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I've been reading a number of online "pop-sci" articles on the subject of "warp drive" - derived from work done initially by Alcubierre.

Some of the most recent articles say that there are researchers at NASA who have found theoretical basis for not only "warping" space in the manner described by Alcubierre, but that estimates on the quantities of "exotic" matter required to make it work are far more reasonable than initially thought (~500kg instead of ~1 Jupiter mass), and that there is bench-top experimentation under way to validate it all. Furthermore, that it would easily permit an interstellar trip of say, 20 light-years to be completed in only a couple of months. Some statements have been made that we may be only a few decades away from a real spacecraft capable of such a voyage.

My question is: What has really been accomplished, proven or disproven to-date?

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  • $\begingroup$ I think my question really had two fundamental parts (1) establishing the credibility of claims in regard to theoretical/experimental research based on the "Alcubierre Metric", and if credible, (2) where does that work fall on the path to implementable technology. I agree, my question(s) probably belong more on the physics SE than here. $\endgroup$
    – Anthony X
    Aug 5, 2013 at 19:08
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    $\begingroup$ This can be a coherent single question if left to strictly focus on legitimacy. The question at hand is if research into faster-than-light (FTL) travel is legit. Some people use definitions of "warp" to deflect. FTL travel is easily definable, and violates special relativity by definition. The answer is two-part, 1) that Alcubierre metric is not necessarily FTL and 2) FTL travel is not possible. $\endgroup$
    – AlanSE
    Aug 5, 2013 at 20:57
  • $\begingroup$ This is confusing to me because I thought the key point is that Alcubierre had found a "loophole" in relativity effectively permitting a form of FTL travel (no speed limit on expansion or contraction of space), and that the theory is sound, leaving only questions of feasibility of implementation. $\endgroup$
    – Anthony X
    Aug 5, 2013 at 21:30
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    $\begingroup$ The alcubierre drive requires a negative mass. So far there is no reason to believe that matter with negative mass exists. 500kg of stuff which doesn't exist isn't more reasonable than 1 jupiter mass of stuff which doesn't exist. $\endgroup$
    – Philipp
    Jan 5, 2014 at 1:09
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    $\begingroup$ It seems that now we do phys.org/news/2017-04-physicists-negative-mass.html $\endgroup$
    – Daniel
    Jun 8, 2020 at 22:01

5 Answers 5

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If you read a lot of Internet forums, like Reddit and Quora, and even this one to some (but lesser) degree, you’ll notice a lot of skepticism about the possible functioning of the Alcubierre drive. However, most scientific papers and other sources that I’ve able to find tend to be less skeptical. Why is this? Hard to say, maybe people outside of formal academia try harder to be skeptical about certain controversial matters.

That said, it depends. 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. However, and this is a big however, what makes AD impossible or implausible for our current civilization is how to make it work. For it we would need whether exotic matter with negative mass (which still hypothetical) or harnessing somehow the Casimir effect which causes negative mass. Both things are not impossible, but we still don’t know how to do either yet. So, maybe tomorrow someone would find the way or maybe never.

So, if for example you’re working on science fiction book and wanted it to be hard sci-fi, the “hardish” way to make FTL is with the AD, but for a lot of people even in that case is then no longer “hard” sci-fi (but this is kind of subjective).

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  • $\begingroup$ Thanks for mentioning the Casimir effect angle. I've seen Alcubierre FTL dismissed because it "requires exotic matter"; this dependency seems to be main focus of skepticism. Since, as you pointed out, the Casimir effect replaces this dependency on exotic matter, the question (and my real question) is whether FTL is flat out forbidden by known physics or whether it is a matter of "how to". It's not a worldbuilding question, just a matter of keeping a rational perspective and not getting caught up in either over-optimism or dismissive skepticism. $\endgroup$
    – Anthony X
    Nov 9, 2019 at 15:33
  • $\begingroup$ Well as other user mentions, even without FTL the Alcubierre Drive would be a incredible avance in technology and would allow the explore the solar system easily and colonized (this is rarely use in sci-fi btw) and even more, near star system would be on reach in a human lifetime (it wil still took decades except in cases like Alpha Centauri and Barnard provided that we figure out certain important practical aspect like dealing with the blast in destination, navigation and how to "turn off" the effect in order to de-acelerate), so investigation in AWD is still a very important endevour. $\endgroup$
    – Daniel
    Nov 12, 2019 at 13:20
  • $\begingroup$ Whether FTL is possible, well the flat out answer to our moment in scientific knowledge is no, technically speaking the AWD does not travels FTL (it just causes the ilusion) in that sense, if ever able to make practial, it is possible and not only by the Casimir effect, some scientists also think the toroidal negative energy density may be use). Of course if such practical aspects are solved and it proves possible, new elements like acausality would have to be re-evaluated. $\endgroup$
    – Daniel
    Nov 12, 2019 at 13:24
  • $\begingroup$ A good news and update, apparently scientists were able to create negative mass ( phys.org/news/2017-04-physicists-negative-mass.html ) making AD much more feasible in reality. I mean, it is still far from been created (the mechanics on how to make it work are still away) but the fact that negative mass does exist and can be created is an important breakthrough as it was the only thing that keep it "hypothetical". $\endgroup$
    – Daniel
    Jun 8, 2020 at 22:04
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Original Answer

