Physics vs. Human Perception: Which Represents Reality? | Janna Levin

Every human being models the world to understand it, and that's cognitively how we're successful. So I don't look at a chair and see a huge number of molecules or some very complex structure; I see a chair. This is something that's very hard to teach a computer to do—to understand conceptual things forward. And we conceptualize right away. We theorize right away. I have a theory of what that object is, and my theory is that it's a chair.

And that's what helps human beings be so adaptable in the world and so fast at moving through the world is precisely this ability to theorize and model. But we also know that by doing so we are projecting a theory of the world on the world, and we trick ourselves; we deceive ourselves sometimes. The trick is to use the power that's given to us by being able to conceptualize and model and have metaphor, but always to remember that that's what we're doing.

And to always—when you come to a point—there is in some sense no such thing as knowing something's true. It's true in the context of the model of the world that you have. And maybe there's a different model of the world where that truth is a little bit different. I mean, I am in no position to talk about interpersonal relationships, but I think that this is a problem between people: that we have a theory of the world, and things mean the certain things in that context, and we forget that somebody else has a different theory of the world and the exact same experience means something very different.

As a theoretical physicist, I rely very much on calculating to understand a result. So, let's say I want to know what happens when a big black hole swallows a little tiny black hole. My starting point will be to think, "What's my first mathematical sentence that I know, if I crack it open, will answer this question?" Even with that step, it can be very hard.

And then, once I do that, I'll be moving in a very structured way through the steps to unlock that, but sometimes it's like a Rubik's Cube, which I'm actually not good at. Some people can just [SOUND] and solve it, and some people just keep making a bigger mess. And so, as a physicist, you want your skill to improve to the point where you could just sort of unlock this thing.

I find it very interesting when I work with much younger students. I like to kind of sit back in the room when we're calculating now and ask them to try to find the solution in a way that we do know how to go one step after another, but I'll be trying, at the same time, to try to find that cute way of unpacking it that's highly non-obvious.

Sometimes I'm sitting there for two days while they're generating 12 pages of very tough, beautifully done calculations, where I'm trying to find a way to try to do it in a half a page. And sometimes I succeed, and sometimes I don't. Sometimes I can't do that; it's just not possible, or I haven't figured out how to do it. And sometimes I do.

And when you do, it's not just that it's shorter; it's that you're working with such bigger structures that you can see so much more at a time. I don't know how else to explain it. How chess players see a lot of the game at one time in one sort of thought; they see many plays. It's also why I don't play chess because I see one play at a time. And I think that's the difference. It's not just that it's shorter; it's that, in some sense, you've seen many plays at a time.

But in terms of the ambiguity, our calculations have to be exact. We can't be like, "I'm not really sure; it's something like this." I mean, there is an art to approximating, for sure, especially in astrophysics, but the kind of calculations I tend to do are very precise and there are no approximations and there's no skipped steps. But that's not reality.

So everything we've ever looked at in the universe is an approximation. We only know the number pi to some number of digits. We don't know every digit in pi, nor will we ever. And so, in some sense, pi can't be measured. It's an abstract thought, but it's not something that can ever exist in reality.

When I tell you the mass of the electron, I always have to end at some precision where I no longer know for sure what the numbers are that follow. And so, in some sense, in reality, we never have the precision we have in the mathematics on the page. And that's an interesting ambiguity to think about.

Do precise numbers exist in reality? Is there anything whose value is one? There isn't, because the best we can do is say it's close to one at some precision that we've been able to observe.