Comment Re:...Why? (Score 1) 328
"The Casimir effect is the best known example of negative energy:" [Dumb Scientist]
This is going to be one of my rare responses to your posts. Prepare to be ignored for the most part, from here on in.
... Get a clue. If you are seriously using that link as a citation, then you lose. You did not properly comprehend what it said. ... Dude. I know you are a scientist. But do you even really know what the Casimir effect is? Of course I expect you will by the time you answer (if you do). And if you do answer, I probably won't reply. But at this very moment, at the time you first read this, from what you have already stated, I suspect that you really don't know what it is. [Jane Q. Public]
Comments like these suggest that you're not really interested in studying physics. On the other hand, John Cramer's Alternate View columns inspired me to study physics in high school. In 1998, FTL Photons introduced me to the Casimir effect. In 2001, I made an offhand remark about these faster-than-light (FTL) implications to my experimental physics professor, and he asked me to give a presentation to the class.
The next comment I wrote summarized the first part of my presentation. The second part showed that virtual particles actually slow down light in the standard vacuum, because photons spend some of their time as electron-positron pairs that travel slower than "true" lightspeed. Because the Casimir effect suppresses some of these virtual particles, light actually travels faster between the plates (perpendicular to the plates) than in the standard vacuum. This is called the Scharnhorst effect.
The Casimir effect can be modeled mathematically as a negative-mass region; Hawking showed that negative energy is necessary for certain effects on WORMHOLES to take place in conjunction with such a negative mass. But he did not claim that the negative energy was supplied by it. But that does not establish a direct relationship between the two. It is a very FAR cry from equating negative energy with the Casimir effect. [Jane Q. Public]
Why are you talking about Hawking? I already pointed you to "Wormholes, Time Machines, and the Weak Energy Condition":
"The following model explores the use of the 'Casimir vacuum'[12] (a quantum state of the electromagnetic field that violates the unaveraged weak energy condition[11]) to support a wormhole..." [Morris, Thorne, and Yurtsever, 1988]
Nevertheless, Hawking's findings did not point at Casimir effect as a source of negative energy; they merely indicated that negative energy was necessary for the negative mass to have the calculated effect. Not the same thing. [Jane Q. Public]
Again, why are you talking about Hawking? You might want [1] to read "FTL Photons":
"Since the energy density of normal vacuum is defined to be zero, the vacuum between the metal plates actually becomes a region of negative energy density." [John Cramer, 1990]
Again, granted: Hawking showed that negative energy might be required for negative mass effects in relation to wormholes. But I have never seen any science indicating that this negative energy is actually related to or a result of the Casimir effect. That is a rather large leap that is not supported in any of the science I have read. The only relationship I have seen is that negative energy is required for certain predicted phenomena; nowhere have I seen any claim that anything related to the Casismir effect is the actual source of that negative energy. [Jane Q. Public]
Then you might want to see the claim in "The warp drive: hyper-fast travel within general relativity":
"We see then that, just as it happens with wormholes, one needs exotic matter to travel faster than the speed of light. However, even if one believes that exotic matter is forbidden classically, it is well known that quantum field theory permits the existence of regions with negative energy densities in some special circumstances (as, for example, in the Casimir effect [4]). The need of exotic matter therefore doesn’t necessarily eliminate the possibility of using a spacetime distortion like the one described above for hyper-fast interstellar travel." [Miguel Alcubierre, 1994]
You might also want to see Hawking's claim in "Space and Time Warps" regarding the Casimir effect:
"So the energy density in the region between the plates, must be negative." [Stephen Hawking]
Your inexplicable references to Hawking's research might have been prompted by this sentence shortly after the part I quoted: "Stephen Hawking has proved that negative energy is a necessary condition for the creation of a closed timelike curve by manipulation of gravitational fields within a finite region of space;[6] this proves, for example, that a finite Tipler cylinder cannot be used as a time machine."
That reminds me...
"No, nothing can go faster than the speed of light because it will violate causality. Which is more or less forbidden by the entirety of physics." [Nyrath the nearly wi]
Incorrect. There is nothing we know of that actually works to prevent the violation of causality. There are a number of ways it can theoretically be done. See Tipler, "Rotating Cylinders and the Possibility of Global Causality Violation". All rhetoric (like the post at that link) aside, all we really have about it is guesses. The fact that we have never observed anything, so far, that would violate causality says absolutely nothing about the possibility. Further, it is not necessarily true that limited instances of causality violation would render the entirety of physics invalid, any more than relativistic situations render Newton "invalid". They are "special cases". That is all. [Jane Q. Public]
I've argued that violating causality isn't impossible if the many worlds interpretation is right, and explained why FTL travel is equivalent to time travel. However, Hawking's research actually seems to show that a finite [2] Tipler cylinder wouldn't even work in theory.
