Photon Stats

[YT2095]

we know the speed they travel at.

we know how much mass they have (none).

 

but how Big are they?

they must have Some sort of Size in order to collide with things.

[jackson33]

the obvious answer is we have no idea, if there is even different sizes.

 

another possible solution, would be to equate the photon, with the wave and frequency of the energy (EME). energy really is absorbed in some manner, opposed to colliding and energy absorption is determined by those factors.

[YT2095]

well the way I was thinking was this, we KNOW it`s smaller than nano-metres and angstroms, otherwise how would it be able to wiggle up and down in these units to give it it`s frequency and wavelength.

so That much is certain.

and that`s about the limit that I know of for smallness.

are there any other ways it can be locked down to units smaller than this.

it may not give us the size, but we`ll know how big it ISN`T, and that`s at least Something

[Klaynos]

well the way I was thinking was this, we KNOW it`s smaller than nano-metres and angstroms, otherwise how would it be able to wiggle up and down in these units to give it it`s frequency and wavelength.

so That much is certain.

and that`s about the limit that I know of for smallness.

are there any other ways it can be locked down to units smaller than this.

it may not give us the size, but we`ll know how big it ISN`T, and that`s at least Something

 

They're spherical wavefronts, so the can be as big as the universe, or confined to a box at least as big as their wavelength

 

As I understand it discussing spacial parameters for photons isn't really physical, in the same way it's not really physical for electrons...

 

It's probably also worth discussing the uncertainty principle in here somewhere...

[grifter]

To be honest it depends what you mean by "how big." An excitation of the electromagnetic field can extend arbitrarily, far across space. However, we only ever detect them at points. (not to say that they are or aren't point particles....as it is a point-like particle)

[timo]

They're spherical wavefronts, ...

You can create wave pakets of pretty much any shape. However, the most common base for photons is [math] A_i \exp(\pm ikx) [/math] with [math]A_i[/math] being the photon polarisation, k, being the wave-vector, and me not being completely sure about the sign, atm (doesn't matter for my statement). That's a plane wave and neither a wavefront, nor spherical.

 

As I understand it discussing spacial parameters for photons isn't really physical,

Yes and no. In QM, the size of a particle usually refers to its sub-structure, like the extent of the electron cloud around an atom which defines the size of an atom. Being elementary particles photons do not have a sub-structure and are therefore considered having a size of zero.

 

@YT: I'm currently thinking how to construct a coherent reply. Might take some time, though. The short answer: When you define size as a sub-structure of a particle, then the photon-size is zero. When you define it as the size of its wave-function, then it can have pretty much any size but the size is no longer a property of the particle-class "photon", but a property of the specific photon you're talking about. Analogy: Mass is a property of the particle class (all electrons have the same mass), kinetic energy is a property of individual particles (different electrons can have different velocities and hence different kinetic energies).

[swansont]

The characteristic size is the wavelength, under the conditions where you'd treat them as waves. If you want to design a waveguide, for example, you exclude photons of longer wavelengths that can't be supported in that structure.