How feasible are superluminal particles?

[Q-reeus]

Hi, Daecon. See if this helps:






The following Q&A is from a previous thread:

Nice bevvy of responses there tashja. Maybe you could try getting a response to my #13 - i.e. does 'charged tachyon' make any sense? Janus58 assiduously avoided engaging on that one.

 

[Daecon]

Thanks Tashja, awesome work as always.

 

[Q-reeus]

tashja - forget my suggestion in #21. Just did a quick search and below passage from http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html is enough for me:

You can now deduce many interesting properties of tachyons. For example, they accelerate (p goes up) if they lose energy (E goes down). Furthermore, a zero-energy tachyon is "transcendent", or moves infinitely fast. This has profound consequences. For example, let's say that there were electrically charged tachyons. Since they would move faster than the speed of light in the vacuum, they should produce Cherenkov radiation. This would lower their energy, causing them to accelerate more! In other words, charged tachyons would probably lead to a runaway reaction releasing an arbitrarily large amount of energy. This suggests that coming up with a sensible theory of anything except free (noninteracting) tachyons is likely to be difficult. Heuristically, the problem is that we can get spontaneous creation of tachyon-antitachyon pairs, then do a runaway reaction, making the vacuum unstable. To treat this precisely requires quantum field theory, which gets complicated. It is not easy to summarize results here. However, one reasonably modern reference is Tachyons, Monopoles, and Related Topics, E. Recami, ed. (North-Holland, Amsterdam, 1978).

(emphasis added)
Imaginationon = charged tachyon reads like a reasonable identity to me. The general view even a neutral tachyon would produce 'gravitational Cerenkov radiation' seals it further.

 

[tashja]

tashja - forget my suggestion in #21.

Too late, Q. The request has been honored by our tachyon experts.

Regarding an earlier post speculating on Cerenkov radiation detection, 'charged tachyon' seems like an oxymoron, given that the very concept of (electric) charge carries with it a necessarily positive energy-momentum content, comparable to that of an electron. So one could in principle have an accompanying greater in magnitude negative and electrically neutral mass somehow? How about 'tachyonic magnetic smonopole' (that's supersymmetric spin-partner monopole) for wow factor!

Nice bevvy of responses there tashja. Maybe you could try getting a response to my #13 - i.e. does 'charged tachyon' make any sense? Janus58 assiduously avoided engaging on that one.

Tashja,

A charged tachyon is very unlikely to exist, for the reason that has already been alluded to: any charged particle that travels through a medium at a speed greater than the speed of light in the medium will emit Cherenkov radiation. For a tachyon, the ordinary vacuum is such a medium, so a charged tachyon will radiate photons. This has never been observed. I think it's safe to say that if tachyons exist at all, they must be neutral particles.

Alan

Regarding an earlier post speculating on Cerenkov radiation detection, 'charged tachyon' seems like an oxymoron, given that the very concept of (electric) charge carries with it a necessarily positive energy-momentum content, comparable to that of an electron. So one could in principle have an accompanying greater in magnitude negative and electrically neutral mass somehow? How about 'tachyonic magnetic smonopole' (that's supersymmetric spin-partner monopole) for wow factor!

Nice bevvy of responses there tashja. Maybe you could try getting a response to my #13 - i.e. does 'charged tachyon' make any sense? Janus58 assiduously avoided engaging on that one.

Hi Tashja,

A charged tachyon would lose energy via Cherenkov radiation and rapidly accelerate to infinite speed where it has zero energy and effectively disappeared from the universe.

Bob Ehrlich

 

[Q-reeus]

Too late, Q. The request has been honored by our tachyon experts.

I should have known that once you start a wheel rolling..... Anyway again many thanks tashja - always good to get a range of expert opinions. Tachyon hunters are doomed to disappointment imho. On the other hand, theorists speculating/modelling such exotica will probably continue to squeeze out government grants for generations to come.

 

[paddoboy]

DELETED STUFF UP.

 

[paddoboy]

I should have known that once you start a wheel rolling..... Anyway again many thanks tashja - always good to get a range of expert opinions. Tachyon hunters are doomed to disappointment imho.

