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Date: Around 1993


Question:
I have read that bosons are particles that convey force (gravtons, photons, etc.) and fermions (protons, neutrons, the heavy stuff) are the particles themselves that are acted upon by these messenger particles. How do messenger particles convey force, ("pursuadine)? Example: How is a graviton going to convince a hydrogen molecule to change direction and head towards the gravitating mass?



Replies:
The question really is, how to get an attractive interaction. Getting a repulsive interaction looks easy - particle 1 fires off an exchange particle in the direction of particle 2, which receives it, and the momentum of the exchange particle causes the 2 interacting particles to head away from each other. Imagine 2 kids on skateboards, exchanging a basketball. This repulsive interaction is just what happens when they throw the basketball straight at each other back and forth. So, how can we get an attractive interaction? If the kids are close enough, they can just hand the ball to one another, and this can be done in such a way that the net momentum transferred is in the other direction - so they really are pulled towards one another. But this does not seem to be directly related to the physical system - particles do not have long arms! Or do they? Remember Heisenberg's uncertainty principle? If you have specified momentum completely, position is completely uncertain. I think this is most of the explanation.

A. Smith



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