What is Faster than light: Definition and 244 Discussions

Faster-than-light (also superluminal, FTL or supercausal) communications and travel are the conjectural propagation of information or matter faster than the speed of light.
The special theory of relativity implies that only particles with zero rest mass may travel at the speed of light. Tachyons, particles whose speed exceeds that of light, have been hypothesized, but their existence would violate causality, and the consensus of physicists is that they do not exist. On the other hand, what some physicists refer to as "apparent" or "effective" FTL depends on the hypothesis that unusually distorted regions of spacetime might permit matter to reach distant locations in less time than light could in normal or undistorted spacetime.
According to the current scientific theories, matter is required to travel at slower-than-light (also subluminal or STL) speed with respect to the locally distorted spacetime region. Apparent FTL is not excluded by general relativity; however, any apparent FTL physical plausibility is currently speculative. Examples of apparent FTL proposals are the Alcubierre drive, Krasnikov tubes, the traversable wormholes, and quantum tunneling.

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  1. Multiple_Authors

    Insights Can I Send a Signal Faster than Light by Pushing a Rigid Rod? - Comments

    Multiple_Authors submitted a new PF Insights post Can I Send a Signal Faster than Light by Pushing a Rigid Rod? Continue reading the Original PF Insights Post.
  2. DoobleD

    EM wave near field propagating faster than light?

    Sources : paper here and http://www.quora.com/What-is-the-phase-of-the-EM-waves (fifth paragraph). This is beyond my knowledge so I am not looking for an explanation of the phenomenon. But I thought nothing could go faster than light so I am very surprised. Are there exceptions to the speed...
  3. Gaz

    Instantanious communication (faster than light)

    I have no idea where to put this and it isn't based on any theory's just common sense and is very simple If you get a tube and put a wire in it make it as long as you want to and to pass information simply move the wire back and forth as the whole wire is moving at the same time the information...
  4. AlexDB9

    Faster Than Light Travel: What Happens to Destination's Time?

    I've read that faster than light travel is possible if we manipulate the space around the craft, but the energy needed is on the order of the sun's output. So, even if not practical, since theoretically it is possible I want to ask what happens to our destination's time. As I understand at...
  5. M

    Entangled "information" sent faster than light (....not)

    Hello^^ It's always interesting to ponder the various ways that quantum entanglement *appears* to allow transmission of faster-than-light information, but on closer examination, actually doesn't. One that occurred to me today was the situation of two persons who receive each of a pair of...
  6. Kyuutoryuu

    Is there a medium in which sound travels faster than light?

    So we all know that the speed of sound increases with greater density of medium. Conversely, the speed of light decreases with greater density of medium. Does there exist such a medium that is so dense that the speed of sound overtakes the speed of light?
  7. Jesus

    Superluminal propagation of fields

    I am reading about the Velo-Zwanziger problem in which particles with spin higher than 1 propagates faster than light when the particles are coupled with an electromagnetic field. In the original paper: G. Velo and D. Zwanziger, “Propagation And Quantization Of Rarita-Schwinger Waves In An...
  8. Cobalt101

    Can EM waves carry information faster than light?

    I'm still having trouble working out why faster than light speed equates to time travel. I understand that for the traveller time slows down the faster he/she travels and have familiarised myself with the standard examples of Earth man and space man using the Lorentz equations. At the extreme...
  9. A

    Information transmitted at speeds greater than C

    Hello, a question for all of you with its experiment. If I have a material that has a Bulk modulus higher, the diamond type (442 GPa) if I create a tube of diamond along 1 miles (or length less) with appropriate supports to decrease as much as possible the friction. At the same time I have a...
  10. M

    Perception of faster than light travel?

    I'm currently taking a modern physics course, I came across this problem which really threw me off guard: Three spaceships A, B, and C are in motion as shown in the figure. The commander on ship B observes ship C approaching with a relative velocity of 0.83c. The commander also observes ship A...
  11. C

    Faster than Light, with no Mass.

