Is that not a fairly fatal problem? [citation needed]. a relativistic rocket rather than an Alcubierre drive (since the Alcubierre drive does require exotic matter, and from what I understand it isn't actually accelerating relative to quasi-inertial observers who are far away in the asymptotically flat spacetime of Alcubierre's solution). Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. This practice means that the solution can violate various energy conditions and require exotic matter. Connect and share knowledge within a single location that is structured and easy to search. How can a warp drive overcome this rule? Enormous tidal forces, however, would be present near the edges of the flat-space volume because of the large space curvature there, but suitable specification of the metric would keep the tidal forces very small within the volume occupied by the ship. Local causality though is preserved. [25] By contracting the 3+1-dimensional surface area of the bubble being transported by the drive, while at the same time expanding the three-dimensional volume contained inside, Van Den Broeck was able to reduce the total energy needed to transport small atoms to less than three solar masses. @innisfree: his spacetime doesnt, because it includes only one of these that doesn't turn around. The interior of the bubble is an inertial reference frame and inhabitants experience no proper acceleration. This book is a self-contained introduction to the field of numerical relativity. The so-called Romanek Equations arose from a UFO contact case in with Mr. Stan Romanek, who has severe dyslexia and a grade-school of mathematics, wrote in his sleep and under hypnosis a series of complex equations. Can one claim copyright over a compilation of (public) data? 119 2082-2089 (1960). The theory of the . In doing this, you wind up with a line element that looks like (see erudite comments from @Jerry Schirmer below, I'm playing catchup): $ds^2 = -d\tau^2 = \gamma_{ij}dx^idx^j + 2\beta_i dx^i dt - \left(\alpha^2 - \beta_i\beta^i\right)dt^2$. Hence we need to use GR instead. Does grabbing someone by the jacket constitute assault? Now, I'm aware that there are problems with the practicalities (or possibilities) of methods involving exotic matter with negative mass, and that kind of thing has been addressed here: Doesn't Warp theory violate causality? But this wild idea falls flat because it is based on the huge assumption that we can even get an object with mass over the speed of light barrier. what travels faster than light. I've also said "nothing can travel faster than the speed of light". Does the heat equation violate causality? I hope to have more details soon, but in the meantime I'll leave you with this quote from Schild regarding the twin paradox and general relativity. [3][20] Van Den Broeck detailed this by saying that the total energy can be reduced dramatically by keeping the surface area of the warp bubble itself microscopically small, while at the same time expanding the spatial volume inside the bubble. The only issues are 1. Remember that the standard rigorous meaning of "violates causality" is that objects move outside the light cones, and that does not happen in a spacetime containing Alcubierre regions. Together, this is enough to rule it out with close to 100% certainty as a serious possibility. Some suggested methods avoid the problem of tachyonic motion, but would probably generate a naked singularity at the front of the bubble. The mechanism described by Alcubierre both invokes an unphysical stress tensor and also violates causality (see point 1). Ins some strange universe on the other side of the speed of light, there is a RW-equivalent page on slower-than-light . [4] If exotic matter with the correct properties cannot exist, then the drive cannot be constructed. Two Aldubierre drives could be used to create a Closed Timelike Curve - which would violate causality. For example, travelling to Vega (which is 25 light-years from Earth) requires arranging everything so that the bubble moving toward Vega with a superluminal velocity would appear; such arrangements will always take more than 25 years. @innisfree: Spacetimes with closed causal curves are forbidden. [8] Furthermore, Alexey Bobrick and Gianni Martire claim that, in principle, a class of subluminal, spherically symmetric warp drive spacetimes can be constructed based on physical principles presently known to humanity, such as positive energy.[9]. While the distortion was present one could then make the journey between those stars quickly. which can be used to show that when the ship reaches Alpha Centauri, 817 years will have passed here on Earth. Alcubierre points out that his metric contains no such closed causal loops, and so is free of their paradoxes. Discusses what people understand about space and time and how science fiction is becoming less fictional as time goes on. In an Alcubierre warp drive spacetime (t ′, x, y, z) which is apparently moving along trajectory x s with velocity v = d x s (t ′) / d t ′, most of the physics depending on the spaceship worldline is concentrated on the two-dimensional spacetime resulting from setting the coordinates y = z = 0, which define the axis about which a . What would be the implications of faster-than-light travel? (Garattini