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In 1656, Christian Hawkins invented a pendulum clock that based on the period of its pendulum swings could measure time down to the second. Now, today we have clocks that measure a second out to 19 decimal places. These clocks have billions of times as many ticks in a single second as there have been seconds since Howens invented his clock. I mean, wo. But also, why? What's the point of subdividing time into such infinitismally tiny fractions? Hi, I'm Cameron and this is Minute Earth. And this is NIST F3, a cesium fountain clock, which I visited at the National Institutes for Standards and Technology in Boulder, Colorado. This video, by the way, is part of 50 by50 science across
America, which is a series of science videos made across all 50 states, and I am proudly representing Colorado. Dr. Greg Hoth is a scientist in charge of running the clock and he explained that it actually works a bit like Howins's pendulum clock. But instead of counting the swings of a pendulum to tick away time, it counts the frequency of radiation from super cooled cesium 133 atoms which can absorb and remit radiation vibrating exactly 9 bill192,631,770 times each second. Now, for comparison's sake, during one swing of a 1 meter pendulum, one tick on Halhens's clock, light can travel about 3/4 the distance from the Earth to the moon. And during one shake of cesium 133 atomic
radiation, one tick on NIST F3, light can travel the width of Hold on, wait, cuz this won't work. Enhance. Okay, there we go. The width of a grape. So with cesium clocks like NIST F3 we are able to accurately quantify incredibly short events like say how long it takes a radio signal to travel from a satellite to your phone which is critical for triangulating your GPS position like if you're trying to find your way through the woods or even just to the nearest coffee shop. In order to calculate GPS positions with say 1 meter accuracy, we need clocks that tick fast enough that light can only travel a meter between ticks, which would require being able to measure a second out to at least nine decimal
places. Now, this kind of uber precise timekeeping is what allows us to accurately time code financial transactions where fractions of a second can translate to millions of dollars. And it lets you play Roblox with friends around the world without your computers going out of sync. But there's another reason scientists want to quantify time ever more accurately. It helps us quantify pretty much every other unit of measurement more accurately as well. Like we used to define the length of a meter as 1 10 millionth of the shortest distance going through Paris from the North Pole to the equator. A distance which isn't only really hard to actually measure, but also thanks to the
centrifugal forces of the Earth's rotation, fluctuating surface temperatures, and a bunch of other stuff, it isn't actually constant. What is constant though is the speed of light moving 299,792,458 m every second. So if you are able to measure time accurately enough, you can define the meter as the distance light travels in 299,7 you can define the meter as the distance light travels in 1 299,792,458 of a second. an actual physical constant. The same goes for most of the rest of the SI units, too. We now define them by physical constants in relation to other units like time, which can become even more precise thanks to the atomic clock's ability to break time into incredibly tiny fractions. But none
of that matters if the clocks aren't also stable, like if they can't track time consistently over time. How's pendulum clock, for instance, might drift as much as 15 seconds per day. Modern watches, which use vibrating quartz crystals to keep time, might differ from one another by as much as 15 seconds per month. But NIST F3 is so stable that had dinosaurs built two of them, today, they'd differ by less than a second. That's because unlike pendulums and quartz crystals, the cesium atoms these clocks used to tick away time are not similar, but they are absolutely existential crisis level identical and radiate with incredible consistency. But NIST F3 isn't even the
most advanced clock we have these days. For that, I traveled to a different wing of the facility to visit the lab of Dr. Roger Brown. You see, although cesium atoms were the fastest, most stable vibrating atoms we knew of back in 1955 when the first atomic clocks were built, we have identified even better candidates since then, like a turbium for example. When these atoms are energized, their radiation vibrates 518 trillion times per second. Which means that while cesium clocks can measure time to 10 decimal places, atomic clocks that use a turbium, like the one I saw at NIST, can measure time up to 18
decimal places, between its ticks, light travels less than the width of a human red blood cell. But amazingly, we can do even better. Two years ago, researchers here at NIST built the newest version of what they call a quantum logic clock, which operates in a similar way as the Ubium clock, but uses a single aluminum atom to measure time. Seeing that clock and meeting part of the research team in charge of it, Dr. Mason Marshall and Daniel Rodriguez Castillo was my last stop at NIST. This bad boy, they explained, ticks 1.12 quadrillion times per second. Between its ticks, light only travels the length of a bacterial phase. That is a virus that infects microbes. Seriously, a virus. Anyway, that kind of accuracy
opens up some wild scientific possibilities. Like if we had two of these clocks running perfectly in sync with one another and then we lifted one, even just a few centimeters, the clocks would start disagreeing with each other because the gravitational pull on each one would be ever so slightly different, making time flow at an ever so slightly different rate. The effect, of course, is incredibly small, but because these clocks measure time in such infinitismally tiny chunks, we'd be able to notice the difference. These kinds of experiments could help us detect the gravitational signatures from shifts in tectonic plates and lava below the Earth's crust, potentially helping us
predict volcanic eruptions. Or we could put pairs of clocks in orbit in order to sense weak gravitational waves from throughout the galaxy, helping us study how black holes and supernova are formed. Or we could potentially track the behavior of individual particles on quantum time scales, watching for irregularities in their behavior that could help us track down dark matter. All of that is a quantum leap from that first pendulum clock. And that's the cool thing about clocks. Like time itself, they keep marching on into the future.
Thanks for taking the time to watch our contribution to 50x50 science across America. I want to thank all of the scientists I got to meet at NIS, who calmly and extremely patiently explained, or should I say blew the lid off my understanding of timekeeping. So much so that we even recorded a 1-hour long Patreon exclusive podcast episode where we talk about all of the incredible stuff that didn't actually make it into this video. My parents bought an atomic clock for their house. What I also want to thank and the 50x50 science across America project for giving me the opportunity to represent Colorado. Go check out science stories from the other states at 5050science.com.
