40,173 reputation
355127
bio website inspirehep.net/…
location Duchy of Grand Fenwick
age 44
visits member for 4 years, 6 months
seen 9 mins ago

Experimental nuclear and particle physicist. These days I'm teaching, but I've spent a lot of time on nucleon structure in fixed target electron scattering and neutrino oscillations using reactors and beam sources.

Been reading Zemansky & Dittman's book on thermodynamics recently. Quote: ``The concept of temperature is rich in interpretations and levels of abstraction.'' Nice.


May
10
answered What does excitation in an atom mean?
May
10
comment can we have a phase transition from superconductor to the normal only by applying magnetic field?
Comments deleted here and on an answer below. Keep it impersonal and focussed on the physics, folks.
May
10
comment why is London penetration depth independent from the magnetic field strength in superconductors?
I've scrubbed a lot of comments that were verging on hostile. Two things to remember: (a) be nice and (b) you can't win the internet, so don't try.
May
10
revised Definition of “first excitation energy”?
edited tags
May
10
comment Paradox in special relativity
The only person claiming that is you, and it's a geometric impossibility in any frame. The reason the inequality you exhibit is not a problem is that you have $A>B'$ and $B>A'$. The length I measure and the length that you measure are not they same thing. A length measurement is the distance between two space-time points with the same time coordinate, and we don't agree on the meaning of "the same time coordinate". If we agree to make the measurement at the moment the leading edges of the two object are coincident we will choose different space-time points with which to compute the difference.
May
10
comment Paradox in special relativity
John, the core paradox has always been about simultaneity. Always. The tip of my craft hitting your net and the rear of my craft passing your hoop are space-like separated events so they do not have an absolute time ordering. Likewise with the question of who enters whose net first (assuming you reconfigure the handles so that their collision occurs after the rest of the fun). The resolution of the paradox has always been that the question doesn't make sense: you are asking to know the absolute ordering of space-like separated events and they don't have one. Full stop.
May
10
comment Coefficient of friction on a loop-the-loop!
Hard problem to do in closed form. Possible harder than you know. If you are worried about the time variation of the friction, then you may need to worry about the atmospheric drag as well. Good candidate for simulation.
May
9
answered Ambiguity with reaction equations
May
9
comment Why is Einstein solution to the twin paradox different from the one on the internet?
My subconscious has been niggling away at the phrase "moment of acceleration" in this context and I had a light-bulb moment tonight. Despite the olde timey feel of it, there is an elegant economy of phrase there which packs a lot of punch into a few words. Think of it in terms of a space-time diagram: acceleration is a change in the angle of the line of simultaneity, and the size of the proper-time difference implied by a fixed acceleration is proportional to the separation of the two actors. Sweet.
May
9
comment Looking for name of mapping procedure
Also this might be better on Computational Science. Would you like me to move it there for you?
May
9
comment Looking for name of mapping procedure
Unfortunately "making small tweaks to the values iteratively until no changes occur" covers a host of algorithms that rely on the convergence of <something> starting with Newton's minimization and moving up from there. Do you recall anything more substantial?
May
8
comment How to prove or disprove that elementary particle has no spatial extention?
While this answer is not wrong, it is a bit of a hodgepodge of ideas from modern physics without a unifying treatment.
May
8
comment Since the gravitational force is only attractive, why does matter not just concentrate into a small sphere?
Somewhat related: physics.stackexchange.com/q/182679
May
8
comment What does “interact via strong force” mean?
Item (4) is completely unrelated to the others, and should be removed. It is answered in part by physics.stackexchange.com/q/142303 .
May
8
answered What does “interact via strong force” mean?
May
8
comment Using Ampere's circuital law for an infinitely long wire & wire of given length
I suppose that for many cases you could assume that the wire ends on a small but finite-sized spherical capacitor, thus avoiding the need for a singularity. Then choose your surface to not intersect the capacitor.
May
8
comment What happens when an anti-proton and an electron collide with each other?
Sorry, that comment was about "sensitive to violations of isospin symmetry". I was trying to think of a use for the reaction you are asking about and comparing the weak amplitudes of $e^+/p$ or $e^-/n$ to get access to isospin violations was all I could come up with. If that is gibberish to you, then just ignore it: the first two sentences contain the answer.
May
7
comment speed of light and conservation of linear momentum
See physics.stackexchange.com/questions/2229/…
May
7
comment speed of light and conservation of linear momentum
"and thus the law of conservation of momentum doesn't apply to them" This is not correct. Even classically light carries momentum and that momentum must be accounted for to maintain the conservation rule.
May
7
revised Why is the strong nuclear force > electrostatic repulsion?
added 294 characters in body