48,769 reputation
230103
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location Greece
age 74
visits member for 3 years, 7 months
seen 5 hours ago

Retired experimental particle physicist.

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


10h
comment How do you add temperatures?
I am curious, why do you want to add temperatures? To get an average temperature for a location?
21h
comment How can blackbody radition be explained by quantization?
Funny. The black body spectrum IS electromagnetic radiation. Those oscillators ARE charged. What you are saying is a parallel projection of similar solutions for non existent matter. Mathematics that is.
1d
comment Why should any physicist know, to some degree, experimental physics?
I take exception with your " It has thus far turned out impossible to come up with a way to test string theory " . String theory is not developed in a vacuum, as mathematical toy. It is being tested for consistency with quantum field theory, the standard model, gravitational theories. It is a higher order theory whose experimental test ground are the lower theories that have been validated to date. It predicts supersymmetry, and this remains to be tested. The large extra dimensions model has not been validated at the LHC energies, but it was a string model that can be checked for validation.
2d
comment Photons to Represent a Wave
@firtree "Photons can be considered waves even if they don't make the classical wave" Important to stress they are Probability waves, not energy-intensity-in-space waves that the classical EM wave is (Poynting vector). The individual probabilities of the photons synergistically create the classical wave front with its phases in space.
2d
comment Photons to Represent a Wave
@Anthony A classial wave composed by agreat number of photons can all be abosorbed impinging on a medium . There would be no reflection and the medium would look totaly blac. Evidently there must have been as many photon-atom interactions as there were photons. As matter consists of order 10^23 molecules per mole this is not impossible to happen, though most of the time there will be some reflection. The photon molecule interactions can be of various types and would be the content of another question.
Aug
24
comment How many volcanic eruptions would be necessary per year to neutralize global warming?
@rob I guess so :). Hope our luck holds.
Aug
23
comment Is the Casimir effect also present between two event horizons?
Physics is not a matter of imagination but of ability to measure and quantify and model. have a look at these figures to see how small the casimir effect is and how close the two planes have to be inspirehep.net/record/1225058/plots?ln=en . We are talking nanometers distance between plates for the force to be measurable.
Aug
23
comment Is the Casimir effect also present between two event horizons?
If you are asking whether the vacuum "sea" exists then yes, it exists (Hawking radiation ) , but certainly not measurable by a Casimir type of effect.
Aug
23
comment Is the Casimir effect also present between two event horizons?
can you really believe that two event horizons can get close enough before the holes absorbing each other to manifest a Casimir effect which appears at distances of neutral surfaces densely packed in a solid, ~10^23 molecules , with an event horizon that even if statistically neutral everything moves towards the singularity and the densities are minimal?
Aug
21
comment Entropy and dark matter structure
It is my opinion, after all. As gravity is quantized ad hoc at the moment maybe we should wait for the definitive work to decide whether only quadrupoles, which after all are a classical construct and should be emergent behavior in a full quantized gravity, are the only source of graviton radiation. It is probable that a dark matter particle interacting gravitationally with another dark particle will radiate as interaction is change . arxiv.org/abs/hep-th/9909012 . There might be a type of black body radiation of bulk matter from an ensemble of quadrupole elementary particles
Aug
20
comment Entropy and dark matter structure
Well, I do not think that the gravitational field disappears even in very small time scales. It is weak but it is there, otherwise there would be no accumulation of this dark matter. gravitons must be exchanged and radiated analogously to the photons always, no?
Aug
20
comment How literally should you take “The Higgs boson gives other particles mass”?
I do not think that the distinction between a field and its excitations is a quibble. A field is defined in all space time, a higgs boson is an excitation of the field, and in our reality it needs 125 GeV to manifest. The mass of the electron is ~o.5MeV, and it is due to the higgs field. "Particles don't acquire masses until the point at which the Higgs boson appears," is wrong.
Aug
19
comment Does this count as moving faster than light?
@babou well, read this en.wikipedia.org/wiki/Four-vector
Aug
18
comment How to understand “accelerating charge radiate” using intuition?
@NikosM. well, physics is modeling observations using mathematical tools with their axioms and physics postulates that relate the mathematics to observations. Unless one follows a sort of platonic world view, "there exist mathematics and nature is molded into it", which I do not.
Aug
17
comment Which electromagnetic radiation is faster in water, microwaves or light?
You have a contradiction here "So, higher frequency waves generally go faster. So, as they have a much lower frequency than visible light, microwaves are supposed to travel faster. "
Aug
16
comment Photon striking a molecule and getting reflected
@jkej There exists total reflection from the water given by the index of refraction and angle of incidence. This is backwards elastic scattering of photons . As the index of refraction is constant in the water, there will be angles where the light will be totally reflected but it will depend on the local geometries of light and water motions. The reflection happens on water molecules.
Aug
16
comment Photon striking a molecule and getting reflected
well there are reflections after a certain angle with respect to the index of refraction, and those reflections are composed of photons. There do exist elastic photon electron scattering at all angles. In this case it will be photon electric-field-from-collective-eletrons scattering in the volume . Some back scattering in the volume will also occur because we can see inside the liquid. Now if it is from solvent or solute is moot, imo. probably from both.
Aug
16
comment Entropy and dark matter structure
we would not be there to measure it :) or even guess at it. probably a negative exponential multiplying 1 kelvin
Aug
16
comment Entropy and dark matter structure
It will depend on what dark matter is. no? fermions? bosons already?
Aug
16
comment Entropy and dark matter structure
I accept that the time taken may be much longer but your argument then would mean that no gravitational collapse of dark matter will exist either. If we assume, as the question assumes that there will be a gravitational collapse of dark matter, then gravitons will take the role of photons. as long as there exists a gravitational force, gravitons are there by construction