What is “nothing”? Says astrophysicist Martin Rees

Philosophers have debated the nature of “nothingness”, “nothing”, “nothing”, “emptiness” for thousands of years, but what can modern science tell? This question will be answered by Martin Rees, astronomer of the Royal society and Emeritus Professor of cosmology and astrophysics at Cambridge University. He explains that when physicists discuss “nothing”, they mean empty space (the vacuum). This may seem quite ordinary, but experiments show that empty space is actually not empty — it hides a mysterious energy that may tell us something about the fate of the universe.

Interview with Martin Rice presented a log of The Conversation.

Empty space is the same as nothing?

The empty space seems to us to be nothing. By analogy, water can appear to be “nothing” for fish — that it remains when you take everything else that swims in the sea. Similarly, the empty space turns out to be quite complicated 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 sparse than any vacuum we can obtain on Earth. But even if you remove all matter, the space has a kind of elasticity, which (as was recently confirmed), allows gravitational waves — ripples of space itself — will spread it. Moreover, we learned that the empty space is an exotic kind 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 scales. It follows from this that empty space consists of field fluctuations of the background energy which gives life to the waves and virtual particles appearing from and disappearing into nowhere. They can even create a tiny force. But what about the empty space on large scales?

The fact that empty space creates large-scale force, was discovered 20 years ago. Astronomers found that the expansion of the Universe is accelerating. It was a surprise. About the expansion has been known for more than 50 years, but thought that the expansion will slow down due to gravitational attraction, which galaxies and other structures have on each other. Therefore, for all was a big surprise that the deceleration due to gravity has been shifted to something that “moved” extension. It turned out that in the empty space there is energy, which creates a kind of repulsion which outweighs the pull of gravity on these large scales. This phenomenon is dark energy — the most incredible manifestation of the fact that empty space is not devoid of wrinkles and is not empty. Moreover, this fact determines the fate of our Universe.

Is there a limit to what we can learn? At a scale a trillion trillion times smaller than an atom, quantum fluctuations of space-time can have not just virtual particles, but virtual black holes. It is within that we are unable to observe and to understand that at least a hypothetical we need to combine gravitation theory with quantum mechanics — and this is incredibly difficult.

There are several theories designed to understand this, among which the most famous is the theory of strings. But none of these theories have not yet connected with the real world — so they are still unfounded. I think almost everyone recognizes that space itself has a complicated structure on a tiny scale, where gravitational and quantum effects.

We know that our Universe has three space dimensions: you can move left and right, forward and backward, up and down. Time is like a fourth dimension. However, there is a strong suspicion that if you increase a tiny point in space until then, until you feel that tiny scale, you will find that it will be impacted origami from five additional dimensions that we cannot see. Like if you looked at the hose from a distance and thought it was just a line. Coming closer, you would see that one measurement is in fact three. String theory involves complex math — as well as rival theories. But this is the theory which we will need if we want to understand at the deepest level closest to the void, that you can imagine: empty space, obviously.

In our current understanding of how we can explain that our entire universe expanded out of nothing? It could really start with small fluctuations of the vacuum energy?

Some mysterious transitions or fluctuations could suddenly cause a portion of the space began to expand — so suggested by some theorists. The fluctuations inherent in quantum theory that could shake the entire Universe, if it was compressed to a sufficiently small scale. It had to happen for approximately 10-44 seconds is the Planck time. At these scales of time and space are intertwined, so the idea of a ticking clock does not make sense. We can extrapolate our universe with a high degree of confidence back to a nanosecond and with high probability back closer to Planck time. But after that our guesses do not have the forces — the physics on this scale is replaced by some other, more complex theory.

If could be that the fluctuation in some random part of the empty space gave life to the universe, why the same cannot happen with another part of the 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 in our telescopes is a small part of physical reality, is very popular among physicists. And there are many versions of a cyclical universe. Only 50 years ago there was powerful evidence that the Big Bang ever happened. But since there is speculation that he could be only an episode in a cyclical universe. There is also a trend towards the understanding that physical reality is much larger than the amount of space and time that we can feel, even with the help of powerful telescopes.

So we have no idea, there was a Big Bang one or there were many of them there are scenarios that predict a lot of Big Explosions, and scenarios that predict single. I think we should explore them all.

What kind of end awaits the Universe?

The easiest forecast for the distant future — the universe continues to expand faster and faster, becoming more cold and empty. Particles it can decay, endlessly dissolving into the void. We can be in a huge amount of space, but it will be even more empty than the space now. This is one of the scenarios. There are others who predict a reversal of the direction of dark energy from repulsion to attraction, which we will squeeze in a tight spot.

There is still the idea of Roger Penrose that the universe will continue to expand, becoming more diluted, but somehow when it’s gonna be nothing but photons, particles of light — the objects in it perekalivatsja and space becomes a kind of generator new Big Bang. It 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 reveal the secret of what is “nothing”? Even if we could prove that the universe began from a strange fluctuations in the vacuum field, perhaps we shouldn’t ask the question, where did this vacuum box?

Science tries to give answers, but every time we find them, there are new questions — we will never have the full picture. When I started to do research in the late 1960s, there were doubts that the Big Bang actually was. Now doubt no longer, and we can say with accuracy about 2% that the universe was the same all 13.8 billion years to the very first nanosecond. This is great progress. Ridiculously optimistic to believe that in the next 50 years we will understand complex issues about what is happening in the quantum or “inflationary” era.

But, of course, another question arises: how science becomes understandable to the human brain? It may be that the mathematics of string theory is in some sense a true description of reality, but we will never be able to understand it well enough to check the background of any genuine observation. Then we may have to wait for some post-people to get a better understanding.

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