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Really? Hmm, i had not known that anything did... could you please post a link to this supposition? It would be logical, that is true... but how would one travel in the other direction?
I haven't read the whole thing because I am at work right now and should probably just quit reading the forums, but it looks like the particle is only hypothetical and hasn't been observed. I thought they had seen it in a cloud chamber but who knows if that tidbit made it into the wiki.
October 7, 2009 at 1:18 pm (This post was last modified: October 7, 2009 at 1:20 pm by Violet.)
It sounds like a graviton... as in it hasn't been proven to exist or not... but this truly is bizarre:
Quote:The existence of such particles would pose intriguing problems in modern physics. For example, taking the formalisms of electromagnetic radiation and supposing a tachyon had an electric charge—as there is no reason to suppose a priori that tachyons must be either neutral or charged—then a charged tachyon must lose energy as Cherenkov radiation—just as ordinary charged particles do when they exceed the local speed of light in a medium. A charged tachyon traveling in a vacuum therefore undergoes a constant proper time acceleration and, by necessity, its worldline forms a hyperbola in space-time. However, as we have seen, reducing a tachyon's energy increases its speed, so that the single hyperbola formed is of two oppositely charged tachyons with opposite momenta (same magnitude, opposite sign) which annihilate each other when they simultaneously reach infinite velocity at the same place in space. (At infinite velocity the two tachyons have no energy each and finite momentum of opposite direction, so no conservation laws are violated in their mutual annihilation. The time of annihilation is frame dependent.) Even an electrically neutral tachyon would be expected to lose energy via gravitational Cherenkov radiation, since it has a gravitational mass, and therefore increase in velocity as it travels, as described above.
Bizarre, but an interesting concept nonetheless. But the next one is even more interesting:
Quote:Quantum field theory
Causality
The property of causality is a fundamental principle of theoretical particle physics; tachyons, if they exist, would not violate causality, even if they interacted with ordinary (time-like) matter[3]. Causality would be violated if a particle could send information into its own past, forming a so-called causal loop, leading to logical paradoxes such as the grandfather paradox. Tachyons are prevented from violating causality by the Feinberg reinterpretation principle[3] which states that a negative-energy tachyon sent back in time in an attempt to violate causality can always be reinterpreted as a positive-energy tachyon traveling forward in time. This is because observers cannot distinguish between the emission and absorption of tachyons. For a tachyon, there is no distinction between the processes of emission and absorption, since there always exists a sub-light velocity reference frame shift that alters the temporal direction of the tachyon's world-line, which is not true for bradyons or luxons. The attempt to detect a tachyon from the future (and violate causality) actually creates the same tachyon and sends it forward in time (which is causal). A tachyon detector will seem to register tachyons in every possible detection model; in reality, the tachyon "detector" is spontaneously emitting tachyons. The effect of the reinterpretation principle on any tachyon "detector" is that any incoming tachyonic message would be lost against the tachyon background noise, which is an inevitable accompaniment of the uncontrollable emission. The counter-intuitive conclusion is that tachyons (if they existed) could be used to transmit energy-momentum, but they can't be used for communication. Thus there is no need to fall back on some quantum field theory form of the Novikov self-consistency principle to preserve causality.
In the theory of general relativity, it is possible to construct spacetimes in which particles travel faster than the speed of light, relative to a distant observer. One example is the Alcubierre metric, another is of traversable wormholes. However, these are not tachyons in the above sense, as they do not exceed the speed of light locally.
That hurts my mind as the idea of the tachyon always has. That last bit makes sense to me in that if a thing was going slightly faster then light it would go backwards in time so to a temporal observer, like us, it would appear to be going very slowly in one direction that is the oposite to the direction that it is actually going at super-light speed. But only that part makes sense to me the other crap about causality just doesn't fit in my head; well, not very neatly at least.
October 7, 2009 at 2:06 pm (This post was last modified: October 7, 2009 at 2:08 pm by Violet.)
Hehe... well, have you ever heard of cause and effect? Cause: I slip on the stairs. Effect: i break my leg and am in general pain. This is causality: that everything has a cause (which is eventually supported by the difference in everything, and change as a result of that difference, because of 1=1). Now, if I went back in time, and stopped myself from breaking my leg: that leg would no longer be broken, because I have changed my past. Simply, if you went back in time, and killed your grandfather: would you still exist?
It is an interesting question, that can be approached in multiple ways... all of which depend on how you define time. Now, under some definitions (single linear path for instance), killing your grandfather would nullify your being born... and therefore you would cease to exist. However, in other versions of time (see quantum theory spiderweb): killing your grandfather would delete all future versions of you that diverge from that thread, although you yourself would probably be fine (you essentially went back into a different time and nullified its causal chain). We call this the grandfather paradox. There are other interesting time paradoxes... but all of them depend upon how time itself is described
