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Hi, I am a string theorist and a publicist.


Jan
25
comment Does the scientific community consider the Loschmidt paradox resolved? If so what is the resolution?
Phil, this is complete nonsense. Every proper undergraduate or graduate course or textbook on statistical physics or thermodynamics says the same thing as I did. Claims that there remains a huge mystery are reserved for pop-science and pseudoscientific books and outsiders from other fields who haven't really mastered basic undergraduate physics.
Jan
25
comment How to choose the right units to compute the phase space volume in classical statistical mechanics?
Taken literally, your question is really strange. "Is there a quantity that depends on the absolute value of the entropy?" - Yes, there is. For example the absolute value of entropy itself. It is a quantity. Strictly speaking, the answer to your question is obvious. But the point is that the absolute value of the entropy is unobservable in the classical limit - which also automatically requires the thermodynamic limit (because the size of atoms is only finite according to QM; the Bohr radius depends on $\hbar$). So it's consistent for the classical limit not to know the additive shift.
Jan
25
comment How to choose the right units to compute the phase space volume in classical statistical mechanics?
Dear @Nick, the entropy is some kind of (lost) information and even the absolute shift of the entropy does contribute to this information. In quantum physics, the absolute shift is determined and $(2\pi\hbar)^N$ is the only right unit. However, classically, the amount of information carried by particles is really "infinite" because there are infinitely many points in the phase space (spanned by $x,p$). Changes of energy etc. only depend on ${\rm d}S$ and if you want to talk about the information consistently, you simply have to acknowledge that matter is made of atoms and ruled by QM.
Jan
25
revised Is the curvature of space around mass independent of gravity?
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Jan
25
answered Is the curvature of space around mass independent of gravity?
Jan
25
revised Does the scientific community consider the Loschmidt paradox resolved? If so what is the resolution?
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Jan
25
revised Does the scientific community consider the Loschmidt paradox resolved? If so what is the resolution?
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Jan
25
answered Does the scientific community consider the Loschmidt paradox resolved? If so what is the resolution?
Jan
25
answered what causes virtual particle pair production to not occur in the space occupied by matter?
Jan
25
comment Expressing a particle's matter wave in terms of its momentum
Sorry, this is a really weak question. It's a straightforward and trivial algebra to get the right power of $\hbar$. Moreover, mature physicists - probably including the author of the textbook you mention - use units with $\hbar=1$, so missing powers of $\hbar$ are "not really mistakes". On the other hand, you have real mistakes in your text, e.g. the claim $\tilde \phi(p)=\phi(k/\hbar)$ at the top. You meant $p/\hbar$ on the right hand side, right? When you make this fix, you do see that the "obtained" and "desired" expressions only differ by $\sqrt{\hbar}$, don't you?
Jan
25
answered Vacuum Wavefunctional
Jan
24
revised How to choose the right units to compute the phase space volume in classical statistical mechanics?
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Jan
24
revised How to choose the right units to compute the phase space volume in classical statistical mechanics?
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Jan
24
answered How to choose the right units to compute the phase space volume in classical statistical mechanics?
Jan
24
comment Cooking pasta: why does adding a lid lead to overflow?
I would guess that without the lid, the vapor is moving rather quickly and escapes from the pot, constantly disrupting and destroying the emerging bubbles of foam. With the lid, the vapor motion slows down and the membranes of the foam have a more time to peacefully form, and ultimately overflow.
Jan
23
comment Does vacuum (empty space) exist?
Zero is natural in the physics sense. By the way, even in a different interpretation of "natural numbers", zero is usually considered a natural number, too: en.wikipedia.org/wiki/Natural_number - In the whole Universe, energy may take any real value, at least any value above the energy of the ground state. Particular physical systems may be affected by a discrete spectrum of energy but their union always has energy with a continuous spectrum.
Jan
23
comment Occam's razor on spin statistics theorem?
Dear @Propaganda, yes, if there are more particles, this gets extended to $\psi(x_1,x_2,\dots , x_n)$. It is completely antisymmetric, so it's enough for two of the arguments to coincide for the function to vanish (all the other arguments that don't participate in the permutations just sit at their place and don't do anything). There's nothing new happening about these simple rules for large $N$, and surely nothing hard.
Jan
23
comment How does Newton's 2nd law correspond to GR in the weak field limit?
Good point, WIMP. Still, deriving mechanics out of field theory of solitons is a bit advanced way for a beginner who wants to see his or her old equations of mechanics...
Jan
23
comment Basic question about law of gravitation
The time needed for two balls to collide by the action of gravity: It's an analytically solvable problem but too mathematically contrived one for a beginner. The resulting formula is pretty messy. One has to find the solution to the Kepler problem (differential equations) etc. Yes, the acceleration is accelerated because the force (and therefore acceleration) itself is increasing as the particles get closer to each other.
Jan
23
answered Conceptual puzzles when using Coulomb's potential in solving the hydrogen atom in non relativistic QM