Dovahkiin789 Posted September 28, 2016 Share Posted September 28, 2016 So I don't have much of a background in physics, since I haven't had the opportunity to take it yet, but I'm really interested in theoretical FTL methods. So my question is- What would it take for some sort of spacecraft to accomplish the speed of light or faster. I understand and methods are probably theoretical I just don't understand the math involved just yet, so I'm hoping for some clarification. Link to comment Share on other sites More sharing options...
zapatos Posted September 28, 2016 Share Posted September 28, 2016 So my question is- What would it take for some sort of spacecraft to accomplish the speed of light or faster. I understand and methods are probably theoretical I just don't understand the math involved just yet, so I'm hoping for some clarification. I think the most likely scenario for achieving FTL travel is for the laws of physics to change. Short of that I am unaware of any circumstance in which you can accelerate a spacecraft to the speed of light or greater. Link to comment Share on other sites More sharing options...
ajb Posted September 28, 2016 Share Posted September 28, 2016 (edited) You can have a speed greater than the global speed of light, but not the local speed. For example, warp drives and wormholes make use of this fact. The general problem then seems to be the actual implementation of these methods - they require exotic matter (negative energy etc) to support them. Along side that, as soon as you can beat a light signal you can create time machines. Causality may also be a problem! Edited September 28, 2016 by ajb Link to comment Share on other sites More sharing options...
Dovahkiin789 Posted September 28, 2016 Author Share Posted September 28, 2016 I think the most likely scenario for achieving FTL travel is for the laws of physics to change. Short of that I am unaware of any circumstance in which you can accelerate a spacecraft to the speed of light or greater. Well that isn't very promising. What about wormholes? From what I've read the main problem would be sustaining it. Is whatever force or particle that does that exist or run with the current laws of physics? Link to comment Share on other sites More sharing options...
ajb Posted September 28, 2016 Share Posted September 28, 2016 Well that isn't very promising. What about wormholes? From what I've read the main problem would be sustaining it. Is whatever force or particle that does that exist or run with the current laws of physics? See what I just posted! Link to comment Share on other sites More sharing options...
Dovahkiin789 Posted September 28, 2016 Author Share Posted September 28, 2016 You can have a speed greater than the global speed of light, but not the local speed. For example, warp drives and wormholes make use of this fact. The general problem then seems to be the actual implementation of these methods - they require exotic matter (negative energy etc) to support them. Along side that, as soon as you can beat a light signal you can create time machines. Causality may also be a problem! So how could negative energy be found or converted from regular energy? Since energy obviously can't be created, there has to be a way. The causualties could be avoided by using robotics at first instead of humans. Link to comment Share on other sites More sharing options...
Delta1212 Posted September 28, 2016 Share Posted September 28, 2016 So how could negative energy be found or converted from regular energy? Since energy obviously can't be created, there has to be a way. The causualties could be avoided by using robotics at first instead of humans. The problem is causality, rather than casualties. If you can outrun a photon, you could return to your starting point and arrive before you left. Robots wouldn't fix that. Link to comment Share on other sites More sharing options...
Dovahkiin789 Posted September 28, 2016 Author Share Posted September 28, 2016 The problem is causality, rather than casualties. If you can outrun a photon, you could return to your starting point and arrive before you left. Robots wouldn't fix that. I accidentally read casualties. Can you elaborate on "return to your starting point and arrive before you left" please? Link to comment Share on other sites More sharing options...
Moontanman Posted September 28, 2016 Share Posted September 28, 2016 I accidentally read casualties. Can you elaborate on "return to your starting point and arrive before you left" please? I'd like some clarification on this as well. You can have a speed greater than the global speed of light, but not the local speed. For example, warp drives and wormholes make use of this fact. The general problem then seems to be the actual implementation of these methods - they require exotic matter (negative energy etc) to support them. Along side that, as soon as you can beat a light signal you can create time machines. Causality may also be a problem! If indeed a method of FTL became possible wouldn't that in of it's self change the laws of physics as we know them? In fact wouldn't that at least show that causality is at least not quite as written in stone as well... Along side that, as soon as you can beat a light signal you can create time machines. Causality may also be a problem! Much like encountering an infinity in an equation wouldn't this indicate a problem with the theory... Link to comment Share on other sites More sharing options...
Delta1212 Posted September 28, 2016 Share Posted September 28, 2016 If you can travel at faster than light speed from point A to point B, there exists some frame for which your arrival at B precedes your leaving at point A. Link to comment Share on other sites More sharing options...
