Talk:Alcubierre drive/Archive 3

Cite your sources!
This is nonsense. Mass bends spacetime. Object would still be subject to relativistic effects. (unsigned 210.55.240.194)


 * Providing more information than just disputing it is preferable. -- Cat chi? 15:38, 20 Mar 2005 (UTC)

There does seem to be some problem in the exposition around the sentence "conventional relativistic effects such as time dilation do not apply in the way they would in the case of a ship moving at high velocity through flat spacetime".

If the author thought about it for a moment, I'm sure he would realize that "moving at high velocity through flat spacetime" is not assigned a meaning within special or general relativity. All velocities in flat spacetime are completely equivalent wrt the spacetime. The claim may be true in some effective sense, but needs rewording. —Preceding unsigned comment added by 199.67.138.153 (talk) 15:35, 8 June 2008 (UTC)


 * From the article conventional relativistic effects such as time dilation do not apply in the way they would in the case of a ship moving at high velocity through flat spacetime. From Alcubierre's paper Since coordinate time is also equal to the proper time of distant observers in the flat region, we conclude that the spaceship suffers no time dilation as it moves. This may be wrong, but it is what Alcubierre's theory says so the article is not wrong to state it. If citeable sources have made this criticism then they can be mentioned.  Sp in ni  ng  Spark  16:14, 8 June 2008 (UTC)

what does the second image mean?
I might be completely missing the point of the Alcubierre Drive, but what exactly does the second image represent ? There are no labels or information telling us anything. Does it represent the distance that the space is contracted behind and in front of the ship, or something else ? There should at least be a descriptive caption (or an explanation in the text referring to this image). I await elucidation. :) Mpatel


 * What second image? I only see one image.  That image alleges to illustrate a characteristic effect of the Alcubierre style warp drives: the expansion tensor of the canonical ADM congruence, which is a timelike geodesic congruence, shows contraction ahead of the bubble and expansion behind.  This is not what causes the bubble to move (no cause or method for creating or controlling it is apparent), but only a description of how the bubble effects this particular family of nonspinning inertial observers.  Jose Notario has introduced another kind of warp drive spacetime which supresses this expansion/contraction effect.

---CH


 * The second image (or diagram to be correct), in the 'maths of the Alc. drive' section, shows a 3D picture of a :sort of crest and trough of a wave - I assume it depicts some sort of contraction/expansion effect, but I'm not :sure.


 * I think both topics, (Alcubierre Drive and metric) should be merged.--Mpatel 09:07, 24 Jun 2005 (UTC)

OK, I just didn't know what you referring to before; now I do. The figure in question (not by me) is a graph of the expansion scalar of the canonical congruence in the ADM chart for the original Alcubierre spacetime. In an unpublished paper I argued at great length (too great, really!) why this spacetime is by no means a "solution" of the EFE.---CH (talk) 01:36, 22 August 2005 (UTC)

Proposal to Merge This with Another Article
Hi all, I have just corrected a misconception and clarified the present status of 'Warp Drives' in the article on the Alcubierre metric. Unfortunately, at present this article suffers from the same problems I pointed out for the earlier version of the Alcubierre metric article. In addition, I think that the two articles on the same topic is redundant, so the two should be merged.

Possibly instead of explaining the original warp drive in great detail, a slighly simpler version should be used? (After all, the original paper is on-line.) Some years ago, inspired by Broeck's paper, I did some work on simple eigenthing objections, similar to some which have now appeared in print, and wrestled with the energy requirement problem. In fact, I wrote a long unpublished paper on the simpler versions I have in mind.

Someone should add something about the Notario variant, which is expansionless and therefore significantly different from the Alcubierre drive and minor variants such as the one I considered.

And, the merged articles should be retitled warp drive spacetimes, since this term is now fairly standard in the small but slowly growing literature on warp drives. ---Chris Hillman


 * The merger sounds like a good idea. ---Mpatel 09:07, 24 Jun 2005 (UTC)

And relatively easy. I was just about to do it when I noticed an edit conflict with another user, User:Roadrunner, which almost resulted in my losing my work while I was modifying the other article! Annoying that the new Wiki software seems to have a bug which requires users to try to manually resolve problems arising from edit conflicts.

It seems that User:Roadrunner and I disagree about whether or not the Alcubierre spacetimes count as "solutions". I am confident that I can support my contention that they are not (I asked him to read the article on exact solutions of Einstein's field equations, but suggested on the talk page of the article that we all lay off these articles and resolve this controversy on the talk page of the other article. Otherwise, I fear than even if everyone tries to behave nicely, if two of us happen to be modifying one of these pages at the same time, we could potentially lose everyone's work.  Presumably no-one wants that!

I think the other article is fair regarding the status of warp drives, but if the two articles can be merged, presumably we don't want to discard the work of the person who made the funky figure. Fortunately, I can elaborate (at arbitrary length!) on the meaning of the expansion tensor, ADM observers, and so forth. Actually, in my unpublished paper I had many more figures which could perhaps be imported to the merged article, but I already fear that it is in danger of getting too long.---CH (talk) 1 July 2005 06:02 (UTC)

Only two people voted so far...
... (myself and Mpatel, both of whom voted to merge), but this message has been up for quite a while, so I'll announce that I intend to carry out the merger as soon as I get a chance.---CH (talk) 01:39, 22 August 2005 (UTC)

A further vote from a relativist to merge!

Captain Future?
Wasn't such an idea used in Captain Future? I saw it in French and they were talking of vitesse|mode ondulatoire (undulating/waving speed|mode) —Reply to David Latapie 15:07, 16 October 2005 (UTC)

New Figure?
Alcubierre's idea is that the spacetime inside the bubble would not be bent (see diagram). Any objects in the bubble would experience no such effects, as spacetime is flat in the center of the bubble, and then gradually becomes more curved towards the edge of the bubble. There would be extreme tidal forces and relativistic time dilations towards the edges of the bubble, where spacetime is extremely bent. A good diagram is given here. (This is a better diagram of the curvature than the one at present, should it be replaced?) Sloverlord 14:21, 10 December 2005 (UTC)


 * You need to know the current image policy before you add any figure. And what is that policy?  Darn if I know, I can never seem to find it when I need it.  Try asking at Village Pump.  If you upload an image which doesn't have the required license (check with the author), it will be autodeleted.