    I have a question: With the detection of the Higgs Boson particle, if one were to remove all said particles from a ship, thus rendering it with no mass. Will it be possible to the travel at the speed of light or faster? Now mind you, this will not break Einstein's E=mc2. Since there is no...
  12. T

    Information Faster Than Light - Thought Experiment

    Assuming it were possible to build a sturdy enough rod like structure, say equal the length it would take light to travel in two minutes. If you were to push one side of said rod and move it, would the far side of the rod move before light were able to travel the length of the rod? If so...
  13. S

    Why does the furthest stars seem to be moving away faster than light?

    I heard somewhere that the amount of redshift in the most distant stars show that they are moving away faster than light and its due to the shape of the universe. I was wondering how do we even know what she shape of the universe is, I thought we couldn't see any boundaries.
  14. P

    Does quantum computer can to send the information faster than light ?

    Does quantum computer can to send the information faster than light ?? I have read many of paper about quantum computer that come from quantum entanglement. The Quantum Entanglement may be use in Quantum computer.Does it can use to send the information faster than light or it can surpass the...
  15. L

    Is Faster-Than-Light Travel Possible in Theory?

    Please help me to understand. In theory with a powerfull enough ship a space man can travel to a distant star, say Proxima Centura (4.2LY away) in 2.1LY by his own clock, yet on Earth and Proxima Centura more than 4.2 years will have passed. My question is why will he not measure Proxima...
  16. shanepitts

    Phase velocity faster than light?

    I am currently taking an undergrads course in atomic physics, and I have just grazed the concepts of matter wave functions, group waves, group velocity, and phase velocity. For the latter, it has been stated that phase velocity can exceed the speed of light. I don't fathom this. Could anyone...
  17. S

    Can the Warp Drive Go Faster Than Light?

    Hi. I'm curious about this: The supposed "warp drive" by Miguel Alcubierre is supposed to go faster than light. But, isn't it a warp in spacetime? Doesn't that make it like a gravity wave? But gravity waves can only go the speed of light, right? So how can the warp drive go faster?
  18. B

    Faster Than Light Travel: Theory and Possibility

    People seem to be getting confused with the concepts involved in some of the faster than light travel methods that have been theoretically proposed. No, it is not possible to travel faster than the speed of light through the normal, physical universe in our current understanding of physics...
  19. A

    Does time go backwards if object is going faster than light?

    Lets pretend I am in my spaceship going in one direction at 0.9c. My brother is in his spaceship going the opposite direction also at 0.9c. Oh and there is a big clock on the side of our ships. When we cross paths, to me it looks as if I'm not moving and my brother is moving at 1.8c. I am aware...
  20. P

    Moving faster than light cannot stop biological aging Or can?

    Hi everyone, before I post I apologize for my bad English! I am not a physicist but I am interested in this stuff (I've read relativity theory and...) But I have a question regarding time traveling Imagine that it is true that we can travel at speed of light...So here is the famous example...
  21. F

    Entanglement to speak faster than light

    OK, now I'm considering this problem with more information. Suppose you construct two beams of entangled particles that travel in opposite directions at or near light speed. At two very distant places where each beam is aimed, you have a double slit experiment at the end of each beam...
  22. Y

    Can neutrinos travel faster than light?

    Hello everyone This is my first post and I am interested in the question about neutrinos... I have many questions that I would love to have answered but I'll stick to the question of whether they can travel faster than light or not... ( please bear with me as I am returning to physics after a...
  23. D

    Moving faster than light in Schwarzshield radius

    When I watch the spacetime diagram of a particle inside the Scharzshield radius, it seems that the particle can move 'horizontal' (they move dr while X0 stays constant). Does this mean the particle can move faster than light inside the Schwarzschield sphere? Or does the meaning of space/time...
  24. B

    Information travelling faster than light

    I don't know if this has been asked but if you imagine a pipe that theoretically extends from one end the universe to another two people at each end, and by twisting the pipe left means "yes" and right means "no" if you twist it what happens
  25. L

    A Falling Rod's Intersection Moving Faster Than Light?

