Talk:Faster-than-light/Archive 1

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Great Article

I just wanted to say that this article was fascinating and informative. Good work!

VERY well written with clear explanations and links to the concepts at hand, so even a silly little linguist like myself could understand it.

Thanks to all the contributors! --161.45.243.157 17:50, 23 February 2007 (UTC)

Can you see and comment this:

http://www.petar-bosnic-petrus.com/work/conical-and-paraboloidal-supraluminal-particle-accelerators/

Odd questions

Please move these to a separate category if they ever evolve into a discussion

• As far as I understand it, an object can not travel faster than light because the faster an object moves the more massive it becomes, and thus requires more force to accelerate it even faster, which causes it to never reach the speed of light without infinite energy to accelerate it. What would happen if a very massive object with a very strong gravitational field had an object accelerated towards it merely by the force of the two objects gravitational attraction? The problem of having to increase the ammount of energy put into acceration in order to counteract the accelerating bodies mass would be solved by the fact that the more rapidly the attracted body is moving the more massive it would become and thus it would become even more strongly attracted to the massive object. If one assumes that the distances between the two objects was great enough and the volume and stregnth of the gravitational field was large enough, wouldn't this cause the attracted object to accelerate past the speed of light before the two object collide?
  • I think that at that point you get an event horizon, and shortly thereafter, a black hole.

• Given a dispersion relation ω(k), the phase velocity is ^ω/_k and the group velocity is ^dω/_dk -- or so said some of my physics instructors in conversation. But if a phase velocity is going at speeds greater than the speed of light, then that means ω > ck. This troubles me, because the graph of the boundary is a line with slope c; it would seem that if ω(k) traversed that boundary, then either ^dω/_dk is greater than c somewhere, to give the graph the upward slope needed to cross the line; or else the dispersion relation is discontinuous. This would meant that when the phase velocity goes faster than light, so too does group velocity. (And that would break the light barrier.) Thoughts? Do violations of the speed-of-light barrier only happen outside of dispersive contexts? 128.253.197.212 18:18, 10 November 2006 (UTC)

• If you absorb light from all sides, is there no limit to the "speed" you can go? After all, there is no light to clock you. - User:hackwrenchRobert Claypool
  • Short answer is that it's useful to imagine using light to measure distances and times due to its properties; the speed limit is a property of spacetime itself, not something artificially applied by light. See special relativity and minkowski space for more details, and ask questions on their talk pages. --Christopher Thomas 02:34, 30 May 2005 (UTC)

• What about quantum entanglement?
  • Short answer is that it lets you transmit gibberish faster than light, but information at the speed of light or slower. See phase velocity, and group velocity for more information. Apparent FTL photon transmission observed to date has been triggering of a reconstructed photon pulse on receiving only the leading edge of the original photon's wavefunction. This turns out to not let you do anything useful. Talk:quantum entanglement is probably the best place to ask about this. --Christopher Thomas 02:34, 30 May 2005 (UTC)

How about lets not confuse reality with theory. Almost none of what you are saying is true. And any movment faster then light falsifies "THE THEORY OF VELOCITY ABSOLUTISM" in any case. The "information" diversion is just a gyp by velocity-absolutists who can't get with reality and who mix up simplistic models with reality. That part of the theory of velocity-absolutism that has not been thoroughly falsified is those parts that are contradictory or non-falsifiable. Time to move on. And a wiki article that presents a dubious theory as reality is a substandard, dishonest and bad wiki article. The wording ought to be rewritten accordingly. —Preceding unsigned comment added by 122.148.183.191 (talk • contribs) 00:46, 4 August 2007 (UTC)

• What about Cherenkov effect? - Superborsuk 12:21, 22 Aug 2004 (UTC)
  • Short answer is, what about it? The speed at which the actual photons are propagating remains C. The phase velocity changes in a medium with a refractive index, which makes anything (like a fast charged particle) causing an EM disturbance that moves faster than the phase velocity to do strange things (in this case, a cone of light is emitted from the point of disturbance). Still, no actual FTL here. --Christopher Thomas 02:34, 30 May 2005 (UTC)

• If a particle had a rest mass that was a negative imaginary number would it's mass at a speed faster than light be a positive real number?
  • See tachyon and tachyon condensation (and their talk pages) for a more detailed discussion of this. --Christopher Thomas 02:34, 30 May 2005 (UTC)

• So going exactly the speed of light in a homogeneous space using exactly infinite energy, is a sensible notion?
  • Not really. Assigning anything "infinite energy" tends to make all of the equations describing the rest of the system blow up. What's usually described instead is asymptotic behavior: as the velocity of an object with rest mass approaches the speed of light, its relativistic mass (and kinetic energy) approach positive infinity. This doesn't mean that the asymptotic value can ever be reached in a meaningful fashion. To give a trivial example of the same type of thing, you can say that the value of 1/x approaches +infinity as x approaches 0 from the positive direction, but you can't say that 1/0 is equal to +infinity, because you can get different answers by attempting to solve the problem in different ways (1/x approaches -infinity if x approaches 0 from the negative direction, for instance). --Christopher Thomas 06:37, 24 June 2006 (UTC)

• An amateur question. Lets say we have enough energy to propel a craft at 0.99c. We also have a sphere of unobtainium. And finally inside our craft is a machine to spin a sphere clockwise at 0.10c. Now the first step is most important, we spin the sphere to full speed. Since it is made of unobtainium, it doesn't break apart. Now we start accelerating the craft. As mass of the craft increases so does the mass of the sphere. So the sphere actually becomes harder to slow down due to inertia. When the craft reaches 0.99c why wouldn't the left side of the sphere be traveling 1.09c ?
  • The short answer is that an observer doesn't see velocities add in the normal way in objects moving at relativistic speeds with respect to the observer. This is covered at velocity-addition formula, and is an aspect of special relativity. That article will give a better example description of it than I can think of off the top of my head right now. --Christopher Thomas 16:28, 24 June 2006 (UTC)

• Another amateur question. At Australian National University, a beam of light was terminated at point A and another beam of light was changed into its exact duplicate at point B. Thus teleporting a beam of light, in effect. It is my understanding that the duplication between point A and B was instant and distance was not a factor. So why not vary the beam intensity or even switch it on an off to send a binary code message any distance without delay?
  • This falls under the "quantum entanglemment" question, above. This experiment sounds more like entanglement than teleportation, as quantum teleportation uses a photon to perform the information transport. Experiments like the one you describe usually work by entangling two photons, separating them by some large distance, and measuring a property (such as polarization) of the first photon, forcing the polarization of the second photon to an opposite value. There are several problems with trying to transport information faster than light with this: We're not sure how fast the wavefunction collapse propopagates, or whether it even actually collapses at all, and because the way the measurements work you end up needing to transport additional information to get the first measurement to transport useful data. This is covered in more detail at quantum entanglement. Various groups have claimed to send information FTL, but to the best of my knowledge, the measurement of this hasn't been universally accepted. If we had a clear, unambiguous demonstration of information being transmitted at FTL speeds, we'd already be working on building devices to send information back in time (the two operations are equivalent). --Christopher Thomas 16:28, 24 June 2006 (UTC)

Article was rewriten since these comments

Loose concepts

"these concepts are outright impossible, as well as being well beyond our current technology"

Isn't this sentence kinda contradictory? It can't be both impossible and beyond our current technology, beyond our current technology implies that it is possible. Fuelbottle | Talk 22:52, 29 Aug 2004 (UTC)

Or does it? It means we can't do that yet, it doesn't specify wheter we'll ever be able to do that.

It's not contradictory, it's just (in its current form) redundant. And not neccesarily true.

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I removed This process cannot transmit information, as nothing is getting closer to anything. since we definitely have transmission of information from high redshift galaxies :). - Boud 15:17, 17 Jun 2004 (UTC)

Would you care to provide a source for this? - 70.18.182.39 03:41, 17 Apr 2005 (UTC)

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Note: I changed the phrase "the limit may not be quite as absolute in general relativity" back to "the limit IS not quite as absolute ...". It is inarguably the case that general relativity allows bizarre metrics that let an object move faster than light, or back in time, from the point of view of a distant observer. Physicists don't like this, so they look for a more comprehensive theory that would prohibit it. Such a theory would supersede general relativity; it wouldn't BE general relativity. (Does anyone know what current hypotheses of quantum gravity say about wormholes and the Alcubierre metric?) - Zack 00:04, 12 Jan 2004 (UTC)

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Removed the following parapgraph. Anyone capable of understanding it can rewrite and replace it: In the context of quantum field theory, in the framework of local quantum physics, this is the requirement that if O is a bounded open subset of spacetime, then the observable algebra of the causal completion of O is the same as the observable algebra over O. There are QFT models where this axiom does NOT hold, and so why this axiom holds is an open question. - Ec5618 10:18, Apr 18, 2005 (UTC)

Mass increase

I had posted an entreaty, asking for further consensus, but got no responses, so I lost patience (sorry) and forged ahead on my own with a major MAJOR revision. Why? because I found the existing approach horribly misleading. I DO however compliment the previous author(s) for their diligent efforts at circumspect wording, but even so, to base the speed limitation (of a rocket propelled craft) on relativistic mass increase is dubious at best. The reader would've been grossly misled and would have concluded that a speeding rocket is ever harder to thrust, which is NOT the case! And that thing about time dilation preying upon exhaust gas speed was likewise awkward and obtuse. So I've replaced all of that.ETP 23:08, 26 Jan 2005 (UTC)

I want to reemphasize that the attribution of relativistic mass increase is quite okay, but it's a lousy way of explaining the speed limitation of a rocket propelled craft. It is a perfectly fine and dandy way to explain the speed limitation of a charged particle in a particle accelerator, because those particles are being pushed along by electromagnetic field-producing coils that are positioned in the (relatively) stationary lab frame. From that viewpoint, the mass increase to the speeding particle is entirely pertinent as an impediment. But the thrust applied to a rocket propelled spacecraft originates in the craft's own rest frame. I hope the readers here can appreciate that crucial difference! If you try to apply the relativistic mass increase explanation to such spacecraft, naive readers will indubitably be misled and will likely end up loosing sight of the fact that motion through space is after all only relative. ETP 00:03, 31 Jan 2005 (UTC)

Pushing a rod; FTL reaction?