 * When I get a chance, I plan to completely rewrite this article, adding my own figures. But this is a rather low priority, since this topic has not been 'hot' in the arXiv for several years.---CH 20:28, 10 December 2005 (UTC)


 * According to Tufts university proffesors Michael J. Pfenning and L.H. Ford (article avaible at xxx.lanl.gov/abs/gr-qc/9702026) the amount of negative energy required for making a warp bubble, that would be big enouph for a person would be unatainable. So I have been trying to use Lorenz contraction to make a ship with incredabley small vollume so there won't be so much negative enregy needed. Unforently not being a physist I don't know how to test my idea, for all I know the warp bubble needs to be a perfect sphere, also to cause lorenz contraction I have to have the ship moving very, very fast, would the ship neccisarly shoot out of the bubble, or is there some way to accomidate the ship which has some non-zero local velocity?


 * Thanks in advance ---Spaceling


 * P.S. Sorrey I had to use the edit function I just didn't know how else to post


 * Hi, Spaceling: first things first: click here to create a free user account. You just need to make up a "handle" or username, such as Spaceling.   Now you can add dated and signed comments in talk pages like this by going to the page you want to edit, clicking the button at top, scrolling down the pane (you should add new comments at the bottom of the appropriate section), and typing something like this:
 * ::Your comment. ---~
 * The colons tab your comment, which is good idea for readability. For example:
 * FirstComment ---FirstUser Date/Time
 * SecondComment ---SecondUser Date/Time
 * ReplyToSecondComment ---FirstUser Date/Time
 * ThirdComment ---ThirdUser Date/Time
 * Does this help? ---CH 06:21, 6 February 2006 (UTC)


 * As for the physics part of your question, you said you are not a physicist, but what grade level are you at and what physics courses have you taken?
 * Lorentz contractions won't help you. Various physicists have suggested possible fixes, but these all seem to raise new objections.  Currently, the consensus is that this notion is a speculation not grounded in any plausible physical mechanism, and which is probably in fact no more possible than perpetual motion.  However, rigorous proofs are lacking.---CH 06:25, 6 February 2006 (UTC)


 * ok I am logged in. This helps very much thank you
 * I a collage senior who took a basic physics course called "Newtonian Dynamics" and an astronmey course. I got a D+ in the physics course which discoraged me from choosing physics as a major, but I got an A- in the astronmey course.
 * I have also taken two basic caculus courses and learned simulation modeling in my econ clases a skill useful for testing out ideas.
 * Everything else I know about physics is self tought something that is possible because physist have been trying to reach out to the common person by writing dumbed down books on advanced physics.
 * At anyrate if what it sounds from what you are saying the Alcubierre drive could be fundemntaly flawed and is cannot be redeemed.
 * Still i have trouble imagining going faster than light with out warping spacetime. I will check out the wormhole section though I would imagine they are equaly as speculative and otherwise flawed.---User:Spaceling 11:21, 6 Febuary 2006

I don't know much about the Alcubierre drive. All i know is that the exotic energy puts it in the impossiblity list. I found a link that states the Alcubierre drive can function without exotic energy: The Positive Energy Spation Warp Drive


 * Use your edit button to see how I put brackets [ ] around the link you found and added title. This is how to quote a link in WP.  As for the content, I haven't looked at this, but I trust you realize that some "paper" you find someplace on the web is even less reliable than arXiv eprints, which in this area at least are not all of acceptable quality.  In the end, there's no substitute for knowledge of math and physics in evaluating physics eprints, but anyone can develop some common sense rules of thumb.  Sounds like you are doing that, since it seems you now recognize that caution is required in evaluating claims regarding warp drives.---CH 23:32, 16 February 2006 (UTC)

Soliton Wave
This sounds similar to the Soliton Wave technology described in episode 110, "New Ground", of Star Trek: Next Generation. --tvleavitt 06:42, 13 May 2006 (UTC)

Star Trek
Fanboy mode on... Alcubierre may not be mentioned explicitly, but the Next Generation Technical Manual has an image of a warpfield which clearly shows a two-lobed structure, one ahead of the ship and one behind. (Note that this isn't a fan drawing, it's a color-inverted scan from the official book.) It looks an awful lot like the graph of the Alcubierre metric. The notion that relativistic effects do not affect warp travel was also mentioned, if memory serves. Obviously the two aren't exactly the same, but the shape of the drawing and the constant talk in the series about various types of "warp bubbles" seems to me a pretty clear reference. Worth a mention, at least?


 * Actually from the look of that diagram it would seem as if there are multiple warp bubbles surrounding the ship, has it been considered that to achieve a usable Alcubierre drive without the requirement of a couble solar masses to power it would be the 'multiplicitive' effect of several of the effects stacked within one another, interesting (who knew science fiction would lead to such thoughts). --Chase-san (talk) 20:46, 7 January 2008 (UTC)

Merged in Spacewarp
I merged in what I could from Spacewarp. Its going to need further refinement. Cwolfsheep 02:40, 24 July 2006 (UTC)

Merged in Alcubierre metric
I'm not proud of this merge, but I disbursed the content as evenly as possible. Someone's going to need to check the math sections: they appear to be the same thing, but they're different formulas. I also tried moving the talk page from the metric article, but not sure if I did it right. Cwolfsheep 03:01, 24 July 2006 (UTC)

Fiction: Dune
In the movie the spice, Melange, has the property of bending space-time in a similar manner to the Alcubierre drive. Dessydes 14:49, 21 August 2006 (UTC)


 * The Guild only uses spice for its Precog effects, the folding is a Holtzman effect. I don't recall the movie munging this, but I'd have to watch it again.  The Alcubierre drive is a warp drive, Dune uses a fold drive (see Holtzman Drive) ---XanMat 20:06, 20 October 2006 (UTC)

Energy Requirements and Effective Travel Times / Speeds
The one thing I think that is both missing from, and of interest to those viewing this article is the (theoretical) values for various energy requirements, travel times and/or relative speeds. Not being a theoretical physicist, I am yet very interested in the field, particularly new developments. Hence, I would be interested to see any statistics relating to the energy requirements (both from the original Alcubierre metric AND from Loup, Waite and Halerewicz' Reduced total energy requirements for a modified Alcubierre warp drive spacetime mathematics.

