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billy_boy_999
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how big is a photon? what are its dimensions?
if this is a meaningless question, please tell me why...
if this is a meaningless question, please tell me why...
The characteristic size of a photon is inversely related to its frequency: (c/f)
It seems sloppily worded. Do you have a link so I can see the context?billy_boy_999 said:that is what the people at arizona.edu have to say...is this not a statement consistent with QM?
danitaber said:I don't know if Billy boy 999 is even reading this anymore, but just in case, I will say that what Billy Boy 999 just witnessed is an example of a physicist's aversion to the phrase "I don't know" (ha!)
Personally, I think it's a meaningless question for the following reason:
We can't measure its "size". No one knows what "size" even is in regard to fundamental or quasi-fundamental particles. We can talk about wavelength, we can talk about points, we can talk about distributions and wave-packets, we can talk about strings, and we can talk about the loudness of a "blip" on a computer. We can't talk about "size". We have a hard time talking about "reality", even! (see many worlds thread, LOL)
We are less concerned with what it is than what it does. I'm sure I'm going to get jumped on (I'm slowly getting used to it) but there it is. OK, who's first for the danitaber-kabob? Refutations are welcome.
ZapperZ said:There is one thing I will pick on, though. "What it is" is DEFINED by "what it does". If you consider carefully, everything that we define is based on its physical properties. An electron has a set of properties that defines what it is. The same with a photon. You recognize a friend or family member based on physical characteristics that you observe, the sound of his/her voice, his/her behavior, etc. These are all physical properties and characteristics that DEFINE what it is.
A photon has a perfectly well-defined wavelength only when it's in a momentum eigenstate, i.e. when it has a perfectly well-defined momentum (and energy). This never happens. A photon is always in a superposition of momentum eigenstates:billy_boy_999 said:i'm having trouble digesting the idea that the size of a photon depends on its wavelength...if photons really are the quanta, the bare constituency of light, then surely they should have a fixed size...
You are absolutely right, but the numbers we are talking about are so ridicilously small that for all practical purposes they are zero. One meter away from the expected position, the probability is less thanTau_Muon_PlanetEater said:Reillly said'
Among the peculiarities of photons and QM, is the fact that the distribution of the photon's energy is spread out to regions where the probability of finding the photon is zero.
- Question, How can the probability of finding the photon be zero at the extremes of the distribution? Wouldn't they approach zero but never hit it
teal4two said:2) X-rays are scattered by crystals, but they are only scattered by part of the crystal. How big is this part?
Redfox said:No-one said it's a point particle.
Do you know anything about x-ray crystallography?inha said:uh.. where'd you get this idea from?
marlon said:Well, a photon IS a point particle...BUT in energy space. A photon is defined as a chunk of energy, nothing more. Ofcourse it is NOT defined as a point particle that has finite spatial boundaries, so asking about the "magnitude" of a photons is useless because this concept is defined (in most cases ) based upon spatial coordinates.
teal4two said:Do you know anything about x-ray crystallography?
Crystals are regular geometric arrays of atoms (molecules, ions). The electrons of the atoms scatter x-rays and by measuring the position and intensity of the scattered rays, information about the structure can be obtained.
Often the structure is not homogeneous. If there is local disruption, the scattering pattern shows the average local structure. If the differences are being larger domains, each containing the same local structure, a superposition of the two patterns is observed. The difference between local disorder and larger scale differences seems like it has to be based on photon size;i.e., how much of the crystal scatters the x-ray.
1) If the entire crystal scattered (large photons), all we would see is the scattering pattern of the averaged structure.
2) If the photon was tiny compared to atoms, we would not see the interference pattern of spots.