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  • What is at the center of the universe?

  • It's an essential question

  • that humans have been wondering about for centuries.

  • But the journey toward an answer

  • has been a strange one.

  • If you wanted to know the answer to this question

  • in third century B.C.E. Greece,

  • you might look up at the night sky

  • and trust what you see.

  • That's what Aristotle,

  • THE guy to ask back then, did.

  • He thought that since we're on Earth, looking up,

  • it must be the center, right?

  • For him, the sphere of the world

  • was made up of four elements:

  • Earth,

  • water,

  • air,

  • and fire.

  • These elements shifted around a nested set

  • of solid crystalline spheres.

  • Each of the wandering stars, the planets,

  • had their own crystal sphere.

  • The rest of the universe and all of its stars

  • were on the last crystal sphere.

  • If you watch the sky change over time,

  • you could see that this idea worked fine

  • at explaining the motion you saw.

  • For centuries, this was central to how Europe

  • and the Islamic world saw the universe.

  • But in 1543, a guy named Copernicus

  • proposed a different model.

  • He believed that the sun

  • was at the center of the universe.

  • This radically new idea

  • was hard for a lot of people to accept.

  • After all, Aristotle's ideas made sense

  • with what they could see,

  • and they were pretty flattering to humans.

  • But a series of subsequent discoveries

  • made the sun-centric model hard to ignore.

  • First, Johannes Kepler pointed out

  • that orbits aren't perfect circles or spheres.

  • Then, Galileo's telescope caught

  • Jupiter's moons orbiting around Jupiter,

  • totally ignoring Earth.

  • And then, Newton proposed the theory of universal gravitation,

  • demonstrating that all objects are pulling on each other.

  • Eventually, we had to let go of the idea

  • that we were at the center of the universe.

  • Shortly after Copernicus, in the 1580s,

  • an Italian friar, Giordano Bruno,

  • suggested the stars were suns

  • that likely had their own planets

  • and that the universe was infinite.

  • This idea didn't go over well.

  • Bruno was burned at the stake for his radical suggestion.

  • Centuries later, the philosopher Rene Descartes

  • proposed that the universe was a series of whirlpools,

  • which he called vortices,

  • and that each star was at the center of a whirlpool.

  • In time, we realized there were far more stars

  • than Aristotle ever dreamed.

  • As astronomers like William Herschel

  • got more and more advanced telescopes,

  • it became clear that our sun is actually

  • one of many stars inside the Milky Way.

  • And those smudges we see in the night sky?

  • They're other galaxies,

  • just as vast as our Milky Way home.

  • Maybe we're farther from the center than we ever realized.

  • In the 1920s, astronomers studying the nebuli

  • wanted to figure out how they were moving.

  • Based on the Doppler Effect,

  • they expected to see blue shift

  • for objects moving toward us,

  • and red shift for ones moving away.

  • But all they saw was a red shift.

  • Everything was moving away from us, fast.

  • This observation is one of the pieces of evidence

  • for what we now call the Big Bang Theory.

  • According to this theory,

  • all matter in the universe

  • was once a singular, infinitely dense particle.

  • In a sense, our piece of the universe

  • was once at the center.

  • But this theory eliminates the whole idea of a center

  • since there can't be a center to an infinite universe.

  • The Big Bang wasn't just an explosion in space;

  • it was an explosion of space.

  • What each new discovery proves

  • is that while our observations are limited,

  • our ability to speculate and dream

  • of what's out there isn't.

  • What we think we know today can change tomorrow.

  • As with many of the thinkers we just met,

  • sometimes our wildest guesses

  • lead to wonderful and humbling answers

  • and propel us toward even more perplexing questions.

What is at the center of the universe?

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B1 TED-Ed universe center aristotle sphere proposed

【TED-Ed】Is there a center of the universe? - Marjee Chmiel and Trevor Owens

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    阿多賓 posted on 2014/04/24
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