Institute of Astronomy

Seeing back in time

Published on 08/11/2013 
Question: 

I was wondering. Is it possible to see back into the past?
I was debating with a friend, about this. And I believe that, it is possible, if you, eg. Travel 3.5 billion light years away from earth in an instant, and if you are able to locate the earth, from where you are, that if you take a REALLY powerful pair of binoculars, and look back at the earth, then you would be able see back into time by 3.5 billion years.
Or, do you just see the present? I would be able to see my house and school, and so on?

I mean, the light reflected, does not come any closer/faster to you, just because you zoom in, right?  It would take 3.5 billion years for you to be able to see, the present?
Or am I completely wrong?

It is indeed possible to 'see into the past' because of the finite speed of light.  In fact it is impossible to see distant objects as they appear in the present.  As an example the Andromeda galaxy, the nearest large galaxy to the Milky Way, is about 2 million light years away, and so when we look at Andromeda (which you can see with the naked eye or a pair of binoculars) you are actually seeing it as it was 2 million years ago.  Now galaxies don't change much in 2 million years so that doesn't make too much difference, but Andromeda is very nearby, if we look at more distant galaxies we see further back in time and then we do see differences with nearby, older, galaxies.

If you imagined an alien 3.5 billion light years away with a powerful enough telescope to see Earth, then they would indeed see Earth as it was 3.5 billion years ago, when it was only a billion years old and the first life was just appearing.

Page last updated: 8 November 2013 at 15:19