A human being and woman and astronomer, Vera Rubin, that the galaxies don't look like they have enough matter to move the way they do.

Galaxies, some of them, rotate around a center. If you figure out how much matter we can see, it's not enough to cause the stars to move as fast as they do.

Rubins solution with which many agree is to say there is more matter in the galaxies--we just can't see it. Dark matter is what its called, and scientists would like to know more about it. But they generally agree it exists.

There's one little thing out that that says maybe the solution isn't that the galaxies have more matter that we can't see. Maybe the solution is that gravity works differently outside our solar system than it does inside.

That is a super-boggler for physicists. They are very big on the laws of nature being trued both hither and yon.

But. Two space probes, Pioneer 10 and Pioneer 11, were launched years ago to fly by the outer planets of the solar system and take pictures.

They did, and they kept flying. They are now out of the solar system and still being followed by scientists at the Jet Propulsion Laboratory in Pasadena.

They are going to fast. By all the scientists know about the laws of nature and expecially gravity, they are going too fast.

So, maybe it's two instances of the same thing--galaxies outside out solar system rotating to fast and space probes outside our solar system moving too fast.

Gravity here and there may be different, and problems can sometimes be solved from another angle that is almost impossible to see, for almost religious reasons.

--Info from "The Trouble with Physics" by Lee Smolin