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Can we travel faster than the speed of light?

  1. Jul 9, 2007 #1
    Im only 14 and I am having a argument with a friend and teacher, and I need to know is is possible in theory to go faster than the speed of light and what is it? Time travel whatever, they dont believe me that you can and I remember reading it somewhere but the fact is no one knows how to do it yet. Please help would be greatly appreciated, sorry if this is quite a stupid q.
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  3. Jul 9, 2007 #2


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  4. Jul 9, 2007 #3
    Assuming special relativity is correct no, we can't. We generally assume relativity is correct at the moment, so you would be wrong. The speed of light is the speed limit for the Universe, as far as we know and as yet no one has disproven this fundamental law.

    This thread might help:-


    * An asymptote is a value that can be approached but never reached. Except in the case given here.
    Last edited: Jul 9, 2007
  5. Jul 9, 2007 #4
    Thanks, appreciated, but im sure there was something that said there is a way to travel faster than light in a sense ie travel between solar systems ie through time or something. I dont know if they were right but thats what they said. Any ideas? One of them was bending the universe if i remember.
  6. Jul 9, 2007 #5


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    You may be interested in reading this article:
  7. Jul 9, 2007 #6


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    No, one cannot travel faster than the speed of light. It sounds like you have read something highly speculative, which may or may not have any sensible background. There have been reasonable suggestions for faster than light travel, such as wormhole theory proposed by Kip Thorne, but these are still entirely theoretical.

    I suggest that, if interested, you learn special relativity instead of attempting to have arguments with your teacher. SR is easily accessible to anyone with knowlege of high school algebra.
    Last edited: Jul 9, 2007
  8. Jul 9, 2007 #7


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  9. Jul 9, 2007 #8
    There are cheats that enable you to seem to travel faster than light, but you never actually do, for example in the highly speculative idea of bending space using high gravity,so you could shorten the distance between two points. However at no point did you actually travel faster than light, you just got there much faster than you could if travelling in normal space at the speed of light. I so wish that made as much sense on paper as it did in my head :smile:

    Hyperspace another sci fi concept involves the bending of space so far it breaks an you end up in some sort of area outside of space. Hyper space is pseudo scientific though like sub space in Star Trek.
  10. Jul 9, 2007 #9
    While I know that matter cannot exceed the speed of light due to GR, I have heard somwhere that there have been quasars moving 2C.
    Is this true or hogwash?- probably hogwash.
  11. Jul 9, 2007 #10


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    It's actually SR that asserts this.
    Obviously I don't know exactly what you've read, but I would conjecture that it has to do with the speed of recession of distant galaxies (or in this case quasars). It does appear that distant galaxies are travelling away from us at speeds greater than the speed of light; however the actual motion of the galaxies is less than the speed of light, with the other apparent speed generated by the fact that the universe is expanding.
  12. Jul 9, 2007 #11
    Not hogwash, just mis-stated. You can observe quasars moving away from us at 2c. The problem here is that they are not actually moving through space at 2c, but the space between us and it is expanding at a rate equal to 2c. Because space has no mass, it can expand at any rate; i.e. 2c.

    To the original question, the true statement would be that nothing with mass can move through a vaccum greater than c.

    CraigD, AMInstP
  13. Jul 9, 2007 #12
    Thanks for the clarification Craig D.
  14. Jul 9, 2007 #13
    Thanks Cristo, just read all of it, really got me into things a bit more and a lot more insight into FTL travel etc. Thanks again.
  15. Jul 10, 2007 #14
    Wait a tick, space doesn't actually expand.

    Wait a minute, this can't be right. I know that it is common to say that "space expands", but that really isn't so. Physical objects move through space, the metric used to describe these objects expands along with them. But it is the physical objects that control the metric. There is no mysterious creation of new space in-between already existing objects. See this recent paper, which clarifies confusion on the phrase "expanding space".


    "Expanding Space: the Root of all Evil?"
    Authors: Matthew J. Francis, Luke A. Barnes, J. Berian James, Geraint F. Lewis
    (Submitted on 3 Jul 2007)

    Abstract: While it remains the staple of virtually all cosmological teaching, the concept of expanding space in explaining the increasing separation of galaxies has recently come under fire as a dangerous idea whose application leads to the development of confusion and the establishment of misconceptions.

    In this paper, we develop a notion of expanding space that is completely valid as a framework for the description of the evolution of the universe and whose application allows an intuitive understanding of the influence of universal expansion. We also demonstrate how arguments against the concept in general have failed thus far, as they imbue expanding space with physical properties not consistent with the expectations of general relativity.

