Monday, April 18, 2022

Is Big Bang wrong?

Learn how scientists try to solve theory problems! Is the Big Bang the beginning of everything? This is perhaps one of the most challenging questions in science. As much as this theory is the most accepted by cosmologists in general, there are some mysteries that the Big Bang cannot answer, and this has led many scientists to create other proposals - not to eliminate the Big Bang, but to complement it, suggesting that it was actually a step in the transition to the cosmos that we know today.

Before proceeding with the proposals for new models of cosmology, it should be noted that the Big Bang is still supported by scientific evidence, observations and research that prove it. Current measurements indicate that it occurred approximately 13.3 or 13.9 billion years ago, with a small margin of error due to the accuracy of each instrument and the methods used. For example, the Atacama Cosmology telescope provides data that points to 13.8 billion years, and that number is well accepted today. Among the evidences that support the Big Bang theory we can mention Hubble's Law, microwave background cosmic radiation, the abundance of primordial elements, the galactic evolution and distribution and the primordial gas clouds. Calm down, we will explain some items of this list soon, because the problems that the Big Bang cannot explain are related precisely to some of this evidence.

Big Bang problems Background cosmic radiation Successive improvements in observations of anisotropies (or fluctuations) of cosmic microwave background radiation. Some of the problems that came with the Big Bang theory have already been solved, but those answers have ended up bringing new questions. These, in turn, could also be answered, but with a catch: it was necessary to create a new cosmological model: cosmic inflation. And that is what we will talk about shortly. One of the problems with the Big Bang is the misunderstanding of why the universe has more matter than antimatter. The theory assumes that when the universe was young and very hot, it was in balance, with equal numbers of baryons and antibarions. However, more recent observations suggest that the universe is made up almost entirely of matter, and conventional cosmology fails to explain this.

 Going back in time The universe is constantly expanding. This was the main discovery by astronomer Edwin Hubble, which showed how galaxies and other structures are moving away from each other, faster and faster. This is evidenced by the amount of light from a distant object that deviates towards red in proportion to the distance to that object. Shifting light to red means that the wave gets longer, as the light itself is stretching (blue shift indicates otherwise, since the wave of blue light is proportionally shorter than the wave of red light). The greater the red shift of an object, the further it is going. That's how astronomers know when an object is billions of light years away from us today than it was when the universe was still young.

The Universe is expanding and extending the light to longer wavelengths today, with lower energies and temperatures, means that if we go back in time we will see the universe if length until it becomes compact, dense and hot. The very gravity of the many structures and objects helps to make everything denser, bigger and more massive. Try to visualize this trip to the past, it will be important to better understand the Big Bang and its problems. If we go further, the galaxies become smaller, denser, more numerous and made up of younger, more blue stars. Rewind further our imaginary video recording of cosmic evolution and we will witness the time when there was still no star. Then, it will be hot enough for the light to divide atoms and neutrons, creating the ionized plasma that we mentioned earlier when talking about the origin of CMB. If we get close to the initial frame of this video, which represents the “Zero Moment” of the cosmos, we will enter a realm where the energies are beyond the limits of known physics. At some point here, something created dark matter and created more matter than antimatter. Something must have happened, at some point, for the universe to exist. In the first frame of our videotape, there is the singularity, the starting point from which everything emerged, a state so dense and warm that the laws of physics are no longer useful.

To better understand the uniqueness, imagine that all places in the universe already existed. The place we occupy now, inclusive. As well as the place that a galaxy billions of light years away also existed. The difference at that time is that all of this was very much squeezed into a smaller than infinitesimal dot. And this point was so dense that it has expanded and continues to expand today. No new places were created - it just expanded, like a balloon that is always being filled with air, but it never bursts (not even the Big Bang can be described as an explosion, but as a mega expansion). But was that starting point really "starting"?

 The Horizon problem Background cosmic radiation This image of cosmic background radiation shows differences in temperature, but don't be fooled by the red and blue tones. The differences are very small. Another problem is related to the Cosmic Microwave Fund (or CMB, in the English acronym), a weak, but detectable radiation, found in any and every place in the universe where we can look with our current telescopes. This radiation goes back to the time when the universe became transparent, that is, the time when the neutral hydrogen became stable. Before this, the universe was a sea of ​​hot, dense photon-barium plasma, where photons were rapidly dispersed. When photons (the particle of light) find a way to freely travel a long path, the cosmos has become transparent.

