Philosophers have been discussing the nature of "nothingness", "nothing", "nothing", "emptiness" for thousands of years, but what can modern science tell about this? This question will be answered by Martin Rees, Astronomer of the Royal Society and Professor Emeritus of Cosmology and Astrophysics at the University of Cambridge. He explains that when physicists discuss "nothing," they mean empty space (vacuum). It may seem quite ordinary, but experiments show that empty space is not really empty - it contains a mysterious energy that can tell us something about the fate of the universe.
An interview with Martin Rees presented by The Conversation magazine.
Is empty space the same as nothing?
Empty space seems like nothing to us. By analogy, water may appear to be "nothing" to the fish - it is the water that remains when you remove everything else that floats in the sea. In the same way, empty space turns out to be quite difficult in practice.
We know that the universe is very empty. The average density of space is about one atom for every ten cubic meters - the environment is much more rarefied than any vacuum we can get on Earth. But even with all matter removed, space has a kind of elasticity that (as recently confirmed) allows gravitational waves - the ripples of space itself - to propagate through it. Moreover, we learned that in empty space itself there is an exotic form of energy.
We first learned about this vacuum energy in the 20th century with the advent of quantum mechanics, which explains the behavior of atoms and particles on the smallest scale. It follows from it that empty space consists of a field of fluctuations of the background energy - which gives life to waves and virtual particles, now and then appearing and disappearing into nowhere. They can even create tiny strength. But what about white space on a large scale?
The fact that empty space creates large-scale force was discovered 20 years ago. Astronomers have found that the expansion of the universe is accelerating. This was a surprise. The expansion has been known for over 50 years, but everyone thought the expansion would slow down due to the gravitational pull that galaxies and other structures exert on each other. So it came as a big surprise to everyone that the deceleration due to gravity was offset by something that "pushed" the expansion. It turned out that in the empty space itself, there is energy that creates a kind of repulsion that outweighs the attraction of gravity on these large scales. This phenomenon - dark energy - is the most incredible manifestation of the fact that empty space is not wrinkled or empty. Furthermore,this fact determines the further fate of our Universe.
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Is there a limit to what we can learn? On a scale of a trillion trillion times smaller than an atom, quantum fluctuations in space-time can give birth not only to virtual particles, but also to virtual black holes. This is within the limits that we cannot observe and to understand which, at least hypothetical, we need to combine the theory of gravity with quantum mechanics - and this is incredibly difficult.
There are several theories to understand this, of which the most famous is string theory. But none of these theories are yet related to the real world - so they are still groundless. I think almost everyone will recognize that space itself has a complex structure on a tiny scale where gravitational and quantum effects meet.
We know that our universe has three spatial dimensions: you can move left and right, forward and backward, up and down. Time is like the fourth dimension. However, there is a strong suspicion that if you enlarge a tiny point in space until you feel that tiny scale, you will find that it will be a densely compressed origami of five extra dimensions that we cannot see. As if you were looking at the hose from afar and thought it was just a line. Moving closer, you would see that one dimension is essentially three. String theory includes complex mathematics - as do competing theories. But this is exactly the theory that we need if we want to understand at the deepest level the closest to emptiness that can be imagined: empty space, obviously.
As part of our current understanding, how can we explain that our entire universe is expanding out of nothing? Could it really have started with a small fluctuation in the energy of the vacuum?
Some mysterious transitions or fluctuations could suddenly lead to the fact that part of the space began to expand, as some theorists believe. The fluctuations inherent in quantum theory could shake the entire universe if it were compressed to small enough scales. This should have happened in about 10 (to the -44) seconds - this is Planck time. On these scales, time and space are intertwined, so the idea of a ticking clock doesn't make sense. We can extrapolate our universe with a high degree of certainty back to the nanosecond and with a high degree of probability we will return closer to Planck time. But after that our guesses are no longer valid - physics on this scale is replaced by some other, more complex theory.
If it could be that a fluctuation in some random part of empty space gave life to the universe, why can't the same thing happen to another part of empty space - and give life to parallel universes in an infinite multiverse?
The idea that our Big Bang is not the only one, and that what we see through our telescopes is a tiny piece of physical reality, is quite popular among physicists. And there are many versions of the cyclical universe. Just 50 years ago, strong evidence emerged that the Big Bang even happened. But since then there have been speculations that he could only be an episode in a cyclical universe. There is also a tendency to understand that physical reality is much more than the volume of space and time that we can feel, even with the most powerful telescopes.
Therefore, we have no idea if there was one Big Bang or there were many - there are scenarios that predict many Big Bangs and scenarios that predict one. I think we should study them all.
What is the end of the universe?
The simplest forecast for the distant future is that the universe will continue to expand faster and faster, becoming colder and more empty. Particles in it can disintegrate, dissolving endlessly in emptiness. We may find ourselves in a huge volume of space, but it will be even more empty than space is now. This is one of the scenarios. There are others who predict a "reversal" of the direction of dark energy, from repulsion to attraction, as a result of which we will be compressed into a dense point.
There is also Roger Penrose's idea that the universe will continue to expand, becoming more and more diluted, but somehow - when there is nothing in it except photons, particles of light - the objects in it will be recalibrated and space will in some way become a generator of a new Big Bang … This will be a very exotic version of the old cyclical universe - but please don't ask me to explain Penrose's ideas.
How confident are you that science will one day uncover the mystery of what this "nothing" is? Even if we could prove that the universe emerged from a strange fluctuation in a vacuum field, shouldn't we be wondering where this vacuum field came from?
Science tries to provide answers, but each time we find them, new questions arise - we will never have the complete picture. When I started doing research in the late 1960s, there were doubts that there was a Big Bang at all. Now there is no longer any doubt and we can say with an accuracy of about 2% that the universe was the same for 13.8 billion years, up to the very first nanosecond. This is great progress. It is ludicrously optimistic to believe that in the next 50 years we will sort out the difficult questions of what is happening in the quantum or "inflationary" era.
But, of course, another question arises: how much science will be comprehensible to the human brain? It may be that the mathematics of string theory is, in some sense, a correct description of reality, but we can never understand it well enough to test against any genuine observation. Then we may have to wait for some post-humans to appear in order to gain a fuller understanding.
Ilya Khel
