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. K

    Topic: Neutrinos and Gravity: Can They Travel Faster in Contracted Space?

    Those faster than light neutrinos were moving through a location of high gravity (inside the earth). In such locations space is contracted more than in empty space. Therefore getting from A to Z is a contracted distance. Question: could neutrinos move through contracted space at a greater...
  2. e2m2a

    Faster than Light Neutrinos at CERN

    Cern has reported they have measured neutrinos going faster than the speed of light. Did they send a light beam as a test case to see any variance in c of the light beam? Also, were two clocks involved in the measurement? One in Switzerland and one in Italy? If so, wouldn’t it be...
  3. C

    E=mc^2, but nothing can travel faster than light?

    I tried to find an answer to this here, but may have missed it. There must be a flaw in my understanding here, since it seems to be contradictory. Mass times the speed of light squared = Energy, and yet (according to Einstein), nothing can travel faster than the speed of light? I'm just...
  4. A

    Traveling Faster Than Light: Effects and Possibilities

    Just curious see if anyone would know exactly or have any ideas on what would happen if an object were to travel faster than the speed of light. I've asked my physics teacher but he didnt know so I figured i would ask a larger audience. So here it goes... If an object were to some how travel...
  5. W

    What if something went faster than light?

    When I heard about the faster than light neutrinos, I began wondering about what changes that would make in physics. I thought one would be that humans may eventually go at the speed of light. Another is that Einstein was wrong on one thing, and could have been wrong on some other things. What...
  6. F

    The nature of causality in special relativity (not faster than light travel)

    I am having trouble understanding how special relativity reconciles the concept of causality. In one frame of reference event A may be followed by event B, but in another frame of reference event B may occur before event A. In the first frame of reference an observer may claim that event A...
  7. M

    Faster than Light Travel Question

    Assuming a spacecraft had a propulsion system and sufficient fuel, what stops it from reaching the speed of light and beyond if a constant force is always being exerted on it? And in the event that it can go beyond the speed of light, will time distortion take place, and the crew on board...
  8. thenewmans

    What if speed limit is slightly faster than light?

    Let’s say some reasonable scientist claims it turns out the speed limit of the universe is actually 8000 meters per second faster than the speed of light. That’s 0.0025% more. What experiment would disprove that? The only thing I know of is the Michelson–Morley style interferometer. I’m not sure...
  9. S

    Faster than light in Quantum mechanics?

    In <Engineering Electromagnetics> written by W.H.Hayt and J.A.Buck( 6th edition,McGraw-Hill,p372), the phase velocity vp of electromagnetic waves in copper at 60Hz (commercial electric power) is 3.2m/s. Substituting the value into vpv = c2 of de Broglie theory, v=108c should be much faster...
  10. A

    How Can Laser Spot Move Faster Than Light?

    I have read this millions of time on internet that laser spot can move faster than light. but i can't understand how. For example if we point our laser source towards moon then after 1.2 seconds our laser light reaches the surface of moon and creates a spot there, now if i move my laser...
  11. A

    What faster than light have to do with cause and effect paradox ?

    I really can't understand how faster than light travel creates the cause and effect paradox. I have spent many days on internet searching this specific problem but not able to get it. Can some one explain it to me in the easiest way. Another question : i have read many times that...
  12. 1

    Faster than light information transfer

    I have what may be considered a rudimentary question, but one which I've actually never asked and have always wondered about. Many people have posed the question as to whether or not a very long, rigid object could be "pushed" on one end and instantaneously transfer information across a vast...
  13. wolram

    More on faster than light neutinos

    http://arxiv.org/PS_cache/arxiv/pdf/1109/1109.6520v1.pdf quote: The velocity anomaly recently reported by the OPERA collaboration appears strikingly at odds with the theory of special relativity. I offer a reinterpretation which removes this conflict, to wit that neutrinos yield a truer...
  14. J

    Can string theory predict faster than light neutrinos ?

    Can string theory or quantum gravity theory predict faster than light neutrinos ?
  15. B

    Could a Tachyon Particle Explain Faster-Than-Light Neutrinos?

    Recent news about neutrinos slightly breaking the speed of light. Wondering if it were possible that an unknown tachyon particle existing 'momentarily' therby beating the speed of light, then becoming a neutrino as it 'collapses', becoming a neturino, could explain the phenomena? Yeah I know no...
  16. E

    Neutrinos faster than light speed? What do you guys think?

