Short Wave - The Great Space (Clock) Race

Episode Date: January 6, 2025

There are hundreds of atomic clocks in orbit right now, perched on satellites all over Earth. We depend on them for GPS location, Internet timing, stock trading ... and space navigation?Today on the show, hosts Emily Kwong and Regina G. Barber learn how to build a better clock. In order to do that, they ask: How do atomic clocks really work, anyway? What makes a clock precise? And how could that process be improved for even greater accuracy?For more about Holly's Optical Atomic Strontium Ion Clock, check out the OASIC project on NASA's website.For more about the Longitude Problem, check out Dava Sobel's book, Longitude. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.Have questions or story ideas? Let us know by emailing [e-mail]!See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey everyone, Regina Barber here with Emily Kwong and a story about time. Yes, a tale about how time tells us our place in the world. So, Gina, are you familiar with longitude? Yeah, so longitude is like the east-west position on Earth. It's relative to the primaridion in Greenwich, England, right? Yeah, the longitude there is zero degrees and extends by 180 degrees westward and 180 degrees eastward. And back in the 1600s, it was really difficult to calculate longitude.

A ship leaving port would set two clocks. One for the prime meridian and another for local time. So crews would update their local time as they sailed, calculating it by using the position of the sun. And by knowing the difference between these two times, you can calculate the in-between longitudinal degrees and know your location. Yeah, you can math. Right. But the clocks aboard these ships were not reliable. Like picture pendulum clocks on rolling seas, right?

Surrounded by salty air and changes in temperature or barometric pressure. The clock parts are going to warp. All of us can ultimately cause the clock to stray from the correct time. We call this clock drift. Ooh, I like that term clock drift. Yeah, clock drift is dangerous regularly throughout the 16 and 1700s. This accumulation of errors through ships so off course that it resulted in shipwrecks and lost lives. and merchants and seamen began calling for a scientific solution.

So the British government created the Board of Longitude, and they announced a contest to solve this problem, the Longitude Problem. Okay. And out of that contest came the Marine Chronometer, a near frictionless pendulum that doesn't need to be reset as often and was therefore more precise. Right, so fewer shipwrecks because now like ships knew the time, and knowing the time, let them know where they were.

Yes. Okay. This really made seafaring possible for the British Empire. So this clock changed world history. And I think history is repeating itself right now, because many governments and companies are setting their sights on space exploration. Right. I mean, so we're planning to go to Mars, maybe even further into space.

Yeah, and the hurdles that were kicking around during the era of the longitude problem are repeating themselves today. To navigate far from home, you need a really real. good clock. That's why today on the show, space clocks, how scientists are pushing the envelope to build an atomic clock with even better precision and what that could mean for addressing some of the biggest mysteries of the universe. You're listening to Shortwave, the science podcast from NPR. All right, you ventured actually a few miles north in D.C. to NASA's Goddard Space Flight Center, which we've been two together and it's like super cool. Yeah. Goddard is a campus.

They have a soccer league, a theater club that performs shows. But I was on shortwave duty, so I went there to see a lab. Cool. So this is Building 33. We're going to walk into the Quest Lab. With Holly Leopardy, an atomic physicist with green glasses and a big grin. And two years ago, she was telling me she joined the Quest Lab. The Quest Lab is like a one-stop shop for atomic physicists to do experiments and pass along those discoveries to NASA engineers.

Quantum engineering and sensing technologies. Quest. Were you like, yes, we made an acronym. Yep. I mean, that's a good acronym. Like, physicists and astronomers, like, we're obsessed with acronyms. Yes, I've noticed. Okay, so the main lab of Quest is a big room with three massive tables.

