Trying to understand time is like trying to grasp air. You can't see it or touch it, but with

every second more of it passes, one day you'll run out of it. That's the terrifying part. But in

theoretical physics, time is something else. It's part of space. It can shift and warp, swallow things, spit them out.

Time is the mother of the universe.

And we swim inside her. That's awe-inspiring.

I'm Anne's Train Champs. Today, on to the best of our knowledge.

Deep Time, The Cosmos and Us. From WPR.

It's to the best of our knowledge.

I'm Anne Strange Champs.

Something about living through the pandemic shifted my awareness of time.

This was back when we were starting working from home, and my days were a lot less rigidly structured.

After a while, clocks kind of receded, and in their place, something else opened up, this deep curiosity about time itself.

I mean, I can count down the seconds in a minute, but I can't explain what I just measured. What is time?

I decided to ask my friend Marcelo.

Marcelo, I don't understand what time is.

Well, good. You are in very good company.

He's a theoretical physicist.

Time is completely embedded in our existence and who we are. And yet, we don't know what it is.

We can give you operational definitions of time.

Physicists are very good at that, but that does not mean we know what time is.

Okay, that is not what I was expecting.

I mean, Marcelo Gleiser works in cosmology and high-energy physics at Dartmouth College.

...