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.

18h
comment Free parameters in the Standard Model
@robertbristow-johnson: Fine, but you've then fixed a scale for everything else and made THEM dimensionless. If you allow the curvature term in the action, it either comes with a dimensionless parameter (which I abstracted to mean G, but fine), or you fix units to make it unity, and that then fixes units for everything else. It's still semantics whether that counts as a "free parameter"
18h
comment Why does $F=ma$? Is there a straightforward reason?
@garyp: a spring scale measures force only because there is a known theoretical construct relating force and acceleration. At heart, force is "amount of push", but how do you define this? You can't, without making some appeal to a deeper law. Your statement about inertial and gravitational mass belies this -- gravitational mass isn't a thing without a gravitational law. There is no a priori reason that there should be such a thing as "gravitational mass"
19h
comment Free parameters in the Standard Model
Well, properly, Newton's constant and the cosmological constant are "free parameters of fundamental physics" and not of the standard model, since the standard model does not deal with gravity. And the particle masses (or at least the combination of yukawa couplings hand the higgs VeV that determine the masses) are most definitely amongst these parameters.
19h
comment Why does $F=ma$? Is there a straightforward reason?
That equation should be the definition of either mass or force.
1d
comment Repelling a weak permanent magnet with an electromagnet
"strong enough" is really a statement about the product of the two magnetic moments, so it's hard to conceptualize one thing being strong enough, but the other one being arbitrarily weak. Put another way, for some fixed nonzero magnetic moment of the permanent magnet, there will always be some current you can push through the electomagnet that will enable levitation.
2d
comment Physics without time
@dmckee: I also think that saying that time is time-reversal symmetric is entirely different from doing without time entirely. A universe that obeys parity symmetry is hardly one in which space does not exist.
2d
awarded Nice Answer
2d
revised How small does sand have to be to get wet?
deleted 9 characters in body
Mar
25
answered How small does sand have to be to get wet?
Mar
25
comment What would it be like "inside" a star?
I'd be more concerned about radiation than I would be about matter.
Mar
25
comment Schwarzschild: Proof that $\{r<2m\}$ is a black hole
It's a choice of whether the geodesic is future-pointing or past-pointing. In the exterior region, $\dot v > 0$ is equivalent to saying that the geodesic is future-pointing.
Mar
25
revised Hawking radiation.time arrow.antigravity
edited title
Mar
24
comment What is the general proof of Earths "True gravity"?
All those things are known effects that are measurable themselves, independently of Newton's law of gravity. Their effects vary over different parts of the Earth or over the earth in different times of the year in repeatable, measurable ways.
Mar
23
comment Magnetic Force $\mathbf{B} = \dfrac{\mu_{0} \cdot i}{2\pi\mathtt{R}}$?
As a warm-up to this, I'd suggest calculating the force on a wire of length L (perpendicular to the big wire) carrying a current $i$, with the bottom edge a distance $r_{0}$ from the big wire. You will need to start from the integral form of the bios-savart law. Once you do this, how to generalize to this case will be pretty clear.
Mar
23
comment Do We Need Maxwell's Equations Since They Fail to Account for An Experimental Fact at Least in One Occasion?
@DavidZ: Fenzik's linked derivation is correct, and in retropsect, you HAVE to be able to derive the Lorentz force law from Maxwell's equation, because you can transfer energy and momentum from the charge distribution to the field, and these things are linked through the Lorentz force law -- if all you knew about was field momentum, you could derive the Lorentz force law by attributing missing momentum to the charged particles.
Mar
20
comment Flaw in Einstein's explanation of the photoelectric effect?
if you do the experiment, the effect isn't sensitive to the intensity of the light (at least until you reach some saturation point, I"m sure).
Mar
20
comment Flaw in Einstein's explanation of the photoelectric effect?
...I don't see what the problem is? The point of the photoelectric effect isn't explaining all ionization and transitions, it's showing that photons are real.
Mar
20
comment Light rays in linearized General Relativity
well, light obviously breaks those assumptions, but you can always look at the appoximate lensing formulae.
Mar
19
comment Light rays in linearized General Relativity
Don't you have to make other appeals to get your result, things like $v \ll c$, which enables you to say that $h_{00} \gg h_{ij}$ and similar conclusions about the christoffel symbols?
Mar
19
answered What observation(s)--if any--confirm that the types & concentrations of energy, which are influenced by gravity, are the same ones that cause gravity?
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