32,171 reputation
343105
bio website inspirehep.net/…
location Duchy of Grand Fenwick
age 43
visits member for 3 years, 8 months
seen 1 hour 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.


3h
comment Variation in measurements of $g$ on the Earth's surface due to the Moon's gravity
My understanding is that "Earth tides" usually means the distortion of the solid planet due to the tidal driving force (which is a small but non-trivial fraction of the ocean tide), not the basic differential gravitational effect due to the finite distance to the moon. No idea which way Feynman meant it. The answers to the follow-up question seem to explain the four-bumped structure of the daily variation.
7h
comment In a neutron star - what force keeps the neutrons from getting closer and closer?
@Michael Hmmm...it's been a while since I wrote that. I have to admit that I have waffled over time on how to answer that question. There is no force carrier, but the effect can be unambiguously and correctly written in terms of a pressure. Alternately the combination of gravity and the residual strong forces (carriers graviton and light mesons) have pushed the Fermi energy too high for further compression to be energetically favored.
8h
comment How can individual photons have different amounts of energy?
This is not a duplicate of physics.stackexchange.com/questions/3541/…, but the answer is the same.
11h
comment Interaction between neutrino and an anti-neutrino?
@jazzwhiz Well, yes, but they have to be off-shell in the first place for that.
1d
comment F-mu-nu notation
Is the questions about the general meaning of tensor indicies or about the distinction between raised and lowered indicies?
1d
comment Active-sterile mixing for KeVins
"I think they call them KeVins (horrible name btw)." Egads, that is bad.
1d
comment In scattering, how does a particle 'know' which direction it is being illuminated from?
@WaqarAhmad The point is that it is not fundamentally any different. Both systems have to conserve momentum and that is what sets and communicates the axis of the interaction.
2d
comment What is it that makes an electron maintain a distance from the positively charged nucleus?
Another good duplciate: Why do electrons occupy the space around nuclei, and not collide with them? and related Why doesn't orbital electron fall into the nucleus of Rb85, but falls into the nucleus of Rb83?.
2d
comment Is this kids experiment a legitimate way to show that air has mass?
@ACuriousMind "If your experiment does not match the theory, it's the theory that's wrong, not the experiment." Or that you have a problem in your analysis. Or in your execution.
2d
comment Why are magnetic fields so much weaker than electric?
Of course @Emilio is right, but interestingly the size of the difference in the forces is a function of the mass of the particle, not it's charge. If we were to imagine a very low mass test particle--say a charged neutrino (!)--then the difference gets to be much smaller
2d
comment Woodwind instruments overtones
Closely related: Why does the fundamental mode of a recorder disappear when you blow harder?. Not sure if it a duplicate or not.
2d
comment Variation in measurements of $g$ on the Earth's surface due to the Moon's gravity
I think "diurnal" is fine. It does not imply a 24 hour period but "happening every day", so something that happen roughly twice a day is fine.
2d
comment Double rainbows
Did you notice that the "second" one was much dimmer than the first? What does that imply about the next...
2d
comment Why aren't units with powers, like cm³, surrounded by parentheses?
@Nit I've made the answer community wiki as well as sticking in GlenTheUdderboat's citation. This is just another case of a throwaway answer getting a lot of attention because the issue is accessible rather than because there is anything deep and beautiful involved.
2d
comment Is duplication of nucleus, electron and proton (sub-atomic particles) possible?
Now that we have a sense of what the questions actually is it seems that the OP has a basic misunderstanding of biology/biochemistry rather than a proper question about physics.
2d
comment Quantum Efficiency Estimation
Alternately, if you can get your hands on a few datasheets of similar devices you may be able to use their performance as a guide to your thinking.
2d
comment Quantum Efficiency Estimation
People who work with devices of that type can probably give you a rule-of-thumb value or range. For instance, I know that high-acceptance, visible-light PMTs typically run between 0.1 and 0.3 (depending on how much you paid for them) simply because I have had repeated encounters with them over the years.
Jul
28
comment Double slit experiment with slit material acting as a detector
It is not at all clear to me what you are asking. Recording particles that don't pass the slit is possible but not very enlightening.
Jul
27
comment Is this air cooling idea feasible?
@thyme Evaporative coolers are still used in some dry areas (I had one for a few years in southern New Mexico). They really do cool the air as well as moistening it as long as the air is dry enough. The air is forced through the fiberous pad continuosly so there are two competing effects: the pad is cooled by evaporation and warmed by contact with the air. The result is an output that is both cooler and moister than the outside air. When the humidity rises much above 30% they start to get a lot less efficient, but in that part of the world it is often 10-15%.
Jul
27
comment How would an X-ray mirror work?
For what it is worth, a lot of the radiation worry on space voyages comes from massive particles of various sorts.