Hence came the CMB, which is an omnidirectional signal that has been fundamental in all cosmological models because it provides information about what the primitive universe was like. But it carries with it a problem, known as the Horizon Problem. It is that the CMB is exactly the same in any corner of the universe where we point our telescopic lenses, and this cannot be explained by classic models like the Big Bang. The radiation is exactly the same, with the same temperature, in regions that could never have interacted with each other, at any time in the history of the cosmos. Isn't it ironic how evidence supporting the Big Bang also brings problems that standard theory cannot solve?

Monopole problem The problem of the magnetic monopole was raised in the late 1970s, and questioned the Big Bang because that event would have caused some topological defects in space. These defects would manifest themselves as magnetic monopoles - a hypothetical elementary particle that would behave like a single pole magnet. According to a theory called the Great Unification Theory, these objects should have been produced in the initial hot universe, and this would result in a much higher density than was noted in observations. Well, no monopolies were found, and the reason why they did not exist was considered an unknown quantity.

Cosmic inflation Big Bang A representation of the Big Bang space-time and the development of the universe. Realize how inflation is at the very beginning of everything happening. All that extrapolated time travel in which we try to describe the formation of the universe in regression is based on a notion that we can really go back and understand all the processes to the singularity. This brought interesting explanations, but it also created the puzzles mentioned above: the problem of the horizon, the problem of the monopole, among others that we do not even mention as the problem of flatness. It is that in the classic idea, there could not be enough expansion for these things to be possible. To answer these problems, some scientists concluded that a new cosmological model was needed. The idea of ​​cosmic inflation then came in the early 1980s, with Alan Guth claiming that in the beginning the universe went through a phase of exponential growth. He didn't just want to accept that "things are like that and that's it", physics demands that the pieces fit together.

 It was the birth of a new approach, a new physical mechanism, that did not rule out the proven ideas of the Big Bang, which helped science to understand the origin of the cosmos. Better still, the new model still made new predictions about phenomena that we could observe, differing from the conventional Big Bang. So, instead of rewinding the Big Bang video until it reaches the singularity, inflation basically proposes a cut: you can return to a certain high temperature and density at some stage of the Big Bang, but no more. This is because in the Inflationary Age, the cosmos would have expanded exponentially at a constant and immutable rate, absurdly fast, within a ridiculously short time - we are talking about a very tiny fraction of a second. When this initial inflation ends, all the energy that was intrinsic to space is converted into matter and radiation, and then we have the events described in the imaginary video recording of the Big Bang. In other words, there was a state of expansion with a rate much higher than the current rate of expansion. This state not only came before the expansion of the Big Bang, but also configured everything that came after. The idea does solve the Big Bang riddles, and it seems quite comfortable for scientists.

Inflation seemed to be a revolutionary idea since the emergence of the theory, because it offers a way to solve the problem of the homogeneity of the universe, proposing a period of expansion so intense and rapid that almost everything ended up incredibly far. Thus, we understand how the distant regions of the universe were once so close that even today they share properties such as the same temperature. But the truth? The truth is that nobody knows for sure.

 Controversies Cosmic inflation This timeline of the inflationary universe shows how inflation came just before the events that left the mark of background radiation. Far from being a consensus among scientists, the hypothesis of cosmic inflation is still debated, and even rejected by a portion of the researchers. Roger Penrose, professor emeritus of mathematics at Oxford University in the United Kingdom, is one of them. Winner of the Nobel Prize in Physics in 2020 for his studies of black holes, Penrose says: "I have always considered inflation to be a very artificial theory." He says that "the main reason this theory did not die at birth" is that it was the only one idea that could explain the Horizon Problem.

But there are also shortcomings in the idea of ​​cosmic inflation. For example, there is no explanation for the mechanism that triggered such a violent inflationary expansion, nor an explanation that can be tested on how it could happen. In science, demonstrations are fundamental, and so each hypothesis is put to the test in the simulations of supercomputers. Defenders of inflation have already proposed that theoretical particles formed something called an "inflation field", responsible for driving hyperaccelerated expansion. This field would have later decomposed into the particles that we see around us today, so we cannot find any traces of it. Other scientists call this idea "fit" for a gap-filled hypothesis and do not seem convinced. Even Paul Steinhardt, one of the original architects of inflationary theory, seems tired of the lack of testability of the predictions that the hypothesis brings. "The theory is completely inconclusive," he said on one occasion. The problem may have to do with the very notion that there was a beginning in space and time, a notion that came with the Big Bang theory and its uniqueness. It may be that this starting point is just a turning point.