    Homework Statement There is a rod falling at a speed v that makes an angle θ with the x-axis as it falls. Is it possible for the intersection point to move faster than light as it falls. Homework Equations The Attempt at a Solution I have done the geometrical calculations and I...
  26. E

    Does this mean the speed of x ray faster than light in vaccum

    http://global.britannica.com/EBchecked/topic/495677/refractive-index refractive index, also called index of refraction, measure of the bending of a ray of light when passing from one medium into another. If i is the angle of incidence of a ray in vacuum (angle between the incoming ray and the...
  27. L

    Tunneling photons travel faster than light?

    I recently found an interesting read on the mysteries of quantum mechanics, here : Don't know about you, but I am personally confused by this result. How can a photon travel faster than itself? If it can travel faster than itself, than what does that mean for the universal speed limit? My...
  28. R

    Is There a Solution to the Faster-than-Light Problem in General Relativity?

    hello I am facing a conceptual problem in general relativity. I realized that according to einstein's theory of gravity, if I start rotating, I can say myself to be stationary and the entire cosmos revolving around me making me feel the outward force(centrefugal force in earlier view)...
  29. M

    Universe expansion faster than light?

    The speed of light is a constant. Yet the Universe's expansion seems to be getting faster and faster. So my question is, when the speed of the expansion of the Universe reaches C the speed of light, what happens. Does it remain at that speed? Does it exceed it? Or does it slow down?
  30. S

    Question about travelling faster than light.

    So when a moving object reaches the speed of light time dilates so I assume if an object that has mass somehow achieves the speed of light time stops moving (since it is traveling slower and slower) and once the object exceeds the speed of light time becomes negative so does that mean the object...
  31. DiracPool

    Faster than light subatomic spin

    I’ve heard in several places that we must view the spin of subatomic particles not as we would that of a classical object since, if we did so, we would find that the velocity of the spin would be so great as to violate the light speed limit to achieve their magnetic moments or whatnot. Can...
  32. DiracPool

    Faster than light electron spin

    I understand that we are not to think of an electron literally spinning on its axis because the equatorial speed would far exceed the speed of light. However, just for fun, I've been trying to find out just what the speed would be to make the numbers come out to agree with the observed angluar...
  33. J

    Faster than light information travel

    Faster than light information travel aparatus Ok, so I am not a physics pro, but I find it very interesting. And I just finished reading about Bell's theorem and I have a question. As I understand it, the laws are like this for entangled photons: 1. If you measure the polarization of photon 1...
  34. T

    Critique This Simple Faster Than Light Mechanism - Possible?

    Ok guys. Picture a bicycle wheel assembly apparatus with several gears and a giant wheel. The giant wheel is constructed in outer space such so that a person is placed on the outside rim of the wheel and then the wheel begins to be rotated at first slowly due to the torque required but then...
  35. T

    Is Warp Drive a Possibility or Just Science Fiction?

    I chanced upon this article in the Huffington Post and would like to ask if anyone is familiar with this work? Is this even feasible? http://www.huffingtonpost.com/2012/09/17/warp-drive-star-trek-feasible_n_1890679.html
  36. B

    Transmitting Information faster than light?

    Hi everybody. I have always wondered something and have not been able to get an answer. Let us suppose we have a 300.000 km long straight rod. It is of graphene, or any very tough material, of absoulte stiffness, without any displacement or absorption between its molecules. Parallel to the rod...
  37. N

    Faster Than Light Travel, Theories.

    Any one who has been following my other Thread (Simulated Gravity) knows that I've trying to write a Hard(ish) Science Fiction novel. I'm looking for help in firming up my "FTL Drives" and trying to use current Real world knowledge Currently there is two ways to "cheat" the speed of light...
  38. D

    Did a Clock Error Make Neutrinos Appear Faster Than Light?

