Hard SF : SF Tech Issues : Tachyons

Tachyons

Einstein's relativity equations can be employed using different starting assumptions. (Not all of these starting assumptions are necessarily valid.) Depending on what you begin with, some solutions suggest that a kind of particle dubbed "tachyons" could exist that travel faster than photons. Scientists do not know whether tachyons really exist. Experiments designed to make tachyons in particle colliders or otherwise find them have so far failed to uncover them.

Even if they exist, that does not mean we can make practical use of them. Solutions that include tachyons indicate that low-energy tachyons travel fastest and additional energy must be supplied to slow one down towards light speed. Just as it would require an infinite amount of energy to make an electron or other normal matter to go faster than a photon, it would require infinite energy to make a tachyon go slower than a photon. A tachyon at the lowest possible energy would have infinite speed. This is related to the fact their mass would be an imaginary number.

Three points related to the above which are not clear to me:

1. Mass converts to energy. If tachyon mass is an imaginary number, I would have thought its energy would be too. However, I have read one place it would be a positive value and in another place it would be negative,
2. What is the lowest possible tachyon energy at which its speed is infinite? If the energy is always negative, the lowest value would be towards negative infinity. If the values are positive, the lowest would be towards 0. In that case, is there something that precludes reaching 0? If it reaches 0, can the tachyon continue to exist?
3. If one tries to apply a faster than light speed to the equation to compute gamma, one gets an imaginary value. (Gamma is used as a [multiplication] factor that indicates the extent of time dilation and length contraction. Also, if one wants to express relativistic effects in a Newtonian-style equation, it indicates the difference between "rest mass" and "observed mass" [in computing energy and momentum]. This also means the relativistic momentum seems to come out imaginary.) Is there some reason this isn't applicable? If applicable, what does it mean?

I don't know what a typical energy level or speed would be considered to be. What I've read leaves me with the impression physicists are neither sure of this or factors that would affect it. For instance, I read that if tachyons had an electric charge, this would tend to cause a vicious cycle of decreasing energy and increasing speed, presumably until infinite velocity was reached. However, theory did not seem to say whether tachyons would have charge. If it is not clear to physicists whether tachyons should have charge, I imagine much about them is hazy.

[In Borderlands Of Science, Charles Sheffield states that scientists no longer believe that faster than light particles would have to give off Cherenkov radiation. This radiation was what was thought to lead to the increasing speed mentioned above. So take this element with a grain of salt.]

One conclusion physicists have drawn experimentally is that if tachyons exist they must interact with other matter even less than neutrinos to have avoided detection so far.

It would seem there would be two avenues to try to use tachyons for FTL.

1. Find a way to transform all of the particles in a spaceship into tachyon-type particles and have the tachyon spaceship fly through space. I don't know whether any theory suggests tachyons can be a kind of particle that you could build a spaceship out of. I have not found clear references to tachyon objects in reliable sources, while I have found references to tachyons, tachyon waves, tachyon fields and issues of tachyon communications in reliable sources. As a result, I suspect it is not considered a serious possibility in the physics community. At best this would seem to be extremely costly and with risks.

   Since there is the previously mentioned problem that would occur if tachyons had charge, it would seem we would have to try to build this tachyon spaceship from tachyons without charge. As charge is important in holding together objects made of regular matter, there might be no way to make a cohesive ship with tachyons. Even if you could make a tachyon spaceship, when you reached the destination, you’d have to change back to regular subluminal matter. However, it would be very difficult to make a subluminal ship while traveling away from it at superluminal speed.

2. The tachyons could be used as a faster means of matter transmitting (teleportation). This is only really applicable after you sent a teleportation receiving station to the destination by slower-than-light means. There are many questions surrounding matter transmitting regardless of what particles are transmitted; click here for articles.

   From what I've read (and what I understand of that), it seems that using tachyons for faster-than-light communications is believed to be impossible because of ways in which a tachyon field would behave. I assume that if tachyon communications is impossible, tachyon teleportation would be also.

   The most concise conclusion I found on tachyon communications is in the article by Scott I. Chase at: http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html "The bottom line is that you can't use tachyons to send information faster than the speed of light from one place to another. Doing so would require creating a message encoded some way in a localized tachyon field, and sending it off at superluminal speed toward the intended receiver. But as we have seen you can't have it both ways: localized tachyon disturbances are subluminal and superluminal disturbances are nonlocal."

You might also check these links:

http://physics.gmu.edu/~e-physics/bob/c.htm

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html This is fairly technical, but ends with an explanation why sending FTL tachyon messages are not feasible. [Original by Scott I. Chase]

http://math.ucr.edu/home/baez/physics/Relativity/GR/time_travel.htmlThis mentions tachyons during a discussion of time travel issues. [Original by Jon J. Thaler]

See also suggested books and articles:
Science Books Useful For SF Issues
Scientific American articles on Teleportation, Faster Than Light, Time Travel

The links below looked interesting, but I don't know the sites' dependability
http://www.safalra.com/science/relativity/tachyons.html
http://scienceworld.wolfram.com/physics/Tachyon.html

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