What is "Nothing"?

Like most videos on YouTube, this is a video about nothing. But we’re a science channel, so we’ll talk about nine levels of nothing. What are the nine levels of nothing? Can you really make a universe from them? And if someone asks you why there is something rather than nothing, what’s a good answer? That’s what we will talk about today.

First things first, what do we mean by “nothing”? A first attempt to define nothing is to look at how we use the word in everyday language. Suppose your birthday is coming up and you say “Oh, I want nothing.” So when I give you a box for your birthday, you expect it to be empty It’s nothing, in the sense that it doesn’t contain any objects. We will call this the level 1 nothing. It’s a pre-science nothing, the nothing you might refer to before you’ve ever heard of physics.  

But of course, you have heard of physics, and so you know that even a box full of level one nothing still contains air, and air is made of something. You wanted nothing for your birthday, and certainly you’ll be disappointed to get air instead. Let’s therefore pump all the air out of this box. We’ll call what’s left the level 2 nothing. It’s what was called a vacuum in the 17thcentury, no objects, and no air either.

Okay you might say, but we don’t live in the 17th century, and when you said you want nothing for your birthday you really meant it. If we just pump out the air, there’s still the occasional cosmic ray inside, or neutrinos, or dark matter particles, if they exist. So, we go one step further and remove all types of matter, this gives us the level 3 nothing. Indeed, since objects and air are made of particles, removing particles includes the previous two nothings.

But even if the box is closed, there would still be radiation in the box, for example in the infrared, which is maybe not much, but it’s something. And the magnetic field of the earth would also still go through the box.  Therefore, we now also remove all types of radiation and all fields. Because you wanted nothing for your birthday and of course I want you to be happy. Now we have a level four nothing: no particles, no radiation, no fields. What you have left then is what you could call the 21stcentury vacuum.

The level 4 nothing is however is still something. For one thing, many physicists argue that the vacuum has an energy density and pressure and associate this with the cosmological constant. As I explained in this earlier video, I think this doesn’t make sense, the cosmological constant is just a constant of nature which determines the curvature of empty space. Empty space just isn’t necessarily flat. Talking about the curvature of empty space as if it was energy density and pressure is just a weird interpretation of geometry.

Even leaving aside the cosmological constant, the 21st century vacuum isn’t nothing because in quantum field theories, like the standard model of particle physics, the vacuum contains virtual particles that are created in pairs but quickly destroy each other again. They come out of the vacuum and disappear back into it. Virtual particle pairs are like couples you’ve never heard of that pop up in your news feed, destroy each other, and disappear back into nothing. Except with maths.

We can’t directly measure virtual particles, that’s why they’re called virtual. But we can infer their presence because we can measure their influence on other particles. Or we could, if we hadn’t removed those from the box already.

For example, if we look at the energy levels of electrons around an atomic nucleus, these are slightly shifted in the presence of virtual particles. This can be measured, and it has been measured. That’s one way we know virtual particles exist.

You could argue that the phrase “virtual particle” is really just a name for a mathematical expression that we use to calculate measurement outcomes, and I would agree. But be that as it may, we can observe their effects and nothing has no effects so it’s got to be something. And you wanted nothing for your birthday, not a box full of virtual particles. Besides, virtual particles can sometimes become real, for example near black holes, so they can actually kick us back from level four to level three.

To get to level 5 nothing we therefore remove the twenty-first century vacuum too. Now we have neither virtual nor real particles nor radiation nor fields and there’s also no way that any of them can reappear from the vacuum. What’s left in the box now? Well. There’s still space and time in it. And time is money, and money is the root of all evil, and that’s a terrible joke, but still something rather than nothing.

This is why for level 6 of nothing, things get decidedly weird because we remove space and time, too. And just to make sure, we will also remove all other equations and laws of nature that might give rise to space and time, such as strings or quantum gravity, or whatever other idea you believe in. Remove all of it. At this point there is nothing left from our theories of physics.

So why is there any physics at all? This question is one of the reasons we’ll never have a theory of everything, because even the best theory can’t explain its own existence. Scientific explanations end at this level, and it’s probably where this video should end, but I admit I enjoy talking about nothing, so let’s see what else there is to say.

I have taken inspiration for this video from an essay by Robert Lawrence Kuhn, to which I will leave a link in the info below. He also talks about it in this video. My first six levels of nothing are similar to his, though not exactly the same because I’ve looked at it from the perspective of a physicist. But Kuhn doesn’t stop there, he has three more levels of nothing.

