21,448 reputation
44785
bio website
location Princeton, NJ
age 25
visits member for 2 years, 4 months
seen 29 mins ago

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.


Sep
19
comment Armageddon prevention
Re: splitting the asteroid. As I understand it, a number of asteroids, including the infamous 1950 DA are actually just loose piles of rubble. See Rozitis et al. 2014.
Sep
19
comment How long before we can take real time pictures of the flag on the moon?
Duplicate of How big should a lens of a telescope be so we can see the American flag on the Moon from the Earth's surface? and Observing lunar lander and footprints on the moon?
Sep
18
comment Is there a Fermi estimations toolbox?
Is this set of notes (by a Nobel laureate no less) the sort of thing you're looking for?
Sep
18
comment “Magic” Speed to Drive Over a Speed Bump: Myth or Reality?
"Driving faster will cause a bigger jolt." I'm reasonably certain going too slow (in my non-fancy car) over a speed bump does jolt me more. There seems to be a minimum, not at say 60 mph but more like 10-15 mph. Maybe it's my imagination, but I could believe the transfer function from my tires to me fails to dampen particularly low frequencies. Perhaps this all hinges on the definition of "jolt."
Sep
18
comment Relationship between thickness and resistivity of thin metal films, finding the characteristic thickness and the cut off resistivity
You fit two differently decaying exponentials. This might be reasonable (see for instance some supernova light curves), but maybe not. There are other ways to add parameters to complicate a single exponential (like add a linear background, or have an $x^2$ in the exponent). As Danu says, though, extra parameters should be justified physically. Also, single exponentials will look straight on log-linear plots, power laws will look straight on log-log plots.
Sep
17
comment Tensor product notation convention?
Do note that the tensor product $\otimes$ is not the same as the direct product $\times$, the latter of which is really more akin to the direct sum $\oplus$.
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 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.