The Physics of Nothing

James Owen Weatherall—

Imagine a house with no furniture. Is it empty? Presumably I haven’t given enough information to answer the question. There may be other stuff in the house: people, clothes, food, pets. Take all of this away, too. Indeed, take out all of the “stuff,” big and small. Mop the floors, scrub the bathroom, and dust the window sills. Now is the house empty?

There is a very old question, famous, or infamous, for its difficulty. Why is there something rather than nothing?  Part of what makes the question difficult is that it’s not clear what could possibly count as a satisfactory answer. Explanations have to start somewhere; this question, however, seems to demand that we explain everything at once, without appeal to anything that does exist. For just this sort of reason, many scientifically oriented philosophers—not to mention scientists—have dismissed the question entirely. It makes sense, these philosophers would say, to ask what there is, how it behaves, how we have come to be in the current state of the universe from earlier states. Not why.

If this were a book about real estate, the answer would likely be “yes.” At least, the house would be ready for a new owner to move in. But is it really empty? Perhaps there’s a sense in which the rooms are empty, but of course the house still has some things inside. It has walls and floors, pipes and electrical wires, toilets and bathtubs and sinks. Take all of this out, too—gut the house completely, imagining, for the sake of argument, that we could do so without the house collapsing. We are left with just a shell of a house. But is it empty?

Of course not. There’s still air inside. And that’s not all. If the house is located in a reasonably well-populated town, it is probably near radio towers whose signals reach the house. Perhaps the neighbors have a wireless network with a similar effect. If the house has windows, then during the day it may be filled with sunlight. Radio waves and light rays are kinds of electromagnetic radiation, so there is radiation in the house. And since the house is on the surface of the earth, if one were to drop an apple, say, it would fall to the floor due to the earth’s gravitational influence. In classical physics, at least, this would be because there is a gravitational field inside the house.

Fine, you think. This is getting a bit pedantic. But we can deal with it. Put the house deep in intergalactic space, far from stars or any other massive bodies. Let the air escape and shield the house from radiation of all sorts. Surely now the house is empty. There is nothing inside. Right?

We are accustomed to looking to physics for our answers to these latter sorts of questions, at least at the most fundamental level. And indeed, physics has yielded some impressive answers: we now know the material world is composed of such things as quarks and electrons, photons and gluons. The physics of stuff is well-trod territory. But what of the alternative? That is, this approach, of asking what there is and how it behaves, puts all of the emphasis on the something half of the question and ignores the nothing half. What, according to our best physical theories, is nothing? What would the world be like if there were no electrons, no quarks, no photons?

My goal is to explain that if we want to understand stuff, if we want to use physics to study what there is in the world, we need to reckon with what the world would be like if there weren’t anything at all. I call this the physics of nothing.

The question might seem silly. Nothing, after all, would just be what we’d have if there weren’t any something. In a sense, one might think, no matter what kinds of stuff exists or could exist, the situation if there were nothing would be the same: empty space, pure and simple. This was how the great seventeenth-century physicist Isaac Newton thought about things. He held that space could be thought of as an infinite container into which stuff could be placed or removed without affecting the structure of space itself. It was a kind of theater in which physics would unfold. According to this picture, the physics of nothing is simple

In fact, this idea may seem so obvious as to pass by without much notice. To say that if we removed all the stuff in the universe, we’d be left with empty space doesn’t seem like a substantive physical assumption—much less one that could be false. But this is as wrong as anything in physics could be.

From Void by David Wolpe, published by Yale University Press in 2016. Reproduced by permission.

James Owen Weatherall is professor of logic and philosophy of science at the University of California, Irvine. He lives in Irvine, CA.

Further reading

Void cover

Featured photo by NASA on Unsplash

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