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Physical Warp Drives
- _Microft 5y agoArxiv: https://arxiv.org/abs/2102.06824 https://arxiv.org/abs/2102.06824
- _Microft 5y agoAm I correct that the interesting thing about subluminal warp drives is that they do not require working mass for propulsion? So if we had such a warp drive, we could put energy in and get motion out of it, without being subject to the tyranny of the rocket equation? It seems like this idea is not correct. The authors write in section 5.2: "Warp drives, being inertially moving shells of normal or exotic material, do not have any natural way of changing their velocities. They are just like any other types of inertially moving objects. Similarly, just like for any other massive objects, achieving a certain velocity for a warp drive requires an externally applied force or, more practically, some form of propulsion.", from https://arxiv.org/pdf/2102.06824.pdf#page=17 https://arxiv.org/pdf/2102.06824.pdf#page=17
- azernik 5y agoYup. But also they're interesting as a theoretical construct for better understanding the whole idea of intentionally warping space.
- deleted 5y ago[deleted]
- pitaj 5y agoAlso the travelers are essentially in an inertial frame, so it acts kind of like "inertial dampeners" in Star Trek.
- akiselev 5y agoThe tyranny of the rocket equation isn't some fixed property of orbital mechanics, it's a limitation of our method for converting energy from chemical propellants to propulsion. Specific impulse for nuclear rockets designed decades ago (i.e. nuclear lightbulb) is in the thousands, which is enough to reach orbit in a single stage without dumping extraneous mass. 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. The sun burns loses about 6x10^9 kg of mass a second which is the upper limit for the amount of energy a Type I civilization can extract in our solar system. Jupiter's mass is roughly 2x10^27 kg, so assuming there are 4x10^11 stars in our galaxy and our star represents the average, a Type II civilization in our galaxy wouldn't have enough energy to produce a warp field. The drive doesn't just need a little bit of working mass to expel, it needs enough energy/mass to bend space time around it!
- jameshart 5y agoThe rocket equation doesn’t only apply to chemical energy propulsion - it applies to any propulsion system that conserves momentum and uses reaction mass - which nuclear drives do too. Chemical rockets are limited in how much energy they can put into the reaction mass (by the energy density of their fuel) and therefore the maximum exhaust velocity they can achieve - which is the input into the rocket equation But while nuclear rockets get away from the constraint of chemical energy density they still have to operate by putting energy into reaction mass and shooting it out the back to create a momentum change. And the rocket equation still applies to the reaction mass and its exhaust velocity. In fact in theory you can build a chemical rocket engine that burns a fuel for heat, then uses that heat to energize some other reaction mass that you eject - it’s just that that is inherently less efficient than using the spent fuel as reaction mass since otherwise you’re needlessly pumping momentum into spent fuel. Far better to throw the exhaust products away as reaction mass.
- akiselev 5y agoAh, my mistake - I thought the "tyranny of the rocket equation" was referring to the rocket equation's consequences on our attempts to reach orbit (i.e. multistage rockets), not the equation in general.
- ben_w 5y agoSlight quibble, but the original needed more negative mass than the universe, it was one of the subsequent improvements which reduced it to only Jupiter.
- zardo 5y agoI don't understand why it would be called a warp drive then. If it doesn't cause movement it's not driving anything.
- marksbrown 5y agoIf general relativity is an accurate model of gravity then distortions in space-time are caused by mass. Traveling at the speed of light can be shown to require an infinite amount of energy to accomplish for a finite mass. However space-time itself could, according to our current understanding, travel faster than the speed of light. So if you could 'warp' space around you rather than travel through it, you could go at an arbitrary speed. Unfortunately warping space-time is typically accomplished by large amounts of mass. Hence a large amount of energy. If I remember correctly it also requires we bend space in a way we have never seen nor have any reason to believe is possible to accomplish beyond it being allowed by general relativity. It's quite a pickle. Without such a device humanity will still populate the galaxy but it'll take hundreds of millions of years. Assuming we don't wipe ourselves out.
- jjk166 5y agoJust a causal reminder that solar sails, beamed propulsion, mag sails, photon rockets, etc are all examples of propulsion methods free from the tyranny of the rocket equation which require no onboard reaction mass. There is really no need for exotic physics if that's all you're looking to accomplish.
- jbdistaken 5y agohttps://arxiv.org/abs/2102.06824 https://arxiv.org/abs/2102.06824 looks like CQG spell-checker added a subliminal typo in the abstract :)
- nynx 5y agoThere is another paper on warp drives that came out around the same time, Breaking the Warp Barrier: Hyper-Fast Solitons in Einstein-Maxwell-Plasma Theory [0]. [0]: https://arxiv.org/abs/2006.07125 https://arxiv.org/abs/2006.07125
- lainga 5y agoWow, is that paper saying what I think it is? Previous papers only found a negative energy requirement (pg. 12) because they only considered interior spaces which could reduce down to a point-like region? That's an extraordinary claim, and, I hate to use the phrase, but "big if true".
