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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).


Feb
21
comment Can walking provide electrical energy?
@Vishwa Iyer there are many ways of turning the kinetic energy of jostled objects into electricity, such as with piezoelectric crystals or electromagnetic induction (magnets near coils). The trick is to make sure the system only pumps the battery rather than discharges it, for which the use of diodes is key. The details of particular designs could probably be hashed out on electronics.stackexchange.com
Feb
20
comment Energy-momentum tensor for dust
Not that this answers your question, but the easy way to get $T^{\alpha\beta}$ for dust is to slip into the frame comoving with the fluid; note that $\vec{v}\to(-1,0,0,0)$, note that there is no momentum flux, pressure, or shear but only energy density $\rho_0$, and say $T^{\alpha\beta} = \rho_0 v^\alpha v^\beta$. As you have a true tensor equation, it must hold in all frames. QED.
Feb
20
comment Meaning of Eigenvalues/Eigenvectors of a linear system of equations
As it stands, though, it sounds like you just have each quantity expressed in terms of the other 40, without reference to inputs and outputs. What is the difference between the column vector being multiplied by $M$ and the result of that multiplication? Perhaps I'm just misreading things, as I'm also not sure where time comes into play.
Feb
20
comment Meaning of Eigenvalues/Eigenvectors of a linear system of equations
Usually such matrices represent a transformation of sorts. You have a black box that takes input $x$ and gives output $y$. You test it with different inputs. The $y$ that corresponds to an $x$ of $(1,0,0,\ldots)$ becomes the first column of $M$, etc. Once you've done this 41 times, you have the full $M$ such that (output) = M * (input). Then there are many directions to go, e.g. (1) fix an output and ask what then input must have been, (2) ask what inputs remain constant modulo scaling when acted upon, (3) ask what those scaling are...
Feb
19
comment Meaning of Eigenvalues/Eigenvectors of a linear system of equations
You have 41 equations, but it's unclear what form they have. If you were to write them out in matrix notation, it looks like $M (B_1, \ldots, B_{41})^T = (B_1, \ldots, B_{41})^T$, where $M$ is 41 by 41 and has zeros on the main diagonal? Is this right?
Feb
19
comment Notation for Propability Amplitudes
I would hope the instructor didn't just write that down in vacuo - was there some additional context?
Feb
19
comment What jobs can you get after Studying Physics at University?
While it may still be true that the subject is not important for jobs in industry, many colleges specialize far earlier than senior year. And outside the US this is even more universally true.
Feb
19
comment How are stellar and galactic ages determined?
@Lucidnonsense See the new second paragraph for Galaxies.
Feb
18
comment Why light can't go faster then 300 000 km/s? What prevents it?
I really want to say this is a duplicate of something - but I can't seem to find a well-worded question (or even many well-worded answers) on the site that deals with precisely the same thing. Everything just keeps linking back to that same addition-of-velocities on a bus thing.
Feb
18
comment If NASA could send a camera into a black hole, could we then see what's inside the black hole?
@CarlWitthoft But none of that matters. Jets and any other observables are produced outside the event horizon, by definition.
Feb
18
comment Why apply voltage on an Si detector only on atmosphere or high vacuum
I on the other hand have come across this phenomenon, in an undergrad lab in fact, where we had to turn off the detector only while pumping down to vacuum. Failure to do this would result in some unhappy equipment and an unhappy grade.
Feb
18
comment While holding an object, no work done but costs energy (in response to a similar question)
This just avoids the question. Why does energy need to be supplied in order to keep in the same thermodynamic state? One can imagine a simple model wherein the polymers in your rubber band tend to (entropically) shorten, but every time they begin down that path they are pulled taut again by a regulatory mechanism. Useful energy is turned into heat via all the little pushes required to keep deviations from tautness small. Gravity, on the other hand, alters the potentials so as to make spontaneous shortening unlikely. There is a fundamental difference.
Feb
17
comment Normal to the Hypersurfaces
$n^a \to n^c$ at the very beginning of your last equation?
Feb
17
comment Weibull distribution
For $0 < \nu < 1$ you seem to be asking for a Dirac delta function plus something else. That's a pretty tall order for just altering $k$ and $\lambda$. Or are you allowing more extreme modifications?
Feb
17
comment Is observation a component of the Lorentz transformation?
Closely related: physics.stackexchange.com/questions/59985/…
Feb
17
comment Self-adjoint and nonpositive differential operators
@MichaelScott Welcome to Physics StackExchange! As comments are somewhat ephemeral, it's always best to edit pertinent information into the body of the post. I also added the DOI link to protect against link rot, as per our (somewhat unofficial but very sound) policy.
Feb
14
comment How fast do large asteroids usually travel?
@AnthonyX You should turn your comments into answers :)
Feb
13
comment Does time exist in a vacuum?
It's a shame, but many physicists will have an immediate negative reaction to your question. If you define "time" to be the direction with the wrong sign in the metric for GR, then John Rennie's answer explains why the answer to your question is yes. If you define it based on a more limited set of observables like changing positions between objects (in the style of Leibniz, Mach, and (in his own mind at least) Einstein), the answer may very well be no. Which definition you take as "right," though, is a matter of philosophy.
Feb
13
comment What changes occur while an atom approches the speed of light?
There's nothing logically inconsistent about a universe with Bohr-style atoms obeying relativity. The OP's conceptual problem lies in Galilean vs. Lorentzian shifting of reference frames.
Feb
13
comment Gaussian Probability Distribution?
Is this the distribution that minimizes uncertainty? On that one note, Wikipedia has this to say: "The normal distribution saturates the [entropic uncertainty principle] inequality, and it is the only distribution with this property, because it is the maximum entropy probability distribution among those with fixed variance." Just don't get mixed up between information-theoretic entropy and Fourier/quantum standard deviations.