Given Alcubierre's math, and White's calculations, it's a viable avenue of research to pursue.

Whether or not it is practical as FTL, and given the expected maximum apparent speed of about 10 times the speed of light (White), and that the math says it should be able to be done, an attempt to implement a prototype series should be of immense benefit. Even if the drive fails to work, the drive testing will provide interesting measurements.

Therefore, investigations of Alcubierre's Warp Drive equations in a practical (rather than theoretical) mode are of use scientifically.

Also note: Any measured effect, even if not what is predicted, will lead to improvements in the theory.

Further, NASA is allowing White to pursue a practical experiment.

Note that Warp Drive, even if it doesn't allow for FTL (or as Alcubierre's theory notes, apparent FTL by STL movement of the craft within STL movement of the space the craft is moving through), a STL version will still massively reduce travel times. A 0.01C drive puts Mars a mere few hours away. At furthest distance, Mars is about 18 light minutes away; 1800 minutes travel time is 30 hours - not even 2 days.

Note that, for logistical and health purposes, a roughly 60-90 day mission (round trip) is about the limit. White has implied that he expects 10 C to be practical - this puts Alpha Centauri, home of the nearest detected extrasolar planet, at 156 days travel time. So, for practical purposes, a 10 C drive isn't an interstellar one. At 40 C apparent velocity, the Alpha Centauri system becomes reasonably practical. This means that, unless apparent speeds higher than White's worked 10 C examples are practical, the Warp Drive is going to still be an in-system drive.


2015 Update

It is worth noting that, as of May 2015, NASA thinks the EM-Drive may in fact be generating an Alcubierre warp, and is in fact generating thrust in a vacuum. Dr. White is working on the team testing this drive.

NASA has yet to release any data that this author can find on Dr. White's approved tests of a pure Warp Drive, but if the EM-Drive is generating a warp field, this may be a result of two lines of unrelated research converging.


References

White, Harold "Sonny", Warp Field Mechanics 101 (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110015936_2011016932.pdf) Retrieved 5 August 2013.

Peckham, Matt, NASA Actually Working on Warp Drive (http://techland.time.com/2012/09/19/nasa-actually-working-on-faster-than-light-warp-drive/) Retrieved 5 August 2013.

José Rodal, Ph.D, Jeremiah Mullikin and Noel Munson, Evaluating NASA's Futuristic EM-Drive, (http://www.nasaspaceflight.com/2015/04/evaluating-nasas-futuristic-em-drive/), Retrieved 3 May 2015.

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  • $\begingroup$ Any info on what experiment White will be attempting? $\endgroup$ Dec 30, 2013 at 19:18
  • $\begingroup$ The paper implies passing a laser through a low-power field off a benched rig and checking for displacement and modulation, but I've no hard evidence. $\endgroup$
    – aramis
    Dec 31, 2013 at 6:23
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    $\begingroup$ @aramis why is 'a 160 day each way trip is a nightmare'??? I mean, in human terms that seems to be a pretty small cost to be the first to get to another solar system! In logistical terms, without knowing how the drive actually works aren't we jumping the gun? $\endgroup$
    – NPSF3000
    Oct 23, 2014 at 11:39
  • $\begingroup$ The issue is one of cabin fever and food supplies. 160 days is past the point where most crews suffer morale breakdowns. Any meaningful trip needs to have more than just the crew needed to keep the ship going, but then you get into "how do we keep them busy and sane during the trip" $\endgroup$
    – aramis
    Oct 25, 2014 at 19:04
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This is a repository community-wiki post with references to current work on Alcubierre drive at NASA (Harold White) and in other places.

