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. Hereweald

    B Curious about this proposition for measuring for FTL

    So the theory relates to measuring yhe state of a quantum particle, say up or down. Specifically this build on the technique described as repeat measurements seen in this video: I understand why repeat measurements wouldn't work. However what if this series of measurements was done multiple...
  2. K

    Why do we need FTL if traveling at the speed of light is instantaneous?

    I notice that quite a number of threads revolve around FTL matters. My understanding is that if a body is traveling at the speed of light, then according to its on-board clock, departure and arrival are instantaneous irrespective of the distances involved. Why then does one need to posit FTL...
  3. Delta2

    I Entanglement and FTL signaling in professional scientific literature

    According to professional scientific literature and to our best understanding, are there any suggestions that entanglement might imply some sort of faster than light signaling between the entangled particles? I know that according to relativity nothing can travel faster than light, but what...
  4. M

    If you are moving in a ship at FTL, could a pilot react at FTL?

    Faster than light travel is most likely impossible (at least in this dimension) BUT hypothetically I was thinking back to Star Wars: The Force Awakens. At the near-end of the movie, Han Solo, Rey, Chewbacca, Finn and BB-8 get through Starkiller Base's shield by exploiting a loophole. The shield...
  5. A

    I Superluminal Quantum tunneling without FTL messaging

    I recently viewed a PBS "Space time" video The video references two articles of which one is paywalled while the other is not. https://iopscience.iop.org/article/10.1088/1367-2630/abb515/pdf https://www.nature.com/articles/s41586-020-2490-7?proof=tIn the discussion section of the free article...
  6. Sirius_Prime

    I FTL Travel: The Matryoshka Paradox

    Okay, so, I hope you all have patience with me. I didn't study physics but enjoy reading and theorizing, so I'm familiar with many concepts but not with the formulas. The thought occurred to me when I was considering that when traveling along with an object you only need to expend enough energy...
  7. Orenshved

    What's needed to use quantum entanglement for FTL data transfer?

    Hey all, I need help with the book I'm currently writing. What would it take (even theoretically) to use quantum entanglement for FTL data transfer? From what I understand, the state of entangled particles can not be changed without breaking the entanglement. Do you think this would ever be...
  8. J

    I Time Dilation & Superluminal Travel: 2 Questions

    Two quick questions on time dilation and superluminal travel for a situation in which two people are in motion with respect to each other. 1) If Jack is moving with respect to Jill, Jill sees Jack's clock move more slowly relative to her clock, so Jill perceives Jack aging more slowly relative...
  9. I

    B Fundamentals of Lightspeed: Questions & Answers

    Hey there, I'm aware this is a bit of a stupid question, and I think that I understand the principle fundamentally, however, my intuition is still having a little trouble catching up, and I'm trying to figure out if it is because of an important detail that I have missed/misinterpreted. I think...
  10. S

    Can FTL Travel Be Used as a Weapon in Sci-Fi?

    I'm just curious, there are a lot of "warp speed" and "Faster than Light" and "Hyperspace" things in movies and books. It seems to me that such technology would be somewhat devastating if not policed or controlled properly. For example - the Death Star in star wars. It is a technology to...
  11. SongDog

    B Exploiting radiocarbon dating for FTL communication

    [Mentors' note: This thread was split from https://www.physicsforums.com/threads/can-we-carbon-date-a-gas.981218/] Empirical test: If one wished to implement a controlled experiment of this sort, start with separating stocks of pure C12 and pure C14 with a mass spectrometer. Use the C12 to...
  12. J

    B Can Info Travel FTL? Understanding Speed of Information

    Summary: Can the speed of information be faster than light? Say you had two people in space and they were 10 light years apart. Each person has a light bulb and battery connected to an electrical switch. Pressing the switch turns the light on, once it is released it springs back to the off...
  13. B

    Can increasing the speed of light lead to more efficient photon rockets?

