I once read a fascinating book called Worlds in Collision by a Russian immigrant named Velikovsky that said most of the miracles in Exodus were caused by near passes of the planet Venus. Can worlds collide?

Yes. In the early solar system it happened frequently when the planets were smaller, there were more of them and orbits were less round. Eventually, the bigger planetoids swept out their orbits by attracting collisions with even smaller planetoids. Non-circular motion tended to average out. The planets that remained were the "winners" and became the familiar planets we know today. However, the planets started out pretty much where they are and just became bigger. The existing solar system has been a quiet place for a long time now.

Could Velikovsky be right?

He is correct in his assumption that the early solar system was a rough-and-tumble place, but he is incorrect in his setting the activity in historical times. In his description, Jupiter ejected what would become the planet Venus before the time of Exodus. The events in Exodus have been fairly accurately placed around 3200 years ago. If Jupiter spit out Venus like a melon seed sometime before 1200 BCE, there would be plenty of evidence for it in the sky now.

Like what?

Earth should be in a less round orbit. With both Venus and Mars caroming around the inner solar system, we actually would have risked being ejected from our orbit in an alarming fashion. The four innermost planets are in fairly round orbits, with Mars being the most elliptical. Also, Venus should have been melted by such a violent event as ejection from Jupiter, and there has not been sufficient time for it to have cooled. Plus, the inner solar system would be a great deal more cluttered than it is now. Every night would offer a meteor shower.

But I heard that Venus's hot temperature is one of the confirmations of Velikovsky. What about that?

Hot as the planet is, it's far too cool to have been melted only a few thousand years ago, which is what the violence of being ejected from Jupiter would do. It emits approximately the same amount of energy as it receives from the Sun, which means that it is in equilibrium.

Why have all the academic scientists piled on top of Velikovsky? They ignore most supposed cranks.

Most cranks don't spin as good a story as Velikovsky. I think that Velikovsky was about the first post-modernist thinker they had run across. Post-modernism is a politically-correct philosophical system that, among other things, accepts scientific principles and cultural traditions at equal strength. Thus, it will balance a many thousand year old folk tale against the conservation of angular momentum. A scientist, on the other hand, has become so accustomed to thinking of the conservation of angular momentum as one of the fundamental building blocks of the universe that any story, folk tradition, or anecdote that has angular momentum not conserved will be rejected out of hand. A scientist puts weights on facts according to how easy they are to check (the conservation of angular momentum is very easy to check; the Epic of Gilgamesh is not). A post-modernist says there is no absolute truth and that truths are all culturally derived.

I take it you don't think much of the post-modernists.

The post-modernists make one excellent point; science itself has a culture and that can itself impede the results. However, science is self-correcting. The uncritical belief in Velikovsky is an indication that we are not teaching the scientific method so much as stuffing the public with facts (as in these FAQs!). When I made statements about black holes elsewhere, I didn't show you the 1200-page book of dense mathematics I pulled them from. Other scientists offer similar pre-digested results. When a Velikovky comes along and spins an attractive and fun tale, and furthermore paints it with a thin enough layer of science to make it seem real, the public can't tell the difference. The public doesn't see that the story has about the depth and structural strength of a Hollywood set.