Black Holes and c

Discussion in 'Physics & Math' started by Xev, Apr 12, 2002.

  1. Xev Registered Senior Member

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    Two stupid questions:
    (There are no stupid questions, only stupid people who ask them

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    When light encounters a black hole, what exactly happens?

    Is it bent so severely by the gravitational field that the photons cannot escape?

    My second question is, does a gravitational field that does this violate relativity theory? I thought that nothing could exceed the speed of light, but here is somthing stronger than the speed of light.....
     
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  3. c'est moi all is energy and entropy Registered Senior Member

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    "My second question is, does a gravitational field that does this violate relativity theory? I thought that nothing could exceed the speed of light, but here is somthing stronger than the speed of light....."

    it is said that their velocity changes, so no violation of relativity
    the second part i don't get:
    force <--> speed of light ... doesn't make sense
    besides, many people here will start telling you about space curvature here
    photons follow the shortest way
    there is no force involved
     
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  5. (Q) Encephaloid Martini Valued Senior Member

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    Light, which is comprised of photons, follows geodesic paths; ie straight lines. Massive objects such as black holes bend the space around it such that the paths, or straight lines the photons travel, are bent so severely they are warped back towards the mass and wrapped around it. Hence the photons travel these paths back towards the mass.

    This does not violate any laws because the photons are still traveling at c.
     
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  7. thed IT Gopher Registered Senior Member

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    There are no stupid questions, only stupid answers.

    Courts out on that one, Q's answer is a good one, as is C'est Moi's, except that a force is involved.

    That's right.

    I'll go aginst the grain here, inside the event horizon of a black hole Relativity is probably violated.

    Is this a problem, no! In the same way that Einstein supplants Newton in extreme cases, a newer theory will supplant Einstein. Hopefully it will explain the guts of black holes.
     
  8. Xev,

    To answer your second question, if light had an infinite mass, and if it travelled at the speed of light at the same time, nothing could stop it. Not even black holes.

    But, light does not have infinite mass. The mass of a particle of light is very small(some people on this board will tell you that light has no mass), so the gravity from a blackhole can curve lights path even though it travels at such a high speed.

    Tom
     
  9. (Q) Encephaloid Martini Valued Senior Member

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    some people on this board will tell you that light has no mass

    Others will tell you light has mass, however when questioned as to where this mass is and what happens to it, cannot account for said mass.
     
  10. thed IT Gopher Registered Senior Member

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    Tom

    If I am following your argument, light takes a curved path in a gravitational field beacuse it has mass, that mass is extremely small. So what of larger masses?

    That is, by your reasoning a larger mass will take a more curved path in the same gravitational field, yes?

    If so, that would give a severely different spectrophraphic signature as larger mass objects would be accelerated more. So why is this not seen?
     
  11. Xev Registered Senior Member

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    Light can be thought of as both photons and waves, right?

    Photons do not have mass, correct? Neither do waves, correct?

    So, light does not have mass.

    But energy and mass are interrelated.....and light is energy, for it is radiation.....

    Thanks, c'est moi, Q, Thed and Joe. That clears a lot up for me.
     
  12. Thed,

    "If I am following your argument, light takes a curved path in a gravitational field beacuse it has mass, that mass is extremely small. So what of larger masses?

    That is, by your reasoning a larger mass will take a more curved path in the same gravitational field, yes?

    If so, that would give a severely different spectrophraphic signature as larger mass objects would be accelerated more. So why is this not seen?"

    You surprise me. I thought you knew this!!! The answer is:

    Because the mass in the acceleration formula eliminates the mass in the force formula. That is why all mass accelerates at the same rate towards Earth.

    Thed, this is elementary school physics. If you still don't understand, I can show you the formulas.

    Tom
     
  13. Xev,

    You have to consider that we are discussing particle physics. Particle physics is still mostly theoretical. You can't touch and feel a particle of light or an electron, you have to measure them indirectly most of the time. These indirect measurements are one of the reasons that there are so many different theories regarding subatomic particles. The true answer is that we don't know, we are just making educated guesses.

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    Tom
     
    Last edited by a moderator: Apr 14, 2002
  14. Xev Registered Senior Member

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    I thought Newtonian physics broke down at speeds as high as c?
     
  15. thed IT Gopher Registered Senior Member

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    Tom

    you are delibrately obfuscating.

    Just answer the question, does a larger mass see a larger curvature of spacetime?
     
  16. Thed,

    No it does not

    Force=g*mass1*mass2/d^2

    A of mass2=Force/mass2

    When you replace "Force" in the second equation
    with "g*mass1*mass2/d^2"

    You get :

    A of mass2=g*mass1/d^2

    As you can see, mass2 is eliminated from the formula. In other words, acceleration is NOT dependent on mass2

    Tom
     
  17. Xev,

    Maybe it does, but in the previous post I was describing mass that is moving much slower than c.

    Tom
     
  18. thed IT Gopher Registered Senior Member

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    Tom

    But we are not talking about acceleration. Does a larger mass cause more curvature of spacetime, than a smaller mass?

    Yes or no.
     
  19. Q,

    I apoligize that I didn't answer your question, but I'm being bombarded by questions from all sides.

    So, what does happen to the mass of a photon...

    I'm not sure, under certain circumstances the photon would bounce of the particle keeping it's mass intact. At other times, it might be absorbed by the particle and the mass of the photon gets added to the mass of the particle. Or there's absorption, but the photons mass gets converted to energy.

    I'm really not sure. I never thought about it.
     
    Last edited by a moderator: Apr 13, 2002
  20. Thed,

    I DO NOT believe in the curvature of space. No mass can cause the space to curve. What you call curvature, I see as the result of gravitational force, and inertia.

    Tom
     
  21. ImaHamster2 Registered Senior Member

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

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    Xev,

    Some of the previous responses are confusing.

    Black holes are a creature of relativity, and so can only be explained in the context of relativity. Newtonian explanations do not apply. The spacetime both inside and outside a black hole is well described by general relativity.

    What happens inside the event horizon of a black hole is that all possible trajectories in spacetime, for every particle and for light, lead to the singularity at the centre of the hole. Once you're inside the event horizon, you <i>must</i> hit the singularity. In fact, no outwards radial motion is possible due to the extreme warping of spacetime.

    Light still travels at its normal speed, but its path through spacetime becomes constrained by the geometry of the hole so that it (along with everything else) cannot escape once it crosses the event horizon.
     
  23. Xev,

    Be carefull!! Some of the people on this board believe that theoretical physics and real physics are the same thing.

    You can recognize these people by their attempt to illustrate that they know everything(like what's inside a blackhole).

    Tom
     

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