The original work:

Limitations:

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  • $\begingroup$ Another potential problem is that an Alcubierre warp bubble may tremendously boost the energy of particles that interact with it. See The Alcubierre Warp Drive: On the Matter of Matter, by Brendan McMonigal, Geraint F. Lewis, Philip O'Byrne (2012). $\endgroup$
    – PM 2Ring
    May 27 at 6:19
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Exotic matter is an area that is worth looking at. The geometry of warp drive (or equivalently, Krasnikov tubes) is not really as interesting for FTL travel as people believe: Something that usually gets overlooked is the causality of the matter-geometry dependency. You need the matter to be deployed first on a space-like region between a home and a destination, and then the space-time will change to allow FTL travel.

It is clear that if you are in Earth, even if you had the exotic matter in adequate quantities, you'll still need some way to deploy it along the road, otherwise there will be no warp!. So, in summary, you need a FTL drive in order to deploy the matter that will enable a warp drive. It still could find other applications though. For instance, could be applied (in principle) for exceeding the bounds of computation rates imposed by the speed of light on local information exchange between different regions of a computer.

A more reasonable proposition for spaceflight applications is researching micro-wormholes that might become stable and large enough to be observable if exotic-matter can be made to persist above the constraints imposed by the weak and dominant energy conditions. Eric Davis is looking into parabolic mirrors that focus high quantum fluctuations in a confined volume. That should be interesting to test the general validity of the energy conditions

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Is warp drive a legitimate avenue of scientific investigation?

Yes! "...researchers did indeed discover a warp drive solution: a method of manipulating space so that travelers can move without accelerating." But FTL warp drive, not so much.

Ars Technica's May 23, 2024 New warp drive concept does twist space, doesn’t move us very fast says:

While tantalizing, Alcubierre’s design has a fatal flaw. To provide the necessary distortions of spacetime, the spacecraft must contain some form of exotic matter, typically regarded as matter with negative mass. Negative mass has some conceptual problems that seem to defy our understanding of physics, like the possibility that if you kick a ball that weighs negative 5 kilograms, it will go flying backwards, violating conservation of momentum. Plus, nobody has ever seen any object with negative mass existing in the real Universe, ever.

These problems with negative mass have led physicists to propose various versions of “energy conditions” as supplements to general relativity. These aren’t baked into relativity itself, but add-ons needed because general relativity allows things like negative mass that don’t appear to exist in our Universe—these energy conditions keep them out of relativity’s equations. They’re scientists’ response to the unsettling fact that vanilla GR allows for things like superluminal motion, but the rest of the Universe doesn’t seem to agree.

related: What is the Current Status of Measurement of the Gravitational Mass of Antimatter? and links therein.

Later, the Ars Technica article goes on to describe new results that do not require "exotic matter", red or otherwise. It links to Jared Fuchs et al. 2024 Classical and Quantum Gravity 41, 095013 Constant velocity physical warp drive solution which is paywalled, but it is also avaiable as an arXiv preprint (lots of plots and drawings)

But there is a way around it, discovered by an international team of physicists led by Jared Fuchs at the University of Alabama in Huntsville. (The team is also affiliated with the Applied Propulsion Laboratory of Applied Physics, a virtual think tank dedicated to the research of, among many other things, warp drives.) In a paper accepted for publication in the journal Classical and Quantum Gravity, the researchers dug deep into relativity to explore if any version of a warp drive could work.

The equations of general relativity are notoriously difficult to solve, especially in complex cases such as a warp drive. So the team turned to software algorithms; instead of trying to solve the equations by hand, they explored their solutions numerically and verified that they conformed to the energy conditions.

The team did not actually attempt to construct a propulsion device. Instead, they explored various solutions to general relativity that would allow travel from point to point without a vessel undergoing any acceleration or experiencing any overwhelming gravitational tidal forces within the vessel, much to the comfort of any imagined passengers. They then checked whether these solutions adhered to the energy conditions that prevent the use of exotic matter.

The researchers did indeed discover a warp drive solution: a method of manipulating space so that travelers can move without accelerating. There is no such thing as a free lunch, however, and the physicality of this warp drive does come with a major caveat: the vessel and passengers can never travel faster than light. Also disappointing: the fact that the researchers behind the new work don’t seem to bother with figuring out what configurations of matter would allow the warping to happen.

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