Many scientists today defend the idea that this image of a hot, compact and dense universe, which began to expand and cool 13.8 billion years ago, would not have been the beginning of space-time, but rather the transition from one previous phase. What was in that previous phase? Well, as usual, an answer always leads to new questions. Perhaps before the Big Bang, a universe prior to ours was contracting until it reached uniqueness. Who knows? Perhaps the pursuit of the origin of everything is still far, far from over.

 Other not-so-popular ideas Penrose is a big proponent of the idea that there was another universe before ours. For him, before the Big Bang, there was another cosmos, which expanded, and then retracted until it returned to singularity. Well, this idea is not exclusively his, but the Nobel-winning physicist ended up becoming one of the most prominent supporters of this hypothesis. For many, the idea may seem a little crazy. What do you mean, another universe before ours? But for those who do not accept the proposal of the inflationary universe, the previous universe is an interesting way to explain the problems of the Big Bang. “The Big Bang was not the beginning. There was something before the Big Bang and that something is what we will have in our future, ”he said when commenting on his award this week. According to Penrose, our own universe will also retract in a process known as the Big Crunch. He also claims that there is evidence that there was a universe before ours, something known as Howking Radiation (nicknames in honor of Physicist Stepheng Hawking), which are about eight times the diameter of the Moon.

 According to the scientists, the hypothetical Hawking Radiation would be emitted by black holes that, in turn, would lose some mass due to this phenomenon. That way, black holes could completely evaporate - but it would take a long, long time for that to happen, possibly longer than the very age of our universe. Penrose, however, believes that "dead" black holes from previous universes are now observable. He went on to say that “our Big Bang started with something that was the remote future of an earlier era and would have similar black holes evaporating, and they would produce these points in the sky, which I call Hawking Points. We are seeing them. These points are about eight times the diameter of the Moon and are slightly warmed regions. There is very good evidence for at least six of these points ”

The idea is controversial, and although Penrose has already published an article about it, his speech this week has heated up the discussion among astrophysicists. One of them is Ethan Siegel, defender of Cosmic Inflation. For him, Penrose, although he deserved to receive the Nobel Prize for work on black holes, was irresponsible in defending so fervently a hypothesis on which there is no way to observe any phenomenon. "The data is completely opposite to what he claims," ​​said Siegel. Siegel made harsh criticisms of Penrose, saying that “the predictions he made are disproved by the data, and his claims of seeing these effects are only reproducible if someone analyzes the data in a scientifically inappropriate and illegitimate way. Hundreds of scientists have pointed this out to Penrose - repeatedly and consistently over a period of more than 10 years - who continue to ignore the field and go ahead with their strife. ” In his text on Starts With A Bang, Siegel not only criticized Penrose, but showed in detail some reasons that point to Inflation as the most likely theory as a complement to the Big Bang, contradicting the idea of ​​Conformed Cyclical Cosmology (or CCC) , defended by Penrose. "The biggest predictive difference is that the CCC practically requires an impression of 'the Universe before the Big Bang' to appear both on the large-scale structure of the universe and on the cosmic microwave background," explains Siegel. As you may have already guessed, this impression of the previous universe is not seen in the cosmic background.

Siegel remains tough on the criticism, stating that “while we must commend Penrose's creativity and celebrate his innovative and Nobel-worthy work, we must guard against the desire to deify any great scientist, or the work they do that is not supported by the data ”. He concludes that Penrose "seems to have fallen so much in love with his own ideas that he no longer looks to reality to test them responsibly." But is Cosmic Inflation so infallible? As we have seen before, there are some good arguments for not getting too attached to it - that's why there is so much debate on the subject. But for now, it seems to work well in answering the mysteries that were before it, and most physicists are satisfied with the idea of ​​inflation. And everything is fine like that, at least until some more concrete theory, with fewer gaps, and that is more observable, appears.

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