Hawking's chronology protection conjecture also poses problems for warp drive. For instance, Hawking radiation could destroy anything inside an FTL warp bubble, or its stress-energy tensor could blow up.
Krasnikov and Everett and Roman pointed out that the spacecraft would be causally separated [3] from an FTL warp bubble, so the spacecraft couldn't activate or deactivate the warp bubble.
So the Alcubierre and Natario drives might "just" be reactionless sublight propulsion systems where arbitrarily high acceleration isn't felt [4] aboard the spacecraft, and where relativistic speed doesn't cause time dilation.
"Exotic matter, by definition, requires violations of the known laws of physics." [Someone]
No, it doesn't. Antimatter is one valid type of "exotic matter", and it has been manufactured in labs in various (small) amounts for many decades now, without a physics violation in sight. [Jane Q. Public]
Antimatter certainly isn't common, but it's not "exotic matter". Stable wormholes and the Alcubierre drive require using exotic matter that has negative mass-energy, which would violate the weak energy condition. [Dumb Scientist]
Okay, I will concede that point, although it is about a Wikipedia entry. If you really want to argue about those... But my point is still valid, since Bose-Einstein condensates of macro-size have been manufactured in laboratories since 1998. Thus, "exotic matter" IS being manufactured, in significant quantities, right here in the real world, for 14 years now with no physics violations in sight. ("Exotic Matter", according to your own citation.) [Jane Q. Public]
Many physicists, including the inventor of warp drive, use the term "exotic matter" [5] to refer to matter with negative mass-energy. I tried (and apparently failed) to make this explicit. BEC's are qualitatively similar to lasers, superconductors and superfluids; none of them have negative mass-energy.
Note that I'm not claiming the weak energy condition is a law of nature. In fact, all these physicists point to the Casimir effect's negative energy as experimental evidence [6] that the weak energy condition can be violated. However, in theory the weak energy condition is supported by "quantum inequalities" that limit the magnitude and duration [7] of negative energy densities.
That's why this Slashdot article focuses on ways to reduce the unphysically large amount of negative energy required for a warp bubble. That's also why John Cramer mused that warp drive is outlawed and celebrated Van Den Broeck's 1999 insight that the required negative energy could be reduced by making the interior of the warp bubble larger [8] than its exterior.
Footnotes
[1] You might also want to read "Averaged Energy Conditions and Quantum Inequalities" and "The Energy Density in the Casimir Effect":
"... AWEC is violated in both two and four dimensions for a static timelike observer in a Casimir vacuum state, with either type of boundary conditions, since such an observer simply sits in a region of constant negative energy density for all time.
"... we have also found that it is possible for the net energy density in the region between the plates to be negative
[2] If cosmic strings exist, they could be literally infinite- stretching across the entire universe. In Stephen Baxter's Ring, the Great Northern travels into the past by repeatedly looping around a pair of cosmic strings. On a related note, the Great Northern's 5,000,000 year voyage was obviously based on figure 2 from Morris, Thorne, and Yurtsever 1988 ("spacetime diagram for conversion of a wormhole into a time machine"), as was the 1,500 year voyage of the Cauchy in Timelike Infinity. back
[3] Alastair Reynold suggests that the Waynet in his Merlin stories was created when the Waymakers tried to build a network of Krasnikov tubes. back
[4] That sounds like the impulse drive from Star Trek, the gravity polarizers/thrusters from Larry Niven's Known Space, and the parametric/frameshift drives from Alastair Reynolds's House of Suns and Pushing Ice. Even a sublight warp field requires lots of negative energy, so the diametric drive proposed by Robert Forward and Jamie Woodward is a sublight alternative. The diametric drive relies on the peculiar effects that Rei mentioned, which were discussed by Geoffrey Landis (small world, eh?). back
[5] Stephen Baxter also calls matter with negative mass-energy "exotic matter". back
[6] Squeezed vacuum experiments also involve negative energy, along with the energy-time uncertainty principle and Hawking radiation. On a related note, the Casimir effect stabilized the first bulky generation of wormholes generators in The Light of Other Days by Arthur C. Clarke and Stephen Baxter. Then squeezed vacuum technology miniaturized the generators until they were the size of wristwatches. back
[7] In 2002, the same authors who introduced "quantum inequalities" showed that arbitrarily large negative energy densities are possible, though their duration still seems restricted. As Cramer notes, renormalization makes it difficult to take quantum field theory's bounds on energy density seriously. back
[8] Van Den Broeck might have been inspired by Doctor Who's TARDIS. back