41,372 reputation
356133
bio website inspirehep.net/…
location Duchy of Grand Fenwick
age 44
visits member for 4 years, 8 months
seen 13 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.


16m
comment How is intensity defined for quantized EM fields?
I suspect that you are thinking of classical waves, in which case the equation you exhibit has the integral already evaluated and it would be much better to use the $\equiv$ on the line in which the integral appears. What you've got is the result under certain assumptions (i.e. a harmonic wave), not the definition. Look at the interpretation of the kernel of that integral and the answer should be very clear.
22m
comment Shawyer EM Drive — Momentum Conservation Violation
There was some discussion of this matter in the h bar (our main chatroom) earlier today. Be aware that it is interspersed with some non-physics content in the way such things often are at the local watering hole.
2h
comment What causes this IR emission in UV 365nm LED?
Most green laser pointers are actually IR with a frequency double. Or so I've read. Might be connected.
2h
comment What force causes massive objects to bend space?
"The visualization of gravity as shown by this video is pretty good at explaining how massive objects bend space" If that the the usual #@&*(#%&*(#% rubber sheet, then I say: no, it's not; it's rubbish. And the question that you've developed here is only one of several reasons for it's being junk.
3h
comment Graviton saturation, alternative explanation of galaxy rotation curves?
Magnus, that is a question for Computational Science.
3h
comment What are mesons and leptons?
Non-answer converted to a comment and meta-discussion purged from the comments.
3h
comment How do rotation counter-weights work?
Have you computed the sheer stress on the vertical member in the absence of the counter weight? What about at the joints at either end of that member? This is basically an engineering concern.
3h
comment How can I add dark matter to my N body simulation?
The fact that the density profile of the regular matter and that of the dark matter differ shows explicitly that the differences in physics are important. The effects are small, but they work inexorable and continuously in the same direction so the differences build up over time.
3h
comment how tough is research work?
The answer is---of course---it is exactly as hard as it needs to be to displace someone who would otherwise have [beaten you to the paper|thought of that first|gotten the position]. So, the question to ask yourself is "Are you competitive with the most able of your peers who want the same thing?". And watch out for the dunning kruger effect when you go to answer that: look for objective measures. Short version: research positions are very competitive.
5h
comment Graviton saturation, alternative explanation of galaxy rotation curves?
I'm assuming that this is related to the trouble that you are having with your simulation, but it is way, way too early for that. First law of debugging: it is always your own damn fault until you can prove to the duck that the problem might lie elsewhere. In this case, both a strong set of unit tests and some "hard" few-body simulations used as regression tests are needed.
5h
comment How can I add dark matter to my N body simulation?
Magnus, did you understand what @Chris said when he asked about the behaviors of the particles in your simulation and about dark matter being pressureless? This is important because a naive simulation based on $N$ gravitating but otherwise non-interacting particles simply doesn't include all the right physics of the ordinary matter. Other question for you: have you validated the physics-engine on 2-body runs? Have you done so in runs that include very close encounters (so that the duration of close approach is less than a time-step? Possible alternate site: Computational Science.
19h
comment Does an ice cube change its core temperature as it melts?
@Frisbee Certainly not the question from the text, but in general the things we tell introductory students can leave them with an incorrect impression about the question in the title.
19h
comment Does an ice cube change its core temperature as it melts?
Concerning the units, see meta.physics.stackexchange.com/questions/15/…. This site is run by people in the US and hosted in the US, but I doubt very strongly that the Stack Exchange team would want to have the network considered as being US centric. It's a big internet out there.
23h
comment Does an ice cube change its core temperature as it melts?
To answer this question exactly, one needs to know how quickly heat is being transferred to the subject. The rules that are generally taught in an introductory course contains the (sometimes hidden) assumption that the heat transfers slowly compared to the time needed for conduction throughout the system.
1d
comment Is momentum an invariant?
This is in no way related to the meaning of the word "invariant" used by relativists.
1d
comment Speed of the train is faster than a car, why?
Er ... one is going faster than the other? Beyond that it is engineering and policy and human performance limits and costs issues, none of which are physics.
1d
comment Is momentum an invariant?
If the nature of the quantity is not clear in you personal, look-how-much-of-a-purist-I-am-I-write-move-complicated-notation-than-you-do way of writing things, then perhaps you should reconsider. Seriously, with as much effort as you put into writing things you have managed to obscure whether you mean the 3-vector, the 4-vector, the magnitude of the 3-vector or the magnitude of the 4-vector. Only one of which invariant, and that is properly called the mass.
1d
comment What do light wave oscillations look like?
physics.stackexchange.com/questions/160042/… physics.stackexchange.com/questions/192365/…? physics.stackexchange.com/questions/163298/…? and I know there were more.
1d
comment Optics phenomenon with my glasses?
Another search term of interest is "chromatic aberration".
1d
comment Inelastic cross section derivation
"The author simply assumes $\vec{p}_1=−\vec{p}_2$ for the momentum of the particles after collision" This still for a two-particle final state and evaluated in the intial-state CoM frame? If so, think a little on the matter. It should be pretty clear, why.