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Dec
27
comment Why don't they use springs as an energy source for cell phones?
Dear Bob, it's entertaining but if taken seriously, one can't improve the energy density by more than an order of magnitude or so. The metallic pieces start to break when one tries much higher tension. The old clockmakers have tried to take it to the limit. One can't really reach the chemical energy density by realistic tension because the chemical energy means that the electrons in each atom are already strongly, qualitatively rearranged. A wound up spring means that they're just "moderately" displaced - a smaller change of each atom.
Dec
27
awarded  Good Answer
Dec
27
awarded  Nice Answer
Dec
27
revised Why don't they use springs as an energy source for cell phones?
added 247 characters in body
Dec
27
revised Why don't they use springs as an energy source for cell phones?
added 247 characters in body
Dec
27
revised Why don't they use springs as an energy source for cell phones?
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Dec
27
answered Why don't they use springs as an energy source for cell phones?
Dec
27
comment Why is quantum entanglement considered to be an active link between particles?
Your assumption that "something else should explain quantum mechanics" is pretty much exactly the same mistake that was done by Einstein when he invented his misleading terminology - and it's done by virtually all other people who have some psychological problem with quantum mechanics. You are just not willing to accept the essential, established scientific fact about Nature that the most fundamental theory describing Nature may be something else than a classical theory describing the "objective state of affairs". But the fundamental theory of Nature is quantum i.e. non-classical!
Dec
27
comment Why is quantum entanglement considered to be an active link between particles?
Einstein called it "a spooky action at a distance" because he didn't understand how quantum mechanics worked and always implicitly and incorrectly assumed that the fundamental theory had to be classical. The correlation in QM occurs without any action at a distance, there is nothing spooky about the entanglement, it's how Nature works all the time, and QM is perfectly compatible with locality and Lorentz symmetry and relativity. Quantum mechanics is consistent and complete and it is the theory. Theories explain Nature. Nothing else may explain a fundamental enough theory such as QM.
Dec
27
comment “Speed” of Gravity and Speed of Light
Yes, that's what I meant. The phrase came from an undergraduate instructor of ours, in this very context of sensible units. The idea is that schoolkids are taught to be very careful about using SI units and nothing else, and so on, and this is the teacher-led "disciplined" attitude that most physicists know even when they're high school students. But in the college,they should get adult and be in charge of the conventions they adopt. They should understand why they adopt a convention and whether and how they may avoid it. As adults, they can drink alcohol and start to use more conveneitn units
Dec
23
awarded  Nice Answer
Dec
23
comment What is the speed of magnetism?
Assuming that by "instantaneous", you mean "permanent" effect of the magnetic field, right? If something exists permanently, one can't say how "quickly" it exists.
Dec
23
comment What is the speed of magnetism?
It's a frequent mistake here in Czechia, too. A few years ago, student leader from 1989 Šimon Pánek (now a charity guy) attended a conference of mathematicians and physicists in Prague and he has used "physicians" throughout his talk. I did tell him, too. "So people could see I didn't have a clue what I was talking about," he said. I didn't object. ;-)
Dec
23
comment What is the speed of magnetism?
The people who study physics are called physicists. Physicians are "doctors" who try to cure other people's diseases - to improve their physical health or condition.
Dec
22
answered Spectrum of Laplacian on one hemisphere
Dec
21
comment Euclidean geometry in non-inertial frame
$\pi=3.14159...$ is never violated. The universality and reliability of this mathematical statement is exactly as high as the universality and reliability of $1+1=2$. One could redefine symbols in various ways except that there exists no useful formalism or theory in which $\pi$ would be "deformed". When we change physical theories, we have to change the statements about physics - the statements purely about mathematics just cannot be changed. It would be so erroneous to say to say that $\pi\neq 3.14...$ as to say that the maximum speed becomes $\infty=299792458$ m/s in relativity.
Dec
21
comment How to define a 'clone' of a mixed state?
The second choice is no good. It is physically and algebraically unnatural because the implicit algorithm is basis-dependent.
Dec
20
comment Why is Standard Model + Loop Quantum Gravity usually not listed as a theory of everything
Dear @Hindsight, if I understand the statement well, I don't agree with it. The violation of the Lorentz symmetry, if it's nonzero and at least slightly natural, just never becomes negligible. A necessary condition for the Lorentz symmetry is that the maximum speed that any particle species (or composite objects) may converge to is the same, we call it the speed of light. If your theory fundamentally violates the Lorentz symmetry, the maximum speeds will differ for particle species and this difference in no way disappears at shorter or longer length scales.
Dec
19
comment Euclidean geometry in non-inertial frame
The decision whether $\pi=3.14...$ is not a matter of pedagogy. It's a matter of basic mathematics and the answer is Yes, it's always the value of pi. There doesn't exist any remotely meaningful way to describe general relativity that would distort the value of pi.
Dec
19
comment Euclidean geometry in non-inertial frame
Sorry, Viesr, but $\pi=3.14159...$ is a mathematical identity that is always valid, whether one talks about physics or not, and whatever model of physics one chooses. $\pi$ is the circumference/diameter ratio of a circle - we mean a real idealized circle in the Euclidean flat geometry. In physics of GR, we need other geometries but we don't generalize the geometry by redefining concepts like pi. We still need the constant pi in general relativity, with the same value. Instead, we appreciate that the space isn't Euclidean and most statements valid in flat space are no longer valid in GR.