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  • A Space Time Vortex Around Earth - presented by Science@NASA

  • Would you believe Earth sits in the middle of a space-time vortex?

  • Einstein predicted this almost a hundred years ago, and it turns out

  • to be true.

  • On May 4th, 2011, researchers announced that NASA's Gravity Probe B

  • spacecraft has detected the vortex and its shape precisely matches

  • the predictions of Einstein's theory of gravity.

  • "The space-time around Earth appears to be distorted just as general

  • relativity predicts," says Stanford University physicist Francis Everitt,

  • principal investigator of the Gravity Probe B mission.

  • Time and space, according to Einstein's theories of relativity, are

  • woven together, forming a four-dimensional fabric called

  • "space-time." The mass of Earth dimples this fabric, much like a

  • person sitting in the middle of a trampoline.

  • If Earth were stationary, that would be the end of the story.

  • But our planet spins, and the spin should pull the dimple around into

  • a 4-dimensional swirl.

  • This is what GP-B went to space in 2004 to check.

  • The idea behind the experiment is simple: Imagine trying to spin a

  • toy top on the dimpled surface of that trampoline.

  • It's going to wobble, right?

  • Something similar happens when you try to spin a gyroscope in curved

  • space-time.

  • Its spin axis will drift or "precess." Gravity Probe B carried some

  • super-spherical gyros into Earth orbit to see what they would do.

  • In practice, this simple idea is extremely difficult.

  • According to calculations, the twisted space-time around Earth should

  • cause the axes of the gyros to drift by a tiny amount - really tiny.

  • It's like measuring the thickness of a sheet of paper held edge-on

  • 100 miles away.

  • Even the slightest disturbance could ruin the experiment.

  • "We had to invent whole new technologies to make this possible,"

  • says Everitt.

  • The Gravity Probe B team developed a "drag free" satellite that could

  • brush against Earth's atmosphere without disturbing the gyros.

  • They figured out how to keep Earth's magnetic field from penetrating

  • the spacecraft.

  • And they created a device to measure the spin of a gyro - without

  • touching the gyro.

  • Pulling off the experiment was a big challenge.

  • But after a year of data-taking and nearly five years of analysis,

  • the Gravity Probe B scientists appear to have done it.

  • The gyros precessed; the vortex is real; and we are in it.

  • Einstein was right again.

  • For more information about the space-time vortex and what it means to

  • us on Earth, visit Science.nasa.gov

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サイエンスキャスト時空の渦 (ScienceCasts: Space-Time Vortex)

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    薛惠綸 に公開 2021 年 01 月 14 日
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