Something that's been bugging me: Imagine a light-year long platform (For the purposes of this experiment we're assuming it wouldn't collapse under its own gravitational field) with two stands on the end, with a super brittle metal rod resting on both stands. If you pushed the rod at one end of the light year long platform, no part of the rod would ever move faster than a few inches per second, but a person at the other end could immediately see that it had been pushed forward a few inches.... Right?

Not quite... No information can be transferred faster than light. Thus, it takes at least a year for the deformation to reach the other end. Otherwise you could send "instant morse" to another person far-far away by just pushing or pulling the rod. From here we can conclude that there is no such thing as infinite stiffness or zero elasticity — one end of the rod is already compressed while the other end is still waiting for the information, lying in perfect peace. The length of the rod is always decreased, when one pushes an end of it and increased, when an end is pulled. Any more interesting questions puzzling you? — Pt _(T) 23:06, 25 Jan 2005 (UTC)

When I push on one end of a metal rod, it compresses the first layer of atoms against the next layer of atoms. The "compression wave" travels at the speed of sound through the rod.

You might also be interested in http://www.amasci.com/miscon/a-rant.html . --DavidCary 03:53, 16 November 2005 (UTC)

Think of this as a proof that even a rod made from Unobtainium can't have a speed of sound that's greater than the speed of light. --Christopher Thomas 04:41, 16 November 2005 (UTC)

There are also some hypothetical cases. 1. Completely rigid object. While no such object was observed, theoretical absolutely rigid object would, by definition, be able transfer information immediately. 2. Object that is in fact a special type of space. A space with significantly increased probability for teleportation of particles in required direction. (imagine how would it speed up computers) 3. A particle that is artificially stretched to both directions, so it appears like solid long rod, or space deforming particle, so the space presents it as a long rod. These rods are extraordinary hard to make, however if they would be made, they could transfer information quicker than constant c in normal vacuum. (Forgot to sign the text) Raghar 20:29, 12 July 2006 (UTC)

Not just hard to make: impossible. PS sign your text. --Michael C. Price ^talk 19:04, 12 July 2006 (UTC)

Eeek, you are talking badly about theoretical physics. ~_^ Raghar 19:55, 26 July 2006 (UTC)

Thanks. But as the previous poster says:

even a rod made from Unobtainium can't have a speed of sound that's greater than the speed of light. --Christopher Thomas 04:41, 16 November 2005 (UTC)

--Michael C. Price ^talk 21:12, 12 July 2006 (UTC)

Note, completely rigid object can't be deformed, so speed of sound in the material is undefined (or defined as much higher than standard c). I wrote these examples because implying an object can't transfer information faster than light, because materials hold together by atomic forces, is rather misleading. Deformations of space, and materials that are in effect one elementary particle are using slightly different rules. Speed of transfer of a shock inside of a black hole would also be very interesting. Raghar 19:55, 26 July 2006 (UTC)

Relative speed

Could someone explain how this works

It is also possible for two objects with mass to travel faster than light relative to one another, from the viewpoint of a stationary observer. For example, particles on opposite sides of a cyclotron.

No. The space-time distortion caused by near-lightspeed travel means that no two objects travelling slower than light can ever perceive each other as moving faster than light, no matter how high their relative velocities with regard to a stationary observer. Lee M 23:45, 11 Jan 2004 (UTC)

Both are correct.

If you put a "stationary" observer in the middle of a circular particle accelerator, they can observe a particle on one side of the ring moving at .999c in one direction, and a particle on the other side moving at .999c in the opposite direction. They will then conclude that the particles are moving at 1.998c relative to each other.

i've tried to correct this. (1) It doesn't matter where the observer is standing. She knows how to measure and calculate distances and times, even if she is not at the centre. (2) i don't understand how she gets 1.998c - she can add up the two numbers, but that just means she does not know how to add up two velocities, it doesn't have any physical meaning. Boud 15:30, 17 Jun 2004 (UTC)

Agreed. There is a difference between Newtonian physics and relativistic physics. --Seraphis 04:54, 16 Apr 2005 (UTC)

Nei'hoor. If I see light travelling to my left, and light travelling to my right, then in my reference frame, I see one with velocity +cê_x and one with velocity -cê_x, and I conclude that the relative motion between the two, in my reference frame, is indeed a speed of 2c. Relativity never disputed that. What relativity disputed was that those photons are moving at 2c relative to each other in their own reference frames. 128.253.197.212 18:09, 10 November 2006 (UTC)

However, an observer traveling with either particle would observe the other particle moving at .9997c (figure made up - I don't remember how to calculate this) relative to themselves.

I'll try to clarify the article.- Zack 23:52, 11 Jan 2004 (UTC)

According to the observer in the lab the two particles would be moving towards eachother at faster than the speed of light. In other words: the distance between the particles would be getting shorter at a rate fater than c. There are other interesting examples of "something" moving faster than light, but no information is ever transmitted. For example: consider a wood plank on the beach, perpendicular to the edge of the water. A wave will pass by and the point where the wavefront and the plank meet will move at the speed of the wave. Now tilt the plank to 45° and this wave/plank meeting place will move a little faster. The more you tilt it the faster it will get and at some point (the plank will be very close to even with the water's edge) this point will move faster than light. (At the limit where the plank really is even you will see "infinite" velocity.) Notice no information can be transmitted down this point. -nick

Nick, can you explain exactly what you are talking about or link to a more complete explanation? As I understand it, there is nothing here illustrating near c speeds. It seems like the situation you describe involves comparing the time difference it takes for a wave to hit the bottom and top of a wooden board and saying that the length of the board divided by time difference is approaching c. The reason being that if the board is 1m and the wave is travelling 5m/s then it will take 1/5s to travel the length of the board. Then if you tilt the top of the board off of the ground so the board is angled at say 89 degrees (approx), it will take a shorter amount of time for the wave to reach the top of the board. Which is true. But what you are forgetting is that the distance the wave has travelled is now shorter. So while it may only take 1/500s to travel to the top, the horizontal distance to the top is now .01m, and the speed of the wave would still be 5m/s. Is this the situation you were trying to describe? 12.135.134.146 00:03, 10 August 2006 (UTC)

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I don't agree with the article's comment that it would be naive for a stationary observer to simply sum the velocities of two approaching near-light-speed objects to find their relative velocity. If, in the observer's frame, the objects are both travelling at c he is perfectly entitled to call their relative velocity in that frame 2c. The photons in two light beams shone towards each other would have a relative velocity of 2c from the point of view of a stationary observer. It is only from the stationary frame of one of the photons that the relative speed would have to be (and is) no greater than c. I think section 5.2 needs a re-write. – drw25 (talk) 16:29, 26 February 2006 (UTC)

Light travels at different speeds?

how can this article incorporate the following:

To quote Richard Feynman "...there is also an amplitude for light to go faster (or slower) than the conventional speed of light. You found out in the last lecture that light doesn't go only in straight lines; now, you find out that it doesn't go only at the speed of light! It may surprise you that there is an amplitude for a photon to go at speeds faster or slower than the conventional speed, c." -- Chapter 3, page 89 of Richard Feynman's book "QED".

That's just "phase velocity" -- the key is that "information" (group velocity) can't travel faster than light. Drernie 20:14, 1 May 2006 (UTC)

NPOV/Clarity

This page is rediculous. While I do not grasp the subject matter (can anyone say they do?) I did notice what I believe to be some obvious problems.

I added a {cleanup-rewrite} tag to suggest this page needs some cleaning up. When I first saw the page, I thought of adding a {tag}. I found more and more that fitted:

• {neutrality} - This article includes just one theory, one interpretation.
• {Limitedgeographicscope} - Please include metric measurements. 12 inches per nanosecond?
• {OriginalResearch} - I guessed this page wasn't put together by people remembering bits from highschool science.
• {disputed} - Without references and source material (even wiki links) no-one can validate this article's claims.
• {technical} - Obviously. Please add some plain descriptions. "Or in other words, how can thrust originating from a rocket's very own rest frame labor under any relativistic effect? It makes no sense at all."
• {cleanup-tone} - The last quote should show that the language leaves something to be desired, for an encyclopedic article.

Well, someone's rewritten the article, and it looks good to my (admittedly unexperienced) eyes, so I'm tentatively removing the {cleanup-rewrite} tag for now, as well as making a few writeovers myself. 70.18.182.39 04:24, 17 Apr 2005 (UTC)

Explaining an edit

I took out this html comment:

"Could someone please re-write this to something Stephen King could understand? What information does this paragraph contain?

The universe on large scales appears homogeneous and isotropic. On second thought, this is rather surprising, since it also holds for those parts that are too far apart to influence each other (for example, seen in opposite direction). Technically, this is expressed by saying they are not within each other's horizon which is limited by the speed of light. Homogeneity and isotropy is explained in the theory of cosmic inflation. The idea is, that objects (such as particles with mass) cannot travel faster than light, but space itself can. In the inflation theory it is assumed that space itself dramatically expands (with velocities much larger than the speed of light) in the first few pico seconds after the Big Bang."

I removed it because the information summarized in that paragraph is the same as that presented lower down:

"The expansion of the universe causes distant galaxies to recede from us faster than the speed of light, if comoving distance and cosmological time are used to calculate the speeds of these galaxies. However, in general relativity, velocity is a local notion, so velocity calculated using comoving coordinates does not have any simple relation to velocity calculated locally."

70.18.182.39 04:36, 17 Apr 2005 (UTC)

Cleaned up wording, sectioning, and removed incomprehensible section on .. eh, something. - Ec5618 10:18, Apr 18, 2005 (UTC)

I think it is pertinent to mention that big bang inflation theory requires space to move ftl. Puddytang 19:06, 3 February 2007 (UTC)

Speed and distance or time

I've been wondering; if adding up velocities isn't as simple as v1+v2=Vtotal, what does that say about the distance covered. Time dilation can't be dependant on the subjective frame of reference, can it. The article doesn't cover this.

So, what is the relation, in relativity, between speed, distance and time?

