Adam Brown

Well, it turns out that that's been an incredibly productive line of thought, A, and B, it also turns out that that is the,

The main fact that we're most confident about, about quantum gravity.

So the two great theories of 20th century physics, gravity, Einstein's theory of the curvature of space-time and gravity and...

All the rest of it tends to make itself felt at the very large scale.

And on the other hand, quantum mechanics, a theory of the very small, to do with Heisenberg's uncertainty principles and atom and atomic spectra, tends to make itself seen at the very small scale.

These are the two most beautiful theories of 20th century physics, the two things that we should be most proud about, that we discovered in the early 20th century.

And it was noticed pretty early on that these two theories seem to be inconsistent with each other.

The...

the most obvious ways to try and reconcile quantum mechanics and gravity break.

You can't really shut them together.

And this is a problem if you think that the world should be comprehensible, that there should be some theory that in fact is consistent that describes the world.

So this has been a big project in theoretical physics over the last...

few decades, is trying to understand how we can take Einstein's general relativity and quantum mechanics and make them meld together in a mathematically and physically consistent manner.

It's tricky in part because there's very little experimental guidance because generativity tends to make itself felt at large scales, quantum mechanics at small scales.

And so trying to find a place where they meet in the middle, I mean, it must be that they do meet, but that trying to drag that out with experiment is very tricky.

But this has been a...

Big project is trying to figure out how to do this.

Einstein spent some years unsuccessfully doing this in the later, less productive part of his career.

And this project of trying to unite these is something that a lot of people have thought a lot about.

The string theory comes out of this project, a number of other lines of thought.