Ftl Definition and 174 Threads

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.

View More On Wikipedia.org
Recent contents Top users
  1. M

    FTL: Is Faster-than-Light Information Relocation Theoretically Possible?

    However the question here is phrased a bit differently: Is the relocation of a piece of information from one spot to another in a shorter time than c-speed light would cover the distance theoretically possible? Or at definitively least not ruled out to be impossible. From what I know of...
  2. J

    I Can Emergent Spacetime Concepts Enable Faster-Than-Light Travel?

    I posted something similar to this in Beyond the Standard Model forum but it's more appropriate here as it is more of a Special Relativity & Spacetime question for SR expert like Peterdonis. My inquiry is with regard to this. Many of you are familiar with this concept about Emergent Spacetime...
  3. M

    B FTL Paradox: Grandfather Paradox Explained

    So here it goes: 2 points in space A & B. 1 superluminal object (fixed at 10c, no acceleration) that periodically transmits photons as soon as it starts moving. 1 observer with a very high accuracy photon counter removed a sufficiently large distance from the 2 points for light to take a small...
  4. Glenstr

    Could FTL Communication be Achieved via Mechanical Connection?

    Say we have this scenario, we have two bodies (big rocks, asteroid etc), existing in the vacuum of space, both are in perfect sync with each other (distance between them remains static) and are 1 light second apart in distance. Bob is standing on one rock and Mary on the other. Each has a radio...
  5. zonde

    Eberhard assumptions and FTL communication

    In this paper http://dx.doi.org/10.1103/PhysRevA.47.R747 Eberhard derives Bell type inequality from these assumptions: A theory is defined as being "local" if it predicts that, among these possible sequences of events [with the same number of events N], one can find four sequences (one for each...
  6. G

    FTL Communication in an Interstellar Civilization

    There are lots of sci-fi settings in which Mankind has become an interstellar civilization and lives on numerous planets throughout its galaxy. However, if the fastest we can communicate is at the speed of light, we will have to wait ages to receive a message between planets. Does this mean...
  7. T

    Faster Than Light Communication Through Space-Time Bubbles

    I think we all know what an Alcubierre drive is, well this is similar in principle. Is it possible to conduct faster than light communication through the acceleration of a bubble of space time? is it even possible to do this without a ship, and just send it out as a warp bubble from a point like...
  8. entropy1

    Bell-state entanglement swapping and retrocausality

    I thought there were already some posts about this, but I can't find them.:frown: In this article of Anton Zeilinger et al. they perform an experiment which suggests FTL or retrocausal influence. Alice and Bob both produce their own polarisation-entangled photon pair, both send one photon of...
  9. SlowThinker

    The Zeilinger experiment being FTL?

    Reading the recent Insight series on Block Universe, Blockworld and its Foundational implications Part 5, the second paragraph talks about an experiment where a photon detected earlier is affected by the position of a detector far away: First, let me round the focal length of the lens to 1...
  10. R

    Using GHz multi-particle entanglement for FTL communication

    Although there are numerous questions about entanglement and FTL communication, I can't find anything directly related to this. I proposed a method for FTL communication via GHZ multi-particle entanglement at...
  11. Stephanus

    FTL: Who Proposed It & What Other Sci Fi Uses It?

    Anybody knows who's the first to suggest FTL? Gene Roddenberry? And what about other sci fi FTL. Do they use warp drive or other means? Thanks.
  12. S

    Excitation of two-atom state by single photon : FTL hope?

    This concept is rather interesting : "Excitation of two atoms by a propagating single photon pulse" -- http://arxiv.org/abs/1411.3445 . They say that, in principle, one can tailor an optical pulse so that it will excite two atoms from the ground state (i.e., the |gg> state) so it ends up in any...
  13. AlexDB9

    FTL Expansion of Space: Rapidity & Infinity

    If the expansion of space in the macrolevel is faster than the speed of light then it should have "more" than infinite rapidity. How does that work out? Thanks.
  14. L.E.N

    The Alice and Bob example of the FTL violates causality

    As many, I wondered why FTL communication has problems with causality. Went over many posts here in PF, and wasn't satisfied. And then I read this explanation, by Richard Baker: (2015-4-2, link is still active) http://www.theculture.org/rich/sharpblue/archives/000089.html His explanation is a...
  15. S

    Hypothetical FTL communication black-boxes and causality

    I found the thread "SR, LET, FTL & Causality Violation", looked through through all of it and read large parts. I believe I found my answer there, but to make sure, I'm asking the question here: Suppose we had some "magical" black-boxes that allow us to communicate information in both...
  16. dragoneyes001

    Exploring Time Dilation: The Effects of FTL Communication on Twin Observers

    EDIT: split from "twin paradox with a twist" thread Re: https://www.physicsforums.com/threads/twin-paradox-with-a-twist.791673/page-5#post-4985729 one question: on the charts I understand the reflections as being at the speed of light correct? what would change in the case of FTL...
  17. Duplex

