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Scientists announce a physical warp drive is possible
- api 6y agoThere is still the problem of FTL information transfer violating causality, but I have wondered if sub-light warp drive might not be physically possible. It wouldn’t be FTL but it would be a kind of “massless” drive in that it would get around the propellant mass issues with accelerating to near light speed. It would “cheat” by warping space instead of accelerating at all in the conventional sense. The Centauri system is a little under 5 years away with such a drive.
- bhaak 6y agoBecause of special relativity, it wouldn't even be 5 years on the ship. A massless drive would open up exploration of the galaxy within the life time of a human being. Even though on Earth, thousands of years would pass, so it's kind of a one-way exploration nevertheless.
- api 6y agoWould you still get time dilation with a warp drive? Are you actually "moving?"
- bhaak 6y agoIf by "warp drive" you mean a drive that would be contracting spacetime in front of the ship and expanding it behind, then this ship wouldn't be subject to time dilation. As it is not the ship that is exceeding the speed of light within a local reference frame (the "warp bubble) but the spacetime. But the feasibility of such a drive is purely understood at the moment as it seems such a drive would allow for causality violations.
- rootbear 6y agoThis is the problem I have with most discussions of a practical Alcubierre style warp drive. They generally don't address the causality violations that are inherent in ANY form of FTL travel. But if it could be useful as an efficient sub-luminal drive, that would be cool and worth pursuing.
- api 6y agoBased on papers like this, I suspect that some form of sub-FTL "warp" drive may be at least physically possible. Whether it's practical to build any time in the foreseeable future is another question. The energy requirements would be beyond what we can do today and would probably require highly efficient compact fusion.
- raattgift 6y agoCausality violations probably aren't really that much of a problem for mathematical physics. Geroch (a very well known and highly cited relativist) takes a shot at this in a short paper considering a "democracy of causal cones" rather than simply the one that matches light: "All systems, and their cones, are on an equal footing: No one set of fields, or one set of causal cones, has priority over any others." Geroch's argument is that one can still do initial-value-formulation physics even in the presence of causal cones whose width is different -- including wider -- than that of light. https://arxiv.org/abs/1005.1614 https://arxiv.org/abs/1005.1614 -- it is highly technical, but has this as the kicker: "we would then insist that the final field configuration is, not what the observer wills it to be, but rather what follows, evolving these data via [dynamical equations]" Notably, this is backwards from the Alcubierre drive's formulation, which starts with a desired final field configuration, and is trapped by having no "before the bubble existed" initial values surface. The Alcubierre solution is eternal, and offers no way to be stitched into our apparently non-eternal universe (it sure seems to have a beginning, or at least an early hot/dense boundary close to which the presence of an Alcubierre bubble seems even less physically plausible than today). Although it is safe to describe really fantastical configurations of matter very near that early boundary, one has to settle things down in far less than seconds, in order to match several different lines of evidence of about the distribution of the first free-streaming photons (and the earlier free-streaming neutrinos, when we figure out how to build observatories to study them in detail). You could put Alcubierre bubbles everywhere during Cosmic Inflation, for instance, but you have to very quickly and aggressively suppress their observables. Let's turn this on its head: we can in principle construct a spacelike values-surface at time today and let it evolve. A problem we have with this is that the presence of either or both of not-yet-formed or formed-but-eventually-evaporating black holes makes a complete calculation of some far future values-surface impossible in principle, as far as we know, which means in the absence some new fundamental theory of quantum gravity that has yet to be discovered. Putting an Alcubierre drive onto the same today values-surface likewise blocks the complete calculation of the future values-surface, in principle. Dusting the cosmos with lots of Alcubierre drives makes things much worse. But maybe that's OK, because the cosmos appears to be dusted with lots of black holes and configurations of matter (like our own Virgo cluster) that will inevitably mostly settle into giant black holes that may one day evaporate. This means we can't really make a concrete prediction about the far future of our cosmos, in principle. I wouldn't sweat it, because we can't set down much more than the barest approximation of the real values-surface in practice anyway. So since we already have problems with causality thanks to gravitational singularities (or if you prefer, apparent trapping surfaces), and we have excellent evidence of them existing in our universe, an argument that "X poses problems for causality and therefore must be unphysical" is not especially