Ec5618 12:21, Apr 20, 2005 (UTC)

Time dilation is a relative phenomenon, although this seems paradoxical. If you and I have high relative velocities, I see your clock as running slow - and you see my clock as running slow. This means that we can synchronize our watches when we pass each other, but after that neither of us can agree which event happens first: an hour passes on my watch, and an hour passes on your watch. That's because for events that are not at the same location, observers may not agree on which one happens first. --Andrew 12:57, Apr 20, 2005 (UTC)

So, you're saying time is relative. What does that mean about distance? When I accelerate to half LS, and so so again (relative to a probe or something I drop at half LS), will I be moving at full light speed? Will I, and my frame of reference, reach alpha centaury in 4.4 years, or will it take longer? Will people on Earth think I've travelled something like 40 years when I land? Is that what the time dilation means? -- Ec5618 13:27, Apr 20, 2005 (UTC)

This is quite complicated; I think it's better explained at special relativity than I can pull off here. --Andrew 13:54, Apr 20, 2005 (UTC)

From the frame of reference of something travelling at the speed of light you will get there instantly. So, from a light beams point of view, it takes zero seconds to travel from the sun to the earth and zero seconds to travel across the entire universe. But because of inflation, light can never cross the entire universe--so does this mean it takes infinite time to cross the universe? If you travelled faster than light does that mean you would get there faster than instantly? The article states that you would appear to time travel from other frames of reference but that's not the real problem. From your own frame of reference you get there just before you left-creating a Zeno's Paradox where you never actually get to leave. Puddytang 19:18, 3 February 2007 (UTC)

In other words: Over a distance of 100 light years, if you were to somehow come up with a method of propulsion that allowed you to traverse the distance in 50 years, you would actually reach the end of the 100 ly distance before you left Since you are taveling double the speed of light, you would seem to reach your destination just as long before you left as it "actually" took you to get there. Thus, at a distance of 100 light years, 50 years = negative 50 years. However, at a distance of 25 light years, reaching a destination in 50 years does not mean you arrived before you left. So the (supposed) relationship between speed, distance, and time, is that if the time it takes to traverse a distance less the same as the time it takes light to traverse the same distance, no time has been taken at all. If the time is half, you've actually traveled backward through time.

Unfortunately, light from Alpha Centauri does not reach us the moment it left Alpha Centauri, and when looking at Alpha Centauri through a telescope, we do not see it as it appears now, but as it appeared four years ago. The whole idea of FTL equalling time travel is bogus. 50 years is 50 years, whether you travel an inch or a thousand lightyears in that time, 50 years is still 50 years. FTL would never result in time travel, nor would it cause problems with causality. These are fanciful "theories" that will one day be looked back upon as humors, blood-letting, and flu-demons: with utter ridicule. Mutability is both science's greatest strength and greatest weakness; a strength in that it is adaptive and constantly improving, but a weakness in that one can never be quite sure which of today's sciences will be tomorrows superstitions. --Þórrstejn [ˡθoɝ.staɪʲn]: Hammer of Thor ^talk 17:39, 8 August 2007 (UTC)

"Impossible" vs. "Probably impossible"

An anonymous user revised the opening paragraph to state that FTL was outright impossible under our current understanding of physics. I've replaced this with a more reasonable caveat (I'll agree that the original version that the anon user replaced was badly worded). FTL isn't outright forbidden by the laws of physics as currently known. It just requires fairly exotic conditions, and would have very peculiar side effects. Anything that generates a closed timelike curve in GR will allow time travel, which looks like FTL from other reference frames (the two are equivalent in SR and GR). Further, the laws of special relativity (and, if I understand correctly, general relativity) are compatible with the existence of particles that travel FTL, for which the speed of light is a _lower_ bound to velocity (see tachyon). While it is strongly suspected that some as-yet-undiscovered mechanism will outlaw all closed timelike curves, and that the idea of FTL particles like tachyons is only valid in certain cases (see tachyon condensation), nobody's actually managed to _prove_ it in an all-encompassing manner yet, so it remains an open question. --Christopher Thomas 02:19, 30 May 2005 (UTC)

Science has a long history of proving things impossible which were later done Puddytang 19:21, 3 February 2007 (UTC)

Cleanup and refocus

I find the current article a) confusing, and b) redundant with the Theory of Relativity article. I propose refactoring the article to precisely define and address the feasibility of FTL based on our current known (and theorized) understanding of physics (I am a former physicist, who gets asked this question a lot, so I'm hoping this article would provide a substantial answer). Look for a lot of commits in the near future, and please let me know if you have concerns/suggestions.Drernie 28 June 2005 23:39 (UTC)

I haven't heard any comments, and the more I look at it the more the "relativity" section seems redundant with the other articles. Unless someone objects, I plan to remove that section, and putting the relevant material under "Possibilities" or "Apparent".Drernie 6 July 2005 15:20 (UTC)

Done. Still rough (additional cleanup welcome), but I find this much more coherent and much less duplicative.Drernie 6 July 2005 15:44 (UTC)

As far as I can tell, FTL is only prevented by conventional physics, but is fully possible in quantum physics, especially with CTC's and wormholes (which have now been shown to exist, alebeit at a sub-atomic scale. But the entirety of existance is awash in them.) —The preceding unsigned comment was added by Starfyredragon (talk • contribs) on 22:53, 29 April 2006.

Sigh. FTL isssues are a feature of "special relativity", which is explicitly consistent with quantum mechanics. The issue is that quantum mechanics is _not_ consistent with "general relativity", and there's areas where it is unclear how all three of them interact. I think the article makes that clear, but if not, please make sure your fixes reflect that distinctions. Drernie

Causality?

"Should FTL travel or communication be possible, problems with causality will almost certainly occur."

Why? --Corvun 05:03, August 15, 2005 (UTC)

Erm did you mean to ask this question so many times?

Sorry, on my end it didn't even look like the question showed up at all, the page didn't show any changes when I refreshed, didn't get put on my watchlist (I'm set up to watch pages by default), or anything. I eventually just gave up. It wasn't until I checked my contributions page just now that I discovered this showed up here. I have no idea why it duplicated so many times like that. A bug, maybe? --Corvun 06:22, September 11, 2005 (UTC)

That's an interesting question. When I asked it as well, I either received tautology, or some examples that used a mirrage effects based on speed of light, and caused no violation of causality (if author wasn't misslead by his own explanation) if converted to a global frame of refference, or if viewed by an observer that wasn't restricted by speed of light. Raghar 19:45, 16 December 2005 (UTC)

I'll try to answer, but it's been a very long time since I learned this stuff, so I may not be able to do better than you've already seen.

In special relativity, observers in different reference frames may not agree on the order of events separated by a spacelike interval. That's fine as long as those events have no causal connection. But, if you send a message from spacetime position A to spacetime position B faster than light, some observers will see it arrive before it was sent. It is possible to argue that those observers are just mistaken... but a basic principle of the theory is that no observer is "privileged", i.e. you don't ever say that an observer was in the "wrong" reference frame to see what "really" happened.

In general relativity, it's worse. If you allow FTL, you can bend a world line into a "closed timelike curve" -- a trajectory that encounters itself in its own past. This is exactly the classic time-travel scenario, leading to situations like the grandfather paradox. (You may not even need general relativity for this; I'm not sure.) There are patches for this problem, like the Novikov self-consistency principle, though.

Personally I think that giving up causality (or weakening it a bit, as the Novikov theory does) would be just fine, but I'm not a theoretical physicist.

Zack 21:51, 16 December 2005 (UTC)

So, using a pop-culture reference as an example, special relativity states that something like "the Picard Maneuver" in Star Trek (in which a starship makes a FTL "jump" toward an observer, causing the observer to see two starships when the light emitted from the starship when it was further away and the light emitted from the starship at the end of its "jump" reach the reciever simultaneously) would not simply be an optical illusion, but an actual case of causality violation? This would seem to imply that if we look through a telescope at something a lightyear away, we are not seeing as it appeared a year ago, but as it appears now, even though it took a year for the light to reach us; so what happened a year ago is actually happening now.

Just because we don't presume any observer is "priveledged", does that necessary imply that every observer is correct? Can't every observer be incorrect? Since observation apparently can't happen faster than light, how do we know FTL would cause contradiction in causality and not just contradictions in the observation of causality? I know observation and expiramentation are the cornerstones of good science, but does that necessarily entail that observation must always equal reality?

I'm forced to wonder: If all our methods of observation were sound-based, would the same "contradictions" be proposed in supersonic travel? Using the pop-culture reference above: The "two" starships could never actually interact with each other, because there has only ever been one. One might be able to create the illusion of interaction, just as if one traveling faster than the speed of sound could create the illusion of answering his own question before it were asked, but this is not the same as a causality violation.

The big question is: Who set the speed of causality at the speed of observation? --Corvun 08:46, 19 August 2006 (UTC)

Well, elsewhere on this page someone comments that using a lightyear-long pole to type a message in morse code instantaneousley a lightyear away would be impossible because it would take at least a year for the "spacetime distortion" to move from one end of the pole to the other. Why, exactly, an instantaneous reception of the message would cause problems in causality has never really been adequately explained. The so-called "explanations" are invariably tautologous — usually something along the lines of an affirmation that the speed of light is instantaneous, and that traveling one lightyear in a year is the same as reaching a location one lightyear away the instant one left. The natural consequence of this is that if someone were to travel to Alpha Centaurii in 6 months, one would reach the destination before having left, even though the destination is actually reached 6 months later. And that is the true paradox. It isn't that FTL would violate causality, it's that the assumption that FTL would violate causality results in paradoxical "solutions" to thought-experiments. Without the assumption that the finite speed of light is somehow infinite, and that traveling a lightyear's distance in under a year constitutes time travel, there is simply no way to justify the idea that FTL will result in causality violations. It's nought but a load of circular reasoning, necessary because were it admitted that events could occur faster than they could be observed, "science" as it is currently misrepresented could not quantify it, making it akin to what circular-minded scientists would term "magic".

As far as the pop-culture reference to Star Trek: Physicists need presume that the appearence of "two" starships would not be an optical illusion (because no observer is "priveledged", even though this does not require any such thing; requiring instead that every hypothetical observer be equally mistaken; such a notion — that observation may, in fact, yield an untruth — being shear heresy to most so-called "scientists" whose fancy degrees show merely that they've paper for brains), that there would actually briefly exist two starships, and that causality would be violated, again, because to admit otherwise would mean that events are possible which are impossible to observe. And once the possibility of things occuring that cannot be observed enters the equation, the science of the day may be found to be inadequate to explain Everything(tm) and the ultra-conservative, backward-thinking dogmatists who in-not-so-many-words hold desperately to the belief that there is simply nothing left in the Universe to learn, find themselves threatened and insulted by the very notion that present-day science could possibly have any room to improve, and will make any excuses they possibly can to ensure that no-one think science in the future might possibly invalidate current assumptions or be in any way superior than the science of today. --Þorstejnn 12:24, 13 June 2007 (UTC)

More Reading

Why Can't We Travel Faster than Light?

