What is Ftl: Definition and 174 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. S

    Idea's for FTL and Space travel

    Hello Everyone this is my first post on the forums and I want to share my ideas on what FTL is how it would possibly work. Now first thing is that I choose this part of the forum because of what FTL would involve. Now I am 14 who greatly interested in mechanical and electrical engineering and...
  2. Q

    Exploring the OPERA Neutrino FTL Result

    Okay, so, the FTL neutrino result from the OPERA experiment is still being questioned, and that's good. But, assuming they really did travel faster than light, I have a few questions: 1. Didn't we learn that if things travel faster than light then they travel back in time? So if the neutrinos...
  3. S

    I've got my FTL boots on (another silly black hole question)

    Good Afternoon, to those of you that are existing in the afternoon. For all else, good morning, good evening and so on. Before I begin, this is more of a question about the behavior of light in immense gravity than anything else. I'm well aware that under the best of circumstances, or the...
  4. F

    FTL and Time Travel: Exploring the Connection

    Hi 'body, ok, this is a well known issue, but i still can't find a valid explanation of why FTL implies time travel. I've read lot of explanations, and each one ends up with a nonsense telling something like "if you drive a FTL car when you'll arrive you'll see yourself opening the car door...
  5. S

    FTL Travel: Is it Possible to Violate C?

    As one may have deduced from my name, FTL (faster than light) travel interests me very much even if it will forever remain in the realm of Sci-Fi. I am a layman, and a deep understanding of the math and equations eludes me, I must admit. However, my question remains. First of all, there are...
  6. U

    Broken law of radiactive decay and broken law of FTL

    There has been a suspicion that solar neutrinos can interfere with the rates of radioactive decay in isotopes. Could this mystery (somehow?)be tied to the neutrinos that are being recorded as 'faster than light'? For example the neutrinos pick up extra energy from the radioactive decay...
  7. W

    FTL Comm: Exploring the Possibility of Neutrino Transmissions

    If FTL was true, shouldn't SETI start searching patterns also in neutrino bursts, and not scan as they do now, only electromagnetic radiation? Wouldn't it be wiser for an intelligent species to cut down transmission time, by sending messages using FTL particles?
  8. S

    SR, LET, FTL & Causality Violation

    In SR. Anything FTL or superluminal can affect causality because there would be some frame where things move backward in time. Since SR is equivalent to Lorentz Ether Theory. And LET is about additional dynamics that occurs in the backdrop of Newtonian absolute space and time. Then how can you...
  9. L

    The principle of inertia and hypothetical FTL particles

    Hello, A recent paper by Cohen and Glashow argued recently that FTL neutrinos would quickly lose energy by pair creation (in vacuum). Starting from the principle of inertia, I had a hard time trying to understand that. According the principle of inertia, the physics should be the same in...
  10. S

    FTL implies Backward Time Effect

    Any faster than light signal can create backward time effect by means of some frames seeing the signal go to the past of the origin. Is there any illustration or website that illustrates this clearly? I'd like to know if the return path carrying the signal needs to travel faster than light...
  11. J

    Question about FTL travel vs. FTL acceleration

    Hello all, this is my first post everyone! I've had a curious mind about the limitations faster than light-speed travel ever since I first heard of the concepts involved as a young kid in science class. Ever since I have inquired about this subject to many teachers and professors. I've never...
  12. A

    Quantum Entanglement FTL Thought Experiment

    I am not sure if I understand quantum entanglement so I will propose a thought experiment which you can tell me if it is correct Say I entangle two quanta of matter, such that by observing one I collapse the wave function of the other immediately. Then I give one of the particles still in...
  13. E

    Is the Speed of Light Really the Limit of the Universe?

    I was watching this show and it was talking about the usual stuff such as wormholes and warping spacetime but the one thing that caught my attention was towards the end. I can't remember the guy`s name but he was talking about observing spectral lines and how when he had looked in one direction...
  14. U

    Walborn and FTL: Exploring Quantum Eraser with Double Slit

    Walborn = ‘Double-slit quantum eraser’ with double slit and eventually quarter wave plates. http://grad.physics.sunysb.edu/~amarch/Walborn.pdf p. 5 section V: ”Figure 2 shows the standard Young interference pattern obtained with the double slit placed in the path of photon s, without...
  15. S

    Mechanism for FTL information exchange.

    First, let me point out that this is probably wrong. Anytime I hear faster than light travel I am automatically skeptical. I just haven’t figured out why it’s wrong yet. Any ideas? 1. Two devices situated in between Bob and Alice produce two streams of entangled pairs of qubits. Each pair...
  16. S

    FTL is not possible via entanglement because you need to compare both the photons

    Faster than light (FTL) is not possible via entanglement because you need to compare both the photons... or in other words entanglement is a single system that is "spread out" (across time-space) , the two photon pair behaves as a single system in which the two photons are within that system...
  17. S

    FTL via entanglement- paper discussing similar

    I just found a paper which was thinking along similar lines: http://casimirinstitute.net/coherence/Jensen.pdf Any comments on why FTL is not possible (after browsing the paper)?
  18. S

    Entanglement - Does FTL via entanglement violate causality or relativity?