    The impossibility of FTL information

    I want to make an index over all things against FTL transmission of classical information. All theories, hypotheses, theorems, axioms and rules... you name it. I'm not looking for explanations or references, only the headlines such as Eberhard's theorem, Special Relativity, and Shanon's...
  18. G

    Exploring a Theory for FTL Communication

    OK, just had a thought. And I would be grateful if someone could explain why this couldn't work:Place A is on a surface Place B in on the same surface but, say 10,000 miles away from Place A. Therefore communication between them is limited the speed of light . But what if, at Place A there was...
  19. S

    FTL & Causality: Understanding Time Travel

    I understand that the questions behind causality and FTL have been brought up numerous times, and I have read several of the old threads. My question isn't with how is causality violated, it is always assumed that any signal sent would appear to travel backwards in time from one point of...
  20. A

    FTL Communication: The Long Pole Experiment & Modification

    Hello! It was some time ago on one of my visits to this forum where I saw a thought experiment about achieving faster than light communication using an impractically long pole of sorts. For example, practicality aside, if we were to construct a pole with the length of 1 light year, and have an...
  21. drphysica

    FTL Neutrinos: Investigating the Failure of the OPERA Experiment

    So did anybody have figured out why did OPERA experiment failed?? Does anyone know why neutrinos appear to travel FTL??
  22. M

    Entanglement, ftl communication and destruction of the entangled state

    my question is about the no-communication theorem in quantum mechanics: Assume that i have a pair of entangled photons which are entangled on their polarization. also assume that i send one to alice and another to bob. and alice wants to send a message to bob. no communication theorem states...
  23. J

    FTL, avoiding time travel issues?

    After reading about everything I can find on the subject while researching for a story, I've come to the conclusion that wormholes (or "jump" drives or gates) are the only potential "class" of FTL mechanisms which are even remotely (not a problem for fiction) plausible while also not opening the...
  24. craigi

    How do gravitational fields and waves interact with black holes and FTL travel?

    How fast do we expect the hypothetical graviton to travel? It seems that if the graviton were to mediate the gravitational force then it wouldn't be subject to the normal FTL rules otherwise black holes would have no gravitational effect on the rest of the universe. What's the current...
  25. M

    Entanglement Swapping and FTL Communication

    Recent experiments realized the thought experiment of Asher Peres on entanglement swapping. Here's the abstract. Couldn't Alice and Bob in the experiment receive information faster than light from Victor? Here's the set up...
  26. N

    Sci-fi FTL and hyperspace jumps and their worries

    I didn't really know where to put this, so I just put it here. What I wanted to discuss was the following: often in sci-fi movies or series they have the capability to travel faster than light one way or another. Whether it is by means of FTL, hyperspace, wormholes or whatever they always...
  27. F

    Problem with quantum FTL communications

    I know its risky to rely on wikipedia, but on the page on quantum entanglement, it claims that possibly instantly, as soon as one of a pair of entangled particles is measured (say A), then the opposite one (say B) takes on the opposite value. Now to know this, I assume B must somehow know the...
  28. F

    Close to Light Speed: Exploring a Wormhole Drive Concept

    Im writing a story in which it is possible to travel very close to the speed of light. Let's say for the moment that this is some kind of wormhole drive. My conceit is that, due to a quirk of physics, its possible to traverse space almost instantly while time passes for everyone else, so a...
  29. F

    Does this article support the existence of FTL particles?

    I would like to know how this article applies to the possible existence of FTL particles. Does it point to a possible violation of c as the ultimate speed limit of a particle? In layman's terms what is this paper saying? http://arxiv.org/abs/1309.3713 Thanks
  30. cyberdiver

    How exactly does FTL travel cause reverse time travel?

    So I look at the Minowski diagrams, and I can understand that moving on the y means moving in time, and moving on the x means moving in space, but drawing some diagrams of my own, I find it impossible to see why it would imply FTL travel. All objects travel either directly on the x...
  31. D

    What is a current view on Nimtz (FTL) effect?

    Based on WIKI, there is no consensus, as I understand, experimentally the effect is confirmed, but there are different interpretations trying to explain that there is no FTL. There are several discussions about Group velocity vs Phase velocity, but I think it we produce very short impulses we...
  32. andrewkirk

    Can Alice and Bob play FTL ping pong?

    Alice entangles a pair of particles and sends one of the pair - particle B - towards Bob, keeping the other one - particle A - trapped within some sort of containment device. Alice is on Earth and Bob is several light minutes away, say on Mars. Alice and Bob each have two apparatus for measuring...
  33. G

    Can the Reflectivity of Newton's Rings be Manipulated for Improved Detection?

    Probably this is an easy question, given that Newton's rings are probably one of the most common and famous light phenomena. In any case, I was wondering that given that say you have the second interface at a position in which the reflectivity on the first is 0, but then you are allowed to...
  34. DevilsAvocado

    What’s wrong with this EPR-Bell FTL Gedankenexperiment?

    I truly believe Einstein was right; Faster-than-light (FTL) communication is not possible. And this far, nobody has proven Einstein wrong, not even “Italian Massive Mountains” could do it. There are hypothetical particles like the Tachyon that (in theory) always moves faster than light...
  35. Crazymechanic

    Could Quantum Entanglement Allow for Faster Than Light Communication?

