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173140
bio website lightandmatter.com
location Fullerton, California
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visits member for 3 years, 10 months
seen May 21 at 15:35

I teach physics at Fullerton College, a community college in Southern California. I have an undergrad degree in math and physics from Berkeley and a PhD in physics from Yale. Back when I was doing research, my field was experimental low-energy nuclear physics.


Oct
20
comment Producing photons with same frequency, different amplitude wave
I am trying to give some justification to the common answer that all photons have the same A ... which is simply false, for the reasons given in my answer.
Oct
20
comment Can light produce weak gravitational waves?
@CuriousOne: Unless somebody does the experiment there is no way of knowing. Not true. General relativity makes unequivocal predictions about this kind of thing, and it is a well tested theory. In particular, the gravitational fields made by light need not be weak, and we have direct evidence of this. The universe was radiation-dominated up until it was about 50,000 years old. This period includes the period of big-bang nucleosynthesis (BBN), so empirical data on BBN are a test of these cosmological models. Therefore we can confidently use GR to address this type of question.
Oct
20
comment Producing photons with same frequency, different amplitude wave
"It" refers to the amplitude. When I said amplitudes are the same, I meant that in a vague sort of way because an individual doesn't even have a constant amplitude of course, as it is really described by a wave function, whose amplitudes are not even real numbers. So what do you think the magnitude of the amplitude is? But in a broad sense this amplitude (or the square of it) must integrate to 1. Right, which is not consistent with the amplitude being a fixed number for all photons of a given frequency.
Oct
20
comment Underdetermined forces in a statics problem
@Michiel: Friction is a `response force' No, I don't think that's true. There is no such physical principle that I know of.
Oct
20
revised Producing photons with same frequency, different amplitude wave
added 415 characters in body
Oct
20
answered Producing photons with same frequency, different amplitude wave
Oct
20
comment Producing photons with same frequency, different amplitude wave
If you insist on thinking of photons as waves (which is fine of course), you can think of all of their amplitudes as being equal. Not true. If you think their amplitudes are all the same, what do you think it is?
Oct
20
comment Producing photons with same frequency, different amplitude wave
This doesn't answer the question.
Oct
20
comment Producing photons with same frequency, different amplitude wave
Two photons of the same frequency have the same "amplitude", No, their wavefunctions can differ.
Oct
20
comment Is there any physical quantity that does not have uncertainty?
@CarlWitthoft: The uncertainty principle does not apply to counting the number of items (even photons). There is an uncertainty relation between number of quanta and phase for a harmonic oscillator: physics.stackexchange.com/questions/67929/…
Oct
20
comment Is there any physical quantity that does not have uncertainty?
The OP is asking about quantum uncertainty, which is qualitatively different from uncertainty in measurements in general.
Oct
20
revised Underdetermined forces in a statics problem
added 701 characters in body
Oct
20
comment Underdetermined forces in a statics problem
@dmckee: Even a small deviation will break the symmetry and make the system determined again. Hmm...I sketched an analysis, and it didn't look that way to me. In the asymmetric case, it seems to me that you have four unknowns ($N_1$, $N_2$, $F_1$, and $F_2$), and three equations: $F_x=0$, $F_y=0$, and $\tau=0$.
Oct
20
awarded  Nice Question
Oct
19
comment Underdetermined forces in a statics problem
@BMS: Yes, but in that example it's clear why it's underdetermined, and how the system knows what solution to pick: it picks the solution that's imposed by the externally determined force on the rope. Here there doesn't seem to be any such external force presently being exerted on the system that could determine which solution to pick.
Oct
19
comment Underdetermined forces in a statics problem
@ja72: I don't think your analysis is right. The problem is underdetermined for any value of $\mu>0$.
Oct
19
revised Increasing matter density in the Friedman equations?
added 351 characters in body
Oct
19
answered Increasing matter density in the Friedman equations?
Oct
19
asked Underdetermined forces in a statics problem
Oct
18
comment Doesn't the second postulate of special relativity imply the existence of “luminiferous ether”?
Huh? The speed of propagation of sound is independent of the speed of the emitter.