Cyclic Model: Infinite Rebirth of the Universe

Cyclic Model: Infinite Rebirth of the Universe
Cyclic Model: Infinite Rebirth of the Universe
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In the early 2000s, two physicists from Princeton University proposed a cosmological model, according to which the Big Bang is not a unique event, but space-time existed long before the universe was born.

Cyclic model of the universe

In a cyclical model, the universe goes through an infinite self-sustaining cycle. In the 1930s, Albert Einstein put forward the idea that the universe can experience an endless cycle of big bangs and big compressions. The expansion of our universe may be the result of the collapse of the antecedent universe. Within the framework of this model, we can say that the Universe was reborn from the death of its predecessor. If so, then the Big Bang was not something unique, it is just one minor explosion among an infinite number of others. Cyclic theory does not necessarily replace the Big Bang theory; rather, it tries to answer other questions: for example, what happened before the Big Bang and why did the Big Bang lead to a period of rapid expansion?

One of the new cyclical models of the universe was proposed by Paul Steinhardt and Neil Turok in 2001. Steinhardt described this model in his article, which was called The Cyclic Model of the Universe. In string theory, a membrane, or "brane," is an object that exists in a number of dimensions. According to Steinhardt and Turok, the three spatial dimensions we see correspond to these branes. Two 3D branes can exist in parallel, separated by an additional, hidden dimension. These branes - they can be thought of as metal plates - can move along this extra dimension and collide with each other, creating the Big Bang, and thus universes (like ours). When they collide, events unfold according to the standard Big Bang model: hot matter and radiation are created, there is rapid inflation, and then everything cools down - and such structures as galaxies, stars and planets are formed. However, Steinhardt and Turok argue that there is always some interaction between these branes, which they call inter-brane: it pulls them together, causing them to collide again and produce the next Big Bang.

Steinhardt and Turok's model nevertheless challenges some of the assumptions of the Big Bang model. For example, according to them, the Big Bang was not the beginning of space and time, but rather a transition from an earlier phase of evolution. If we talk about the Big Bang model, then it says that this event marked the immediate beginning of space and time as such. In addition, in this cycle of colliding branes, the large-scale structure of the Universe must be determined by the compression phase: that is, this happens before they collide and the next Big Bang occurs. According to the Big Bang theory, the large-scale structure of the universe is determined by a period of rapid expansion (inflation), which took place shortly after the explosion. Moreover, the Big Bang model does not predict how long the universe will exist, and in the Steinhardt model the duration of each cycle is about a trillion years.

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The good thing about the cyclic model of the Universe is that, unlike the Big Bang model, it can explain the so-called cosmological constant.The magnitude of this constant is directly related to the accelerated expansion of the Universe: it explains why space is expanding so rapidly. According to observations, the value of the cosmological constant is very small. Until recently, it was believed that its value is 120 orders of magnitude less than predicted by the standard Big Bang theory. This difference between observation and theory has long been one of the biggest problems in modern cosmology. However, not so long ago, new data on the expansion of the Universe were obtained, according to which it is expanding faster than previously thought. It remains to wait for new observations and confirmation (or refutation) of the data already obtained.

Steven Weinberg, 1979 Nobel laureate, tries to explain the difference between observing and predicting a model using the so-called anthropic principle. According to him, the value of the cosmological constant is random and differs in different parts of the Universe. We should not be surprised that we live in such a rare region where we observe a small value of this constant, since only with this value can stars, planets and life develop. Some physicists, however, are not satisfied with this explanation due to the lack of evidence that this value is different in other regions in the observable Universe.

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A similar model was developed by the American physicist Larry Abbott in the 1980s. However, in his model, the decrease in the cosmological constant to low values ​​was so long that all matter in the Universe over such a period would have scattered through space, leaving it, in fact, empty. According to Steinhardt and Turok's cyclic model of the universe, the reason the cosmological constant is so small is that it was initially very large, but over time, with each new cycle, it decreased. In other words, with each big explosion, the amount of matter and radiation in the Universe is "zeroed", but not the cosmological constant. Over many cycles, its value has dropped, and today we observe exactly this value (5, 98 x 10-10 J / m3).

In an interview, Neil Turok spoke about his and Steinhardt's model of the cyclic universe as follows:

“We have proposed a mechanism in which superstring theory and M-theory (our best combined theories of quantum gravity) allow the universe to go through the Big Bang. But to understand whether our assumption is fully consistent, further theoretical work is needed."

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Scientists hope that with the development of technology, there will be an opportunity to test this theory along with others. Thus, according to the standard cosmological model (ΛCDM), a period known as inflation followed shortly after the Big Bang, which filled the universe with gravitational waves. In 2015, a gravitational wave signal was recorded, the shape of which coincided with the prediction of General Relativity for the merger of two black holes (GW150914). In 2017, physicists Kip Thorne, Rainer Weiss and Barry Barish were awarded the Nobel Prize for this discovery. Gravitational waves from the event of the merger of two neutron stars (GW170817) were also subsequently recorded. However, gravitational waves from cosmic inflation have not yet been recorded. Moreover, Steinhardt and Turok note that if their model is correct, then such gravitational waves will be too small to be "detected."

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