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Gravity affects light

  1. Aug 24, 2010 #1
    I heard that gravity can affect light (according to Einstein). So does it mean that all we can see is fake? We know that light comes to an eye in a straight line, but if gravity affects it, how can we be sure were seeing real things and not an illusion?
  2. jcsd
  3. Aug 24, 2010 #2
    Gravity bends light, and light doesn't come to you in a straight line. My glasses also bend light. So do windows, and so does the atmosphere. Your eye also bends light. Do you look in a mirror in the morning?

    What you are seeing is simply your brain's interpretation of a tiny silver of the spectrum of the outside world. It's just as "real" as a dream...but that's a philosophical discussion, not one for this site.
  4. Aug 25, 2010 #3
    You are saying that something you see in a mirror or through a telescope is an illusion?

    In a sense, you might claim that it is (an 'optical illusion') but the object you see is still real.
  5. Aug 25, 2010 #4
    I think the point is that you can't see objects, you can only see the light coming from the object. Which is nice, cause it allows you to take pictures/movies and look at it later on ;)

    On a side note, I wouldn't know how else it could work though :p
  6. Aug 25, 2010 #5
    It's not what I would call "fake" but very different than you might expect. Light is electromagnetic radiation, like that used in X rays for example, just a different frequency. And different observers may "see" things differently when moving relative to one another and at different observation locations.

    Because light travels at a finite speed, distant cosmological objects, like stars, appear to us as they existed weeks or months or years ago...because the light takes that long to reach us. So a star you see right now may have exploded and the light reflecting that might not reach us for weeks or months. An analogy is fireworks explosions: you see the light after the detonation...but the sound takes a lot longer to reach you, so you hear the effects seconds later.

    Also, as light passes a large mass gravity bends the light so an object is not exactly where it appears to be. That's called gravitational lensing.
  7. Aug 25, 2010 #6


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    Worth repeating:
    This puts gravitational bending of light in perspective.

    If light were not bent, you would not be able to see anything at all.

    Gravitational bending is far, far down the list of ways that light is altered before it reaches your retinae.
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