    This is discussed in the new thread on this forum:

  16. Jul 10, 2007 #15
    Can we travel faster than the speed of light? See these 2 websites

    This is not a stupid question. It is a fascinating and important question, which touches on the principles of both special and general relativity. The short answer is this:

    * Most ideas about travelling faster-than-light (FTL) are based on a total misunderstanding of Einstein's theory of special relativity. FTL, in any simple way, is impossible.

    * Some ideas about FTL are based on a misunderstanding of quantum mechanics. As we understand QM, there is no way that any information (let alone objects!) can be transmitted FTL. There may be a tiny amount of wiggle room left to find some loophole in this, and research is ongoing, but don't let your hopes be lifted. It is almost certainly forbidden in any way.

    * Einstein's theory of general relativity does seem to allow for travelling faster than light, under very special and nearly impossible circumstances. No one has ever tested these specific predictions, and no one knows for certain if such FTL, or time travel, is actually possible.

    I won't get into it here, but I believe that FTL travel (via wormholes, which is a sort of cheat) may be possible, but time travel is impossible. That's my opinion, and nothing more.

    See these websites for details:



  17. Jul 10, 2007 #16


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    p.s. The link to baez's page is pretty cool. Luke, if you have not yet found it there is an explaination of how one can travel to the center of the galaxy (which we measure to be 30000ly away) in a relativistic rocket in what feels like only about 20 years to the astronauts in the rocket (of course much longer than 30000 years pass on earth so it's not really FLT travel, but it could be what you are looking for).

    here's a link:

    http://www.math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html [Broken]
    Last edited by a moderator: May 3, 2017
  18. Jul 10, 2007 #17
    I’m surprised that no one has mentioned tachyons in this thread.
  19. Jul 11, 2007 #18


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  20. Jul 11, 2007 #19
    I think the reason they're not explicitly mentioned is they are hypothetical, thus the sentence "the speed of light is the speed limit for the Universe, as far as we know", is still is perfectly consistent, that and such hypothetical ideas merely confuse the issue and may well be wrong anyway.
    Last edited: Jul 11, 2007
  21. Jul 11, 2007 #20


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    Even if tachyons weren't hypothetical, there would be no problem with the speed of light being a local limit. Just like massive particles must travel at speeds less than c, and particles with zero mass must move at the speed of light tachyons would always have to travel at speeds greater than the speed of light. So, the speed of light really is a limit that any particle cannot pass through.
  22. Jul 11, 2007 #21
    I know but imaginary mass? Do we really need to go into the properties of hypothetical particles :smile:

    for all values [itex]v>c\rightarrow[/itex]

    [tex] E = \frac{mc^2}{\sqrt{1 - \frac{v^2}{c^2}}}\rightarrow E = \frac{mc^2}{i}\rightarrow m=\frac{E.i}{c^2} [/tex]

    I am well aware they would change nothing, but they are hardly well accepted hypothetical particles. Most people think they belong only in Star Trek anyway, is what I meant by confusing the issue.

    I originally wrote out some stuff detailing what they were etc, but I deleted it all so as not to confuse the issue.

    To clarify what I mean by confusing the issue :smile:
    Last edited: Jul 11, 2007
  23. Jul 11, 2007 #22
    I understand how special relativity shows show objects cannot travel faster than the speed of light, in any inertial frame. The part I didn't understand is how this means that "action at a distance" type phenomena are also prohibited. For example, why it is that gravity or quantum entanglement are prohibited in the SR framework. It didn't seem to extend itself to these effects from what I saw.
  24. Jul 11, 2007 #23
    Some other interesting points, I would love to argue or debate these points, but the fact that I dont understand some the stuff posted, I will have to learn over the next few days if possible, which is the only obstacle. If that makes any sense. ;]
  25. Jul 11, 2007 #24
    You are absolutely right. Superluminal propagation of classical particles is inconsistent with the principle of causality. However, "action at a distance" is not forbidden by this principle. The key is in the less-known fact that in any quantum relativistic interacting theory (where the Hamiltonian [itex] H = H_0 + V [/itex] has interaction term [itex] V [/itex]) the boost operator [itex] \mathbf{K} = \mathbf{K}_0 + \mathbf{W} [/itex] must be interaction-dependent too (see S. Weinberg "The quantum theory of fields" vol. 1, eq. (3.3.20)). You can find more discussion in

    E. V. Stefanovich, "Is Minkowski space-time compatible with quantum mechanics?", Found. Phys., 32 (2002) 673; http://www.geocities.com/meopemuk/FOPpaper.html

    and section 11.1 in

    E. V. Stefanovich "Relativistic quantum dynamics" http://www.arxiv.org/physics/0504062 [Broken]
    Last edited by a moderator: May 3, 2017
  26. Jul 12, 2007 #25


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    Meopemuk, are you Stefanovich?
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