If possible, maybe an addition could be made to the original article outlining these three statistics for easily recognised distances, for example: From Sol to Earth, Jupiter, Pluto, the Alpha Centauri system, Rigel, Betelgeuse, and the Milky Way's centre, as well as including other recognisable distances, such as: crossing Milky Way's diameter and from the Milky Way to Andromeda (M31).

Where the variation of energy usage may increase/decrease the values for effective travel time and effective speed, this additional data could be included, also.

This data (I feel) would be of great interest to those of us unable to sift through the mathematics and the background physics necessary to fully comprehend the complexity of the Alcubierre metric. Twphillips 12:15, 13 January 2007 (UTC)

Possible re-structuring?
I see this article is tagged "may be confusing or unclear for some readers". There are at least 2 classes of potential reader: those with no mathematical understanding of general relativity (including me) and those with at least some. So I suggest the article should have 4 major sections (including table of contents):
 * Introduction. Something like "In 1994 Alcubierre proposed a hypothetical models of: a space ship drive capable of 'faster than light' travel; a model of space-time (the Alcubierre Metric) which described the 'warp field' which the drive would use. The intro should use pop-science terminology to avoid frightening off the non-specialist reader.
 * Table of contents. This will reassure more mathematically-inclined readers that the article also contains material that meets their level of interest.
 * "Popular"-level explanation. The second paragraph of the current article describes the basic idea in terms which are just about simple enough. This should be followed by explanations of the difficulties: is it possible at all (exotic matter?)?; is it economically feasible, even after the later refinements (how much exotic matter?)?; how to get it started and does this require slower-than-light space travel?; the difficulty of flying blind because the warp bubble is causally disconnected from the rest of space-time; etc. The "popular" section would also contain the Trekkie stuff ("The Alcubierre drive and science fiction" and "Warp fields")
 * Mathematical exposition, covering much the same ground but more technically.

Of course a competent physicist would have to check the "popular" section to ensure that it contained no gross blunders or misrepresentations beyond those inherent in trying to describe a very mathematical subject in ordinary language.

It might even be a good idea to split the article into a popular and a technical article, with the popular article titled "Alcubierre drive" and linking to an article titled "Alcubierre drive (technical analysis)". This would give Wikipedia the option to freeze the popular article after sign-off by a competent physicist and leave the technical article open for editing to take account of new technical publications.

Such a division might also help to get rid of the "requires authentication or verification by an expert" and "missing citations and/or footnotes" tags.Philcha 23:00, 16 February 2007 (UTC)


 * Perhaps a brief popular-level section might be a good idea (not a real article; there already exist articles with the Trekkie stuff, Warp drive for one). But it is rather hard to write such a section without over-simplifications and misleading notions like the (non-existing) 'warp field' which would put off any serious reader. --Seador 13:55, 17 February 2007 (UTC)


 * I'd put "warp field" in quotes to show that it's just a label, not an accurate description. Or can you suggest another term which is more correct but still brief and easily understood by non-specialists? And similar replacements for any other terms you're concerned about in my proposal?Philcha 16:30, 6 April 2007 (UTC)


 * "Warp field" is not a misnomer, but a misconception. That's why I wouldn't use it at all. As for a popular intro, it seems that the first paragraph (that above the Contents) is precisely what you proposed?--Seador 13:20, 7 April 2007 (UTC)

Warp fields
I would delete that section, because 1) it seems to be more appropriate in Warp drive. 2) The passages like "they allow the transport of physical objects or the transmission of information faster than the speed of light, which is currently understood to be impossible under most circumstances in the real universe", or "While there are natural phenomena that might be likened to warp fields, such as the area of distorted spacetime thought to exist around a black hole, no feasible method of artificially generating one has yet been proposed" look terribly strange amid the discussion of the Alcubierre bubble, which is exactly a means of transportation of physical objects or the transmission of information faster than the speed of light and which is an area of distorted spacetime (though not around a black hole). --Seador 01:30, 21 February 2007 (UTC)

Importance
Dear Edward, Aren't you a bit more positive than consistent? If the light speed barrier is important, than apparently so is one of very few proposed ways to overcome it. Whether this way is obscure is disputable (I, for one, find it quite transparent). But in any case obscurity can be a demerit of an article, not of a metric. So, just tell me what exactly you regard especially obscure in the article and I'll try to clarify that point (with perhaps somebody's help). --Seador 14:43, 25 February 2007 (UTC)


 * By "obscure" I mean not very well-studied, and there is little that you can do to remedy that unless you want to do a Ph. D. thesis or two on this. Let me put it to you this way:  There are plenty of important solutions of the Einstein field equations, such as the Schwarzschild solution, the Kerr solution, and the FLRW metric.  This one involves that use of an undefined "negative energy" which most physicists consider to be unphysical.  I know that this metric is not a joke and do not dispute its notability.  However, the assessment is done in regards to physics as a whole and not interstellar travel.  This is a minor topic even within the scope of relativity.  The Alcubierre drive iteself is highly speculative, and as I keep trying to emphasize is not expected to work.  Now if someone should produce a working Alcubierre drive, then the status of this article will change dramatically.  In the meantime, please keep the broad scope of Wikiproject Physics in mind, and remember that Wikipedia is not a crystal ball. --EMS | Talk 18:00, 25 February 2007 (UTC)

Well, tastes (and assessments of importance) differ. However I'd like to dispute your arguments.

