The questions in the title are usually not discussed by physicists, since there is no generally accepted theory capable of answering them. However, recently, within the framework of loop quantum gravity, it was still possible to trace the evolution of a simplified model of the Universe back in time, right up to the moment of the Big Bang, and even look beyond it. Along the way, it became clear how time appears in this model. Observations of the Universe show that even on the largest scales it is not at all stationary, but evolves over time.
If, on the basis of modern theories, this evolution is traced back in time, it turns out that the currently observed part of the Universe was earlier hotter and more compact than it is now, and it began with the Big Bang - a certain process of the emergence of the Universe from a singularity: a special situation for which modern laws physicists are not applicable.
Physicists are not happy with this state of affairs: they want to understand the process of the Big Bang itself. That is why numerous attempts are now being made to construct a theory that would be applicable to this situation. Since gravity was the main force in the first moments after the Big Bang, it is believed that this goal can be achieved only within the framework of the quantum theory of gravity, which has not yet been built.
At one time, physicists had hoped that quantum gravity would be described in terms of superstring theory, but the recent crisis of superstring theories has shaken that confidence. In such a situation, more attention began to attract other approaches to the description of quantum-gravitational phenomena, and in particular, loop quantum gravity.
It is within the framework of loop quantum gravity that a very impressive result has recently been obtained. It turns out that the initial singularity disappears due to quantum effects. The Big Bang ceases to be a special point, and it is possible not only to trace its course, but also to look into what was before the Big Bang.
Loop quantum gravity is fundamentally different from conventional physical theories and even from superstring theory. The objects of superstring theory, for example, are various strings and multidimensional membranes, which, however, fly in space and time prepared for them in advance. The question of how exactly this multidimensional space-time arose cannot be solved in such a theory.
In the loop theory of gravity, the main objects are small quantum cells of space, connected to each other in a certain way. The law of their connection and their state are governed by some field that exists in them. The magnitude of this field is for these cells a kind of "internal time": the transition from a weak field to a stronger field looks exactly as if there was some kind of "past" that would influence a certain "future". This law is arranged in such a way that for a sufficiently large universe with a low energy concentration (that is, far from the singularity), the cells seem to “fuse” with each other, forming the “continuous” space-time familiar to us.
The authors of the article argue that all this is already enough to solve the problem of what happens to the universe when approaching the singularity. The solutions of the equations obtained by them showed that under the extreme "compression" of the universe, space "crumbles", quantum geometry does not allow its volume to be reduced to zero, inevitably a stop occurs and expansion begins again. This sequence of states can be traced both forward and backward in "time", which means that in this theory, before the Big Bang, there is inevitably a "Big Bang" - the collapse of the "previous" universe. Moreover, the properties of this previous universe are not lost in the process of collapse, but are unambiguously transferred to our universe.
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The described calculations are based, however, on some simplifying assumptions about the properties of the universal field. Apparently, the general conclusions will be preserved even without such assumptions, but this still needs to be verified. It will be extremely interesting to follow the further development of these ideas.
