Big rock, little rock

 It seemed like a good idea: Big rocks fall faster than little rocks.

The idea was widely accepted. Galileo pointed out a problem.

If you tie a little rock to a big rock, the little rock, falling more slowly, should act as a drag on the big rock, almost like a parachute. The combo deal should fall more slowly than the big rock alone.

On the other hand, if you tie a little rock to a big rock, the combined weight is greater, so the package deal should fall faster than the big rock alone.

Therefore, tying the rocks together should make them fall faster and more slowly than the big rock alone.

It was Galileo’s way of saying: There’s something wrong with this idea.

When I was in college decades ago, this argument was called a “thought experiment,” which seemed unfortunate to me. The term suggested that philosophers were doing something that was similar to what the chemists were doing in the lab.

Galileo was working on a concept. He was not conducting an experiment.

The scientists who taught me how to do research would have denied it, but they did a lot of philosophy in going about their work. They tinkered with concepts all the time. Often, what counts as data is a philosophical question. Sometimes it takes a leap of imagination to see what data might look like.

You can see obvious examples of conceptual problems in neuroscience, where notions such as “consciousness” are famously thorny.

I gather that the term “thought experiment” is outdated, replaced by “intuition pump,” a coinage of Daniel Dennett, who recounts Galileo’s thinking as an example.

I don’t like that term either. Maybe, instead of being philosophical or scientific, I’m just grumpy.

• Source: Daniel C. Dennett, Intuition Pumps and Other Tools for Thinking; New York: W.W. Norton & Company, 2013. His account of Galileo’s argument is on p. 5.