How would Tachyons affect the spacetime continuum, [would they create gravity] if they were shown to exist.
Could they possibly be harnessed by an advanced civilisation.

 

[rpenner]

In quantum field theory, one can describe hypothetical free tachyons. But a theorem of quantum field theory says all disturbances in quantum fields propagate with speed = c. Thus while formally the tachyonic particles travel faster than c, you can't signal with them faster than c. If this seems like a contradiction from the particle point of view, the tachyons seem to lack an essential property of Newtonian particles -- they don't seem to be localizable as point-like objects.

So quantum field theory, a theory about relativistic quantum physics of point-like objects, says tachyons don't act like points. Bleah. Perhaps a better thing would move them from "hypothetical objects" to "very hypothetical objects."

See section 2.3 of Relativity, Groups, Particles: Special Relativity and Relativistic Symmetry in Field and Particle Physics

https://books.google.com/books?id=iyj0CAAAQBAJ&lpg=PA27&pg=PA24#v=onepage

 

[brucep]

In quantum field theory, one can describe hypothetical free tachyons. But a theorem of quantum field theory says all disturbances in quantum fields propagate with speed = c. Thus while formally the tachyonic particles travel faster than c, you can't signal with them faster than c. If this seems like a contradiction from the particle point of view, the tachyons seem to lack an essential property of Newtonian particles -- they don't seem to be localizable as point-like objects.

So quantum field theory, a theory about relativistic quantum physics of point-like objects, says tachyons don't act like points. Bleah. Perhaps a better thing would move them from "hypothetical objects" to "very hypothetical objects."

See section 2.3 of Relativity, Groups, Particles: Special Relativity and Relativistic Symmetry in Field and Particle Physics

https://books.google.com/books?id=iyj0CAAAQBAJ&lpg=PA27&pg=PA24#v=onepage

Nice analysis. As usual for you. The reference is great. 2.8 on page 37 is interesting.

 

[tashja]

How would Tachyons affect the spacetime continuum, [would they create gravity] if they were shown to exist.
Could they possibly be harnessed by an advanced civilisation.

Hi Paddo,

Wasn't sure if you specifically wanted Q to answer your questions, so I went ahead and forwarded your questions to the experts. Here's their reply:

How would Tachyons affect the spacetime continuum, [would they create gravity] if they were shown to exist.
Could they possibly be harnessed by an advanced civilisation.

Yes tachyons would create gravity. In fact if they are a source of dark energy as some have suggested they would create repulsive gravity. Whether they could be harnessed by an advanced civilization depends on whether they could be used to transmit information. If so, then as Paul Ehrenfest first showed (see tachyon antitelephone wiki), they could theoretically send information back in time.

Bob Ehrlich

How would Tachyons affect the spacetime continuum, [would they create gravity] if they were shown to exist.
Could they possibly be harnessed by an advanced civilisation.

Hi Tashja,

As far as we know, anything that carries energy affects the spacetime continuum, in a way that is mathematically described by Einstein's equations of general relativity. If they exist, tachyons carry energy, so we would expect that they would contribute to the curvature of spacetime. For an imaginative illustration of how tachyons could be harnessed by an advanced civilization, I recommend the book "Timescape" by Gregory Benford.

Alan

 

[Q-reeus]

Hi Paddo,

Wasn't sure if you specifically wanted Q to answer your questions, so I went ahead and forwarded your questions to the experts. Here's their reply:

Good work again tashja. A topic where basically it seems there are as many finely-detailed opinions as authorities polled. Referring back to the highlighted text of the passage quoted in #23, such bizarre 'physics' implies a huge overall gravitational footprint, despite negative/imaginary mass of tachyon itself. Then again, here's another view:
http://www.quora.com/How-would-tachyons-interact-with-ordinary-matter-via-the-gravitational-force
And on it could go. I stick with tachyon = imaginationon..

 

[Q-reeus]

It's interesting that while Pavel A Cherenkov was co-awarded a Nobel Physics prize for his experimental discovery, in 1934, of the radiation named after him, it turns out the unsung genius Oliver Heaviside wrote quite a bit on 'conical radiation' owing to hypothetical faster-than-light electrons, way back in the 1880's. See the second quoted passage and following, p25 here: https://books.google.com.au/books?i...24&source=gbs_toc_r&cad=3#v=onepage&q&f=false
He was as noted there, wrong in assuming the possibility in vacuo, but nevertheless was the first to predict shock-front EM wave propagation whenever v > c in a medium.
There have been numerous similar cases where credit for earlier work was very slow in coming or not at all.

