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Origins of the idea of a tachyon? (and a greeting)

  1. Jul 22, 2011 #1
    Firstly, I'd like to say this is my first post, as I could not find a "new members" sub forum or anything of the sort. I'm a high school student (technically junior, but one year off) with a keen interest in the sciences, particularly in the fields of cosmology, particle physics, and astronomy (and astrophysics), not to mention I get all gitty with excitement and intrigue when they're related to each other. ;)

    Anyway, to the question:
    Note: This is not a history question; I'm asking for their reasoning more than the people who did it. Wikipedia and other web sites didn't give me a satisfying enough answer, so I'm posting here.
    So, I understand that nothing can (at least in the most commonly accepted theory) move faster than light. What, then was the purpose of proposing the existence of a tachyon? Was it wishful thinking? I'd really think it's a bit more than that... I understand there are a lot of people/theories that oppose their existence, but what are the works that support them? Why/how would they exist? (I know, I'm asking a question in search of a specific bias, but I've already read A LOT about the opposite side)
    In short:
    Why bother?

    Thanks in advance!

    PS: I apologise if this is in the wrong subforum. Wasn't entirely wure where to put it...
  2. jcsd
  3. Jul 22, 2011 #2


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    Special relativity has a universal speed. The universal speed is defined by the http://www.physics.fsu.edu/users/ProsperH/AST3033/relativity/Interval.htm" [Broken]
    Last edited by a moderator: May 5, 2017
  4. Jul 22, 2011 #3


    Staff: Mentor

    Hi Phlippieskeze, welcome to PF!

    Whenever there is a new theory one of the most important things that you can do (besides perform experimental tests of the theory) is to determine the limits of the theory. What kinds of things does the theory permit, and what kinds of things does the theory forbid? For permitted things that we have not discovered, what would be the experimental consequences? The tachyon is interesting in that context wrt special relativity.
  5. Jul 25, 2011 #4
    It is quite often argued that nothing in Special Relativity prohibits the existence of tachyons as long as they "born" travelling FTL and remain FTL. I would disagree. While the link given by atyy gives a convincing argument that the energy and momentum of a tachyon are real positive numbers it also requires that the rest mass is a negative imaginary number. To me imaginary quantities are not real in more than just the mathematical sense but are not real in the physical sense. It is also quite easy to show that the length and relative clock rates of a FTL object are also imaginary, casting serious doubts on their physical existence.

    As for who first came up with the idea of a tachyon, I am not sure of the answer, but it would be quite natural for any person seeing the equations of SR for the first time to ask what would happen if v>c. I do not find the argument, that if v is initially greater than c then everything is OK, at all convincing. I guess it all depends on the physical significance we give to imaginary quantities. All the evidence so far indicates tachyons do not exist because we have never detected any and if they interacted with real matter then the theoretical consequences would cause havoc with our sense of cause and effect. In other words IF tachyons did exist, we would never be able to detect them and we could not use them for communicating, so they can only ever exist in the mind and are of no practical use. However, if tachyons existed in large quantities in the background then their contribution of imaginary mass and positive real energy to the universe as a whole would possibly have consequences on the shape and expansion rate of the universe in cosmology (Dark matter? Dark energy?).
  6. Jul 25, 2011 #5


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    To answer this, you have to look at the reasoning behind the statement that nothing can move faster than c.

    One reason is that if you could transmit information faster than light, you could violate causality. (Some observers would see the signal as being received before it was sent.) This doesn't mean we can't have FTL, it just means that we can't have FTL and causality as well.

    Another reason is that if an object is initially moving at less than c, then no continuous process of acceleration can bring it to greater than c. But that has no implications for something that always has been FTL.
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