27,770 reputation
173141
bio website lightandmatter.com
location Fullerton, California
age
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
2
answered If an antenna must be $\frac{1}{4}$ of the wavelength, how can car antennas be so small?
Oct
2
comment Does accelerating generate gravitons?
@OscarCunningham: Yes. The system you describe has a varying mass quadrupole moment, so it radiates.
Oct
2
comment Does accelerating generate gravitons?
The real question here would be (1) whether a free-falling object radiates gravitational waves. If so, then it would presumably be true that (2) those gravitational waves are quantized as gravitons, but we don't have a theory of quantum gravity, so we don't really know. The answer to #1 depends on whether the system has a changing mass quadrupole moment. It is definitely possible to come up with scenarios in which there is acceleration but no gravitational radiation, e.g., two parallel, uniform, infinite sheets of mass.
Oct
2
comment Einstein's special relativity beyond the speed of light
There is a no-go theorem by Gorini that shows you can't do this in 3+1 dimensions. V. Gorini, "Linear Kinematical Groups," Commun Math Phys 21 (1971) 150 adsabs.harvard.edu/abs/1971CMaPh..21..150G open access via project euclid: projecteuclid.org/…
Oct
2
comment Can speed be defined in the complex plane?
Another way to see that it can't be of interest physically is to consider the case where $v=c$, which is intermediate between $v<c$ and $v>c$. You get nonsense for $v=c$.
Oct
2
comment What experiment disproved single fluid theory of electricity?
This doesn't address single-fluid versus two-fluid. I doubt that the fluid theories were though of at the time as implying anything about the corpuscular or continuous nature of charge.
Oct
2
comment Vector fields and tensors in E&M
The EM field tensor - as a tensor - does change under change of reference frames. Many people do prefer to describe tensors as invariant. When people adopt that convention, they say that the tensor's components in a particular basis are basis-dependent, but they consider the tensor itself to be invariant.
Oct
2
comment Would an ideal gas be colder at higher altitude due to gravity?
The answer is no. This was a controversy in the 19th century. The putative effect can be referred to as the Loschmidt gravito-thermal effect. Boltzmann, Maxwell, and Guthrie debated the question.
Oct
2
awarded  electromagnetic-radiation
Oct
2
awarded  Nice Answer
Oct
1
revised What is the difference between xrays and ultra violet rays?
added 36 characters in body
Oct
1
answered What is the difference between xrays and ultra violet rays?
Oct
1
comment Can we prove Conservation of Angular Momentum without assuming internal forces are central?
Conservation of angular momentum can't be proved from Newtonian mechanics, because conservation of angular momentum is true in general, but Newtonian mechanics is not true in general. Conservation laws are fundamental. Newton's laws are not.
Oct
1
answered Does nature of singularity in black hole depend on material that fell in?
Oct
1
comment How come we talk about gravitational potential energy and not gravitational potential?
The metric is the central object of study in general relativity, and the metric is essentially the gravitational potential.
Sep
30
awarded  Explainer
Sep
30
comment Can gravitational waves be red-shifted?
@arc_lupus: Cite: "Yes, gravitational waves will undergo the same red-shift as any wave that propagates at c." This is simple kinematics. It has nothing to do with the specific characteristics of the wave. For an example of how this is derived, see section 3.2 of my SR book: lightandmatter.com/sr
Sep
30
comment Can gravitational waves be red-shifted?
@arc_lupus: Isn't this true for all waves without respect for their speed? No, it can't be. If a wave travels at some velocity v that is less than c, then v depends on the frame of reference, and the Doppler shift can't just be a function of the emitter's state of motion relative to the receiver. For example, the Doppler shift of a sound wave depends on the emitter and receiver's states of motion relative to the vibrating medium.
Sep
29
answered Do perfect spheres exist in nature?
Sep
29
comment How do we know that there is more than one photon in the universe?
A photon is massless and travels with lightspeed, which means for the photon itself, that time stands still and space shrinks to zero. Not true. See physics.stackexchange.com/questions/29082/…