Speed of Gravity

I've removed the long speculation that used to be here to a sub-page: /Is Gravity Faster than Light? I have nothing against the author, in fact I credit him or her for not putting it in the article proper (where it would be inappropriate, being unconfirmed scientific speculation) but I'm a bit tired of seeing the tweaks go by on my watchlist. On a subpage, those who are interested can follow. (I'm not sure it belongs in Wikipedia at all, but I will give the author the benefit of the doubt for now.)

It would be good to say something about the speed of gravity in the article proper -- perhaps something like

How fast gravity propagates is an open question in modern physics. General relativity assumes(?) that it propagates at the speed of light; most theories of quantum gravity postulate zero-mass gravitons as the force carrier, which would move at the speed of light, like all other zero-mass particles. However, this has not yet been confirmed experimentally, due to the difficulty of detecting gravity waves.

and then go on to mention that recent experiment that I remember reading about but not in any detail... also, could someone factcheck me on general relativity?

Zack 20:04, 18 December 2005 (UTC)

FTL in fiction

An anonymous contributor added a paragraph about accomplishing FTL travel using hyperspace. I've cleaned it up so that it's in approximately appropriate form, but I'm not sure if it belongs in the section it's in. It might be useful to split the "possibility of FTL" section into "approaches to FTL in non-fiction" and "approaches to FTL in fiction" to address this. Comments? --Christopher Thomas 04:28, 10 February 2006 (UTC)

I have seen a very good article that explained that if gavity wasn't instantaneous propagating, but rather at the speed of light, the planets wouldn't have stable orbits. Think of it !

Gravity does propagate at the speed of light. I can imagine this might cause planets to not have stable orbits for an infinitely long time, but they would still be stable for a very long time. Rotiro

'Hyper'Luminal speed

I found a USA today article about the Big Bang. This is the opening paragraph:

The universe expanded rapidly — growing from the size of a marble to billions of light years across — within the first trillionth of a second after its cataclysmic birth, astrophysicists reported Thursday.[1]

I know that light is much slower that this. I don't know if it would fit somewhere within the FTL article, but I am a bringing it to your attention.--Doom Child 22:21, 17 March 2006 (UTC)

The USA Today article is talking about cosmic inflation -- have a read of that page for starters. In inflationary theories, the speed of expansion of the universe is not limited by relativity, but I'm afraid I can't explain why (however, notice that such expansion cannot violate causality, as nothing ever gets closer to anything). We should mention this in the article, yes, it deserves a couple sentences under "Universal expansion", but I'm not the person to write it. -- Zack 08:28, 12 April 2006 (UTC)

The article is right and it doesn't contradict the theory or relativity. I've added plain-english explanation to the article: "In other words, the galaxies (or more accurately, galaxy clusters) do not physically move away from each other. Rather, the fabric of spacetime between them expands. This also explains the Inflationary epoch during the Big Bang, when the universe expanded from a size a hundred billion times smaller than a proton to approximately one hundred million light years in diameter in just 10^-32 of a second." -- Ron g 18:14, 24 June 2006 (UTC)

Re: Option E

[2] May I point your attention towards this article, New Scientist 01/06?

Certainly, the drive mentioned based on Heim theory seems to satisfy the requisite of "going somewhere Special Relativity doesn't apply." At any rate, having been recognised by the American Institute of Aeronautics and Astronautics would definitely qualify as having been "seriously proposed by mainstream science." --Xanthine 14:58, 27 March 2006 (UTC)

Superluminosity In General

I find that most people discussing this topic are unaware of the more important works by such people as Lambert Dolphin (on the speed of light versus time), Laro Schatzer (on flaws in relativity), Leo Van Dromme (on causality versus the superluminal), Guenter Nimtz (on superluminal microwave communication as accomplished fact), Lijun Wang (on light rephasing to achieve v > c to the tune of 1,000 times or better), Lene Hau (slowing light down to zero, holding it, and releasing it again), and a host of others published in various journals including New Scientist (a protege of Kantor, demonstrating that velocities do indeed add, and that "demonstrations" to the contrary fail to take into account the renormalization of c to the local reference upon absorption and re-emission). And all this is barely scratching the surface. I could throw in a list of references from the book "Mysterious Universe" by Dr. William R. Corliss, but most people I encounter have never even heard of either him or his book. I could really clobber this subject, but I'll just post these comments and see what hits the...well, you know. Here's something to chew on: http://www.geocities.com/your_neighbor_2000/Super_1B.html ---MAS 03 April 2006 2:45 PM CDT

On the contrary, most of the editors who have physics backgrounds are aware of most of these items that you cite. No demonstration to date has unambiguously demonstrated transfer of information faster than light. If superluminal microwave communication was an "established fact", as you state, then it would have been front-page news, as it has a number of very substantial consequences that are beyond the scope of this reply. As for your other points, you can easily make the phase velocity of light anything you please; this is where the "1000 times faster than light" and "slowing and stopping light" reports come from. Altering the phase velocity doesn't let you send particles or data faster than C. Lastly, you will find that it'll be extremely difficult to get people to take a Geocities page seriously as a reference. Research papers _will_ be available directly online, or at minimum cited on the web pages of the researchers involved, which will be hosted by their respective institutions. Your user page's assertation to the contrary is, frankly, rather puzzling. --Christopher Thomas 22:07, 3 April 2006 (UTC)

RE - If superluminal microwave communication was an "established fact", as you state,

then it would have been front-page news.... It has been done, and it was front

page news. This was some years ago. It's even been on PBS in reruns. But...well...it's

the 1890s all over again.... ---MAS 04 April 2006 6:03 PM CDT

I have scanned some of your references on a varying speed of light. I can't tell from the references what the speed of light is varying with respect to. According to the Wikipedia article called meter, a meter is defined as the length of the path travelled by light in an absolute vacuum during a time interval of 1/299,792,458 of a second. Thus the speed of light is 299,792,458 meters/second in a vacuum, always. Even if it "wanted to change" it couldn't, because the length of a meter would change with it. So when your references say that the speed of light is changing, they mean with respect to something other than meters/second. For example, some authors compare it to the electromagnetic coupling constant. It may well be changing with respect to the electromagnetic coupling constant, but one could equivalently say that the speed of light is fixed and the coupling constant changes. The speed of light also changes if I measure it in units of the speed of my car. That said, maybe a set of units in which the electromagnetic coupling constant is fixed are better than units in which the speed of light is fixed for certain applications, in that case, you can use those units and say that the speed of light changes. But the statement that the speed of light changes without fixing a reference velocity is vacuous.

I have also looked at your geocities reference. While the author seems to have read some articles, the article has a lot of mistakes. He even catches his own mistake when he uses a Newtonian approximation in the ultrarelativistic regime (its no surprise that you can break the speed of light in a Newtonian approximation).

However one part of this article I found to be very concrete, in the very beginning the author cites a unique piece of evidence for superluminal velocities, ultra high energy cosmic rays. So here's something concrete that one can use to set up an argument. There is no frame of reference with respect to which these cosmic rays move faster than the speed of light. My guess is that the faster than light number was arrived at as follows. Consider a cosmic ray that flies from the center of the Milky Way to Palo Alto. In the reference frame of an experimentalist on Earth, this cosmic ray traveled 30,000 light years, and it took just over 30,000 years to complete the trip so everything is fine with relativity. From the point of view of the particle, the trip took a few minutes. Thus, I'd guess that the author divides the experimentalists distance (30,000 light years) by the particle's time (a few minutes) to arrive at a velocity much bigger than the speed of light. The resulting velocity may be an important figure to consider, for example if a space tourist wants to see the center of the galaxy before he dies. However it doesn't pose any problem to special relativity, because in the frame of the particle the distance from the center of the galaxy to the south bay is only a few million kilometers, and so the Earth doesn't really hurl towards it any faster than the speed of light (as a few million kilometers divided by a few minutes is less than the speed of light). So relativity is saved, as nothing exceeded the speed of light in any frame, and space tourists are happy too because they can get where they like during their lifetime, although whoever they were going to visit will be long dead when they arrive. JarahE 20:56, 6 April 2006 (UTC)

Please elaborate on what you mean by, "his mistake?" And the subsequent "correction?"

I should be interested to see what you are talking about. ---MAS 06 April 2006 5:55 PM CDT

I am refering to the first few sentences in the section "Calculating the superluminal velocity". The mistake is to use the Newtonian approx where it doesn't apply. He knows it. His only comment is to remember that the relativistic mass is the sum of two terms, which while true, is a nonsequator. The Newtonian approx isn't compatible with special relativity at high speeds, so if you use it, you are considering a different theory (ie, not relativity, which experimentally has been very well tested, for example its corrections to the GPS work perfectly, a Newtonian approx there would give you the wrong answer).Jarah

Ok here's where some scientists are saying that yes you can send information faster than the speed of light Reference = http://www.pbs.org/wgbh/nova/transcripts/2612time.html

GUENTER NIMTZ: Yeah, some colleagues are claiming that you cannot send information and then we started to transmit Mozart 40 and this is for instance the original tape. That's what we sent at a speed of 4.7 times the velocity of light and a distance of about 14 centimeters, whether you can recognize Mozart 40 or not.

NARRATOR: Despite the randomness and uncertainty of the tunneling process, Mozart seems to have gone through the barrier.

RAYMOND CHIAO: The essential question is: what is a signal, or what constitutes information? Has he really sent a signal in the sense of information faster than the speed of light? This is where Professor Nimtz and I part company because we don't really have a rigorous definition of what is information at the quantum level.

GUENTER NIMTZ: Maybe that this is not information for American colleague, but for a German or a British colleague, I think Mozart 40 has some information in it.

NARRATOR: Transmitting Mozart is one thing, convincing others that you have sent it faster than light is another. And so the debate continues, with neither side budging.

