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459104
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location Princeton, NJ
age 26
visits member for 2 years, 11 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.


May
26
comment Perfect fluid and Cauchy momentum equation
I'm pretty sure $\nabla_\mu(\rho u^\mu) = 0$ is the correct continuity equation. It holds in arbitrary spacetimes for any perfect fluid with conserved rest mass density $\rho$.
May
25
comment Confusion about two forms of connection coefficients
While you could use the same dummy index in multiple locations (e.g. $g_{\alpha\beta} g^{\beta\gamma} + \Gamma_{\alpha\beta}^\gamma X^\beta$), this is a bit risky, and might lead to mistakes later on.
May
24
comment Confusion about two forms of connection coefficients
Yes, you can always replace all occurrences of an index with another one that is not already in use.
May
23
comment Confusion about two forms of connection coefficients
Hi Sayan Datta, and welcome to Physics Stackexchange! Note that we support LaTeX-style MathJax for math formatting. You can click "edit" to see how I formatted your equations if you're not familiar with the syntax.
May
22
comment What speeds are “fast” enough for one to need the relativistic velocity addition formula?
I've heard the centimeter-level precision claim too, though I can't fathom how they deal with the varying light travel time though a dynamical atmosphere to the point where GR becomes relevant.
May
21
comment Number of significant figures
Nitpick: In a digital instrument where there is no doubt the displayed digits are correct, the discretization error is $1/\sqrt{12}$ times the scale step, not $1/2$, if you're going for the standard deviation.
May
20
comment What would happen to the human body if we went almost at the speed of light?
possible duplicate of Would travelling at relativistic speeds have any impact on human biology? and What happens to body chemistry at the speed of light?
May
6
comment Magnetic monopoles and special relativity
In relativity, B is not a vector field, and monopoles are extremely unnatural (they are the diagonal terms in an otherwise antisymmetric tensor). This whole "just add a monopole to Maxwell" philosophy only works accidentally in non-relativistic settings.
Apr
30
comment Is “eco” shower mode actually using less power?
I think this is very much a physics question at heart: can the energy used to heat water vary by using more heat sources at a lower temperature?
Apr
30
comment What is third cosmic velocity?
@JohnRennie I think the OP just means "studying a chapter about <lowercase> gravitation," since "third cosmic velocity" is not an actual term and certainly appears nowhere in MTW. Perhaps it's a literal translation from some other language.
Apr
21
comment Why U235 over U238?
I guess so, but for all I know some grad student somewhere manipulated 30 pages of QFT symbols to show heuristically that this is to be expected. And even if not, the result should be calculable in principle if not in practice.
Apr
17
comment What are the tidal effects of Io on Jupiter?
"But I think the effect is more complicated than that, affecting the isosurface of equipotential" -- honestly, altering the equipotential surface is all tides directly do. On Earth's oceans, the presence of the continents together with the thinness of the ocean hampers the response to this forcing, resulting in complex patterns as detailed here, but I can't see this mattering for Jupiter.
Apr
17
comment Ratio of two RMS values in recorded audio
Questions simply about volumes are certainly physics, though when you start mixing in human perception (dynamic range), this becomes less clear. For similar questions, note there is a sound design beta site that might be more appropriate.
Apr
16
comment Is it possible that Mercury collided with Earth, thus creating the Moon?
@BowlOfRed Well, Mercury is easily tugged by the other planets. For example its orbit is precessing at a good fraction of a degree per century relative to an inertial frame. And it has been proposed that its orbital parameters vary chaotically on very short timescales (for example having no eccentricity some times).
Apr
15
comment Can the event horizon save conservation laws for black holes?
The information paradox is a lot more subtle than often presented. In particular, even if you can account for all the information at the end and the beginning of the process, I think there is an issue in the middle. Most of the Hawking radiation comes out at the end of the black hole's life, when the hole itself is already too small to contain much information. Perhaps someone can fill in the details in this line of thinking.
Apr
14
comment Does air density influence a football player's ability to “bend” the ball?
@wim Yes. I meant 11.
Apr
14
comment Which lamp is brighter, the one through which electrons flow or current
I don't know why this has sparked such a negative response, and I certainly don't understand the cries of homework. There is I think a misunderstanding here, but it is very subtle, revolving around the difference between steady state and transience in a circuit.
Apr
13
comment Expectation value of Commutator of Hermitian operators
@user40330 It is good practice to edit questions that have been placed on hold, in order to make them better. That said, I still don't see what is actually being asked here.
Apr
11
comment Are the Voyager spacecraft rotating in space or are they completely still?
Those are extreme time lapses caught on 1960s-era cameras -- the video quality is what one would expect. And as for engines, you don't get billions of kilometers over the span of decades by constantly running some noisy engine; you simply aim for planets in just the right way and let gravity handle the rest.
Apr
10
comment The actual space curvature
Paradigm shift? I don't know of any credible evidence against homogeneity. Just lots of pet theories looking for zebras (new physics!) among horses (galaxy clusters).