Hello everybody and welcome to the Mindscape Podcast.

I'm your host Sean Carroll.

A few years ago I was being interviewed on camera for a TV show, a documentary about physics,

and we were talking about black holes and crazy things about quantum mechanics and some speculative

ideas.

And during a break the director said to me, I love doing shows on this kind of topic, but

my brain always hurts.

It's just so hard to think about this stuff.

And I said immediately, now you know how I feel every day.

That's what I do for a living when I'm not podcasting.

I'm thinking about theoretical physics and crazy ideas.

And physics works at the boundaries of what we know.

Physics is driven by puzzles and mysteries by things that we don't yet understand.

If we're lucky those puzzles come from experiments.

We get some data that we can't fit together that doesn't quite make sense in our current

conception.

So we try to improve our theories.

But sometimes we have two theories that individually make perfect sense, but don't fit together.

That is the case with perhaps the single biggest looming question in modern theoretical physics,

how we reconcile quantum mechanics, our best theory of how the world works at a fundamental

level, especially at the level of tiny particles in the subatomic realm, and gravity, the

theory that is explained by Albert Einstein's theory of general relativity, the idea that

...