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Questions regarding the constant of light and photons

  1. Sep 8, 2010 #1
    Hi I am curious about a few things i have read about light and would appreciate some help.

    First of all to my knowledge the speed of light is 186,000 mps and of course its impossible to exceed or reach the barrier of light for any other object other than light. But im curious as to why lights limit is only 186,000 mps and not faster, aren't photons weightless and would not have any resistance while traveling through space? Is there some sort of universal constant that cannot allow anything to achieve speeds higher? Help would be greatly appreciated.
  2. jcsd
  3. Sep 8, 2010 #2


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    Special relativity is the basic theory that says nothing material can reach or exceed the speed of light. When things are traveling close to the speed of light, applying additional force gets converted mostly into increased mass.
  4. Sep 8, 2010 #3


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    Firstly: as to why the speed of light assumes the value that it does, nobody really knows. The majority of current theories take it as a constant.

    As mathman says, relativity explains nicely why the speed of light is, in effect, a universal "speed limit". All massless particles, such as photons, travel at precisely the speed of light. No less, no more. Massive particles (i.e. any particle that is not massless), will always travel less than the speed of light. As you accelerate them to higher and higher speeds, you find that more and more force is needed to produce a smaller increase in speed. This can be interpreted as the particles "gaining mass" in a reference frame at rest.
  5. Sep 8, 2010 #4
  6. Sep 8, 2010 #5
    My 2 cents:

    Why not faster? You could pick any number. It just so happens that from that particular number, the universe evolved as it did.

    That speed is a universal constant. That is what Albert assumed and everything (special relativity) worked out perfectly.
  7. Sep 8, 2010 #6
    thanks everyone for the feedback. Is it possible that space is expanding at the speed of light no faster no slower?
  8. Sep 8, 2010 #7


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    You would have to define what you mean by the "speed of expansion of space" to get a completely meaningful answer to this.

    However, intuitively I think it we can say that it cannot be expanding at the speed of light. Just consider two points in space, A & B, separated by some distance. We define the speed of expansion of space as the relative speed of separation of these points. Now, if they were receding at the speed of light, then no light emitted from A can reach B, nor vice versa. As such these two points cannot communicate with one another (and cannot see each other...).

    Since A & B could be any points in space, (although this step is dependant on how you define speed of separation exactly), then it follows that no such points could communicate with one another. This is not what is observed.
  9. Sep 8, 2010 #8
    why would it be?
  10. Sep 9, 2010 #9
    Last edited by a moderator: Apr 25, 2017
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