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Hi, I am a string theorist and a publicist.


4h
answered Could the universe have non-vanishing net colour charge?
5h
comment Do randomness and indeterminacy in Quantum Physics mean the same?
"Quantum indeterminacy may refer to both Indeterminacy of time evolution and Indeterminacy of measurement results." - Sorry but there is only one indeterminacy. Results of measurements are the only thing that is supposed to be predicted by science - the observables meant to predict the measurements are evolving in time - so the predicted quantities are either determined or not. It is completely wrong - an artifact of classical intuition - to try to divide physics into two different processes, evolution and measurement. There is no such division in Nature. QM predicts the outcomes directly.
6h
comment Do randomness and indeterminacy in Quantum Physics mean the same?
They are really the same thing.
19h
answered Do randomness and indeterminacy in Quantum Physics mean the same?
20h
comment CPT invariance of Dirac equation
The Dirac equation is invariant under C,P,T even separately, so of course it is invariant under CPT in this form as well. However, the true general CPT invariance shouldn't be tested on one-particle equations or classical fields such as Dirac's equation. The general argument why CPT works only makes sense on the full multiparticle quantum field theory.
20h
comment Why is Entropy's Definition Useful?
The situation with "units of temperature and energy are equal" is fundamentally analogous to the different units for heat and work (calories for heat, of course) that people used to have before Mr Joule and before joule. Of course that if one isn't transforming heat to work and vice versa, i.e. lives in a non-industrial or otherwise crippled or immature civilization, he can use different units for heat and work, thinking that they're unrelated quantities with different units. But the conversion is possible and very natural if one allows oneself to see it. The temperature=energy is analogous.
20h
comment Why is Entropy's Definition Useful?
Right, I wrote the general right definition, too. The "per degree of freedom" is a shortcut indicating that it's some way of counting energy at the microscopic level. The right way to do so is that the density matrix or probability distribution for everything is given by $\exp(H/kT)$, that's the most general and accurate microscopic definition of temperature. The thermodynamic limit effectively sees $k=0$ so it doesn't see the microscopic origin of thermal phenomena, but they still exist, in all of Nature including chemistry and engineering, much like $c=1$ is always the maximum speed.
20h
revised Traces in different representation
added 34 characters in body
20h
revised Traces in different representation
added 34 characters in body
20h
answered Traces in different representation
21h
comment Why does smashing a TV remote load its batteries?
Ions are matter, Olin. Nuclei have to be able to migrate from one side to another, so it's clear that the room left by them will be filled by something else.
21h
comment Why is Entropy's Definition Useful?
You could use a different convention for measuring hypotenuses of triangles than the legs, and then the Pythagorean theorem would be $a^2+b^2 = 4\pi^2 c^2$. This is exactly analogous to your choice of units. A clever schoolkid knows that the length of any line interval is ultimately the same thing, so he uses the "same" normalization for both lengths. In the same way, a particle physicist uses the "same" normalization for the energy and temperature. The operations proving that the two objects are "the same" are slightly nontrivial in both cases and one may deny them - but they're possible.
21h
comment Why is Entropy's Definition Useful?
Dear @Void, great, if you don't use some fundamental properties of the temperature, you won't be able to see that it's a form of energy. But that's true for any insight about the world. If you overlook something, then you overlook something. Concerning your second comment, it's surely at least a "lack of taste" to argue that $h=1$ would be as natural as $\hbar=1$. But both of them are the same up to constants of order one, anyway. And similar redefinitions - like inserting $2\pi$ into all fundamental equations of quantum mechanics, which is what you did - could be done everywhere.
21h
comment Why does smashing a TV remote load its batteries?
Great Olin, I may agree, but isn't a paste nothing else than a viscous liquid? Moreover, alkaline (AA) batteries as well as NiMH and Lithium-ion batteries seem to contain classic liquids, don't they? At any rate, if nothing "moves" inside the battery - like in a liquid - then the battery cannot work!
23h
comment Why is Entropy's Definition Useful?
@Void: the original value of the units is $c=\hbar=k=1$, it's how Nature Herself intrinsically sees all these things. Non-unit values to these constants were only assigned 13.8 billion years later, when humans evolved and started to compute things, and they accidentally used inconsistent units for different visualizations of the same quantities - for various historical reasons. The temperature is fundamentally the same thing as the energy per elementary degree of freedom. Learning it in a different way may be the first way that a kid encounters but it is not the scientifically "original" one.
23h
comment Why is Entropy's Definition Useful?
And setting $k=c=\hbar=1$ isn't really a "trick". On the contrary, using values different from one is an artificial cultural complication that is added on top of science for various historical, sociological, and other silly reasons and that has no justification in science whatsoever. Units and dimensionful quantities are only legitimate in two related classes of contexts, namely if 1) there is no natural "unit" value of the quantity, 2) if one wants to perform dimensional analysis.
23h
comment Why is Entropy's Definition Useful?
Dear @DavidHammen, apologies but I completely disagree. The temperature always means exactly the same thing in all of science. A physical system at temperature $T$ is described by the density matrix $C\exp(-H/kT)$ where $H$ is the energy. Whenever this is exact, the temperature is fully well-defined. It may also be "close" to this idealization, in which case, temperature is approximately defined, and so on. This is true in nuclear physics, chemistry, engineering, and everywhere in Nature, and everyone who understands temperature incompatibly with adult physicists is understanding it wrong.
1d
comment Why does a Resistor cause a potential drop?
Please don't worry about that! ;-)
1d
comment Why is Entropy's Definition Useful?
Well, adult theoretical physicists surely do consider entropy to be dimensionless because energy and temperature are fundamentally the same thing, after all, or converted to each other through Boltzmann's constant $k$ that we set equal to $k=1$ in theoretical physics.
1d
answered Why does a Resistor cause a potential drop?