# Q & A: Explaining attractive forces with particle exchange

Q:
Bring two magnets close and they attract and repel accordingly. Throw an apple up and it falls back (attracted) towards the earth's surface. I know the answer is magnetism and gravity but actually what are these forces? I have been taught that at fundamental level force is a "thing" passed between two particles...aka force carrier particles. They gave me a nice picture of its working by assuming two people standing on ice pond. If one of them throws a ball to another then they both gets displaced. It clearly explains the repelling force but how do we account for attractive forces?
- sumit (age 16)
A:

Hey Sumit,

As far as I know, this analogy is very weak, and not to be taken too seriously. I also did a google search and didn't find any explanation for attractive forces in this model.

However, here's one way that this could work:

If you had two people facing each other inside an ice rink with solid walls, then each one could throw the ball backwards over his head, pushing him towards the other person. The ball could then bounce off the wall, change direction, and then fly towards the second person. Now, if the second person catches the ball, it will push him away from the first person, and they won't get any closer together. So, instead, the second person lets the ball fly over his head also, after which it bounces off the second wall, changes direction, and approaches him from behind. If he catches it, then he too will be pushed towards the first person, and the two will feel an attractive force.

As far as I know, there is absolutely no reason to think of attractive (or even repulsive!) forces by this exact particle exchange model... Although forces really can be thought of as carried by particle exchanges, the particles are just little packets of the field which they "carry".

Cheers,

David Schmid

p.s. Versions of this question have come in before, but as you can se we don't really know how to answer it:

p.p.s.  Here is another question that is even more puzzling.  The answer lies deep within the subtlies of quantum field theory.

(published on 05/27/2014)