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location Princeton, NJ
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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).


Sep
17
comment Why does the Zodiacal light vary between dawn and dusk?
My wild guess (and I may have gotten my directions all mixed up) is that this avoids looking toward the brightest part of the Milky Way. Hopefully someone more qualified can chime in.
Sep
16
comment Notation regarding the continuity equation for conservation of mass
Mathjax supports \iint and \oint but not \oiint. In a pinch there's \unicode{x222F} for $\unicode{x222F}$, but it doesn't scale beyond inline math.
Sep
16
comment Notation regarding the continuity equation for conservation of mass
Possible duplicate: math.stackexchange.com/q/551485
Sep
16
comment What's wrong with this temperature-in-space calculation?
Fun fact: Earth would be frozen over without the greenhouse effect (and if it were perfectly conductive). Note that your factor of 6 for a cube becomes a factor of 4 for a sphere, so a cube will be colder.
Sep
16
comment Is there an alternative to dark matter?
physics.stackexchange.com/questions/tagged/… is not a bad place to start
Sep
15
comment Blowing your own sail?
@Olcayto Because upon reversing direction, the air lost all its forward momentum (pushing the vehicle forward exactly enough to balance out the backward thrust it imparted to the vehicle upon getting its initial push), and then it got more momentum going backward thus pushing the vehicle forward. The change in airspeed is greater than the original speed.
Sep
13
comment What causes the lines in these photos of a flourescent tube?
This is marginally on topic here at best, but it is definitely appropriate for photo.stackexchange.com
Sep
12
comment How to determine your position underground?
Of course the perfect uniformity assumption is wrong, but we can correct for it (barring some degeneracies due to the non-monotonic nature of the curve).
Sep
12
comment Direct observations of a black hole?
A skeptic might point out that stars' orbits tell us the mass of the thing in the center of the galaxy (4 million solar masses), but only put an upper limits on its size (45 AU), and these upper limits are technically larger than $r_s$ (0.1 AU for 4 million solar masses). That said, 4 million Suns inside the Solar System would be unimaginably unstable and bright, whereas we see almost nothing at all.
Sep
12
comment When blowing air through a tube, why does it act differently if I press the tube against my mouth, or hold it an inch away?
I wonder if there isn't also more momentum in the entrainment case. One could imagine the entrainment leading to a higher impedance so to speak, so the OP unconsciously blows harder.
Sep
12
comment Has NASA confirmed that Roger Shawyer's EmDrive thruster works?
Oh dear not these clowns again. Every name you see on that NASA paper is a fraud. Whether or not NASA has given them its blessing, no amount of bureaucratic stupidity can change the laws of physics, and the laws of physics are very clear that one cannot violate conservation of momentum as this device claims to be able to do.
Sep
11
comment Formation of atoms question
Gnatt? Do you mean Gibbs?
Sep
11
comment Basic understanding of stress tensors in a fluid
This confusion is what I get for mixing basic mechanics with differential geometry at 5 AM. In a basic mechanics sense, $\vec{r}$ is the vector from $(x_0,y_0)$ to the point on the edge where the force is being applied, and then $\tau = \epsilon_{ij} (r^i F^j - r^j F^i)$ applies without ambiguity. I'll think on how I can rewrite this all to be clearer. As for angular acceleration, that's just from the angular form of Newton's Second Law: $\vec{F} = m \vec{a} \to \tau = I \alpha$.
Sep
11
comment Basic understanding of stress tensors in a fluid
Exact duplicate of Basic understanding of stress tensors in a fluid. For future reference, we generally discourage cross-posting between sites.
Sep
10
comment Searching for Big Bang Neutrinos
@r_kramer Alternatively, imagine the universe as presently infinite. Now rewind time and contract it. If you make it half its linear size, it will be 1/8 the volume. But $\infty/8$ is still $\infty$. This holds true for any denominator you choose. No finite amount of expansion can change whether or not the universe is infinite.
Sep
10
comment Searching for Big Bang Neutrinos
@r_kramer This is something a lot of people get caught up on. I'm sure there are similar questions already asked on this site (and if none satisfy you you should post new ones). But a quick answer is that "expansion" really, honestly, only means stationary objects end up being separated by larger distances over time. This is a property an infinite space can easily have.
Sep
10
comment Is it possible to determine whether distant galaxies are gravitationally bound
Let's not forget Tully-Fisher and Faber-Jackson. I hesitate to make this an answer though - I have no experience with the practical method of determining cluster membership given incomplete data.
Sep
8
comment Equation regarding the Riemann tensor in the Cartan formalism
I don't know if you are intentionally overstacking the indices on the Riemann tensor, but in case not: $R^{\alpha\beta}{}_{\nu\rho}$ can be hacked R^{\alpha\beta}{}_{\nu\rho} or {R^{\alpha\beta}}_{\nu\rho}. The former risks breaking across line wraps, and the latter is semantically wrong, but they work in a pinch.
Sep
8
comment Is data which rides on the carrier frequency dangerous?
-1 For "substantial danger": You can strap your cell phone or wireless router to your head and crank up the transmission all you want - absolutely nothing will happen.
Sep
8
comment Measuring more accurately the distance of remote galaxies
A very good question about a subtle issue. I think this touches on the oft-neglected aspect of cosmology (which would certainly be an appropriate tag here) that homogeneity/isotropy kicks in only at a certain scale, but I'm not confident enough to turn such into an answer. By the way, there's no fixed definition of "group" - just whatever algorithm you choose to employ.