47,042 reputation
229100
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location Greece
age 74
visits member for 3 years, 6 months
seen 49 mins ago

Retired experimental particle physicist.

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


47m
comment Philosophical thoughts on Reconciling Different Relativity and Quantum—Motivation behind String Theory
Here is a blog post on string theory by a theorist motls.blogspot.gr/2011/02/… . The first reason is "natural quantization of gravity".
1h
comment Philosophical thoughts on Reconciling Different Relativity and Quantum—Motivation behind String Theory
@KyleKanos I do not think it is too broad. A person well based on string theory could give a 500 word precis on how general relativity emerges from strings, with a bit of handwaving possibly, but appropriate for the level of the question,
1h
comment Philosophical thoughts on Reconciling Different Relativity and Quantum—Motivation behind String Theory
Moderators again you are trigger happy in closing a theoretically inclined question. The site will end up as a popular physics site because no senior theorist will take the trouble to look in after a while. I voted to reopen and I would love to see a concise answer by a theorist who knows his string theory. I am sure I would learn something. I do not think the question is opinion based, it is an honest question from somebody who wants to learn a bit about string theory and GR.
2h
comment Philosophical thoughts on Reconciling Different Relativity and Quantum—Motivation behind String Theory
AFAIK string theory naturally weds general relativity and quantization of gravity, and has group structures that easily accommodate the standard model of particle physics. The problem with string theory is that there is no unique vacuum and no prescription yet to choose a particular string theory model.
2h
comment Is there any argument explaining why light speed is constant no matter how it is measured?
When one asks a "why" question in physics on fundamental postulates, the only real answer is "because" by assuming this, the theory describes the data and it has not been falsified up to now.
21h
comment How does the nature of nuclear force change between attractive or repulsive based on distance?
did you notice it is a high school student asking a question?
21h
comment How does the nature of nuclear force change between attractive or repulsive based on distance?
@BenCrowell The analogy does not hold, because there is no repulsive strong force between quarks in analogue to the same charge repulsion of electromagnetism in atoms. The strong forces is always attractive except where the pauli principle applies.
1d
comment number of gravitons launched by a proton
@JerrySchirmer Sure. But the very concept of a virtual particle comes from such diagrams , i.e. the format of calculating crossections for a process. It is the successful fitting of data with calculations that gives them "existence" , as poles, with the quantum numbers of the "real" particles.
Jul
23
comment Why do I hear the telephone ring through grandpa’s hearing aid before the actual phone rings?
so the question is "what type of hearing aid?" maybe as Chris says it is designed to catch phone signals which, as they come, must radiate electromagnetic waves too.
Jul
22
comment How do substances with like charges repel each other?
then you should try and make more coherent statements not left to the imagination of the reader.After all excess electrons do not exist in normal matter, which has as many electrons as protons, unless set up on purpose. I am clarifying how this excess can happen, and then look at the effects.
Jul
21
comment How do substances with like charges repel each other?
@VolkerSiegel Not to worry, your answer is on a higher level than the question.
Jul
20
comment Differences between wavefunction, probability and probability density?
+1 for addressing the wavefunction connection to probabilities clearly. I think if people can have clear in their head that quantum mechanical probabilities are the same as probabilities for classical or even for economics events, then the famous "collapse" of the wavefunction can be seen as trivial as picking up an "instance" that builds up a probability distribution, the same as with population probability functions, for example.
Jul
19
comment For a planet which has a temperature gradient, hot in the center and cooler on the surface, why do we get absorption lines?
so you really mean planet? I will edit because as is it is very confusing
Jul
19
comment Has the photon both gravitational and inertial mass?
The photon in the standard model has 0 mass, no adjectives attached. en.wikipedia.org/wiki/Standard_Model . This question belongs to science fiction. I reacts to to gravity through its energy, by special and general relativity rules that have been validated over and over. Mass is defined as the length of the four vector describing a particle and it is an invariant. en.wikipedia.org/wiki/Invariant_mass
Jul
18
comment What is the frequency of a photon emitted by an accelerated charged particle?
there are spectra for brehmsstrahlung en.wikipedia.org/wiki/Brehmstrahlung ands synchrotron in en.wikipedia.org/wiki/Synchrotron_radiation
Jul
17
comment How to understand “accelerating charge radiate” using intuition?
OK, the animation is about a single bunch of photons. Maybe after "nudge into the charge" you should put in parenthesis "giving an instantaneous d(v)/dt " or some such, would make this clear. nudge is too general.
Jul
17
comment How to understand “accelerating charge radiate” using intuition?
It is a pretty annimation but at what point does the acceleration enter? it looks unifromly moving.
Jul
17
comment Can an electron spontaneously be emitted/ejected from a hydrogen atom?
In a sense, the probability that the ground state bound electrons can be found very far away allows for the interactions between atoms to form molecules, crystals, and lattices in general. Matter as we found it.
Jul
16
comment If dark energy is accelerating the expansion of the universe, why can't I feel it?
Yes, from each point (x,y,z,t) in every direction. Please note that if it were not for the cohesive forces (gravity, nuclear electromagnetic) we would not be able to measure expansion anyway! It is the fact that our local surroundings do not change that we can see everything else expanding and an accelerated expansion in our time frame.
Jul
16
comment If dark energy is accelerating the expansion of the universe, why can't I feel it?
The acceleration comes from all around each point, not from one direction as when you are in a plane. It is weak enough so that it does not pull clusters apart or galaxies or planets or atoms.