String theory is considered by many physicists to be a prime candidate for unifying quantum physics and gravity in a unified theory of everything. But there is also an opposite opinion, according toto whom this concept is practically pseudoscience, since it is impossible to test it with the help of experiments. Yet some researchers believe that we may have a way to do it - according to a new hypothesis that contrasts string theory with cosmic inflation. It all boils down to the following question: are the quantum secrets of the universe hidden from our eyes, or are there some details by which string theory can be explained?
Inflationary model of the universe - hypothesis about physical condition and lawexpansion of the Universe, which began immediately after the Big Bang. Inflation implies a period of accelerated expansion of the universe (compared to the standard model of a hot universe).
One way to rule out this idea is toto prove that it does not predict the peculiarity of our universe. And string theory, as it turned out, is constantly faced with the problem of describing the most popular explanation for what happened in the first moments of the existence of the universe - right after the Big Bang: inflation.
"Inflation is the most compelling explanation for why our universe looks the way it looks, and where its structure came from," said Marilena Laverde, a physicist at Stony Brook University. Inflation explains how, in a sense, we got everything in the universe from nothing. Theory claims that the early universe passedthrough the phase of extreme expansion. This process amplified random bursts in the quantum vacuum and turned them into galaxies and other objects around us.
However, theorists found it difficult to show how - anddoes it work at all - inflation works in string theory. The most promising way to do this is the so-called KKLT construction, which does not convince everyone. Some researchers note that in the depths of the minds of many people involved in string theory, a doubt has long settled: does it really work?
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In 2018, a group of string theoristsargued that perhaps inflation simply could not happen in theory. This so-called de Sitter hypothesis argued that any version of the concept that could describe de Sitter space — a term for the type of universe in which we assume inflation — would have some kind of technical flaw that would put it in a "swamp »Rejected theories.
I note that any inflation limitation increasedwould be the likelihood of testing string theory on real data. According to Kumrun Wafa, a physicist at Harvard University and one of the authors of the hypothesis, researchers can begin to build evidence of this idea if they can connect it to well-known physical laws. One approach to building confidence might try to explain which physical rule limits inflation - or, more practically: How can theoretical physicists convince cosmologists to revise their preferred theory?
The answer, as often happens, came from somewhere notwaited - it turns out that inflation already has an unsolved problem: not all physicists agree with what happens to the smallest quantum particles (we are talking about the expansion of the vacuum and the increase in its statics).
The theory of everything
Physicists lack a working theory thatwould describe the world below the level of the so-called Planck length - the extremely small distance at which they expect quantum gravity to appear. Proponents of inflation tend to believe that one day they will be able to include all the "trans-Planck" details and that they will not matter much in any forecasting. But how exactly this will happen remains unknown.
According to Scientific American, according to the newhypothesis, extremely tiny quantum fuzzy should always remain extremely tiny and quantum, despite the increasing effect of expansion. If this idea is correct, it implies limits on the amount of inflation that can occur, because too much of it would mean too much of an increase in trans-Planck detail.
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Thus, in a new approach to string theoryresearchers can actually search for answers by peering into the starry sky. There are several different models of the real process of inflation and astrophysicists do not yet have data to confirm at least one of them.
Another important point in conflict withstring theory is gravitational waves. Their existence was proven in 2017, so scientists know for sure that gravitational waves leave behind a faint but distinct imprint in the cosmic background microwave radiation (relic radiation). However, according to the new hypothesis, the existence of gravitational waves is allowed, although there should be very few of them. So much so that any sign of gravitational waves would mean that string theory is not applicable to our universe. So physicists will probably have to come up with another explanation for them.