See post #10 as well... this is where your enquireys start to need more of a physics lesson approach.
Remember, if we could explain it all to you using common sense type approaches, then we would not need quantum mechanics at all and there would be no such theory The virtual particle model for force is something students seldom meet in detail before they graduate... you are asking post-grad level questions: there's a reason it take most people 3+ years to get to this stage.
Distant Meteors said:
I can't say I totally buy it because if it were "proven" or "hypothesised" then there would be a robust mathematical theory (like Relativity or like QM or QCD or QED) laying it out rigorously and I would have been referred to it by now ?
There is one - it is called "the standard model of particle physics" and it comes from Field Theory which includes wave mechanics and QED.
As I understand it so far from the article it relies on a Feynman interaction and momentum exchange and to do with the properties of the exchange photons as to whether the force is attractive or repulsive ? If it is to some degree random then it's hard to see why these forces are always either repulsive or attractive ?
They are not always repulsive or attracting ... at "random" is not the same as saying that just anything can happen: some things are more likely than others. What sort of photon is possible depends on the situation ... in this case, two charged particles with some momentum is one state, and two particles with other momenta and a photon is another state, and two charged particles with some other momentum is another state. The QM tells us about the probabilities of transitioning between the states. We like to limit inquirey to specific subsets of the set of all possible states depending on what we are interested in, but quite a lot of stuff is possible, most of which averages out.
One thing to get out of is the idea that the virtual photons are somehow fired from the charge ... that's not the right picture.
Like vanadium says, there is a lot of cartoony handwavey stuff in the explaining.
I'm working on it though.
Have I given you a link to Feynman's QED lecture series?
http://www.vega.org.uk/video/subseries/8
... watch all of them since he does a better job than most at describing this stuff. Be warned, itis not intended for a lay audience: the lectures were delivered to staff and grad students at the University of Auckland NZ. However, he is not expecting an audience conversant with the ideas or the rigorous maths.
One of the lectures shows you how the photon statistics model works for reflection, I think it will help you here.
... I suppose I could find you a post-grad lecture series on virtual particles if you like.... that would count as directing you to the math laying it out rigorously.
Probably nobody has yet because they are trying to pitch to their perception of your math background. Would you like the real maths?
What sort of wavelength are we looking at for these exchange photons ?
Depends on the momentum being transferred.
But these are virtual photons - they exist primarily as a step in a calculation, a bit like the steps in calculating a long division.
Or, for example, you may want to bake a small cake but only have a recipe for a huge one ... so you take the amounts of ingredients for the big one and, say, divide them in half 3 times (for a cake 1/8th the size). At each step the mathematics represents a certain amount of ingredients, but when you come to make the actual cake, you don't actually gather all the ingredients and physically half it etc. The amounts of ingredients in each step are virtual ingredients.
If someone asked you what the virtual ingredients cost, you know, the ones that didn't make it into your cake, you'd look at them funny right? Same sort of thing with asking what the wavelength of a virtual photon is.
However, QM is not like that. In QM, the steps in a calculation that look like virtual particles can be tested for in particle accelerators - they, or at least the real versions of them, have been detected. be clear on this - the virtual particles are never detected.
There is a decent illustration of the principle in the lecture series above - the reflection part.
There, an experiment is set up where there is a source and a detector and a mirror and we consider those photons, from the source, that reach the detector via the mirror.
The classical law of reflection is ignored, and a calculation done involving the possibility that photons may reflect from any part of the mirror to derive the classical law of reflection as an average over all possible paths. All the non-classical paths are "virtual" in a sense.
So each individual path used is just maths right? A photon wouldn't really follow the non-classical path right?
This can be tested - and it turns out that it is possible to make the reflection brighter by removing most of the mirror... this only works if there is more to this idea than "it's just steps in a calculation". On the other hand, I cannot expect a reflection from putting a mirror just anywhere ... what this tells you is that the cartoon description we are handing you as a stop-gap is incomplete.
Does a magnetic force have infinite range ? (like gravity) - I'm guessing the immediate answer is yes ?
The immediate answer is "sort of" ... the range of the electromagnetic interaction itself has no absolute maximum - however, there are lots if charged particles so the vast majority interact with the ones nearby. This is how most everyday objects do not have much of a charge even though they are composed of charged particles ...
...but
Maybe gravity and EM forces don't have infinite range after all and that explains the theoretical necessity for Dark Matter and Dark Energy under General Relativity as is ?
There are people who like to think that the electromagnetic interaction, by various means, explains "dark matter" etc. This is junk and can be safely ignored. This is something that has been thought of and discounted a long time ago.
You don't even need to go to QM to get there ... the gravitational force is much weaker than the EM one, however, there is only one kind of gravitational "charge" while there are two kinds of EM charge. The two EM charges result in fields that can cancel each other out on large scales, while mass is only additive on large scales. On the scale of, say, a room, the gravitational interaction is dominant over EM for pretty much anything in the room. So much so that the Cavendish experiment works.
