h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I think the second electron absorbs the virtual photon, combining their momentums.

Probably a silly question - but how does the electron "know" when to emit the virtual photon? Or do they do that all the time, but mostly reabsorb them themselves?

Noggin

"if you have a virtual photon, which travels from one fast electron sideways to the other, would the other be bumped away?"

I *think* you're confusing cause and effect.

When two electrons approach, they exchange a virtual photon. This - the completed exchange - is CAUSE.

The repulsion - the change in their momentum, what you refer to as one of them being 'bumped away' - is EFFECT.

Without the cause - the completed exchange of a virtual photon - you have no effect - no change in momentum. So the second electron couldn't be bumped away before the photon exchange takes place, because it's that exchange which causes the bump.

There IS a good explanation for spooky action at a distance, the only problem with it is it's a bit like the Higgs boson - explanation tend to be handwaving analogies so far removed from the mathematics of it that their value is questionable...

So in other words they would smash together?

Mathematically speaking

Ye cannae change the laws of physics...

Well, if you're a god perhaps you can.

Somebody still haven't explained to me how you can have both time slowing down due to acceleration, and the idea that space is relative.

My understanding was that electrons cannot bump into eachother. All electrons have a negetive charge and will repell from eachother, much as they do in orbit about the nucleus of an atom.

Yes, but if the signal was unable to travel between then because they were moving too fast perhaps they would. They do smash them together in particle accelerator I suppose, so can't be that difficult. You probably just need more kinetic energy than the negative charge anyway.

According to Einstein, kinetic energy weighs something. What about potential energy, does that have a weight as well?

Kinetic energy has *mass*.

Potential energy *is* weight. (Mass in a gravitational field)

Noggin

What about the potential energy of for example a spring?

I should probably check this before posting, but I think potential energy has a technical meaning which has largely been replaced by the term gravitational energy.

A coiled spring has an energy potential, but this is stored in the bonds between its molecules, and probably has its own technical name.

Noggin

But would a coiled spring need more of a push to move than an uncoiled one, if it was floating in space?

Anyone ever seen me play pool?

The laws of physics have _some_ flexibility

NB: Light travelling through materials with a refractive index lower than zero (i.e plasma [not the blood thing, but the really hot ionised gases]) travels faster than c!!!

I don't think a coiled spring would need more of a push than an uncoiled one, unless being coiled increased its mass. (I suspect it should, albeit by a *very* small amount, but I'll leave that one to the experts.) Of course, in the absence of anything to keep it coiled it would immediately uncoil anyway.

Noggin

Energy stored in chemical bonds is potential energy - coiled spring, explosives, fuel etc - and has mass just as the energy stored in nuclear bonds does. In the latter case it is this mass which is converted into energy in a nuclear reaction. (And in the former case too in effect although, as you say, the mass is very small.)

F

So the coiled spring would be a slight bit heavier then?

Pretty slight, yes.

F

You could stick a magnet through the coils, send an electrical current through the spring and produce your electromagent (or leckymagnet to our Scottish comrades)!!!

Yes, but that would require a shuttle mission to retrieve the coiled spring, insert the magnet and attach the energy source and wiring. The shuttle fleet is currently grounded and all future missions will be to service the space station until the shuttle replacement is available in 2011. You're probably looking at 2012 before we can schedule the flight.

Have you tried Baikonur?

F