How do atoms keep time?

Scientist, author and a self-proclaimed “Science Evangelist, Ainissa Ramirez joins Hari Sreenivasan to discuss her latest podcast episodes about how atoms keep time.


Ainissa Ramirez is a scientist, author, and a self-proclaimed science evangelist.

She is the creator of a podcast series called 'Science Underground.'

She joins me now to discuss one of her latest podcast episodes about how atoms keep time.

Before we had atomic clocks and all this fancy stuff or even watches, we just used to look up and say, 'It looks like it's really kind of near the middle.

It must be midday.'

Mm-hmm. Mm-hmm.

That's not the most accurate way to do it?

[ Chuckles ] Well, it's a way that we did it for a very long time, looking at what was noon.

In fact, different cities would have different times because noon was different depending on where you are.

You could just be six miles down the road, and your noon's gonna be different than my noon.



But you didn't have the Internet back then to know that.

We didn't have the Internet.

And by the time you got over there, it didn't really matter.

It wasn't noon anymore.


But yeah, it's all about having something that keeps some kind of periodic pattern.

So it was the Earth at first.


And then we figured out how to make different mechanical contraptions that can keep time.

And then we got to quartz.

Quartz, which I have right here, if you zap it, actually wiggles.

It wiggles like jello.


And it wiggles thousands and thousands of times, and then that's counted, and a certain number make up a second, and that's what's inside of our watch.

Tiny pieces of quartz wiggling.

That's right.

A tiny piece of quartz, just like a tuning fork, and it's wiggling, and it's being counted, and that's how we determine a second.

Because it's at a very exact frequency of measure, and then you can say, 'Okay, well, if it wiggles this much at this time, this is now four seconds.'

That's right, that's right.

That's how we determine.

However, before things like GPS or satellite missions, quartz is not enough because it's precise.

It's more precise than what we used to do, but it's not precise enough for going into space.

What's the difference in the precision of an atomic clock versus what's on your wrist?

Oh, I don't have that number off the top -- I mean, this is scientific numbers.

It's on the order of like micron parsings for a scientific level.

For us, we don't care if it's one second or two seconds.

It doesn't really matter.

But a GPS cares a lot.

Exactly, because it's all about the minutia, microseconds that can be all the difference of different things that are going on, plus there's other effects that are going on.

Ends up that Einstein figured this out that when you change your position, if you're moving, your clock is actually a little slower than if a clock is stationary, so you have to take that into account if you're a satellite, as well.

So if you have --

It's a lot of math just to tell time.

It is.

It's a lot of math just to know where your packages are.

Because when we think about locations and when we see GPS location, it's kind of written differently.

It's not at this intersection and this intersection.

It's sort of hours and minutes and look at longitude and latitude, right?

So it all kind of matters on that exact moment because if you're off by a second, depending on how far away you are in space, that second could be a couple of feet, it could be much, much worse.


And a couple of feet up in space could be a larger distance if you get back to Earth, so we need something much more precise, and that's where atoms come into play.

How do we measure them and the movement that they're in?

Well, the atomic clock actually has a piece of quartz inside of it, wiggling again, and there's also another part that's counting those number of wiggles.

And then the atom comes into play because atoms have different electrons at different levels.

And if you zap it, an electron will move up, and then it will get rid of that energy and it will come back down.

And when it does, that energy actually has a wiggle to it, and that wiggle is very, very precise, more so than quartz, so that's compared to the quartz.

And depending on how off it is, then you can determine what the time is.

So the atomic clock has this thing that kind of checks the quartz.

But there are different types of atomic clocks, or are they all kind of at the same level?

Because there's one in Colorado, there's one at the U.S. Naval Observatory, and then there's ones that you can buy, like, on some catalog on a plane.

Like, 'Oh, I can put this on my desk.'

That's right.

Little atomic clock.

Well, I mean, they're around $10,000, so if it's less than $10,000, it might not be an atomic clock.

It might just be named atomic clock.

Got it.

But yeah, there's different sensitivities.

Usually we use cesium, and cesium is a standard.

In fact, we used to think about time as a certain duration, but now it's the number of wiggles that a cesium atom gives off.

That is the benchmark...

Go to Wikipedia.

...against which everything else is measured.

Yeah, so cesium was the benchmark.

But now we can use a range of different atoms, as well.

Is there a backup plan, right, if the cesium stuff for some reason stops working?


GPS goes all haywire.

And we are dependent on GPS, and we're dependent on lots of different technologies that have this very fundamental, basic understanding of what time is.

If our measurement of time goes haywire, it's not like we can sort of back up the satellites by looking up and saying, 'Oh, it looks like it's noon again,' right?

Yeah, I mean, if we want to know the time, it goes back to astronomy.

And we can look and see when certain planets and when certain objects are moving across.

And from that, we can determine the time.

That's just what we used to do, you know, 1600s, 1700s, 1800s.

But in terms of like will your Amazon Prime package get to you on time, if we have a problem with the satellite, that's a different issue.

It kind of goes back to a fundamental, you know, lack of understanding of basic science that I think we sort of stopped paying attention after we get out of that science class at fourth grade or seventh grade.


I mean, it's almost like you -- It's not like I want you to prepare to live in a shelter and a dark cave or anything, but it's like we should know some basic things on, I don't know -- Like, I'm just thinking to myself as I'm having this conversation with you.

It's like, if I didn't have a watch, if I didn't have a GPS, if I didn't have a smartphone, how would I tell what time it is today on a cloudy day?


You don't have a sundial?

I haven't made one, but I'll look it up online.

Maybe we should put that online.

Definitely have a sundial.

But remember, it changes, you know, depending on --

Where you are and the seasons, et cetera.

That's right.

Anyway, it's a lot of math.

Ainissa Ramirez, thanks so much for joining us.

Thank you.