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location Princeton, NJ
age 25
visits member for 2 years, 8 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.


Jan
5
comment What does 1714 mean in hydraulics?
The same thing occurs in any unit system. You could measure lengths in meters on one side of the equation and in light years on the other side, and then the dimensionless (but not equal to 1) quantity $(1\ \mathrm{ly})/(1\ \mathrm{m})\approx9.5\times10^{15}$ will probably appear somewhere in the equation.
Jan
5
comment What does 1714 mean in hydraulics?
@Dennis The problem is that $1\ \mathrm{HP}$ is not the same magnitude as $(1\ \mathrm{psi})(1\ \mathrm{gpm})$, even though they both have dimensions of $\mathrm{(mass)(length)^2/(time)^3}$. You could use Imperial units such that $k = 1$; one such way is to measure pressure in psi, flow rate in cubic inches per second, and power in inch-pounds per second.
Jan
5
comment When did people start to regard “time” as a physical quantity?
It's not clear to me the whole "5 senses" thing is accurate either cognitively or historically. Certainly there is a sense of time, and philosophers hundreds of years ago (and maybe thousands of years ago; I'm less familiar with the literature) had no problem saying it was natural to perceive the passage of time and to order things in time just as they are located in space.
Jan
5
comment Does the stationary object deform more than the moving one after a collision?
@Nagora Has it right (and this was known to be true many centuries before Einstein). By the way, AlJo, the way comments ping people is complicated, but note I only saw your message above coincidentally.
Jan
5
comment Walter Lewin's physics lecture 8.03 Waves and Oscillation
@alarge I'm aware of the backstory. As Kyle Kanos said, it's an issue of whether we become a "please give me this file" site, copyright and lecture quality aside. This can always be brought up on Meta for further discussion.
Jan
5
comment Walter Lewin's physics lecture 8.03 Waves and Oscillation
I'm voting to close because we are not a file-sharing service, though I don't know how much precedence there is on this. We'll see what the rest of the community says.
Jan
4
comment Why do the errors in a formula depend on how it's written?
@DevgeetPatel You seem to be under the same (wrong) impression that sparked the question Why propagation of uncertainty is linear? I don't know who's out there teaching everyone the wrong formula for error propagation, but you should be aware of the right way to calculate these values. This won't make your problem go away, but as it stands you aren't really calculating any statistically meaningful quantity.
Jan
3
comment Is the change in cochlear potentials dependent on perilymph velocity?
This question appears to be off-topic because it is about the biological particulars of the human ear. Physics can solve abstract models inspired by living organisms, but it is biology that is tasked with developing those models.
Dec
30
comment Tensor Product vs. Direct Product for three spin-1/2 particles
Related: Should it be obvious that independent quantum states are composed by taking the tensor product?
Dec
30
comment Tensor Product vs. Direct Product for three spin-1/2 particles
tex tips: \mathbb{C} has got to be faster than finding a character to copy and paste, and similarly for \otimes, \oplus, \equiv, and \in. | doesn't always have the same spacing rules as \lvert, only the latter of which is an actual delimiter, and \hbar and \sigma typeset differently from (i.e. better than) ħ and σ in MathJax. (+1 on the content though.)
Dec
27
comment If neutron would be lighter by 1 MeV, how stability of Hydrogen could be changed?
Presumably you meant the decay reaction $p \to n + \bar{e} + \nu_e$? (Note also electron capture would be $p + e \to n + \nu_e$.)
Dec
27
comment In physics, what is the importance of distinguishing between a matrix and a group?
You're not the only one to list the closure property, but it is certainly unnecessary given the definition you provide of a binary operation on $G$. If we have $* : G \times G \to G$, then automatically we know $a * b \in G$.
Dec
26
comment How is the Horizon Problem really a problem?
@Wood Don't worry, I at least understand your concern. But I've searched for years without finding a satisfactory answer, instead just seeing the same unjustified dogma repeated over and over. If you don't get a good answer over the next few days, feel free to ping me, since I would probably put my own bounty on the question then.
Dec
26
comment Exoplanet Mass-Radius Diagram
That diagram is from a paper that is seven years old. You might be interested in playing around with exoplanets.org, where you can make more up-to-date plots like this.
Dec
24
comment I was told that if the Moon had a retrograde orbit, tides would have a faster rhythm. Why is that?
@User58220 Yes. Most major bodies in the Solar System rotate and revolve clockwise as viewed from Earth's South.
Dec
24
comment What is “special” and what is “general” in Relativity?
"you can't find more physics in a theory by allowing more general coordinates and frames" -- agreed. But that doesn't mean SR can handle arbitrary parameterizations of flat spacetime, which is almost what you seem to imply. At least, when people speak of SR my mind jumps to the Minkowski metric, not Minkowski spacetime in arbitrary coordinates. The latter isn't as rich as full GR, admittedly, but at the same time I'd hesitate to call it strictly SR. (I'm not downvoting by the way, just pointing out a slight difference of opinion on terminology.)
Dec
23
comment What do units like joule * seconds imply?
This isn't a physics answer, but an English one, so I leave it as a comment. Division seems natural to you, but I contest this is a quirk of the English language, which has the words "per" and "for each" but not multiplicative analogs. Really, though, "12 eggs for each carton" is a way of saying "X, where X times 1 carton equals 12 eggs." In fact I've seen opinions that division is naturally conceived as multiplication with a variable factor and a fixed product. Multiplying units is so natural we never came up with English phrases to encapsulate the idea.
Dec
23
comment How would a fractal refract light?
While one might hope that simple ray optics -- regardless of its absolute correctness -- is internally consistent even in the presence of fractal surfaces, I'm not sure we're that lucky. Before considering something really complex, think about a perfect 0-width ray hitting a perfect convex corner in a mirror, right on the corner. Which way does the ray go? Alas it's not defined, since the normal to the surface is not defined at corners. A fractal just makes things worse, with normals failing to exist possibly on sets of measure greater than 0.
Dec
19
comment Lightning strikes the Ocean I'm swimming in - what happens?
You never did fix what Mark was taking about. If $R = \rho L/S$ is the resistance of one such wire, then the current through that one wire is $I_\mathrm{wire} = V/R = VS/\rho L$. Then the current through your body is $I_\mathrm{body} = (A/S) I_\mathrm{wire} = AV/\rho L$. In particular, $S$ must drop out of the final formula, since the current in a continuous medium shouldn't depend on how you imagine chopping it up. Moreover, the proper calculation involves integrating $\rho/r^2$, which diverges unless the lightning strikes an extended area.
Dec
18
comment What is the average mass of galaxies according to Hubble Deep and Ultra Deep field observations?
@AbanobEbrahim Your (1) could be quite difficult. Where do you make the low-end cutoff? For a warmup, how many satellite galaxies orbit the Milky Way? This number was revised not long ago, and is still debated. And what is a galaxy anyway? Do you count globular clusters?