- nynx 5y agoIndeed it is. There are still significant (in the case of the required mass-energy, massive) issues. The writer has a blog [0], which is worth reading if you're interested in next steps for the theory. [0]: https://eriklentzphd.blogspot.com/ https://eriklentzphd.blogspot.com/
- Gravityloss 5y ago> Once the energy requirement is lowered, the space–time signatures of positive-energy solitons may be studied in a laboratory setting using existing or novel methods. ... The highly magnetized energetic and diffuse atmospheric plasma of magnetars may also bea natural place to look for signatures of positive-energy soliton geometries even prior to advances in energy reduction.
- threesongs 5y agoIt is an important paper. However, it is also important to realise that superluminal solutions introduced there are still prohibited by the laws of physics. Making such superluminal drives is at least as hard as making superluminal matter, which we believe requires infinite amount of energy. In physics, they say that such spacetimes violate the dominant energy condition. The issue is relatively clearly stated in E.Lentz's paper accepted in the journal, but not in his arxiv paper or the press-release.
- mdorazio 5y agoI've only gotten a few pages into this, but it looks like their general solutions still require negative energy? Regardless, it's been very interesting to see the development of warp drive theory over the last ~20 years.
- imdoor 5y agoDoes an Alcubierre warp drive violate causality? From my understanding, it's no different than regular FTL travel, which implies time travel, which implies violation of causality. To me that would indicate that an Alcubierre warp drive still shouldn't be possible despite the negative energy requirement being lifted.
- shepardrtc 5y agoNo, for the original Alcubierre, its warping spacetime around the information and moving that pocket. The ship or information or whatever is still traveling inside the pocket at its normal speed. So while it could be virtually instant (ignoring energy requirements), it wouldn't be time travel. However, I believe you could arrive to your destination and look back and see yourself before you warped - and maybe as you traveled - as the light catches up to you. At least that's my understanding.
- Filligree 5y agoNo, every FTL construction can be used to violate causality. There’s no way at all around that. Fundamentally it’s a geometric problem — relativity has a hard barrier at light speed, but if you can get past that, there’s nothing at all special about infinite speed. Is the same sort of 4-momentum as standing still, and you can accelerate in any direction from there. The warp drive in the article is subliminal, though, so it doesn’t have that problem.
- imdoor 5y agoAh, i somehow read the subluminal as superluminal in the abstract and got all excited. But the subluminal restriction makes the paper's findings make more sense.
- ben_w 5y agoThat’s something I’ve been meaning to ask about: Does FTL really inevitably mean that, or is that a consequence of saying “no preferred frame of reference” and therefore having e.g. “100c” meaning different things to observers in relative motion?
- feynmanzhou1 5y agocool
- haydnv 5y agoI think what's really interesting about this that most readers seem to overlook is the claims about subluminal warp drive, which is practically realizable in a way that the science-fictional faster-than-light case is not
- sosuke 5y agoBaby steps! Every step is worth it. I know the math and science doesn't support me but I'm convinced FTL is possible and that the universe won't die a heat death. The universe heat death theory makes me think of comics where people extrapolate the data they have while lacking other critical data. https://xkcd.com/605/ https://xkcd.com/605/
- douglaswlance 5y agoThe heat death theory assumes life has zero impact on the universe.
- krapp 5y agoMost of the universe is void. Most of the rest is whatever dark matter is. What we consider to be the entirety of material reality is a fraction of a fraction, and out of that, as far as we can tell, Earth has the only life that exists. There's probably more life out there, but if there is, as the Fermi Paradox points out, they're awfully quiet. I think it's fair to assume that life will have practically zero impact on the universe. Even if the universe was teeming with it, it would be of such little significance at scale that it might as well be a rounding error in reality.
- Teever 5y agoThere is merit to your thought process but it could just as easily be that life is the spark that sets off an explosion that irrevecobly changes the universe. Think of a virus. A handful of specially shaped molecules has permanently changed human society.
- 5y ago
- fnord77 5y agoI thought the Alcubierre effect was theoretically possible by getting near a rapidly rotating neutron star?
- ben_w 5y agoThere isn’t anything with that name, AFAICT. Did you mean “frame dragging”?
- jonplackett 5y agoI think they mean Alcubierre Drive: https://en.m.wikipedia.org/wiki/Alcubierre_drive https://en.m.wikipedia.org/wiki/Alcubierre_drive
- ben_w 5y agoWhile the name is similar, the drive has nothing to do with spinning neutron stars
- fnord77 5y agothere was an article a while back claiming the possibility of Alcubierre drive effects (displacement of space/time) in close proximity to a neutron star that is spinning rapidly. I'll try to find the article.
