barry@ames.UUCP (Kenn Barry) (11/24/84)
[]
The following bit of speculation came to me a while back, and
since I'm not competent to evaluate it, I offer it to the net for comment.
Some of the responses to the recent request for an explanation
of the impossibility of FTL have pointed out that, while travel *at*
the speed of light is impossible, travel *faster* than light may not
be impossible (thus the hypothetical tachyon).
If this is the case, it is not clear to me that moving between
the two states (slower-than-light and faster-than-light speeds) is
necessarily impossible, either. Suppose velocity is itself not continuous,
but a quantized phenomena? I have heard it suggested that space and time
may be quantized; if this were so, then it would seem that velocity is
also necessarily quantized. If velocity *is* quantized, and velocity
changes occur in quantum increments, it seems that one could, indeed,
move from slower- to faster-than-light speeds without ever having traveled
at *exactly* the speed of light. No messy infinities in the equations.
Comments?
- From the Crow's Nest - Kenn Barry
NASA-Ames Research Center
Moffett Field, CA
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Electric Avenue: {dual,hao,menlo70,hplabs}!ames!barryjin@hplabs.UUCP (Tai Jin) (11/25/84)
i've heard that the problem in attaining ftl speeds is energy (going negative?) and the same is so for objects moving at ftl speeds (tachyons), they cannot travel slower than light speed. it's been a while since my college physics days, so i can't provide any equations to show this.
fons@mcvax.UUCP (Fons Kuijk) (11/28/84)
In article <654@ames.UUCP> barry@ames.UUCP (Kenn Barry) writes: > Some of the responses to the recent request for an explanation >of the impossibility of FTL have pointed out that, while travel *at* >the speed of light is impossible, travel *faster* than light may not >be impossible (thus the hypothetical tachyon). > If this is the case, it is not clear to me that moving between >the two states (slower-than-light and faster-than-light speeds) is >necessarily impossible, either. Suppose velocity is itself not continuous, >but a quantized phenomena? I have heard it suggested that space and time >may be quantized; if this were so, then it would seem that velocity is >also necessarily quantized. If velocity *is* quantized, and velocity >changes occur in quantum increments, it seems that one could, indeed, >move from slower- to faster-than-light speeds without ever having traveled >at *exactly* the speed of light. No messy infinities in the equations. > Comments? ---------------------------------------------------------------------------- How does one measure velocity? Velocity is length divided by time, both quantities that behave 'stange' under lorentz transformation (as does the mass). The things that are quantized are the invariant quantities such as impuls (=mass*velocity!) and energy. Increasing the impuls with one quantum in order to try to increase the velocity in the region of the speed of light does also increase the mass (remember?). The closer one gets to the speed of light the more impuls will contribute to the increase of mass. Also remember the rules one has to apply on adding speeds close to the SOL. Increasing the speed means adding a speed to it, but the result is less than the plain adition. The relativity theory indicates that space and time are not the physical entities they were thought to be, they are merely elements of a language we mortals use to describe our environment. --- No joke Fons Kuijk No graphics ...mcvax!fons No maxim [for insiders:-)]
abeles@mhuxm.UUCP (abeles) (11/30/84)
You ought to read up on tachyons which are particles moving faster than light. They can't slow down in the same way that we can't speed up to c. There is no known evidence of tachyons.
act@pur-phy.UUCP (Alex C. Tselis) (11/30/84)
> ---------------------------------------------------------------------------- > How does one measure velocity? > Velocity is length divided by time, both quantities that behave 'stange' > under lorentz transformation (as does the mass). > The things that are quantized are the invariant quantities such as > impuls (=mass*velocity!) and energy. > Increasing the impuls with one quantum in order to try to increase the velocity > in the region of the speed of light does also increase the mass (remember?). > The closer one gets to the speed of light the more impuls will contribute > to the increase of mass. It is stated that impulse and energy are quantized and invariant. Really? Although momentum and energy are quantized for particles moving in certain kinds of potentials, this is certainly not always true. Furthermore, neither is a relativistic innvariant. In fact, the momentum and energy form the components of a four-vector, which has the same Lorentz transformation properties as any other four-vector, such as {x,y,z,t}.
