26,200 reputation
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location Princeton, NJ
age 25
visits member for 2 years, 9 months
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I am a graduate student studying astrophysics at Princeton. I received my bachelor's in physics and mathematics from Caltech (2011).

My primary interest is in general relativistic magnetohydrodynamics simulations of black hole accretion.


Feb
11
comment Would an Alcubierre drive actually allow FTL travel?
possible duplicate of How does "warp drive" not violate Special Relativity causality constraints? (see Jerry Schirmer's answer, which is the clearest and is quite correct)
Feb
10
comment Cosmology: proper evolution of energy density ratios with time?
@Kagaratsch Yes, see the edit.
Feb
9
comment Intuitive understanding of Lagrange point L3
For the first equation, the exact formula (for circular geometry) would have an extra $r/R$ multiplying the RHS, since you really want to set the gravitational acceleration equal to the centripetal acceleration at $r$ rather than $R$, keeping angular velocity constant. Not that this changes the approximation.
Feb
8
comment Hamiltonian System Outside Physics
This is explicitly not about physics, and so is off-topic.
Feb
7
comment Can a cubic meter of space at absolute zero have any object with mass inside?
I'm not so sure about point 3 either. Temperature as a thermodynamic concept requires energy and degrees of freedom, not rest mass. Sure it's hard to build a human-readable thermometer out of photons, but that's just because it's hard to build anything human-interactable out of photons. And besides, if some massive particles can claim photons' temperatures are undefined until they affect those same massive particles, couldn't a photon gas claim the reverse, that massive particles only have temperature insofar as they emit blackbody radiation?
Feb
5
comment “Where” does dissipated enstrophy go?
Hi @Kimusubi I wrote your equations using the MathJax formatting we encourage here. You should check to make sure they're still right (I couldn't tell if that was a nu or a v, and I'm not sure on the subscript on $\Phi$). If you want a more thorough guide to latex-style MathJax, see here.
Feb
4
comment Is there a limitation on Gauss' law?
See also Anti-gravity in an infinite lattice of point masses, infinite grid of planets with newtonian gravity, Infinitely many planets on a line, with Newtonian gravity, Finite or ∞ set of masses & ∃ gravity center? for how common this issue is (note Newtonian gravity and electrostatics obey the same equations).
Feb
4
comment Is there a limitation on Gauss' law?
I would upvote but for "infinite sums don't exist." Infinite sums are defined to be the limits of the finite partial sum, and so they very much exist as a concept. The problem is that one can only reorder terms in absolutely convergent series, and in this problem we have neither absolute convergence nor any a priori ordering on the terms.
Feb
2
comment How to experimentally reconstruct Maxwell's equations from scratch
@NeuroFuzzy You're right. In fact $E$ and $B$ are just mathematical conveniences, no more "real" than the vector potential or the gravitational field. All observable consequences of E&M can be derived from Coulomb + SR.
Feb
1
comment Why does non-commutativity in quantum mechanics require us to use Hilbert spaces?
Just to be clear, since often in QM we say "Hilbert space" when we mean something less than that: Are you asking why non-commutativity forces us to use complete inner product spaces, or are you asking why we need to use an inner product space at all?
Jan
31
comment Calculating length contraction at speed $c$ (not near it)
I don't see how this is a duplicate, since the other questions doesn't deal with length contraction at all.
Jan
31
comment Does irrotational imply inviscid?
You should check your definitions. What you describe as rotation is also called vorticity. Also, the Euler equations most definitely only apply to inviscid flow. What was being said in the other answers is that some solutions (flows) to the viscous fluid equations can be irrotational, in which case viscosity happens to not matter.
Jan
29
comment components of mixed tensor with same indices
Repeated generic indices ($\mu$ or $i$ as opposed to $3$ or $y$) not meant to be summed over are a bit dangerous, but assuming no mistake is made I would interpret them the same as non-generic indices, just unspecified. So $a^{\nu\nu}$ would be a single, unspecified diagonal component of a rank-2 tensor, just like $a^{33}$ would be a single, specified component.
Jan
27
comment Is $∣1 \rangle$ an abuse of notation?
@AlfredCentauri As someone who codes in C and works with relativity, I see nothing wrong with counting "zeroth," "first," "second," ... :)
Jan
27
comment Metric tensor in SRT
While we're on the topic of how that webpage is misleading, note that there are two different SR sign conventions. The one it uses -- (+1,-1,-1,-1) -- is favored by particle physics and such. The reverse -- (-1,+1,+1,+1) -- is always used in any relativity for relativity's sake, sans quantum mechanics.
Jan
27
comment Why do we call a white led with high color temperature “cool”?
Exactly. It should be noted that only incandescent bulbs give off mostly blackbody light; LEDs and fluorescent bulbs have entirely different amounts of various wavelengths, so them using color temperature is a little out of place anyway.
Jan
27
comment Why do particles have spins such as $1/2$, $3/2$, $5/2$?
possible duplicate of Why does spin have a discrete spectrum?
Jan
27
comment Group theory and quantum optics
Worth noting that apparently "commutant" is another word for "centralizer," for those who were confused like me. Maybe this is a regional thing?
Jan
27
comment Infrared Vs Visible Light
All the close votes, and I'm not sure why. Two comments so far answer the question, so clearly they understand what is being asked (and should endeavor to make complete answers...).
Jan
22
comment Can I simply find the Christoffel symbols by dividing by $g$?
Since there are $3$ indices, there are $d^3$ Christoffel symbols in $d$ dimensions. However, the symbols are always symmetric in the lower two indices, so we usually only bother writing one of the pair, meaning you should check for $d^2(d+1)/2$ symbols, none of which should be obtained from the others by merely switching the lower indices. In your case of $d=2$, you do indeed list $6$ symbols, and they satisfy the no-reversed-indices condition, so you are good.