Tachyons are faster than light

[Jay-qu]

Why not? Well.. You are saying they are predicted by numerous theories, could you please name a few? I know of one, string theory.

 

You say most things that are allowed in relativity seem to exist, well thats because we have accepted relativity as a discription of the universe we live in. String theory is not yet at that point. AFAIK relativity does not predict tachyons, but feel free to prove me wrong.

 

J

[snoopy]

It was the american physicist Gerald Feinberg who coined the phrase in the 1960`s long b4 string theory.

 

If your saying Gerald Feinberg had some sort of mystical insight into string theory ok... but I doubt it.

 

Relativity allows Tachyons to exist it doesnt prove them....

Relativity allows black holes to exist it doesnt prove them either.

You need experimental evidence to prove things not just theoritical.

 

You also say Tachyons only are predicted in string theory.

This is just plain wrong as far as i know

they are allowed in Relativity as a particle with a `spacelike` four momentum

and they are also in Quantum field Theory as a quantum of a field whose squared mass is negative.

 

I have posted the following from Baez

 

"a well known fact that nothing can travel faster than the speed of light. At best, a massless particle travels at the speed of light. But is this really true? In 1962, Bilaniuk, Deshpande, and Sudarshan, Am. J. Phys. 30, 718 (1962), said "no". A very readable paper is Bilaniuk and Sudarshan, Phys. Today 22,43 (1969). I give here a brief overview.

 

Draw a graph, with momentum (p) on the x-axis, and energy (E) on the y-axis. Then draw the "light cone", two lines with the equations E = +/- p. This divides our 1+1 dimensional space-time into two regions. Above and below are the "timelike" quadrants, and to the left and right are the "spacelike" quadrants.

 

Now the fundamental fact of relativity is that E2 - p2 = m2. (Let's take c=1 for the rest of the discussion.) For any non-zero value of m (mass), this is a hyperbola with branches in the timelike regions. It passes through the point (p,E) = (0,m), where the particle is at rest. Any particle with mass m is constrained to move on the upper branch of this hyperbola. (Otherwise, it is "off-shell", a term you hear in association with virtual particles - but that's another topic.) For massless particles, E2 = p2, and the particle moves on the light-cone.

 

These two cases are given the names tardyon (or bradyon in more modern usage) and luxon, for "slow particle" and "light particle". Tachyon is the name given to the supposed "fast particle" which would move with v>c. (Tachyons were first introduced into physics by Gerald Feinberg, in his seminal paper "On the possibility of faster-than-light particles" [Phys.Rev. v.159, pp.1089--1105 (1967)]).

 

Now another familiar relativistic equation is E = m*[1-(v/c)2]-1/2. Tachyons (if they exist) have v > c. This means that E is imaginary! Well, what if we take the rest mass m, and take it to be imaginary? Then E is negative real, and E2 - p2 = m2 < 0. Or, p2 - E2 = M2, where M is real. This is a hyperbola with branches in the spacelike region of spacetime. The energy and momentum of a tachyon must satisfy this relation. "

 

 

If you want to tell John Baez that Tachyons are not allowed in relativity and that his post is wrong be my guest.

here is the full thing

Tachyons

[Jay-qu]

It was the american physicist Gerald Feinberg who coined the phrase in the 1960`s long b4 string theory.

 

If your saying Gerald Feinberg had some sort of mystical insight into string theory ok... but I doubt it.

 

no, he merely came up with a name for particles that travel faster than light. When string theory had such particles arrising why would they bother making a new name?

 

Relativity allows Tachyons to exist it doesnt prove them....

Relativity allows black holes to exist it doesnt prove them either.

You need experimental evidence to prove things not just theoritical.

 

there is a difference to allowing and predicting,

 

You also say Tachyons only are predicted in string theory.

This is just plain wrong as far as i know

they are allowed in Relativity as a particle with a `spacelike` four momentum

and they are also in Quantum field Theory as a quantum of a field whose squared mass is negative.

 

well as far as I know, all you are doing is desribing the particle in these different frameworks - not predicting.

 

If you want to tell John Baez that Tachyons are not allowed in relativity and that his post is wrong be my guest.

here is the full thing

Tachyons

 

again, I didnt say they wherent allowed, but merely they arent predicted by it.

[jungjedi]

no, he merely came up with a name for particles that travel faster than light. When string theory had such particles arrising why would they bother making a new name?

.

 

im not following the logic.why would they adapt that particuar name?

[snoopy]

 

 

well as far as I know, all you are doing is desribing the particle in these different frameworks - not predicting.

 

 

 

again, I didnt say they wherent allowed, but merely they arent predicted by it.

 

Where in my previous post did I say They were a direct prediction of relativity ? Im guessing nowhere.