GUENTER NIMTZ: I consist - no, no, I not consist, I insist on it that we have and we can transmit signals faster than the velocity of light.

This seems pretty reliable to me you can read the whole transcript if you want to understand the debate.. and i think it is a debate wikipedia should not state unequvocally that no information transfer is possible..

From PNA/Physics

• Faster-than-light: Talk:Faster-than-light has attracted the attention of a user editing from IP 199.80.75.2 (talk • contribs), using the signature of Masolis (talk • contribs). I don't have a strong enough physics background to make an ironclad rebuttal of his claims; if one of the lurking physicists could spell out all of the things he's misinterpreting, it would be greatly appreciated. I just caught the phase velocity vs. signal velocity mistakes. --Christopher Thomas 22:13, 3 April 2006 (UTC)

I'm not sure how to make an ironclad rebuttal, because the article that he cites seems completely disconnected from our world. For example, it uses the Newtonian approximation in the very relativistic regime, with a surreal justification. The only connection of this article to the real world is the Oh my god particle, which it mentions in the beginning in its evidence of the discovery of superluminal particles. These aren't superluminal. The small time that, according to this article, it takes these particles to go large distances is probably the time as measured in the particle's frame, and the distance is measured in our frame. The ratio of one observer's distance to another observer's time can be more than the speed of light, as it doesn't correspond to a speed in anybody's frame. But maybe that's all he means by faster than light travel? JarahE 20:01, 5 April 2006 (UTC)

Even telling him what you've posted in your first three or four sentences here could help. --Christopher Thomas 21:31, 5 April 2006 (UTC)

In Talk:Faster-than-light, User:Masolis (apparently an EE by training) mentions a number of names which he thought would be unfamiliar to us at WP. Alas, they are not:

• Lambert Dolphin has published in the crank journal Galilean Electrodynamics and used to host Tom Van Flandern's writings before the appearance of Van Flandern's Meta Research, Inc. website. In the Galilean Electrodynamics paper, Dolphin was listed as a "physicist" and his coauthor, Alan Montgomery, as a "mathematician", but I don't recall whether they had any academic affiliations. Years ago Dolphin posted to UseNet; his writings are still sometimes mentioned at one or two crank websites.
• Laro Schatzer was on the physics faculty of the University of Basel, but I think he has retired. Schatzer wrote a paper promoting the cranky Yilmaz theory of gravitation (I don't recall if this was ever published anywhere); his ideas are promoted as such websites as Borderland Science, the ufo crank website National UFO Reporting Center, the freelunch/anti-gravity crank website Keely net (see John Ernst Worrell Keely for their hero), etc.
• Lijun Wang's work reports on phase velocity; no energy or information is transmitted faster than c.
• Lene V. Hau (she's a she, BTW) has slowed light in a Bose-Einstein condensate; I don't know why Masolis thinks this is relevant.
• William R. Corliss has a cranky website called Science Frontiers Digest of Scientific Anomalies which seems to have been set up for him by Ian Tresman, to whom are registered an impressive number of pro-catastrophism, pro-plasma cosmology and generally anti-Big Bang websites.

Masolis remarked that he regards someone as (a protege of Kantor, demonstrating that velocities do indeed add, and that "demonstrations" to the contrary fail to take into account the renormalization of c to the local reference upon absorption and re-emission). This parenthetical comment probably refers to Laro Schatzer.

Hope I'm not annoying anyone with * -> : since I find it easier to track who is replying to whom with indentations. ---CH 22:35, 7 April 2006 (UTC)

String Theory?

What if you consider FTL from String Theory? How does it then work then? Is it possible when you add String Theory as a factor?

Nope, String Theory -- like everything else in modern physics -- is explicitly built on top of special relativity.Drernie 16:12, 13 April 2006 (UTC)

Superluminal effects can be immaginated with the M-Theory wich links main theories about superstrings. .Bastien Sens-Méyé 14:59, 05 sptember 2007

Question from inexperienced person

IF we managed to travel at or faster then the speed of light, and we were in an object with mass which had a "window" or a thing which allowed you to view space in real time, and send messages like sound or light through it. If you shone a flashlight from this object that was moving at or faster then the speed of light, would this light beam be going faster then light? What would be the effect? RandomGuy7 11:30, 6 June 2006 (UTC)

The speed of light is relative. A simpler example would be "what would happen if you walk forward with a lit flashlight in your hand?" The answer is yes, the light would be traveling faster than "the speed of light." That is why the speed of light in a vacuum is explicitly stated to avoid confusion when talking about such situations. Ziiv 08:05, 30 June 2006 (UTC)

This is a little unclear. What actually happens (under SR) is, observers in all (non-accelerating) reference frames see the emitted light moving at C relative to themselves. The person in the FTL craft sees light moving away from themselves at C, while people in the "stationary world" (people relative to whom the craft was moving FTL) also see the light moving at C relative to themselves. This causes very odd effects with observers moving FTL relative to each other (see tachyon), and is usually assumed to be unphysical (in other words, to correspond to a situation that can't actually occur). --Christopher Thomas 14:32, 30 June 2006 (UTC)

Delete this?

"Almost every thought that says that something cannot be accelerated past lightspeed makes one major case: We cannot generate infinite energy. However, if infinite energy could be created, it would be quite possible to get past light speed.[citation needed] Although this may at first thought violate the idea of conservation of energy, this is not completely the case. The idea of conservation of matter is the idea of a universal constant amount of energy, not necessarily a local. To put it simply, "To create infinite from 0, you need to also create negative infinite."[citation needed]"

My TI-89 says that infinity minus infinity is undefined. I propose that this section be deleted. Ziiv 06:52, 30 June 2006 (UTC)

This sounds like gibberish and/or OR. Go ahead and axe it. --Christopher Thomas 07:19, 30 June 2006 (UTC)

done. Ziiv 08:01, 30 June 2006 (UTC)

FTL without reference to information transmission possible? And a timing question

Now, this is coming from someone without sufficient physics background - however, what I see here in the article regarding some problems and paradoxes with FTL is that since information cannot travel faster than c, FTL would violate rule of casuality. Are we assuming information must be conducted via light or similiar particles though? I am not proposing something else can be the medium or a medium is not required, I am not clear enough on the subject to discuss about that; rather, I am asking why must these be included in the possibility of FTL as a constraint? Consider the following:

Suppose we are all blind and we have no method of perceiving our surrouding (and thus, transmit information) other than, say, the sense of feeling by touching something tangible, such as each other. In which case, how is the law of casuality violated? It matters not the speed of travel, since information is transmitted from person A to person B by the physical presence of person A near person B (and touching person B via some body language). Person B need not be aware of person A before receiving this information (the time "before" base on the frame of time reference of person B).

Another unrelated question which puzzles me - if someone travels at c to a location that is 1 year away, it takes 1 year from other observers in their frame of reference, but what about the traveler? DIscussions on relativity indicates that a clock that is traveling with greater velocity will slow down more (and stop at c), relative to observers. Does that mean the traveler will experience instantaneous transportation since time does not flow in his own frame of reference? Further on this idea, what would happen to the local time of the traveler if the speed exceeds c? Would time flow become negative? --Allan Lee 20:20, 30 June 2006 (UTC)

Without addressing all your points, it is relevant to note that Gerald Feinberg showed that even FTL particles (tachyons) can't transmit information FTL, via a mechanism he proposed called the reinterpretation principle. (Yes, I realise how insane such a proposal sounds, believe me!) At some stage I'll be updating the tachyons article to incorporate this, so far it just contains the Feinberg reference. --Michael C. Price ^talk 20:35, 30 June 2006 (UTC)

Updated. --Michael C. Price ^talk 04:07, 5 July 2006 (UTC)

I guess I am trying to figure out why is it that we limit ourself by creating a limit (speed of light being the limit, and we created such limit due to the fact it's the fastest thing we can observe directly or indirectly). What's fundenmentally different for c from any other (lower) speed if we temporarily ignore the fact light is also a primarily medium of conducting information for us?

We do not "limit ourself" with c, we observe that c is the speed of light predicted by Maxwell's equations.--Michael C. Price ^talk 04:07, 5 July 2006 (UTC)

What's the difference between I travel from one place to another at 60 mph and say "Hi" to someone, and I travel at c or faster than c to do so? Information is trasmitted when I arrive, the difference is the time expended. Or, why is it problematic if I shine a beam of light towards you, travel faster than the beam of light to you, and say that a light will be coming soon? Why is that different than, say, me sending a regular mail to you, and before the mail arrive, drive to your place (or email you) to say that a mail from me is coming? Allan Lee 18:14, 4 July 2006 (UTC)

FTL = For The Lose

Please Fix

Uncited

Mitchell Pfenning worked out the math involved and discovered that you could only warp a small amount (1/100th the size of an atom) and the energy required is 10 billion times that of entire universe.[citation needed] Does Wikipedia put up with such allegations? --195.210.193.14 12:31, 26 July 2006 (UTC)

speed of thought

What about thought? According to Heisenberg’s uncertainty principle at a point in the curve of the space time continuum energy becomes thought. if things without mass can travel beyond the speed of light then what about things with no mass, or energy out put? if so how fast would thought travel, and how would we measure something that moves faster than the fastest thing we can perceive. —The preceding unsigned comment was added by 158.135.1.92 (talk • contribs) on 17:52, 29 August 2006.

The Heisenberg uncertainty principle says nothing at all about thought. It says you can't simultaneously measure the position and momentum of an object with arbitrary precision, because measuring one perturbs the other. Speed of signal propagation is performed by measuring the relative arrival times of the signal being measured, and a signal with a known propagation time (typically a laser beam). --Christopher Thomas 18:36, 29 August 2006 (UTC)

Tunneling can be instantaneous

In the last years there were many observations of superluminal transmission of signals at specific conditions. If these observations are real - they were fixed in different laboratories by known experimentalists - there was two possibility: or really at certain conditions can exist superluminal phenomena with different speeds, or at some part of way the transmission can be instantaneous, but on other way with usual speed. Then the averaging over all path can give different results at different experiments. Just the last possibility became real, so in my article: Annalen der Physik (Leipzig), vol.14, p.733 (2005) and also in the arXiv:phys/0309123 is strongly proved in the covariant form such theorem: at very specific conditions signal transmits instantaneously in the limits of near field. For this phenomenon is needed a definite deficit of energy ΔE relative momentum, i.e. tunneling regime on the distance Δx such that ΔEΔx=π. This expression is near to the uncertainty relation, but slightly bigger and it can describe all recent observations of superluminal transfer of excitations. Such phenomenon represents "the nonlocality in the small". Mark Perel'man 12:24, 31 August 2006 (UTC)Mark Perel'man

Negative energy undiscovered but only insignificantly

I'm having trouble following this sentence in the article:

"Unfortunately, such warping would require the emission of negative energy, which has not yet been discovered or created in significant quantities."