    Radiation pressure that light provides is weak. The photon rocket only gives thrust on par with rockets if you are willing to exhaust way more energy than normally used for rocketry (antimatter/matter annihilation). By that time your exhaust beam will be loaded with enough photons to nuke...
  14. M

    I Length Contraction & FTL Speeds: Are Lower Grades Faster?

    I’m not a physicist but let’s say hypothetically ;we have the Millennium Falcon. It’s FTL hyperdrive can go Class 0.5 past lightspeed. Then we have an X-wing which has a Class 1 past lightspeed drive. This is all from the lore. MF is 0.5 and X Wing is 1 but MF is faster. Anyway even though the...
  15. BoMbY

    B Why is it assumed communication through entanglement would be FTL?

    As far as I can tell nobody actually knows how quantum entanglement really works, and yet everyone assumes that quantum states are teleported faster than light. But what if there isn't any actual teleportation, because both sides still share the same position? Maybe in a dimension we cannot...
  16. Alex Torres

    B FTL Communication: Closing Bell Test Loopholes for Quantum Integrity

    Have followed the work of Anton Zeilinger for some time, noticed it's mostly centered in a quest to close Bell test loopholes for the sake of quantum communication integrity but how about if by relaxing this he could overcome the need of the classical channel for communication...take for...
  17. BWV

    Is is just me, or is FTL dead in SF?

    Grew up reading Larry Niven and a host of other legit SF writers that all incorporated some form of FTL travel in their books, then Alistair Reynolds came along and wrote even more interesting interstellar SF without any violations of relativity, now that seems to be a trend. Anyone know of...
  18. Orest

    B Solve FTL Problem with Faraday Cage and Relativity Theory

    Is it possible to solve a problem of overcoming of speed of light with solid objects using faraday cage Theory with equivalent charge?
  19. W

    B Implications of FTL signals in SR

    As I understand if it were possible to send a single faster than light then one can send a signal back into the past. What is the simplest way to explain how this would happen?
  20. Alex Torres

    I FTL communication via delayed choice measurement

    <Moderator's note: 2 threads merged as it is an identical topic.> Given Kim's version of DCQE, let's say Bob in on Earth looking at d0, Alice is on Mars holding the prism that deflects the idler coming from (a) to d3 or (b) to d4. After the experiment run ends Bob should get clump at d0 without...
  21. A

    B Observational Effects of "FTL" spotlight from laser pointer?

    So from what I understand, it's possible to have a very powerful laser pointer where you point at an arbitrarily large and far away surface and make the spotlight appear to move at faster than light. E.g. you can be holding the laser in your hand and you simply flick your wrist. My question is...
  22. yerty4235437y

    B Could Gravitational Waves Allow for Time Travel?

    it seems to me that during a high energy event that a space time compression wave would be created which would then normalize as it spread out. A particle on a back end wave would become close enough to the front end wave that it could tunnel between the two as "distance" is compressed. We...
  23. G

    B FTL train + FTL communication thought experiment

    Please move this if it belongs to other subforums. So i thought about some other stuff and then somehow this idea appeared to me, now according to physics it is impossible to communicate information faster than the speed of light through vacuum which is "c". So for any two bodies moving in...
  24. Y

    I Interstellar Travel Without Propulsion or Time Dilation

    I hope this is the right forum for this question. Imagine alien tech allows them to travel 1 million light years to Earth instantaneously. No thrust, vector, propulsion was involved. They didn't have to approach the speed of light, with its attendant increase in mass. Having arrived at earth, in...
  25. Lunct

    B Can FTL Travel be Achieved With Mass of a Photon?

    Really silly question, but if we assume that our current science is correct, is it plausible that we can move faster than light in a vacuum? Say, for example, can we make the mass of something less than a photon so it then can it move faster than light in a vacuum. I know this sounds like a...
  26. C

    B Why doesn't this FTL communication scheme work?