 

But as I said b4 Black Holes are not a direct prediction of relativity either and they have been actually `have` been proven to exist.

 

When you couple this with QFT and the string theories that Tachyons pop up in then there is a least the suggestion that they could indeed actually exist.

 

Relativity

QFT

String theory

They all have something to say about Tachyons that to me acconts for the `various` theories I was mentioning earlier. Thats pretty much all I was saying it was a discussion on things that are allowed to go faster than light. I think Tachyons should get a mention sorry you dont agree but then I dont agree with you either on this one. sorry ;) .

 

To continue the discussion further `Shadows` are also allowed to go faster than light even when the object they are the shadow of isnt travelling at superluminal speeds.

 

So there you go Shadows possibly the fastest thing in the universe ?

[Jay-qu]

funny you say that :lol: my dad has always maintained that the speed of dark is faster than that of light!

 

You dont have to apologise for disagreeing with me

 

I dont mean to start an argument, but I think you need to read posts a little closer - maybe I do to sometimes too, but some of the things you accuse me of doing I havent said ;)

[snoopy]

To the best of my knowledge Jay-qu I havent accused you of anything.

 

I have pulled your leg a couple of times but it is hard to convey emotions and humour through texts... maybe I should make better use of the emoticons ;)

but they kind of bug me so I dont..

[CraigD]

My impression of the theoretical speculation about tachyons I’ve read to date is

• They’re a class of particles with speed relative to an arbitrary observer greater than the speed of light
  
• According to special relativity, they
  • have real number-valued observed mass if they are assumed to have imaginary number-valued rest mass
    
  • have imaginary number-valued observed mass if they are assumed to have real number-valued observed mass
    
  • approach infinite mass and energy as they approach speed c
    
  • approach zero mass and energy as they approach an infinite speed
    

  (What observable predictions one would make concerning an “imaginary number-valued observed mass” particle, I’m unable to determine)

  [*]If they interact in any way with any know particle (eg: have charge, interact with the weak force, etc.) they are in principle detectable

  [*]Experiments have been conducted to detect them via at least 2 kinds of interaction, and have detected nothing

  [*]Using the formalism of quantum mechanics (which describes all particles in terms of a quantum wave function, which can be used to describe the probability of a particle being measured at a particular time in a particular volume of space), tachyons either don’t travel faster than the speed of light (contradicting their definition, so effectively denying they exist), or can’t interact with non-tachyons (so can’t be detected) (source: Tachyons, as linked to by post #19)

My bottom-line impression is that, if tachyons do exist, then they must be considered an alternative to quantum wave functions (requiring a complete update of the formalism of quantum mechanics).

 

Such an alternate quantum mechanics has 2 major cases

• All tachyons travel at an infinite speed
  
• Some tachyons travel at a finite speed (greater than c)
  

In the first case, I can see no way of formulating a testable prediction that can distinguish the alternative quantum mechanics from the standard (quantum wave function-using) one, in which case tachyons are unprovable, so effectively irrelevant.

 

In the second, the following experiment can decide if tachyons or a quantum wave function is responsible for quantum entanglement:

• Conduct an actual version of the EPR paradox experiment (a Bell test experiment)
  
• If quantum entanglement is “action at a distance” via tachyons, the experiment should fail (the particles should not appear entangled) when measurements of the distant entangled particles are made close enough to simultaneously that a tachyon can not have traveled between them
  

In other words, prove that a locally realistic solution to the EPR paradox involving finite speed signals exists, and you prove the existence of observable tachyons.

 

It would then be necessary to construct a theory explaining how tachyons can explain all of the wave-like behavior of particles observed in numerous experiments, and currently explained by quantum wave functions.

 

I strongly doubt that a Bell test experiment failure will be observed, or that tachyons exist.

[snoopy]

It would then be necessary to construct a theory explaining how tachyons can explain all of the wave-like behavior of particles observed in numerous experiments, and currently explained by quantum wave functions.

 

I strongly doubt that a Bell test experiment failure will be observed, or that tachyons exist.

 

Hmm well yes CraigD I have said that `tachyons` are highly theoretical

and If I could `prove` that they do actually `exist` I would not be bumping my gums about them in this forum I would be recieving various grants from communication companies.

 

That said your post can be replied to in 2 main bits

 

I have said that if tachyons do exist they probably dont `interact` with the universe or they do so very `weakly`.

 

In reply to your statement if that Tachyons dont interact with the rest of the

they are `meaningless`.

 

I dont agree with this at all in relativity the work of Charon suggests an `ordering` role for Tachyons and that they are responsible for the `order` in the universe. Hardly `meaningless`.

 

In QM the recent work of Recami suggests that they might be responsible for `action at a distance` phenomena again hardly `meaningless`.

 

Good Reasons to allow for the possiblilty are as I have stated that other `questionable` phenomena such as

1. Black Holes

2. Neutrinos

 

were eventually proved to exist !!

