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As you guys know that we see at the speed of light, it means that we see the past of stars and galaxies. So say a star went supernova right now, how are we able to know current state of that star that is thousands of light years away or is it possible!!!

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    $\begingroup$ Who told we can see its current state? But astronomers can predict how the star's will turn out to be by looking at their past. That's how they make predictions. $\endgroup$ – N.S.JOHN Jan 27 '16 at 1:45
  • $\begingroup$ The "current state of the universe" is not a well defined concept in relativistic physics. Will there be a sunrise tomorrow? Most likely. Will we see the same star tomorrow? Most likely. $\endgroup$ – CuriousOne Jan 27 '16 at 2:13
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We wouldn't be able to see it if a star went supernova right now because the light wouldn't have reached us yet. If a star 100 light years away from us went supernova 100 years ago we would see it now because the light would have had enough time to travel to us.

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While some galaxies are billions of light years away, there are hundreds of galaxies withing just a few dozen million light years away. Astronomically speaking, a few dozen million years is pretty brief. We can be fairly certain that the galaxy hasn't changed much in this time.

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The speed of light isn't an infinite value and light does not travel instantaneously. The speed of light is defined as 299,792,458 meters per second. This means that if a star that is 1 billion light years away went supernova right now, humans would not see the effect until 1 billion years from now.

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