26,204 reputation
162135
bio website lightandmatter.com
location Fullerton, California
age
visits member for 3 years, 5 months
seen Dec 7 at 20:09

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
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 Is it correct to say “like poles attract, unlike poles repel” while two magnets are placed such that one is inside another?
Magnets don't actually have poles. Magnetic monopoles don't exist: en.wikipedia.org/wiki/Magnetic_monopole
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/…
Sep
29
comment How do we know that there is more than one photon in the universe?
Photons simply make a full rotation from the time-like to the space-like coordinate axis. No, this is wrong.
Sep
29
revised How can I measure the speed of a figure skater's spin?
fix capitalization and punctuation of title
Sep
29
comment Impact force in a fall
@Qmechanic: Thanks for pointing me to that info. After reading it, I still don't think this should have the homework tag.
Sep
29
revised Is the amount of radiation you receive in space constant regardless of velocity?
delete general-relativity tag
Sep
29
awarded  Revival
Sep
29
comment Why $r^2$ and not other power of $r$ in mutual force of gravitation?
This is fine as a heuristic argument, but as a matter of taste, one may or may not like it. Gravity isn't a physical substance that spreads out over an area like peanut butter.
Sep
29
comment Why $r^2$ and not other power of $r$ in mutual force of gravitation?
You've asked an intellectually sophisticated question, and you deserve an intellectually sophisticated answer. The trouble is that there is no uniquely defined answer to this type of "why" question. If there's an answer that you will find satisfactory, it will be an answer that appeals to something you consider more fundamental. But we don't know what you'd say was more fundamental than this law. That's a matter of taste. Empirical observations? General relativity? Heuristic arguments about the commonness of inverse-square laws, because we live in three dimensions and area goes like $r^2$?