21,110 reputation
142106
bio website lightandmatter.com
location Fullerton, California
age
visits member for 3 years, 1 month
seen 2 hours ago

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.


2h
comment Why is everything colder nowadays?
Link-only answers are discouraged on stackexchange.
3h
answered Is the second law of Thermodynamics an immense tautology?
3h
comment Is the second law of Thermodynamics an immense tautology?
related: physics.stackexchange.com/questions/20401/…
1d
comment Is gravity not a force?
I don't see a question here.
1d
comment How was the formula for kinetic energy found, and who found it?
There is no "energy formula." Two important names in the discovery of conservation of energy are Joule and Helmholtz.
1d
comment What forces determine the distance of the electron from the proton in a hydrogen atom?
allowing the electron to be found inside the s1 orbital 90% of the time What do you mean by this? This doesn't make sense.
2d
answered Does the definition of the SI unit “second” require that possible perturbation of primary frequency standards should be measured?
2d
comment Does the definition of the SI unit “second” require that possible perturbation of primary frequency standards should be measured?
This seems like two different questions to me. Most of the question is about the perturbing effect of blackbody radiation, but the final paragraph seems to be about anomalous shifts in clock rates over time.
Aug
26
comment Snells Law: Does the $k$ vector change on the boundary between mediums?
I think his statement is that the component of the k vector parallel to the boundary, say $k_y$, must stay the same. But $k_x$ and/or $k_z$ will have to change. As an aside, is that volume of the Berkeley Physics series good? AFAIK the E&M volume by Purcell is the real classic (and still in print).
Aug
26
comment What is the metric of Vaidya black-hole horizon?
What do you mean by "the degenerate metric?" Are you talking about a metric whose signature has a zero in it?
Aug
26
comment Are Lorentz transformations linear transformations?
My question is: why coordinate systems are vector spaces? In general, they're not. For example, spherical coordinates aren't vector spaces. In GR, coordinates are never vectors; only vectors in the tangent space are vectors.
Aug
26
comment Gravity and the Second Law of Thermodynamics
See en.wikipedia.org/wiki/Black_hole_thermodynamics
Aug
26
comment Gravity and the Second Law of Thermodynamics
Firtree is correct that gravitational collapse of massive particles to a black hole leads to an increase in entropy. That doesn't contradict the statement that Hawking evaporation into (mostly) zero-mass particles also leads to an increase in entropy. Here is a paper on the latter issue: arxiv.org/abs/gr-qc/0609022
Aug
25
comment Angular momentum, what is it, is it conserved, and how do we know?
The question is extremely long and not very focused, so it's hard to tell what you're asking. With respect to GR, the foundational status of angular momentum is exactly the same as the foundational status of energy-momentum. Both are locally conserved. Neither is globally conserved, because GR doesn't have global conservation laws. There's a good discussion of this in Hawking and Ellis.
Aug
25
comment Angular momentum, what is it, is it conserved, and how do we know?
Killing vectors in GR are not really a fundamental way of describing conservation laws, and I think what the OP wants is a description of the fundamentals. Quantities like energy-momentum and angular momentum are locally conserved in GR regardless of whether there is a Killing vector. The Killing vector just gives a conservation law for test particles.
Aug
25
awarded  Revival
Aug
25
comment What are those characteristics by which every sound can be identified uniquely?
This doesn't relate to the question.
Aug
25
comment What are those characteristics by which every sound can be identified uniquely?
This is not really true, as explained in my answer.
Aug
25
answered What are those characteristics by which every sound can be identified uniquely?
Aug
25
comment Sound difference between musical instruments
This is not really true, as explained in my answer.