    Neutrinos faster than light SOLVED ? Heya all, I was thinking about the neutrinos going faster than light (yes, it has been some time ago), and thought, on Einstein's side, that they couldn't have. So I conjured something up. What if the clocks they used were not on equal, because of the...
  39. S

    If you could travel faster than light

    Supposing that you could travel faster than the speed of light, what would you see, feel, or experience? Since an object travels slower in time as it approaches light speed, wouldn't the object, if it did travel faster than light, enter into a complete and absolute void because nothing else in...
  40. F

    MHB Experiment finding particles travelling faster than light

    Has the discovery of particles traveling faster than the speed of light had any more backing or refuting? A Los Angeles Times Article talked of a repeat of the experiment that does not match the same speed. However in a BBC article claims they repeated the experiment with the same speed. Now I'm...
  41. A

    Faster than Light - Summary Wanted

    Faster than Light travel is often discussed, but it seems that facts and fiction are often mixed together. (FTL not nessesarily from point A to point B at a velocity greater than C, just move object from A to B faster than light could travel.) To make it quick; there are some theories right...
  42. coktail

    Faster than light relative speeds (I know it's impossible)

    We have particle accelerators on Earth that can speed up particles to near the speed of light. Earth itself is hurtling through space, as is the solar system and galaxy that its a part of. If an observer were to float outside of our galaxy and observe those speeding particles in the...
  43. C

    Far away galaxies moving faster than light?

    Good evening. I just watched a documentary called The Universe-Light Speed. In it, astrophysicist Alexei Filippenko said that galaxies which are very far are moving away from us faster than the speed of light. Also, cosmologist Alan Guth said that during inflation the universe expanded faster...
  44. M

    Can an electric field change faster than light?

    I found the thread "Can magnetic field expand faster than light?" but no thread on electric fields. For example: If, in the above setup, the dielectrics used in capacitors were physically very long (the distance between plates very high) and the capacitors were charged up to high...
  45. A

    Faster than Light Information Sending Solved?

    I may have figured out a way to do that, unless there is some fundamental principle I am not currently aware of. I should preface this by saying that I am not an expert. I have only recently decided to major in physics, and have not even begun school. But I just had a eureka moment. It works by...
  46. K

    Faster Than Light Travel: Exploring Hypothetical Technology & Causes

    From what I understand, space (not matter) can expand at a speed faster than that of light, and when it does, it goes in all directions. Would it be possible to create a controlled expansion of space behind a vehicle along a single path, like a corridor, that would change your position in space...
  47. R

    Doesnt information travel faster than light in case of black holes?

    hi, i was wondering, for a black hole, as everyone knows,the escape velocity is greater than light. this means that the information about the existence of the black hole in terms of light never reaches the observer. so if the black hole were the cease to exist at an instant of time, the...
  48. R

    The Elegance and Complexity of Theories Beyond Special and General Relativity

    Star moves faster than light! Cosnider a universe with only two objects, a planet and a star... From the rest FoR of the Star, the planet appears to be revolving around the star.. And also the planet rotates in its own axis.. (just like our Earth and sun)... The planet takes 1 second to...
  49. D

    The Mysteries of Faster-Than-Light Travel: A Physicist's Guide"

    Dear Physicists, Do you know why there was a massive fuss made last year about the experiments at CERN which recorded neutrinos traveling faster than light speed? Do these results contradict any previous experiment? I hear a lot of talk about said results conflicting with the equations...
  50. A

    Nothing is faster than Light, Right?

    First of all, let's consider that this question is asked before neutrino's speed was discovered. " Let's consider a rod, a rod which is as long as 1 light year. Consider that it is a rigid rod of steel with diameter 1m (to prevent bending) I gave a nudge to it from one side, then the whole...
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