21,165 reputation
142107
bio website lightandmatter.com
location Fullerton, California
age
visits member for 3 years, 1 month
seen 15 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.


Oct
12
revised Equivalences and derivations in Newtonian/Classical Mechanics
added 68 characters in body
Oct
12
comment Equivalences and derivations in Newtonian/Classical Mechanics
@RS: You need both the 2nd law and the 3rd law to prove conservation of momentum. Can you give a link to the proof you're referring to re angular momentum? It's either wrong or it invokes additional assumptions.
Oct
12
comment Riemann tensor notation and Christoffel symbol notation
The standard notation for that would be the following. Rather than writing $T_{ab}-(a\leftrightarrow b)$, you would write $T_{[ab]}$.
Oct
12
answered Equivalences and derivations in Newtonian/Classical Mechanics
Oct
12
comment Equivalences and derivations in Newtonian/Classical Mechanics
As originally formulated by Newton, the first law was a special case of the second. Later, influenced by Mach, textbook authors started presenting it as a statement about the existence of inertial frames. See physics.stackexchange.com/questions/13557/… .
Oct
12
comment Are Stephen Crothers' claims legitimate?
I'm downvoting for the reasons given here: meta.physics.stackexchange.com/q/4918 . If the OP wants to replace or supplement the video link with a link to Crothers' papers on vixra, I'll be happy to remove my downvote.
Oct
12
comment How faster is the effect of force exerted by gravity?
Now let us say, hypothetically if the sun were to suddenly extinguish (or disappear), This would be inconsistent with general relativity, which requires local conservation of mass-energy. You can move the sun away very quickly, but you can't just make it disappear.
Oct
12
comment How faster is the effect of force exerted by gravity?
The answer to this question is not resolved yet. Not true. The issue is well understood and has been tested empirically, as discussed in the answers to the question that this one duplicates.
Oct
11
reviewed Approve suggested edit on How to find the compression of a spring attached to an object
Oct
11
comment Riemann tensor notation and Christoffel symbol notation
What is $(\rho\leftrightarrow\mu)$? Is this a notation indended to mean that you're antisymmetrizing on those two indices?
Oct
11
answered Can I use two SI prefexes
Oct
11
comment Trying to understand infinite gravitational energy
downvoting for the reasons given here: meta.physics.stackexchange.com/q/4918
Oct
11
comment Trying to understand infinite gravitational energy
related: physics.stackexchange.com/questions/2838/…
Oct
11
comment What is so special about speed of light?
related: physics.stackexchange.com/q/3644 physics.stackexchange.com/q/35404/4552 physics.stackexchange.com/q/76492
Oct
10
revised Is General Relativity applicable for all coordinate systems?
edited body
Oct
10
answered Is General Relativity applicable for all coordinate systems?
Oct
10
comment Entropy as an arrow of time
So in the absence of time-asymmetric laws and boundary conditions, what can one actually say about the time-evolution of ρ? You can say all kinds of things about the time-evolution of the density matrix. What you can't say is anything that's logically equivalent to the 2nd law.
Oct
10
comment Entropy as an arrow of time
@dj_mummy: That isn't what I claimed. For a detailed discussion of what I did claim, see Callender, Craig, "Thermodynamic Asymmetry in Time", The Stanford Encyclopedia of Philosophy (Fall 2011 Edition), Edward N. Zalta (ed.), plato.stanford.edu/archives/fall2011/entries/time-thermo .
Oct
10
comment 2N Fermions $\stackrel{?}{=}$ N Bosons
related: physics.stackexchange.com/q/75403
Oct
10
comment Entropy as an arrow of time
To say the number of accessible microstates W of the universe is constantly increasing is nothing more than saying 'ignorance begets ignorance'. No, this is wrong. To explain the second law microscopically, you need either time-asymmetric boundary conditions or time-asymmetric laws of physics (Penrose).