"Laws of Physics"

Discussion in 'Physics & Math' started by thinker, Sep 1, 2003.

  1. thinker Registered Senior Member

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    I'm having an argument with a teacher of mine about the speed of light. I know that nothing is faster than the speed of light (or at least anything proven). Are there any arguments that I could use to help my case that there is the possibility of something faster than the speed of light? Our physics laws don't allow for it, but could there be something?
     
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  3. (Q) Encephaloid Martini Valued Senior Member

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    Sure - science fiction.

    You could argue that the Enterprise uses warp drives to surpass the speed of light.

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  5. James R Just this guy, you know? Staff Member

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    A particle going at speed v has energy given by:

    E = mc<sup>2</sup>/sqrt(1-(v/c)<sup>2</sup>)

    As v approaches c from below, E gets larger and larger, until it is infinite when v=c. It is impossible for an object to ever accelerate to the speed of light because it has to get its energy from somewhere, and there are no infinite supplies of energy.

    BUT...

    There are theoretical particles called <b>Tachyons</b> which always move faster than the speed of light. Consider the energy equation with v>c. Then, the square root is the square root of a negative number, which has an imaginary value. To make the energy real, tachyons must have imaginary mass. (Note: the word "imaginary" here is used in its technical, mathematical sense.)

    A tachyonic particle with mass im (i=sqrt(-1)) would have energy:

    E = mc<sup>2</sup>/sqrt((v/c)<sup>2</sup> - 1)

    This energy decreases as v increases. The energy is zero when v=infinite. The energy is infinite when v=c.

    This means that tachyons would always travel faster than the speed of light. To slow a tachyon down to the speed of light would require infinite energy.

    The important thing to remember, though, is that nobody has ever detected a tachyon. Such particles are purely theoretical for now. We don't know what something with imaginary mass would look like.

    It's an interesting possibility, though!
     
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  7. thed IT Gopher Registered Senior Member

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    What James said.

    But I have the approach that if something is allowed in Physics then it happens routinely. We have never seen anything surpass the speed of light so chances are nothing can. This does not preclude the possibility that we may some day find something that does exceed c, but it is unlikely.

    Ask your teacher what happens to the velocity of something that crosses the event horizon of a Black Hole, chances are it exceeds the speed of light.
     
  8. Persol I am the great and mighty Zo. Registered Senior Member

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    No. Even after crossing the event horizon, matter would still obey the c limit.
     
  9. (Q) Encephaloid Martini Valued Senior Member

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    thed - long time, no see!

    chances are it exceeds the speed of light

    Why do you think so?
     
  10. thed IT Gopher Registered Senior Member

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    Indeed. Been busy with one thing or another. Families, work, you know.

    How's it hanging, dude?

    One of the precepts of GR/SR is that no information can be carried faster than c (in a given medium). Providing you carry no information you can travel faster than c, see the difference between group and phase velocity of waves as well. The former is why it is given that objects beyond our light horizon are extraluminal and the Universe expands extraluminally initially (Guths' inflation).

    Known physics breaks down at the event horizon, why shouldn't things exceed c if the information they carry is destroyed. This assumes Black Holes are destroyers of information/entropy, which I can't prove, so I'm a loon.

    To be honest, I was trying to make the OP think a bit, or at least give cases where they are right. Might even make the lecturer think a bit as well.
     
  11. (Q) Encephaloid Martini Valued Senior Member

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    How's it hanging, dude?

    As Ron Jeremy puts it, "Two inches - from the ground!"

    Known physics breaks down at the event horizon, why shouldn't things exceed c if the information they carry is destroyed. This assumes Black Holes are destroyers of information/entropy, which I can't prove, so I'm a loon.

    A loon? You? hehe

    I would think that some form of information remained intact - mass, charge and angular momentum for example.
     
  12. Persol I am the great and mighty Zo. Registered Senior Member

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    Originally posted by thed
    Known physics breaks down at the event horizon
    No, it doesn't. Matter rotating around the blackhole inside the event horizon is still be subject to the laws of physics. If you have a reason it might not be then fine... but you haven't shown it.
     
  13. thed IT Gopher Registered Senior Member

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    1,105
    No bragging, please. It makes me feel inadequate

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    .

    You have no idea. My wildest ideas remain private. But then I know when I am entering pure speculation. Brad Guth, are you out there?

    Hmmm, fair point here. Total loss of information includes things like m, Q and &omega; . The idea is that spacetime becomes so curved that it loops back on itself in a black hole. Shirely this is an example of faster than light?
     
  14. thed IT Gopher Registered Senior Member

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    1,105
    Please note that I said 'known' laws of physics. Last I saw GR does not explain what happens inside a Black Hole, except very loosely. Again, the light speed barrier only pertains to information and SR is only valid in local inertial frames of reference. Astrophysicists have discovered superluminal jets around AGN's, this is allowed as the frame of reference is neither inertial or local, IIRC.

    If you look up the 'No Hair' conjecture for black holes you will find that 'information' is lost as it crosses the event horizon and as I say, you can exceed c if no information is carried.
     

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