Be Smart

- 354 years ago, John Wilkins, a bishop and founder of the Royal Society published a 638 page essay laying out a scheme for a universal global language, a common tongue to be used among scholars, philosophers, and governments for the sharing of knowledge.

Buried among a handful of pages in that essay is another idea, one that would end up changing the world forever.

A standard and universal system of measurement based on the natural world.

And at the base of that system of measurement would not be a rod of particular length, or a mass of metal, instead it'd be based on time.

Today, other than a handful of notable exceptions, (clears throat) the modern world relies on a shared system of measurement much like what Wilkins first proposed, the metric system.

But at its root there's always been a problem, a measurement system tied to physical objects will only ever be as precise as those physical objects.

So, in 2019, the base units that make up the foundation of the metric or SI system were redefined to no longer rely on imperfect human artifacts.

Now, they're defined by natural mathematical constants that never change.

This standard system of measurement is the foundation of modern science and society, but for any of it to work, there's still one unit we must physically measure, one unit to rule them all, the second.

So, who decides what a second is?

These are the things that keep me up at night.

(upbeat music) Hey smart people, Joe here.

And this is the US Naval Observatory in Washington DC.

This is one of the best rooms I've ever been in in my life.

(inhaling) I wish you could smell this, it just smells like knowledge and important stuff.

- Yeah, yeah.

- That is Geoff, and inside of the building there, you will find, I kid you not, what are probably the most precise measuring devices ever built by human hands, and they are clocks, very, very fancy clocks.

It's also where the Vice President lives, that's her helicopter taking off while we were filming.

You're right, I do take that for granted.

- Yeah.

- Helicopter time.

(claps) - [Geoff] I'd love to wait for that.

I always tell people that of all the things in nature that we can measure, the one that we can measure with the highest precision is the one that we know intrinsically the least about.

- Time.

- Time.

I cannot tell you what time is, but I can tell you exactly what time it is.

This is where time more or less begins.

So, let's look over here.

- We're at the beginning of time, right here, is that what you're saying?

- We're at the beginning of time, right.

- Cell phone networks, the internet, power grids, financial transactions, air travel, the very fact that some server somewhere is letting you load this video right now, none of it would be possible without machines like these.

And what those machines do is figure out exactly how long a second is.

So, how do we do that?

Okay, so let's lay this out for a second.

See what I did there?

Prepare for a bit of massively oversimplified history.

Since humans became humans, our species has marked the passage of time using various cycles, the Earth's orbit and the seasons, the rising and setting sun, even tides.

For most of our history these worked well enough, but as everyday life changed we needed to divide and measure time in smaller and smaller slices.

The ancient Egyptians were the first to slice up the night and day, into smaller parts called hours, And the Greeks were like "Hey, can we borrow that?"

Then, bam, there's 24 hours in a day.

Fast-forward to around 1,000 years ago, and since people were using round things to keep track of time, astronomers were all about this weird base-60 number system from the Babylonians.

(dramatical music) It's actually pretty genius, because you can easily divide anything with 60 units into one, two, three, four, five, or six parts.

Anyway, the first recorded person to subdivide time into 60 parts was an Iranian astronomer named al-Biruni, and later European astronomers put some Latin on those base-60 slices.

The first small part they called the minute, and the second small part they called the second.

That's literally where the word comes from.

But normal everyday people didn't have any use for minutes or seconds until 100s of years later.

The first clock with good enough mechanics to even count seconds was made by Christiaan Huygens, using a pendulum just under a meter long that swung once a second.

Apologies to the Dutch for my pronunciation of that name.

- Christiaan Huygens.

- This evolution from planetary cycles to ticking machines established the divisions of time we still use today, 24 equal hours divided into 60 equal minutes, sliced into 60 equal seconds, the fundamental unit of time, 1/86,400th of an Earth rotation long.

This clean and simple mathematical definition has just one problem, Earth is a terrible thing to base time on.

Over long time scales, Earth's rotation is actually slowing down.

A year in the Devonian period was 400 days long, a day only lasted 22 hours, and even on a day-to-day basis Earth slows down and speeds up because of other planets, the moon, how mass moves around inside the planet, all kinds of things.

So, history had invented this basic unit of time based on a fraction of a day, and then scientists came along with all this new, precise mathematical astronomy, and realized that definition stunk.

So, by the early 20th century, science decided to find a more precise way to measure seconds, they tried using the stars, they tried basing it on the year, but what they eventually settled on was atoms.

Okay, atomic clocks sound really complicated.

- Caesium beam frequency standard, external oscillator generates a microwave frequency and induce those atoms to go into resonance, oscillating at that frequency for equal flux of atoms in the two hyperfine states.

- And they kinda are, actually, but here's the most important thing you need to understand about clocks, except for sundials and hourglasses, every single clock does the same thing.

It has something inside that wobbles at a very precise rate, all any clock does is count up those wobbles and convert them into a unit that we actually understand.

