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location Princeton, NJ
age 26
visits member for 3 years, 1 month
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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.


Aug
20
comment Effective theories and unbounded operators
A theorist might see this as an argument against ignoring parts of the spectra of operators. On the other hand, an experimentalist (and even a logical positivist) could take this as an indication that $x$ and $p$ are pretty bad operators to be working with.
Aug
20
comment What the lifetime of a massless black hole of photons?
You cannot point to any place and say "aha, here is the mass!" -- Just as you couldn't do the same for the original system of gravitationally interacting photons. In fact this sort of concept of properties only defined for a system predates GR -- you can't locate the potential energy of a system of interacting particles, nor can you pinpoint where the entropy of a gas resides.
Aug
19
comment How “large” is a Lagrange point?
@Kyle True in the sense of sitting stationary at a Lagrange point. But as long as the mass ratios are within tolerance, L4 and L5 will be dynamically stable -- there will exist bounded planar orbits around them, taking into account not only gravity and centrifugal force, but Coriolis force as well (which can't be incorporated into an effective scalar potential).
Aug
18
comment Why is the Hamilton-Jacobi equation important?
We already have $F = ma$, so by your reasoning Lagrangian and Hamiltonian mechanics are also unneeded. I may be able to cook just about anything on a stove, but sometimes it's nicer to work with a toaster or a microwave.
Aug
18
comment Why isn't spent nuclear fuel used as a heat source?
If it actually generated a "tremendous" amount of heat, it wouldn't be spent, by definition. Also, nuclear waste explodes less than nuclear power plants, which don't explode at all.
Aug
17
comment Where is the Hydrogen the Sun consumes?
@Steve 74.9% hydrogen and 23.8% helium, by mass. This is about what you find for everything in the universe except rocky planets like Earth.
Aug
16
comment What is the utility of ADM decomposition of the space-time metric?
@Danu It's not just computers, but science and human experience too, that is based on evolution in time. Without separating out time, we lose any notion of prediction as far as I can tell.
Aug
15
comment What happens when breaking simultaneity leads to different outcomes?
@1110101001 Feel free to answer your own question :)
Aug
15
comment 3D Simulation Software
Indeed, the programs you've tried are rendering programs, not simulators. (And game "physics" engines are in no way related to real physics.) Even if you were happy with their treatments of units, you should not trust their results to match the real world.
Aug
14
comment Halley's Comet as a “Free Taxi”
@GoodChessPlayer No, because the exact same mass you want to account for appears in Newton's second law as well. Thus the acceleration on the probe, which is all we need to determine its subsequent motion, is independent of its mass. This is the same reason a feather and a hammer fall to Earth at the same rate in vacuum.
Aug
12
comment How does uncertainty/error propagate with differentiation?
Also, while this is good (+1), I think the OP's problem is that $\Delta t$ is small so the uncertainty in the derivative is large (as it should be, since noise will add more to the slope). But this is all assuming just 2 points. Since the OP must have more points to be fitting a spline anyway, perhaps they should be fitting a (differentiable) model to the full dataset rather than to every adjacent pair of points.
Aug
12
comment Restrictions on theories which describe particle which is the dark matter candidate
@AcidJazz "Lifetime" refers to mean lifetime or half-life, i.e. how long its expected to live. Not how long it has lived.
Aug
12
comment Restrictions on theories which describe particle which is the dark matter candidate
@AcidJazz For something created billions of years ago to be around today, it either (1) can't decay (the proton), (2) decays over a very long time (uranium, some proton models), (3) is being newly created (carbon-14), (4) is stabilized by being in bound structures (the neutron), or some combination of the above. If we think 3/4 don't apply to dark matter, we are left with 1/2.
Aug
12
comment Definition of Sievert (Sv) unit - is it whole body mass?
Note that, in the regime where risk is proportional to exposure, it makes sense to normalize by only the exposed mass, since overall risk is also proportional to exposed area. That is, if a given amount of grays/rads is absorbed, you want the equivalent dose in sieverts/rems to be the same whether it was a large exposure over a small area or a lesser exposure over a larger area. This is why the USNRC can say "For practical purposes, 1 R (exposure) = 1 rad (absorbed dose) = 1 rem or 1000 mrem (dose equivalent)."
Aug
11
comment How to understand the lifespan of large-scale cosmological structures?
Wouldn't the SR effect be of a similar magnitude? We go around the Sun at $10^{-4}c$, so you'd expect $\sim10^{-8}$ deviations of $\gamma$ from unity.
Aug
11
comment Can there be eternal stars?
Note that many cosmologists don't study anything as small as even a galaxy. Cosmology certainly isn't concerned with anything as small as the workings of a single star.
Aug
9
comment Finding the configuration space and degrees of freedom of spherical pendulum
Note that $S^1 \times [0,\pi]$ is not entirely the same as $S^2$. Describing the configuration space as the former is only correct insofar as using polar coordinates is correct (i.e., only as long as you don't care that you introduced unnecessary coordinate singularities).
Aug
9
comment Do anodes emit virtual photons representing their positive electrostatic potential?
I think the question here is what mechanism allows the electrons to "know" there is a positive terminal at a distance toward which they should be moving.
Aug
9
comment Why is there no formula for some energies?
The troubling subtext here is that you seem to be focused on formulas, and you might even be thinking there is a one-to-one correspondence between physics vocabulary words and physics formulas. This is really just not the case -- formulas are just another method of communicating ideas. Sometimes there are 15 formulas for a single concept, sometimes it's hard to point to any.
Aug
9
comment Infinite dimensional manifolds in general relativity
Manifolds in GR aren't just finite-dimensional, they're 4-dimensional. Sure you can go from 4 to $\infty$, but why would you? In QM you can easily construct physical scenarios for any finite dimensionality of the Hilbert space, so it's no surprise to make the leap to $\infty$. But our universe is simply 4-dimensional, and any other dimensionality you come up with is pure differential geometry, not GR.