Thursday, September 17, 2020

Gedanken Experiments

Environmental & Science Education, STEM, History of Science, Nature of Science, Models

Ed Hessler

Who was the scientist who reportedly said "Imagination is more important than knowledge?" 

 Einstein and how can I help but add, of course.

 What in the cosmos did he mean? There are two meanings.

Stripped from the full quote, this short aphoristic sentence became a well known poster and T-shirt headline; a bumper sticker providing confirmation to many that studying and learning stuff was not too important. It was imagination...daydreaming. But this was from a scientist who spent nearly a decade to learn the really hard mathematics to develop the theory of General Relativity so he must have meant something different.

Barbara Wolff, an archivist at the Albert Einstein Archives from 1995-2016, has written in Quora: Now we know that Einstein did not speak English, so Viereck (American writer/poet George Sylvester V. who interviewed Einstein) translated Einstein’s words. "As for 'imagination' the term Einstein used (if !) must have been “Vorstellungskraft” which is the ability to visualize = imagine (make an image of) an idea, a process. connections, whatever… and has nothing to do with phantasy = loose creativity."

I thought of Einstein's famously popular quote when I read Sabine Hossenfelder's post on Einstein's greatest legacy; not the one(s) many of us would immediately think, e.g., general relativity (there are other qualifying candidates). It was, Hossenfelder writes, the Gedankenexperiment (German for 'thought experiment'). I don't implicate her in the connection I made for she never mentioned the quote.

Here are a few execrpts from Hossenfelder (read and/or watch at the link above) on thought experiments which, she says "are common in theoretical physics.  We use them to examine the consequences of a theory beyond what is measureable with existing technology, but still measureable in principle. Thought experiments are useful to push a theory to its limits, and doing so can reveal inconsistencies in the theory or new effects. There are only two rules for thought experiments: (A) relevant is only what is measureable and (B) do not fool yourself. This is not as easy as it sounds." (emphasis added)

Professor Hossenfelder traces the short history of thought experiments, some of the ways in which they have been used, including Einstein's best known, the famous elevator thought* experiment, that seemed to Einstein a challenge to quantum mechanics (a real experiment was subsequently done and has been shown to be real), and a famous one on black holes.

 Hossenfelder concludes with a reminder: "So, yes, thought experiments are a technique of investigation that physicists have used in the past and continue to use today. But we should not forget that eventually we need real experiments to test our theories." (my emphasis)

This is another of her posts that challenge us to think hard and often differently about physics and in general about science--what we think we know. Please click on the Hossenfelder link and read/view. I especially recommend  the responses, many of which slide right by me but provide additional slants on the nature of science. 

*"In 1907, while still a patent clerk, (Einstein) was pondering how one might produce a relativistic theory of gravity and he was not having much success. Then he was struck by the fact that an observer in free fall no longer feels his own weight. He then hit upon what he called 'the happiest thought of my life.' One can produce gravity in gravity free space merely by reversing the process. Acceleration creates a gravitational field. This is his 'principle of equivalence'." (from J. D. Norton) (My emphasis).

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