and Lobo 2007 ), and time-machine metrics, e.g. http://www.washingtonpost.com/news/post-nation/wp/2014/06/11/this-is-the-amazing-design-for-nasas-star-trek-style-space-ship-the-ixs-enterprise/, this series of lecture slides by Alcubierre. Rindler applied them to the problem of relativistic space travel for the first time in 1960 in a Physical Review article titled "Hyperbolic Motion in Curved Space Time" [1]. I'm saying we should not so eagerly dismiss it. In principle one could arrange for two places in the universe which were previously far-separated to be brought near to one another. mean one can zoom around the universe at the press of a button. The argument against the Alcubierre drive cannot stem from special relativity as it would only apply if there were a violation of local causality. Rev. What basically happens is that the alcubierre drive allows an object to seperate it's frame of reference from any object around it aka a "warp bubble". So, the line element equation above describes a globally hyperbolic system in space time. Dolphus333 mentioned in his answer that Alcubierre demonstrated in his paper that there is no violation of causality in the spacetime he constructed, but I believe this is just for the case of a spacetime containing a single warp bubble--if you have multiple warp bubbles moving in different directions you can indeed violate causality in a manner similar to the tachyonic antitelephone. How to discourage players from attacking everything they encounter? The Alcubierre drive, Alcubierre warp drive, or Alcubierre metric (referring to metric tensor) is a speculative idea based on a solution of Einstein's field equations in general relativity as proposed by theoretical physicist Miguel Alcubierre, by which a spacecraft could achieve apparent faster-than-light travel if a configurable energy-density field lower than that of vacuum (that is . But because of the speed of light limiting flow of information and therefore causality itself every observer internal to the system has a consistent point of view in which causality is maintained. [8] According to White, a modified Michelson–Morley interferometer could test the idea: one of the legs of the interferometer would appear to have a slightly different length when the test devices were energised. A short video clip of the hypothetical effects of the warp drive. However, I was under the impression that any faster than light communication could result in a causality violation. The Alcubierre drive or Alcubierre warp drive (or Alcubierre metric, referring to metric tensor) is a speculative idea based on a solution of Einstein's field equations in general relativity as proposed by Mexican theoretical physicist Miguel Alcubierre, by which a spacecraft could achieve apparent faster-than-light travel if a configurable energy-density field lower than that of vacuum (that . I understand time dilation and that things with mass cannot travel at the speed of light, but using the Alcubierre drive, hypothetically speaking, I was still able to outpace the photons while also having mass. Alcubierre drive power requirments it is . The result is that from the global perspective there is no violation of causality: it is a planned trip and the preparations take time. the use of the Alcubierre drive requires one to be at the outskirts of a star system. (I think we can all agree, can we not, that the threshold should be extremely high before breaking assumptions that we're in a causal universe?). An interesting musing is the possible side effect as experienced in sound where a plane travels at Mach1 we get sonic booms cuased by compression of sound waves at the same speed of thier creation, would a photonic boom also happen in light? This is a question that is asked the world over and the answer seems obvious to me, yet everyone deems it to be from perception which for me seems to be the issue apply some 1st grade logic to the situation and the answers reveal themselves quite simply. In fact, Alcubierre was inspired by Star Trek when thinking about his hypothetical model. "Person A heads in one direction at 0.75*c and person B travels in the opposite directs at the same speed, neither is breaking the speed of light but taken from a relative perception of person A, person B has to be travelling at a resultant speed of 1.5*c." - No, velocities don't add the same way in relativity that they do in classical physics--see. So why are Alcubierre drives theoretically OK? Hypnosifl's answer is good but I want to add some context. We regard as a maximum extension beyond the event horizon of that spacetime its embedding in a three-dimensional Minkowskian . The Alcubierre drive makes use of a supply of negative energy whose gravitation creates a carefully shaped distortion in the space-time of General Relativity, nicknamed a "warp bubble" because Alcubierre was a Star Trek fan. [32][33], The amount of negative energy required for such a propulsion is not yet known. Global causality is violated. There are all sorts of observers, not on the spacecraft or anywhere near it, who would see the events as violating causality if the craft were FTL. A possible type of effect that would accomplish this is a buildup of vacuum fluctuations on the border of the region of spacetime where time travel would