It is by no means a minor topic in relativity (and even in physics as a whole). For about a century people thought there is a fundamental limit on how soon a signal can get from one point to another. Now, owing to Alcubierre's paper (and the works inspired by it) we know that there is no such limit. I think this a very significant step. The fact that his bubble cannot be built in the foreseen future is immaterial, just because the paper is importance to (theoretical) physics, not to interstellar travel. And that is why the status of this article will not change at all, if someone produce a working Alcubierre drive (which is not impossible, recall that in 1944 many physicists, including Heisenberg, considered the A-bomb to be unphysical by exactly the same reason – an unrealistic quantity of exotic (fissionable) matter was thought to be necessary). That would be a revolution in engineering, applied physics – whatever but theoretical physics, in which its possibility is already understood. I also don't think that most physicists consider "negative energy" to be unphysical. That the WEC breaks down sometimes is an experimentally confirmed fact, see Casimir effect.--Seador 19:51, 26 February 2007 (UTC)


 * First of all, this metric does not at all remove the light speed barrier, which always applies locally in relativity and even applies within the "bubble" created by this pseudo-warp drive. This is instead a special type of spacetime curvature which (if real) is able to propagate itself at superluminal speeds.  Secondly, the Casimir effect is not all that relevant, as the type and amount of "negative energy" are quite beyond that.  In fact, not only is the WEC violated by the Alcubierre, but the strong and dominant energy conditions are also.
 * The real issue here seems to be that you like this metric. That is not a reason to up-rate it.  I repeat that this metric is not taken seriously by most physicists, which very much reduces its importance in the overall scheme of things.  Let me put it to you this way: If I was creating an overview course on physics, the Alcubierre drive is not something that I would immediately think of including.   That is the test for being of high importance IMO. --EMS | Talk 21:47, 26 February 2007 (UTC)

Yes, I do like the metric and you obviously don't. But apart from that there are some rational considerations. And yours confuse me:

"First of all, this metric does not at all remove the light speed barrier"

It is 26 lyr from the Sun to Vega and the metric is flat between them. For a century people inferred from this that it cannot take less that 26 yr to reach Vega. Now we know that this is not necessarily the case. To me it looks removing the light speed barrier.

Secondly, the Casimir effect is not all that relevant, as the type and amount of "negative energy" are quite beyond that. In fact, not only is the WEC violated by the Alcubierre, but the strong and dominant energy conditions are also.

The Casimir effect produces the "negative energy" of exactly the required type (the WEC violation always implies the SEC and DEC violations). As for the "amount" the estimates range from 10^67 g to 10^{-5} g and are based on the "quantum inequality" which has never been proved in the 4-dimensional case. Isn't this a too feeble basis for proclaiming something "unphysical"?

I repeat that this metric is not taken seriously by most physicists

I cannot even imagine how you know what most physicists think. Well, you wouldn't include the Alcubierre drive in your imaginary overview course on physics. But I would. So, I don't think this is a good criterion.--Seador 21:34, 28 February 2007 (UTC)


 * Seador - I have studied general relativity, and regularly meet with other physicists to discuss my own ideas on the topic.  I also regularly read the articles in various science news site as well as subscribe to Nature and Science.  I can tell you for a fact this time metric raise quite a few eyebrows when it came out, but as more details were gleaned was quickly dismissed as a most impractical scheme for interstellar travel.  Look at it this way:  A metric that allows superluminal speeds can also act as a time machine, and this is not the first time travel metric to be derived from GR.  They all require some condition that at best is well beyond the ability of modern technology to produce.


 * You also claim that WEC violations imply SEC and DEC violations, but QM does violate WEC but not SEC and DEC. You also poo-poo the mass requirement, but apparently several stellar masses of both positive and negative energy are needed to create a warp bubble that size of a small room even if this metric is real!


 * Overall, I agree with you that this is a neat metric. However, in the overall scheme of physics it is at best controversial when people stop to consider it at all.  If you can show me evidence that this is a topic of regular and intense discussion at this time, I will agree to the "high" importance designation.  However, if all that you can show me are at best a dozen or fewer articles a year on this, that only shows that it is on the sidelines at this time. --EMS | Talk 22:25, 28 February 2007 (UTC)


 * P.S. This point that I am trying to make is that importance is a function of how often a topic is considered and/or put to use either direction or indirectly. General relativity is the basis of scolarly articles that are submited on a daily basis, and you cannot dirve your car without making use of classical mechanics.  For high importance, I have found topics like acceleration and black body.  If the Seador Interstellar Lines existed and was regularly selling tickets for ships operating using the Alcubierre drive, I would consider that to be a higly important topic.  Instead, I must ask you not to count your chickens before they hatch (unless you have used this drive to peak into the future). --EMS | Talk 22:45, 28 February 2007 (UTC)

I agree that being a subject of numerous research papers or being a part of every lawn-mower is a sufficient condition for being acknowledged important. The question is whether this is a necessary condition as well. You probably wouldn't deny the importance (for physics) of the string theory or of the concept of causality. But how many papers a year are published on causality? Have you ever seen a string-power lawn-mower?

Also, as you attach such significance to realizability, let me be pedantic here: a) It takes only a few milligrams (and not several stellar masses!) of exotic matter to support an advanced version of the Alcubierre drive and even that is true only if we believe in "quantum inequalities", b) The Casimir effect does violate all three Energy conditions (as follows from the fact that it violates even the Null energy condition).--Seador 17:16, 1 March 2007 (UTC)


 * The more I look at energy condition and Casimir effect, the more it hits me that the WEC is also obeyed by the Casimir effect. I was equating the WEC with conservation of energy, which QM violates in a time-dependent was in accord with the equation I gave above.  However, the energy conditions are dealing with mass-energy densities.  In the case of the Casimir effect, the cause is a loss of real energy (in the form of reduced virtual pair production) between the plates instead of the appearance of negative energy.  There is a difference here.  Other than in the form of potential energy, noone has ever observed a negative energy, and potential energy is not harnessable for the Alcubierre drive.  (What it needs is something more in accord with a "negative mass", being a piece of matter that it repelled by gravitation.)


 * So this brings me back to the starting point: It is a neat metric, but if the enabling conditions are not physical, then neither is the metric.