 

Im sorry you hate Tachyons so much I quite like them and think they are quite `furry` and `cuddly` :lol:

[CraigD]

In reply to your statement if that Tachyons dont interact with the rest of the they are `meaningless`.

 

I dont agree with this at all in relativity the work of Charon suggests an `ordering` role for Tachyons and that they are responsible for the `order` in the universe. Hardly `meaningless`.

 

In QM the recent work of Recami suggests that they might be responsible for `action at a distance` phenomena again hardly `meaningless`.

I agree.

 

However if tachyons “order” the universe, of are responsible for “action at a distance”, then it’s unreasonable to say they "don’t interact with other particles", so the statement “if tachyons don’t interact with the rest of the they are `meaningless`” is arguably correct.

 

PS: Please note that nowhere did I write the statement you attribute to me, or even use the word “meaningless”. Perhaps you are referring to my paraphrasing of the arguments in Scott Chase’s Tachyons, which argue using quantum wave function formalism that tachyons cannot interact with tardyons or luxons?

Good Reasons to allow for the possiblilty are as I have stated that other `questionable` phenomena such as

1. Black Holes

2. Neutrinos

 

were eventually proved to exist !!

I don’t see the validity of this argument. Black holes and neutrinos are predicted by several well-accepted theories, and these predictions confirmed by experiments and observations. Tachyons are predicted only by very speculative theories with effectively no experimental or observational validation, and only a few very speculatively proposed experiments, such as the one described in post #25.

 

Snoopy’s argument appears to me to be an instance of the argument “once, X had not been shown to exist. Later, X was shown to exist. Y has not been show to exist. Therefore, Y will be shown to exist.” I believe this is a logical fallacy.

Im sorry you hate Tachyons so much I quite like them and think they are quite `furry` and `cuddly`

I don’t hate tachyons! On the contrary, I find thinking, reading, and writing about them fascinating. However, just because they’re fun to think about, doesn’t require that they physically, objectively, exist. :)

 

PS: “furry and cuddly”?! :lol:

[snoopy]

PS: Please note that nowhere did I write the statement you attribute to me, or even use the word “meaningless”. QUOTE]

 

Sorry you called them `irrelevant` not `meaningless` my bad....

although I feel your splitting hairs... but I apologise anyway cos Im generous like that. ;)

 

Snoopy’s argument appears to me to be an instance of the argument “once, X had not been shown to exist. Later, X was shown to exist. Y has not been shown to exist. Therefore, Y will be shown to exist.” I believe this is a logical fallacy. QUOTE]

 

This isnt really what Im saying at all.... Im saying once X was only `highly theoretical` but now X has been proven to exist, the same theories that proved the existance of X suggest Y `might` exist therefore there is good reason to believe that Y `might` exist this is logically self consistent and not as you allude ` a logical fallacy `.

 

But I thank you for playing !!

 

P.S.

Yes i think Tachyons are `furry` and `cuddly` so what.... would you like to put forward the idea that they are `hard` and `spiky` ?:eek_big:

[Jay-qu]

We dont hate tachyons we are merely following good old scientific method here... An argument that says "highly theoretical tachyons might exist because once highly theoretical black holes have now been shown to exist" has just about as many legs as a fish!

[snoopy]

We dont hate tachyons we are merely following good old scientific method here... An argument that says "highly theoretical tachyons might exist because once highly theoretical black holes have now been shown to exist" has just about as many legs as a fish!

 

 

Some fish did have legs they hauled themselves onto land eventually and became `reptiles`.

 

The `mammal like reptiles` became us !

 

Tachyons and/or black holes dont have legs they dont need them !

 

I do not see your point or I refuse to :eek_big: (pick the one that pleases you most)

 

Again I am not merely stating that because black holes have been proven to exist (a fact that still annoys me on so many levels) *anyone not annoyed by black holes just doesnt understand them that well* but anyway I digress back to the topic at hand I am not merely stating that cos black holes exist this must mean `leprechauns or dragons exist` I am not even saying that it must mean `Tachyons` exist.

 

What I am saying.

If numerous theories are mentioning Tachyon particles it increases the chances that Tachyons do really exist. If it was one single theory I too would just say `ahh so what, big deal, move on.`

 

Especially I feel relativity has a great deal to say about them and Tachyons are logically self consistent with relativity. In relativity they are just nice and nice things should exist (my own personal opinion).

 

What the moderators/staff seem to be saying is that `black swans cant exist` and `only white swans can exist` and the only reason they give is because `we have never seen a black swan`.