How can something be both undiscovered and not created in significant quantities?

The sentence implies a contradiction. If deliberately so, the connection with the concept of "un/discovered" could be clarified here. Best wishes. Anon. 58.178.197.225 00:00, 6 September 2006 (UTC)

Maybe I missed this somewhere on the page

If a traveller were going near the speed of light (relative to Earth observers), that traveller would still perceive the speed of liught to be the same from their viewpoint. i.e. the traditional, is the traveller moving away from the Earth at the speed of light, or is the Earth moving away from the traveller at the speed of light?

If the speed of light is constant independent of the velocity of the vessel, for example, of where he is being measured, the speed of light should be the same when measured on the earth and on the travelers ship. Furthermore, although the mass of the traveler would be increasing as they approached the speed of light, their perception of time would be slower relative to the earth.

So although the traveler would be approaching the speed of light (from the earth's prospective) and it might appear that their mass is approaching infinity (and thus it would require them more and more energy), to the traveler their relative observations would be that their mass has not changed and they are still putting the same amount of energy to achieve the same acceleration.

If I'm not mistaken, the traveler, although going near the speed of light as seen from the earth, from the traveler's perspective they are not near the speed of light. It could even be seen that they are not moving, and it is instead the space around them that is.

I'm sure that somebody has already posed this theory, so perhaps my understanding of the subject matter is mistaken. Could somebody please clear this up for me? Thanks. 68.81.198.36 19:13, 4 October 2006 (UTC)

Yep, that's abot it. Even when accelorating, people can think of themselves as still and everything else as moving. This is coered in Special and General Relativity. 67.190.111.238 00:53, 11 October 2006 (UTC)

page revamping

Considering this page is a mess, I'd like to spend next 3 months improving this page. Basically I'd like to split it into at least three pages, to make it more consistent, and allow modification of possible recent events without affecting the core page.

First I'd like to create something like a preview section, where would be the new page until reasonably ready to replace the old page. Considering I don't have too much experience with advanced editing of the wikipedia. How should I create preview section?

Is anyone here able to visit a US/UK library and look into old books for proper quotes? I'd post on Usenet a little to get some list of recommended citations, and pieces of history I might forgot.Raghar 17:53, 16 October 2006 (UTC)

So first round of reference gathering is done, and the concept looks nice. In fact it looks too nice, I'd post simplified (and safer) version here for future editing, and a more complex and more fragile version at some free server. I doubt wikipedia would survive article over 2.5 pages long. ~_^

So plan for action is this. In a few days create a preview subpage to avoid shock of all viewers. Do things, then after two-five weeks verify if that preview subpage didn't change itself into bloatware, and count amount of death threats. If all passes reasonably, copy the result as the main page.

Also I would like to add some FAQ subpage with questions like these from Ahmed, and other questions from talk pages. Raghar 15:30, 20 November 2006 (UTC)

---

Time travel may or may not be possible, i would like to know the contraints for faster than light travel Is it possible any object that is constantly accelerated will reach infinite velocity ? If it is . Then particle accelerators which circularly accelerate the plasma to near speed of light can be arranged to overshoot the light velocity barrier, objects can be magnetically levitated in a vaccum and constantly thrashed to gain velocity in the ring arrangement of particle accelerators. please tell me what are the constraints the object will not attain the velocity of light ?
thanks
Ahmed 14:01, 26 October 2006 (UTC)

---

FTL and Negative Energy

According to this article, it has been shown that any scheme for faster than light travel requires the useage of negative energy.

And, also according to the afformentioned article, quantum mechanics poses stringent restrictions on the separation of negative energy from positive. A pulse of negative energy must be followed up with a positive pulse that cancels it out.

Which is good news for physicists. Unrestricted negative energy would violate the laws of thermodynamics, allowing perpetual motion machines, time travel, violation of cosmic censorship etc.

However, I'm curious. I've got a question for a lurking physicist

On plank scales, small quantum wormholes popping in and out of existence all the time.

So what if you used a short pulse of negative energy to inflate one of these wormholes (which might be helped by the wormhole's own gravity providing it's own negative energy via hawking radiation - which leads to a degree of self-inflation), and then used the following pulse of energy to collapse the wormhole); would you be able to keep it open just long enough to sneak through before it collapsed?

So you would stand as close to the expanding wormhole as you could, so that you're roughly central when it expands, and then when you collapse the wormhole with the ensuring pulse of +ve energy, you do so at a point 'behind' your current position, so that when the wormhole collapses, you are already on the other side. Is this allowed by the laws of physics, or have I gone seriously wrong somewhere?

--195.93.21.105 20:02, 3 November 2006 (UTC)

The problem is, that *because* it is all happening under the quantum limit, you can never know it is there. Plus, these really gets into the realm of quantum gravity, where "the known laws of physics break down." Thus, it is possible that sub-Planck-scale particles could use, but we don't know (yet). More importantly, though, anything macroscopic enough to convey information would disrupt the wormhole.

Worse, last I checked it still takes an infinite amount of time to enter or leave a wormhole (unless you violate cosmic censorship) so from the perspective of an outside observer the message would never quite enter (or leave) the warmhole. Sorry. :-) Drernie 21:17, 3 November 2006 (UTC)

Tachyon revamp

Most of the material at the tachyon section -- which seems rather confused or irrelevant -- is duplicated within the tachyon main article (the latter has a lot of extra information). Anyone object to this section just being a main article redirect? --Michael C. Price ^talk 08:27, 7 November 2006 (UTC)

I agree, as it stands now it only clutters the article and distracts from the main subject. 81.70.212.33 00:13, 13 November 2006 (UTC)

Done. Section trimmed and main article pointer added. --Michael C. Price ^talk 10:28, 13 November 2006 (UTC)

Opening question??

The opening question to this article reads 'Unsolved problems in physics: Is it possible to go faster than the speed of light? If so, would it violate the theoretical principles of the universe?'. I think this is poorly phrased. If something is observed in nature then by definition it does not violate nature's 'theoretical principles'. Changed it to something less ambiguous. 81.70.212.33 00:10, 13 November 2006 (UTC)

Revisions are required to improve the "scientificness"

I have made a number of revisions in an attempt that this page will not give the wrong impression to anyone who doesn't know much about science. I think more revisions are needed to express the fact that at this time there is no physically realistic mechanism for faster than light travel/communication. None of the approaches for FTL listed on the page are viable. Rotiro 04:15, 11 December 2006 (UTC)

Rotiro, who died and made you God? Wikipedia is not the same as a refereed journal of physics and therefore does not require YOU to make this entry so. All the FTL approaches are indeed fictional and there DO deserve mention as equally viable, or unviable. So quit deleting the one I quoted from Catherine Asaro!!! —The preceding unsigned comment was added by 67.142.130.30 (talk • contribs) on 08:14, 14 December 2006.

I meant no offense, I'm not trying to "play God", just make the article scientifically accurate. No need to get all worked up about it. :) Wikipedia may not be a refereed journal, but obviously to be a good encyclopedia, its science articles should be as accurate as possible, hopefully as accurate as a refereed journal. Unfortunately it seems very unclear whether this article is trying to be a science article or a science fiction article. By "viable" I meant physically viable, in reality, non-fictionally. So as long as we agree that most of these approaches to FTL are purely fictional, that's fine. Unfortunately I think this article as a whole is muddled and kind of directionless and self-contradicting because it has real science mixed up with science fiction. Which is it going to be?

Anyway I'm just going to add a note to that section, by all means we can keep it as long as it's clear that it's fictional. Rotiro 23:59, 13 March 2007 (UTC)

Furthermore, WP:RS requires that any article about a topic presenting itself as being scientific _requires_ references considered "reliable" by the scientific community. In this case, peer-reviewed articles in respected journals for anything presented as mainstream science. Items not considered mainstream still require some form of paper citation, and per WP:NPOV should be given space according to how big a splash they've made. FTL in fiction a) should be clearly presented as fictional, and b) should be given space in proportion to its notability among fictional works as a whole, in the section allocated for it (this article primarily concerns non-fiction treatments of FTL). --Christopher Thomas 03:08, 14 March 2007 (UTC)

To the anonymous editor at 67.142.130.30, may I cordially remind you of some of the The Five Pillars of Wikipedia such as assuming good faith. Christopher, about references for scientific stuff, are you saying that there should be a reference about Asaro's plot device? Or that there should be a reference supporting my statement that "It is a universal tenet of physics that all observable quantities must be real"? I doubt there would be, e.g. a journal article, about the latter because it is really just basic common sense.Rotiro 08:30, 14 March 2007 (UTC)

Aside from the "complex speed" scheme, I think this article has several problems. I intend (does not mean I will get around to it :) ) to make a few changes (not many), and as a preface to that let's start a general discussion here. I find the current state of the article kind of directionless and self-contradicting. The article presents and examines some options for FTL, but then discards them all as impossible, as indeed they are. Also some of the claims related to science are a bit flakey and should be corrected/clarified. Perhaps the biggest problem is the question of whether this article should be science fact or fiction. Other articles, such as this separate article about fictional FTL refer to this article as "real world faster-than-light physics concepts". I think this article should be about real world, nonfictional faster-than-light physics concepts, in which case "Option G: Consider speed as a complex quantity" should definitely be deleted. Even if this article is going to include sci-fi that section is of limited relevance.Rotiro 08:47, 14 March 2007 (UTC)

The article as-written is intended as an overview of mechanisms that have been seriously proposed for travelling faster than light. Fiction would be best put in its own article (such as "Faster-than-light in fiction"); I'm surprised it hasn't been already. While mechanisms allowing FTL travel or communication are considered _unlikely_ to be possible by mainstream science, calling them "impossible" misrepresents the scientific consensus view. There is general consensus that mechanisms for travelling faster than light allow the construction of closed timelike curves (and so time travel) in the absence of additional constraints, and that most plausible mechanisms require negative mass to form the required spacetime geometries. There is no scientific consensus, to the best of my knowledge, as to whether or not negative mass is a meaningful concept (my impression is that it's considered plausible enough to write papers about, but implausible enough that few scientists expect to find a lab-bench method of producing it in the forseeable future). There are suggestions that CTCs are unstable, potentially ruling out certain spacetime geometries, but to the best of my knowledge this hasn't been proven (though it's considered likely). If CTCs are unstable, it rules out FTL that's used in a causality-violating manner, but not any specific FTL mechanism unless that mechanism is _impossible_ to use in a manner that does not violate causality. This is not the case for most mechanisms I've heard proposed.