Taking away everything physical still leaves us with something in your birthday box because you might grant the existence of non-physical entities. For example, some people believe in god, or other religious ideas, like the belief that consciousness is non-physical. In level 7 we remove those, too. Theological explanations end at this level. If you think that god necessarily has to exist then you have to get off the bus at level 7 and accept that the question why god exists doesn’t have an answer.

Is the box finally empty? Not quite. There’s still mathematics that could be said to exist in some sense. That is, we have abstract ideas and objects, numbers, sets, logic, truths and falsehoods, and the entire platonic world of ideals. For the 8th level of nothing, we remove those too.

Has this finally removed everything? Are you finally happy with your birthday gift? Well, there’s still the possibility that something comes into existence even if that something doesn’t exist. And a possibility is something in and by itself. So, for level 9, we also remove all possibilities. This is Kuhn’s final level of nothing. It’s the best nothing I can give you for your birthday. I hope you’re happy now.

The ninth level of nothing leaves us with the always interesting question whether the absence of something is also something, which is why philosophers like to discuss whether holes in cheese exist. Personally, I’m more interested in the cheese. I guess that’s why I’m a physicist and not a philosopher, but I found Kuhn’s classification of nothings useful because it explains why we sometimes talk past each other apropos of nothing.

For example, “inflation” is a currently popular theory in physics according to which our universe was created by a quantum fluctuation from a vacuum. We have no evidence that this is correct, but let us leave this aside for today, and just ask what kind of creation this would be if it was correct. The idea of inflation is that you have a big space that’s filled with a quantum vacuum, and every once in a while a quantum fluctuation succeeds in becoming so large that it begins to grow. Indeed, it grows into an entire universe like ours, with cheese, and holes in it, and all.

In such a vacuum there are many fluctuations, and therefore the creation of a universe doesn’t happen only once, it happens over and over again. It’s a type of multiverse called “eternal inflation”. We just talked about this some weeks ago. The beginning of our universe in this eternal inflation would be a creation from a level four nothing.

Physics can get you a little further than this because you can write down a theory in which space and time is created from a state without space and time. It’s arguably somewhat hard to imagine what this means, but you can certainly write down mathematics for it.

You see, I just define a symbol for a state without space and time, and an operator that creates space and time, then I let the operator act on the state, and voila, I’ve created space and time. Ok, I have oversimplified this a little, but basically this is how it works. I really think people are way too respectful of all the stuff that physicists made up and get away with just because their maths is incomprehensible.

Lawrence Krauss’ book “A Universe from Nothing” is about this idea of creating space and time from nothing. And this would be a creation from a level 5 nothing. But even if you don’t believe in God, a level 5 nothing is still something. To begin with it has the mathematics that give rise to all the rest.

If physics doesn’t answer the question why there is something rather than nothing, then what could? Philosophers have discussed that back and forth. I’m not much of a philosopher and have a nothing worthwhile to add. That’s a ninth level nothing. But just in case someone stops you on the street and asks “why is there something rather than nothing”, let me tell you the three most popular answers that I have come across.

The most popular answer at the moment seems to be that nothing is absurd. It doesn’t make sense in and by itself and can’t be. It’s just a confusion of human language that we have inflicted on ourselves. The difficulty becomes apparent if you try to explain what nothing is, because any statement about it requires something. I mean if I can talk about nothing, then nothing it’s the thing that I talk about and it's therefore something?

Another answer is that no explanation is needed, or there is no explanation. God made it, que sera, sera, please move on, nothing to see here. See what I did there?

A third answer might be that our universe, or at least any universe, is in some sense the best option, and nothing doesn’t live up to the requirement because nothing can’t be any good.

If someone asked me on the street why there is something rather than nothing, I’d probably just shrug. I can’t think of any way to answer the question, and I also don’t see what difference it would make if we could answer it. I mean, suppose someone came tomorrow with a 2000 page proof that something must exist, what would it be good for? I guess I could do a video about it.

More seriously, just because it’s not a question that I want to spend my time on doesn’t mean I think no one should. In fact, I am glad that we are not all interested in the same questions and I’m happy to leave this one to philosophers. Do you have an answer that I didn’t mention? Let me know in the comments.