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visits member for 3 years, 6 months
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Hi, I am a string theorist and a publicist.


Mar
10
comment Gravity theories with the equivalence principle but different from GR
Dear Moshe, I agree that you may write many diff-invariant theories etc. but the sense of the original question could have been that "GR is just one among many theories respecting the EP and there's no good reason to be sure that it's right" which is a vague but wrong assertion, or at least, it's a conclusion one may naturally make out of your strictly correct but oversimplified answer. ;-)
Mar
9
revised Why are unorientable strings with reversed orientations different?
added 173 characters in body
Mar
9
comment Does vacuum (empty space) exist?
Dear Helder, I have down-voted your answer because it has nothing whatsoever to do with physics. It's a sequence of vacuous philosophical clichés and random combination of physical concepts that have nothing to do with emptiness of the vacuum in GR or in quantum field theory. Moreover, you misspell "philosophy" as "phylosophy" which is just too bad given the fact that philosophy is the only discipline into which your comment could perhaps be included. By the way, your answer has 4 negative votes now and 1 positive one.
Mar
9
comment Does vacuum (empty space) exist?
Dear Roy, the "hole argument" is just complete nonsense from the modern physics' viewpoint, see en.wikipedia.org/wiki/Hole_argument - This "argument" was just a denial of the fact that configurations related by diffeomorphism are exactly physically equivalent (classically as well as quantum mechanically). The "argument" is just a ban on the concept of gauge symmetry. Given the importance of gauge-invariance and diff-invariant descriptions in modern physics, a misunderstanding why the "hole argument" is just nonsense prevents one from understanding any modern physics.
Mar
9
comment Does vacuum (empty space) exist?
Dear GJ, yes, I have already noticed that I can't prove elementary facts such as "the real space may have zero energy" to you. The rest of us knows that spaces - and other objects - with vanishing energy are totally real and there is nothing "dreamy" about them. Energy is just a quantity that can take any real value and zero is just one number that is as real and non-dreamy as any other real number. Your introduction of ghosts, dreams, "abstractions" etc. into this physics debate is totally irrational. Your thinking is fundamentally incompatible with the scientific method.
Mar
9
comment Does vacuum (empty space) exist?
Dear GJ., you asked the (so far) five negative voters of your question to explain their vote. I am one of them and there are many. I gave this question thumbs down because it is a bad one, especially after your updates. It's not really a question. You're trying to promote your complete misunderstanding such as "space with zero energy must only be abstract" and all this staggering nonsense. This is a physics forum, so all discussions about space are about real space, as accurately as we can, not an abstract space. You just refuse to accept the laws of physics and learn from your own mistakes.
Mar
9
revised Why are unorientable strings with reversed orientations different?
added 356 characters in body
Mar
9
comment Active gravitational mass of the electron
And if you were asking why the inertial mass is the same as the gravitational (active or passive) mass, it's because of the equivalence principle. It's been tested by showing the same acceleration of all objects in the gravitational fields. Also, if you ask why electrostatic potential energy influences mass, uranium bombs are an example because the fission energy comes primarily from a reduced positive electrostatic potential energy after the big uranium nucleus decays.
Mar
9
comment Active gravitational mass of the electron
The identity of an object surely includes its charge, so if the charge of object A is different than the charge of object B, it follows that A and B "cannot be the same". There is no one-to-one map between charge and uncharged objects, certainly not one that would universally preserve the mass. So your question makes no sense. Also, there are no "passive" and "active" masses. If you ask why the mass given by the "strength of gravitational field" is the same as the mass "how much an object responds to an external g. field", it's because of momentum conservation.
Mar
9
answered Why are unorientable strings with reversed orientations different?
Mar
9
comment Does vacuum (empty space) exist?
No, it is not "abstract" space, whatever you mean by "abstract space". It is a damn real space. The energy of the space around us is zero. Well, it is the cosmological constant, the tiny number $10^{-123}$ in the natural Planck units, but it is zero for all terrestrial purposes and it could be exactly zero, too. Your statement that "zero energy space can't exist in reality" is just wrong. I have explained this basic point already several times and I doubt it makes any sense to try to explain it again. There is absolutely no contradiction in physics; there is just a contradiction in your mind.
Mar
9
answered Gravity theories with the equivalence principle but different from GR
Mar
9
comment Orbifolds of the $c =1$ Bosonic theory on a circle
Dear Axion, first, your last question: there is no bound on energy of a particle or string moving on a compact manifold. Obviously, the motion may always be faster and faster, which means more energy. In the first question, the truncation of the spectrum, you probably mean that the Fourier modes of the $j^\pm(\sigma)$ current are truncated - which means that $:(j^\pm)^l:$ vanishes for $l>k$. This fact may be derived in any realization of the SU(2) current algebra. At any rate, you may check the spectra level-by-level to see that the two theories are equivalent.
Mar
9
comment Does vacuum (empty space) exist?
Dear @GJ., nope, what you write isn't right. By definition, the space without energy is the space whose total value of energy is equal to 0 - one particular number. It doesn't follow that such a space with vanishing energy has to be abstract or totally boring. Energy has both positive and negative contributions and they may always cancel. In fact, the real (nearly) Minkowski empty space with $E=0$ contains virtual particles of all kinds - and "knows" about everything that can ever exist in the Universe. It's you who is mixing different statements about the space and fail to distinguish them.
Mar
9
comment $B\mu$ from $\tan\beta$ and $\mu$
A vastly superior answer, I deleted mine. +1
Mar
9
comment How to understand order emerging from many-body system?
Dear Z. Sun, when the resolution is high enough, the number of posisibilities is infinite, diverse, and huge. But when one describes it as a systematic expansion, the number of starting points is limited.
Mar
8
answered Which metals can cause magnetic interference (passively)?
Mar
8
comment Why are four-vectors needed in the Dirac equation, when there are 4 linearly independent 2D matrices?
Dear Rubenvb, you don't mean 2D Dirac equation but 2-component Dirac equation, right in 4D, right? But if I understand your question, it's the same one that was answered by Jerry and me above. No, you can have Majorana masses, $\sigma^\mu \partial_\mu \chi = m\bar\chi$. That only makes sense if $\chi$ on the LHS and $\bar\chi$ on the RHS have the same charges - which must therefore be zero because they're opposite to each other. Moreover, I don't understand what graphene has to do with it. Theories of dynamics of graphene are 3D (2+1) theories, not 2D and not 4D.
Mar
8
reviewed Approve suggested edit on Calculate stainless steel pole necking limit
Mar
8
answered M2-brane wrapped twice around $S^1$