That having been said, this article needs a rewrite. It's been through many stages of people making unstructured additions without concern for the rest of the text or for proper referencing. I've considered doing the rewrite, but am not likely to do one soon. --Christopher Thomas 19:52, 14 March 2007 (UTC)

Ok, well by "impossible" I meant "practically impossible" or, if you like, "impossible given current knowledge and technological wherewithal". Rotiro 03:44, 18 March 2007 (UTC)

Okay, since this article is intended to cover serious scientific options for FTL, I'm going to remove the "complex speed" section. If anyone wants to create an article about FTL in fiction, and add the complex speed stuff there, feel free. Also, since this article is intended to be about serious scientific approaches, the paranormal tag should be removed. Paranormal gives the definition "any phenomenon that in one or more respects exceeds the limits of what is deemed physically possible according to current scientific assumptions", which is specifically not what this page is intended to be about. If no one objects I will remove the paranormal tag. Rotiro 04:34, 18 March 2007 (UTC)

Option F

Could someone do some more in depth fact checking on the "Become faster without Acceleration" section? I did some cursory research and could find absolutely nothing on the topic. The only pages that I found were connected to this article. —The preceding unsigned comment was added by 66.160.78.254 (talk) 01:53, 16 January 2007 (UTC).

• And could somebody translate the following paragraph into English? PLEASE?

Events of acquiring speed without prior acceleration are inherent in processes of particle creation. Theoretically thus, it is possible to "switch" velocity of an object by a controlled annihilation and a subsequent recreation of the object but with a different velocity. A relevant technology for objects of a macro scale would be equivalent to teleportation which provides opportunity to travel at light speed by default—even when used conventionally.

Thanks! 86.138.41.109

Who the hell is 86.138.41.109? I am not a number! I am Burt Gummer!!

Hmmm, just realised 'Gummer' sounds like 'Number'. Sheesh, and golly darn it!

In English: The problem (in relativity) is not with particles moving faster than light, it's with particles passing through the speed of light while you're trying to boost them to FTL velocities from STL velocities. The idea behind the paragraph is that because you get particles with any velocity you like when creating them out of thin air by pair production, you should be able to produce pairs of particles moving FTL as easily as STL. The idea has been considered (see tachyon), but we don't observe this happening (meaning that any particles capable of moving FTL, if they exist, are of high enough energy that they haven't been produced in particle accelerators). Tachyons themselves represent an unstable state, rather than observable particles, as described in that article.

I'm not going to modify this article. It needs a massive overhaul, again. --Christopher Thomas 02:38, 13 March 2007 (UTC)

measuring gravitons?

i'm all about getting rid of "will always measure zero-mass particles (e.g., gravitons as well as photons)" until there is an actual measurement of a graviton. otherwise this statement could lead the uninformed to believe gravitons are measureable... to clarify, get right of the gravitons...

Propagation of information relative to rotational phasing

I have noted from observation that if a body is rotating, i.e constantly changing direction. IOW going round and round as for example the Earth does or a Gramophone record. Surely it will be moving relative to distant objects at an infinite speed. IOW if you could extend an imaginary radius line from the centre to say one light year a 33rpm long playing record would in effect be traversing 2x pi x r approximately 6.3 light years in 1/33rd of a minute. This of course is well beyond the speed of light.

Of course one could argue that no such imaginary line actually physically exists.

However in the case of stars that are known to rotate, it is common to see rotation periods considerably shorter than their distance in light years. Surely this means that information should (in theory) be observable at any point of a circle of the same radius distance.

In this particular case whilst the actual beams of light or photons carrying the information are not in themselves exceeding the speed of light it should be evident if the rotation period can be viewed simultaneously from two different view points (Which it can) the information in regard to rotational periods is travelling at an infinite speed.

So it would appear where information is phased with rotation there is in effect no upper limit.

Of course this would also seem to indicate, whilst there is a such thing as space time, it would also mean events occur at source at the time they occur. In which case the same present would have to exist throughout the entire Universe regardless of the speed of transmission.

I also wonder (although this is more conjecture) if this aspect of rotation (in regard to solid objects) would explain centrifugal force which appears to work opposite to gravity. So might be considered a type of anti-gravity. I also wonder if the real result of rotating light beams at extremely high speeds would in effect create an anti-gravity field, particularly insofar as a light beam could be easily rotated globally as opposed to in a single plane. --Artberry 22:08, 23 January 2007 (UTC)

Question: did everything sometime, somewhere moved faster than light?

I mean if a black hole is an object so massive with such a strong gravitational pull that not even electromagnetic radiation can escape (like light) and at some point in time all the matter that now makes up the universe was 'clumped' toghether in a very dense region and exploded (big bang), then it must mean that everything moved faster than light (considerably faster) for some time. I mean, i think i'll be a preaty safe assumtion that the excape velocity of what was in escence the biggest of all black holes would be A LOT faster than light. right? Please i know this is not the right place to ask this, but i already tried the refference desk and i got no satisfactory answer.Nnfolz 19:47, 2 February 2007 (UTC)

Yes, in order for the big bang to work you must assume inflation--the whole universe moved much much faster than light for a very brief time. Since space itself is expanding faster than light, this scenario does not violate relativity. If that sounds like gobbledygook to you, you're not alone. I think that this either proves that the big bang is not true or that gravity is faster than light--since gravity is just a curvature of space time after all. The physicists will tell you that gravity is due to gravitons--which have never been obseved. Gravitons are going out in every direction, so every atom would constantly be losing mass due to the conservation of energy, otherwise gravitons would be in violation of the laws of physics. I don't see why you need a hypothetical particle when the obvious canditate is matter--which is a big heavy particle. Do you need a hypothetical particle to explain the property of inertia? Some crackpots have theorized that inertia could be due to the mass-distribution of an infinitely large universe. Until the mystery of gravity is solved, ftl travel is an open question in physics.

Of course the best evidence for faster than light travel is the large number of alien spacecraft that have visited earth--of wait...that was just a bunch of burned up monkeys in a weather balloon Roswell UFO incident.

Puddytang 20:37, 3 February 2007 (UTC)

This need not devolve into backhanded insults directed at no one in particular. Discussion on the ludicrous weather balloon theory on Roswell should be reserved for its own talk page. --Chr.K. 05:14, 25 February 2007 (UTC)

Communicate FTL with Time Machine

1. Build a time machine that can recieve messages from the future. 2. Get next years mail today. 3. Send it via USPS yesterday air. 4. It gets there before you sent it! Puddytang 20:20, 12 February 2007 (UTC)

Enough energy in our solar system to attain FTL travel?

Is there enough energy found in our solar system to even achieve FTL travel through any of the proposed methods? It seems kind of silly to mention wormholes as a means of FTL travel when it requires two black holes. Since there aren't any black holes in our solar system (thankfully), that means we would have to generate one. How can we use the energy found in our star system to create black holes like that? Malamockq 21:30, 27 February 2007 (UTC)

FTL velocity dependent on how distant objects can be seperated -- this may partialy demolish the backlog

The argumental answer, "nothing can travel faster than light", is false. Faster than light travel is dependent on how objects are seperated (if a dwarf galaxy is seperated from a galaxy about 2.3 billion ly, the object is traveling at about 7.13c) -- there is no limit on how fast space can expand. the following citation to this is [http://www .atlaso ftheuniverse.com/bigbang]. Fbs. 13 02:04, 1 March 2007 (UTC)

Of course, this is due to the expansion of space. Special relativity says the velocity of objects travelling through space can never be faster than c for any observer. As I understand it, SR restricts motion through space, not expansion or contraction of space itself. I guess that would be related to GR. Rotiro

FTL and Distant Galaxies

Hi,

I believe that this assertion is not well founded- if objects are being carried apart faster than the speed of light by expanding spacetime, there is no frame of reference in which a measurement of their relative speed can be made. Neither galaxy can detect the existence of the other, because photons (or any type of information) will never cross the gap between the galaxies. There is no common reference of time, and no reference of speed or distance. It doesn't make sense to say that the galaxies are receding from each other faster than the speed of light because spacetime is as effectively disconnected between the two realms as it is across the event horizon of a black hole.

