Is it possible to measure the size (not wavelength) of light?

Question

Think about this. Hubble Deep Field is a picture of galaxies about 15 billion light years away that was composed by the hubble space telescope staring at a single spot in the sky for 15 days. As we all know, light waves spread out as they become farther away from the source. But even after traveling 15 billion light years we can still resolve images of entire galaxies. That has got to give you an idea that photons, the particles that make up electromagnetic radiation, have to be incredibly small. But do you think it is possible, since we already know the distance of stars, to possibly figure out the size of photons in relationship to protons, neutrons, or electrons?

Answer 1

I think time is the problem, stick with speed distance mass energy and try to guess the time, time is all messed up and all made up, stay with the facts, the string theory is interesting but i believe time is the BLOCKER for the truth

Answer 2

No, I don't think we can calculate or deduce anything useful this way. Actually, we cannot treat photons as little spheres or whatever traveling at the speed of light and work out their size or mass. For example, if we consider the photon nature of light, then because photons travel at the speed of light, it makes their mass infinitely small, according to relativity theory.

I suggest you read about the double slit experiment http://en.wikipedia.org/wiki/Double-slit...

to get a feel of the nature of light and understand why measurements of the kind you suggest cannot lead to anything useful.

Answer 3

Photons are bosons, not fermions.  (Yes, this is going to get into some deep quantum physics, but not TOO deep, as I don't really have that expertise.)

Fermions are particles that obey the Pauli exclusion principle which states that no two fermions can occupy the same quantum state.  Basically, this gives fermions an extent in 4-dimensional space -- or in other words, a "size".  The "size" of these particles is the minimim distance that the two particles can approach without having their quantum states overlap.

Photons are bosons, which do not obey the Pauli exclusion principle.  Since there is no distance that defines how "close" two such particles can approach, there is no "size" to such particles.  Photons are defined by wave vectors, which define their wavelength and direction, and by probability functions that define the probability that photon will be observable at any given place at any given time.

So, while the light from a distant galaxy spreads out over distance and thus the probability of any given photon being observed at a specific point decreases with the distance from the source, such probabilities NEVER reduce to zero, and therefore one can never define the minimum "size" of a photon.