I read that the Hubble has taken pictures of the earliest form of the universe that it has ever gotten, 600 million years after the Big Bang. If the universe now is somewhere like 32 billion years after the Big Bang, how does that work? Be kind for my ignorance.
All light you see is from the past, because light takes time to go somewhere. It’s just for most objects we look at, that time is relatively short. Light from across the room (say 3 meters away) takes 10 nanoseconds to get to you. So what you see is not what is happening right now, but what happened 10 nanoseconds ago. Of course, that’s such a short time that for most purposes it makes no difference at all. (It makes a difference for atomic clocks, which do keep time down to the nanosecond. A clock in the US trying to synchronize with a clock in Europe has to account for the fact that it takes millions of nanoseconds for the message from the clock in Europe to get here).
Light takes a little over a second to get here from the moon. So when you look at the moon, you are seeing it as it was about a second ago.
When you look at the sun, you see it as it was 8 minutes ago, not right now.
When we look at the more distant planets in our solar system, the information is hours old.
And the stars are so far away that it took their light years to get here.
Edit to Glen: I’m not quite sure what distinction you see between that answer (which says light takes time to travel a distance, so the light we see is old), and the other answers such as mine (which says light takes time to travel a distance, so the light we see is old).
January 13th, 2010 at 6:52 pm
light travels at a certain speed, about 300,000 kilometers per second, if you look far enough away, you can see into the past, for the 31.4 billion years youre talking about, Hubble is looking at light sources about 3,300,000,000,000 kilometers away
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January 13th, 2010 at 7:02 pm
List travels at the speed of light. By being able to tell how far away something is when we see it, we can tell how many years ago its light left and started its journey to us.
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January 13th, 2010 at 7:45 pm
never heard that before, i thought they was just a bunch of pretty Colors but what do i know?
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January 13th, 2010 at 8:02 pm
All light you see is from the past, because light takes time to go somewhere. It’s just for most objects we look at, that time is relatively short. Light from across the room (say 3 meters away) takes 10 nanoseconds to get to you. So what you see is not what is happening right now, but what happened 10 nanoseconds ago. Of course, that’s such a short time that for most purposes it makes no difference at all. (It makes a difference for atomic clocks, which do keep time down to the nanosecond. A clock in the US trying to synchronize with a clock in Europe has to account for the fact that it takes millions of nanoseconds for the message from the clock in Europe to get here).
Light takes a little over a second to get here from the moon. So when you look at the moon, you are seeing it as it was about a second ago.
When you look at the sun, you see it as it was 8 minutes ago, not right now.
When we look at the more distant planets in our solar system, the information is hours old.
And the stars are so far away that it took their light years to get here.
Edit to Glen: I’m not quite sure what distinction you see between that answer (which says light takes time to travel a distance, so the light we see is old), and the other answers such as mine (which says light takes time to travel a distance, so the light we see is old).
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January 13th, 2010 at 8:20 pm
The light of the images that the Hubble telescope takes take a measureable amount of time to reach it; it’s not instant.
The best way I can think to explain it is in an example. The star Beetleguese is about 500 light years away from Earth. It takes one year for the light of a star that is 1 light year away from Earth to reach us (1 year for light to travel 1 light year), so technically we’d be seeing what that star looked like one year ago had we been right next to it at the time. So in the case of Beetleguese, we see it as it looked 500 years ago. It is suspected that that star will go supernova relatively (in terms of space) soon, and it could have even done so already, but we won’t know until the light from the event actually reaches us.
I hope that helps explain things.
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January 13th, 2010 at 8:50 pm
I just asked a similar question, see below.
http://answers.yahoo.com/question/index?qid=20100106074958AApWyJ4&r=w
BA’s answer seems to make the most sense as to how we can actually look backward into the past. Everyone else is describing how things take a long time before we see them.
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January 13th, 2010 at 9:26 pm
Go outside and look at the sun. You aren’t seeing it as it is (in one sense of simultaneity, at least), but as it was a few minutes ago, because you’re looking at sunlight that left the sun then and had to travel to your eyes, and that takes time.
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