    If Alice and Bob had a large number of particles entangled together (with state of either 0 or 1), could Alice send information by breaking the entanglement of particles with state of 1 (by flipping the state for example) so that Bob measures 50% of particles to be in the state opposite of 0...
  27. T

    I Quantum entanglement, wave-function collapse

    I have 2 questions i would really like to find an answer to: if we have a quantum pair, we can determine whether 2 quanta are entangled or not assuming that we have access to the information of both of them. so if we have a quantum "trio" instead of a quantum pair, does the information about 2...
  28. S

    Relativity's role in forbidding FTL Information Transfer

    Imagine a (purely hypothetical) situation where someone proposes a scheme that exploits non-classical, nonlocal interference effects to transfer information between Alice and Bob. Apart from the accuracy and plausibility of the quantum mechanical part of the paper, would it be necessary for the...
  29. C

    B Can Relativity Theories Actually Permit Faster-Than-Light Travel?

    Hello, recently elsewhere on the interwebs I was subjected to a discussion on whether it is possible to travel faster the light under relativity. My general rule of thumb is that if you ever think you've found a way to travel FTL under relativity then you don't understand relativity. Especially...
  30. M

    B Could this FTL idea with a fast moving large mass be possibl

    Could this FTL idea with a fast moving large mass be possible? I have recently come up with a possible way to achieve faster-than-light (FTL) travel by using a high speed singularity or large mass. Background As everyone knows, according to relativity, under normal conditions, it is impossible...
  31. S

    I How does this not get me traveling to another star FTL?

    Hi, Please not too many sighs but I'm stuck with this my miracle realisation - the scenario is - I'm in a rocket (tons of fuel ) - I blast away (from Earth say) - accelerate hard for ages and by my special onboard inertial calculator I have got to 100 000km/s (with respect to earth). Switch the...
  32. B

    Is a FTL Drive with a Preferred Frame Enough to Resolve Temporal Paradoxes?

    Lets assume a FTL drive that works only with respect to CMB rest frame (technobabble probably something about inflation/dark energy). So drive speed would vary depending on whether the ship is moving along CMB peculiar velocity (371 km/s towards constellation Leo), or against it. Would that be...
  33. MattRob

    B WSU Shows Negative Mass Exists: Implications for Faster-Than-Light Travel?

    While the title may seem to overblow it, showing that negative mass exists may be just that big. After all, as I understand, the primary obstacle to the reality of the Alcubierre Drive or Krasnikov Tubes is the negative energy density requirements. This of course violates certain energy...
  34. S

    B Trying to understand how FTL would violate causality....

    So I'm not a professional scientist, but rather an avid physics fan. This is one question that no matter how much I research I can't find a clear answer... So for the sake of argument, let's assume that you could actually build something like the Alcubierre Drive and go FTL (I know a lot of...
  35. T

    I Is it Impossible for Entanglement > FTL Communication?

    Lots of people have wondered about whether we can get FTL communication from entanglement. My question is slightly different. Is it impossible to get FTL communication out of entanglement? If it has been shown to be impossible, then we can shut off the entanglement-FTL avenue altogether and...
  36. S

    FTL Travel: Is It Really Impossible?

    Okay, against my better judgment, I'm going to go ahead and kick the hornet's nest. Superluminals. FTL. Whatever you want to call it, moving faster than the speed of light. One of the things a lot of physicists have a conniption over is that FTL would mean causality violations. Special...
  37. T

    I Do laws of physics apply below the event horizon?

    Do laws of physics apply below the event horizon? It appears as if black holes had such gravity as to have an escapr velocity higher than c, which means that things are pulled inwards at higher speeds than the speed of light. Or am I overlooking something?
  38. C

    B Delayed choice experiment and FTL communication

    I've been thinking about a communication system that could allow faster than light communication. The basic principle that would make this system work come from the double-slit experiment and Wheleer's delayed choice experiment, taking advantage of the different patterns that would appear on a...
  39. Stephanus

    B Can we travel faster than the speed of light?

