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Why is light the fastest possible speed

  1. Jun 24, 2013 #1
    Why is light the fastest "possible" speed

    With no reference to the higgs field. Could I get an explanation about why the momentum increases as speed increases of an object with mass? And why objects can't travel at light speed which have mass?
     
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  3. Jun 24, 2013 #2

    Simon Bridge

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    Momentum increases with speed because that is what "momentum" means, p=mv.
    There is no "why" for the invarient speed - it just is.

    You may prefer this approach to the subject.
     
  4. Jun 24, 2013 #3

    bhobba

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    Well by the principle of relativity if there is a speed limit then its the same in any inertial reference frame so is a constant. The question really boils down to why is there a speed limit. Think about it for a minute - what we notice generally is if something happens it is caused by something nearby happening which was caused by something nearby to that. In general we do not see something on the other side of the universe instantaneously causing something here on earth. This is called the principle of locality and more or less implies a maximum speed to things. This means there is an invariant speed and if you work through the math there is only one invariant speed. So we have a constant of nature and it just a matter of experimentally determining what it is. For all sorts of reasons it turns out to be the speed of light.

    Thanks
    Bill
     
  5. Jun 24, 2013 #4
    Thank you. That cleared some things up :)
     
  6. Jun 24, 2013 #5

    Simon Bridge

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    ... so the question of "why is there a speed limit?", in turn, really boils down to: "why do things generally happen one-after-the-other?"

    The answer is still the one I gave: that's just the way it is.
    But it sounds better the way bhobba put it :)

    (This is why I hate "why" questions!)
     
  7. Jun 25, 2013 #6

    bhobba

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    That's exactly it. When explaining the why of something often all you are doing is expressing the same thing a different way. However that different way may be more intuitively appealing.

    Its like when you find out about Noether's Theorem. It's not stating anything different but symmetries are more intuitively appealing.

    Thanks
    Bill
     
    Last edited: Jun 25, 2013
  8. Jun 25, 2013 #7
    bhobba can you do that same thing with QM....Please! :smile:
     
  9. Jun 25, 2013 #8

    bhobba

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    Sorry mate - that's a bit harder. I have my own private basis for QM but its very mathematical.

    It goes like this. Consider a system and measuring apparatus with n possible outcomes yi. This is obviously a vector and to bring this out will write it as Ʃ yi |bi>. But we are now faced with a problem - the |bi> are arbitrary man made things freely chosen ie a coordinate system. The physics must be independent of that. What QM does - and this is really the key idea - is replace the |bi> by |bi><bi| to give the operator Ʃ yi |bi><bi|. That way it's basis independent. You need to appeal to Wigners Theorem a bit later to see it must be a complex vector space. Another reason is you can't get the action principle from going over to the sum over histories unless you use complex numbers. This is the first axiom of the approach you will find in Ballentine - QM - A Modern Development. The second axiom follows from Gleason's Theorem. And you have the two axioms Ballentine uses.

    But like I say - its very mathematical.

    Thanks
    Bill
     
  10. Jun 25, 2013 #9
    The philosophical "why" is always hard to answer. For example, if you approach special relativity from a certain viewpoint it seems fairly arbitrary (e.g. this paper http://arxiv.org/abs/1005.1614).

    But basically, special relativity predicts that as momentum tends towards infinity, velocity tends towards c, not infinity.
     
  11. Jun 25, 2013 #10

    robphy

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  12. Jun 25, 2013 #11
    that's a bit of an understatement :tongue2:
     
  13. Jun 26, 2013 #12
    Try to imagine what it would be like if there were no 'speed limit'.....at every instant every event in the universe would flash it's evidence at you....our current senses would likely be unable to sort out all those 'instantaneous' signals....of course distant activity might remain weaker, say as the ratio of 1/r2 so common already, but still you'd still get a 'lotta stuff' thrown your way.

    I like things better as is....time keeps everything from happening at once, and space keeps it from all happening to me.
     
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