 * I also take issue with your claim that the level of consideration is not a necessary consideration in terms of importance. An important topic is one the you cannot keep from using, and this one is very, very easy to avoid. --EMS | Talk 18:06, 1 March 2007 (UTC)

Hmm… I, for one, find it much easier to avoid Brown dwarfs. This obviously depends on the field of interest and expertise. You probably keep from using the concept of FTL travel just because yours are sufficiently far from relativity (I judge from your response: the null (and hence weak, strong, dominant...) energy conditions actually are violated by the Casimir effect in the case of two parallel plates; conservation of energy, on the contrary, does hold in quantum (as well as in classical, relativistic,…) mechanics; finally, in general relativity there is no such thing as  potential energy). If it were for me I would perhaps rate the topic as "Top", but as a compromise I propose "High" ("Subject contributes a depth of knowledge", doesn't it?). Or shall we seek a mediator?--Seador 13:53, 3 March 2007 (UTC)

Though I am not expert enough on the topic to judge whether this model is physically possible or not, it appears to be an interesting 'loophole' through the light speed barrier. On the other hand, an the article like for example Einstein field equations is rated mid importance, though it clearly has a broader impact on the field of physics than this one. Let me propose a compromise. It seems like you are arguing between 'low' and 'high' importance, why not settle for 'mid'? Then focus your energy on making this article meet GA standards.--V. 21:38, 3 March 2007 (UTC)


 * Well, looks fair. (Though now that I've learnt that the Einstein equations are regarded in Wikipedia less important than, say, the Kondo effect I'm not sure any more that I understand what importance is).--Seador 01:02, 6 March 2007 (UTC)


 * Kondo effect was called "high" for the same reason as this one was given that rating: Someone really likes that topic.  "Importance" is a measure how essential the topic is in a given subject area, in this case physics.  I could argue for the Einstein field equations as being of high importance, but they are very arcane and so I suspect that mid importance is actually fair.  (In the scope of relativity, they would be of top importance, but that is another matter.)  This metric that is arcane even within the field of relativity.  It really is a filling in of details than an essential topic itself.  I argue against "mid" since that is contribiting to a depth of knowledge, and I have a hard time seeing where I would place this metric ahead of or even beside other more accepted EFE solutions such as the Schwarzschild solution. --EMS | Talk 02:21, 6 March 2007 (UTC)


 * I think you are missing the point. The importance of Alcubierre's (in contrast to Schwarzschild's) metric has not to do with its being a solution to the arcane Einstein equations (in fact, it is not any more a solution than any other metric whatsoever). Suppose one day the Einstein equations prove to be wrong. That would undermine significantly the importance of the Schwarzschild solution, but would in no way affect the light-speed-barrier problem (that is, as long as we believe in the equivalence principle and special relativity; is there anything arcane in them?) and, correspondingly, the Alcubierre drive as its element.


 * Thus, it seems we need a mediator after all. Shall I look for one at Third opinion?--Seador 23:56, 6 March 2007 (UTC)


 * 3rd opionin: Since I'm not an expert in this area it's hard for me to access the importance of "warp drive" I think the bigger problem with this article is a lack of clarity and sources. You both really need to use references tags and footnotes so that readers will know where each specific claim is coming from. futurebird 00:45, 8 March 2007 (UTC)


 * Just a comment about this discussion. In my opinion the Alcubierre metric seems to cause an space inflation or expansion behind the propelled space time area and a space deflation in front of. Now as the current model of physical cosmology propose a cosmic inflation driven by a negative-pressure vacuum energy density in the early history of this universe, the idea of such a kind of a metric should not be ruled out by declaring it unphysical. werner 11:58, 8 March 2007 (UTC)

Also coming from 3O, it would really help if someone would quickly sum up the problem, i.e., "we disagree on whether the text '...' should be in the article; I think yes because ..., while User:Foo thinks no because ...". Otherwise, people may have trouble helping out here. Sandstein 21:57, 8 March 2007 (UTC)

Like it is stated in the request the disagreement is not about a text, but about the rating of the topic. EMS lowered it to "Low" because it is 1) not mainstream and 2) at the moment cannot be implemented in any working device. And I think that it should be "High", because it is the (first) proof of the very important (in my view) fact: in contrast to once common belief, general relativity doesn't put any fundamental restriction on how soon a signal from one point can get to another. --Seador 23:27, 8 March 2007 (UTC)


 * Seador - Wikipedia is not a soapbox, and wormholes already have scooped the Alcubierre metric in providing a means to propogate signals in a faster-than-lightspeed fashion anyway. Your argument keeps boiling down to this being important to you, but what matters is whether this is important to the scientists in the field.  I am somewhat involved in the field, and I see no sign that the Alcubierre metric is taken seriously within it.  If this was the first metric of its ilk, there may have been more excitement.  However, wormholes and time travel have been part of the GR landscape for quite some time, and the Alcubierre metric fits very nicely into that collection. --EMS | Talk 16:23, 9 March 2007 (UTC)

My advice to the wisest of you would be to let the matter rest, and rest assured that the reader will judge this article on its worth and not its rating. Importance is after all a personal affair, even in physics, and only nature can prove us wrong in the end. An article that is well written will win the most attention and such an article, being coherent and comprehensible, requires no rating to commend it. --V. 18:18, 9 March 2007 (UTC)

Response to a Warp Bubble Criticism (About controlling the direction/movement of a warp bubble)
"Sergei Krasnikov is a theoretical physicist at the Central Astronomical Observatory at Pulkovo in St. Petersburg, Russia. He identified what he saw as a critical flaw in Miguel Alcubierre's space warp proposal for space travel: if the space warp moves faster than the velocity of light, it cannot be controlled from inside. Krasnikov's analysis shows that at superluminal speeds the interior of the bubble is causally isolated from its surface and exterior. Photons cannot pass from the inside to the outside. Therefore, there would be no way of controlling the space warp—of stopping, starting or steering." If you were to set up a track, of sorts, a series of devices strategically placed throughout space that could sustain and move the warp bubble onward through space, which would allow an object to be steered through space at superluminal speeds to an intentional destination. This would mean we would first need to have reached the destination using conventional methods to deploy such devices, but at least it would make the trip much faster for future travelers. --Steakpirate 04:52, 27 April 2007 (UTC)


 * Question: Does this kind critics forbid to use a method of jumping into the blind, that is to use a hypothetical device together with a hypothetical ship in such away to load a hypothetical device (what ever this means) and jump a few light years with superluminal speed and repeat this procedure at least to reach the destination. Ok this looks like the triple jump known in track and field athletics but it allows to reach the destination. --werner 12:01, 27 April 2007 (UTC)


