Re: What came first Gravity or Magnatism, and which is stronger?

This is a very good question! First, the easy part: the magnetic force, and its sister electric force, are much, much stronger than gravity. This is why magnets can be used to pick up objects: even though the earth is so enormous, and thus has a fairly large gravitational force, a tiny iron magnet can pick up another piece of iron relatively easily. However, in most of the universe, gravity is by far the most important force. That's because the electromagnetic forces only work on charged objects, and almost all objects in the universe are electrically neutral. (If an object somehow acquires a negative electric charge, for example, it will quickly get rid of this charge by sending it to nearby objects. This is what happens when you shock someone or something: your body has acquired an extra negative charge and is getting rid of it by trying to send it back to the ground.)

The question of which force "came first" is a bit more complicated, and physicists have only really come to understand it recently. There are actually four "fundamental" forces in the universe: gravity, electromagnetism, and the strong and weak nuclear forces. The last two are only significant on very small scales (about the size of an atomic nucleus, a millionth of a billionth of a meter), but they are responsible for holding nuclei together and for radioactive decay. Within the last few years, physicists have come to realize that all four of these forces are probably aspects of a single force.

This is strange because they certainly seem to be completely different forces. After all, gravity works on everything, but electromagnetism only works on charged particles. What physicists have found is that if you can make the universe hot enough, or give it enough "energy," the distinctions between the forces start to disappear. So far, this has only been observed to happen between the electromagnetic and weak nuclear forces. In particle accelerators like Fermilab and CERN, physicists have made particles move so fast that these two forces combined into one. At higher energies, the strong nuclear force combines with these as well, and at even higher energies (we think) gravity joins with all the other forces into one. To combine these forces takes so much energy that we haven't been able to achieve that on earth yet. Technically, each force is "carried" by a particle. At high energies, it turns out that the particles that carry the different forces have exactly the same characteristics---so they are the same force!

Here's a picture that might help you understand this a little better. On a piece of paper, draw three hills---a big one, a medium one, and a small one, from right to left. Now imagine that you drop a ball from very high above the hills. The ball represents a force-carrying particle. Each valley is one of the four forces: if the ball lands to the right of the big hill, it carries gravity, if it lands between the big and medium hills, it carries the strong nuclear force, if it lands between the medium and small hills, it carries the weak nuclear force, and if it lands to the left of the small hill, it carries electromagnetism. Now imagine that the ball can bounce. If the ball has a lot of energy (meaning that it can bounce very high, and quickly), then it can bounce right over all of the hills. It will land in each of the valleys lots of times. This corresponds to a hot universe: every ball bounces between the four valleys, just like every force-carrying particle carries all four forces at once.

Now imagine that the balls aren't quite so bouncy (or energetic), so that they cannot get over the big hill. Some particles get stuck to the right of the big hill, while other particles can bounce between the other three valleys. This means that gravity is now a separate force, but the other three forces are still combined into one, because balls can bounce freely between those three valleys but not into the valley representing gravity. As we make the balls less bouncy, some will get stuck between the big and medium hills. This means that the strong nuclear force has separated from the rest. Finally, when we decrease the bounciness further so that balls get stuck between the small and medium hills, the weak nuclear and electromagnetic forces will separate as well.

This is exactly what happens in our universe. Just after the "Big Bang," the universe was very hot, and all four forces were one. As the universe got older it cooled (in the terms of our analogy, the force-carrying particles got less bouncy), and first gravity, then the strong nuclear force, and finally the weak nuclear force split off. So in this picture, gravity was the first of the forces to separate, and is therefore the "oldest." Electric and magnetic forces are the "youngest." However, really all four forces were there all the time---it's just that very early on they were combined into one. The technical term for this process, through which the one original force breaks into four, is "symmetry-breaking."

This is some heady stuff and may not all make sense to you right now. Don't worry; physicists themselves don't understand it completely! Many are currently working on understanding how the forces combine at high energies (particularly gravity; you may have heard of "string theory" as a recent development in physics---this is the latest method people are trying to use to combine the forces). I hope this picture does help you to understand the four forces and their relationship. Good luck, and keep asking questions!