 

[paddoboy]

Hi Paddo,

Wasn't sure if you specifically wanted Q to answer your questions, so I went ahead and forwarded your questions to the experts. Here's their reply:

Once again tashja, thanks. Great stuff!

 

[Dinosaur]

From my Post #19

I thought that Martin Gardner shot down the notion of tachyons circa 1965 due to the following.

The equations supporting tachyons indicate that they travel backwards in time.

Suppose you built a device to generate them & intended to turn it on at noon. Some time prior to noon, you would see Cerenkov radiation & could decide to turn off the generator.

The above paradox indicates that tachyons cannot exist. ​

BTW: Cerenkov radiation occurs whenever something travels faster than light in some medium. While this is impossible in a vacuum, it is possible in some medium through which light travels at lest than c (light velocity in a vacuum). Cerenkov radiation has been observed in media in which light ravels slower than c.

so far, nobody has commented relating to the above.

 

[rpenner]

Dinosaur, that was partially addressed in post #28 where they were considered as superluminal quantum particles instead of superluminal classical particles.

 

[Dinosaur]

I have a lot of respect for Martin Gardner. From my Post # 19

I thought that Martin Gardner shot down the notion of tachyons circa 1965 due to the following.
The equations supporting tachyons indicate that they travel backwards in time.

Suppose you built a device to generate them & intended to turn it on at noon. Some time prior to noon, you would see Cerenkov radiation & could decide to turn off the generator.

The above paradox indicates that tachyons cannot exist.

BTW: Cerenkov radiation occurs whenever something travels faster than light in some medium. While this is impossible in a vacuum, it is possible in some medium through which light travels at lest than c (light velocity in a vacuum). Cerenkov radiation has been observed in media in which light ravels slower than c.

I stand by the above until some Poster can refute Gardner's POV.

BTW: Circa 1965 some very bright folks other than my self accepted Gardner's analysis.

 

[rpenner]

I think Martin Gardner may have been talking about a 1917 model of FTL communication rather than a quantum field theory of a FTL fundamental particle. The term tachyon was coined in 1967.

In the December 8, 1977 issue of the New York Review of Books, Martin Gardner has this to say about tachyonic communication:

To send a message faster than light means sending it back in time, and this leads directly to logical contradictions. If A sends a tachyonic message to B, in another galaxy, and B replies tachyonically, then A gets the reply before he sent the message.

I believe this is not Martin Gardner's original idea, but one based on Tolman's paradox.

In the preceding section we have called attention to the fact that the mere composition of velocities which are not themselves greater than that of light will never lead to a speed that is greater than that of light. The question naturally arises whether velocities which are greater than that of light could ever possibly be obtained in any way.

This problem can be attacked in an extremely interesting manner. Consider two points A and B on the X axis of the system S, and suppose that some impulse originates at A, travels to B with the velocity u and at B produces some observable phenomenon, the starting of the impulse at A and the resulting phenomenon at B thus being connected by the relation of cause and effect.

The time elapsing between the cause and its effect as measured in the units of system S will evidently be
$$\Delta t = t_B - t_A = \frac{x_B - x_A}{u}$$ , (28)
where $$x_A$$ and $$x_B$$ are the coordinates of the two points A and B.

