If gravitons are particles, how is it that they can hold us to the ground, or create gravity between two stars millions of miles away from each other?
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Imagine you are sitting a rowing boat on a lake. Stern-to-stern is another boat with an accomplice in it. You are both sitting facing each other (and the stern of your boat). The lake is still, there is no wind. You have a brick on your lap.
You take the brick and gently lob it to your accomplice who catches it. What happens?
By conservation of momentum, the boats drift apart.
Your accomplice lobs the brick back to you, you lob it back to him and so on. The boats accelerate away from each other.
Now, someone on the mountain beside the lake sees the boats but can't see the brick, so to him it looks like an invisible repulsive force is driving the boats apart.
This is how a force, mediated by bosons, works.
To get an attractive force, just replace the brick with a negative momentum particle.
Gravitons work pretty much like that. As to how they can work at great distance; they are stable (so don't decay) and there is nothing stopping them.
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$\begingroup$ This is a brilliant conceptual visualization! $\endgroup$ Commented Apr 29, 2015 at 12:03
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2$\begingroup$ Very nice heuristic explanation for the repulsive bosons. But what is "negative momentum"? $\endgroup$– pelaCommented Apr 29, 2015 at 12:11
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$\begingroup$ I read a book by Alan Guth where he wrote about gravitons having negative mass, so that collisions would attract positive masses. $\endgroup$ Commented Apr 29, 2015 at 19:54
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$\begingroup$ Negative momentum is a mathematical quantity in a path integral, just like the bricks that were thrown forth and back in the above example. Nature does not throw either bricks or gravitons with negative momentum. It has a quantum field that permeates the universe. That field can be repulsive or attractive. A path integral is just one of several possible mathematical ways of calculating the quantum field with perturbation series and it suggests that particles are going forth and back everywhere. That's a suggestion which is very useful for some purposes and completely wrong for others. $\endgroup$ Commented Apr 29, 2015 at 19:55
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$\begingroup$ The boat-brick analogy works well for repulsion but it's a bit harder to explain attraction. However, if you trust the maths then attraction and repulsion are the same thing with just a change of sign. $\endgroup$ Commented Apr 30, 2015 at 13:02