# Alcubierre drive - theory changes/breakthrough? **URL:** \ **Category:** Factual Questions\ **Created:** [December 3, 2013, 5:13pm UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384 "2013-12-03T17:13:01Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![Terr](https://avatars.discourse-cdn.com/v4/letter/t/839c29/32.png) [@Terr](https://boards.straightdope.com/u/Terr)\ **Post date:** [December 3, 2013, 5:13pm UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/1 "2013-12-03T17:13:01Z")
> **[How NASA might build its very first warp drive](https://gizmodo.com/how-nasa-might-build-its-very-first-warp-drive-5963263)** > > A few months ago, physicist Harold White stunned the aeronautics world when he announced that he and his team at NASA had begun work on the development of a faster-than-light warp drive. His proposed design, an ingenious re-imagining of an Alcubierre... Looking past the woo in the article, would be great to see a lab result, even on miniature scale, that would do away with the exotic matter requirement. What do you think - possible? ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [December 3, 2013, 5:52pm UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/2 "2013-12-03T17:52:43Z")
Previously brought up [here](http://boards.straightdope.com/sdmb/showthread.php?p=16663519&highlight=Alcubierre#post16663519), there doesn’t seem to be much new on the topic as far as I can tell. ---
**Author:** ![Terr](https://avatars.discourse-cdn.com/v4/letter/t/839c29/32.png) [@Terr](https://boards.straightdope.com/u/Terr)\ **Post date:** [December 3, 2013, 6:00pm UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/3 "2013-12-03T18:00:46Z")
> [@Czarcasm](#): > > Previously brought up [here](http://boards.straightdope.com/sdmb/showthread.php?p=16663519&highlight=Alcubierre#post16663519), there doesn’t seem to be much new on the topic as far as I can tell. Well, the non-reliance on exotic matter is new, I think. If I understood the article correctly… ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [December 3, 2013, 6:07pm UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/4 "2013-12-03T18:07:04Z")
White’s version of the Alcubierre metric still requires a negative energy density, so it doesn’t do away with the requirement for exotic matter. Additionally, it’s not clear that these proposals work even with unobtanium, as it’s [been argued](http://arxiv.org/abs/1001.4960) that while these solutions exist in classical general relativity, once one takes quantum effects into account (as one must for a realistic description), the ‘warp bubbles’ won’t be stable. ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [December 3, 2013, 6:40pm UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/5 "2013-12-03T18:40:36Z")
> [@Terr](#): > > Well, the non-reliance on exotic matter is new, I think. If I understood the article correctly… I think you did, and the fascinating part is how that was accomplished: > [@](#): > > “My early results suggested I had discovered something that was in the math all along,” he recalled. “I suddenly realized that if you made the thickness of the negative vacuum energy ring larger — like shifting from a belt shape to a donut shape — and oscillate the warp bubble, you can greatly reduce the energy required — perhaps making the idea plausible.” White had adjusted the shape of Alcubierre’s ring which surrounded the spheroid from something that was a flat halo to something that was thicker and curvier. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 3, 2013, 6:54pm UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/6 "2013-12-03T18:54:28Z")
You can reduce the energy required (that is, bring it closer to zero) in a number of ways. Personally, I’m fond of putting the whole thing in a TARDIS. But no matter how clever you get with the tricks, you still always need some. And we’re so far from lab results, even preliminary ones, that one shouldn’t even bother worrying about that. If it’s possible at all (don’t bet on it), it’s going to take some major work from the theorists, first. The only “laboratory” that’s relevant is a computer. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [December 3, 2013, 7:28pm UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/7 "2013-12-03T19:28:16Z")
> [@Czarcasm](#): > > I think you did, and the fascinating part is how that was accomplished: Maybe I misread you, but the very part you quoted says that negative energy density—and thus, exotic matter—is still necessary. Any such bubble will require a region in which light rays defocus, which means a region of negative energy density. (In fact, IIRC, any scheme of FTL travel requires negative energy density.) ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [December 3, 2013, 8:03pm UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/8 "2013-12-03T20:03:29Z")
I think the idea is that the stress-energy operator of a quantum field in semiclassical gravity cannot be made to satisfy the same energy conditions as can be imposed on a classical stress-energy tensor in bog standard general relativity which allows for negative energy density without the field itself being exotic. That said the ‘Alcubierre drive’ is still highly implausible as an actual method of transportation for a lot of reasons. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [December 4, 2013, 2:32am UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/9 "2013-12-04T02:32:10Z")
The show stopper I see is time travel slash paradoxes. This is used as a common disproof : if the drive worked you could arrive before you left. I search Google looking for an alternate theory that would allow you to use this kind of engine, but not be able to go into the past. Or, at least not your past. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [December 4, 2013, 2:36am UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/10 "2013-12-04T02:36:37Z")
How does functioning as a time machine invalidate its purpose as a drive? ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [December 4, 2013, 2:56am UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/11 "2013-12-04T02:56:41Z")
Because it would violate causality, which would make lot of people very angry and be widely regarded as a bad move. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [December 4, 2013, 3:18am UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/12 "2013-12-04T03:18:02Z")
