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Name: Ilian T.
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: Saturday, April 20, 2002 8:17:44 PM

Can someone please explain how exchange particles cause attractive forces? The analogy of two ice-skaters throwing tennis balls at each other illustrates how an exchange of momentum can cause a repulsive force, but I fail to see how a force such as gravity can be explained in this way.

I am really at the edge of my expertise on this, but it is my understanding from reading the "popular" literature, that every field (or force) can be interpreted as an exchange of particles. Photons for the electromagnetic field.

That is just the way the mathematical physics turns out. Like many of the concepts that arise from quantum mechanics, we do not have any experience or any very good "pictures" for what is going on. We just do not live in that world. Spin is a good example of a quantity that is certainly "real", but what "is" it? It is the result of the Q.M. treatment -- that is the best we can do.

An even more elusive, but familiar, quantity is "energy". What "is" energy? We really do not know. We know how it behaves, we know how to calculate it for various formulas. But that does not really tell us what it "is".

Vince Calder


One thing very important to consider with such theories is the wave/particle nature of matter. On a large scale, objects all have a clearly defined energy and momentum. On the scale of an individual particle, such is not the case. Quantum research shows that what we commonly think of as particles sometimes behave as waves and sometimes as a combination of wave and particle. An individual particle does not necessarily have a clearly defined momentum or energy. Interactions between two particles is not the same as interaction between two charged balls. Particles don't even have clearly defined positions: they have states of existence. Interaction between individual particles is not understood. We know that particle interaction is not just force, momentum, energy. We know interaction can be viewed according to many different models. We do not know which model is correct, if any are even close. The basis for the graviton model is the fact that gravity is a 1/(distance-squared) force. If a mass emits gravitons in all directions, the density of gravitons will decrease as 1/(distance-squared) as they move away from that emitting mass. If the effect on another mass is proportional to the number of gravitons that hit the second mass, a graviton law automatically produces a 1/(distance-squared) relationship.

It is very similar to electric force being "transmitted" between particles by photons of light. In either case, I do not believe the actual mechanism is understood. It just seems to match the data that has been measured.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College

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