Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: yor_on on 06/06/2010 17:29:18

Title: How is virtual photons thought to be repulsing / attracting?
Post by: yor_on on 06/06/2010 17:29:18

I saw an idea dividing virtual photons in those attracting as well as those repulsing?
How exactly are they thought to do so?

Not only virtual but also containing two opposite 'forces'?

Title: How is virtual photons thought to be repulsing / attracting?
Post by: Geezer on 06/06/2010 18:39:29

I've no idea [;D] but welcome back!

Title: How is virtual photons thought to be repulsing / attracting?
Post by: Ron Hughes on 06/06/2010 21:22:01

Since virtual particles are hypothetical particles invented for no other reason than to support the the standard model it is doubtful you will get an answer but, I would love to see some of the believer's answer it.

Title: How is virtual photons thought to be repulsing / attracting?
Post by: JP on 07/06/2010 02:42:57

Welcome back, yor_on.  It's been quiet here without you!

I can't answer your question in a simple way, I'm afraid.  I'm not an expert in virtual particles, but I know a little about them.  Basically part of the question is answered if you don't think of the photons as "little bullets," but rather smeared out objects existing between two charged particles.  Because the photon doesn't have to act like a particle until it interacts, it has some probability of giving the particles a kick away from each other and some probability of sucking them towards one another.  (This is basically because the photon can have momentum in different directions, but when it interacts with a charged particle, it has to pick a momentum value.)  Because of the way QM works, when you calculate the net effect of many virtual photons on two like charges, they add up to repulsion, and when you do so for two unlike charges, they add up to attraction.

For a slightly more complicated explanation, check here: http://www.xs4all.nl/~johanw/PhysFAQ/Quantum/virtual_particles.html

Title: How is virtual photons thought to be repulsing / attracting?
Post by: yor_on on 08/06/2010 12:41:39

Ah, thanks Geezer, JP.
I've been slightly occupied :)

But it's nice being back.
==

The funny thing JP, is that I've read that one several times without reaching that conclusion :)
I will have to read it much more slowly to see what I can understand there.

but if I cite this then?

"A virtual particle with momentum p corresponds to a plane wave filling all of space, with no definite position at all. It doesn't matter which way the momentum points; that just determines how the wavefronts are oriented. 

Since the wave is everywhere, the photon can be created by one particle and absorbed by the other, no matter where they are.  If the momentum transferred by the wave points in the direction from the receiving particle to the emitting one, the effect is that of an attractive force."

Now, either we then treat 'virtual photons' as particles it seems to me? And then we can associate a 'momentum' too it, or, we assume it 'smeared out'. If we do so, and then after that 'VPs' :) probability have fallen out see a attraction or a repulsive effect, can we then assume that this VP suddenly had a defined 'momentum'?

I don't think so, not if we by 'momentum' means the 'force' created by its speed/velocity and mass. As far as i understand a virtual photon have no speed at all, as long as it's virtual? So why do we call it momentum at all?

Maybe it's more like a deformation of our space where it happens?
A tiny bump creating a 'push' or a hole creating a 'show' :) ?

Or is it a 'momentum'?
But where did that came from?

You can say that a EM wave also is 'smeared out' right?
But there we talk about something with a direction as I understands it?

Title: How is virtual photons thought to be repulsing / attracting?
Post by: yor_on on 08/06/2010 17:00:05

Let me clarify myself, not that I might become any clearer because of that :)

A momentum is for me associated to something moving inside SpaceTime, at least in a classical sense? Even 'normal' photons give us that experience. But when discussing 'virtual photons' we are talking about something not really here. The only thing that makes us expect them are the indirect evidences we see for something having to be there to explain the behavior of the objects we do can observe. So they in themselves don't even 'move' the way we expect ordinary photons to do, at least not as anyone experimentally can prove.

Which make my 'space bumps & holes' seemingly more plausible to me, as the particles receiving in themselves are quite undefined maybe the 'bumps' are something taking place in a ordered sequence inside what we define as 'real particles' creating what we would call a momentum? Like a very local stress on whatever it is creating that particle.

Not that it makes that much sense, but neither does the idea of something not there, and without even a speed, having an momentum? Or maybe there are some better way to describe momentum that I missed?

Title: How is virtual photons thought to be repulsing / attracting?
Post by: JP on 09/06/2010 08:20:54

I definitely have to think about this more and re-read that article I linked.  I'm mostly using what I know on the subject to interpret other articles, so it'll take me a while, I think. . .