 * If the warp bubble is generated from a device internal to the bubble, then stopping and starting is not a problem despite Krasnikov's objections. Steering might also be possible, except that you can't see to steer.  But so what?  Space is mostly empty space.  If you know the meta-velocity of your bubble (the rate at which it propagates itself through space, you can't exactly call it a real velocity), whether that's 50c, 500c or whatever, you just (a) point the ship in the desired direction and (b) turn the warp drive on for the required travel time, then off. (If there's something in the way, you'll have to make a couple of "jumps" at angles.)  To get even more hypothetical, while photon interaction with outside may be disallowed, the gravitational space curvature near massy objects may have influence on the warp bubble that the warp generator can detect.  This of course is highly speculative. -- AJWM 04:59, 11 May 2007 (UTC)


 * As far as I understand the quotation, the point is: the warp bubble cannot be generated from a device internal to the bubble (that is unless one uses tachyons). --Seador 13:06, 11 May 2007 (UTC)

Just out of curiosity, is there a plan to re-do the criticisms section? Most of the text is really confusing and doesn't really seem to do much, nor does it have any sort of reference section for these criticisms, indicating that they're likely just somebody's opinion. Thanks. —Preceding unsigned comment added by 199.31.3.195 (talk) 16:08, 12 October 2007 (UTC)

Tachyons
I have removed the last item because 1) Coule just retold Krasnikov's result and 2) it is, in fact, what is already said in the first item. Kidburla, if you feel that the idea should also be expressed in terms of tachyonic matter, maybe you'd better expand that item? --Seador 12:40, 2 May 2007 (UTC)

Usage of the Field of Equations in Physics of the Alcubierre drive
I would like to question the purpose of this part of the entry.

"Because nothing can travel faster than the speed of light, it has been stated that bending spacetime itself would cause an object to travel faster than light; this idea has been utilized in the Warp Drive concept in science fiction, but also is the Alcubierre drive theory. The following formula, based on general relativity, permits the travel of an object faster than light provided that spacetime is curved[1]:

$$G\mu\,v+8\pi\,GT\mu\,v$$

If spacetime is warped in this way, then technically the object(s) are not moving faster than light, instead, the space around them shifts so that that object(s) arrives at its destination faster than light would in normal space. Space would be collapsing at one end of the "bubble" and expanding at the other end."

This seems to me to be a case of someone blindly quoting something they do not understand and have no idea what it means. My main problem is, $$G\mu\,v+8\pi\,GT\mu\,v$$ this does not mean anything. One can only assume that he means the Einstein Field Equations which are, $$G_{\mu \nu}=\frac{8 G \pi}{c^4} T_{\mu \nu}$$

I am really not sure about what this person is getting at. First off the Field Equations always assume that space is curved, otherwise we can use simple old Newtonian Physics(or SR if we are traveling sufficiently fast) to describe the interactions. Also if my memory serves me right(and since I am currently a few hundred miles away from my copy of Misner Thorne and Wheeler's Gravitation it will be a few days before I can look it up), you can travel faster than the speed of light in an inertial reference frame, ie that matter can only travel less than or equal to the speed of light is constraint of SR that gets broken under GR. So this seems of little importance to the topic. Since the rest of this section simply says that normally we take the Strss-Energy Tensor and try to find the Curvature Tensor, but with this instance there was a proposed Metric and the Curvature Tensor was Created, I suggest that the portion that was quoted be deleted.Jetherrie 04:40, 12 May 2007 (UTC)


 * Done --Seador 18:57, 12 May 2007 (UTC)

Warp Drive - An Alternative
I may not be an expert in quantum/time physics but.. there is theoretical proof that an electron (or quantum) can appear at random from "nothing" at any given time or place. However, the act of observing this event determines the outcome of the event. Therefore, if the event is unobserved it must take place. To enable travel at FTL two things must occur: Unobservence and creation of randomness on a molecular (subatomic) scale. The mechanics of acheiving this state would be reliant on Einstein's e=Mc2, where there is enough energy imposed to translate the mass of each individual atomic and sub-atomic particle to the speed of light, and a "directional" component to control the randomness.The entire event to be unobserved may be reliant on the uncertainty principal. Just a thought....

Reverted changes - explanation.
I just reverted two changes by Harold f, and wanted to explain why. First, he changed


 * The ship would ride this wave inside a region known as a warp bubble of flat space.

to


 * The ship would ride this wave inside a region known as a warp bubble which itself moves faster than light through flat space.

But the intent of the original sentence was that the space inside the bubble is flat. I think it's clear from context that the space outside is flat and that the warp bubble effectively moves faster than light. Secondly, he changed the sentence


 * Thus, the Alcubierre drive does not contradict the conventional claim that relativity forbids a slower-than-light object to accelerate to faster-than-light speeds

by adding "provided that the warp bubble itself is not considered an object". But this condition is unnecessary, since what's being referred to here is the prohibition on local superluminal travel (i.e. with respect to the local metric), and the warp bubble doesn't violate this in point of fact. -- BenRG 11:05, 19 August 2007 (UTC)

Removal of the page
I object to the removal of the page. There are a number of references at the bottom of the page, and though the page needs work, it is an important article in discussing the attempts of science to explain the theorhetical world of faster than light travel. This article should not be removed, rather improved over time. - Eisenmond —Preceding unsigned comment added by 192.91.171.36 (talk) 21:22, 13 November 2007 (UTC)

I'll add a few necessary references within a couple of days. But could you help me by explaining what do I do to get the references in the usual style (when I can refer a few times to the same source), like "It was shown in [1] and [2], while that was proven in [1] and [3]...

[1] Smith, PRD...

[2] Brown, PRL...

[3] Green, CQG...

--Seador 22:53, 13 November 2007 (UTC)


 * It is not a question of whether or not the article is interesting, but whether it is verifiable by using reliable sources. In order to show that it is, and that it isn't original research, inline citations are the way to "show your work" so to speak.  Full information and suggestions for citing information can be found at WP:REF.  The easiest method (for me) is:

Blah, blah, statement of fact.

and then, at the end of the page, add the following section

==References== which will cause the footnotes to be listed there. Hope this helps. Pastordavid 15:43, 14 November 2007 (UTC)

I don't know if you still want this information as this thread was quite stale when I came across it, but this is how you do multiple cites to the same reference:

The first time you put in an inline reference like so;

Then on subsequent uses you just insert;

I prefer to use a template for the references section like so

==References==

And it will end up looking like this in the article;

Peter Piper picked a peck. ..

Ring a ring a roses. ..

