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Apr
15
comment Were Michelson-Morley results a surprise?
@Marco: Historical accuracy aside, they had this line of thought along these lines: "Maxwell's equations require Lorentz invariance. Lorentz invariance is wrong. Thus we expect to see violations of Maxwell's equations".
Nov
8
comment Do Events Take Place Inside Black Holes?
@JohnDuffield: IMO that's a misleading description, since it's the Schwarzschild coordinates that gives that depiction of events.
Nov
5
comment Dirac notation - specific acting orientation for operators
I have to disagree with this, strongly. The action of a linear transformation on a covector is defined to be compatible with its action on vectors; the only potential source of confusion is if you do things like mix up vectors and covectors or mess up the translation back to non-braket notation. And even then the notation helps you; when translating $\langle u | T | v \rangle$ only one of $uT$ and $Tv$ makes sense. (which one depends on your convention of whether linear transformations act on vectors from the right or left)
Oct
10
comment Why does rolling down opposite windows create a breeze?
While this clearly depicts what happens, it doesn't depict why it happens that way; e.g. why doesn't version 2 have an inward arrow on the bottom just like version 1?
Oct
10
comment Why does rolling down opposite windows create a breeze?
That the motion of the car causes a pressure high in front and a pressure low in back was exactly the thing I was missing!
Oct
10
awarded  Scholar
Oct
10
accepted Why does rolling down opposite windows create a breeze?
Oct
10
awarded  Student
Oct
10
asked Why does rolling down opposite windows create a breeze?
Oct
7
awarded  Teacher
Oct
6
answered What happens if locally manifold is seen as an Euclidean space?
Oct
5
comment Interpretation of the Dirac-measure property
The quoted argument is bad. $\delta'(t)$ vanishes everywhere except at $t=0$, however the values of $f$ away from zero do matter: usually, $f(t) \delta'(t) \neq f(0) \delta'(t)$. (in fact, $f(t) \delta'(t) = t f'(0) \delta'(t)$)
Oct
4
comment What really is a Dirac delta function?
It's a point that's annoyingly often left implicit, but $\lim \int \delta_i(x) f(x) \, dx = \int \lim \delta_i(x) f(x) \, dx$ is true if the right hand limit is meant as a limit of distributions.
Oct
4
comment What really is a Dirac delta function?
@HDE: While true, the physics context suggests the theory of Schwartz distributions is the right answer, rather than other notions of generalized function (e.g. measure theory) that could be used instead.
Sep
16
comment When I boil a kettle, what stops all the water from turning (exploding!) in to steam in one go once it reaches 100°C?
It's not that water at 100°C boils -- it's that at 100°C, water prefers to vaporize when heated, rather than get warmer.
Aug
31
comment Intuitive definition of electromagnetic field
Definitions are for putting words to ideas. They can't teach you anything on their own.
Jul
12
awarded  Commentator
Jul
11
comment Need mathematical explanation for different musical notes sound different on different instruments
This is a question of physics, or maybe biology, not mathematics.
Jun
6
answered Thought experiment - would you notice if you fell into a black hole?
Jun
1
comment How electrons move so fast in a electric circuit?
@paul: That doesn't mean any individual electron ever drifts over a distance anywhere near that size. In fact, wikipedia says that they only travel a couple micrometers.