For this week’s post, I want to explore the relationship between philosophical thought experiments and scientific thought experiments. When people think about science, they usually think about empirical experimentation, not philosophical conjecture; however, many of the greatest scientists have also been philosophers, and their philosophy has had a profound impact on their scientific discoveries. This is perhaps most obvious with older scientists/philosophers; such as Aristotle, Galileo, Newton, and Descartes (yes the same one from last week); but it is no less true of more recent ones like Bohr, Einstein, Turing, and Heisenberg. While it may seem counter-intuitive, many of science’s greatest developments in the last century have come from thought experiments rather than physical ones. To better illustrate this, I want to give a famous example.

There is perhaps no more famous modern scientist than Albert Einstein. While many people are vaguely familiar with some of his most notable work (E=MC², Special and General Relativity, etc.), fewer people are familiar with his research methods. Einstein himself described the process through which he discovered relativity as a “Gedankenexperiment,” gedanken being the German word for thought. This experiment was simple.

Einstein imagined that he was riding on a beam of light and looking at another beam of light parallel to his own. Reasoning from classical mechanics, the second beam should appear to be still, yet according to the laws of electromagnetism, light’s speed must always be 3×10⁸ meters per second. Both classical mechanics and electromagnetism claimed to be universal, meaning that the laws were the same for all observers, but Einstein’s thought experiment led him to conclude that either classical mechanics or electromagnetism was wrong, or that neither was universal. Confident in the laws of each, he reasoned that neither could be universal. It was from this insight that special relativity was born.

He was not done yet though. He then thought about a man in a falling elevator car. He knew that the car and the man would fall towards the center of the earth at the same rate, and reasoned that the man would thus be unable to feel his own weight. He then realized that the man would also be unable to determine, from within the car, whether he was falling due to gravity or accelerating up as the result of a force. While this was a revolutionary insight at the time, it probably should not have been. If you replace the elevator in Einstein’s experiment with the earth, which is constantly in motion, it is obvious that our measurements of motion here on earth are relative to our frame of reference. We do not express the speed at which cars travel as the observed speed (say 60 MPH) in our reference frame plus the speed of the earth’s rotation around the sun (roughly 1000 MPH) plus the speed at which our solar system is moving within our galaxy (roughly 514,000 MPH) plus the speed at which our galaxy is moving within the universe (indeterminate, because we have no external frame of reference, like the man in the elevator!!).

The fundamental insight Einstein had was one that scientific experimentation could never have arrived at empirically, since its entire premise is that empirical observation itself is relative. Without philosophy, the theory of relativity and the scientific breakthroughs that came with it would have been impossible. While this is just one example of the intersection between philosophy and science, I hope it has been helpful in understanding their relationship. If you guys are interested, I have dozens of similar examples and would gladly write a few posts about them, so let me know in the comments.