    Hello. I have a question suppose we have two entangled electrons , now we take them a sufficiently large distance away from each other so that the EM (light) wave would have to travel a certain distance/time.When one electron is measured at one place and the other at the other place they botch...
  36. A

    Something I don't understand about FTL travel

    Okay first of all, I know it's impossible to travel faster than light. But they say that IF... IF you could, then you would arrive at your destination before you left. That's what I don't understand. Like for example, it takes light 8 minutes to get to us from the Sun. So if a person...
  37. dbmorpher

    Can Black Holes Be Used for Faster-Than-Light Travel?

    Hello dbmorpher here, I am an avid Halo fan, and in the lore the ability to go faster than light is from the http://halo.wikia.com/wiki/Shaw-Fujikawa_Translight_Engine I wanted to know if miniature black holes and hawking radiation would be able to rip a hole in space-time. If not what are...
  38. T

    Can We Send Information FTL Through Entanglement?

    I know its been asked a lot of times, but reading all those threads convinced me that through entanglement we can not send information faster than light (FTL). We can just correlate the result of random experiments. Nevertheless, reading this articles (and a lot of other similar articles)...
  39. M

    QED, partial reflection, Feynman, FTL

    I would like to discuss partial reflection of the photons and how thickness of the material (let's say glass) affects reflection (originally from Feynman, QED). Let's say we have a glass 1m apart from the detector, and another glass 100m apart. The thickness of second glass affects probability...
  40. K

    Help understand FTL causality implication

    First of all, I am fairly new to relativity, but not clueless. I am not saying that FTL is possible. I am not denying relativity principles. I am stating that FTL may be plausible. Relativity gives flexibility to how you can synchronize clocks and that does not affect outcomes of most...
  41. G

    FTL warp experiments: Media hype or significant?

    FTL "warp" experiments: Media hype or significant? http://www.huffingtonpost.com/2012/09/17/warp-drive-star-trek-feasible_n_1890679.html This is just one article, but they're are plenty more to be found. There is one thing that confuses me though. Alcubierre's warp drive idea seemed to...
  42. X

    FTL Travel - Are we in trouble when the oil runs out?

    Is there a race against time to discover FTL travel? Hey guys. I would like to ask your opinion on a possible crisis for humanity. If humans havn't discovered practical FTL space travel before oil becomes scarce... could we be in trouble? When oil runs out, lots of things will change. Could it...
  43. J

    What is the FTL drive model that is not the Alcubierre?

    This is driving me nuts and I'm forced to ask this question. The Alcubierre FTL drive model had some limitations, so another physicist whose name began with a D or an N, I think, came up with a revised/improved model. Can you please remind me what it's called? Thanks
  44. MattRob

    Best Shot at FTL Travel in 21st Century?

    Hello, So, I'm writing sci-fi and I'm "doing my homework" to make this thing a pleasant read to those in the know, and my own standards demand I make this as possible as... Possible. So what's the best shot at an FTL-capable vessel, that's practical in a century? (i.e, not wormholes or...
  45. S

    FTL, causality, QE - some questions

    There are numerous posts on (attempting) FLT information via QE and whether causality is violated. I believe that there are definite answers to them and are buried (out there somewhere) in the gazillion posts/replies in the forum. FTL = faster than light, QE = quantum entanglement I hoping...
  46. S

    Understanding communication via QE - is filtering the only obstacle? to FTL

    Understanding communication via QE - is filtering the only obstacle? to FTL communication FTL = faster than light In a two-photon (i.e. entangled photons) double slit or similar experiments - Information cannot be sent FTL because there are no patterns (mapping to which-way or no-which-way)...
  47. G

    Non-unitary process? Doesn't that mean FTL?

    OK, in the quantum eraser set up, you get a bump because of decoherence in the beam that does not pass through the double slit. In that beams causes the vector states of the left and right slit to be orthogonal. Even if you put the pi/4 POL in that beam, there would be two orthogonal states (the...
  48. C

    Can Light Travel Faster Than c in Diamagnetic Materials?

    The speed of light in vacuum is 1 / sqrt(mu_0 e_0). In matter, this is modified using relative permittivity and permeability, so the speed of light in matter is c / sqrt(k_m k_e). In diamagnetic materials, isn't k_m < 1? Then we'd have light going faster than 3 * 10^8 m/s in, say, nitrogen...
  49. D

    Does SR actually forbid FTL travel?

    Does SR actually imply that FTL travel would allow for violations of causality? Here is some reasoning to suggest that it does not: (I would be surprised if there were no holes in the reasoning. My desire to find these holes is what motivated me to post this here.) Consider the following...
  50. E

    Is travel at almost infinite speed (FTL) actually possible?

    Relativity is a truly fascinating and interesting subject that I don't fully understand. I'm currently in the process of studying it and this idea popped up in my head. This is just pure speculation from my side, which I expect to be wrong. I'll now try to explain the foundation for my...
Back
Top