing the accelerating expansion of the universe.
Working on the most difficult part - rebound - three scientists used a second, largely forgotten loophole in the theorems of singularity. They took inspiration from the strange universe of the model proposed by the logician Kurt Gödel in 1949, when he and Einstein worked at the Institute for Advanced Study in Princeton. Gödel used the laws of general relativity to create a rotating universe theory that the rotation kept it from the gravitational collapse in the same way as the Earth's orbit does not allow it to fall to the sun. Gödel was especially emphasized by the fact that its rotating universe allowed "closed time-like curves" that is in fact the time loop. Until his death, he believed that the universe revolves exactly as its model. Today, scientists know that this is not so; otherwise one direction and order in space would be preferable to others. But Graham and company think about the small, twisted spatial dimensions that may exist in space, such as six extra dimensions postulated by string theory. Can a shrinking universe rotate in these areas? Imagine that there is only one of these extra dimensions curled, a tiny circle at each point in space. Graham says, "in each point in space has an additional direction in which you can move the fourth spatial dimension, but you can only walk a short distance and back to the place from which to start the movement." If the compact extra dimensions will be at least three, as the compression of the universe matter and energy can start to spin them, and the measurements themselves are spinning with matter and energy. Rotation in the extra dimensions could suddenly trigger a rebound. "All this stuff that was supposed to be compressed into a singularity, due to the rotation in the extra dimensions will not get there," Graham says. "All this stuff was supposed to be compressed at one point, but instead, it will fly away."
The work of scientists has attracted the attention of people outside the usual circle of cosmologists rebound. Sean Carroll, a theoretical physicist at the California Institute of Technology, are skeptical about it, but calls the idea "very clever". He believes that it is important to develop an alternative to the traditional history of inflation, in order to understand better how the theory of inflation will look in comparison - especially when a new generation of telescopes will be launched. He also believes that if the alternative theory is at least a 5% chance of success, it is worth checking out. And this work - is no exception.