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The Speed of Light and Beyond

  1. Dec 28, 2006 #1
    One of my greatest idols is Albert Einstein. He was obsessed by light and provided so much input into his theories on motion, gravity and even space time it's self because of it. When I think about it all though I find a lot of argument. One thing I think about a lot is how he said nothing can travel faster than the speed of light.

    If nothing can travel faster than the speed of light, then how do black holes "exist" in our dimension? There's theories on the graviton right? Then shouldn't the graviton be traveling faster than the speed of light if it's strong enough to make light break it's own barrier? I don't understand how light could be the last barrier when things theoretically accell that speed.

    I guess what I'm asking is, do you believe light is the final barrier or do you believe gravity could have a barrier of it's own?
  2. jcsd
  3. Dec 29, 2006 #2
    I suggest you try asking this question in relativity forum, You might get some good answers there but here is what I know;

    To answer this question you'll have to follow mathmatical equations provided by Einstein, Lets not forget that when an object is travelling with certain velocity it's mass increases where the increased mass is:

    m = m0 / (1 - (v/c)^2)^0.5

    where m = increased mass (somtimes called relativistic mass) m0 = mass at rest v=velocity of the object with mass m0 c=speed of light.

    As you increase the velocity v for a fixed mass m0 you'll see that the value of m increases and as v aproches c, m aproches infinity.
    And using the Energy mass equvalence its obvious that you'll need an infinite energy to keep an object of mass m0 travelling with the speed of light, hence its imposible.


    Because photons have m0 = 0 as a result even if their velocity aproach c their relativistic mass is zero hence no energy required.

    Results: The only objects which can travel with the speed of light are the objects with zero mass when at rest.

    hope its clear enough.
    Last edited: Dec 30, 2006
  4. Dec 29, 2006 #3


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    What reason do you have for saying that Einstein was "obsessed" with light? Einstein was working on problems related to electro-magnetism: of course he talked about light (actually as a term for general electromagnetic waves).

    What does the one have to do with the other?

    I'm sorry, why SHOULD the graviton be different from other "-tons"? Is there any reason to think that a graviton can " make light break it's own barrier"? Perhaps you are thinking that a photon increases its speed as it goes into a black hole in the same way a material object increases its speed as it falls into a gravitational "well". That's not true. A photon increases its energy in a situation like that by increasing wavelength, not its speed.

    What things are you referring to?

    Actually, relativity does not say there can be no "things" going faster than light. It says that anything with positive mass must move, relative to any observer, slower than the speed of light. It is theoretically possible to have objects, called "tachyons", that move faster than the speed of light and can never move slower than the speed of light. Tachyons have never been observed (except on "StarTrek"!) and there is some reason to believe that if tachyons exist, it would be impossible for us "tardyon" folks to observe them (in which case, in what sense do they exist?).
  5. Dec 30, 2006 #4
    Photons are probably very different from gravitons. However, no one knows because no one has ever produced or directly observed one. One would only be guessing if one were to speculalte why gravitons could or could not exceed the speed of light. Gravitons could be composed of components that we are not even aware of or that have no mass 'at speed' or at rest. We just do not know.
  6. Dec 31, 2006 #5
    What does one have to do with the other? Well Einstein theorised that if you where to catch up to and go beyond light, you would be invisible. This would explain why light can't escape a black hole, other wise the light would be visible. If a black hole has the power to manipulate light, then shouldn't there be barriers beyond light? It's just wierd how so many equasions (i.e E=MC2) use the constant of light...
  7. Dec 31, 2006 #6


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    He did? When?
    No. If an object is moving faster than the speed of sound, can you still hear it?

    I'm not sure why this is in philosophy, but the basic problem here is that you are speculating about things that you have no actual knowledge of. The basic concepts here aren't that difficult to understand, and you'd be able to avoid a lot of spinning your wheels if you would try to learn them instead of making it up as you go along.
    Last edited: Dec 31, 2006
  8. Dec 31, 2006 #7
    Why don't you stop posting like a wise ass and tell me then? That is the whole point in the thread... If I knew these things I wouldn't be here...

