I understand (I can’t get past the paywall) that it describes how the Caismir effect creates an area that violates the positive energy condition, proving that it’s not a law of physics. This is only part of their more general point (which is time machines, which are, of course, equivalent to FTL drives in any case. Harder to build though.)
IIUC, while the Caismir effect has been observed, it is still debated whether it is actually evidence for the vacuum zero-point energy, since the calculations aren’t completely developed and there are other proposed mechanisms.
Anyway, even in the vacuum zero-point energy explanation, the vacuum energy density in the geometrically constrained region is still positive, it is just smaller than the vacuum energy density in the unconstrained empty space. It’s only negative if you arbitrarily consider the energy density of empty space equal to zero.
Without a theory of quantum gravity, the speculative connection between vacuum energy density and gravitational effects (the cosmological constant) is highly debatable: typical attempts at calculating the cosmological constant from vacuum energy yield absurdely high values, while astronomical observations are consistent with a very small strictly positive cosmological constant.
Even if the vacuum energy density generates gravitational effects by influencing the cosmological constant, the lower than average energy densiity of a “Casimir vacuum” is probably not the same thing as the absolutely negative gravitational effect of exotic matter with negative mass, which, IIUC, is required by the Alcubierre drive (I don’t know about wormholes).
And in any case, the Casimir effect can’t be used to extract energy out of nothing: the Casimir forces are attractive or repulsive depending on the geometric configuration. If you use these forces to extract work, the system will eventually transition to a configuration where the attractive and repulsive effects are balanced. You have to pay back the same work you extracted to return the system to the original configuration. You can’t complete a cycle with a net gain.
This is the same problem of most of the proposed perpetual motion contraptions: you can extract work in an one-shot transition, but you have to perform the same work on the system (actually more, once you account for the inevitable thermodynamic losses) to return to the initial configuration.
Just one last technical nitpick, if you don’t mind: Zero-point energy is a property of all quantum systems, and this is essentially uncontroversial. The existence of a quantum vacuum with a positive zero-point energy is considered less certain, but relatively plausible in the mainstream models such as the Standard Model. The idea that is possible to extract work from the zero-point vacuum energy is generally considered wild fringe science speculation/crackpottery/fraud.
Zero-point energy is a property of all quantum systems, and this is essentially uncontroversial. The existence of a quantum vacuum with a positive zero-point energy is considered less certain, but relatively plausible in the mainstream models such as the Standard Model.
I was referring to using it as an energy source, as in the original comment.
The idea that is possible to extract work from the zero-point vacuum energy is generally considered wild fringe science speculation/crackpottery/fraud.
That seems a little strong. Still, it’s certainly impossible with current tech, and there’s no method anyone’s come up with to do it with a higher tech level.
That seems a little strong. Still, it’s certainly impossible with current tech, and there’s no method anyone’s come up with to do it with a higher tech level.
It’s not just matter of technology. Such a feat would most likely require a violation of the principle of conservation of energy. While there are still some unresolved issues with renormalization and general relativity, it is generally believed that conservation of energy applies to the universe. The discovery of a violation of conservation of energy (which would imply that the laws of physics are not invariant under time translation) would be a groundbreaking result.
IIUC, while the Caismir effect has been observed, it is still debated whether it is actually evidence for the vacuum zero-point energy, since the calculations aren’t completely developed and there are other proposed mechanisms.
Anyway, even in the vacuum zero-point energy explanation, the vacuum energy density in the geometrically constrained region is still positive, it is just smaller than the vacuum energy density in the unconstrained empty space. It’s only negative if you arbitrarily consider the energy density of empty space equal to zero.
Without a theory of quantum gravity, the speculative connection between vacuum energy density and gravitational effects (the cosmological constant) is highly debatable: typical attempts at calculating the cosmological constant from vacuum energy yield absurdely high values, while astronomical observations are consistent with a very small strictly positive cosmological constant.
Even if the vacuum energy density generates gravitational effects by influencing the cosmological constant, the lower than average energy densiity of a “Casimir vacuum” is probably not the same thing as the absolutely negative gravitational effect of exotic matter with negative mass, which, IIUC, is required by the Alcubierre drive (I don’t know about wormholes).
BTW: I’ve found this post on Physics Forums
EDIT:
And in any case, the Casimir effect can’t be used to extract energy out of nothing: the Casimir forces are attractive or repulsive depending on the geometric configuration. If you use these forces to extract work, the system will eventually transition to a configuration where the attractive and repulsive effects are balanced. You have to pay back the same work you extracted to return the system to the original configuration. You can’t complete a cycle with a net gain.
This is the same problem of most of the proposed perpetual motion contraptions: you can extract work in an one-shot transition, but you have to perform the same work on the system (actually more, once you account for the inevitable thermodynamic losses) to return to the initial configuration.
You know, you’re right. ZPE is far less certain/accepted than Alcubierre drives.
I’m going to go on being amused just the same, though. Those really were unfortununate examples to pick :)
Thanks ;)
Just one last technical nitpick, if you don’t mind: Zero-point energy is a property of all quantum systems, and this is essentially uncontroversial. The existence of a quantum vacuum with a positive zero-point energy is considered less certain, but relatively plausible in the mainstream models such as the Standard Model. The idea that is possible to extract work from the zero-point vacuum energy is generally considered wild fringe science speculation/crackpottery/fraud.
I was referring to using it as an energy source, as in the original comment.
That seems a little strong. Still, it’s certainly impossible with current tech, and there’s no method anyone’s come up with to do it with a higher tech level.
It’s not just matter of technology. Such a feat would most likely require a violation of the principle of conservation of energy. While there are still some unresolved issues with renormalization and general relativity, it is generally believed that conservation of energy applies to the universe. The discovery of a violation of conservation of energy (which would imply that the laws of physics are not invariant under time translation) would be a groundbreaking result.