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Light Speed and life

  1. Feb 3, 2012 #1
    If light from long dead stars is only just reaching us, does this mean that if I shine a Lazer pointer into space, the light beam will continue long after I have turned of the power .. If this is true would a light beam continue to travel indefinably ?
  2. jcsd
  3. Feb 4, 2012 #2


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    Yes, the light pulse from your laser pointer will continue to travel out into space indefinitely, unless it hits something ( a star, a planet, gets absorbed by dust, etc.)
  4. Feb 4, 2012 #3
    Actually, the light will dim slightly as it goes. This happens for 2 major reasons.

    For one, the outer space isn't completely empty. It is actually a very thin gas, but it still blocks some of the light. The second reason is that a laser is not perfectly collimated, instead the light spreads (usually a few cm/km for laser pointers), and if someone looks at it from very far away it will be very dim.
  5. Feb 5, 2012 #4
    also the photons that make up the laser beam will become redshifted with the expansion of space itself, causing them to become dimmer over a long period of time
  6. Feb 8, 2012 #5
    that brings me to a question, is the speed of light, or indeed anything, affected by the expansion of the universe?
  7. Feb 8, 2012 #6
    galaxies are getting further apart
    it's not really fast enough to be thought of as a force however

    but if the universe were to be expanding incredibly fast gravity wouldn't be able to hold the galaxies together for example
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