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What do I see if I walk forward through a superdense transparent medium?

  1. Jun 16, 2011 #1
    I am walking at 2 metre/sec and light, from a flashlight behind me, is moving at 1 m/s.

    So my eyeballs are catching up with the photons ahead of me. Do I see the flashlight? Do backward photons look strange? Are they red-shifted, blue-shifted? Assume my optics have been replaced with hyperdense refracting material.
  2. jcsd
  3. Jun 16, 2011 #2


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    If you're in a medium where light effectively travels at 1m/s, there's no chance in hell you're going to be able to move at 2m/s in it.
  4. Jun 17, 2011 #3


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    Never mind photons, this is a classical E&M problem, and a nonrelativistic one at that since you're only moving at 2 m/s. No paradoxes involved. There's a changing E&M field in front of you and you're moving through it faster than the fields are advancing. You'll see this "light" blue-shifted, since you're encountering crests at a faster rate. You'll also see the flashlight behind you, but as you move away from it you'll see it with light that left it farther and farther in the past.
  5. Jun 17, 2011 #4
    Yes it's a classical E&M problem (Heaviside and Cherenkov), but how can you receive the light from behind if you are going faster than the light? Or do you mean that you will receive the light from in front of you?
  6. Jun 17, 2011 #5
    It's a gedankenexperiment. I can do whatever the hell I want :biggrin:. Within theoretical reason.o:)
    Last edited: Jun 17, 2011
  7. Jun 17, 2011 #6
    I just mean the flashlight's been on for a while.
  8. Jun 17, 2011 #7
    I should think I'd be seeing it red-shifted. I'm catching up with the wave-crests at a relative speed of half, 1 m/s, what would pertain simply facing the light--2 m/s.

    I'm using photons because they are trendy. I don't believe in relativity paradoxes, just used to posting in the relativity section. I'm just curious about what I'd see.

    Now that I think of it, the experiment could be realized using acoustic imaging analogues.
    Last edited: Jun 17, 2011
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