    I feel like this is one of those things where they say "oh my god this will change physics forever" but it ends up being being incorrect. Either way it is odd that they would measure faster then light speed at all, I'll give them that. But 60 nanoseconds? Not quite enough to make me convinced...
  17. A

    Faster than light and time travel into the past.

    Hey i am new in this forum and just want to share my thoughts with you guyz at the recent finding at CERN . If the findings of CERN experiment are correct then does it means that time travel into the past is proved WRONG.? Because according to relativity theory if something moves faster...
  18. J

    Neutrinos can travel faster than light

    Hi , It is experimentally shown that neutrinos can travel faster than light http://www.nature.com/news/2011/110922/full/news.2011.554.html What are the implications of that discovery ?
  19. D

    Is Faster Than Light Travel Possible?

    I came across this article today and thought you guys would be interested. http://online.wsj.com/article/SB10001424053111903703604576588422968704078.html?mod=WSJ_World_LEFTSecondNews
  20. E

    Neutrino discovered to travel FASTER than LIGHT?

    Neutrino discovered to travel FASTER than LIGHT? http://online.wsj.com/article/AP58b5aed0a77c45ddb163d90951b36b35.html I don't know if this is old news, but I do know that the news often gets information wrong is this correct has anyone heard of this? Apparently neutrinos were discovered to...
  21. C

    Strange Particles May Travel Faster Than Light

    Oh my. <facepalm> http://www.livescience.com/16183-faster-speed-light-physics-breakthrough.html
  22. B

    Faster than light and time travel

    Why does faster than light travel or propagation mean time travel backwards to violate causality?
  23. vhbelvadi

    HST-1 moving faster than light?

    I'm no expert in astrophysics so forgive me if this is a trivial question, but I read in (the abstract of) a recent paper in the Journal of Astrophysics and Astronomy that "... It appears that HST-1 moves with an apparent speed of 1.23c±0.91c ..." Now I want to clarify what this means. I take...
  24. A

    2cars moving slightly less than speed of light look faster than light to each other?

    if the cars are moving towards each other.
  25. M

    Whether the speed of alternative/direct current is faster than light?

    Whether the speed of alternative/direct current is faster than light? What's the speed of alternative and direct current in metals? c, less or greater? It is impossible to be c because metal is not vacuum.
  26. R

    Is the speed of expansion of the universe faster than light?

    the speed of light is C and the age of universe is 15 billion years so can't we assume that the radius of the universe can't be more than 15 billion light years? also has the speed of light changed since the beginning of the universe?
  27. marcus

    You should be shot for asking: how does matter move faster than light?

    We got some questions like: how did our matter get here ahead of the ancient light that is just now catching up? How can matter move faster than light? In normal expansion cosmology there is a uniform pattern of expanding distances. When distances expand uniformly nobody gets anywhere. There...
  28. B

    Does quantum entanglement allow information to travel faster than light?

    Does quantum entanglement allow information to travel faster than light? http://en.wikipedia.org/wiki/Faster-than-light if you scroll down to quantum mechanics.
  29. C

    Big Bang Expansion: Faster than Light?

    I was watching 'Into the Universe, with Stephen Hawking', and it said that once the big bang began, in a few minutes the universe was the size of a galaxy. Einstein said that nothing could travel faster than the speed of light, if so, how did the big bang expand that fast?
  30. A

    Is Faster than Light Time Travel Possible?

    Hello, I'm a high school senior interested in studying physics in college. I was listening to a podcast by Neil deGrasse Tyson in which he stated that if one could travel faster than the speed of light, it might be possible to travel back in time. He didn't really expand on that so I was...
  31. K

    Barber's pole - appear faster than light?

    Hi, so imagine this: You have (for this theoretical situation) an entirely massless barber's pole. When it spins, the speed of the of the circumference of the pole is less than the speed the line appears to travel up (or down) the side of the barber's pole. If you were to spin the pole, could...
  32. A

    Exploring the Mystery of 'C': Is It Faster Than Light?

    Is it same as 'c'? or is it greater (though it may be very small difference) than the normal speed of light?
  33. Alain De Vos

    Hubble law&galaxies w speeds faster than light

    As speed of galaxies is proportional to distance. Can we assume some galaxies have speeds grater than c? And do they have a negative time with a reference frame bound to earth? And the light they emit does it have red shift below cosmic background radiation? ...
  34. V

    Can't we transfer information this way? Still faster than light?

