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bio website motls.blogspot.com
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Hi, I am a string theorist and a publicist.


May
11
answered Does the Planck scale imply that spacetime is discrete?
May
11
comment Noether's theorem and “translations” of the Hamiltonian function
Well, if one defines a Hamiltonian to differ from energy, so that the gravity may be sourced by yet another formula, then such a Hamiltonian is really a totally bureaucratic concept only and it can't affect anything of physical value. In that case, one may totally change it. Square it or cube it. Define a new $H$ which is the old $H^3$, modify the require formulae appropriately (you modified your Einstein's equations as well, so I am allowed to modify other equations, too). Clearly, if the concepts are not sharply defined to enter equations in a unique way, they're vacuous.
May
11
revised The meaning of action
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May
11
answered The meaning of action
May
11
comment The meaning of action
OK, I will strip the "dialog" form and promote it to an answer, @Approximist.
May
11
comment Why is the Yang–Mills existence and mass gap problem so fundamental?
And so does the definition of rigor in theoretical physics. ;-)
May
11
comment Why is $\frac{dx}{dt}=0$ in this average momentum calculation?
+1, Marek. Interestingly, the question contains the first formula for $\langle p \rangle$ which shows perfectly what the objects depend upon. It says that $\psi$ and $\psi^*$ depend on $x,t$ while $x$ doesn't depend on anything, especially not on $t$. So despite this detailed notation, the dependence was ignored by the OP. Moreover, to claim that $x$ depends on $t$ in those formulae would be totally preposterous because $x$ is being integrated over in the formula - it takes all real values simultaneously and "all real values" (the real axis) clearly can't depend on $t$.
May
11
comment Is fire matter or energy?
Richard Feynman has answered a similar question asked by young rabis: myspace.com/richard_feynman/blog/332429588 The question was: "Is electricity fire?" His answer may be used for your question, too. So read the chapter of his book carefully to catch the answer which may be more important than the detailed question. ;-)
May
11
comment What is the value of the fine structure constant at Planck energy?
BTW one can't even say that it's possible to find an electron-positron-photon QED that agrees with the real world up to the electron mass scale. It's because the real world also has neutrinos and gravitons that are lighter, and maybe axions.
May
11
comment What is the value of the fine structure constant at Planck energy?
Dear Claude, what do you exactly mean by QED? Just photons, electrons, and positrons? Or do you include muons, tau, and quarks? When you do, why don't you also include W-bosons which will destroy your "QED" at the electroweak scale, anyway? The incorporation or not incorporation of muon - and all other things - has a profound impact on all the numbers and running. It's straightforward to compute the running in any of these (wrong) toy models, as long as they are consistent, but why would you do it?
May
11
answered Why is the Yang–Mills existence and mass gap problem so fundamental?
May
11
comment A lightning protection device physics
Dear Martin, if you think that you cannot draw energy from an electrostatic field, how do you explain that some people claim that they use batteries in their cell phones or even laptops? ;-) Is that unimaginable that the electrostatic fields allow one to lift charged objects from one place to another, doing work along the way, and reducing the strength of the electrostatic field (which is why batteries get discharged)?
May
11
answered What is the value of the fine structure constant at Planck energy?
May
11
revised How is perturbation theory applied to the Bunch-Davies state for an interacting quantum field theory?
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May
11
comment How is perturbation theory applied to the Bunch-Davies state for an interacting quantum field theory?
And by the way, the de Sitter space's radius was still much larger than the Planck length even during inflation. That's why the non-uniformities of the CMB temperature today are of order $10^{-5}$ only. These non-uniformities are predicted from the correlation functions. Whether the number of particles in a state is conserved doesn't play any role; the number of particles in the states relevant for inflation can't even be sharply well-defined because they're thermal from all real observers' viewpoint.
May
11
revised How is perturbation theory applied to the Bunch-Davies state for an interacting quantum field theory?
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May
11
comment How is perturbation theory applied to the Bunch-Davies state for an interacting quantum field theory?
I wrote it clearly. It's a thermal state and there exist standard rules how to compute all correlators using Feynman diagrams that are conceptually on par with Feynman diagrams in a thermal ensemble in the Minkowski space. BTW this comment of yours should have been posted as a comment, not as an answer. Because it answers nothing about the question above, I rated it -1.
May
11
revised How is perturbation theory applied to the Bunch-Davies state for an interacting quantum field theory?
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May
11
answered How is perturbation theory applied to the Bunch-Davies state for an interacting quantum field theory?
May
11
answered What is the risk from radiation on imported food from Japan