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seen Jul 7 '13 at 6:03

Jul
7
comment Do photons have acceleration?
This doesn't really describe acceleration. Is there a point at which the velocity of the photon is half way between the velocity it travels through the two media? If not, the jump in velocity is discontinuous, is not differentiable, and so, cannot be described as having an acceleration.
Jul
7
comment Do photons have acceleration?
@BenCrowell: Of course. But it made for a shorter response and was only a little wrong.
Feb
9
comment Thought experiment regarding an object approaching a mirror
The entire point of relativity is that c + v = relative velocity is completely wrong. Superman will always see light coming towards him at c.
Apr
21
comment Isn't the uncertainty principle just non-fundamental limitations in our current technology that could be removed in a more advanced civilization?
Uncertainty can be described in terms of commutation relations. This may not be an answer you're looking for, but it's a pointer that it exists in the maths if you start looking for it.
Apr
21
comment Isn't the uncertainty principle just non-fundamental limitations in our current technology that could be removed in a more advanced civilization?
If a tree falls in a forest that may or may not exist, does it make a wavefunction?
Apr
16
comment Work Done by Rockets in Orbital Motion
I figured an integral here would be too much detail for the required answer. And it doesn't really matter for such a simple potential.
Apr
13
comment Work Done by Rockets in Orbital Motion
Hmm... I suppose a $g_{eff}$ would be more appropriate...
Apr
12
comment Does Polytetrafluoroethylene (Teflon) have low wind resistance?
I see. The short answer, I suppose, is no. At least not necessarily. Friction is due to microscopic factors while resistance in a fluid is mainly due to macroscopic factors.
Apr
12
comment Does Polytetrafluoroethylene (Teflon) have low wind resistance?
Note: against any solid.
Apr
12
comment Why are alpha particles made of 2 protons and neutrons?
Because "isospin" and "spin singlet" requires a good bit of background knowledge. This graph gets the point across much more effectively.
Mar
31
comment Why is light described by a null geodesic?
+1 for coord transformation.
Mar
31
comment Do photons have acceleration?
This is not exactly acceleration of a photon. The photon is still following a null geodesic, so in the frame of the light, there is no acceleration. There might only appear to be some acceleration to another observer.
Mar
31
comment How to interpret the derivative in the momentum operator in quantum mechanics?
Never assume commutativity in QM unless you're sure of it.
Mar
31
comment Why you need a graviton when you have the higgs boson?
In the linear approximation, GR predicts gravity waves, which can be described by gravitons. This explanation comes up independent of the Higgs Boson. The need for one doesn't really have any bearing on the other.
Mar
31
comment Is 4-velocity normalized to -1 even for non-geodesic timelike curves?
A geodesic, being defined as a curve whose tangent vector doesn't change along that curve (parallel transports its own tangent vector), will always return the same norm for that unchanged tangent vector. The same can't be said of other curves, because they don't necessarily have the same tangent vector at different points.
Mar
29
comment More on the Feynman Path Integral Formula in Brian Cox' Lecture and its Consequences
Comment 3: Typo. Fixed it. That line was just multiplying both sides of the inequality by $\Delta t$.
Mar
29
comment More on the Feynman Path Integral Formula in Brian Cox' Lecture and its Consequences
Comment 2: Since you've divided both sides of the equation by the same number, they're still equal. You then say this new number is less than 1, because of the inequality you had before.
Mar
29
comment More on the Feynman Path Integral Formula in Brian Cox' Lecture and its Consequences
Comment 1: $m(\dfrac{\Delta x}{\Delta t})^2 \Delta t = m \dfrac{\Delta x^2}{\Delta t^2} \Delta t$. The $\Delta t$ on the left cancels out the $\Delta t$ under the line.