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Hypothetical situation, what is seen before light arrives?

  1. Oct 2, 2011 #1
    Before I get pounced on by academics from near and far, I just want to mention that I'm no longer a college student and never took a course in physics. All of my knowledge on the subject is practical and thus the answer to this eludes me. So in advance please forgive me if the answer to this seems elementary and/or a waste of time.

    Hypothetical situation:

    One day, an gigantic opaque barrier of some kind is placed between the earth and the sun, completely blocking the view and the light of the sun visible from earth for an entire hour.

    In a period of a few seconds, that barrier is removed.

    What would this situation look like from the perspective of an observer on earth? What does the sun look like before it's light has arrived on earth, can it be seen at all?

    Would the observer still see the sun's light for minutes after the barrier had been put in place, as the remaining light particles finished their journey to the eye of the observer on earth?
  2. jcsd
  3. Oct 2, 2011 #2
    The light from the Sun takes about 8 minutes 19 seconds to travel to Earth.

    You can think of light as particles - much like marbles - but much smaller. Particles of light are called photons and they travel in straight lines at the Speed Of Light, which is the speed limit for everything in the universe.

    Photons travel out in all directions from the sun, but the light we see from the sun is only the photons that travel straight towards Earth.

    Let's say you stick a giant barrier directly between the Sun and the Earth at time t=0.

    Then at time t=0 the photons between the barrier and the Sun will hit the barrier and either get absorbed, reflected or whatever else, but for the sake of argument, let's assume they don't get passed the barrier, and so they don't reach Earth. These photons are normal photons travelling at light speed.

    The photons in between the barrier and the Earth will continue towards Earth at Light Speed. However, there are only 4 minutes 9.5 seconds before the photons that were passed the barrier at t=0 run out, and so you will get 4 minutes 9.5 seconds of light, and then sudden darkness.

    If you are still confused, think about a tap with water running out of it, and then suddenly you place a card in between the tap and the bottom of the sink.
  4. Oct 2, 2011 #3
    No that makes sense to me actually, it's just such an unthinkable situation that it's hard to imagine what would really happen in real time.

    Thanks for the reply :biggrin:
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