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bio website math.mit.edu/~shor
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comment Quantum Simple Harmonic Oscillator Interpretation
And phonons are also very close to being harmonic oscillators.
1d
comment Quantum Simple Harmonic Oscillator Interpretation
Isn't a single mode of an electromagnetic wave (i.e., photon states) a really good approximation to a harmonic oscillator?
Dec
15
comment What would happen if a negative mass crossed the event horizon of a black hole?
If negative mass is attracted to positive mass, while positive mass is repelled from negative mass, can't you tie a string between them and set up a perpetual motion machine? The combined object will accelerate because both objects will be accelerated in the direction of the positive mass. Of course, this doesn't actually increase the energy of the system because the combined object has zero mass.
Dec
15
comment Can the weight of a bird be measured, considering air friction?
Does the friction of water mean that the fish swimming in the ocean don't contribute to the pressure at the ocean floor?
Dec
14
comment Physical examples where changing the order of limits yields wrong result
Just because operators are linear, it doesn't mean that you can change the order of limits. You never see counterexamples in physics books or lectures because physicists are clever enough not to present calculations that don't work. (And in fact, even in math, you can usually exchange the order of limits and still get the right answer. But not always.)
Dec
14
comment Physical examples where changing the order of limits yields wrong result
In physics lectures, you do not change the limits so as to get the wrong results because you don't actually want to present the wrong result to the class.
Dec
3
comment Exorcism of Maxwell's Demon
A system cannot cool itself by performing work on another system. This breaks the laws of thermodynamics. And out of curiosity, what do you think standard refrigerators perform work on?
Dec
3
comment Quantum Wavefunctions Without Space
Maybe you could actually reference something this handful of physicists have written.
Dec
2
comment Exorcism of Maxwell's Demon
You say: "To cool something, you either need something cooler or you must let the system perform work." ... You cannot have a system cool itself by performing work. This breaks the laws of thermodynamics.
Dec
2
comment Exorcism of Maxwell's Demon
Let me modify my previous comment ... if you have a device with an infinite amount of memory, it can also be viewed as a heat engine running on the difference of temperature between its memory and the system.
Dec
2
comment How was it proven that a quantum entanglement measurement of particle A, affects properties of particle B
Where did John Bell say "something is moving there faster than light". If I remember Bell's paper correctly, he made no such speculation.
Dec
2
comment Exorcism of Maxwell's Demon
@PlasmaHH: if the Demon has an infinite amount of memory, then it can indeed break the Second Law. But a device with an infinite amount of memory also violates physical laws.
Dec
2
comment Will Quantum Computation fail if spacetime is discrete?
The 10,000 entangled qubits don't "store" $2^{10,000}$ states in the same way that you might guess from reasoning about classical computers. Holevo's theorem says that you can extract at most 10,000 classical bits from 10,000 entangled qubits.
Dec
2
comment Will Quantum Computation fail if spacetime is discrete?
Spacetime being discrete is different from spacetime being a classical cellular automaton. A classical cellular automaton cannot do quantum computation, but a quantum cellular automaton can.
Dec
2
comment How can a black hole zap a galaxy into existence?
... which link contains the quote “Our study suggests that supermassive black holes can trigger the formation of stars, thus ‘building’ their own host galaxies." So even if you had just bothered to find and actually read that link, you could have reported the science that the rather inaccurate picture was based on, which would have led to a much better answer.
Dec
2
comment How can a black hole zap a galaxy into existence?
-1: You could have found the actual science the picture is based on. What the black hole jets actually do (according to some astronomers' hypothesis) is trigger star formation in the galaxy. So even if it doesn't zap it into existence, it zaps it into visibility.
Dec
1
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
Let me comment that I don't think the answer is a bad one, and I think it does accurately reflect the conventional wisdom. I was just trying to give a possible answer to "Why the downvote?" And as you have probably gathered, I also don't think the conventional wisdom is very wise.
Dec
1
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
But if an external line ever interacts with another particle, doesn't it automatically become an internal line in a bigger Feynman diagram? And if we don't observe it, won't it interact?
Dec
1
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
@jld: what is the definition of an external line if it not something that is observed? And so an internal line is something that is not observed.
Dec
1
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
It sounds like you're saying that anything that is not actually observed (that is, not an external line in a Feynman diagram) is by definition virtual. So particles are virtual because they're not observed, and particles are not observed because they're virtual. And they don't exist because we can't observe them because if we observed them, then by definition they wouldn't be virtual.