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Oct
13
comment What is the significance of the imaginary unit in Deutsch gate?
While it could be improved with more context, I don't think someone with the knowledge required to answer the question will need it. (The question is quite clear to me. I don't know the answer.)
Oct
8
awarded  Popular Question
Oct
6
comment Does the poisson bracket $\{f,g\}$ have any meaning if neither of $f$ or $g$ is the system's Hamiltonian?
But the question is about Poisson brackets in classical mechanics, not commutators in quantum mechanics...
Oct
6
comment Is Bekenstein entropy limit inconsistent with universal continuity?
Does this really have anything to do with black holes? There are plenty of other things in physics that are continuous (including any wavefunction), but which are considered to have finite entropy - this argument would apply equally well to all of them.
Oct
4
comment What really is a Dirac delta function?
See meta discussion here about whether this is on topic.
Oct
1
comment Artificial planetary magnetic field
@KeithMcClary in the superconducting case it doesn't, as far as I know, though I am not an expert on superconductors. (In the case of a normal conductor it dissipates via Joule heating.) But that's just my point - if you're storing the energy in a system with no dissipation then you can generate the energy at as slow a rate as you like (slower just means it takes longer to spin it up) so the rate at which we generate energy isn't the relevant figure.
Sep
30
awarded  Yearling
Sep
28
asked Pluto's internal heat source
Sep
25
comment What will be destroyed? The Moon or the Death Star?
(Of course, in the Star Wars movies the Death Star can travel faster than light, and most things that look like laser beams seem to travel slower than light. But that's all movie stuff and has nothing to do with physics.)
Sep
25
comment What will be destroyed? The Moon or the Death Star?
I'm curious why you think that "Since Death Star is traveling almost at the speed of light, when the laser gets to the Moon, the surface of the Death Star is already there." The Death Star is only travelling at almost the speed of light, whereas the laser is travelling at the speed of light, so it should get there before the Death Star.
Sep
20
comment Why fast eye movement splits a white LED into the RGB components?
It might be clearer if you move the light while keeping your eyes still, but then you have to move it really fast. I see this all the time with many different types of light and can even use it to estimate the frequency of the pulses - it always amazes me that other people don't notice it.
Sep
20
comment Why fast eye movement splits a white LED into the RGB components?
@Sparkler try this: in a dark room, focus your eyes on a point about a foot to the left of the phone, then move your eyes rapidly to a point about a foot to the right of it, so that the light passes right through the centre of your vision. You should notice that it leaves a trail across your visual field for a split second, and with a bit of practice you should see that trail broken up into distinct red, green and blue segments, caused by the light changing colour as you moved your eyes across it.
Sep
17
revised Operator algebra in integral form
Removed inappropriate bickering about style
Sep
9
comment How would Boltzmann Brain function with all anti-matter in it?
@MatasVaitkevicius that's a fair point. Perhaps you also have to imagine that the antimatter particles are emitted with sufficiently low velocity that they eventually return due to gravitational attraction, after the brain has done all its imagining of the universe, and then annihilate all the matter particles again.
Sep
9
answered How would Boltzmann Brain function with all anti-matter in it?
Sep
6
comment Second law of thermodynamics (in terms of entropy)
@DanielSank The "closed" versus "isolated" distinction is very common in thermodynamics texts. Essentially "isolated" means the situation where the microcanonical ensemble is appropriate, "closed" means canonical ensemble and "open" means grand canonical ensemble. The terminology might be irritating, but it's standard.
Sep
4
comment Can I electrify a pin by applying current in its base?
Cross posting is generally discouraged, but its not a legitimate reason to vote to close.
Aug
31
comment Would this pump water up? and if so, how far?
@adrian a Stirling engine does not turn ambient heat into work, it extracts work from the temperature difference between two thermal reservoirs. It is impossible to do it with only one. That is exactly what "perpetual motion machine of the second kind" means.
Aug
30
comment Is the MaxEnt “interpretation” of statistical mechanics the current mainstream approach?
I would advise leaving this question open for a while to get a few answers rather than accepting the first. The currently accepted answer is not wrong and is fairly balanced, but it is only one person's view, not an authoritative answer.
Aug
29
comment Why Does The Moon Apear White/Grayish and The Sun Yellow?
To add to @MarcvanLeeuwen's point, the moon is often clearly visible in broad daylight, and as far as I've ever noticed, always appears pure white in such conditions.