Dovahkiin789 Posted September 28, 2016 Author Share Posted September 28, 2016 If you can travel at faster than light speed from point A to point B, there exists some frame for which your arrival at B precedes your leaving at point A. Ok, that makes it a bit simpler, thanks Link to comment Share on other sites More sharing options...
Strange Posted September 28, 2016 Share Posted September 28, 2016 Ok, that makes it a bit simpler, thanks The article on the tachyonic antitelephone explains the idea a bit more: https://en.wikipedia.org/wiki/Tachyonic_antitelephone Will there ever be a physics term greater than "tachyonic antitelephone"? According to this message from the future, the answer is "no" https://xkcd.com/1699/ Link to comment Share on other sites More sharing options...
Phi for All Posted September 28, 2016 Share Posted September 28, 2016 The talk here at the International Astronautical Congress is mostly about system projects, but I'm hoping to hear a technical paper about FTL. So far, all the talk is about shrinking spacetime in front of a vehicle while expanding it behind. From what I've heard, stopping or slowing down this way doesn't work. Link to comment Share on other sites More sharing options...
Mordred Posted September 28, 2016 Share Posted September 28, 2016 (edited) Along with generating enough gamma rays to wipe out the planet you leave and arrive at. I'll see if I still have the arxiv Alcubierre drive paper correlating the gamma ray aspects. located it. http://www.google.ca/url?sa=t&source=web&cd=3&ved=0ahUKEwjvlqC-8bLPAhVK7GMKHUutAjAQFggfMAI&url=https%3A%2F%2Farxiv.org%2Fpdf%2F1202.5708&usg=AFQjCNHjTF6Xb8C0z-xXv6nqIAL1sNJLsA&sig2=CAAP4G_fAX8isctE934MTg Edited September 28, 2016 by Mordred Link to comment Share on other sites More sharing options...
Moontanman Posted September 28, 2016 Share Posted September 28, 2016 (edited) The talk here at the International Astronautical Congress is mostly about system projects, but Im hoping to hear a technical paper about FTL. So far, all the talk is about shrinking spacetime in front of a vehicle while expanding it behind. From what I've heard, stopping or slowing down this way doesn't work. Along with generating enough gamma rays to wipe out the planet you leave and arrive at. I'll see if I still have the arxiv Alcubierre drive paper correlating the gamma ray aspects. located it. http://www.google.ca/url?sa=t&source=web&cd=3&ved=0ahUKEwjvlqC-8bLPAhVK7GMKHUutAjAQFggfMAI&url=https%3A%2F%2Farxiv.org%2Fpdf%2F1202.5708&usg=AFQjCNHjTF6Xb8C0z-xXv6nqIAL1sNJLsA&sig2=CAAP4G_fAX8isctE934MTg Engineering problems guys... engineering problems only... Edited September 28, 2016 by Moontanman Link to comment Share on other sites More sharing options...
ajb Posted September 29, 2016 Share Posted September 29, 2016 So how could negative energy be found or converted from regular energy? Well, particles with negative mass might exist, but we don't have any evidence of such thing - they would break the various energy conditions imposed on general relativity. Interestingly, negative energy densities are common in quantum field theories on curved backgrounds, one may be able to exploit quantum effects and manufacture the necessary conditions. However, it is not at all clear that this is possible as subtle effect in quantum theory may render wormholes and so on unphysical. The causualties could be avoided by using robotics at first instead of humans. That could avoid free will issues, but causality is a problem whatever you send through time machines. If indeed a method of FTL became possible wouldn't that in of it's self change the laws of physics as we know them? The speed limit is that of the local speed of light. By using non-trivial geometry and maybe topology we can beat a light ray by taking another path. A soon as you do this you have questions about causality and time travel. However, none of this violates what we know of general relativity. Link to comment Share on other sites More sharing options...
Sriman Dutta Posted September 29, 2016 Share Posted September 29, 2016 Pass the light through such a material that has an unusually high refractive index. Then, it will be possible to overtake light in that material. LOL!!! Link to comment Share on other sites More sharing options...
Janus Posted November 17, 2016 Share Posted November 17, 2016 Pass the light through such a material that has an unusually high refractive index. Then, it will be possible to overtake light in that material. LOL!!! You'd be surprised at how many people think that this is an actual loophole in Relativity. Link to comment Share on other sites More sharing options...
swansont Posted December 16, 2016 Share Posted December 16, 2016 ! Moderator Note Hijack about alternative propulsion methods has been split, along with my modnote, so let me reiterate: Stay on-topic here (FTL travel, answers involving mainstream physics only), and do not hijack the discussion Link to comment Share on other sites More sharing options...
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