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seen Feb 22 at 9:32

Apr
15
comment Will a hole cut into a metal disk expand or shrink when the disc is heated?
@Mallik: But it would also try to expand along the ring, and if it moves inward, it has even less space. Therefore it has to move outwards in order to expand (with the outer parts moving outwards more).
Feb
1
awarded  Commentator
Feb
1
answered Does the Banach-Tarski paradox contradict our understanding of nature?
Jan
30
answered Why can't electromagnetic radiation from magnets be used for apparent perpetual motion?
Jan
30
revised Quantum information science references
added another reading suggestion
Jan
30
comment What makes some laser beams visible and other laser beams invisible?
@Revo: Exactly. So any movie showing laser beams in outer space is simply wrong (unless in the future outer space is full of dust from all the space ships crossing it ;-))
Jan
30
answered What makes some laser beams visible and other laser beams invisible?
Jan
30
answered Quantum information science references
Jan
30
answered Does it make sense to have a theory of thermodynamics about coldness?
Jan
30
answered How are the Pauli matrices for the electron spin derived?
Jan
19
answered How many colors exist?
Jan
18
revised Is it possible to bind an entangled electron to the outer shell of an atom or just a proton?
added 311 characters in body
Jan
18
answered Is it possible to bind an entangled electron to the outer shell of an atom or just a proton?
Jan
18
comment Why does the water rise?
I'd question one thing from that answer, though: Nowhere is a vacuum created. There's always air in the glass, and it always fills the whole space not occupied by water. When the air cools down, it doesn't contract by itself, only its pressure goes down (intuitively: Since the molecules get slower, they hammer less onto the water surface). As result the water is pressed more in by the air outside than out by the air inside, and thus flows inside. This rising water compresses the air inside, which causes air density and thus pressure inside to rise again until equilibrium is reached.
Jan
16
comment How is the classical twin paradox resolved?
According to Misner, Thorne, Wheeler, Gravitiation, Chapter 6: "When spacetime is flat, move however one will, special relativity can handle the job."
Jan
16
comment Why is cold fusion considered bogus?
There's a big difference between cold fusion and multiverses: Cold fusion, if it exists, should be experimentally demonstrable (indeed, Pons and Fleischmann claimed to have done exactly that), but would violate current theories. On the other hand, multiple universes are not observable in principle, but don't violate any known law of physics, and can only be proven false by proving false one of the physical theories they are supposed to explain. Therefore the question of cold fusion is a physical one, while the question of multiverses is basically a philosophical one.
Jan
16
comment How do I express the Kepler general orbit $r(\phi)$ in rectangular coordinates?
I don't think you have to do the general calculation; however I think it is important that the reader is aware that the calculation is for a special case, hence my comment.
Jan
16
awarded  Editor
Jan
16
revised How can indeterminacy in quantum mechanics be derived from lack of ability to observe a cause?
deleted 2 characters in body
Jan
16
answered How can indeterminacy in quantum mechanics be derived from lack of ability to observe a cause?