ultramadscientist wrote:Wouldn't the photon's "size" be approximately the plank length? A string would vibrate to create a particle, and a string is at the minimum a plank length in diameter. Being massless I would hope that a photon holds the minimum size.
If a photon behaved like a wavepacket with a diameter of a planck length, what size orifice would we need in order to see photons diffract
? At what size orifices do we start to see photons diffract in the laboratory? This is the sort of empirical gut check that should have told you that this guess wouldn't work.
And remember that size is not mass. In our everyday life lighter things are usually smaller, but the fact that size and mass are different units should make you stop and think "is that a universal law, or is there some mediating factor that might not be present for fundamental particles?" The mediating factor is density
, and density indeed does not work intuitively for fundamental particles. If you wanted to make a sculpture of a fundamental particle you would use clay or wood or metal, and all have pretty much the same density, so a light particle would have to be smaller. But a photon isn't made out of clay, it's made out of electromagnetic fields, which can have any density at all - and so the relation between size and mass breaks down.
having originated the original question a long time ago, the conclusion I get from this debate is that nobody knows the answer. Is that a fair conclusion?
Given the state of the thread it's not an unreasonable conclusion, but it's incorrect. "What is the size of a photon" is like the question "what is the depth of a poet?" It doesn't make quite enough sense to have one exactly right answer, but it has several almost right answers ("about a foot and a half", "the wisdom she imparts to her writing"), and unlimited wrong answers ("a lightyear"). You may have to do a bit of legwork to separate the almost right answers from the wrong answers in this thread, but you should think of it like an adventure
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