The tables are made of metal, and they have holes in them drilled every inch on, like, the surface of the table. And that's to screw down different optical components. Kind of the classic first mistake that, you know, you know, when you walk into an undergraduate physics lab, is they make a nice aligned optical system, and they don't screw the mirrors and things down on the table, and then they move. Okay, I loved optical benches when I was like a physics undergrad,

and I was always the student that screwed in the beam splitters in the mirrors. Of course you were. And not only is the precise alignment important, but the system has to be really durable. Right. Whatever is invented here has to survive, being jettisoned into space. We're not developing technologies for them to sit on a shelf. somewhere. We want to actually fly them in space, and we want them to make a difference for our

science measurements. Assistant Chief for Technology, Renee Reynolds, has been at NASA for 25 years. And in the last few years, she's really been the person to build up the quantum program and hire scientists like Holly. We do see quantum technology as a path to be able to move beyond some of our classical techniques that may be reaching their limits. And one piece of technology that NASA wants to improve is the atomic clock. They want to build new atomic clocks for space. Right. So tell me about the atomic clocks that are like in space orbiting like right now.

There are hundreds. Many of them are perched on navigation satellites. I had no idea actually like navigation uses time. It's just like in the 1600s. But here in the U.S., you know, our satellite-based navigation system is GPS. Each satellite emits a timing signal and you receive those timing signals on your GPS receiver on your phone. And from those timing signals, it triangulates where you are. So GPS is kind of like a clock? GPS is all clocks. And so if we have better clocks on GPS, we would know our location to

higher degrees of accuracy. GPS, internet timing protocol, stock trading, all of these things rely on more accurate systems. But the atomic clock system, as it stands right now, is error prone. Yeah. GPS clocks are estimated to drift by about 10 nanoseconds a day, which I know doesn't sound like a lot, but an error of even a microsecond in space can translate to an error of 300 meters on the ground. Right. So to correct for clock drift, GPS clocks will send a signal a few times a day down to Earth and ask, you know, hey, am I on time? And then the Earth says, okay, your clock has accumulated this much error, it's this much seconds off or time off, and then they send another signal back.

But this process is kind of a pain, you know, this constant like phoning home. So for years now, NASA has been searching for a clock that is capable of autonomous navigation, able to operate as its own unit with minimal updates and be even more precise. All of this reminds me of what the Board of Longeitude was trying to do all those centuries ago. Holly, she calls her clock OASIC. Optical Atomic strontium ion clock. OASIC. It's a cover. It's a science oasis cover band. I'm going to explain why OASIC holds such promise, what all those different words in that sentence mean.

But I need to call upon the spirit of my grandfather, Bob, who was a clock repairman, and first explain how an atomic clock works. As a physicist, I still struggle with this, so let's do it. It's like the Mr. Potato Head of Science. You have to smash so much tech together. to make it go. So all you need to know about a clock, this is true of all clocks, is they are feedback loops. And there's generally three elements that talk internally to each other within the clock to keep it steadily ticking. The first part is an oscillator, which is something that swings back and forth. Like a pendulum, which swings back and forth once per second. In modern clocks, their pendulum is actually a crystal of quartz.

That's so cool. When indulged with electricity, the quartz will vibrate at a precise frequency. And emit electrical pulses, which can then be measured by a counter. Which counts up those swings, those cycles, and displays them. Okay, so you got your oscillator, you got your counter. What's the third thing that makes it a clock? Your reference. So the reference ensures that the oscillator vibrates at the right frequency

and doesn't cause the clock to drift. And that's where the atoms come in. An atomic clock is called that because it uses part of an atom as its reference. atoms have this really special quality. And I'm going to turn it over to you now, Gina, to explain how atoms go from a grounded state to an excited state. Yeah, so most atomic clocks use an atom of cesium or rubidium. But in general, I think it's like easiest to explain this process with like the element hydrogen because it just has one proton at its center and one electron orbiting it.

And, like, orbit is a bit of a simplification for now, but let's just say orbit. Electrons, they have these different orbits. Each of them are associated with, like, a different energy. And if an atom absorbs energy, let's say through, like, a little chunk of lighter or a photon, the electron will change its orbit. It'll go to, like, this higher energy state. It'll go to a higher orbit. And then when the electron eventually goes down, energy is released from that atom as another photon.

