# Why fundamental forces change their strength?

1. Apr 21, 2006

### heartless

Yeah, same as above, Why do fundamental physical forces change their strength with distance? Shouldn't the force be the same everywhere? Why or Why not? :tongue2: (how do you know, and what did you get the answer from)

Thanks,

2. Apr 21, 2006

### Haelfix

Every fundamental force changes its strength with distance, for instance 1/r^2 and so forth.

Why? Well it depends on which formalism you want to take, certain theories posit it as a sort of axiom that fits experiment. For instance classical newtonian gravity and classical electromagnetism (well you can derive it from Maxwells laws but thats sorta trivial enough that it means more or less the same thing).

In quantum mechanics, the notion of 'force' becomes somewhat of a derived quantity, whereas energy and 'potentials' are enforced as more fundamental and natural to the theory. There again, you might ask, why that particular lagrangian/hamiltonian that gives such and such a derived force concept that varies with distance? Again, the ultimate justification is experiment, but in some instance you can argue that such and such a fundamental lagrangian *has* to be in that form b/c of various symmetries and so forth.

3. Apr 22, 2006

### arivero

1/r^2 is an easy case actually, because it is just from the density of radiated field, decreasing as the surface of the sphere increases. In fact the people searching extra dimensions look for 1/r^{2+something}.

Constant force in QCD is understood because the force carriers are themselves colour-charged particles, reinforcing the charge. Well, that is one naive explanation, but one needs a lot of CPU time to get the tubular string force field (the "QCD string").

Weak forces are understood because the force carriers are massive, thus they get a yukawian potential shape.

4. Apr 22, 2006

### Meir Achuz

Do you mean something like e^2/r^2, or the QED result that e^2 itself changes with distance?