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  • This video was made possible by CuriosityStream.

  • When you sign up for an annual subscription at curiositystream.com/HAI, you'll also

  • get access to Nebula, where you can watch HAI videos early and ad-free.

  • The great philosopher Theophrastus once said, “Time is the most valuable thing a man can

  • spend.”

  • Theophrastus, of course, was an idiot, and had forgotten about Kohl's Cash.

  • You try buying khakis with time and see how it goes.

  • But Kohl's Cash has a problem: it's dropping in value, because it's only good for a certain

  • number of days, and since 2011, days have gotten shorter.

  • You see, back in 2011, LMFAO released the hit songParty Rock Anthem,” which called

  • on everyone to party rock, to have a good time, and most importantly, to shake that.

  • Unfortunately, it turned out the earth lovedParty Rock Anthemtoo, and when told

  • to shake that, took the instructions literally and caused an earthquake in Japan.

  • In addition to being the costliest natural disaster in historythe World Bank estimated

  • the damage at $235 billionthe 9.0 magnitude Tohoku earthquake also did a bunch of crazy

  • stuff to the earth: it cracked the sea floor, it broke icebergs and sped up glaciers 8,000

  • miles away in Antarctica, it reduced the gravity in Japan by thinning the earth's crust,

  • and, finally, it even shortened the length of a day, something that usually only happens

  • once a year as part of a deep-state conspiracy to mess up my sleep schedule calleddaylight

  • savings time.”

  • To understand how an earthquake managed to steal away your precious hours of shut-eye,

  • you first have to understand something calledThe Moment of Inertia,” which sounds

  • like a Coldplay album from the late 2000s, but is actually a physics term forthe

  • torque needed for a desired angular acceleration about a rotational axis,” which is basically

  • fancy-talk forhow hard is it to make a round thingy go spin.”

  • When the earthquake quaked the earth and all, it redistributed mass closer to the earth's

  • core, which decreased the earth's moment of inertia.

  • To help illustrate, picture a figure skater pulling their arms close to their body to

  • speed up their rotation.

  • In the same way the figure skater spins faster when they pull their arms closer to their

  • body, the earth spins faster when an earthquake pulls mass closer to its centerof course,

  • this paragraph might have sounded similar to one 139 HAI episodes ago, but we'll ignore

  • that.

  • As a result, days are now 1.8 microseconds shorter.

  • A microsecond, by the way, is one millionth of a secondfor perspective, one microsecond

  • is how long it take for light to travel 300 meters.

  • For another perspective, one microsecond is how much time I spent trying to think of a

  • joke to put here before I gave up and moved on.

  • So 1.8 microseconds isn't really that much, and actually, it's natural for the length

  • of a day to varyin a normal year, it can fluctuate as much as 0.34 milliseconds, mostly

  • due to changes in atmospheric winds.

  • While slight changes in the earth' rotation speed are pretty common, the 2011 earthquake

  • had another, more unusual consequence: it shifted the earth's axis.

  • To understand how it did that, we have to talk about a bunch of space and physics and

  • geophysics stuff, which is going to be confusing enough on it's own, so for now we're going

  • to take all the jokes and put them in a little box that we'll keep in the corner of the

  • screen, and once we're done explaining, we'll open it.

  • Okay, so, the earth rotates around what's called a rotation axis, which is an imaginary

  • line that runs through the north and south pole.

  • If you picture spinning a globe, the little rod it spins around is the rotation axis,

  • and the earthquake didn't change thatthe rotation axis can only be shifted by something

  • in space, like the moon or the sun or whatever.

  • But the Earth isn't balanced along the rotation axis; it's balanced along something called

  • the figure axis, which is an imaginary line that's usually located about 10 meters from

  • the north-south rotation axis.

  • In theory, if the earth were a perfect sphere, the figure axis and the rotation axis would

  • be the same line, and the earth would spin smoothly, but the earth isn't a perfect

  • sphere: there's a bunch of stuff like glaciers and water sloshing around and changing atmospheric

  • pressure and also something called Ice Age Rebound, and the result of all those things

  • is that when the earth spins, it wobbles a little bit, and the earthquake seems to have

  • made that wobble worse, by moving the figure axis about six and a half inches further from

  • the rotation axis.

  • Okay now we'll let out the jokes.

  • Let's see what I missed.

  • Ice Age Rebound sounds like a Dreamworks movie, Drake meme about the axes, there's a dance

  • called the wobble, could have worked that in, alright doesn't seem like anything too

  • important, let's keep going.

  • Now, you might be thinkingso what, the earth wobbles a little more now; who cares?”

  • Well first of all, I care; I made a whole video about it, so show some respect.

  • Second of all, this stock footage bear cares.

  • I paid for the stock footage so I get to decide what he cares about, and I've decided he

  • cares about earth wobbling.

  • And finally, the earth's wobble matters a lot for NASA and other space agencies.

  • They have to account for the wobble when spacecraft plan their flight paths, because if they miscalculate

  • the earth's rotation at launch, they could end up miles away from their intended destination.

  • But hey, if there's one thing history has taught us, it's that when explorers accidentally

  • end up in the wrong place, it turns out great for everyone involved.

  • Nobody ever gets enslaved, and the explorer who enslaved people definitely doesn't get

  • a holiday named after them.

  • If you were enjoying a poorly-conceived holiday and needed something to watch, you might think,

  • hey, I sure do wish all my favorite educational creators had gotten together to create a streaming

  • service where they're able to make cool, fresh, and sometimes exclusive content without

  • worrying about demonetization or algorithms.”

  • Well guess what: your weirdly specific wish came true.

  • It's called Nebula, and it's got all our YouTube content, ad free and early, plus exclusive

  • Nebula originalsfrom HAI, from Wendover, even from people like Tom Scott, who made

  • an incredible, backstabbing game show called Money, that I got to be part of.

  • The best way to get Nebula is through a bundle deal with CuriosityStreamthe fantastic

  • documentary streaming service with thousands of great titles, including originals from

  • people like David Attenborough and Jane Goodall.

  • On there, you could even watchSaving Tokyo,” which is about the massive infrastructure

  • projects they're conducting to protect the city from earthquakes just like the one we

  • discussed.

  • Right now, for less than $15, you can get an entire year of CuriosityStream and Nebula

  • when you go to curiositystream.com/HAI, and you'll be supporting the channel while you're

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