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A duck walks into a bar. Animal control is promptly called and the duck is released into a near by park.


Mar
7
revised Naive visualization of space-time curvature
added 5 characters in body
Mar
7
comment Naive visualization of space-time curvature
@StanLiou: Then you are assuming you can explain the notion of a local interial frame to a layman.
Mar
7
answered Naive visualization of space-time curvature
Mar
5
answered Do Dirac Gamma Matrices act like Tensors?
Mar
5
comment Is there a limit to acceleration?
@Carterini: Not that a factor of 2 is of any relevance if we're already speaking of $10^{51}$, but no, $2.2$ is the value you get if you plug in "(speed of light)^(7/2)/((Plancks constant)*(Gravitational constant))^(1/2)" into wolframapha and so here I bet against your back of the envelope calculuation. And I say it again, I'd just sit down and see how fast momentum can translate between two particles, say with a $\left|r_1(t)-r_2(t)\right|^{-2}$.
Mar
4
comment Is there a limit to acceleration?
Afaik, there is no slogan about maximal acceleration. You could cook up a Planckian acceleration $c^{3.5}/(\hbar G)^{0.5}\approx 2.2\,10^{51}m^2/s$, but I don't see the use for that here. Seems the latter must ask for r'' vs. W. We should maybe make it a little more concrete. Consider a particle at rest with $r_1=0$ at some time and set up a potential $V(|r_1-r_2|)$ with another particle. You can consider a) a free collision (where total momentum is constant) and compute $r_1''(t)$. b) try to compute the energy cost it takes to move the second particle in some way to push the other one.
Feb
27
revised Group of translations in two dimensions - A weird treatment
check it out
Feb
27
suggested suggested edit on Group of translations in two dimensions - A weird treatment
Feb
27
comment What's the real fundamental definition of energy?
...and call this the Lagrangian, for the map $t\mapsto q(t)$ it should read action there, alternatively you can speak about the image of that map.
Feb
26
comment Why do we use $\psi$ instead of a straightforward probability?
This thread should answer the question.
Feb
25
comment Quantum frequency vs classical frequency and Energy dependence
From the point of view that a QFT starts by setting up the states and the Hamiltonian $H\sim \nu\ a^Ta$, the QED energy is given like this and is responsible for both of course $\nu$'s. I.e. $\langle H\rangle\propto \nu$ and "$\mathrm{e}^{-itH}\sim>\sin{(t\nu)}$".
Feb
24
comment Discrete sum over a gaussian function
@EmilioPisanty: ListPlot3D
Feb
24
revised Discrete sum over a gaussian function
added 9 characters in body
Feb
24
answered Discrete sum over a gaussian function
Feb
23
comment Why is introductory physics not taught in a more “axiomatic” way?
@TerryBollinger: Doesn't the abstract S-matrix approach do exaclty that?
Feb
23
comment Why is introductory physics not taught in a more “axiomatic” way?
@TerryBollinger: Uncomfortable similarities? Stop worrying and learn to love the bomb. ;)
Feb
20
comment What is the difference between translation and rotation?
That's vague. Can you give an example for a situation where "a rotation motion corresponds to a force acting on a body towards a direction perpendicular to its velocity." and where you can make precise what the "velocity", acting "force" and "rotation" is?
Feb
19
comment Does the 1-D poisson's equation have monotonic potentials if $\rho=\rho(\phi(z))$?
@Anode: "It's no surprise that $\phi(z)=0$ in your example." What do you mean by that? The solution is $\phi(z)=a·z+b$ and these are valid for all $a,b$. The conclusion you should draw isn't that $\phi(z)=0$ follows.
Feb
19
comment Does the 1-D poisson's equation have monotonic potentials if $\rho=\rho(\phi(z))$?
@Anode: So? $\rho(\phi):=0$ fulfills $\rho(\phi=0)=0$. So I'm pointing out that for the trivial case, the concluded relation is already broken. That's a general tool for investigating mathematics: If you're skeptical of a result obtained with free parameters, go back and choose particular examples for those parameters to see at which point in the derivation the system breaks down.
Feb
19
comment Does the 1-D poisson's equation have monotonic potentials if $\rho=\rho(\phi(z))$?
For $\rho(\phi):=0$ the solution is $\phi(z)=a·z+b$ and the equation reads $0=0$. You say you "integrate up" and end up with $\frac{1}{2}a^2=0$. Magic.