Objection to removal of this article
I've come across this article a few days ago, and reading the talk page I get the idea that the article has been proposed for removal. I sincerely object to the proposal for removal, as it did indeed seem a very good article by now - citing a lot of references, while explaining clearly the idea behind it. Also, I did not find any part of the article ambiguous or unclear, in my opinion the authors have done a really wonderful job of making the concept understandable in layman's terms. I really found this article useful. I hope this post helps in preserving this article for the future. Thanks, Hirak 99 (talk) 16:46, 10 January 2008 (UTC)

González-Díaz' paper
Could the author explain: What exactly does this mean? Did he propose to consider time machines? Together with the bubbles? Instead of them? How can consideration of time machines allow for multiply-connected spaces? What is meant by "closing the geodesic incompleteness"? What are the "quantum instability requirements" and why would one wish to satisfy them? --Seador (talk) 01:07, 14 January 2008 (UTC)
 * 1) "González-Díaz proposed considering closed, time-like curves. This refinement allows for multiply-connected spaces"
 * 1) "closing the geodesic incompleteness and satisfying quantum instability requirements."

Collisions
What would happen if a spaceship travelling with an Alcubierre drive ran into some object? Would it shatter to pieces like you'd expect a really-really-fast impact to or would something more exotic happen? What if instead of a physical object, the spaceship collided with another warp bubble? -- Milo —Preceding unsigned comment added by 81.171.2.42 (talk) 19:52, 26 February 2008 (UTC)


 * You should ask this question at the Science Desk. This page is for discussing how to improve the article, not to discuss the subject itself.  Sp in ni  ng  Spark  00:14, 27 February 2008 (UTC)

Needs Clarification
I'm sorry but the following quote (and section of the article) makes very little sense to me, even when I try to put it into context in terms of this article.

"The pilot inside the bubble is causally disconnected with its walls. Therefore the bubble cannot be used for the first faster-than-light trip to a distant star. In other words, to travel to Vega (which is 26 light-years from the Earth) one first has to arrange everything so that the bubble moving toward Vega with a superluminal velocity would appear and these arrangements will always take more than 26 years (Krasnikov, 1998)."

Am I just, for some reason, incapable of understanding this and it's written correctly or am I right and there's something wrong with it. I've reread it several times and it still makes very little sense to me. Rajrajmarley (talk) 03:50, 3 March 2008 (UTC)

At first glance everything seems clear. What exactly is the problem? Seador (talk) 16:43, 4 March 2008 (UTC)


 * What is clear from Krasnikovs' 1998 paper, but is not clear in the article, is that there is a requirement for ". . . placing in advance some devices along the pilot’s way . . ." (page 10). The trip to place these devices must, of course, be at sub-light speed since the Alcubierre drive is not yet constructed.  Maybe this is Rajrajmarleys' difficulty.  Can I suggest this as a useful addition to the article?  Sp in ni  ng  Spark  12:29, 8 March 2008 (UTC)


 * What you are saying sounds absolutely correct. If you think that (important!) point is not clear enough in the article, please do clarify it Seador (talk) 23:53, 8 March 2008 (UTC)


 * Thank you  Sp in ni ng  Spark , I think that was all the clarification I needed, I really couldn't figure out exactly what that section was talking about, I think the language of the quote is a bit to abstract/artistic for my taste. Rajrajmarley (talk) 07:21, 2 June 2008 (UTC)

Neutrality.
This article seems to have a slight anti bias to it. Does anyone else think so? Zazaban (talk) 23:29, 8 April 2008 (UTC)


 * What exactly would you propose to change? Seador (talk) 09:06, 11 April 2008 (UTC)
 * Well, the whole article seems to be an attempt to refute the idea. There should be at the very least some positive information. Zazaban (talk) 02:49, 12 April 2008 (UTC)
 * That is not what I get from the article. It is saying that this is possible under the known laws of physics.  If you mean that the article shows that there is no known means of constructing a practical drive, well this is merely reflecting the mainstream published scientific opinion and not a bias of Wikipedia.  As Seador said, if you would like to point out specifics, then maybe we can change the article.  I also suggest that you remove the POV tag you placed on the article as this is likely to be read by most people with precisely the opposite meaning to what you seem to intend.  Sp in ni  ng  Spark  08:49, 12 April 2008 (UTC)
 * You're right. My major problem was with the unusual criticism section. I'll move the template there. Zazaban (talk) 16:56, 12 April 2008 (UTC)
 * Now that you have me looking at that section, I have found a problem with it. The energy quoted is -1067 g.  What units are those supposed to be?, not SI that's for sure. Energy in gram mass equivalent maybe.  Secondly, Ford and Roman's paper cited does not quote an energy requirement for the Alcubierre drive at all (in any units).  It only says that Pfenning has done an unpublished calculation which appears to place severe constraints on the Alcubierre drive.  I am going to reword it to comply with the cited sources - unless someone can come up with a published version of Pfenning.
 * Also, this section used to be called "Drawbacks" rather than "Criticisms" which is only appropriate for the second paragraph - I will take care of that too. And the "confusing" tag which has been there a long time and the article has moved on a lot since then.  Sp in ni  ng  Spark  18:42, 12 April 2008 (UTC)


 * A negative slant is appropriate; the fact is that the Alcubierre drive solution has essentially no scientific merit. It's a solution to general relativity only in the sense that any spacetime whatsoever is a solution to general relativity, because you can always work out the Einstein tensor corresponding to any geometry and declare that to be the stress-energy tensor by fiat. Geometries aren't physically meaningful unless the stress-energy tensor you get is consistent with known or at least conjectured physical laws, which is not the case for the Alcubierre geometry. Its popularity is due to wishful thinking, nothing more. In fact I don't think the article is nearly forceful enough in making this point. -- BenRG (talk) 20:24, 17 April 2008 (UTC)


 * "the Alcubierre drive solution has essentially no scientific merit". Isn't it a bit too strong? Something personal? I, for one, can see a lot of merits in it. And I know no inconsistency in it "with known or at least conjectured physical laws". Do you? Seador (talk) 10:54, 18 April 2008 (UTC)


