Does a photon contain an electron ?

Originally posted by cosmictraveler
Does a photon contain an electron ?

Absolutely not. 2 completely different types of particle

Thank you.:)

Originally posted by cosmictraveler
Thank you.:)

That is, if u cud call them particles of course. (before someone else adds that comment!)

Originally posted by John Connellan
That is, if u cud call them particles of course. (before someone else adds that comment!)

why wouldn t you call them particles?

Originally posted by lethe
why wouldn t you call them particles?
==============================================

From a layman's point of view, this is something I have never quite
understood. Using the photon as a particle, and not as a wave,
how would you explain a laser? Would the photon in an x-ray be
more energetic than the photon in a radio wave, more concentrated,
or just a property of the method of travel, the wave length? If a
single photon traveled by itself, would it travel in a wave or a straight
line? Sorry, I know the questions sound dumb, I know the example
of a particle that travels as a wave, but I can't figure out the
mechanics of how that would happen. Is it made clear in physics?

Originally posted by 2inquisitive
==============================================

From a layman's point of view, this is something I have never quite
understood. Using the photon as a particle, and not as a wave,
how would you explain a laser?
oh... well i meant particle in the quantum theoretical sense (is there any such thing as a classical particle?).

in this case, particles have phases. the photons in a laser are all coherent, meaning they all have the same phase.

Would the photon in an x-ray be
more energetic than the photon in a radio wave,
you betcha
more concentrated,
no, i don t think that has any meaning, since a photon has no size.
or just a property of the method of travel, the wave length?
all photons propagate the same way: changing electric field induces a magnetic field, and vice versa.

If a
single photon traveled by itself, would it travel in a wave or a straight
line?
why can t a wave go in a straight line? that is what i think happens.

Sorry, I know the questions sound dumb, I know the example
of a particle that travels as a wave, but I can't figure out the
mechanics of how that would happen. Is it made clear in physics?
i think it is made clear. at least it seems clear to me...

Thanks for your answers, lethe. I guess I was trying to think of
a photon as more of a "packet of quanta" or something like that
that was taken FROM the wave.

I think of a photon as a particle with a wavefunction shaped like a sphere. As I understand it, it can be thought of as a particle in the same way that an electron can be thought of as a particle becsause, when it interacts, the wavefunction collapses to the point in space where it interacts.

Originally posted by 2inquisitive
Thanks for your answers, lethe. I guess I was trying to think of
a photon as more of a "packet of quanta" or something like that
that was taken FROM the wave.

well in my mind, i don t really distinguish a quantum from a wave. a single quantum of electromagnetic field is a plane wave. i think localised wave packets don t have definite numbers of quanta...

Originally posted by errandir
I think of a photon as a particle with a wavefunction shaped like a sphere. As I understand it, it can be thought of as a particle in the same way that an electron can be thought of as a particle becsause, when it interacts, the wavefunction collapses to the point in space where it interacts.

strictly speaking, a single photon has to be a plane wave. as i said above, a localised wavefunction is not in an eigenstate of N, the number operator, which counts how many quanta there are. so if you want a more general wavefunction, you have to abandon the idea of a your field being described by a particular particle or quantum

Originally posted by lethe
... a localised wavefunction is not in an eigenstate of N, the number operator, ...This sounds vaguely familiar. Is this a^†a, or something like that, where the a's are the raising and lowering operators? I have only heard of this in the context of the HO.

Originally posted by errandir
This sounds vaguely familiar. Is this a^†a, or something like that, where the a's are the raising and lowering operators? I have only heard of this in the context of the HO.
Yes. a^†(k) is the operator that creates one photon with momentum k.
The state a^†(k)|0> is a one photon state.

What I write here is a little bit inaccurate, since the photon is a vector, the creation operators have also vector indices. But because of gauge invariance, it's more complicated than what I have wrote.
However, the principle remains the same. The creation and destruction operators of a photon are the same as for a HO. The operator a^†(k)a(k) is the number operator.

Originally posted by errandir
This sounds vaguely familiar. Is this a^†a, or something like that, where the a's are the raising and lowering operators? I have only heard of this in the context of the HO.

yeah that is the number operator. it tells you how many quanta you have. for example, in the harmonic oscillator, it will tell you which energy level you are in.

in fact, a free bosonic field is just like an infinite number of harmonic oscillators, something you can derive from the mass shell condition. (this should ring a bell from stuff we talked about in the Higgs thread).

so the raising and lowering operators you know from the quantum harmonic oscillator are the same as the creation and annihilation operators in particle physics.

Originally posted by lethe
why wouldn t you call them particles?

Only back now Lethe!

I wouldn't call the particles because they only behave like particles. If something behaved like particles alone then they could be called particles but since they also behave like waves we cannot. Is that ok?

Originally posted by John Connellan
Only back now Lethe!

I wouldn't call the particles because they only behave like particles. If something behaved like particles alone then they could be called particles but since they also behave like waves we cannot. Is that ok?

i m not at all clear on what you are saying here.

photons, like all particles, have wavelengths, frequencies, the exhibit phenomena like diffraction. if you refuse to call things that do this "particles", then you can t call anything a particle, particles don t exist in nature.

for me, it is more useful to call something a particle which comes in discrete packets of energy. if it also does weird wave stuff, the so be it. i will just have to get used to that. fortunately, it is something i got comfortable with a long time ago.

so for me, not only are guys like quarks and electrons particles, but also photons and phonons, gravitons and atoms.

Originally posted by lethe
if you refuse to call things that do this "particles", then you can t call anything a particle, particles don t exist in nature.

Exactly!!!

As we have discovered (only this century), there are no classic particles at a quantum scale which behave only like classic particles. They also behave like classic waves. Thus the term perticle is simply an idea and one which is very successfully used in classical physics. I suppose its a bit like infinity, an idea, but I don't want to open another can of worms here!!!

You can call them whatever u like if it helps you but I prefer to regard them as NEITHER waves nor particles but displaying behaviours of both.

Originally posted by John Connellan


You can call them whatever u like if it helps you but I prefer to regard them as NEITHER waves nor particles but displaying behaviours of both.

i prefer to regard them as quantum particles.