-pi

Metrology

"Our universe has seven basic dimensional quantities, which can be taken to be distance, mass, time, electric current, temperature, amount of substance, and luminous intensity"

The above sentence mixes up metrology with physics. Temperature, amount of substance and luminous intensity are derived units. Electric current is electric charge in a unit time, if you include electric charge, there are a host of other quantized units such as the three colors of quark you should be including. Quirkie 21:43, 26 March 2007 (UTC)

"Faster without acceleration" section

While I agree that this removed section needed to be cited, and was far too long, I do recall similar concepts being proposed. The idea is usually given in any "SR doesn't forbid FTL" introduction, stating that as SR doesn't directly forbid FTL travel, particles travelling FTL may exist. In some of these descriptions, the idea of generating these particles via pair production for purposes of communication is discussed. No citation handy, which is why I'm not restoring the section myself. Tachyons in conventional physics don't represent something that could be used in this manner, so I'm not suggesting that this method of FTL communication is actually practical (just one that's been proposed).--Christopher Thomas 03:22, 4 April 2007 (UTC)

Quantum Entanglement

As I understand, this is not true communication because there is no way to relay information--the electron collapses its waveform, but we can't make it spin a certain way. But I was wondering what prevents the development of a device in which an array of particles were used. For example, imagine we each have six particles, which are entangled in pairs. In other words, each of my particles is entangled with one of his, and our sets are laid out in a 2 x 3 grid. My partner and I decide that we want the top row to be "dots" and the bottom to be "dashes". I then force the electrons in the top row of all the columns to collapse, sending a "signal" of three dots--the Morse code letter S. I could also collapse the bottom row if I wanted to, giving me O. Or, I could do teh bottom two in the first two columns and then the top one in the remaining, producing G. What law of physics prevents me from doing this, and thus sending information FTL? Sir Elderberry

From what I understand, once two particles become entangled, they can be separated by any distance and still remain their entanglement. Then one can measure one of two paired characteristics that can't both be measured for the same particle and that same characteristic immediately (no matter the distance) becomes the only (of the paired characteristics) that can be measured for the other entangled particle. However, every article that I've read about this says that this cannot be used for faster-than-light communication without explaining why; it just is. So I am equally baffled about why. Val42 16:19, 21 April 2007 (UTC)

Characters in Charles Stross's books communicate over interstellar distances via quantum entangled bits that must be shipped at sub-light speeds between the planets. I suppose that one planet acts as a switch-board to route calls so that it is not necessary to carry bits to talk to everyone everywhere. Once the bits are exhausted the only option is to wait for another shipment of qu-bits to arrive. People are able to travel at FTL speeds, as long as they remain in their light cone and travel in closed space-like paths, but this messes up the quantum entanglement of the bits. He doesn't explain any physics behind the communication methods, so I assumed that something like a binary encoding onto the bits works in fiction. Autopilot 19:50, 16 June 2007 (UTC)

Link to possibly referenced...

http://terra.gg.utah.edu/ls/1325-001.html Maybe that would be of use. --Remi 05:44, 25 April 2007 (UTC)

Supraluminal accelerator

Particles faster than light.

Unfortunaly I can not edit this article, but you can find it at:

http://www.petar-bosnic-petrus.com/work/conical-and-paraboloidal-supraluminal-particle-accelerators/

--195.29.48.180 09:05, 23 May 2007 (UTC)Petrus B

Archive 1

Archive 2

Archive 3

Archive 4

Information Transfer

Source: SkewsMe.com

No information transfer from quantum entanglement? Try telling that to the cryptologists.

Say you have 4 pairs of entangled matter such that (x0,y0) are distinct from and won't affect (x1,y1), (x2,y2), etc. If y0 changes you know that x0 changed, the same being true for the other pairs. Right there you have a nibble's worth of information transfer any time x0, x1, x2, etc. are changed immediately altering y0, y1, and y2 respectively. Monitoring the y bits will immediately tell you when the entangled x bits are updated. —Preceding unsigned comment added by 97.113.163.36 (talk) 03:29, 6 May 2009 (UTC)

I'm not sure I understand you here. In your example if y0 changes x0 does change but you won't know it because you can't monitor and have them entangled at the same time. Well at least that is the state of the situation at this time. There is soft collapse of the wavefunction but that is new and I have only heard of a few physicists working on that. --Ldussan (talk) 04:14, 21 April 2010 (UTC)

Attention from expert

I started fixing sections from this article, but it's a real mess. This article needs serious attention from people who know GR, or even just general science. Some of the problems here are basic convolutions of grammar and clearly amateur science writing. I will work on it a bit more tomorrow. SamuelRiv 05:41, 5 November 2007 (UTC)

Thanks, Samuel. I tried a while ago, but couldn't keep up. I'll try to pay closer attention to the work you're doing.Drernie 17:21, 5 November 2007 (UTC)

The section on Hartman is unreadable for grammar and, for the little bit of intelligibility it has, it seems unsubstantiated or perhaps a little crackpottish.

A refutation for non-constant c might include maxwell's equations. To see how this works, try to derive a wave solution when c is not constant.

Another historical refutation is that c defines the measure of time and space, there is no independent ruler or clock against which to measure its change. But this is similar to an argument offered in the article at present.

The seven quantities cited, are not all basic units; energy for example comprises mass, time and distance, and amount of material is just mass. Mcnelson 15:55, 7 November 2007 (UTC)

Objection

I am very glad to say that the matters are standing much more simple than you are talking. See:

http://www.petar-bosnic-petrus.com/science-articles/conical-and-paraboloidal-superluminal-particle-accelerators/ —Preceding unsigned comment added by 195.29.134.166 (talk) 09:15, 1 April 2008 (UTC)

MAJOR CORRECTION NEEDED

In the section named "Possibility of FTL", it is correctly stated that "Faster-Than-Light travel or communication is prohibited by Einstein's theory of relativity".

I don't think that can be correct. The theory can't prohibit it. The theory can, however, give a reason why it isn't possible. Though, in fact, as far as I can tell the theory only explains why in certain circumstances you can't SEE FTL. DeniseMToronto (talk) 06:13, 18 December 2008 (UTC)

It is just a form of words, meaning more or less what you said, that is, according to the theory it is not possible. The theory of relativity in not about what you can see but about what you can detect or measure in any way. Martin Hogbin (talk) 22:27, 18 December 2008 (UTC)

You can't detect a star that has, because of expansion of the universe, gone beyond the observable universe, but you can logically infer that, barring unforeseen events, it still exists. And someone else, from another place in the universe that's closer to it, might still be able to see or detect it. 216.239.68.212 (talk) —Preceding undated comment added 20:39, 24 March 2010 (UTC). 216.239.68.212 (talk) 21:03, 24 March 2010 (UTC)

Thanks. I understand that observability and measurability are a fundamental aspect of science as we conventionally understand it, making verifiability possible, etc. But still ...

I meant "see" in the sense of detect or measure. But to say it isn't possible is to say that, though I can't detect or measure it is any way, you can't DO it. How does my inability to detect or measure it, stop you from accelerating still a bit more so that you become undetectable and unmeasurable by me?

An example would be stars that have, due to the expansion of the universe, gone beyond the observable horizon of the universe. At what would be the speed of light from our point of view, they become unobservable. But they don't hit a wall and stop moving. They can't be seen or measured from our framework, but do we really think they've actually disappeared? DeniseMToronto (talk) 08:40, 30 January 2009 (UTC) I notice that, though a number of people insist it isn't possible to go faster than the speed of light, no one has claimed those stars suddenly stop, don't accelerate out of view, or no longer exist. We can't SEE them, but we can logically infer their existence. --- —Preceding So basically, the article is wrong the SR says you can't go faster than c. It says that can't be seen or measured, or detected, but it provides no method to stop such movement, and one can infer those stars did travel as they did. SR provides no valid way to say they didn't. 216.239.68.212 (talk) 21:03, 24 March 2010 (UTC) unsigned comment added by 216.239.68.212 (talk) 20:33, 24 March 2010 (UTC)

However in the section "Tachyon" it is stated: "In special relativity, while it is impossible to accelerate an object to the speed of light, or for a massive object to move at the speed of light, it is not impossible for an object to exist which always moves faster than light." This second statement is incorrect. Special relativity does not allow any particle (even with zero mass) to move faster than c, the speed of light in the vacuum (there are valide discussions on which "vacuum" should be taken as "the vacuum").

How is SR supposed to stop it? Put out a hand? Quite a number of people here talk as if SR is a thing that controls or manipulates the universe. It is SUPPOSED to be a descripton of how the universe IS. Keep accelerating, and if you had enough fuel and time etc., what stops you from going faster than c? And since all such speed measurements are relative, what gives more validity to the measurement that one person says is more than c while another observer says it isn't greater than c? 216.239.68.212 (talk) 216.239.68.212 (talk) 21:03, 24 March 2010 (UTC)

The simplest way to realize that special relativity does not allow any particle moving faster than c is to remark that spoecial relativity works with four REAL numbered axis and a FTL would make Lorentz equation to produce complex numbers. So the vary basic mathematical meaning would be lost.

Of course, some one may claim that we can extend special relativity to deal with complex numbers. That is true. However, as this article correctly points out any change to special relativity has to be very careful since it is very well confirmed by experimental data, and changing the spce-time to have four complex numbered dimensions, may sound mathematically easy, but it is a rather bold and extreme change from Physics point of view. —Preceding unsigned comment added by 189.24.6.58 (talk) 14:22, 7 September 2007 (UTC)

I have corrected the bland statement about FTL being impossible because of SR. It isn't -- see here and tachyon article. --Michael C. Price ^talk 10:36, 16 September 2007 (UTC)

189.24.6.58 said: The simplest way to realize that special relativity does not allow any particle moving faster than c is to remark that spoecial relativity works with four REAL numbered axis and a FTL would make Lorentz equation to produce complex numbers. So the vary basic mathematical meaning would be lost. Actually, all that this shows is that it doesn't make sense to use the Lorentz transformation to try to define the "frame" of an FTL particle--but that's no big deal, you can't define the frame of a photon either (try plugging v=c into the Lorentz transformation and see what happens). And as explained here, if you assign the tachyon an imaginary rest mass, all its measurable properties in our own sublight frames will be real-valued. Hypnosifl 06:31, 25 September 2007 (UTC)

A thought about complex numbers that I have not found in science to date- in electronics complex numbers tend to arise in connection with phase shifted values like impedance and capacitance. If you think of spacetime as a 4-d system, then 90 degrees out of phase with 3-d space is just a 4-d location, but not in time. Most consider time as the 4th dimension, but in this case it would be a spacial location. According to the Lorenz transformations any object moving faster than light has a negative complex coordinate. Instead of seeing this as a reversal in time, consider it as a phase shift in 4-d space. If you think of the universal 3-d space as a flat sheet expanding into 4-d space, then an object at light speed has come to a dead stop in the 4 d direction while the sheet continues away from it, causing a gravity funnel, one which light cannot escape. when an object moves faster than light, the location will actually travel below the dead stop point and slightly curved, futher into 4 d-space but not backwards in time...in time, its forward momentum in 3-d space will continue to show slightly less than light speed as the only thing visible will be an event horizon that is moving at less than light speed.Jiohdi (talk) 21:11, 8 April 2008 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Faster-than-light/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

This isn't of much relevance in physics, though of high popular interest. I vote "mid". The article needs serious cleanup from anybody from a scientific background, as some of the logic in the article is just ridiculous. From quantity over quality, however, the article is a "B". SamuelRiv 05:47, 5 November 2007 (UTC)

Last edited at 05:47, 5 November 2007 (UTC). Substituted at 20:33, 2 May 2016 (UTC)