What proof is there that the universe is evolving?
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Light moves at 186,000 miles per second. As fast as light speed is, when you think about how large the universe is, light takes time - a lot of time - to actually get to us from distant objects.
The sun is about 93 million miles away. At 186,000 miles per second, it takes about eight minutes for light from the sun to actually reach us here on Earth.
Because of this, when you look up at the sun - with eye protection - you're actually seeing the star as it was nearly 10 minutes ago, not as it is in real time.
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MICHELLE THALLER
Dr. Michelle Thaller is an astronomer who studies binary stars and the life cycles of stars. She is Assistant Director of Science Communication at NASA. She went to college at Harvard University, completed a post-doctoral research fellowship at the California Institute of Technology (Caltech) in Pasadena, Calif. then started working for the Jet Propulsion Laboratory's (JPL) Spitzer Space Telescope. After a hugely successful mission, she moved on to NASA's Goddard Space Flight Center (GSFC), in the Washington D.C. area. In her off-hours often puts on about 30lbs of Elizabethan garb and performs intricate Renaissance dances. For more information, visit
NASA.
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TRANSCRIPT:
MICHELLE THALLER: One of my absolute favorite things about being an astronomer is we are actually time travelers-- real time travelers. We work all the time with looking back into the history of the universe. And there's a wonderfully simple reason why. And that's that light only has a finite speed. As fast as light speed is-- light goes at 186,000 miles per second. That's incredible. But as fast as that speed is, when you think about how large the universe is, light takes time, a lot of time, to actually get to us from distant objects. So let's start off with the nearest star. It's kind of the simple way to begin.
So the sun is about 93 million miles away. And at 186,000 miles per second, it takes about eight minutes for light to actually get to us from the sun. So when you stand on the surface of the Earth today and look up at the sun-- with eye protection-- you're actually seeing the sun as it was eight minutes ago. There's no way you can see the sun as it is right now, because the light has to take time to travel that 93 million miles to us. So even in our own solar system, you actually look back into the past. Depending on where the planets are-- planets like Mars, maybe you're looking at something on the order of 15 minutes away, by the time you get to the outer planets, you're looking at things that are many hours away.
So even our own solar system is looking back into the past as you look farther out into space. But then things start to get much more dramatic as you look farther and farther away. And in fact, the nearest star to us in the sky, Alpha Centauri, is four light years away. That's the time it takes light to travel in one year. One light year is about 6 trillion miles. There's no way you can see Alpha Centauri the way it is now. You're seeing it as it was four years ago. You go farther out, and soon this becomes very dramatic. The nearest galaxy to us, Andromeda, is 2 million light years away. So when you look up at Andromeda, you're looking at light that came to the earth at the very, very dawn of the human species.
Two million years ago, we were fairly different than we are now. The farthest we can see, you're actually looking back billions of years-- you're actually looking back at light that's coming to you today, the light is actually arriving at your eyeballs today-- before the earth even formed. And the farthest away we can see is actually quite breathtaking. We can see a distance that corresponds to a time about 400,000 years after the Big Bang. That's something like 13 billion years ago. The light actually took 13 billion years to get to us. And the thing that's so powerful about that as a scientist is, over that much time, things start to look very different. Even in the course of a few million light years away, galaxies look pretty much the same way they do now. The stars look very much the same, the galaxies look a lot like the Milky Way.
But as you go farther and farther out into space and the light has taken longer to reach you, things begin to change very dramatically. Galaxies don't look the same. They tend to be smaller, they tend to be more active, they have very active black holes at their center...
For the full transcript, check out bigthink.com/videos/michelle-...
29 июл 2019
