One of the most fundamental questions about the Universe that anyone can ask is, “Why is there anything here at all?”
Explaining where all the matter in the Universe comes from is one thing. What you traditionally think of as something — that is, the plants, animals, elements, planets, stars, galaxies and galaxy clusters — that’s one question.
How and when all of that got here? That’s something we think we can answer.
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But there’s an even more fundamental question than that. In order to have our Universe, you need to start with what, as a physicist, I call nothing.
You need to start with empty spacetime.
And you can start with the emptiest spacetime imaginable: something flat, devoid of matter, devoid of radiation, of electric fields, of magnetic fields, of charges, etc. All you would have, in that case, is the intrinsic zero-point energy, or the ground state, of empty space.
From a physical point of view, that’s what nothing is. Only, perhaps perplexingly, that zero-point energy? It isn’t zero.
If it were, we wouldn’t have a Universe filled with dark energy, and yet we do. Instead, spacetime has a fundamental, intrinsic, non-zero amount of energy inherent to it; that’s what’s causing the Universe’s expansion to accelerate! What’s even more bizarre than that is the fact that all the matter and energy in the Universe today came from a drop, long ago, from an even higher zero-point-energy state. That process — reheating — is what comes at the end of an indeterminately long phase of exponential expansion of the Universe known as cosmic inflation.
The regions of space where this drop in zero-point energy occurred gave rise to regions of the Universe like ours, where matter and energy exist in abundance, and where the expansion of spacetime is relatively slow. But the regions where it hasn’t yet occurred continue to have an extremely rapid rate of expansion. This is why physicists state that inflation is eternal, and this is also the physical motivation for the existence of multiverses.
That’s the physical story of where all this comes from. Of where our planets, stars, and galaxies comes from, of where all the matter and energy in the Universe comes from, of where the entire 93-billion-light-year wide section of our observable Universe comes from.
From a scientific perspective, we think we understand not only where all of this comes from, but also the fundamental laws that govern it. So when a physicist writes a book called: A Universe from Nothing, I know that some version of this story — the scientific story of how we get our entire Universe from nothing — is the one you’re going to get told.
It’s a remarkable story, it’s perhaps my favorite story to tell, and it’s certainly been the greatest story I’ve ever learned. But in at least one way, it’s a dissatisfying story. Because the scientific definition of “nothing” that we use — empty, curvature-free spacetime at the zero-point energy of all its quantum fields — doesn’t resemble our ideal expectations of what “nothing” ought to be.
No one sufficiently versed in the science of physical cosmology (and being sufficiently honest with themselves about it) would argue against this: that the entire Universe that we know and exist in comes from a state like this, that existed some 13.7 billion years ago. But you may rightfully ask, “Is that truly nothing?”
This empty spacetime definition of what is physically nothing stands in contrast to what we can imagine as what I’ll call pure (or philosophical) nothingness, where there’s no space, no time, no laws of physics, no quantum fields to be in their zero state, etc. Just a total void.
This has been the source of much argument recently, as the answer to the physical question of where everything comes from does not necessarily answer the philosophical one. It certainly pushes it off for a while, but it still leaves unexplained the existence of spacetime and the laws of physics themselves. There has been bickering back-and-forth with a handful of physicists andphilosophers arguing as to whether this physical story really explains why there is something rather than nothing?
It is a remarkable story, of course, and it explains where every galaxy, every star, and every atom in the Universe comes from, an astouding feat.
But it doesn’t explain, existentially, why spacetime or the laws of nature themselves exist, or exist with the properties that they have. In short, understanding how something comes from nothing does not explain how this physical state of nothing comes from an existential nothingness. This question of why, as enunciated by Heidegger, is not addressed by our physical understanding of the Universe. But is it a fair question?
Like the oft-dismissive Wittgenstein, I’m not sure. We make this inherent assumption that both spacetime and the laws inherent to our Universe come from somewhere. Yet our classical notions and intuitions about causality are violated even within our known Universe; do we have good reason to expect that this non-universal form of logic applies to the very existence of the Universe itself? Furthermore, how can something, even figuratively, come from anything else if you remove time?
One can, of course, imagine answers to these questions: an entity of some sort that exists outside of time and thus has access to all times equally, a type of hidden-variable logic that exists as part of reality but requires the knowledge of things that are presently unobservable to us, a higher-dimensional being who sees our entire Universe no differently from how an animator sees the elements of a two-dimensional cartoon, etc.
None of these answers are convincing or compelling, mind you, and I am not sure that the questions do even make sense as far as reality is concerned. But just because we cannot yet know the answers, or whether the questions are sensible as far as reality is concerned, doesn’t mean there isn’t value to asking them and thinking about them. To me, that’s what philosophy is. I would encourage everyone to remember the words of my favorite philosopher, Alan Watts:
The reason for it is that most civilized people are out of touch with reality because they confuse the world as it is with the world as they think about it, talk about it, and describe it. On the one hand, there is the real world, and on the other, a whole system of symbols about that world that we have in our minds. These are very very useful symbols — all civilization depends on them — but like all good things, they have their disadvantages, and the principal disadvantage of symbols is that we confuse them with reality.
For whatever it’s worth, when I think of nothing, I think about empty spacetime and the physical Universe: that’s where my interests lie, and that’s where I believe the knowable lies. But that doesn’t mean there isn’t something wonderful to be gained from philosophizing.
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