    Hi, I was reading the thread previously posted on faster than light, I don't know why it's been locked. I didn't understand this myself. What does it mean to say there seem to be ways for something to go faster than light... but not convey information? What about this arrangement: Consider...
  35. L

    Instantaneous Particle Decisions: Why Isn't the Property Set Upon Splitting?

    I was watching a lecture by Prof Wolfson, and he said there was an experiment where a particle was split, I can't remember which, and so either charge was positive in one direction and then negative the other, or spin up and spin down, but in any event the two new particles were sent to two...
  36. B

    Is Faster Than Light Travel Really Traveling Backwards In Time?

    On wikipedia it says that nothing travels faster than light but yet their things that do travel faster than light,even though these processes do not carry information do they still travel backwards in time? In the context of this article, FTL is transmitting information or matter faster than c...
  37. T

    Galaxies travelling away from each other faster than light

    This might seem simple to some of you on here, but I have a question that's been bothering me, most likely due to my lack of understanding, not an actual problem. If two Galaxies, A and B, are traveling away from each other, say each at 3/4 the speed of light, does that not mean that if you are...
  38. R

    Faster than light travel: it either constantly happens or never

    I'd like to share some thoughts I have had on faster than light travel, and hear from you if it really can be that simple. In short, it can be said that if we believe to have proven the relativity of the speed of light, faster than light travel is, by definition, impossible. No formulas, no big...
  39. P

    Information transmitted faster than light?

    Hi everyone, neat forum you got here. This one's been bothering me for a while, I hope you can help me. I've often seen this question satirized, but I've not yet come across the answer. I've often heard it asserted that information of any kind cannot be transmitted from one place to another...
  40. G

    Why do x rays travel faster than light in some states of matter

    hi All, why is this? some matter has a refractive index of slightly less than one for light in the x ray region. This implies a phase velocity faster than c, right? could someone explain what is actually happening here? THANKS!
  41. M

    Am I missing something or is this faster than light

    suppose we use a machine that can fire two lasers at opposite direction at the same instant after 1 second the one laser would have traveled |C| distance to right and the other laser would have traveled the same distance to the left so from the lasers point of view the other one in moving -2c...
  42. A

    Faster than light and way smaller than electrons

    how can this hypothesis be disproved that matter exists made of particles having million times less mass than electrons and million times faster than light and not interacting with the the matter or waves we know of making a universe surrounding our universe
  43. D

    Faster Than Light Travel: Exploring Kinetic Energy

    They say that faster than light travel is impossible. However, if you made a rod 1 light year long and someone was standing at the other end when you bumped it. They would feel it immediately. The kinetic energy generated by the poke reaches the person before the light. Kinetic energy is an...
  44. S

    Why faster than light is impossible?

    hi, could you tell me why traveling faster than light is impossible? thank you!
  45. D

    Faster than light? Faster than light Faster than light

    I'm amazed at how often the question arises, and how many people are interested in "faster-than-light" travel. So in anticipation of the next passer-byes who may want to ask the question, here is a preemptive, answer (yeah, a jeopardy-type thread I guess), just to show how it can make perfect...
  46. O

    Possibility of Traveling Faster Than Light?

    Hi. I'm a currently 17 years old and a physics student in high school. I am obviously not very educated in the sciences yet but we were discussing black holes in class and something caught my attention. This is mainly a "is this possible" question and I'm sorry if i am breaking any rules... it...
  47. P

    Could the Discovery of Faster-Than-Light Speed Rewrite Physics?

    if it was discovered that something can be made to travel faster than the speed of light, does that completely rewrite physics as we know it ?
  48. B

    Frames can really travel faster than light?

    I've read about 'ergosphere' in wiki and surprised at the information presented that ergospheres around very fast spinning black holes can drag space time many times faster than light! Such that any object that falls into this spinning ergosphere, will also begin to 'accelerate' to match the...
  49. E

    Scharnhorst, faster than light

    In http://www.nat.vu.nl/~scharnh/m16newsc.htm it is described correction to the speed of light, if a measurement is made on 1 um. But, let us ignore practical problems: what happens at very small distances. Does speed of light converge or diverge? What QED calculations show?
  50. J

    Does general relativity allow for faster than light travel?

    I understand special relativity enough to know that for anything traveling faster than light, there will exist a reference frame for which it is traveling back in time... However, I've heard claims that general relativity allows for the possibility of traveling faster than light by...
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