361 reputation
16
bio website
location
age
visits member for 2 years, 6 months
seen 2 days ago

Feb
14
comment Divergence of One and Two Graviton Exchanges
Both statements are just dimensional analysis. For instance that the graviton exchange between two particles goes like $E^2/M_P^2$ can be derived as follows. The amplitude is dimensionless. Since the coupling to gravity goes like $1/M_P^2$ there must be something with dimensions of [$Energy^2$] in the numerator to compensate. The only Lorentz invariant quantity with energy dimensions is the energy in the center of mass frame $E$, thus the amplitude goes like $E^2/M_P^2$
Dec
12
answered The Equivalence principle of General Relativity and the Doppler Effect
Apr
14
awarded  Nice Answer
Mar
29
awarded  Yearling
Mar
8
awarded  Commentator
Mar
8
comment Are W & Z bosons virtual or not?
very nice. I was hoping somebody would write something like this so I wouldn't have to do it myself.
Mar
8
awarded  Critic
Mar
8
comment Are W & Z bosons virtual or not?
This answer is wrong! "Virtual" particles has nothing to do with decaying quickly. There are virtual electrons and virtual photons!
Nov
3
comment Gauss' law giving zero field where field is not zero?
The field is uniform but the flux over the left face of the box is negative because the field is entering the box. The flux over the right face of the box is positive because the field is leaving the box. If you sum them you get zero. In the Gauss law, the area element is a vector paralell to the field for the right face and antiparallel for the left face and hence the minus sign.
Oct
26
comment Can two spaceships go fast enough to pass straight through each other?
The probability of collision will never be negligible as vividly shown by the fact that cosmic rays interact quite non negligibly with the atmosphere even at the highest energies.
Oct
26
comment Is there a contradiction of the theory of relativity here? — Length contraction and EMR amplitude
nope, read below. Whatever it is that you are referring by the amplitude of light, it is NOT a length and it doesn't simply contract along the direction of motion.
Oct
26
comment Is there a contradiction of the theory of relativity here? — Length contraction and EMR amplitude
My answer is as "good" as it can be using a particular set of tools. Different proofs of the same problem will highlight different aspects and in any case, that is not even the point. Another thing that's simpler is p-forms and yet most people still study the classical Maxwell equations. In the OP's message there is no mention of photons and plenty of mention to the amplitude of a laser. The question seemed to me to correspond to a typical course on classical electrodynamics and special relativity. Thus, I provided the answer in that spirit.
Oct
26
revised Is there a contradiction of the theory of relativity here? — Length contraction and EMR amplitude
edited body
Oct
26
answered Is there a contradiction of the theory of relativity here? — Length contraction and EMR amplitude
Oct
25
answered Difference between momentum and kinetic energy
Oct
24
answered Can Laplace's equation be solved using Fourier transform instead of Fourier series?
Oct
24
comment How do we resolve a flat spacetime and the cosmological principle?
A sphere was an even more obvious example. However, I think that what Jerry is trying to tell you is that, quoting your original question, there's nothing to resolve between flat spacetime and cosmological principle. The 3D spaces are tipically assumed infinite. Voilà. Edit ok, settled then, you beat me by some seconds.
Oct
24
comment How do we resolve a flat spacetime and the cosmological principle?
In any case, even if the 3D volume of the universe is finite, that doesn't mean the curvature needs to be different from zero. There are (several) compact manifolds with curvature zero everywhere. Some 2D analogues are easily visualizable like the doughnut. Curvature depends only on what is happening in a local neighborhood of the point of interest. Therefore, in first approximation, it can't have anything to do with you travelling all over the manifold and returning to the same place. Curvature at point P tells you how a vector will change if you take it around a closed path enclosing P.
Oct
24
comment How do we resolve a flat spacetime and the cosmological principle?
when you speak about the "universe size" I assume you mean the universe three-dimensional volume. Now, why would the universe be finite in volume?
Oct
24
comment How do we resolve a flat spacetime and the cosmological principle?
"If the observable portions overlap, it must be possible to continue traveling in one direction and eventually end up where you started." why?? Observers situated at the integer locations in the real line (...-2 -1 0 1...) with a horizon of 1 unit in both directions have overlapping "observable portions" and yet if you travel in any one direction you will never end up where you started.