111,482 reputation
7163326
bio website motls.blogspot.com
location Czech Republic
age 41
visits member for 4 years, 3 months
seen 7 mins ago

Hi, I am a string theorist and a publicist.


Jun
1
reviewed Approve Statistical physics of molecular dissociation of a diatomic gas
Jun
1
comment Does a magnetic field do work on an intrinsic magnetic dipole?
Dear @Joss, the formula you wrote down is the fundamental one that applies to all situations, so there is nothing else to derive. A magnetic moment $\vec \mu$ in a magnetic field has the energy $-\vec\mu\cdot \vec B$. Any configuration of currents and magnets may be written as a volume density of magnetic moments, usually known as magnetization $\vec M$. See en.wikipedia.org/wiki/Magnetization Then the energy is $-\int \vec M \cdot \vec B$. The force is always the minus gradient of the energy in a magnetic field and the energy change is the work that has been done.
Jun
1
comment Does a magnetic field do work on an intrinsic magnetic dipole?
Dear @kmm, what you write is silly, indeed. The objects known as "magnets" - such as iron, you know, they are ferromagnets, some children have already heard about it - have most of their magnetism coming from the spin of the electron that is not moving at all. Again, it is nonsense that one cannot do work with magnetic field. Magnetic moments in magnetic fields are clearly doing work. What matters is a nonzero $\vec j$, and it can be nonzero with arbitrarily small loops, including "vanishingly small" ones, as the spin example shows.
Jun
1
revised Wigner's friend and intersubjectivity in quantum mechanics
added 2611 characters in body
Jun
1
revised Wigner's friend and intersubjectivity in quantum mechanics
added 47 characters in body; added 1198 characters in body
Jun
1
answered Wigner's friend and intersubjectivity in quantum mechanics
Jun
1
comment Wigner's friend and intersubjectivity in quantum mechanics
Sorry, I think it's plagiarism that you copied my text without the correct attribution. In particular, the formulation that the other observer says to the first one that "you're just a dull bound state of electrons of protons" was taken verbatim from motls.blogspot.com/2011/05/…
May
31
reviewed Approve Experimental evidence of a fourth spatial dimension?
May
31
reviewed Approve Why are extra dimensions necessary?
May
31
answered Calculating threshold energy of particle reactions
May
31
reviewed Approve Why are extra dimensions necessary?
May
30
answered If the multiverse and many-worlds don't exist, how should we interpret probabilities?
May
30
answered Does a magnetic field do work on an intrinsic magnetic dipole?
May
29
reviewed Approve Uniqueness of Helmholtz decomposition?
May
29
answered Do we need a quantum deformation of the diffeomorphism group in string theory?
May
29
answered self-antiparticles and broken symmetries
May
28
comment Why is global conservation of energy not considered a tautology?
Dear @Anna, Noether's theorem is a theorem, i.e. it is tautologically true, so it is surely not sufficient for the validity of any other statement - except for other tautologies - but it is a necessary condition for the validity of anything because if theorems and tautologies fail, everyone is screwed. ;-) You probably meant that a symmetry is not necessary for the existence of a conserved quantity. But in theories obeying mild assumptions of Noether's theorem, the symmetry is both necessary and sufficient. That's what can be established by those Noether techniques.
May
28
comment Conservation law of energy and Big Bang?
No, @Dan, they're equivalent statements because energy, for it to be called energy, has to be conserved, so if it is not conserved, it is not really an energy, so energy doesn't exist.
May
28
answered How can one reconcile the temperature of a black hole with asymptotic flatness?
May
28
comment Correlation between outstanding hints in experimental particle physics
Funny two-step methods to link the observations, thanks, @Julius! ;-) A combination of a Z' interaction with dark matter is somewhat creative.