Okay, so that. In the 1950s, scientists hack. this particular ability of an atom and forced this energy transition in the atom at a regular interval and designed a clock that would count every time energy is released as the electron goes back down and that is the frequency of the atomic clock. Okay and they did this with light right? Right so traditional atomic clocks the ones used for GPS use microwaves which is a form of light. How the clock works is it bombards an atom with microwaves and that forces the atom from its grounded state to its excited state, and that transition happens at a steady pulse by which the whole clock

is referenced. But those clocks are accurate to the 10-the-minus, the best ones are 10-minus 16. Which is not good enough for Holly as an atomic physicist. I know, but microwave is not precise enough for her. She and other atomic physicists work with optical light. Optical light has a shorter wavelength, so it's a better light source by which to control an atom. Instead of going from shining microwave light on the atoms, we can go shine optical light or use lasers on the atoms. We can get to 10 to minus 17, 10 the minus 18, and even 10 to minus 19.

So these are up to three orders of magnitude improved over current microwave clocks. That level of precision means the clock should be better at staying on time without needing to dial Earth nearly as much for a time check. And it's more precise because it's more precise because it's, using optical light instead of microwaves. Yes, and because the clock is powered by a strontium atom. Oh, I don't know anything about strontium. Strontium, it's a weird, it's like in the periodic table. No one talks about it.

But Holly chose strontium because it's good at withstanding temperature swings, good for space. And also because strontium requires a very precise frequency to get excited. So she told me to think of the laser like a drumbeat. Boom, boom, boom. But the atom is like a conductor. And if you've ever seen an orchestra, you know, a conductor will only tolerate the correct drumbeat. Strontium is a very strict conductor. Okay, so like in this case, the atom will only get excited if the laser is on beat. It has that specific frequency. Yes, the laser

being precise makes the strontium atom precise, which makes the clock precise. Peter Brereton, who runs the lab, says this is the power of quantum technology of systems that use the physics of atoms to be more accurate than systems using like classical physics. Her clock is referenced to an atom. And an atom here is the same as a Adam on Mars. And so that long-term stability, that reference, inherently can't change. So what will OASIC the clock, like, look like once it's built? Like the Tesser Act in the Marvel movies. Really?

It'll be a blow. No. It will be a cube, though. It will be a cube. With all these optical systems bolted into place and a single strontium atom at its core. And I asked Holly what she ultimately hopes for these clocks where she wants them to live. So my goal is to have a clock network in space, especially an optical clock network, because when you start getting down to the 17th, 18th, and beyond level of precision, digit of precision, you can start doing really cool fundamental physics. So if multiple oASIC clocks get installed up in space,

scientists can compare how their frequencies change relative to, each other. And this data will allow them to tackle some big questions, like changes to Earth's gravitational field, which could tell us how sea ice is melting or groundwater is flowing. And you could start looking for how does gravitation and quantum mechanics interact. Can we understand dark matter interactions, things like that? Wow. Okay, so gravity and quantum mechanics interacting is like the holy grail of physics. Okay, so how far along are these new clocks? Holly says the team wants a prototype system done by fall 2025, and she hopes OASIC could fly within six years. Okay.

She is determined to do this for timekeeping and also for the field of physics. The field wants this, and it would take a lot of academics, a lot of companies, a lot of even nations, to make this happen. It's bigger than just me and my lab. Because for her, a clock's real power is as a sensor to tell us where we are and how the universe is changing around us. This was a great story. I loved it. I loved learning about atomic clocks.

Thank you for bringing it to us. It's always time for physics, Gina. It's always time for physics. Always. Special thanks to Deva Sobel, who wrote the incredible book, Longitude. All about the Longitude Problem and the creation of the Marine Chronometer. It's a great read. Check it out. This episode was produced by Hannah Chin.

It was edited by showrunner Rebecca Ramirez and Tyler Jones Check the Facts. Jimmy Keely was a showrunner. audio engineer. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber and I'm Emily Kwong. Thank you as always for listening to Shortwave, the science podcast from NPR.