    Does FTL transmission of information (via 1 entanglement or 2 any means) violate causality? FTL = faster than light1. I argue that FTL (of information) does NOT violate causality or relativity. 2. Also FTL (of massless information) is possible via quantum entanglement. All you need is a DCQE...
  19. S

    Is FTL Communication Possible Through Quantum Entanglement?

    Does that mean if there were zero (or close to zero) "noise" ...faster than light (flt) transfer of information would be possible? i.e. if the experiment was conducted in some dark & quite region of space-time...where only the entangled pairs were allowed strike the detectors (Ds and Dp)my...
  20. S

    Why would FTL not be possible even in a noiseless place?

    I am illustrating this via both questions and an experiment both of which are conceptually are dealing with the same idea. http://en.wikipedia.org/wiki/Coincidence_counting_(physics ) Question: 1 a) if there were zero noise, and only single photon was sent, do we need a co-incidence...
  21. J

    Exploring the Standard Model's Role in Prohibiting FTL

    I was reading Baez's FAQ at http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html#17" and I came across this nugget Except for gravity, all physical phenomena are observed to comply with the "Standard Model" of particle physics. The Standard Model is a relativistic quantum...
  22. S

    What's wrong with this FTL experiment?

    Back to Alice and Bob. Alice is trying to transmit solar flare information faster than light to Bob, say 8 minutes earlier. Alice is sitting close to the sun, watching for solar flares. Bob is sitting on earth. The deal is: Alice if there is solar flare before noon, alice will...
  23. Ryan_m_b

    Why Does FTL Travel Lead to Time Paradoxes?

    I'm not a physics student but have always been interested. That said my knowledge is very slim. I've always wondered why traveling faster than light would lead to time travel, I've poured over websites and other forums but they tend to descend into physics that is beyond me. Here is an outline...
  24. D

    Entangled Photon Repeater = FTL Communication?

    Allow me to create a scenario and ask questions first, then subsequently make an admission of ignorance. Assume we create a device (the source or repeater) that produces two beams of entangled photons at a steady, pulsing rate. Each beam is focused on a target at a far-away station. The...
  25. MattRob

    Is it Possible to Travel Faster Than Light?

    First, let me be perfectly clear that I'm not implying Einstein was wrong. The lorentz equation clearly states that reaching the speed of light from a stationary perspective relative to the immediate gravitational potential is impossible ("relative to the immediate gravitational potential" i.e...
  26. F

    Information Abou FTL Video Needed

    Hello, I am searching for the equipment used in the Youtube/BBC video posted below. I have looked for contact info at Cologne University, but a lot of their sight was not translated over to English. Specifically, I am searching for the barrier used in the video. Also I hope this is the...
  27. Z

    Why can't we use quantum bit entanglement for FTL information?

    I don't understand. Why can't we use quantum entanglement by the means of altering a state of an entangled electron so we can send an instantaneous bit of information to anywhere in the universe infinitely fast by the other electron changing its quantum state? We can can in theory transmit...
  28. B

    Causality violation from FTL signaling within the same reference frame only?

    I apologize if this has been asked before. I searched numerous times and couldn't find any discussion on this specific topic. Every description I've read of the impossibility of FTL signaling uses some variation of this diagram: http://www.theculture.org/rich/sharpblue/archives/000089.html...
  29. I

    Using Black Holes for FTL travel

    So... my first post, and bear in mind, all I know of Black Holes is what I've read of Black Hole and Penrose Effect articles on Wikipedia. (don't hate me) Would it be possible to use Black holes' Ergosphere for FTL travel? And this is all on the "if" that we, or some other race, achieved...
  30. D

    Can the Scharnhorst Effect Be Overcome by Gravity in a Long Tube?

    http://en.wikipedia.org/wiki/Scharnhorst_effect I found one attempt to explain why it can't be used for FTL signalling: http://arxiv.org/abs/gr-qc/0107091 but I don’t find that article convincing. But I’ve got an alternative idea. Say, we make a very long tube. Because of the Casimir...
  31. R

    Can Quantum Entanglement Transmit Information Faster Than Light?

    Hi everyone, first post here :) Someone told me that information could be transmitted faster than light using quantum entanglement. I do not believe this, but I'm not really knowledgeable in this area so I started to investigate, and I haven't found an answer. I came here hoping you could help...
  32. M

    Quantum Entanglement: Bell's Telephone - Possible FTL Comms?

