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seen Jan 10 '12 at 15:28

Oct
3
comment Is it true that quantum mechanics technically allows anything to happen?
You know, to me this is actually an interesting question, which it will take some precision and subtlety to discuss properly. As an aside, what is the level of education of the questioner, and his/her friends? I have known a least one biology Nobel Laureate who disagreed with me about this. A way of restating the question might be, "Are all quantum mechanical propositions necessarily probabilistic?" Lederberg said yes. I very much appreciate the comment below, that events with 0 measure could also actually happen.
Sep
10
comment Why are the antimatter compositions of neutrons and protons different? Why by about 1%? References?
I assume that as well as gluons, a considerable amount is also carried as kinetic energy of the various particles. I would accept these two answers, but would like to first ask some "ab initio" people for their results, which may be better because of all the nonlinearities at the low quark energies involved. By the way, how low is that in nuclear matter at rest?
Aug
23
comment What are the average matter, antimatter, and binding energy composition of protons and neutrons?
Having read a (very) little, I now assume that the 0 momentum limit will require ab initio calculations because at 0 momentum the situation is highly non linear and non peturbative approaches must be used.
Aug
23
comment What are the average matter, antimatter, and binding energy composition of protons and neutrons?
Thank you for this very patient and helpful answer, which teaches me much. Is there anyway to extrapolate this down to 0 momentum probes, e.g. nucleons in a glass of water? Does nuclear structure in the higher elements change the zero momentum limit situation much? For the zero momentum limit, are we forced back to ab initio calculations?
Aug
22
comment What are the average matter, antimatter, and binding energy composition of protons and neutrons?
Here is an example of the type of answer I was looking for, from quark.phy.bnl.gov/~pisarski/talks/Colloquia/Fodor.pdf (last slide) "95% of the mass of a proton comes from the kinetic energy within the proton: very different from any other mass" The standard model of particle physics (most particularly the theory of strong interaction, QCD) can explain this phenomena via a full ab-initio calculation of the masses. (controlling all systematic uncertainties)
Aug
21
comment What are the average matter, antimatter, and binding energy composition of protons and neutrons?
This is rather beyond me, but don't I want something like lim(scale -> infinity)
Apr
6
comment How does ATP transfer energy to a reaction?
I think you actually measure the enthalpy at constant pressure and temperature. It is then closely related to the entropy. This really requires a physical chemist. I believe
Apr
6
comment How does ATP transfer energy to a reaction?
I think you actually measure the enthalpy at constant pressure and temperature. It is then closely related to the entropy. This really requires a physical chemist. I believe
Apr
5
comment How does ATP transfer energy to a reaction?
Finally, I think you are confusing the free energy changes of the reaction with the free energy of activation. The hydrolysis of the ATP provides the first to make the reaction products more likely than the substrates, the enzyme or catalyst lowers the second to increase the rate. They are different.
Apr
5
comment How does ATP transfer energy to a reaction?
b) I just meant that there are many different mechanisms of catalysis, even when ATP is involved. You have to find out about each one individually, by searching under "reaction mechanism", or "active site". Different enzymes use fundamentally different mechanisms. c) You seem to be mostly asking about reactions in which the high free energy in ATP is transferred to another high free energy bond in another reaction product. Is that right?
Apr
5
comment How does ATP transfer energy to a reaction?
a) This is very rough, but it's the same idea as why gas molecules fill out a room, rather than stay, by chance, in one corner. There are many more ways of distributing the free energy when it's divided up into small packets, than when it's all concentrated in the one bond. So it is vastly more likely that the macrostate looks like the energy packets diffused all over. The logarithm of the number of ways (microstates) is the entropy.
Apr
4
comment Does quantum mechanics allow us to formulate causally sufficient conditions for the occurrence of an outcome?
I think (guess, really) that he is really asking whether there is anything in quantum mechanics itself which says that a particle cannot somehow disappear into another parallel universe or spontaneously unilaterally annihilate or some some such, or whether this is actually restricted by the other symmetries we find, e.g. conservation of energy, etc. Perhaps it could, since the inverse process of creation from more or less nothing in curved space-time can be described. He uses this strange and idiosyncratic language of "no outcome", however, which greatly confuses the issue for me.
Apr
4
comment Why does the air we blow/exhale out from our mouths change from hot to cold depending on the size of the opening we make with our mouth?
Cool experiment for kids, wet thermometers, dry thermometers, blowing different ways, etc.
Apr
4
comment In quantum mechanics, why do the probabilities of the possible outcomes of a measurement add up to 1?
Sorry, ran out of space. My basic criticism is that there is way too much theory in your definition of the "outcome" of an experiment. As an experimentalist, to me, the outcome is whatever comes out, which can more or less be anything. Your question has to do more with the rescalings of probabilities which occur all the time in real experiments, as you indicated. So to me you want to know whether there could be theories which always predict missing probability of detection, like missing energy or spin before neutrinos were discovered? But wouldn't we just call that particle decay?
Apr
4
comment In quantum mechanics, why do the probabilities of the possible outcomes of a measurement add up to 1?
Do this first with ants, in a Y shaped maze with cameras as detectors. There is the possibility that the ant a) "gets reflected", i.e. turns around, or b) "gets absorbed" in the apparatus, i.e. stops or gets eaten by a spider. To you both of these are "no outcome" results. Similarly, for atoms in a Stern-Gerlach apparatus, there can be poor beam focusing, or poor vacuum, etc. However, to me, in both these circumstances, there was indeed an outcome, namely that neither detector registers an ant or an atom (in the delta t assumed). Another outcome is that both detectors could register.
Apr
3
comment In quantum mechanics, why do the probabilities of the possible outcomes of a measurement add up to 1?
@Koantum, your definition seems circular. I am asking, operationally, i.e. in terms of apparati we can really build or actions we can macroscopically do, what could "no outcome" actually be. Please see my extended answer below
Apr
3
comment In quantum mechanics, why do the probabilities of the possible outcomes of a measurement add up to 1?
What could you possibly mean by "no outcome"? The experimenter is transported backwards in time and the experiment never happened? I think this is what Vladimir was alluding to above. At any rate try to define "no outcome"
Mar
6
comment What's a better phrase than “speed of light” for the universal spacetime speed constant?
I call it the maximal velocity of any physically causal interaction. One could also say the maximal physical speed of transmission of any sort of information. Is this what you were asking for?
Feb
14
comment Example of a time varying function which can be easily measured
Watch out not to use a medical thermometer; it will break. Maybe an oven thermometer. Or could use a different temperature range, e.g. from 100 deg. F to room temp., i.e. letting it cool in different shaped vessels
Feb
12
comment Can Noether's theorem be understood intuitively?
Well, Vladimir's question/answer is now clearer to me. He apparently wants to know the relationship between Noether's therem and what Landau calls additive, conserved quantities. Relating it back to the original question, what parts of Noether's Thm. imply that the resultant integrals of motion are additive? This obviously relates to the intuitive understanding of the theorem and its interpretation, assuming the above is true.