Talk about the recent changes in our understanding of physics.

Well we’ve discovered that the atom is almost entirely empty space. If you took a baseball and put it in the middle of Madison Square Garden, that would be like the nucleus, and the first level of electrons are as far away as the exterior of the Garden. So you can think of this baseball, this nucleus, as a tiny dot all alone.

So the atom is almost entirely empty space. But why don’t I fall through the floor here, because the floor is mostly empty space and I’m mostly empty space? If you look at it on the micro level, this apparent solidity is the product of a pair of purely mathematical relations: the Pauli Exclusion Principle and the Heisenberg Uncertainty Principle.

And if you study quantum field theory, which is what all physics graduate students now begin with in graduate school, you discover that even particles are unreal. They are just temporary properties of what are called fields, and fields are just distributions of mathematical quantities through spacetime. So particles don’t seem to be grounded in anything tangible. And the pervading theory in quantum mechanics says that a field is like a stream of numbers — pure information — numbers that tell you where an electron might be. But you can’t observe it, only its effect on other things.

And if something is in principle unobservable, you may as well say it doesn’t exist.

So what is a rock? A rock looks like a good, solid, persisting object. But it really, in our perception of it, is energy transitions — changes in the distribution of energy from one state to another. And when that happens, energy is radiated. It goes through my pupil, and strikes my retina, and I perceive the rock.

So I don’t know, Jim, if you would call a rock — like Bishop Barkley did — a thought in the mind of God. But he might say that deep down, what a rock is is an expression of rules, or math, it’s just here like the shadow of an idea.

I’ve heard one physicist say that the cosmos is ultimately a concept. Maybe, a hundred years from now when String theory is worked out, we might have a very different conception of it. But it looks like the universe is mathematics and structure all the way down.

You’re okay with this?

Well I’m a sort of mathematical romantic. I love the idea that the essence of reality is not stuff — stuff is kind of ugly, you want to get rid of stuff, there’s too much stuff in your apartment —

I like stuff.

Well this is a temperamental difference between us. I like the idea that reality consists of a flux of pure information with no further substance.

I don’t know why this makes you so happy. I would love if I’m clapping or hitting someone in the face, that the billiard ball of me is hitting the billiard ball of them. 

But we’re living in an almost spiritual realm, you want to live in this gross material realm…

And if you go back to the 19th century view, that we’re all these hard particle atoms just bumping around, is that any more plausible? Is it any more plausible that you and I are just dumb, hard particles in a certain configuration? And if that’s true, how are certain configurations of these particles tantamount to the horrible feeling of pain?

Whether it’s a mathematical object, or whether its little billiard balls knocking around, it’s still miraculous and improbable that it should produce subjective experience, that it should produce pleasure and pain. I find it to be exhilarating to worry about the metaphysics of physics and the nature of reality even though it doesn’t lead you to any sort of comfortable intellectual closure. It’s a good way of idling away an otherwise boring afternoon.

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Selections from Jim Holt in conversation with Robert Krulwich discussing physics and the material universe.

I’ve just discovered Radiolab, the nationally syndicated radio show and podcast hosted by Jad Abumrad and Robert Krulwich. I’d bet that you, the voluntary reader of this blog, will enjoy the stuff done at Radiolab. The program devotes entire episodes to a particular scientific or philosophical idea — like “time” or “free will” or “morality” — and approaches it in a highly accesible and absorbing, though still informative, way. The hosts are clever without coming off as obtuse, and the show features incredibly rich sound design. Check out an archive of all of their episodes here.

Read excerpts relating to these same subjects taken from Holt’s new book Why Does the World Exist?:

Could the World Cause Itself?

This Planet and the Stars were Once Bounded in a Point the Size of a Period

Try to Wish into Nonbeing the Entire Contents of the World

The Arithmetic of Nothingness