# Gravity

Gravity has nothing to do with the microcosmos.

I've only included this page at all, because it just seems wrong to talk about three of the forces without mentioning the fourth.

You see, here's the thing. Gravity appears to be this mighty force that literally moves planets, stars, and galaxies. But that's all on a large scale. On a large scale, gravity rules. Here's why: Roughly speaking, the property that gravity latches onto, like electric charge for electromagnetism and color for the strong force, is what physicists call mass. (Mass is sort of like weight, but not exactly.) And unlike charge, which comes in two kinds, and color, which comes in three kinds (and three anti-kinds) there's only one kind of mass. Mass is mass. So when you take a large object like the moon, it's made of lots of colored particles, but the net color is zero. It's made of lots of charged particles, but its net charge is approximately zero. And it's made of lots of particles with mass, but it's net mass is HUGE!!! So the dominant force exerted by a really large object such as the moon, is gravity.

But on a microscopic scale, gravity is unimportant. It's weak. Not just "weak force" weak. Compared to gravity, the weak force looks like..., well..., it looks really strong. The particle that's supposed to mediate gravity, the graviton, has never been observed. In fact, nobody has ever even observed a gravitational interaction between two microscopic particles. The only reason we know about gravity at all is because of it's effect on large objects. And we only assume that the gravitational force has a mediating particle, the graviton, because, well, all the other forces have one. In the microcosm, gravity just isn't a player.

I don't know diddly about gravity.

Well, okay, I know a little bit about it. It was once described by Newton's Law of Gravity, which says that any two objects exert a mutual gravitational force on each other that's proportional to their masses, and that decreases with the square of the distance. And I know that this was replaced in the early part of the twentieth century by Einstein's General Theory of Relativity, which leads to almost (but not quite) the same results, but is totally different conceptually with objects following the shortest path possible between two points in curved four-dimensional space-time. I once took a class in general relativity, but I never quite got it, and I certainly couldn't explain it.

But even that's not the whole story. You see, general relativity doesn't take into account quantum physics, as any really correct theory really has to. So what you need is a quantum gravity theory. One with gravitons in it, because in quantum physics, forces have mediating particles. (The gravitons would be massless, since the gravitational force appears to have an infinite range.) And I really don't know anything about quantum gravity.

Except that nobody else does either.

Okay, that's not quite true, but it made for another good one sentence paragraph. But the fact of the matter is, that nobody has a good theory of quantum gravity that completely works.

So with all that in mind, you can go ahead and skip this page without worrying about missing anything relating to Dave's Microcosmos. Well, I guess it's a bit late at this point, isn't it?

How do we know all this?
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