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Physicists are still trying to understand time


This show starts at six minutes and 30 seconds past the hour exactly. And we measure everything we say and record to the hundredths of the second. Knowing the time is what keeps this show running. And it's the same time you see on watches, phones and walls. But time has another side to it, one that the clocks don't show. As part of our series Finding Time, NPR's Geoff Brumfiel went on a quest to uncover the truth about time.

GEOFF BRUMFIEL, BYLINE: America's official time is kept at a government laboratory in Boulder, Colo. It seemed like kind of a logical place to go learn about time. I was supposed to show up at 9 sharp.

COMPUTER-GENERATED VOICE: Turn right onto Rayleigh Road.

BRUMFIEL: Well, I'm just driving, and they have a clock out front, and I can see I'm about seven minutes late.

I rushed across the campus of the National Institute of Standards and Technology, fumbling with my recording gear...

Sorry. Just give me one more sec.

...And arrived at a lab run by a guy named Jeff Sherman.



BRUMFIEL: Hi. I'm sorry I'm running late.

SHERMAN: Well, we only measure the nanoseconds. It's OK.

BRUMFIEL: (Laughter).

Sherman takes me straight into a room where they measure the time. This lab is actually owned by the Department of Commerce, which he says makes sense when you think about it because time is a commodity.

SHERMAN: No one disagrees that if you're measuring out gold, you're going to do so with the best possible scale, the best possible balance. You're going to care about micrograms. Well, time, in a sense, is the least renewable resource there is. At least the present moment, once you experience, you're never getting back.

BRUMFIEL: There are three big boxes in here, each of which holds a high-precision atomic clock.

This one's called George, Fiona, Elvis.

SHERMAN: They all have quirks and personalities. And when they fail at 2 a.m., you want to have a little bit of compassion for them, so you give them names.

BRUMFIEL: We walk over to the big gray box marked Elvis.

SHERMAN: So this thing is not a clock. This is a chicken egg incubator that's been repurposed, repainted and tripled in price and sold to us.

BRUMFIEL: The incubators are used to keep the delicate atomic machinery at just the right temperature. Except today, Elvis is broken.

SHERMAN: We think it's got a small air leak. And one of these days, we're going to get around to fixing it. But in the meantime, I don't mind pulling the doors off.

BRUMFIEL: We open Elvis, and inside is another box with a tube sticking out the bottom.

SHERMAN: And the interesting bit is if you lean down and look thataway, you should see a pink glow through a little hole.

BRUMFIEL: Oh, yeah.

The glow comes from atoms of hydrogen. The atomic clock works by exciting hydrogen and then measuring the light waves that come off the atoms. Sherman says think of it as striking an atomic tuning fork.

SHERMAN: It's a tone of light. And then this is an instrument that tries to sample, tries to listen to a little bit of that light and count the cycles of oscillation in that light.

BRUMFIEL: Those light cycles are the tick of this clock. There are 21 clocks like Elvis spread across the campus, and they're all used to set America's time. It's an incredible system that's accurate to better than a trillionth of a second. But here's the thing - you've got to keep counting all those little trillionth seconds. If you stop, if you blink, you don't know the time anymore.

SHERMAN: In exchange for this wonderful idea, you're now beholden to count forever and not lose track.

BRUMFIEL: This feels like the most Sisyphean job, the most sort of, like, rolling the ball up the hill forever and ever job I've ever heard.

SHERMAN: You said it, brother (laughter).

BRUMFIEL: So this is time - 21 government atomic clocks counting to infinity in tiny, precise increments. And we all look at our watches and cellphones, and we know exactly what time it is, right? Well, as it turns out, maybe not.

CHANDA PRESCOD-WEINSTEIN: A lot of us grew up being fed the idea of time as absolute.

BRUMFIEL: Chanda Prescod-Weinstein is a theoretical physicist at the University of New Hampshire. She says this absolute ticking time is only what the government wants you to think time is because it keeps us all in line. Think about it. The official time runs our lives. It says when planes take off and land.

