66,656 reputation
345172
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location Greece
age 75
visits member for 4 years, 6 months
seen 24 mins ago

Retired experimental particle physicist.

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


Jul
21
answered What is the most common form of antimatter in the universe?
Jul
21
revised Are there any attempts to directly detect dark energy?
correction
Jul
21
revised Are there any attempts to directly detect dark energy?
added 50 characters in body
Jul
21
answered Are there any attempts to directly detect dark energy?
Jul
21
comment Are there any attempts to directly detect dark energy?
the short answer, not at the moment. some people are thinking about it technologyreview.com/view/417243/…
Jul
20
comment Why are tidal forces pointing away from the Moon?
thats right, it is the relative motions we see as tides.
Jul
20
answered Why are tidal forces pointing away from the Moon?
Jul
20
comment How many dimensions does a singularity have?
Not the value of the dimensions, the value of the variable that is assigned to that dimension. It is a clear cut mathematical concept. The x axis is mapped from -infinity to + infinity ( two singular points at the very large positve and negative limit ) on the real numbers, but in between the numbers are real. x is the variable assigned to the x axis dimension
Jul
20
answered How many dimensions does a singularity have?
Jul
19
answered Isn't the 'slit' in a double-slit experiment also a wave?
Jul
19
comment What variable is the conjugate momentum for angular momentum?
have a look at en.wikipedia.org/wiki/Conjugate_variables#Derivatives_of_action
Jul
18
comment Why it is colder in mountains, at high altitudes?
@RecognizeEvilasWaste There are different frameworks to study the behavior of bulk matter: thermodynamics defines temperature with the thermometer and a whole theory is built up without involving molecules. Statistical mechanics on molecules can be shown to underlay the thermodynamic quantities, i.e. thermodynamics emerges from statistical mechanics, and in this emergence the average KE of the molecule and the temperature are connected. But the lapse rate is due to the bulk behavior of 10^23 molecules (per mole) and not individual molecules.
Jul
18
answered Why it is colder in mountains, at high altitudes?
Jul
18
comment Did the Big Bang happen at a point?
The popular answer is popular to theoretical physicists, which is the grand majority of people answering these questions (experimentalists are too busy chasing the experiments). They tend to think that mathematics defines nature and not the mathematics is a tool to fit observations of nature. There is no contradiction, I am just stressing the experimental foundations for the need of a Big Bang model. look at the expanding balloon analogue for the BB oneminuteastronomer.com/6949/…
Jul
18
comment Quantum operators in classical mechanics
The operators were developed in a trial and error method in the beginning of quantum mechanics, looking for a consistent set. hyperphysics.phy-astr.gsu.edu/hbase/quantum/qmoper.html#c1 , hyperphysics.phy-astr.gsu.edu/hbase/quantum/schr.html. There is a finite way that variables and derivatives can permute. see how Shrodinger arrived at his equation which started the whole operator ball game en.wikipedia.org/wiki/…
Jul
18
awarded  quantum-electrodynamics
Jul
18
comment Is it possible to walk in a friction-less world?
your are right, one would have to combine it with ski poles with a nail as with your proposed shoes to transfer horizontal momentum.
Jul
17
comment What are the longest half-lives we can detect experimentally? What stops us going further? Are we trying to?
Have a look at the proton decay experiments which give limits for its lifetime order of 10^33. hep.bu.edu/~kearns/pub/kearns-pdk-snowmass.pdf
Jul
17
comment Did the Big Bang happen at a point?
@DJphy the x axis in this plot is time. The perpendicular to it is one of the three space directions, for purposes of the graphic. All three are expanding in the same way with time.
Jul
17
comment How does a Black hole attract light?
@Paul did you notice the link? it is a solid standard university link. This is possibly the only relevant case where relativistic mass earns its keep. One can talk in the framework of gravity, and one can talk about general relativity geodesics. The question is in the framework of gravity, and in that framework the statement is correct, because energy acts as a mass in the case of the photon. Relativistic mass is useless in particle physics but earns its keep in gravitational situations.