17,765 reputation
13393
bio website lightandmatter.com
location Fullerton, California
age
visits member for 2 years, 9 months
seen Mar 30 at 19:12

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.


Sep
13
answered Is it possible to deduce the Archimedes' law of the lever using only the laws of conservation of the physics?
Sep
13
comment Hypervelocity black holes
Re the first question, the dynamics are exactly the same for a black hole as for any other star of the same mass.
Sep
13
answered Does the total mass of an isolated object include the mass stored in its gravitational field?
Sep
13
comment Weak force: attractive or repulsive?
Since there is no classical field theory of the weak force, I'm not convinced that this is a meaningful question.
Sep
13
comment Weak force: attractive or repulsive?
related: physics.stackexchange.com/q/39229
Sep
13
comment Is a spinning object heavier than a non-spinning object?
@joshphysics: Yes, I think my definition is standard. For example, there's a discussion of this in Taylor and Wheeler, Spacetime Physics. The reason it doesn't work to say the mass is the sum of the rest masses is simply that that would be inconsistent with what we get in ordinary laboratory measurements of mass. E.g., a lot of the rest mass of a rock comes from kinetic energy of the gluons. We also don't necessarily know the ultimate constituents of matter.
Sep
13
comment What is the difference between the Balmer series of hydrogen and deuterium?
Look at the equation that defines C. It has a mass in it. That's the reduced mass.
Sep
13
comment What is the difference between the Balmer series of hydrogen and deuterium?
The reduced mass is slightly different, so $C$ is slightly different. There would also be different hyperfine structure.
Sep
13
comment Is a spinning object heavier than a non-spinning object?
@joshphysics: When you make the claim about non-additivity of mass, do you have in mind squaring the total four-momentum and calling the result the mass of the system? Yes, exactly. So, e.g., two EM wave packets with energy-momentum vectors $(p_t,p_x)=(E,E)$ and $(E,-E)$ have a total energy-momentum of $(2E,0)$, corresponding to a mass of $2E$.
Sep
12
revised Proper Time for Deceleration in Special Relativity
added 130 characters in body
Sep
12
answered Proper Time for Deceleration in Special Relativity
Sep
12
comment Does Hawking radiation break asymptotic flatness?
Or I would say that a stream of matter does extend to certain points at null infinity, but not to other points at null infinity.
Sep
12
comment Does Hawking radiation break asymptotic flatness?
Also, if a radiation field falls off like $1/v$ along some null geodesic, where $v$ is the kind of null coordinate described in my answer, the mass-energy density falls off like $1/v^2$, not $1/v$.
Sep
12
comment Does Hawking radiation break asymptotic flatness?
@JerrySchirmer: We could work out the explicit power counting, but I don't think the sketch in your comment works. Birkhoff's theorem doesn't apply because this isn't a vacuum spacetime. Also, on a surface of simultaneity, the density isn't $\propto 1/r$; the Hawking radiation is a spherical shell with a finite thickness.
Sep
12
comment Why does Platinum evaporate if left long enough?
A related counterintuitive fact is that for a gas in the limit of low pressure, the equilibrium state is one in which every atom is ionized.
Sep
12
comment Why does Platinum evaporate if left long enough?
Temperature is a bulk property, not a property of individual particles. Some atoms have high kinetic energies.
Sep
12
asked Is there valid physics behind the bodybugg?
Sep
12
comment Background radiation: radon vs potassium 40
@dmckee: Yeah, all my "[decay products]" edits in square brackets were "progeny" in the original article. I assume that's what they mean by that word. The first sentence seems to be talking about radon itself that has been ionized so that it sticks to things.
Sep
12
answered Background radiation: radon vs potassium 40
Sep
12
comment Background radiation: radon vs potassium 40
But the OP is asking about a factor of $10^6$ discrepancy.