 

I think that is what you were tryin to say with your `legless fish` story although it was a bad analogy as I can point to the fossil record and say `look that fish had legs, Tachyons exist I win`

but I wont do that as that would be unfair and annoying

 

But by all means stick with your `there are only white swans` position its a safe position to be in. But just because you have never seen a `black swan` doesnt mean they dont exist. Just because Tachyons havent yet been proven to exist doesnt mean your right about them either.

 

Really if Tachyons were proved to exist in 50 years time would it shock you ?

I am betting it wouldnt and you will all be there 50 years from now saying saying damn I knew they existed all along. :)

[CraigD]

Yes i think Tachyons are `furry` and `cuddly` so what.... would you like to put forward the idea that they are `hard` and `spiky` ?:hyper:

I’m thinking more of “mind-boggling” and “hypothetical” :D

 

As one might expect, discussing furry/cuddly/hard/spiky/mind-boggling/hypothetical particles carries a big risk of everybody imagining a significantly different thing to an extent that makes the blind men discussing an elephant seem the epitome of consensus! With that in mind, I’d like to be as untechnical and communicative as possible for the first part of this post, and consider the differences in our imaginings of the tachyon.

 

In the starting post of this thread, snoopy said

If you do manage to build a Tachyon detector you could in theory build a communication device …

From this, I get a strong impression that he’s imagining tachyons to be much like photons, except propagating faster than the speed of light – in short, a measurable, objectively real particle that could be used by a sort of super-luminal radio.

 

My read of the science literature (which is small in comparison to the fictional) on tachyons is that no knowledgeable theorist view them this way. Rather, they are viewed more as non-physical things, like an object that appears to move across a computer screen, when in underlying reality, there is no such object, only an ordered sequence of switching on and off of pixels. Although useful in expaining the underlying cause of observable phenomena, tachyons as they appear described in quantum field, string, and brane theory aren’t a new kind of particle that can be used to signal more quickly than is possible with photons. Even if these theories gain experimental validation and widespread acceptance, they don’t appear to predict that any device will be capable of sending a signal into between 2 locations more quickly than ordinary light/radio/etc.

 

There’s a second idea in snoopy’s post that I think need scrutiny

… that could send messages to the past as long as they were using the same communication standard as you were or the same paradoxically if you did manage to build such a device you might have to wait 40 years before you started to use it to send messages to yourself in the past but the moment you switched it on you should get a message from your self from 40 years in the future probably saying something like `testing....testing` :D

This reminds me a lot of one of my favorite novels, James Hogan’s 1980 ”Thrice Upon a Time” (although the story’s protagonist, fictional physicist Sir Charles Ross, doesn’t propose faster-than-light particles, rather backward-time-traveling quarks, which propogate backward in time only a minute interval, requiring that the receiver rebroadcast the signal many times to allow it to travel minutes, and ultimately 193 days, into the past).

 

The idea that an object traveling faster than the speed of light in vacuum travels backward in time is an old one, much used in science fiction. However, I believe it’s a scientific misconception.

 

The idea appears to arise from examining the graph of [math]\tau = \sqrt{1-\left ( \frac{v}c \right )^2}[/math] (tau). For v= 0 to c, this graph is a quarter circle, indicating a value of 1 (no time dilation) for v=0, 0 (time stands still) for v=c. Intuition suggest that tau should have a negative real value (time goes backwards) for v>1. However, the real part of tau for all v>0 remains 0, while its imaginary ([math]\sqrt{-1}[/math]) part increase as v increases.

 

What “the imaginary part of tau” might imply, physically, is difficult to imagine, but it’s almost certainly not the same as implied by a negative real value (time goes backwards). So, despite the common perception and science fiction precedent for it, the idea that a body that exceeds c travels/is projected into the past doesn’t follow from Special Relativity.

[snoopy]

To CraigD

 

oh come on I was hardly being serious about building a communication device.

 

No you cant build Tachyonic radios........... thats very true !!

 

But I was kidding about that bit sorry you never noted the :D

 

Also yes ok Tachyons arent part of physical reality but sort of underlie it but maybe the photon and neutrino are in the same boat doesnt mean they dont exist.

[CraigD]

Also yes ok Tachyons arent part of physical reality but sort of underlie it

Maybe. :D Though I know more about them than when this thread started (one of my favorite hypographical effects ), they still feel mostly mind-boggling and hypothetical to me. Word is, quantum field, string, brane theory, and others with formalism involving tachyons, are not the sort of thing you learn overnight.

but maybe the photon and neutrino are in the same boat doesnt mean they dont exist.

I’d not say the photon and neutrino are in the same boat as the tachyon at all!

 

Photons are very tangible, interacting strongly with nearly everything that isn’t a gauge boson. Experiments confirming their existence are older than most living human beings, and have been performed by practically every student who’s taken a Modern Physics lab class.

 

Interacting only via the weak force and gravity neutrinos are much more difficult, but have been detected experimentally since the 1950s.