first become possible, causing the energy density to become high enough to destroy the system that would otherwise become a time machine. However, in the previous slide he brings up the possibility that Hawking's chronology protection conjecture might be true in quantum gravity, so that solutions in general relativity involving closed timelike curves could be destroyed by quantum effects, without ruling out the possibility of constructing FTL solutions that don't involve CTCs. ", "How NASA might build its very first warp drive", "Nasa physicist says warp drive is more feasible than thought", Miguel Alcubierre's Twitter feed, 29 July 2013, "2013 Starship Congress: Warp Field Physics, an Update", "Warp Drives May Come With a Killer Downside", Journal of the British Interplanetary Society, "Star Trek Adventures: A Star Beyond the Stars - Modiphius | Star Trek Adventures | DriveThruRPG.com", Marcelo B. Ribeiro's Page on Warp Drive Theory. Alcubierre even shows that causality won't be violated. This book explores the idea of time travel from the first account in English literature to the latest theories of physicists such as Kip Thorne and Igor Novikov. Apart from this error, dolphus333 seems to just assume without argument that these equations can be generalized to the case of an Alcubierre bubble, since the "end edit" first calculates the time for a relativistic rocket with an acceleration of 188G, and then goes on to say "You might point out that 188 g's would surely smush everyone against the back wall of the ship, but the beauty of the theoretical drive described is that you carry your own gravity well along with you and therefore, you're always in freefall and don't feel the acceleration." In any discussion of Alcubierre's warp drive, it's important to understand that there are no rules. to 1 light-minute, and this need not take very long. Found inside – Page 408That is, any star ship capable of warp drive will have to be itself an artificially ... The Alcubierre and similar solutions can then be implemented. The original Alcubierre drive required the energy equivalent of the mass of Jupiter to create the warp field, with an impossible shortcut in the form of exotic particles with negative mass. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. It is not exactly certain if this means they must be in principle invalid. When I last read about the Alcubierre drive, one relevant point that was mentioned was that the inside of the warp field is causally separated from the outside, which solves the problems of causality while in transit, but raises the question of how one starts or ends the journey. Yes, Alcubierre drive is a sound way, under the current laws of physics, to explain a valid way of travel faster-than-light and the only way (unless wormholes are ever observed) to "break" the speed of light. where $a$ is the acceleration of the ship and $c$ is the speed of light. González-Díaz, Pedro F. Abstract. But thats just me. g00 = (c + v) (c - v) The metric inside the Tic Tac warp bubble Oin = Oout,cois simply the flat. [37], Alcubierre briefly discusses some of these issues in a series of lecture slides posted online,[38] where he writes: "beware: in relativity, any method to travel faster than light can in principle be used to travel back in time (a time machine)". Alcubierre recently exhibited a spacetime which, within the framework of general relativity, allows travel at superluminal speeds if matter with a negative energy density can exist, and conjectured that it should be possible to use similar techniques to construct a theory containing closed causal loops and, thus, travel backwards in time. How does the Alcubierre drive warp space in the vicinity of it's destination? causality considerations do not prevent . It just states that if a method to travel faster than light exists, and one tries to use it to build a time machine, something will go wrong: the energy accumulated will explode, or it will create a black hole. You can take any smooth spacetime manifold you like, plug it into the GR field equation, and get a corresponding stress-energy tensor. Neither the Alcubierre theory, nor anything similar, existed when the series was conceived—the term "warp drive" and general concept originated with John W. Campbell's 1931 science fiction novel Islands of Space. The Alcubierre Drive is a potential solution, allowing hyperfast travel within general relativity. However, the idea that the relativistic rocket equations apply to the Alcubierre bubble is completely unjustified, since the relativistic rocket equations calculate the effects of uniform acceleration in the flat spacetime of special relativity, whereas the Alcubierre bubble is a spacetime that is highly curved in the vicinity of the bubble, requiring general relativity to deal with it. Is interstellar flight possible in near future in a way that would keep our civilization alive? Now consider this in terms of causality because again this is all about perception. Although it requires a little bit of reading, the paper explains how some formulations of the metric do not necessarily result in CTC, but imply that one could do so. Would this violate causality and 2. New comments cannot be posted and votes cannot be cast. 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