act@pur-phy.UUCP (Alex C. Tselis) (12/01/84)
> > > You ought to read up on tachyons which are particles moving faster > than light. They can't slow down in the same way that we can't speed > up to c. There is no known evidence of tachyons. *** REPLACE THIS LINE WITH YOUR MESSAGE ***
gjk@talcott.UUCP (Greg J Kuperberg) (12/02/84)
> You ought to read up on tachyons which are particles moving faster > than light. They can't slow down in the same way that we can't speed > up to c. There is no known evidence of tachyons. Tachyons are dead. Some respected physicist published a paper on them once. There were many replies, to the effect of, "you made a mistake in your physics." The guy then said, "oops", and that was the end of it. The some non-physicists discovered the original article and published much literature about it. Sorry that I don't remember any of the names involved. --- Greg Kuperberg harvard!talcott!gjk "Eureka!" -Archimedes
act@pur-phy.UUCP (Alex C. Tselis) (12/05/84)
> > You ought to read up on tachyons which are particles moving faster > > than light. They can't slow down in the same way that we can't speed > > up to c. There is no known evidence of tachyons. > > Tachyons are dead. Some respected physicist published a paper on them > once. There were many replies, to the effect of, "you made a mistake in > your physics." The guy then said, "oops", and that was the end of it. > > Then some non-physicists discovered the original article and published much > literature about it. > > Sorry that I don't remember any of the names involved. Theoretically speaking, tachyons are not quite dead, but as the second correspondent says, they are dead in practice. Even if they do exist, they interact with matter only very weakly. (Some searches were done for them, but uncovered naught.) The physicist who first talked about them was, I think, Gerald Fineberg, at Columbia University. There's an interesting paper on the violation of causality by tachyons: Thouless, D.J., "Causality and Tachyons", Nature, vol. 244, pg. 506 (1969) There's also a nice discussion in: Harwit, Martin, ASTROPHYSICAL CONCEPTS, John Wiley & Sons, New York (1973) But practically speaking, no physicist takes them all that seriously anymore. The non-physicists also escape me, but I guess there are lots of science fiction writers who use tachyons for their own purposes.
cpf@lasspvax.UUCP (Courtenay Footman) (12/05/84)
In article <> gjk@talcott.UUCP (Greg J Kuperberg) writes: >> You ought to read up on tachyons which are particles moving faster >> than light. They can't slow down in the same way that we can't speed >> up to c. There is no known evidence of tachyons. > >Tachyons are dead. Some respected physicist published a paper on them >once. There were many replies, to the effect of, "you made a mistake in >your physics." The guy then said, "oops", and that was the end of it. Tachyons are not dead. In the latest Physics and Astronomy Clasification System, (PRL 26 Nov), classification 14.80.Pb exists, with the following definition: The Physics of Elementary Particles and Fields (the 1) Properties of specific particles and resonances (the 4) Others and hypothetical (the 80) Others (including tachyons) (the P; the b is a check sum) The last 4 Physics Abstracts (~two months worth) describe three papers with the word tachyons in the title. This is not a very active field, but neither is it "dead". It is true that most practicing physicists (including me) do not believe in tachyons and that tachyons seem to have serious diseases, most notably with causality. Also no evidence for tachyons has yet been found, and there is strong evidence that charged tachyons with a "mass" less than a few times the electron mass do not exist. (If they did, they would strongly affect the rate of light by light scattering; since QED correctly predicts this rate with the electron being the only light charged particle, other light charged particles, including tachyons, do not exist). However, some people are still doing research on the subject, and while I think most of them would also agree that tachyons probably don't exist, they would insist on the "probably". -- Courtenay Footman arpa: cpf@lnsvax Newman Lab. of Nuclear Studies usenet: cornell!lnsvax!cpf Cornell University
gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) (12/06/84)
> > You ought to read up on tachyons which are particles moving faster > > than light. They can't slow down in the same way that we can't speed > > up to c. There is no known evidence of tachyons. > > Tachyons are dead. Some respected physicist published a paper on them > once. There were many replies, to the effect of, "you made a mistake in > your physics." The guy then said, "oops", and that was the end of it. > > The some non-physicists discovered the original article and published much > literature about it. > > Sorry that I don't remember any of the names involved. Aarghh! "Tachyons" were first taken seriously in modern times around 1970 when Gerald Weinberg brought them to the attention of the physics community. Almost every standard argument I hear for them is a repeat of what he originally said. As soon as one takes tachyons seriously, he has to deal with the purely imaginary quantities that turn up as the value of various physical quantities (proper time, perhaps mass, and so forth). The conventional way to do this is by one of a number of "reinterpretation" principles. In 1970 I studied this concept and wrote a paper on it for my honors research class. I tried once to get the paper published but the referees appeared not to understand it; since they were dependent on continued interest on tachyons for their research funding and my paper demolished the concept, I do not wonder that they refused to hear what I was saying. Basically, what I discovered was that when one carefully analyzes the physical meaning of faster-than-light motion, it turns out to be just another (rather peculiar) way of describing precisely the same phenomenon as slower-than-light motion. I have twice posted the demonstration of this to this newsgroup, so I will spare everyone and not do so now. As far as I know, the physics community at large still believes in the possibility of tachyons as something special, although they have never been able to detect them (e.g. by Cerenkov radiation).
gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) (12/06/84)
Oops! I meant Gerald Feinberg, not Weinberg (I've been in computing too long!)