compelling. Instead, the problem grinds down into [a] laying out an initial values surface gets harder, especially if we can't rely on a programme of pushing it further and further back in time so that unusual configurations of matter (black holes, Alcubierre bubbles) have the ability to develop through dynamical laws (which is what we do with physical cosmology, for instance); and [b] writing down the dynamical laws that relate neighbouring values-surfaces (which gets harder because we need more than the Lorentz symmetry group and GL(4). It might be fun to try to make [a] and [b] work in the presence of various FTL mechanisms, and indeed to some extent we do this in very specific settings (cosmic inflation, for instance). However, from the time of the CMB to now there is nothing to suggest a need to account for FTL material (or normal material embedded in a dynamical spacetime that moves it around FTL-style) at any scale, from the cosmological to the laboratory. The theory would undoubtedly be much more complicated than what we already have (which has already evolved and become more complicated as more evidence has become available), so there would not be much point to it. Finally, two extracts from the Geroch paper: "[I]n a similar vein, there exist solutions of Einstein’s equation in general relativity that manifest closed causal curves. But we do not ... allow observers to build time-machines at their pleasure. Instead, we permit observers to construct initial conditions — and then we require that they live with the consequences of those conditions." which is exactly the opposite of Alcubierre's approach in https://arxiv.org/abs/gr-qc/0009013v1 https://arxiv.org/abs/gr-qc/0009013v1 where he starts with a time machine first, and never describes the initial conditions before it exists. One would usually expect that for any artifact such as a spacecraft, there is a time before which it is fully built and switched on. One might compare that with an eternal Schwarzschild black hole and a black hole that forms via gravitational collapse of a massive star (or direct collapse of matter in the early universe). And, "from the present viewpoint the problems associated with superluminal signals do not seem nearly as severe as they did at first glance", a statement that is likely safe should such signals ever be proven.
- nabla9 6y agoThe article is incorrect. If you check the paper, they are clear that physical warp drive do not allow faster than light travel. It moves only at subluminal speeds. In any case, warp drives (physical or non-physical) are just theoretically interesting. Taking mass of few solar systems and building a tiny microscopic vehicle that fits inside the bubble is not practical way to travel.
- the_local_host 6y ago> Taking mass of few solar systems and building a tiny microscopic vehicle that fits inside the bubble is not practical way to travel. Fully agree. If interstellar travel ever occurs, it seems more practical to simply freeze people for thousands or millions of years for the journey and stop trying to fit it into the current human lifespan.
- jasperry 6y agoI don't know about the physics of the article, but they get the lore of Star Trek wrong right off the bat. Warp drive is certainly not explained in Star Trek in terms of direct propulsion from matter-antimatter collision. That is how the impulse (sub-lightspeed) engines work. Warp is explained as a reaction involving exotic matter that creates a field surrounding the ship to warp spacetime.
- happytoexplain 6y agoWait - the warp engine doesn't generate power using matter-antimatter annihilation??
- jasperry 6y agoMy memory is a little fuzzy. Matter-antimatter may in fact be involved in the warp drive, but it's definitely not direct propulsion.
- rsstack 6y agoWarp engines are powered by annihilation, since it's an "easy" fuel, but the annihilation itself doesn't move the ship. Similar to how nuclear-powered ships and submarines don't detonate nukes to push themselves forward.
- klyrs 6y agoExcept when that's the plan? https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propu...
- gizmo385 6y ago> Similar to how nuclear-powered ships and submarines don't detonate nukes to push themselves forward. Picturing this in my head was certainly a treat :)
- rootbear 6y agoThe original series was a bit fuzzy on just what role the matter-antimatter engines (and dilithium crystals) played in making warp drive possible. From the Next Generation era onward, the idea was basically that a matter-antimatter engine was the only practical way to generate the enormous power required to generate the warp field needed to go FTL via warp drive.
- WJW 6y ago> warp speed travel is now a lot more likely in a much shorter timespan than we previously thought. That is cool, but at the same time it only works for subluminal speeds so not really what "warp" speed usually refers to. Offtopic, but it kinda reminds me of the science fiction story of a young scientist trying to get funding for hyperspace research. In the end it turns out that hyperspace has been explored decades ago but the speed of light is even lower in hyperspace than in real space.
- AlgorithmicTime 6y agoWell, then you need to go to hypospace.
- wmeredith 6y ago> warp speed travel is now a lot more likely in a much shorter timespan than we previously thought. That's some cold comfort, since all timespans are much shorter than "never".