PRESCOD-WEINSTEIN: When does the market open? When does the market close? Can I make that trade right now?

BRUMFIEL: Are my kids at school on time? Am I late to work? Am I late to the lab where they keep track of the time? Governments around the world aren't giving us the time to be nice. It's to increase efficiency. This is about the economy.

PRESCOD-WEINSTEIN: Yeah, capitalism sucks. And I think - like, I think a lot of people's relationship to why time is, like, not cool is structured by the resource pressures that we feel.

BRUMFIEL: OK, so the time I just saw in the lab, the one you see on your cellphone, that's just counting, a social construct. It's not true time. So what is? I ask Prescod-Weinstein.

PRESCOD-WEINSTEIN: Time is not an absolute. And that's radical.

BRUMFIEL: She's not talking about time zones. She means time itself changes depending on where you are in space. Space and time are tied together. And space time can bend. It can curve.

PRESCOD-WEINSTEIN: The way to think about it is that that curvature is stretching out time.

BRUMFIEL: As time stretches, it slows. The best-known force that stretches time is gravity. So take people on Earth and compare them to people aboard the space station.

PRESCOD-WEINSTEIN: The gravitational field of the International Space Station is much weaker than the gravitational field here on Earth. So we are feeling stronger gravity on Earth. So for us here on Earth, time is flowing differently.

BRUMFIEL: These effects are minuscule compared to a human life span. But get further from Earth and time gets really freaky. Katie Mack is an astrophysicist at the Perimeter Institute for Theoretical Physics in Canada. She says that the universe is expanding from the Big Bang, and that expansion is stretching time, too.

KATIE MACK: When you see things in the really, really distant universe because of the expansion of the universe, it takes longer for things to happen.

BRUMFIEL: Compare, for example, two identical stars that explode, one nearby and one that blows up far away.

MACK: If we see a star exploding and that star takes about 10 days to go from the sort of brightest part of the explosion to dim again, if we look at it in the very distant universe, it might take 20 or 30 days.

BRUMFIEL: Again, that faraway star isn't exploding more slowly. Time is ticking more slowly, at least from our perspective. In fact, when Mack looks at really big events in the universe, like the Big Bang, time becomes so twisted she doesn't even bother with it.

MACK: We don't really use time as the marker for the passage of time, if you see what I mean.

BRUMFIEL: No, I don't. And I still don't know what time is. And then Mack drops a real time bomb. She tells me that when she talks to scientists who study the most fundamental particles in the universe, they tell her that they suspect time might be an illusion, a side effect of something else that's going on in the cosmos.

MACK: And it is a little bit maddening because you're just trying to have a conversation. They're like, oh, yeah, you know, space and time are, you know, probably not real. And you're like, wait. What is, then, actually?

BRUMFIEL: So I can't tell you what time is because I'm not even really sure what's real anymore. OK, deep breaths. Back to NIST, that government lab where the clocks keep ticking. Tara Fortier is another physicist. She reassures me that time actually exists.

TARA FORTIER: I'd say time feels pretty real whenever I look in the mirror (laughter). Whenever I get a new passport photo, time feels very real to me.

BRUMFIEL: And look. She gets it. They all do. All they're doing is counting. True time, whatever it is, isn't on a clock. And her personal time reflects that. Every night before bed, she meditates.

FORTIER: And those 10 minutes, every night that I meditate before sleep, are very slow. Just sitting and listening and feeling my body helps me enormously.

BRUMFIEL: And how do you know when you're done? Do you have a timer?

FORTIER: I have a timer that's attached to the NIST atomic clock (laughter).

BRUMFIEL: Geoff Brumfiel, NPR News.


FORTIER: (Laughter). Transcript provided by NPR, Copyright NPR.

Geoff Brumfiel works as a senior editor and correspondent on NPR's science desk. His editing duties include science and space, while his reporting focuses on the intersection of science and national security.