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I know that a massive object cannot reach the speed of light as it would require an infinite amount of energy to do so (though my knowledge of the reasons of this phenomenon is very limited). Couldn't it "leap" through the "light barrier" instead, perhaps the same way a particle can "leap" from place to place due to the uncertainty principle? Say we found a way to instantly "accelerate" a massive particle beyond the speed of light. Does this even make sense or I'm just misunderstanding something?

Seeker
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    you might find this interesting: https://en.wikipedia.org/wiki/Tachyon –  Oct 30 '15 at 14:11
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    @brucesmitherson: You might find the answers to this question interesting. Tachyons do not, in fact, travel faster than light. – ACuriousMind Oct 30 '15 at 14:27
  • @ACuriousMind I honestly didn't read the wikipedia article, but I do remember people working on tachyons and they stated that they traveled faster that light. I guess you can interpret it both ways, or that the concept of tachyon evolved over time –  Oct 30 '15 at 14:51
  • You have a misunderstanding of the uncertainty principle. Additionally, are you thinking that the object with "leaps" to $v>c$ would stay at that speed? If so, the $E^2-p^2c^2$ of that object would not be $m^c^4$ or the SR $\gamma^2$ factor would be negative and would present quite a conundrum. – Bill N Oct 30 '15 at 16:54
  • (Grrrr. Stupid 5 minute rule!!) $m^2c^4$ – Bill N Oct 30 '15 at 17:00
  • Yes, one can make tachyons on paper... with imaginary mass, which means that they are unstable. As far as I know the Particle Data Book folks have basically stopped reporting on them with the simple statement "We no longer list for limits on tachyons and centauros. See our 1994 edition for these limits.". For me that indicates a pretty dead concept. Would you like some aether with that? We also carry phlogiston and lapis philosophorum in our sister store of dead scientific ideas. ;-) – CuriousOne Oct 30 '15 at 21:05

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The rules of relativity theory basically tell you the following about velocity-related transformations: First, the vacuum speed of light is an invariant and second, the "inside" of the light cone (slower-than-light motion) and the "outside" of the light cone (faster-than-light) never get mixed up. So no matter how you manipulate your velocity, no matter what contrived acceleration schemes you can come up with, what is inside of the light cone stays inside, what is outside stays outside, and the lightcone itself stays fixed.

Tachyons are hypothetical particles with trajectories that exist outside the light cone, i.e., they are faster-than-light. As such, they always stay outside the light cone. Moreover, because they are outside the light cone, there is no rest frame associated with a tachyon; it is not possible to talk about things "from the tachyon's perspective", i.e., a frame in which a tachyon is at rest, because there is no frame with respect to which the tachyon is at rest. (The same also applies to photons, by the way.)

One of the problems with particle quantum mechanics, even the relativistic variety, is that it leads to violations of relativity theory, effectively allowing some superluminal "leakage", perhaps along the lines of the question as stated. However, these loopholes are eliminated in relativistic quantum field theory. So no, the uncertainty principle won't help you either: you cannot "tunnel" yourself past the light speed barrier that way.

Viktor Toth
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