- rbanffy 6y agoWhen the whole universe is in a stable thermal equilibrium after the last proton decays, what's the meaning of time and space anyway?
- slowmovintarget 6y agoProtons don't decay (as far as we can tell), they get ripped apart in black holes which evaporate into photons, mostly. All that's left are photons, moving at the speed of light, experiencing no time, and never meeting each other as the universe expands away faster than they move. "It's hard to bore a photon." -- Roger Penrose
- rbanffy 6y agoThey may decay, but when the lower bound for their half-life is more than 10^36 years, it'll certainly be very hard to observe it.
- Iolaum 6y agoArxiv link for people interested in the source rather than a journalists take. https://arxiv.org/abs/2102.06824 https://arxiv.org/abs/2102.06824
- ppeetteerr 6y agoPhysicist: we have proven that warp drive is possible. Here you go engineers, your move.
- airhead969 6y agoEngineers: Uh, okay, physicists. With which kind of magic?
- krapp 6y agoConjuration?
- airhead969 6y agoI was thinking transmutation.
- tyingq 6y agoSabine Hossenfelder video specifically about this paper: https://www.youtube.com/watch?v=8VWLjhJBCp0 https://www.youtube.com/watch?v=8VWLjhJBCp0
- deleted 6y ago[deleted]
- mrfusion 6y agoPerhaps a good time to post this short story “The Road Not Taken”: https://eyeofmidas.com/scifi/Turtledove_RoadNotTaken.pdf https://eyeofmidas.com/scifi/Turtledove_RoadNotTaken.pdf It’s a fun read. (20 pages)
- gala8y 6y agoThanks. There are lots of files one directory up. If we are at short sci-fi stories... I fell in love with Marc Stiegler's ' The Gentle Seduction' which I revisit every few months for pure enjoyment. Found it listed here https://news.ycombinator.com/item?id=7203702 https://news.ycombinator.com/item?id=7203702
- SamBam 6y agoI had never read that. I'm glad I took the time! Good story.
- ACAVJW4H 6y agoOh thanks esquire. So instead of negative energy particles we only need floating bubbles of spacetime! How did we miss that
- nostromo 6y agoIf you’re saying traveling faster than the speed of light is possible, you’re also saying traveling backwards in time is possible. And yet people tend to be very skeptical of backwards time travel claims.
- eutropia 6y agoHow does FTL imply time travel?
- akvadrako 6y agoA few explanations I've collected: https://www.askamathematician.com/2012/07/q-how-does-instantaneous-communication-violate-causality/ https://www.askamathematician.com/2012/07/q-how-does-instant... http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-ti... http://www.theculture.org/rich/sharpblue/archives/000089.html http://www.theculture.org/rich/sharpblue/archives/000089.htm... The important bit is that it doesn't matter HOW information is transmitted FTL – it can be via wormholes or magic. For observers in another reference frame it will still result in causality violations.
- nostromo 6y agoAn easy-to-understand example: If I got in a faster than light spaceship and traveled to Jupiter, and then turned around and came right back, I would arrive before I left and could shake my own hand on the launchpad. If we think humans will soon figure out FTL, it makes one wonder why we've not yet seen any human FTL spaceships from the future.
- diggernet 6y agoThat...doesn't make sense. Let's say your spaceship can go to Jupiter in one second (Edit: as measured from Earth), which would require FTL speed. Then you turn around and come back. You've still arrived two seconds after you left. At Jupiter, you could look through a super-telescope and see yourself still on Earth, but you still aren't really seeing yourself, because you are not still on Earth. You are just seeing the photons you passed during the trip, catching up to you.
- beefman 6y agoPreviously: https://news.ycombinator.com/item?id=26307572 https://news.ycombinator.com/item?id=26307572
- orf 6y ago> Essentially, an Alcubierre drive would expend a tremendous amount of energy—likely more than what’s available within the universe—to contract and twist space-time in front of it and create a bubble. What does this actually mean? We’d have two giant Tesla coils buzzing with a universe worth of electricity? Giant magnets? Super space lasers?
- sabujp 6y agothis paper is extremely annoying, they could have at least given some examples of the amount of energy that would be required to create their warp teardrop bubbles using their new equations
- Octopodes 6y agoThis is going to be about that shitty Alcubierre drive again isn't it?