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  • When life gives scientists lemons, they look at those lemons and say, “how can we use

  • this to test general relativity?”

  • Hi everyone, Julian here for DNews. I know we've been doing it for a while now, but

  • launching stuff into space is still pretty tricky. You've got to get a giant rocket

  • on a launchpad without it exploding. You've got to start it up without it exploding. You've

  • got to send it into space. Without it exploding.

  • But assuming the payload still stays intact, sometimes the rocket puts it in the wrong

  • place. that's what happened in August of 2014 with a Russian Soyuz-Fregat rocket carrying

  • two of the European Space Agency's Galileo satellites. The rocket worked flawlessly most

  • of the way up there, and then in the last stage it pointed in the wrong direction and

  • shot them off at an orbit that made them useless for their intended purpose. Ah, so close.

  • Of course we're talking close by space standards. Which is just another way of saying the orbits

  • were really far off. They were supposed to be in circular orbits a constant 23,222 km

  • (14429 miles) away from the earth. Instead they were set on elliptical orbits, twice

  • a day they were 2,000 km (1242 miles) too high, and twice a day they were 10,000 km

  • (6213 miles) too low.

  • The Galileo program is going to be fine. The plan is to launch 30 satellites to use them

  • for global positioning, and really 24 of them are needed for the system to be fully operational,

  • while the remaining 6 are there for backup. So two of them whizzing about in the wrong

  • place is a minor setback, rather than a dealbreaker.

  • But, heck, while they're up there, we may as well do something with them. They've

  • still got fully functioning atomic clocks onboard, so what experiments could you do

  • with a spacecraft traveling in an elliptical orbit around a massive object while carrying

  • a super-accurate clock?

  • If you said test time dilation, you must watch this show a lot. Hi mom!

  • Yes as you're probably aware, according to Albert Einstein's theory of general relativity,

  • near massive objects, time moves slower. GPS satellites already have to constantly adjust

  • their atomic clocks back slightly because of their distance from the Earth. And yes,

  • according to special relativity their speed also means that their clocks should run a

  • little slower, but the overall effect is the super accurate clocks in space are a little

  • fast on the order of microseconds.

  • The wayward Galileo satellites have had some course corrections because they have thrusters

  • and a bit of hydrazine fuel. Now their orbits change by 8,500 km (5,281 miles) twice a day

  • instead of 12,000, but that's still a difference greater than the radius of the Earth (6,371

  • km) and then some. So what that means is compared to our atomic clocks down here, the misplaced

  • Galileo clocks with run a little faster, then a lot faster, then a little faster, then a

  • lot faster as they gets closer and farther away from this massive hunk. I mean the earth,

  • not me.

  • Using those differences, we'll be able to check Einstein's math. Sure we did it once

  • before with an atomic clock in 1976 that hitched a ride 10,000 km into space, but that experiment

  • only lasted a few hours. We can pull data from these satellites for over a year and

  • be four times more accurate than before. We'll be able to test the math vs the measurements

  • to an accuracy of 0.004%. And we'll be able to do it thanks to a mistake that we turned

  • into a happy little accident.

  • And I've got more good news, everybody!

  • TestTube now has a newsletter!

  • Get a weekly round-up of our most popular videos across all our shows at TestTube.com/fwd

  • So I glossed over how GPS satellites work, and though I'd love to ramble all about

  • them, Trace's clock was a little faster than mine and he beat me to it. Check out

  • the amazing science behind knowing where on Earth you are right here.

  • Have you

  • ever turned an almost fail into an epic win?

  • Sure you have, so let us know in the comments, subscribe for more, and I'll see you next

  • time on DNews.

When life gives scientists lemons, they look at those lemons and say, “how can we use

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用一種不尋常的方式來證明愛因斯坦的相對論 (An Unusual Way To Prove Einstein's Theory Of Relativity)

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    siuwai618 發佈於 2021 年 01 月 14 日
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