The universe could have been different

What was before the big bang?

It is probably the greatest mystery in the universe: What was before the Big Bang? Did the universe arise from nowhere or was there something before that? For decades, physicists have been approaching this question with experiments, formulas and theories. What they find out sounds like bold science fiction - and could revolutionize our worldview

We know one thing for sure: our universe is expanding. A finding from which fundamental conclusions can be drawn about the past of the cosmos: If we could go back in time, the universe would become smaller and smaller. From a purely mathematical point of view, everything finally shrank to one point.

It is precisely from this consideration that the theory, widely accepted by scientists, grew that the world arose from this point about 13.8 billion years ago. That space and time were born at this point. The beginning of this spectacular process is known as the Big Bang.

But a possibly unsolvable puzzle arises with the obvious question:

What was before the big bang?

Cosmologists simply have no answer to that. Because how should one be able to look scientifically before the beginning of time and space?

Of course, one can speculate: Perhaps the universe already existed before the Big Bang. It contracted until the matter was compressed incredibly tightly. Then there was some sort of rebound and the universe began to expand again. That rebound would be the big bang. But it wouldn't have been the beginning of everything.

What the universe that preceded our world might have looked like is the subject of various theories.

String theory is based on ten spatial dimensions

In the eyes of some physicists, the best theory of the moment is string theory. It says that the building blocks of the universe are made up of "strings", tiny threads. After that there are a total of ten room dimensions. However, we only notice three of them. Those dimensions that we do not recognize are rolled up into tiny little ones. This makes them invisible to us.

In a certain way it is like a wire, which also has three dimensions, but from a distance looks like a one-dimensional object - one that is only extended in length. And the geometry of the coiled dimensions determines the physical laws in the three spatial dimensions known to us.

It is true that this theory is beyond the human imagination. After all, our brain is set up to think in three dimensions of space and one dimension of time.

But if we let ourselves once in a while that these many dimensions exist, it becomes clear: Their geometries determine the laws of nature in our universe. When going through the rebound phase, however, the geometries could change - and with them the constitution of the cosmos. The previous universe may have looked very different from what we know.

It is possible that the universe came out of nowhere

One of the reasons why the Big Bang causes such problems for cosmologists is that it emerges from Albert Einstein's theory of relativity. At the same time, the big bang is also the point at which the theory of relativity collapses. So it cannot make any statement about how exactly the world was like in the Big Bang.

It seems paradoxical, but the theory of relativity manages to predict its own failure. What would be needed would be a theory that goes beyond the theory of relativity. And what it will look like is not yet certain.

However, before the Big Bang, there need not have been any other universe or - in other words - no other something. There is also the possibility that the universe actually came into being from nowhere.

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One might think that this violates the law of conservation of energy. Because energy cannot just appear or go away. It can only change its appearance - for example, kinetic energy can become thermal energy.

But interestingly, the total balance for the energy in the universe is: zero. In a complex way, the energy contained in the matter is balanced out, compensated for by the gravitational energy, which has a negative value in the Einstein equations. That is at least true for a finite cosmos.

The theoretical physicist Jean-Luc Lehners from the Max Planck Institute for Gravitational Physics in Potsdam is working with his team to figure out how a universe can be formed from nothing. To do this, they make use of quantum effects. Particles can appear briefly and then disappear again even in absolutely empty space. This does not work in the context of classical physics, it is possible in the world of quanta. Physicists also speak of quantum fluctuation.

And just such a fluctuation could - at that time, around 13.8 billion years ago - have expanded into our universe.

All these considerations, theories, and calculations are beyond the imagination of most people (even that of many physicists). They contradict our everyday experience - and the perception of the world in which we live and which we know.

But even with the two major recognized theories of physics - quantum mechanics and relativity - the physical consequences were not properly understood at the beginning. It was only over time that researchers developed a deeper understanding.

Maybe it is the same with the Big Bang.