1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Can Light be used to see what's in the past?

  1. Jan 7, 2012 #1
    This is technologically impossible, I'm just curious if this is even possible theoretically.

    AFAIK light travels forever in vacuum unless they are absorbed/inhibited by something.

    So is it true that:
    At a distance of N light years from earth, we can view the light that came from earth N years ago, given that those were not inhibited by anything? So, in theory, can we view whatever has happened in the past from those light?

    Example:
    Currently, we can see galaxies billion-light years away with Hubble. The lights actually came from billion years ago.
    Suppose we upgrade Hubble somehow so that it is much much more sensitive to light and can focus to the inside the planet. Then suppose we instantly (yes, we have discovered instant teleportation!) put a massive amount of Hubbles spherically around earth within distance of 1 light years from earth to N light years from earth (so that it covers light from most part of earth). Then we take all the picture at the same time. Then we can view what's in the past starting from 1 years ago to N years ago given that the light is unobstructed.
     
  2. jcsd
  3. Jan 7, 2012 #2

    DaveC426913

    User Avatar
    Gold Member

    If you could instantly teleport yourself to a star 1000 light years away, you could see the Earth as it was 1000 years ago, yes.

    Problem is, you cannot get to that star any faster than the speed of light - so it would take no less than 1000 years to get there to see the light coming from Earth.
     
  4. Jan 8, 2012 #3

    D-C

    User Avatar

    Interesting thought that. If you had a mirror, or mirrors, or anything that turned light around "however" far away, you could see light from earth "however" long ago it took to make the trip out and back. Isn't some of the moon's glow at eclipse, "earth history?"
     
  5. Jan 9, 2012 #4

    DaveC426913

    User Avatar
    Gold Member

    Yes but it would not be focused, you just get light, not an image. And since there are no mirrors out there in space, you'd have to place one there, so you would not be able to see anything at a time previous to you visiting the place to leave a mirror there.
     
  6. Jan 9, 2012 #5

    Ryan_m_b

    User Avatar

    Staff: Mentor

    If you could travel faster than light you could build a time machine anyway.
     
  7. Jan 9, 2012 #6
    I heard something somewhere about the possibly of using black holes to turn the light around with their gravity, but it wouldn't give nearly good enough resolution.
     
  8. Jan 10, 2012 #7

    D-C

    User Avatar

    I see Word's point better. Got thrown back with mention of a bunch of them.

    A Hubble quility scope, say we could position one ten light years out. It's radio signal taking as long to return might provide, (for our great grandchildren), actual images of earth twenty years ago for them. Granted that at that distance they wouldn't see much, could see much better pics in an old Sientific American, but it seems the basic idea works. (you might look through the lens once before launch though, and see if it focuses!)

    Yea, jetwaterluffy, I guess I saw that also. Maybe someday with the right software........
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Can Light be used to see what's in the past?
Loading...