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location New York City
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visits member for 3 years, 1 month
seen 11 hours ago

I do not participate on this site any longer, except to respond to comments regarding my own text, if that text is unavailable in another form. I do not accept the political moderation atmosphere here, it is not compatible with open science. I participate at physicsoverflow.org.


Sep
17
comment Is the universe a quantum computer - is light speed barrier a computational constraint
@celtschk: here universe==the observable universe. The number of bits is assumed by the number of Planck areas on the cosmological horizon. The U atom with electrons has 350 particles, which, with even a coarse quantum description swamps the size you can simulate with a classical computer that size. But of course, for ground states, or low excited states there are better methods like DFT.
Sep
16
awarded  Nice Answer
Sep
13
awarded  Nice Answer
Sep
11
awarded  Nice Answer
Sep
5
comment An electromagnetic space elevator?
@Floris: You don't need to do work to get the thing off the ground, you supply the current once, it's next to no work, then you cool it to superconducting and it traps the current in there. Then you let it go, and it rises up, the Earth just slows down as it lifts the thing. The magnetic field of the Earth is ultimately because the core is rotating. The cryostat doesn't need to be heavy compared to the wire, the wire can be a bundle of wires 1m in radius, the cooling is at the boundary. This is perfectly feasable.
Aug
29
comment When we define the S-matrix, what are “in” and “out” states?
@A.Zerkof: The asymptotic plane-wave states are already smeared out over infinite volume and are "noninteracting" in the sense that the scattering is a subleading correction to their behavior. This is why the Fock space is already in the theory.
Aug
29
comment How Exactly Does Linear Regge Trajectories Imply Stability?
@annav: This kind of string theory is now known as AdS/QCD, and nobody disagrees that it is predictive for hadron resonances, although the degree of quantitative agreement can be disputed. This stuff predicts things like hidden local symmetry (Hidden Regge theory in the 80s), topological baryons (Large N physics of the 80s), and Polchinski-Tan Pomerons (BFKL pomerons in string theory, early 2000s). There's a ton of work, this should give good handles, but AdS/QCD is most recent and most direct. This is not the same as predictions of fundamental string theory, the results are not controversial.
Aug
27
comment Does a Weak Energy Condition Violation Typically Lead to Causality Violation?
No, I didn't ask for an example of a spacetime that violates weak energy and doesn't have a CTC (reread the question). The negative mass Schwartschild solution is such an example. I asked for a spacetime which violates weak energy where you can't use the violation to produce a different spacetime, which is necessarily present in the theory if the first is, which does contain a CTC.
Aug
27
awarded  homework
Aug
26
comment Does a Weak Energy Condition Violation Typically Lead to Causality Violation?
I don't see how to model shrinking black holes classically in any way that doesn't have negative focusing somewhere. Regarding M<0 Vaidya spacetime, there is no CTC in one of these, but if you put together two boosted copies of these moving relative to each other very fast, you get CTCs.
Aug
26
comment Does a Weak Energy Condition Violation Typically Lead to Causality Violation?
The Hawking radiation is not in a consistent classical theory, it's semiclassical (classical gravity and quantum fields) and the back-reaction is inferred, and is not added in a self-consistent way to make a new theory. The answer does not answer the question which is about pure classical GR. If you mocked up Hawking radiation as some sort of classical negative-energy flux into the black hole accompanied by positive energy emissions, it is not clear you would not get causality violations at the same time.
Aug
26
revised Can every particle be regarded as being a combination of Black holes and White holes?
fix
Aug
25
comment Is the EmDrive, or “Relativity Drive” possible?
@Nathan: No they didn't do the test in a vacuum. They did the test in a vacuum chamber at ambient pressure, after putting the device through a vacuum cycle to simulate space. Their excuse for not running it in vacuum was that the microwave cavity devices wouldn't operate, they weren't built to work in vacuum (I suppose because they had parts using air as insulation), but if they had run the machine in vacuum, it would not push. I have no patience for this type of fraud, and I don't participate on this site, I am on physicsoverflow now, but I am responding because you asked me to.
Aug
24
awarded  Yearling
Aug
22
awarded  Good Answer
Aug
22
awarded  Nice Answer
Aug
5
awarded  Nice Answer
Aug
3
awarded  Nice Answer
Jul
2
awarded  Curious
Jun
27
awarded  standard-model