The Power of the Gedankenexperiment
Humans have an ancient relationship with them.
They’ve changed the course of human history, time and time again.
And yet, they operate entirely in our minds.
In ancient Greece, it was the deiknymi.
In German, it is the Gedankenexperiment.
In English, we call them Thought Experiments.
I remember learning of Einstein’s famous thought experiments from my father as a child. It fascinated me that Einstein could run an experiment entirely in his mind and that decades later, I could run the very same experiment in my mind. Not only could he formulate these thought experiments, but they could be used to understand the nature of the universe more deeply. They could be used to formulate groundbreaking theories and make falsifiable predictions.
But what is it about the Gedankenexperiment that makes it so powerful? How can framing a question lead to breakthroughs in our understanding? Thought experiments have always been about expressing a hypothesis or principle so that one can think through the consequences.
In ancient Greece, philosophers like Socrates used deiknymi (meaning demonstrations or proofs) as conceptual thought experiments. These were largely dialectic, aiming to dissect and understand philosophical concepts such as justice, virtue, and knowledge. They weren't designed for empirical testing but for intellectual exploration and the refinement of logical reasoning. For instance, Plato's Allegory of the Cave is a classic example where he explores the nature of reality and human perception without any empirical testing.
Similarly, in Zen Buddhism, koans (which originated in China from the Chan School of Buddhism) were used as riddles or paradoxes to promote “the great doubt.” It was intended to aid in the attainment of enlightenment and to demonstrate the inadequacy of logical reasoning. A famous example is the koan: “What is the sound of one hand clapping?” These koans were introspective tools meant to transcend conventional thinking and were not designed for empirical validation.
Later, figures like Galileo Galilei played a crucial role in this transition. Galileo’s thought experiments, such as his musings on falling bodies, were conceptual but closely tied to empirical reality. They were designed in a way that they could, at least in principle, be tested through physical experimentation.
Over time, thought experiments evolved into how we think of them today—in the 20th century, thought experiments in physics, especially in the realm of quantum mechanics and relativity (like Schrödinger's Cat or Einstein's light beam thought experiment), bridged the gap between philosophical speculation and empirical science. They led to real experiments that could be empirically tested.
Errors can lead to the most significant breakthroughs.
Of course, thought experiments are powerful, even if they are incorrect (or partially incorrect). A famous example is the Einstein–Podolsky–Rosen paradox (EPR), covering non-locality and “spooky action at a distance.”
Albert Einstein, Boris Podolsky, and Nathan Rosen proposed the EPR thought experiment in 1935 to challenge the completeness of quantum mechanics. Instead of claiming that the universe is inherently probabilistic and that “coupled” particles have a way of instantaneously communicating over a distance, there must be “hidden local variables” missing from quantum mechanics.
Years later, in 1964, physicist John Stewart Bell introduced Bell's Theorem, which provided a way to test the predictions of quantum mechanics against the idea of local hidden variables proposed by Einstein. Bell's Theorem states that if local hidden variables (as EPR suggested) were responsible for quantum phenomena, then the results of certain types of quantum experiments would be constrained within specific statistical limits (Bell inequalities). By the 1980s, physicist Alain Aspect and his team had successfully proven violations of Bell’s inequalities. This proved that EPR’s conjecture that there must be hidden local variables was wrong. Quantum-coupled particles do have non-locality. Something else must be introduced to explain the phenomenon of “spooky action at a distance.”
Of course, this doesn’t mean there aren’t hidden variables. If they exist, EPR could still be partially correct, but those hidden variables must be global (or at least non-local). What I love about the EPR thought experiment is that it led to John Bell’s life’s work and eventually a 2022 Nobel prize in physics to Alain Aspect, John F. Clauser, and Anton Zeilinger based on Bell’s work, all because a cleverly constructed Gedankenexperiment from 1935.
What I love most about the Gedankenexperiment is that anyone can participate. Embracing the legacy of the Gedankenexperiment means joining a timeless journey of intellectual exploration, a path treaded by ancient Greek philosophers, Zen Buddhists, and groundbreaking scientists. These thought experiments, transcending the bounds of physical experimentation, have historically propelled us into profound realms of understanding, challenging existing beliefs and unveiling new ways to see the world. This rich tradition invites everyone to engage in this creative process. By allowing our minds to question, imagine, and explore, we partake in the continuous narrative of human discovery, potentially sparking the next significant breakthrough in understanding our world and the universe.
Notable links this week
I’d never thought about comparing Battleships & wigwams
I have always been curious about How Much Horsepower is a Horse?
This video on how electrons really flow in wire blew my mind
Russ Cox shares solid code-testing advice and tactics