Can something move faster than light?

[Tormod]

Okay, this question pops up now and then so let's have a new poll.

 

What do you think - can anything move faster than light?

[Thelonious]

What do you think - can anything move faster than light?

 

In theory or in practice?

[bumab]

Yes. (mainly because I think people will figure out a way to do what the past has considered impossible).

 

But, I don't think it will be "moves faster then the speed of light" but rather, "gets from point A to point B faster then light could." Some sort of space warping, or moving into some other thing (warp field anyone?) where the distance between two places is smaller.

[GAHD]

I don't know what i think in that matter.

 

But then again, I'm rethinking how I look at movevement because of that question. Such an eternal puzzle.

[Fishteacher73]

I'm with bumab, I think that in terms of velocity, C is it. But thare could be other methods that could allow one to reach point B from A in a quicker manner than a straight line at C. What and how is up in the air, but with our understanding of how elastic space/time is, it seems somewhat reasonable that if we can streach it we can compress it as well.

[maddog]

I am not sure how answer the question... Theoretically possible if you expand what is definition of the

Lorentz Transformation by allowing Complex properties such that no mass particles crosses the C

boundary and massless particle move at C (or some harmonic of C). In this way symmetry is preserved

and Causality is not locally violated (assuming Tachyons don't openly interact with Tardyons).

 

Observably, no (this would violate the principle I said above). :cup:

 

Just a way of looking at it. :cup:

 

Maddog

[Qfwfq]

can anything move faster than light?

If you mean "anything" then yes, quite likely. One thing that probably can't is causality, even by whatever shortcuts.

 

Theory doesn't actually rule out any superluminal velocity but, if something goes faster than light for some observers, it goes backward in time for others. The same would hold for causality, hence superluminal causality being possible makes the time-reversed causality possible and vice versa. This doesn't depend on how it would get from A to B, it's enough for the two to be at a spacelike separation.

 

If anyone can find a way to accomplish it, send me those lottery numbers and I'll play the ticket. Current jackpot €50 million! 1 euro is over a dollar thirty US.

[C1ay]

'Something' is such a broad term. If you could turn gravity on and off with a switch might it move faster than light? Could a magnetic field be propogated faster than light? Are there forces we haven't even discovered yet? Could they be faster than light. SInce the question is not limited to matter then I think it is entirely possible. Who knows, maybe even tachyons are real...

[sanctus]

And if something is as well what is defined as group velocity in optics then as well we got something moving faster than light.

[Qfwfq]

If you could turn gravity on and off with a switch might it move faster than light? Could a magnetic field be propogated faster than light?

No, according to GR and no, according to electromagnetism (and SR).

[Qfwfq]

And if something is as well what is defined as group velocity in optics then as well we got something moving faster than light.

When is group velocity superluminal?

[C1ay]

No, according to GR and no, according to electromagnetism (and SR).

 

I realize that. I also realize that both of these are simply theories so there might be somethings we just don't know yet that they don't cover. That's just me though, I like to remain skeptical until someone proves something.

 

I wonder for instance. We use gavitational assist to accelerate space vehicles. Might it be possibles to use some type of electromagnetic assist to accelerate photons in the future? If so, could those photons travel faster than C? Just wondering.....

[Qfwfq]

I also realize that both of these are simply theories so there might be somethings we just don't know yet that they don't cover.

Certainly. There are things that GR and EM don't fully cover. What we are talking of is, however, covered quite well by SR, which covers the very geometry of space-time. GR isn't quite as well tested as SR but there are things we don't expect to see ever being contradicted.

 

While people often say "but, they said the same about Newton's theory and then it turned out to be wrong..." I say that, in a certain fundamental sense, Newton wasn't wrong at all. SR should be viewed as a change more than as a contradiction to Newton's dynamics.

 

Our understanding became more complete with SR, and we don't find we can do anything that Newton's theory explicitly proves impossible. Not that we can now explicitly prove superluminal causality to be impossible, I haven't completely, totally, quite 100% lost hope for that jackpot. B)

[Qfwfq]

A few examples of "things" that certainly can "move" faster than light:

 

The locus of points on a surface, at which the phase of an incident wave is equal to a specified value, can move faster than the wave's phase velocity.

 

Phase velocity of electromagnetic waves in some dispersive media can be greater than c.

 

Correlation between measured values for a QM state may be instantaneous according to Born interpretation.

 

These things, especially the last one, can hardly be described as "something moving" and none of them amount to a propagation of causality.

[paultrr]

If you mean "anything" then yes, quite likely. One thing that probably can't is causality, even by whatever shortcuts.

 

Theory doesn't actually rule out any superluminal velocity but, if something goes faster than light for some observers, it goes backward in time for others. The same would hold for causality, hence superluminal causality being possible makes the time-reversed causality possible and vice versa. This doesn't depend on how it would get from A to B, it's enough for the two to be at a spacelike separation.

 

If anyone can find a way to accomplish it, send me those lottery numbers and I'll play the ticket. Current jackpot €50 million! 1 euro is over a dollar thirty US.

 

I'd agree on that. Even Warp drive and wormhole cases don't actually get around causality. Both of those theories are pure theory since we have no experimental support at present for either. One might actually suggest that the theory on such moves superluminal while the experimental support in any of these areas tends to move rather at a turtle's pace.

 

But given time someone will find a way. Good Poll and you're right the question keeps coming up under a lot of varients.

