Originally posted by: Legendary
Originally posted by: DrPizza
There are 4 forces in nature.
Of those 4: gravity, strong, weak, and electomagnetic,
gravity is the LEAST understood.
(and the weakest of the 4 forces)
Weakest, but greatest distance of travel
Actually, that's not true. We just feel gravity from large distances because there is no (known) negative gravity charge. All mass/energy has attractive gravity so it's cummulative. EM is infinite in range as well, but EM has +/- charges which usually completely cancel each other out.
The weak force is practically limited in range due to the mass of the W/Z bosons. They decay before they can get very far, but I guess you could have one reach as far as you want.
The strong forces is really messed up. The potential decreases from r=0 out a very short distance, but then it increases rapidly again (ie, the strong force gets stronger the farther out from a colour charge you go). Basically, the strong force between two infinitely separated colour charges is infinite! This never happens though as the potential energy stored in the field is large enough that the field spawns new particles. A drawing:
legend:
r : red colour charge particle
R : anti-red colour charge particle
= : gluon
A pion:
r=R
Try to pull the pion apart:
r====R
The gluons contain energy. As you stretch them, the field they make up increases in energy to the point where they "pinch off" and form new particles:
r========R -> r==R r==R
quantum electrodynamics (electromagnetism + electroweak) is VERY well understoood
quatnum chromodynamics (strong) has a theory written out, but the problems you end up writing down are so difficult to do that no one in the world has been able to solve many of them algebraically
quantum gravity doesn't even exist as a theory yet.