    Faster than light communication w/ Quantum Entanglement (Bell's telephone)--Possible? I got intrigued by the following description: of a faster than light communications grid over interstellar distances: http://www.seti.org.au/spacecom/quantumcom.html Normally I'd ignore such things on...
  33. K

    Why FTL travel of light spot can't carry any information?

    http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html#3 But it didn't explain why. I just don't get it, let's say the spot travels from A to B, why can't I say some information travels from A to B, for example the shape of the spot?
  34. T

    A non-technical explanation for FTL quasar motions

    A non-technical explanation for "FTL" quasar motions I was trying to think of an accurate but non-technical explanation for quasar motions that seem to be faster than light, and I came up with one. A have a friend in Atlanta and he sends me a book via UPS. That book takes three days to get...
  35. I

    Dangers of FTL Space Drives: AIAA/NASA Report Analysis

    For kicks, I have been reading the following AIAA/NASA paper on hypothetical space drives: http://www.grc.nasa.gov/WWW/bpp/1997-J_AIAA_SpaceDr.pdf Now, I have to admit that I only have a cursory understanding of general relativity & differential geometry. But assume for a moment the...
  36. A

    Can Dark Matter Travel Faster Than Light?

    Hi! I'm sure this has been done before, but is it possible for dark matter to travel faster than light (at least some candidates for dark matter)? We know that ordinary matter is limited by the speed of light, but what about dark matter? For all we know, dark matter may not use c-limited...
  37. U

    FTL communication: might QM entanglement trump relativity?

    FTL communication: might QM entanglement "trump" relativity? As we presently understand entanglement, it can't be used for FTL communication, since some speed-of-light exchage of information between Bob and Alice is required. So c apparently still remains the communication speed limit. But...
  38. K

    Having trouble understanding why FTL implies time travel

    I found a decent page explaining this but it's a little deep for my understanding. I think I understand the basics of special relativity where the speed of light remains constant regardless the velocity of 2 observers, the laws of physics do not depend on location or motion, and that length...
  39. S

    Can a pole traveling at 0.88c fit inside a 2 light year long garage?

    before I start, I should say that I'm a layman and as such will probably say something which sounds quite stupid to the rest of you. I will clarify anything that needs clarifying Ok, so we have A - a 2 light year long garage with two doors that can swing open and closed B - a 4 light year...
  40. X

    Physicists Theorize New Method for FTL Travel

    New method would not break Einstein's Theory of Relativity -xCross Source: http://www.dailytech.com"
  41. P

    MWI and FTL Communication Possibilities

    I know that currently accepted theory is that entanglement cannot - and never will - be used to send FTL communications. Leaving that minor detail aside, what I am not clear on is why _quantum_ FTL communication would necessarily violate SR if one believes in MWI. Let's say Cramer's...
  42. R

    Doesn't QM allow for FTL travel?

    My knowledge of QM is far from great, but I can't figure out what I'm missing here. When looking for e.g. an electron, it has a certain probability to be at a certain location, right? So how does *not* this allow for the electron to travel faster than light? If I take two measurements, one...
  43. M

    Why does quantum entanglement not allow ftl communication

    quite simply the above question. Why does quantum entanglement not allow for faster than light communication? Thanks
  44. P

    What if Cramer's FTL Experiment Worked?

    I hope this isn't considered too speculative for your guidelines, but I'm very interested to hear what people think would be the implications for QM if Cramer's FTL experiment actually worked. Would it prove or disprove any of the current interrpetations (transactional, Bohmian, MWI)? My...
  45. Lord Crc

    Faster-than-Light Communication: Exploring Double Slit Quantum Eraser

    Hi, I stumbled upon http://grad.physics.sunysb.edu/~amarch/" about a double slit quantum eraser experiment. Reading it I got the idea that it could be used for faster-than-light communication. The problem is that I couldn't figure out in which way this method would fail (other than being a...
  46. L

    FTL travel: Do you think we can do it?

    I think YES! I'm a fan of quantum tunneling, or put simply, raising the speed of light. There have been a few successful experiments proving this, like the one performed by Günter Nimtz in 1994, who sent a FM broadcast of Mozart's 40th at 4.7 times the speed of light.
  47. S

    Is there any truth to this? FTL Gravity and EM Waves

    http://www.youtube.com/watch?v=5wnk6FVXCmc&feature=related That is one of several parts, 4 or 5 I believe. So is there any real science or truth to what he is saying? If he is correct it could quite possibly be the most important discovery in human history. Mind you, I'm not talking so...
  48. Y

    Solving the Capacitance Circuit: Time Constant & Charging Process

    capcitance again FTL :( Homework Statement All capacitors of the open circuit in Figure 3 are discharged at time t = 0, when the switch S is turned on and capacitors starts to be charged. What is the time constant \tau of the charging process? What is the charge on capacitor C2 at an...
  49. P

    Has FTL communication really never been tested in this way?

    http://cosmiclog.msnbc.msn.com/archive/2007/07/17/274531.aspx I know most physicists reject the idea of FTL communication but I'm surprised the experiment described in this article wasn't carried out years ago or has it? Wouldn't the existence or absence of an interference pattern created by...
  50. Y

    Quantum Leap FTL: Is it Possible?

    Various quantum states are described as existing in one state or another, but nothing in between. A simplified example is an electron moving from one shell to another. When that electron transfers from one orbit to another does the electron not exist for a period of time or is the transfer...
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