Jerry Schirmer

Austin, TX

Age: 35

I am a Ph.D. general relativist working as a software engineer. I like to still go and do physics as a hobby, and to keep up my skill and knowledge.

38m
comment I am writing a gravity sandbox program but the energy is not constant
If reducing the timestep reduces the problem, all you're seeing is computational error. Also, try an orbit with a perigee farther from the central body, and see if the problem decreases.
18h
comment Which way do black hole jets spin?
It all depends on what mechanism for jet formation you pick. If it's just the geodesic model, then they will certainly spin -- angular momentum in equals angular momentum out, minus what is exchanged with the star.
1d
revised What dynamical system could this $\dot y = \alpha(y-\lambda), y\geq \lambda$ equation describe?
added 201 characters in body
1d
answered What dynamical system could this $\dot y = \alpha(y-\lambda), y\geq \lambda$ equation describe?
2d
awarded Necromancer
2d
comment form of manganese with highest magnetic permeability
Are you building something? You might as well just characterize it yourself.
2d
comment What is the physical significance of the negative amplitude of a light wave?
Other than "The electric force on a positively charged particle is in the negative x direction"?
Jan
21
comment Curvature gravity and a falling apple?
Done, but I do feel that John Rennie's answer is about to be better.
Jan
21
answered Curvature gravity and a falling apple?
Jan
21
comment Curvature gravity and a falling apple?
the key point is that it's not space that's curved, it's spacetime. The apple falls because the accelerating downward path through spacetime is the geodesic through curved space, rather than the "straight" hovering path through spacetime.
Jan
21
comment How to conclude that some correlation does imply causation
And "proved" is really a dirty word for this sort of thing. In physics, we typically use "proved" in the mathematical sense -- showing that if we make a set of assumptions X, then it is logically and universally true that a set of conclusions Y are true. In this sense, it is impossible to "prove" a scientific law true, because we can't do universal experiments.
Jan
21
answered How to conclude that some correlation does imply causation
Jan
21
comment What is the relativistic mass of this spinning ball?
Right, I don't expect the answer to be expressible in terms of simple transcendental functions (though it may be)
Jan
21
comment What is the relativistic mass of this spinning ball?
Now, the reason why people aren't given this as homework is the calculus is a bit non-trivial.
Jan
21
comment What is the relativistic mass of this spinning ball?
Here's the hint on how to start: you have to split up the mass into tiny regions with mass dm, and then integrate over them, so you'll have $M = \int \frac{dm}{\sqrt{1-v^{2}}}$. If you do this in cylindrical coordinates, $dm = (M/V)2\pi r dr dz$ and $v(r) = \omega r$, and the rest is just calculus.
Jan
21
revised Can $1\over 1$, $1\over 2$, $1\over 3$, $1\over 4$, etc. be calculated by the added fractions below?
expanded answer
Jan
21
answered Can $1\over 1$, $1\over 2$, $1\over 3$, $1\over 4$, etc. be calculated by the added fractions below?
Jan
21
comment Does gravitational time dilation affect apparent mass?
@AdamHovorka: In general relativity, that's not a parameter of the orbit. The full solution of the orbit is specified by an initial position and an initial velocity. The equations don't predict closed elliptical curves like the Newtonian theory does.
Jan
21
answered Does gravitational time dilation affect apparent mass?
Jan
20
comment How eliminates the general relativity the Newtonian action at a distance? By the mediation of which "carriers"?
AH. That bit is best not thought of as a gravitational wave. Think of it as a static gravitataional field that the Earth drags around with it as it moves. It orbits the sun, just like the Earth. And it's out there because it's always been out there.
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