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232116
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location Greece
age 74
visits member for 3 years, 9 months
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Retired experimental particle physicist.

The picture is a fayum . It looks like aunts and cousins of mine :).


May
24
answered Can a single molecule have a temperature?
May
24
answered The Univere's mass-energy and uncertainty
May
23
comment Magnitude of a photon?
@twistor59 That is the probability for the photon to go through or be reflected. The individual photon is not split of course. It certainly is very sloppy terminology.
May
23
comment Magnitude of a photon?
@OndřejČernotík a photon is an individual particle withe energy hnu and a spin (+/-1). It cannot be split. It can Compton scatter on an electron and change its frequency, be absorbed kicking an electron to a higher level, or pair produce in the field of a nucleus for high energy gammas. thats about all.
May
23
comment Magnitude of a photon?
It does not make sense at all. One can split classical electromagnetic waves, not individual photons. There is nothing there to split. what is the book?
May
23
comment Magnitude of a photon?
sounds wrong in my opinion. Missprint or something. A photon is one of the elementary particles, cannot be split, it has mass 0 and is only characterized by its energy/frequency and spin orientation (=/-1). en.wikipedia.org/wiki/Photon
May
23
comment Calculate energy from an reaction
@DeerHunter and the other downvoter: why such hostility to a new user? You could ignore the question after all. kudos to Nivalth for taking the risk you perceived in the link.
May
23
comment Calculate energy from an reaction
have you thought of energy conservation given the special relativity relation of mass with energy?
May
23
answered Non-isolated universe and arrow of space
May
22
revised Collision between a photon and an electron
after edit of question
May
22
answered Collision between a photon and an electron
May
22
comment Quantum mechanics and everyday nature
but @joshphysics accepting the existence of photons in a beam of light is a circular argument, because a photon is the quantum of light.
May
21
comment Best current bounds on nonconservation of momentum?
handwaving, I would expect that the small error in mass of J/Psi mdelta(m)~pdelta(p) ; in Mev (c=1), 3000*0.01=30 so p*delta(p)~30MeV for momenta in the low GeV range where experiments are more accurate.
May
21
comment Best current bounds on nonconservation of momentum?
All the masses in the particle data group listings are the result of many different experiments and are found by summing up in histograms the invariant masses of the sum of particles composing the resonances. m^2=E^2-p^2. The whole Standard Model would flop if energy and momentum are not conserved within the experimental errors.If one had the experimental data one could easily get the momentum errors typical of particle experiments. It is not easy to find these particularly at low energies, where the accuracies are higher so I cannot write it up in an answer.
May
21
answered Convergence of Light on the Retina
May
21
comment Best current bounds on nonconservation of momentum?
I am trying to say that conservation of momentum and energy are continually experimentally tested in particle physics, because they are the lynch pin of mathematically analyzing the data. Another example, the mass of the Psi. pdg.lbl.gov/2012/listings/rpp2012-list-J-psi-1S.pdf Within less than MeV it has a very stable value and used as a gauge for the measurement errors in higher energy experiments. These numbers can be converted to momentum conservation estimates. That it was not done explicitly does not mean it is not an experimental error for momentum conservation too.
May
20
comment Best current bounds on nonconservation of momentum?
I am puzzled by this question, since conservation of momentum is a basic tool in particle physics in order to study the interactions. For example in four constraint fits of interactions all the momenta are accounted for. In one constrained fits a neutrino or photon may be missing and is thus identified. If it did not hold the masses etc of all the standard model would be all over the place. Are you saying that the accuracy in particle physics is not enough for what you are looking for?
May
20
comment Why is the temperature zero in the ground state?
Have a look at this nature.com/news/quantum-gas-goes-below-absolute-zero-1.12146
May
20
comment Why is the temperature zero in the ground state?
It is just an intuitive feeling, when I see =0 in a quantized environment. the ground state has an energy and that would couple with a delta(t), so I would expect maybe an infinite time to reach T=0. I may be wrong. intuition is not mathematics
May
20
comment Why is the temperature zero in the ground state?
What about the HUP? would it not exclude the exact T=0?