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  • How and when did our universe begin?

  • How did it get to look like this?

  • How will it end?

  • Humans have been discussing these questions

  • for as long as they've been around without ever reaching much agreement.

  • Today, cosmologists are working hard to find the answers.

  • But how can anyone hope to find concrete answers to such profound questions?

  • And how is it possible to explore and study something as huge as the universe,

  • most of which we'll never be able to reach?

  • The answer is light.

  • And although light from distant parts of the universe

  • can take billions of years to reach us,

  • it carries six unique messages that, when put together,

  • can disclose an amazing amount of information to astronomers

  • who know how to look for it.

  • Just as sunlight can be split up into the familiar rainbow,

  • splitting the light from distant objects exposes different patterns of colors

  • depending on its source.

  • This distinctive light barcode can reveal not only an object's composition,

  • but also the temperature and pressure of its constituent parts.

  • There's even more we can discover from light.

  • If you've ever stood on a train platform, you might have noticed

  • that the train sounds different depending on its direction

  • with the pitch ascending when it approaches you

  • and descending when it speeds away.

  • But this isn't because the train conductor is practicing for a second career.

  • Rather, it's because of something called the Doppler effect

  • where sound waves generated by an approaching object are compressed,

  • while those from a receding object are stretched.

  • But what has this to do with astronomy?

  • Sound does not travel through a vacuum. In space, no one can you hear you scream!

  • But the same Doppler effect applies to light whose source is moving at exceptional speed.

  • If it's moving towards us, the shorter wavelength

  • will make the light appear to be bluer.

  • While light from a source that's moving away

  • will have a longer wavelength, shifting towards red.

  • So by analyzing the color pattern in the Doppler shift of the light

  • from any object observed with a telescope, we can learn what it's made of,

  • how hot it is and how much pressure it's under,

  • as well as whether it's moving, in what direction and how fast.

  • And these six measurements, like six points of light,

  • reveal the history of the universe.

  • The first person to study the light from distant galaxies was Edwin Hubble,

  • and the light he observed was redshifted.

  • The distant galaxies were all moving away from us,

  • and the further away the were, the faster they were receding.

  • Hubble had discovered our universe is expanding,

  • providing the first evidence for the Big Bang theory.

  • Along with the idea that the visible universe has been constantly expanding

  • from a densely packed single point,

  • one of this theory's most important predictions

  • is that the early universe consisted of just two gases: hydrogen and helium,

  • in a ratio of three to one.

  • And this prediction can also be tested with light.

  • If we observe the light from a remote, quiet region of the universe and split it,

  • we do indeed find the signatures of the two gases in just those proportions.

  • Another triumph for the Big Bang.

  • However, many puzzles remain.

  • Although we know the visible universe is expanding,

  • gravity should be applying the brakes.

  • But recent measurements of light from distant dying stars

  • show us that they're farther away than predicted.

  • So the expansion of the universe is actually accelerating.

  • Something appears to be pushing it,

  • and many scientists believe that something is dark energy,

  • making up over 2/3 of the universe and slowly tearing it apart.

  • Our knowledge of the behavior of matter and the precision of our instruments

  • means that simply observing distant stars can tell us more about the universe

  • than we ever thought possible.

  • But there are other mysteries, like the nature of dark energy

  • upon which we have yet to shed light.

How and when did our universe begin?


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B1 中級

TED-Ed】光が宇宙について教えてくれること - ピート・エドワーズ (【TED-Ed】What light can teach us about the universe - Pete Edwards)

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    Ashley Chen に公開 2021 年 01 月 14 日