[paultrr]

Excerpt from Wikipedia:

 

The inability of a spacecraft to achieve a given displacement in less time than it takes light to traverse the same span, is often attributed to relativistic mass increase necessitating eventual infinite energy consumption for thrust, as the speed limit is approached. That notion is in widespread belief but there is scant truth to it. How fast you are moving per the reckoning of some arbitrary onlooker cannot change anything intrinsic to your craft, ie. its mass. Think about how many different arbitrary onlookers you can imagine, each on a different relative trajectory... which one of those onlookers' viewpoints should be the determining factor in impeding your progress? Or in other words, how can thrust originating from a rocket's very own rest frame labor from any relativistic effect? It makes no sense at all.

 

Aside: On the other hand, it is pertinent to ascribe relativistic mass increase as the impediment preventing a charged particle in a particle accelerator from reaching the taboo speed. Why?? because those particles are being pushed along by electromagnetic field-producing coils positioned in the (relatively) stationary lab frame. From the viewpoint of that frame, the mass increase to the speeding particle becomes perfectly germane.

Now let's get to some real truth about FTL space travel. Yes, it would require an ever more disproportionate expenditure of fuel to increase speed, as you approach the limit, but not because your craft has gotten any heavier. Light propagates at just about one foot per nanosecond, or 12 inches per nanosecond (12 IPN). Let's say you accelerate away from Earth in a spacecraft until you reach a cruising speed of 10 IPN, as seen from Earth. You can then apply another rocket thrust, based simply on conventional Newtonian calculations, and readily achieve an additional 5 IPN. But because of relativistic clock and ruler distortions, that additional 5 IPN in your frame constitutes only an additional 1.13 IPN as far as Earthbound observers are concerned. So the steep climb has nothing at all to do with being heavier; it is more due to the unusual way that velocities add.

 

And yes, you truly did add 5 IPN to your speed with just the normal non-relativistic thrust application. This can best be envisioned by imagining that your craft was side-by-side with a sister ship, likewise cruising at 10 IPN away from Earth. (Space offers no resistance, so "cruising" means engines completely off.) Because all motion is relative, both you and your sister ship can rightly claim to be stock still in space, while it is Earth that is speeding away. After your rocket engine thrust, you find yourself moving 5 IPN away from the sister ship that you left behind, so you have truly added that velocity, using only conventional thrust force. To Earthlings however, you've sped up by just 1.13 IPN.

 

 

 

While special relativity says that an object with mass can not be accelerated to the speed of light or beyond and that no object with mass can exist at the speed of light, it does not deny that an object with mass (albeit a complex number rather than real) can exist that is already going faster than light. Any particle already going faster than light is called a Tachyon, no proof has been obtained if these exist or not.

 

One possibility for overcoming this is to use the force of gravity to pull the ship along. At this point we must leave special relativity and enter the realm of general relativity.

 

[edit]

General relativity

The limit is not quite as absolute in general relativity. That theory forbids a massive object to accelerate to the speed of light, just as special relativity does. However, it allows spacetime to be distorted in a fashion which causes an object to move faster than light from the point of view of a distant observer. That object still moves slower than light in its own reference frame. One such arrangement is the Alcubierre drive metric, which can be thought of as producing a traveling wave in spacetime that carries an object along with it. Another possibility is the wormhole, which provides a "short cut" between two distant locations. To date there is no feasible way to construct any such special curvature; they all require unknown exotic matter, enormous (but finite) amounts of energy(There are a couple of exceptions here), or both.

 

General relativity predicts that any technique for faster-than-light travel could also be used for time travel. This raises problems of causality. Many physicists believe that the above phenomena are in fact impossible, and future theories of gravity will prohibit them. One theory states that stable wormholes are possible, but that any attempt to use a network of wormholes to violate causality will result in their decay.

 

 

I might add that quantum theory sets some very strong requirements about what's allowed as far as exotic energy goes also.

 

Myself and a few others here have mentioned some of the alternative or outside our spacetime frames that show up within modern brane theory. The problem with these as real shortcuts around C is that in a lot of cases when one uses a path there one ends up going forward in time here. So while one appears to move FTL there in relation to here its actually forward time travel that one achieves when you try to come back to here. You actually in the end run never beat C as far as our frame goes because in using the higher velocity there you have simply traveled to some far off point here with the earth having aged way ahead in time. So these alternative frames of reference all tend to not solve the problem. In general, if C is ever really exceeded it has to be in our frame of reference or the universe we exist in.

 

I ran one example that actually appeared suggesting such in Peer reviewed format by a few friends out of NASA and when they did the same caculations of frame compared to frame they got the same answer myself and other discovered on this. These hyperspace short cuts simply do not work to get travel times any faster than C as far as our frame goes. Yes, I still believe it can be done and is not ruled out at this time. But nature does offer some very strong constraints on how to do it.

[paultrr]

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".

 

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. Under inflation theory the Universe once expanded faster than light. The general idea is space itself can move FTL without violating relativity. But it also must be remembered that inflation was brought about by the decay of a false vacuum into a stable state. The energy of the vacuum never reaches below zero in such a case which has raised the idea that perhaps the exotic energy of say an Alcubierre metric could be simulated via an inflation field, thus providing a way around the exotic energy problem. However, at current time the type of inflation field needed is beyond our ability.

 

Hawking rather put things right when he made the statement that such ideas are not ruled out fully at this time. But a lot of constraints on the subject has come about through such theory and research of such, I might add.