    Dear PF Forum, Before I get a NO answer, I'd like to ask a few question. https://en.wikipedia.org/wiki/Hubble%27s_law#Observed_values As of 13th July, 2016 Hubble flow is 67.6 km/s per mega parsec. Or 67km/s per 31 trillion * 1 million km or per 3.26 million light year. Say a galaxy 11.68 giga...
  40. Ontophobe

    B FTL Spin 1 Gauge Boson: Impact of Dark Matter Discovery

    What would be the ramifications of discovering that a) dark matter radiates something non-electromagnetic, and that b) this radiation always travels at a constant velocity according to all inertial reference frames, but c) this constant velocity is equal to, say, c times pi?
  41. Ontophobe

    B FTL Gravity Waves: Is Faster-Than-Light Travel Possible?

    On the one hand, gravity waves travel at c, but on the other hand, spatial expansion has no speed limit; ie, it can happen at FTL speeds. At first one might think, "So what? Gravity waves are gravity waves and spatial expansion is spatial expansion." But what is a gravity wave other than the...
  42. Gary0509

    I Quantum nonlocality in relation to FTL Communication

    With a modest understanding of 'spooky action at a distance', I've been informed that using entangled particles as a form of quantum bit system would not work for vast distances. It wouldn't be a viable option to communicate instantly with points like our moon, satellites orbiting Jupiter, or...
  43. Claude DeBris

    Why did the FTL Drive fail and strand the aliens?

    I’d like to start off by thanking everyone that’s posted on this site. I just spent two days reading everything on Writing and World Building. Actually that’s a lie, I didn’t read everything, I read every thread on the Writing and World Building forum that might possibly answer the five...
  44. F

    A Experiment design FTL particle though magnetic field

    Hi. I was browsing Wikipedia on a topic, went to magnetic bearings, etc etc...ended up on synchrotron radiation then the phrase about how a moving or accelerat/ing/ed particle passing through a magnetic field generates electromagnetic radiation. Then I has a revelation. How to get a particle...
  45. EnumaElish

    Aliens as FTL Humans: Scenario from Sci-Fi Novel

    What do you think of the following scenario*? Aliens are future humans who discovered faster than light travel. They propagated throughout the universe. In so doing they traveled back in time, to our time, or even earlier times. *I read this in a popular space opera novel. It may have been...
  46. D

    B FTL communication by Quantum Entanglement

    I recently stumbled across quantum entanglement and thought of an experiment. I know that the laws of physics forbid FTL communication, can anyone tell me what's wrong in my following experiment? Information, in classical bits, consists of two states, 1 and 0. To my shallow knowledge, when an...
  47. secur

    A Misunderstanding Eberhard's paper on FTL communication?

    As far as I can tell Eberhard and Ross didn't "prove" quantum entanglement can't implement FTL communication in "QUANTUM FIELD THEORY CANNOT PROVIDE FASTER-THAN-LIGHT COMMUNICATION", 1988 (http://link.springer.com/article/10.1007%2FBF00696109). But it's often cited as such a proof, in threads on...
  48. wolram

    Is a FTL communicator more plausible than a time machine or a preferred frame?

    What is the most plausible FTL communicator, could we in some way use Tachyons?
  49. Stephanus

    B Can FTL communication violate causality without one party moving?

    Dear PF Forum, I've tried to googled how causality can happen by FTL communcation (I use communication, because if it "travels", I'm having trouble calculating ##\gamma## imaginer). But from all examples that I've found it can violate causality if one of the party is moving relative to the...
  50. entropy1

    Non-locality: (FTL) 'influence' at all?

    I have a basic question about the concept of non-locality in QM. I'll explain as I understand it (correct me if I'm missing the essence): The so called 'non-local' property of two entangled photons (for instance), suggests that the measurement of one of the pair 'communicates' with the other...