I'm Steve Strogatz and this is The Joy of Why, a podcast from Quantum Magazine that takes you into some of the biggest unanswered questions in science and math today.

In this episode, we're going to be discussing the mysteries of space and time and gravity too.

What's so mysterious about them?

Well, turns out they get really weird when we look at

them at their deepest levels, at a super subatomic scale where the quantum nature of gravity

starts to kick in and become crucial. Of course, none of us have any direct experience with space

and time and gravity at this unbelievably small scale. Up here, at the scale

of everyday life, space and time seemed perfectly smooth and continuous. And gravity is very well

described by Isaac Newton's classic theory, a theory that's been around for over 300 years now.

But then about 100 years ago, things started to get

strange. Albert Einstein taught us that space and time could warp and bend like a piece of

fabric. This warping of the space-time continuum is what we experience as gravity. But Einstein's theory

is mainly concerned with the largest scales of nature,

the scale of stars, galaxies, and the whole universe. It doesn't really have much to say about

space and time at the very smallest scales. And that's where the trouble really starts.

Down there, nature is governed by quantum mechanics. This amazingly powerful

theory has been shown to account for all the forces of nature, except gravity. When physicists

try to apply quantum theory to gravity, they find that space and time become almost unrecognizable.

They seem to start fluctuating wildly. It's almost like space and time

fall apart. Their smoothness breaks down completely, and that's totally incompatible with the

picture in Einstein's theory. As physicists try to make sense of all this, some of them are coming

to the conclusion that space and time may not be as fundamental

...