A pendulum makes one beat per second, a quartz crystal and a $5 digital watch beats 32,768 times per second, atomic clocks wobble billions of times per second.

The most widely used atomic clocks use cesium atoms.

When microwave radiation is humming at the exact right frequency, it does something special to cesium atoms.

So, you turn the dial on your little radiation machine until you hit the sweet spot that excites the cesium atoms, then you count 9,192,631,770 wobbles of that radiation.

They took this old unit of time, based on something that might change every day and changed its definition using something that never changes, physics.

- Since 1967, the second has been defined as the interval of 9,192,631,770 hyperfine transitions of the valence electron in a undisturbed cesium-133 atom.

Now, I will be brutally honest and tell you when I started working here, I thought a second was one Mississippi, and for the most part it still works that way.

- The most precise atomic clocks today can accurately measure a second to more than 15 decimal places, and what makes them so precise is they tick 9 billion-something times per second.

Today's best atomic clocks won't loose a second in something like 300 Million years, which means if aliens had come down and dropped one on Pangaea, it would still be accurate to within a second today, as long as some clumsy T-Rex didn't trip over the power cord or something.

The second as currently defined is the most precise measurement of the universe we've ever accomplished, but as science continues to advance the definition of a second may have to become even more precise to keep up.

- The technology is getting to the point now where that microwave frequency isn't precise enough for the applications that require precise time, so we are now working to develop optical frequency standards.

- [Joe] It would be-- - Optical frequency is five orders of magnitude higher, so-- - Five more decimal places of precision on what a second is.

- Right.

- Where modern atomic clocks use long-wavelength microwave radiation, the next generation of atomic clocks will measure atomic changes based on visible light frequencies, filling in even more decimal places of precision for what a second is.

But even though cesium atoms do the same physics everywhere in the universe, atomic clocks are imperfect things built by people, environmental conditions, relativity, magnetic fields, a bunch of things can make two atomic clocks disagree by minuscule fractions of a second.

- What we do here at the Naval Observatory, there's an old saying that a person with one clock knows what time it is, a person with two is never sure.

Here at this facility, we operate about a 100 atomic frequency standards.

All the information of each of those clocks comes up here where we have a computer system that analyzes the whole ensemble of clocks, about every 100 seconds.

The output of this then goes into this rack of equipment over here, where it generates a one pulse per second tick, if you will.

- In fact, because we can measure seconds more precisely than anything else in the universe, since 2019, the basic units for length, mass, electrical current, temperature, light intensity, are all now fundamentally based on the second.

Atomic time almost works too well because it keeps time better than the planet itself, so we have to constantly correct atomic time to stay in line with messy old Earth.

That basically happens like this, at midnight on January one, 1958 two clocks were both set to 00:00:00.

One clock marks each day by measuring Earth's rotation with respect to the distant stars, and counts off 86,400 Earth seconds between each rotation.

The other clock ticks off 86,400 precise atomic seconds every day.

But because Earth's rotation speeds up and slows down, the first clock's seconds aren't always the same, and these two clocks eventually get out of sync, so every so often atomic time counts off one extra second at the end of a day to bring Earth rotation time and atomic time back in sync.

That's a leap second.

Since 1972, 27 leap seconds have been added to keep Earth in sync with the more precise atomic wobbles.

(upbeat music) It isn't the numbers on a clock that keep our society functioning on time, measuring the basic unit of time is far more critical, the hidden anchor at the foundation of modern life.

Every financial transaction, every cellphone call, every Netflix show or YouTube video you watch, scientific observations, an Uber driver picking you up, the power grid staying on.

There are billions of things on this planet, maybe more, that have to know exactly what a second is in order to work.

And that comes from rooms full of servers like this.

- Network time protocol is the time backbone for the internet, and that's distributed by this rack of equipment that's in here, that says network time protocol.

- So, the internet-- - The internet-- - ... gets its time-- - Gets its time from here.

- ... from there.

There are other servers like these at the National Institute of Standards and Technology in Colorado.

Altogether these respond to millions of requests every second, sending back tiny packets of data containing official certified time.

And if you watched my previous video you Know that every time you use GPS, you're actually measuring time.

One of the primary missions of the Naval Observatory is to tell GPS satellites exactly what time it is, and if those time signals are off by even a millionth of a second, your GPS position could be off by hundreds of meters.

The second is not a fundamental bit of the universe, a second is a long and pretty random number.

That's because every method we've used to define a second has been based on the definition that came before it, it's something that we made up because some people a long time ago divided up the day in this weird way.

We've been stuck with seconds for 700-something years, and we've just figured out new and better ways to measure it, and now we orient our whole lives around this.

From the moment we wake up to when we fall asleep, everything we do revolves around what time it is, school, work, meetings, our social lives.

We just take knowing what time it is for granted, but there's an astonishing amount of technology and science, and lots of very smart people, working every second to give us seconds.