 * Sorry about never replying to this. The thing is that you can write down pretty much any metric you want. For example, say you want a metric in which the universe is empty until $$t_i$$, at which point a star spontaneously appears out of nowhere at the origin, becoming fully formed at $$t_f$$. This is not difficult. The exterior metric after $$t_f$$ is the Schwarzschild metric with $$m = m_{\text{star}}$$, and the metric before $$t_i$$ is flat space, which we can think of as the Schwarzschild metric with $$m=0$$. We can smoothly blend these together by letting the $$m$$ in the Schwarzschild metric be a function of $$t$$ and choosing an $$m(t)$$ that's equal to zero for $$t < t_i$$ and to $$m_{\text{star}}$$ for $$t > t_f$$ and increases smoothly in between. We can then plug this metric into the field equations of general relativity and it will give us a stress-energy tensor. And we can do the same thing for the geometry describing the star's interior. So as far as GR by itself is concerned it's fine for a star to appear out of nowhere. But the stress-energy tensor we get isn't realistic; it says, for example, that there's a flow of energy through regions of spacetime where the energy density is zero.
 * For a second example, suppose we want a cosmological model which agrees with the ΛCDM model until next Thursday, when the expansion suddenly reverses and the whole universe recollapses to a big crunch over a time interval of 42 minutes. Again this is easy: we just write down a function $$a(t)$$ which has the form we want and put it in the FLRW metric, then we plug that into general relativity, which tells us what the stress-energy tensor has to be.
 * For a third example, say we want a geometry with a warp bubble which moves faster than light without inertial effects. The spacetime outside the bubble should be ordinary Minkowski space, $$ds^2 = dt^2 - d\mathbf{x}^2$$. The spacetime inside the bubble should also be Minkowski, but "moving" with respect to the outside space: $$ds^2 = dt^2 - \left[d(\mathbf{x}-\mathbf{x}_0(t))\right]^2 = dt^2 - (d\mathbf{x} - \mathbf{x}_0'(t) \, dt)^2$$. We can blend between those with a metric $$ds^2 = dt^2 - (d\mathbf{x} - f(\mathbf{x} - \mathbf{x}_0(t)) \, \mathbf{x}_0'(t) \, dt)^2$$, where $$f(\mathbf{x})$$ varies smoothly from 1 inside the warp bubble to 0 outside. That's the Alcubierre geometry, or rather a generalization of it. Alcubierre used a particular $$f(\mathbf{x})$$ which gave a spherical warp bubble, and he restricted the bubble to linear motion.
 * A theory which allows these metrics is a theory without any predictive power at all. If physics were like that, we would have no reason not to think that the universe will recollapse tomorrow or the Sun disappear without warning (the time reversal of the appearing-star metric). The predictive power comes from imposing constraints on the stress-energy tensor. For example, one constraint that's used in cosmology is that matter thins out as the universe expands—when the scale factor $$a(t)$$ doubles, the matter density goes down by a factor of $$2^3 = 8$$. Constraints like that are enough to rule out all of the geometries I wrote down above.
 * The ontological status of the Alcubierre warp drive is actually very similar to that of the starship Enterprise. A television screen is just a collection of pixels, and you can depict anything you like by coloring the pixels in just the right way. This fact has no bearing on the real-world plausibility of what's shown on screen. It's the same with spacetime metrics. They're just tensor fields of a certain form; the fact that you can write one down has no bearing on the theoretical or real-world plausibility of the thing you're describing.
 * Now, you could argue that it's interesting that you can write down a globally hyperbolic warp-drive metric at all. It might have been the case that there was no way to interpolate between the inside and outside regions without getting a Euclidean signature somewhere. The thing is that it wouldn't really have mattered. People would still be trying to argue that the metric was plausible, but instead of talking about exotic Casimatter they'd be talking about gravitational instantons or something. They would do this because people want warp drives to be possible, and they'll put significant intellectual effort into chasing the most farfetched idea if it looks like it will make them possible. The interest people have shown in this metric has nothing to do with its physical plausibility. -- BenRG (talk) 16:00, 15 May 2008 (UTC)
 * The references to criticisms in the article (Ford and Roman, Pfenning) do not seem to put it so strongly. Essentially, they are practical criticisms, this would not work because of a,b or c, for instance, the energy requirement is too large.  I do not see them saying this is wrong because it bears no relationship to known scientific laws.  It would be hard to write critcisms into the article as you suggest without a citeable reference saying something on those lines.  Do you know of any?  Sp in ni  ng  Spark  07:55, 2 June 2008 (UTC)

Claims about the drive needing a road
Currently, this article states, "The Alcubierre Drive vessel is not able to go dashing around the galaxy at will. It is only able to travel routes which, like a railroad, have first been equipped with the necessary infrastructure." This is very definite statement about a theory that is far from definite. Do all versions of this theory require a road? If not, qualifiers are needed, such as "in some versions of this theory, an Alcubierre Drive vessel must travel routes . . . ." Either way, more citations are needed. 98.209.154.40 (talk) 06:36, 11 June 2008 (UTC)
 * Sorry, I was the one responsible for that colourful phrase. In my defence, I wrote it in response to complaints that the original text was not understandable, however I do not believe I actually changed any of the original meaning.  It comes from Krasnikov (the meaning, not my strange way of phrasing it) and the relevant paper is already referenced at the end of the section.  I will fix this to make clear that it is Krasnikov and that also he proposes this after eliminating the possibility of using tachyons.  Sp in ni  ng  Spark  08:11, 11 June 2008 (UTC)
 * It was also discussed in detail in Ref. [7]. Seador (talk) 12:33, 11 June 2008 (UTC)

Sounds good Spinningspark. Thank you. 98.209.154.40 (talk) 18:21, 11 June 2008 (UTC)

Star Trek graphic
The Star Trek diagram in this article has been bothering me for some time and I wanted to test what others think of it. The image licence claims that it was created by the uploader and appears to have been made by plonking a starship image on an Albubierre field diagram. If it is self-created and not based on anything in the Star Trek fictional universe then it is WP:OR and should be removed. The text of this section also seems to indicate that the scriptwriters have not strongly aligned themselves with Alcubierre. Retaining this diagram gives the false impression of the opposite. On the other hand, if it is based on something in the Star Trek technical manuals then a reference should be provided to indicate its in-universe provenance.  Sp in ni ng  Spark  18:39, 29 November 2008 (UTC)