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Dec
8
comment Why is uncertainty divided by $\sqrt{3}$?
Except if the ruler has tick marks every $b-a$ and you are saying all you know is that the true value is uniformly in this range, the uncertainty is $(b-a)/\sqrt{12}$. This is called discretization error and the $\sqrt{12}$ is a standard result. Saying it's $\sqrt{3}$ off from $(b-a)/2$ is, well, bizarre, since $(b-a)/2$ is meaningless.
Dec
5
comment I don't see that general relativity is really needed for GPS to work correctly
@Danu If you read the only correct answer on that page you'll note that the necessity of GR for GPS is a complete and utter myth.
Dec
2
comment Why do astronomers call all elements heavier than helium “metals”?
Those most prominent signatures being something like the Fraunhofer lines.
Dec
1
comment Can sugar be affected by a magnetic field?
@KRyan We do hold that ideal too, but perhaps we grant a little leeway only in the case of links to Wikipedia. Many users here in fact take Wikipedia as a starting point of minimum assumed knowledge -- we have no desire to compete with the definitive knowledge base on basic concepts.
Nov
30
comment Turbulent spacetime from Einstein equation?
@tpg2114 Unfortunately vanishingly few people know both the Einstein and Navier-Stokes equations, but they're not terribly different. Their orders and degree of nonlinearity are the same. The big difference is that relativity has no good notion of diffusion; the equations are purely hyperbolic with elliptic contraints. As such, one would imagine "turbulence" to be quite commonplace, though I've never seen it described as such.
Nov
29
comment Compute affect of a shower on density altitude
As a non-pilot, I must say I had never heard of density altitude before. Makes sense, since who else but pilots would measure density or pressure in terms of how high you would have to fly to experience them?
Nov
28
comment The final parsec “problem”
Jupiter isn't going to fall into the Sun. But if there were 20 Jupiters within 5 AU of the Sun, many of them would fall in.
Nov
28
comment Safest place to store a laptop in a car?
I don't think we can reasonably give car safety advice here.
Nov
28
comment The final parsec “problem”
At very large distances it's dynamical friction, not gas drag, that brings black holes together. Also, a large swarm of black holes would be incredibly dynamically unstable -- very rapidly, some would be ejected while the rest merged.
Nov
28
comment Mutual or same set of eigenfunctions if two operators commute
For part 3, replace "B" with "the identity" and see if there's still no sense to be made ;)
Nov
27
comment Pulley Friction
I'm confused. Usually we assume the pulley has no internal friction as it rotates about its axle. But the friction between the pulley and the rope should be arbitrarily large to ensure the rope doesn't slip. So which friction is being referred to here?
Nov
27
comment What are some ways to justify the Einstein field equations?
@AGML It's being downvoted because it's devoid of anything right, and is just a collection of at best meaningless words. Unfortunately for every one person who is impressed by such expositions, it takes five of us experts to issue enough downvotes to counter the reputation gained.
Nov
25
comment Rocket altitude
This only works for ballistic rather than powered motion (so the engine has to explode instantly on the launchpad) and also only if air resistance is ignored (so at the very least the rocket can't use a parachute to land).
Nov
25
comment Does the International Space Station always travels in the same path?
More specifically, it's in an inclined low-earth orbit.
Nov
25
comment Is there any aspect of an explosion resulting from a nuclear weapon test that cannot be simulated using super computers?
It's not entirely clear what aspect of a nuclear weapon you are asking about -- the triggering or the explosion? The only reason we do tests or experiments is to check that the components of the bomb properly initiate an explosion. Stockpile stewardship is very much concerned with the breakdown of electronics and chemical triggers in the vicinity of radiation. On the other hand, pencil and paper are more than sufficient to determine how effective an explosion is; you need neither an experiment nor a computer.
Nov
25
comment Most stationary object in the universe
Not sure why there is such a bad reaction to this question. It's a natural thing to wonder about. Moreover, to everyone saying there's no way to compute something like this, it should be pointed out that there is a preferred reference frame in our universe, that of the CMB, and we have measured our motion with respect to it.
Nov
24
comment Proof of conservation of energy?
The question was whether there was a general proof for all situations, but this just gives a specific example (and no proof of it).
Nov
23
comment Drawbacks of single-field inflationary models with $\phi^2$ or $\phi^4$ potential?
"existing models of inflation ... explain observations perfectly" -- citation needed. Note too that inflation was born a purely retrodictive theory; the point was not to confirm predictions with observations, but to be more aesthetically pleasing in the eyes of its creators, and some people find other models of inflation more aesthetically pleasing.
Nov
22
comment What is the sum of the angles of a triangle on Earth orbit?
Essentially the same as physics.stackexchange.com/q/196754
Nov
19
comment How we can detect a magnetic monopole?
I'm inclined to not close as a duplicate, since this gives a very specific line of reasoning that would seem to preclude measuring them in principle, while this other question is about practicality.