54,283 reputation
234123
bio website
location Greece
age 74
visits member for 3 years, 10 months
seen 2 hours ago

Retired experimental particle physicist.

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


3h
answered Quantum Entanglement Versus Inflation in the Early Universe?
10h
comment How do two electrical charged particles know to repel or attract each other?
@Sofia I am an experimental physicist. For me , exists means "can be measured by some proxy" , not that a mathematical formula exists. As there are other ways of measuring and fitting the crossections etc not needing the mathematics of virtual particles, I do not apply the verb "exists" to a virtual electron, as I apply it to the on mass shell electron that can leave a track in my chamber :).
17h
revised How do two electrical charged particles know to repel or attract each other?
clarification
1d
answered How do two electrical charged particles know to repel or attract each other?
1d
revised What role does the Higgs Field play in the universe?
addressing last part of question
1d
comment Why does iron sink in molten iron instead of floating?
you are missing a concluding sentence to the effect that iron in solid form is denser than in liquid, to complete the answer.
1d
answered What role does the Higgs Field play in the universe?
1d
comment Pre-Higgs Energy of electron
Without the higgs mechanism all masses are zero. Energy is a variable depending on context. Have a look for essentials en.wikipedia.org/wiki/Higgs_mechanism
1d
comment Decoherence, collpse, and WHEN does the collapse occur?
what is your time zone? It is almost seven in the morning here . I will be able to chat after 15:00, my zone
2d
comment Why does the blackbody radiate even at thermal equilibrium?
The cavity is an idealized model where only photons exist in equilibrium exchanging energy with walls of fixed temperature, . It is an analogue model for the observed black body radiation from matter. As @garyp says there is not equilibrium with the environment for the black body radiation that all matter emits at a given temperature. en.wikipedia.org/wiki/Black-body_radiation
2d
revised Why did “tickling the dragons tail” by Louis Slotin not cause an explosion?
corrected mistake
2d
comment Why did “tickling the dragons tail” by Louis Slotin not cause an explosion?
The crucial point here is that the mass available was subcritical. Criticallity was induced by hand with the reflectors, not with an increase in mass. The time constants of the system "subcritical +reflectors" by the unfortunate experiment itself show that supercriticallity was not attained, since there was time for the reaction of the physicist. Supercriticallity goes off into explosion in miliseconds.
2d
answered Why doesn't the electron lose or absorb energy while remaining in a selected orbit?
2d
comment Why did “tickling the dragons tail” by Louis Slotin not cause an explosion?
@AlanRominger Ifyour read the link about the accident, the plutonium lump was subcritical , the reflections just turned it to critical, i.e the beginning of the chain reaction, not supercritical, the explosive state. It is not a molotof bomb, where it is enough to have a spark. the three stages of k are crucial as well as the geometry.
2d
answered Why did “tickling the dragons tail” by Louis Slotin not cause an explosion?
Nov
23
answered Collapse of the wave function and Heisenberg uncertainty
Nov
23
comment Decoherence, collpse, and WHEN does the collapse occur?
Coherence means that the phases are known. If you have two particles you need a different hamiltonian from one particle, you need a different one for each particle under considerations, but coherence means that the phases are known. The density matrix formalism disposes of hamiltonians , but shows up the coherence in the off diagonal elements for as many particles as the problem needs. The part of the dm that belongs to macroscopic apparatus is diagonal only, and it is due to the above mentioned dimensional difference
Nov
23
comment Decoherence, collpse, and WHEN does the collapse occur?
well quantum mechanics exists because h_bar is different than zero. Commutation relations, if h_bar is zero, the whole apparatus of quantum mechanics stops having a meaning. It is because h_bar is so small that classical mechanics works macroscopically. Only the classical hamiltonian would make measurement sense. if you substitute numbers in the picture in the other question the HUP is always obeyed because the measurement errors are large and there is no constraint. The density matrix formalism gives a handle on how this can happen, since in principle the underlying frame is QM.
Nov
23
comment How does Gravity behave at high energy?
have a look at the big bang cosmological model en.wikipedia.org/wiki/Big_Bang and TOE en.wikipedia.org/wiki/Theory_of_everything
Nov
23
revised Why are neutrons present in an atom?
added 429 characters in body