Now in another system , which has the velocity V with respect to S, the time elapsing between cause and effect would evidently be
$$\Delta t' = t'_B - t'_A = \frac{1}{\sqrt{1 - \frac{V^2}{c^2}}} \left( t_B - \frac{V}{c^2} x_B \right) - \frac{1}{\sqrt{1 - \frac{V^2}{c^2}}} \left( t_A - \frac{V}{c^2} x_A \right)$$ ,
where we have substituted for $$t_B$$ and $$t_A$$ in accordance with equation (12). Simplifying and introducing equation (28) we obtain
$$\Delta t' = \frac{1 - \frac{uV}{c^2}}{\sqrt{1 - \frac{V^2}{c^2}}} \Delta t$$ . (29)

Let us suppose now that there are no limits to the possible magnitude of the velocities u and V, and in particular that the causal impulse can travel from A to B with a velocity u greater than that of light. It is evident that we could then take a velocity u great enough so that $$\frac{uV}{c^2}$$ would be greater than unity and $$\Delta t'$$ would become negative. In other words, for an observer in system S the effect which occurs at B would precede in time its cause which originates at A. Such a condition of affairs might not be a logical impossibility; nevertheless its extraordinary nature might incline us to believe that no causal impulse can travel with a velocity greater than that of light.

We may point out in passing, however, that in the case of kinematic occurrences in which there is no causal connection there is no reason for supposing that the velocity must be less than that of light. Consider, for example, a set of blocks arranged side by side in a long row. For each block there could be an independent time mechanism like an alarm clock which would go off at just the right instant so that the blocks would fall down one after another along the line. The velocity with which the phenomenon would travel along the line of blocks could be arranged to have any value. In fact, the blocks could evidently all be fixed to fall just at the same instant, which would correspond to an infinite velocity. It is to be noticed here, however, that there is no causal connection between the falling of one block and that of the next, and no transfer of energy.

This old (1917) argument did not argue against quantum field theory tachyons, but rather against the possibility of signaling faster than light. In quantum field theory, this you cannot do, even if tachyons are real. Martin Gardner's reliance on a Newtonian model of tachyons equates travel speed with signaling speed, but that's not the quantum field theory case.

http://journals.aps.org/prd/abstract/10.1103/PhysRevD.18.3610
http://www.nybooks.com/articles/archives/1977/dec/08/only-joking/
http://journals.aps.org/prd/abstract/10.1103/PhysRevD.2.263
https://archive.org/details/theoryrelativmot00tolmrich
https://en.wikipedia.org/wiki/Tachyonic_antitelephone
https://en.wikipedia.org/wiki/Tachyonic_field

 

[Walter L. Wagner]

It's interesting that while Pavel A Cherenkov was co-awarded a Nobel Physics prize for his experimental discovery, in 1934, of the radiation named after him, it turns out the unsung genius Oliver Heaviside wrote quite a bit on 'conical radiation' owing to hypothetical faster-than-light electrons, way back in the 1880's. See the second quoted passage and following, p25 here: https://books.google.com.au/books?i...24&source=gbs_toc_r&cad=3#v=onepage&q&f=false
He was as noted there, wrong in assuming the possibility in vacuo, but nevertheless was the first to predict shock-front EM wave propagation whenever v > c in a medium.
There have been numerous similar cases where credit for earlier work was very slow in coming or not at all.

Very interesting. I wasn't aware of Heaviside's contribution. I wonder if Cerenkov had read or relied on Heaviside's insight?

 

[Q-reeus]

Very interesting. I wasn't aware of Heaviside's contribution. I wonder if Cerenkov had read or relied on Heaviside's insight?

Hard to say, but if so his/their avoiding giving any credit due had imo a parallel of sorts in Einstein's failure, in his seminal paper "On the Electrodynamics of Moving Bodies." to so much as mention any of the earlier very important contributions from the Likes of Poincare, Lorentz, Michelson-Morley and various others who collectively basically handed SR to him on a platter. Of course there was inevitably much subsequent referencing owing if nothing else than to debate over interpretations etc., but I suspect that initial silence may have been a significant factor in him not getting a Nobel prize for SR. Not that I have studied that issue and historians may disagree.

Anyway while it's entirely possible Cherenkov et al. genuinely were unaware of prior work by Heaviside at the time of discovery, hard to believe that would still be the case by the time a Nobel award was being bestowed in Stockholm.
There remains a sizable cult following for Tesla, yet Heaviside was imo far better grounded especially mathematically: https://en.wikipedia.org/wiki/Oliver_Heaviside
An interesting article by J.D.Jackson on credit misapplied - see in particular part III.A on Heaviside: http://arxiv.org/abs/0708.4249v2
Will belatedly point out my typo in #32 where the second line should have read p125 not p25.