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Author Topic: If we put a mirror millions of light years away and reflected earth, could we see what earth looked like millions of years ago?  (Read 920 times)

Offline thedoc

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david tompkins  asked the Naked Scientists:
   
The light we see from distant stars varies from star to star due to how far they are from earth. So say we see a stars light that is a million light years from earth then we are seeing the light from a million years ago. Is it the same for that star that they are seeing light from us a million years ago? If so is there anyway that we could see mirror the light coming towards us to see earth from a million years ago?

I hope that made sense.

I just recently found the podcast and im working my way through all the episodes and im loving it.
 

   

What do you think?
« Last Edit: 28/09/2015 19:50:01 by _system »


 

Offline alancalverd

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In principle yes. In practice a mirror would not be the best device to use.

The television images we get from earth survey satellites show the earth as it was maybe a second ago, and a telescope on Mars would show us what we were doing about 30 minutes ago.

However the idea has no merit since the time it would take more than a million years to get the device in place a million lightyears away. So you might as well take photographs now, and wait.
 

Offline Bored chemist

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"If we put a mirror millions of light years away and reflected earth, could we see what earth looked like millions of years ago? "
Yes, except that we would have had to put the mirror there a million years ago- and we didn't.

The interesting idea is if we find something that was already there, and acted like a mirror
 

Offline PmbPhy

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david tompkins  asked the Naked Scientists:
   
The light we see from distant stars varies from star to star due to how far they are from earth. So say we see a stars light that is a million light years from earth then we are seeing the light from a million years ago. Is it the same for that star that they are seeing light from us a million years ago? If so is there anyway that we could see mirror the light coming towards us to see earth from a million years ago?

I hope that made sense.

I just recently found the podcast and im working my way through all the episodes and im loving it.
 


What do you think?
If it was possible to create a stable wormhole so that we can place the mirror there in a short time then in principle it would be possible, but impossible in practice.  The amount of light that was emitted from the Earth and sent back would be far too small to be able to see it. You'd have to make a mirror so large that it'd be impossible to build in practice.

By the way. If you placed the mirror a million light years away then you'd be looking back two million years in the past because it would take two years for light to make a round trip from the Earth to the mirror and back.

 

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