I see no need to invalidate a star drive just because some people are pissy about exactly when you’ll arrive at your destination. People who want to stand around saying “It can’t be done because it can’t be done!” can go invent generation ships, or cryogenic suspension. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [December 4, 2013, 3:22am UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/13 "2013-12-04T03:22:09Z")
It’s not when you get there that is the problem, it’s when you get back. If you get back before you leave you can destroy your own ship before it takes off and a bunch of other weird stuff that could end up destroying the universe. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [December 4, 2013, 3:41am UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/14 "2013-12-04T03:41:30Z")
Then don’t come back right away. If you get someplace 4 light years away 4 years before you leave, pack 8 years worth of supplies and plan to set up a camp somewhere. There’s gotta be years and years worth of exploration to be done out there. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [December 4, 2013, 3:42am UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/15 "2013-12-04T03:42:21Z")
> [@eburacum45](#): > > … and a bunch of other weird stuff that could end up destroying the universe. I _hate_ when that happens. ---
**Author:** ![Zakalwe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zakalwe/32/270_2.png) [@Zakalwe](https://boards.straightdope.com/u/Zakalwe)\ **Post date:** [December 4, 2013, 5:06am UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/16 "2013-12-04T05:06:53Z")
> [@eburacum45](#): > > It’s not when you get there that is the problem, it’s when you get back. If you get back before you leave you can destroy your own ship before it takes off and a bunch of other weird stuff that could end up destroying the universe. This is the part I don’t understand. Let’s say I leave Earth now. 00:00:00 on December 4, 2013. I immediately (for some value of immediate) accelerate to 2_c and fly out 2 light hours. Now, the light waves generated by my travel have only traveled 1 light hour from Earth. I bang a U and head back (still 2_c), somewhere along the way, I pass the light waves generated by my outbound travel. I get back to earth and it’s now 02:00:00 December 4, right? It still took _time_ to go out and back, just not as much time as light would have taken to travel that far, but why does that matter? How did I go “back in time”? ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [December 4, 2013, 5:12am UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/17 "2013-12-04T05:12:13Z")
> [@Zakalwe](#): > > This is the part I don’t understand. > > Let’s say I leave Earth now. 00:00:00 on December 4, 2013. > I immediately (for some value of immediate) accelerate to 2_c and fly out 2 light hours. > Now, the light waves generated by my travel have only traveled 1 light hour from Earth. > I bang a U and head back (still 2_c), somewhere along the way, I pass the light waves generated by my outbound travel. > I get back to earth and it’s now 02:00:00 December 4, right? It still took _time_ to go out and back, just not as much time as light would have taken to travel that far, but why does that matter? How did I go “back in time”? Apparently it’s when you try to mix and match Alcubierre and relativistic effects, as I recall. At least, it works that way for wormholes. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [December 4, 2013, 6:54am UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/18 "2013-12-04T06:54:20Z")
From [another thread](http://boards.straightdope.com/sdmb/showthread.php?p=15473197#post15473197) on the subject (I only considered information transfer, but you can replace this with any mode of transmission you want; additionally, I’ve covered only the limiting case of instantaneous transmission, but basically the same story works for all speeds greater than c): > [@Q about "warp" drives](https://boards.straightdope.com/t/q-about-warp-drives/634206/5): > > Special relativity: Say two spaceships meet each other at time t[sub]0[/sub]. They travel at a relative speed of 0.87c. On both spaceships, there’s an instantaneous transmitter, i.e. a device that transmits information at ‘infinite’ speed (this works for any speed greater than c, but the math gets more complicated for finite speeds). Now, say, a minute after the meeting, people on ship A notice that ship B’s back light is broken, so they instantaneously send a message to ship B informing them of their gross violation of intergalactic traffic codes, which as everybody knows are enforced with extreme rigidity. However, since ship B moves at a speed of 0.87c relatively to ship A, it is subject to time dilation, and thus, only thirty seconds have elapsed since the two ships met. > > So far, so good. The engineer on ship B, being of the swift sort, fixes the back light, mumbles something about how he cannae change th’ laws o’ physics, Captain, and then sends back a thanks, at about 45 seconds after the ships met. However, again, since ship A is moving at 0.87c relatively to ship B, it is subject to time dilation; thus, if 45 seconds have elapsed on ship B, only 22.5 seconds have elapsed on ship A. Thus, the thank you arrives on ship A 22.5 seconds after the ships have met, and thus, 37.5 seconds before ship A ever sent its message to ship B, which of course, seeing as how the problem’s already fixed, they now don’t have to. > > Or, with more detail, see the story [here](http://www.theculture.org/rich/sharpblue/archives/000089.html). ---
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [December 4, 2013, 7:45am UTC](https://boards.straightdope.com/t/alcubierre-drive-theory-changes-breakthrough/675384/19 "2013-12-04T07:45:33Z")
Personally I think our best bet at FTL travel is the current research thats showing some signs that the entire universe is actually a simulation: > **[Cosmic rays offer clue our universe could be a computer simulation](https://www.wired.co.uk/article/universe-computer-simulation)** > > If recent measurements of cosmic ray particles are correct, then we may have the first evidence that the universe as we know it is really a giant computer simulation We just need to figure out the equivalent of an SQL injection attack that lets us rewrite the position matrix for our desired object.