Comments by "B. Xoit" (@b43xoit) on "Stanford" channel.

  1. So gracious of the good prof to give elementary lectures, given the depth and breadth of his accomplishments.
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  2. Mike Fuller, I don't know that "trapped time" denotes any meaning. Don't know how you would test for that.
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  3. Yes, it bends space; see General Relativity. A photo does not trap light; it measures the light and represents the result of the measurement with some kind of analog or bits.
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  4. Of course there are other laws.
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  5. I had to replay this to get this key lesson straight: when we prepare the electron by putting it in a magnetic field, the way to find the quantum state we're putting it in is first, take the dot product of the direction cosines of the direction of our magnetic field with the vector of "sigma" matrices (elsewhere identified as Pauli matrices), and consider the result as an operator for hypothetically turning on the magnetic field again without changing the direction of the magnet and looking for whether the electron emits a photon. We know very well that if we did that, it wouldn't. We associate that result (no photon) with one of the eigenvalues of the operator. The associated eigenvector is the state we are putting the electron into. End of procedure.
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  6. Sexes, not genders.
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  7. Constraining the six such that the sum of their squares is 1 removes in effect a variable. Then saying that multiplying by a phase makes no difference eliminates the second variable.
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  8. Energy found in what form? For example, say you have a raised mass and you know you can lower it by a certain distance, and you want to know the energy that represents. Then you multiply the weight by the distance. Or, say you want to know the energy consumed by a space heater in a day. Multiply the voltage by the current by the time, and there it is.
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  9. The constraint that the sum of the squares of the magnitudes has to add up to 1 removes one variable, and the irrelevancy of phase removes a second variable. Phase means multiplication by exp(i θ) for any angle θ.
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  10. It's just the way a complex number is usually conceived. i is assumed to belong to the number system and to have the property that i^2 = -1 (which no real number would satisfy).
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  11. A photon's rest mass is zero, but it has mass because it has energy.
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  12. Modern black-and-white photographic film uses a compound involving silver. But even-more-modern digital photography senses light with "charge-coupled devices", which produce an electrical output encoding the measurement result.
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  13. Color film, I don't know from; much more complex.
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  14. Wikipedia gives the general formula for dotting the sigma vector with an arbitrary unit-length vector in threespace. I don't know whether the following is particularly beautiful or interesting, but here's what I got when I expanded the elements in that general formula to their respective 2x2 representations of complex numbers as matrices of real numbers: a3 0 a1 a2 0 a3 -a2 a1 a1 -a2 -a3 0 a2 a1 0 -a3 I observe that: - All the a3s are on the main diagonal, and the main diagonal is a3, a3, -a3, -a3. - All the a2s are on the counterdiagonal as a2, -a2, -a2, a2. - The remaining elements are 0, 0, 0, 0, a1, a1, a1, a1.
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  15. Well, you mentioned the two things, and each of them removes a variable.
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  16. <chocolate chip | M | chocolate chip>
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  17. What is the context of your question? What "it" are you referring to?
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  18. I don't understand at all what you are trying to ask. What Thing?
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  19. So referential transparency isn't worth anything?
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