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Ancient Earth Light

We recently received the following interesting question:

 Hey guys

…I understand that when we look at the stars we are actually seeing back in time to what happened to them millions of years ago. Therefore theoretically would it be possible to send a rocket into outer space to look back on the earth to see what happened in the past?

Particularly useful would be to see around 33AD to prove exactly what happened with that Jesus guy…!

James, UK.


Thanks for the question James.
Yes, theoretically you could see earth’s past by looking at its reflected light that left long ago. I have thought of this many times before. This reminds me of the Classic Trek episode The Squire of Gothos….please…indulge me here.


A powerful yet child-like alien welcomes the crew of the Enterprise to his planet. He seems to like earthlings since he’s been studying them from his remote vantage point for a while. He is puzzled though because he never thought they had the ability to leave the planet let alone travel interstellar distances. He of course has been studying the earth as it was hundreds of years ago since he is so far away and the light/information took that long to reach his super-telescope.


Using this idea as a method for us to peer into our past though would unfortunately not work.


The fundamental problem is that you’d have to catch up to that old light to observe it. This would require faster than light travel which is likely impossible since you’d need infinite energy to do it.
Further, the farther away you are from earth, the more problematic it is to get a good picture of what was going on in the past. To resolve one person on the planet from many trillions of miles away (if not impossible) would probably require a lens bigger than the solar system. Good luck grinding that baby.


As I see it, to see this ancient light would require one of the following scenarios:
  • An alien would have to travel to earth and give us a recording of the earth he made from a great distance
  • Gravitational lensing would have to cause light to bend into a 180 to head back to us so we can observe it.
  • We discover a cloaked alien satellite that has been orbiting and surreptitiously recording the earth for millenia.
I’d be very happy with any of these.

4 comments to Ancient Earth Light

  • When I read about the improbability of time travel, I always curse Hawking for his chronology protection conjecture.

    Then again, I don’t think he ever thought of installing a Brown Industries Flux Capacitor(tm) in a modified 1982 DeLorean DMC-12. You see the stainless steel construction makes the flux dispersal…. oh, my god, they found me. I don’t know how but they found me.

  • klox

    Or we might be able to expand space behind us faster than the speed of light (like how the universe is expanding). I mean, it’s only 2000 light years away! Detecting it would definitely be tough since the light reflecting off of a person isn’t like a star radiating. There is a non trivial difference in power there.

  • puffoflogic

    I believe Superboy used this trick a number of times in the 60’s–flying into space, overtaking old light rays, and then observing the past. Of course, his super-vision was capable of seeing events happening on far-distant worlds in real time, so his comic-book physics were a little bit muddled.

  • nowoo

    Most of the stars we see at night (without binoculars or a telescope) are tens, hundreds, or maybe thousands of light years away, but not millions (except for the barely visible Andromeda Galaxy at ~2.5 million light years), so we aren’t seeing them as they were millions of years ago. I think a lot of people confuse the huge numbers used when talking about stellar distances in km, like the almost 10 trillion km to the nearest star (other than the Sun) and they assume the numbers are similarly huge when talking about distances in light years and therefore also the age of that light. If my calculations are correct, the light from Alpha Centauri is only about as old as SGU Ep. 65, and a mirror positioned there would currently let us see a reflection today of Earth as it appeared in mid-2002.

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