96,987 reputation
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bio website motls.blogspot.com
location Czech Republic
age 40
visits member for 3 years, 6 months
seen 4 hours ago

Hi, I am a string theorist and a publicist.


14h
comment P-N junction voltage under polarization
The things you claim don't imply that they obey a superposition principle. You could only say that they obey superposition principle if the relevant calculated quantities were linear in the voltages, e.g. for current $I(V_1+V_2)=I(V_1)+I(V_2)$. This is surely not true for semiconductors. Here, the things are nonlinear. One only adds a bias and the bias means - it is defined - as effectively reducing the voltage.
16h
comment The physical definition of work seems paradoxical
@Addem, good to hear. Just to re-emphasize this insight. There are many forms of energy and work and many "quantities with the units of one joule". But the words denoting them are not synonyma. So energy isn't quite the same thing as work and it isn't the same thing as heat or mechanical work or something else (also, debt and profit aren't the same despite the same unit of a dollar). The energy conservation law says that the sum of several quantities of this kind are zero or equal etc. but the different terms have to be distinguished and in these contexts, "work" really means "mechanical work"
16h
comment What is the meaning of non-compactness in the context of $U(1)$ in gauge theories?
Sorry, I don't understand what your confusion could possibly be, @symanzik138. Your assertion is also correct when formulated correctly but I probably needed a different, "converse" statement. I said that an operator identity $\exp(2\pi i Q)=1$ holds if the spectrum of $Q$ is a subset of integers. If there is no non-integer, the equation holds, if there is a non-integer, it fails, therefore "iff". It's an equivalence. If there were two correct statements in maths, then they are equally correct and one cannot be "more correct" - at most, it may be "more understandable to you".
17h
comment About Shor's error correcting algorithm
Hi @user6818, you mean equation 4.3 not 4.2, right? The barred-c is different because it is an element of a smaller Hilbert space than the broader Hilbert space into which the right hand side vectors belong. Therefore it's an "encoding transformation", as explained in the text around the equation. Do you read the paper as well or are you just taking equations out of the context?
1d
comment Why do some hand dryers blow hot air?
LOL, it is not true that the hair dryer throws droplets just like if you shake your hand. Most of the water from the hair evaporates, one H2O molecule after another - evaporation doesn't require one to reach boiling point - and a higher temperature surely increases the evaporation rate, doesn't it? The relative humidity of the air decreases which encourages the hot air to absorb more H2O molecules.
2d
comment Coleman-Weinberg potential: resum at 2 loops?
Bechira, in all the cases, one simply writes down all the Feynman diagrams with the appropriate external lines containing the allowed vertices. If the insertions are zero, they're either guaranteed to vanish, or assumed to be subtracted in a different way before you write down the action for the quantum part.
2d
comment Lagrangian description of Brownian motion?
These are interesting research projects, I think, not questions about established science. ;-)
2d
comment Is Red-Shift experiment correct?
Yes, I would. I think that the "magic" words make it sound more controversial than it actually is but the beef is right.
Jul
19
comment Mathematical formalism to include wave and particle perspectives of light
It's called "quantum field theory".
Jul
19
comment Do the laws of physics that apply to all observers also apply to a non-observer?
It's not like saying that, but even in your triplet of statements, there would still be no contradiction. Whether sugar "contains" sugar is debatable :-) but otherwise your statements are still true.
Jul
19
comment What is the complete quantum description of a free electron
Dear Wildcat, no, $m_e$ and $q_e$ are universal constants - also and especially in quantum field theory - so they are $c$-numbers, not $q$-numbers. They are not observables. Well, the total energy/mass $E=mc^2$ and the total charge of a physical system obviously is an operator, it can have different eigenvalues. But these things evaluated at a single electron are just constants, $c$-numbers.
Jul
19
comment Do the laws of physics that apply to all observers also apply to a non-observer?
Please learn basics of logic before returning to this server. There is no contradiction. It is just like saying "All fruits contain sugar", "butter is not a fruit", "butter contains no sugar". No contradiction.
Jul
19
comment Do the laws of physics that apply to all observers also apply to a non-observer?
Dear Derek, the laws of physics have the same form for all observers - in all inertial systems. Light isn't an observer - it doesn't have any inertial system associated with it. There is no contradiction whatever in between the two sentences, is there? Light obeys the laws of physics we know but we don't formulate these laws from the light's inertial system because the latter doesn't exist. I have already answered this question of yours, now it's time for you to stop writing confused comments and read the answer.
Jul
19
comment What is the complete quantum description of a free electron
Why did you include $m,q$ to the "information"? These are not dynamical variables. They are constants of Nature. One may enumerate many other such constants, like the electron's magnetic moment. But none of them changes with time. I suppose that if your classical starting point is bizarre and unexplained in this way, any "analogous" thing in the quantum theory will have to be similarly bizarre, right? The dynamical information about the electron is only carried by 3 components of the momentum (or similar 3 variables) and 1 quantum bit about the polarization of the spin, that's it.
Jul
19
comment Do the laws of physics that apply to all observers also apply to a non-observer?
Dear Derek, I don't sufficiently understand what it means to "reinforce" your question. Instead, I tried to answer your question. Light doesn't have its own inertial system because it can't be at rest. It always moves at the speed $c$ relatively to any inertial system. This is not a contradiction with special relativity. Instead, it is one of the two fundamental postulates of special relativity, the constancy-of-speed-of-light postulate! As I have already told you, your (non-existent) "light's inertial system" isn't needed for anything in science. Light is understood without it.
Jul
18
comment If there were fundamental forces weaker than gravity, would we know about it?
I like Slovakia! And the idea that Czechia is on par with a "superior landscape" inside a swampland is surely a bit exaggerated. Yes, I think it's a test but there are subtleties that prevented us from formulating and/or proving a truly general version of the inequality, so there may still be loopholes. But I think that it's important to look at both types of evidence in science - not only that "something is possible and goes" but also on general enough principles that resemble "no-go theorems". It's really the latter principles, "something isn't possible", that mostly underlie modern physics.
Jul
17
comment Eigenstates of an observable
Every eigenstate is only orthogonal to another eigenstate if the eigenvalues of the two differ - which isn't guaranteed exactly because one operator isn't (usually) the complete set of commuting observables.
Jul
17
comment Is a “shift in the meaning” of Accuracy and Precision occurring?
No, Brandon, you're wrong. The "shift in the meaning" isn't a claim about linguistics data - usage of language by the physicists or other parts of the public - but a statement about a particular document, ISO 5725, which decided to interpret the terms a bit differently.
Jul
11
comment Electroweak interaction: From $W^{1}_{\mu},W^{2}_{\mu},W^{3}_{\mu},B_{\mu}$ to $W^{\pm},Z_{\mu},A_{\mu}$
In the last two formulae, you meant the squared couplings under the square roots and not the couplings themselves, didn't you? When you make this fix, the eigenstate combinations clearly work out.
Jul
10
comment Is entropy in quantum mechanics emergent or fundamental?
Dear @user53081, I don't know how this comment differs from the original question, and if I would write something, it would probably not differ from what I already wrote. Just one extra comment: a large(r) number of degrees of freedom – if not the "thermodynamic limit" (infinitely many degrees of freedom, or atoms, if you wish) – is necessary for the entropy to be any accurate. One may formally define entropy even for the elementary particles or tiny systems but its exact value will depend on conventions and subjective knowledge too much. What's important is that these errors may average out.