This is an I-Hart podcast.

Guaranteed Human.

We all know that quantum mechanics is plenty confusing already.

Particles can weirdly maintain multiple possible states at the same time? There's instantaneous

collapse of entangled particle states across various spacetime distances. And on top of all

of that, there are these articles you see in popular science venues claiming that quantum

mechanics proves you can change the past. Well, spoiler alert, these are wrong.

They're wrong when they were written, which means that they can't use quantum mechanics to go back in time to fix them later.

But there are some fascinating issues about how time works in quantum mechanics,

and there are some amazing and crazy ideas for retro causality, where the past can depend on the

future. These ideas might actually help unravel some confusion about instantaneous collapse

and also avoid creating signaling paradoxes. So we can't send you back in time to kill your grandfather, but today we are going to dig

into all of that and hope that you understand time in quantum mechanics better after you

hear this episode than you did before.

Welcome to Daniel and Kelly's extraordinarily timely universe.

Thank you. extraordinarily timely universe. Hello, I'm Kelly Weider Smith.

I study parasites and space.

And after looking at Daniel's outline for today,

I wonder why physicists are always trying to confuse us.

Hi, I'm Daniel.

I'm a particle physicist, and I'd like to go back in time and tell young Daniel that instead he should work on quantum foundations.

But I can't because time flows forwards.

...