416:. In fact, the ADM form of the metric guarantees that Alcubierre style warp drive spacetimes do not admit any closed timelike curves, if that is what you had in mind. Hint: construct a simplified two-dimensional warp drive using a compact bump function with metric in ADM form as in the Alcubierre spacetimes. Draw some light cones. Study the nature of the timelike geodesics. You will see that in fact the ADM form guarantees that they cannot turn around in time. ---
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274:. Can you read that (and hopefully the CQG papers I cited) before making any drastic changes in the article? Again, because of the edit conflict problem with current Wikiware, let's try to settle this on the talk page, since neither of us want to lose a lot of work if an edit conflict messes up the article itself!
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Also I disagree about the statement on falsibility. Mathematically the EFF *is* unfalsibility because it is consistent. The physical question is whether or not EFF matches observations. To illustrate the point I'm making, you can't argue on mathematical grounds that
Newtonian physics is incorrect.
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I think the present version fairly describes the currently dubious status of warp bubbles in the research literature, but could add much more detail in support of my comments regarding the apparently "unphysical" energy flux near an
Alcubierre bubble, and their suspiciously "spontaneous" appearance
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Hi, Roadrunner, we might have an edit conflict since I was actually modifying the page just now, not knowing that you were also doing so. Did you know that the new Wiki software has a problem? I didn't want to lose my work and couldn't see what you did, so maybe we should avoid making drastic
190:(according to Maxwell's theory, and following some general principles for getting from a field equation to the corresponding contribution to the matter tensor), and of course this stress-energy tensor must match the Einstein tensor computed directly from the Riemann tensor.
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Einstein himself had a rather stringent notion of 'solution' in mind, similar to what I described above in the special case of 'electrovacuum'. Others with a more speculative turn of mind have proposed to allow matter tensors which merely satisfy one or more of a list of
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are easy to recognize, since the matter tensor vanishes identically in a vacuum region, so vacuum solutions have purely a mathematical characterization: they are
Lorentzian manifolds whose Einstein tensor vanishes (equivalently, whose Ricci tensor vanishes).
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Lorentzian spacetime is a 'solution' of the EFE! If we allowed this, gtr would be unfalsifiable-- hence useless! Of course, it is not useless, because in fact physicists have stringent expectations about what can stand as a legal matter tensor.
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Put in other words: in principle, we could take any
Lorentzian spacetime, compute its Einstein tensor, and declare this to be the 'matter tensor' of some funky field. But this would be an absurd procedure, since it would imply that
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which may (or may not) characterize some properties shared by all (or some) known matter tensors which everyone would agree are acceptable, such as electromagnetic field energy/momentum/stress, or a perfect fluid.
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I added a bit more about the interpretation of the warp bubble and pointed out a significant difference between the
Alcubierre and Notario warp drives. I still think the existing article on
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OK, I rewrote the article and added citations to the series of CQG papers. A bibliographic note: according to Broeck, the proper way to parse his name is Broeck, Chris Van Den. ---
209:) there is no well-defined classical field theory which gives contributions to the matter tensor which could match the Einstein tensor of a nontrivial Alcubierre spacetime.
389:. If so, I think you missed my point. If we allowed any symmetric second rank tensor field on any Lorentzian spacetime to be a "solution" to the EFE, we would have no
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Hi, 63.201.230.31 from SBC, the statement you added is meaningless as stated, and the page you cited certainly doesn't imply anything about time travel in the sense of
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should be deleted, since I think this one adequately describes the concept. However, there might be some reason for a similar article on
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I have extensively discussed elsewhere the question of what it means to be a "solution" of the EFE. See for example the article on
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I've been looking everywhere for my "statement on falsifiability" and can't find it. Unless you mean what I said about "divide
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and disappearance. If anyone is greatly interested in seeing that, say so here and I'll add it to my list---
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Neutralized the wording a bit. Mathematically the
Alcubierre metric is a solution of the
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Accordingly, I propose to rewrite this article to correct the mistaken impression. ---
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and declare the result to be the stress-energy of the spacetime" in the article on
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changes for a few days to the article and discuss our difference of opinion here.
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If you wish to start a new discussion or revive an old one, please do so on the
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If you wish to start a new discussion or revive an old one, please do so on the
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However it is incorrect, because the predictions don't match observerations.
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There are other kinds of classical fields which one can propose besides
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of the EFE, this must agree (up to a certain constant factor) with a
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observation whatever could be declared to "agree with theory". ---
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This article is seriously misleading in one important respect.
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