    As for the invisible thing... Einstein was once trying to think what it would look like if you caught up to light. He imagined he was traveling along side the speed of light and had a mirror infront of him. What he came up with was that since you're traveling at the speed of light, the light never leaves your eyes to bounce off the mirror, thus making you appear invisible.
  9. Dec 31, 2006 #8


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    I'm trying to make you think. You're philosophizing about things that aren't philosophy and speculating about things that are already known. That isn't a good way to approach learning.

    Consider an airplane traveling twice the speed of sound (the speed of sound is 1100 feet per second). It is 1100 feet from you. It emits a very loud noise. Will you hear the noise and if so, when?
    If light doesn't hit your eyes, you won't see anything, but that does not mean that light can't still bounce off you (or be created by you) to be seen by someone else. You're not invisible. Also, the only light you won't see is light traveling directly behind you (or in a cone shape behind you if you are going much faster than light). Someone can still stand next to you and shine a flashlight on you when you go by, no matter what speed you are going.
    Last edited: Dec 31, 2006
  10. Jan 1, 2007 #9

    Gib Z

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    I just like to add, hes trying to help and hes not posting like a wise ass. And hes a mentor, dont talk sh*t to him lol.
  11. Jan 1, 2007 #10
    And moderator status means what exactly?

    Yeah thanks, I kind of get the idea now. It really just shows how little information casual science references actually give you...

    So, do all "tons" (neutons, protons, electrons) have zero mass? Or only some of them like photons? It kind of makes sense now how zero mass objects can travel so fast because they have no value to increase at progressive speeds. I guess thinking about it logically is the hard part...
    Last edited: Jan 1, 2007
  12. Jan 1, 2007 #11
    He didn't say moderator, he said mentor. On physicsforums, mentors are appointed to help others grasp, understand and apply concepts that they need help with.

    If by casual science, you mean your casual approach to understanding it, yes. Physics is an empirical science using the rigorous language of mathematics as a method of quantifying and describing material reality. To deeply understand and grasp Einstein's General Theory of Relativity, it takes years of mathematics and physics. Russ is trying to help you understand the conceptual physics using visually descriptive thought simulations and I don't think he is trying to sound condescending if that's how you percieve his dialogue.

    In modern quantum mechanics, particles of matter called fermions possess mass, however, particles of force called bosons do not possess mass. Read up on Quantum Electrodynamics and Qunatum Chromodynamics for more information.
  13. Jan 2, 2007 #12
    Its actually just photons when concerned with light, The tons (as you define) do have a mass.
  14. Jan 2, 2007 #13


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    Is there any specific reason that the gravitational force from the black hole is so strong that it would take years for light to even reach a nanometer? The light would most likely be bent towards the surface of the black hole, even though the point in the middle is not a singularity. Just wild guessing. The objects that passes through the black hole even horizon...is there any specific reason we know they exceed the speed of light?
  15. Jan 2, 2007 #14
    I'm not completely sure about this. What I think SR says is that given the postulate of <<light's speed independent on the inertial frame reference>>, then we can show that light's speed is the maximum possible speed. So, if, somwhere, light's speed is not independent on the inertial frame reference, then it's not the maximum possible speed. Example: inside glass.

    You could say: "but we are talking about light's speed in the void". Ok, but I don't think it's really so important. What if we lived in a universe made of glass?
    Not realistic, of course, but, what would happen in a region of void if, hypotetically, the constants mu_0 and epsilon_0 where different?
    Would it be possible? Maybe, if the density of virtual particles where different. I don't see the void, in principle, very much different from any other medium with specific electromagnetical properties, from this point of view.
  16. Jan 2, 2007 #15
    So why are black holes black? Why can't we actually see the matter that's inside of them? Or photons for that matter...
  17. Jan 2, 2007 #16


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    Reason? You can calculate it. I'm not sure what you are asking...
  18. Jan 2, 2007 #17


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    It is a void. How can there be different voids? Isn't that like saying there is more than one value of "0"?
  19. Jan 2, 2007 #18


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    The escape velocity of a black hole is greater than the speed of light, therefore light does not escape.
  20. Jan 2, 2007 #19
    Then why can't the light be seen? Wouldn't that suggest it would be invisible to the eye? To an outside observer? This is what confuses me...
  21. Jan 2, 2007 #20


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    I'm not following. The only light we see is light that reaches our eyes. If light does not escape a black hole, it never reaches our eyes and thus cannot be seen.
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