The One Time Carl Sagan Got It Wrong

Or: Why Reductive Explanations Don’t Work

We should avoid reductive explanations in scientific communication wherever possible because they create an illusion of understanding.

You’re probably familiar with the following reaction GIF.

Here’s the context. Sagan was visiting his former sixth-grade classroom, talking about space stuff, as expected. He invited questions, and a student asked, “Why is the Earth round instead of some other shape?” He liked the question — hence his reaction. (Though the GIF is not typically used to react to questions.)

This was his answer.

It has to do with gravity. The Earth has a strong gravity. If you were to make a mountain very high, higher than Everest, you know it’s the biggest mountain on the Earth, it would be crushed by its own weight. You see, gravity pulls everything towards the center, so any really big bump on the Earth is crushed. But if you had a small object, a tiny world, the gravity is very low, and then it can be very different from a sphere.