Paul Davies - What Exists?

Paul, I have followed you in being obsessed with the nature of existence. What is all reality? How can we explain it? And the way I like to start with that kind of question is to see what we're trying to explain. What are the categories of all reality? And being as broad as possible so we can encompass everything that exists, and then we can decide can we explain it or how they interrelate. So everybody has a different way of describing the categories of existence, so how do you do it? They do. And particularly in physics, it often amuses me that physics deals with the phenomena that we see in the world, and then we can ask for a chain of explanation, and usually it goes back to the laws of physics. And I always want to say, well, where do the laws of physics come from? Why do they exist? Why those laws and not some other laws? And many of my colleagues will say, oh, that's outside the scope of science. I will accept the laws as brute facts and not ask where they come from. But then I will press them and I say, well, do these laws of physics exist independently of the universe? Are they transcendent of space-time? Were they in some sense already there before the Big Bang? And that makes them feel uncomfortable. But the alternative is that they sprang into existence miraculously at the beginning of the universe. Or if you want a multiverse, an eternal multiverse, well, then you have to just assume that they're always there but hovering somewhere outside of this multiverse. And so the question is, do the laws of physics exist in some sense? And I think, well, they do. And of course, I want to know why those laws and not some other. And then you get into this, not just with the laws, but with anything you'd like to think of, this problem that does everything. There are only really two natural states of affairs. One is where everything that can exist does exist, and the other is where nothing exists. Well, I think we can rule out the latter. And Max Tegmark, of course, has famously championed the idea that everything that can exist, including all laws and all mathematical statements and so on, really exists. There are some people who believe it beyond him, like David Lewis and everything that is even conceivable. Yes. Max at least has a coherent mathematical system. Well, he wants to limit it to mathematics and physics. What do you expect from a mathematical physicist? That's exactly right. But we might consider, yes, all possible beauty or all possible evil or something. Of course, it goes on and on and on. Now, I think almost everybody would say that not everything that can exist does exist. There may be a lot more than we can see that exists, but most people would say that there are some things which could exist but don't. But then that raises a very difficult question. Who gets to decide, out of all of those things that could exist, which ones are dignified with being promoted to actual existence? I like to think of this as a huge pile of possibly existing things, you see, and then there are two urns. One is actually existing and the other might have existed but doesn't. And somehow, these tokens have been apportioned between these two urns, and that seems a very strange thing because who is the great apportioner and why that apportionment and not some other? How come that there is a boundary between those things that really exist and those things which might have existed but don't? And that's a mystery, but you're stuck with it so long as you insist that not everything that can exist does exist. That's why the people who say that everything that can exist does exist, at least they say we don't have to explain that question. Right, right. But then that seems a bit unsatisfactory as well. Not only because it makes me very uncomfortable to think that literally everything you can think of is out there somewhere, but somehow if you just declare that everything is there, then you haven't really explained anything. So I'm a fan of the smaller question, which is that given that there's a very large number of things which do exist, why do we only perceive a subset of those? And that can be explained by so-called anthropic reasoning, that we are located in a region of the universe or we have access only to a subset of all possible phenomena. An example that's easy to give is we don't know what goes on inside a black hole. We can't see what's inside a black hole, but nevertheless we assume that something exists inside a black hole, it's just we don't have access to it. So that's a much simpler question. Now most of the physicists here at the FQXI conference would say that when I ask the question they would talk about either quantum field theory or the wave function of quantum mechanics, and that's the totality of what they would explain. And the question is, are there things that are worth explaining in all reality that go beyond a linguistic human creation? Abstract objects, non-physical worlds, spirits, gods, angels, whatever you put in those worlds, cosmic consciousness, which Eastern religions, I mean there are a lot of categories. They may be null sets, there may be nothing's in them, but I want to put all the categories on the table. If you declare that everything that can exist does exist and all possible gods and all possible devils and all possible universes that are without guardians, spiritual guardians, it's all got to go in there. Again, I think most people would be uncomfortable with just a hodgepodge of everything that could be there. But you raise a very interesting question, which is if you ask somebody say 100 years ago, what exists? They would probably say, well, the matter and maybe energy at this particular moment in time throughout the universe, however far that goes. Today you get a very different answer, that the fundamental objects of existence to a physicist today would be something like the wave function. It wouldn't actually be material particles. It would be this abstract entity, the excitations of which are particles. But the particles are rather secondary. It's the wave function that's fundamental. They wouldn't declare that it's at this particular moment of time is existence. It stretches through all of time. And so existence now is this rather shadowy wave function extending across space and time. And that thing is, existence is vested in this rather peculiar entity, which we certainly don't see in daily life. And that in turn is supported by mathematical laws and relationships, which we don't ever see, but they manifest themselves in the way the world is put together. So what's your current view at this moment in time? My current view is that I think that the underlying laws are real. That is, they do exist. I think some people want to make the argument that what we call the laws of physics, relationships between different events and things, are just human inventions. They're not really out there. I think the laws are real. And I think we should try to explain them, that we don't say they just, they are what they are. Let's forget about it. And to use the term shut up and calculate, I think that it's a legitimate question to ask why those laws and where they've come from, and whether they are genuinely independent of time, immutable, eternal, as is traditional in physics. I think all of these things are up for grabs. But I think that the laws really are part of what exists. I don't think we can separate out the stuff of the world and separate it from the laws and say the stuff has existence and the laws some sort of human creation. I think it all exists. And if we ever get an ultimate theory of existence, it's going to be at the level of those underlying laws.