Sten Odenwald

And my clock, because I'm in one part of Earth in a gravitational field sitting in a chair, is going to be very different than the clock that's carried by an astronaut in the International Space Station.

400 kilometers above the surface.

That's guaranteed by general relativity.

So those two clocks are not synchronized and they're only, you know, 400 kilometers apart.

But yet we carry on perfectly good conversations with the the astronauts and we do physics experiments with them and all that.

up to the point where that difference makes a difference and that difference is on the order of microseconds you know if we tried to coordinate experiments on the ground and in the space station to better than a microsecond we would not be able to do that because there are two different clocks and we can measure them very accurately how they're carrying on time measurements and they're not the same so that's why you can't say that there is a single coordinated universal time

You know, that's good to, you know, a nanomicrosecond across several light years.

That just doesn't work.

But there is an overall clock that says today is 13.85 billion years after the Big Bang.

You know, and that's something that you can pretty much count on.

Now, we don't know why we're living at a time that's at that time.

Why aren't we living at a time that's a billion years earlier or a billion years later?

That's the mystery of why there is such a thing called now.

And we have no idea why now exists.

Well, it was replaced 100 milliseconds later by another now that your brain processed information about and gave you a complete picture of your environment and so on and so forth.

But your sequencing of nows is different than mine.

I'm geographically in a different place.

My brain operates perhaps a bit slower than yours because I'm a little bit older, I would suspect.

And so now is a slippery thing, even at the biological level.

So it's better to say that that no two people share exactly the same nouns.