- ben_w 5y agoThat sounds like a journalist read a bit about both frame dragging and the Alcubierre metric and had as much wishful thinking as is usually my own personal weakness with all things GR: https://en.wikipedia.org/wiki/Frame-dragging https://en.wikipedia.org/wiki/Frame-dragging
- gmartire 5y agoHey all, I'm one of the authors of the paper Introducing Physical Warp Drives and a Y Combinator alum (YC W'14). This video does a great job explaining our paper and Erik's as there a few misunderstandings in this forum https://youtu.be/PA66ah9b0U4 https://youtu.be/PA66ah9b0U4. We all know each other and all have the warp bug as we now have a path; it's just going to be difficult. If you would like to join our warp drive cohort, please email us a bit about yourself and your ideas for warp at create at appliedphysics dot org. Our cohort is composed of PhDs and engineers from several STEM disciplines, we meet weekly and have more papers in the works, perhaps you can join the fun! https://thedebrief.org/new-warp-drive-model-requires-no-exotic-matter-scientists-say-we-can-build-it/ https://thedebrief.org/new-warp-drive-model-requires-no-exot...
- lainga 5y agoDo you have any thoughts on Lentz's comment that IPWD "made a rush to judgement" on his draft of Hyper-Fast []? Or has anything changed in your assessment between the draft and publication of his paper? (I did not see anything on his blog) [] https://eriklentzphd.blogspot.com/2021/04/review-and-response-to-bobrick-and.html https://eriklentzphd.blogspot.com/2021/04/review-and-respons...
- threesongs 5y agoThe version accepted in the journal clearly states that superluminal warp drives are physically unachievable because they violate the dominant energy condition. It means that superluminal drives require superluminal matter. This is in agreement with the conclusions in the IPWD paper. However, the version E.Lentz uploaded on arxiv or the press-release did not state this clearly.
- Causality1 5y agoIf superluminal matter existed, would we know it?
- drran 5y ago
- pranade 5y agoThe subluminal application is particularly interesting, because it seems almost feasible. Is there a practical path to meeting these mass/energy requirements though?
- andruc 5y agoMerely an engineering problem!
- yosito 5y ago> 10% the mass of the sun Where could we source so much mass? That is far more than the mass of the earth, and surely altering the mass of the sun by 10% would have catastrophic effects. > physically possible Does an element exist that is dense enough to compress 10% of the mass of the sun into a 620m sphere? If not, how can the claim that this is physically possible be supported?
- ithkuil 5y agoAccording to Wikipedia "The entire mass of the Earth at neutron star density would fit into a sphere of 305 m in diameter" So I assume 610m in diameter would be 8 earth masses? That's still 4000 times less than 10% of the mass of the sun
- mabbo 5y agoAnyone selling "warp drives" that do not go faster than light kind of missed the point of why people are excited about warp drives. And if the video @gmartire just posted is explaining the paper correctly, this warp drive also doesn't accelerate anything. You have to figure out how to speed up on your own. I don't really see why anyone would bother doing any of these things. To dilate time better? I'd rather invest the same amount of mass towards a larger engine/fuel so that I can go faster, dilating time further and getting me there sooner.
- threesongs 5y agoIMO the paper clarifies the misconceptions about all warp drives. They all need propulsion, for example, to be consistent with physics.
- handol 5y agoDoesn't that mean that warp drives are not possible? I mean if the device can't produce a driving force why call it a "drive"?
- krapp 5y ago>I mean if the device can't produce a driving force why call it a "drive"? Because Star Trek called their thing a warp drive and that's become the general term for this kind of speculative technology.
- hinkley 5y ago> I'd rather invest the same amount of mass towards a larger engine/fuel The rocket equation is every bit as unsympathetic to your desires as the laws of thermodynamics are. Fuel requirements go infinite very quickly.
- blamestross 5y agoThe FTL part of the warp drive is the useless part. The real obstacle to space exploration is the rocket equation. Going FTL doesn't help if fuel needs still scale quadratically with distance.
- aidenn0 5y agoWhat makes something a "warp drive?" Per TFA this is subliminal, so it's clearly not "superliminal."
- jpw2020 5y agoThis is a nice paper. A couple thoughts that I haven’t seen raised yet in the thread: 1) this paper exhibits, for the first time, a continuous family of warp drives which contains Minkowski space (see the end of S.4.3). This means that it is, in principle, possible to turn on/off a warp drive, which is a basic requirement if you ever want to build one. The next basic feature we need to understand is how/whether warp shells can accelerate/decelerate. No paper in the literature does this yet, afaict. Would be very exciting if Bobrick and Martire can exhibit this in a sequel!