I find thought experiments absolutely fascinating. In theory, they should not work. How can we learn something new about the world from thought alone? Is this a strange remnant of rationalism?

A thought experiment considers a hypothesis, theory, or principle for the purpose of thinking through its consequences (wikipedia). It takes an imaginary scenario, usually one which would be hard or impossible to experiment with in practice, and asks “what if”.

Thoms Khon, an American physicist, historian and philosopher wrote (Kuhn, 1977, p. 241 and 261):

“Historically their role is very close to the double one played by actual laboratory experiments and observations. First, thought experiments can disclose nature’s failure to conform to a previously held set of expectations. Second, they can suggest particular ways in which both expectation and theory must henceforth be revised.”

Here is an early Thought Experiment called “The Ship of Theseus,” described by Plutarch, the ancient Greek historian, in Life of Theseus (75 CE):

“The ship wherein Theseus and the youth of Athens returned had thirty oars, and was preserved by the Athenians down even to the time of Demetrius Phalereus, for they took away the old planks as they decayed, putting in new and stronger timber in their place, insomuch that this ship became a standing example among the philosophers, for the logical question of things that grow; one side holding that the ship remained the same, and the other contending that it was not the same.“

Plutarch questions whether Theseus’s ship would remain the same ship if it were to be replaced piece by piece until none of the original planks of wood remained. While we could conceivably perform this experiment in practice, there’s no need for us to do so as we will not gain any new insights into the question “is the ship the same ship?”. Some thought experiments, such as Quantum Suicide, are simply too dangerous to try, and even if we did try, there would be no way for the scientific community to know the results.

Yet somehow, despite the fact that they are all in our head, scientists find thought experiments astonishingly useful. Prevalent in a host of disciplines including philosophy, history, mathematics, biology, computer science and economics, but most of all in physics, the most empirical of all sciences. Chemistry, by contrast, has none at all. Why is this the case? We don’t know, but a good explanation would likely tell us a lot about the structure of the discipline itself. Here’s another interesting question: are computer models (say of a universe which differs than ours by some fundamental physical constant) executable thought experiments? Will they replace them?

What is widely agreed upon is that Thought Experiments are routinely used to challenge the limits of our understanding and often result in significant paradigm shifts within the discipline where they are used.

If this sounds intriguing then this blog is for you.