In Munich in the days of the great theoretical physicist Arnold Sommerfeld (1868–1954), trolley cars were cooled in summer by two small fans set into their ceilings. When the trolley was in motion, air flowing over its top would spin the fans, pulling warm air out of the cars. One student noticed that although the motion of any given fan was fairly random—fans could turn either clockwise or counterclockwise—the two fans in a single car nearly always rotated in opposite directions. Why was this? Finally he brought the problem to Sommerfeld.
“That is easy to explain,” said Sommerfeld. “Air hits the fan at the front of the car first, giving it a random motion in one direction. But once the trolley begins to move, a vortex created by the first fan travels down the top of the car and sets the second fan moving in precisely the same direction.”
“But, Professor Sommerfeld,” the student protested, “what happens is in fact the opposite! The two fans nearly always rotate in different directions.”
“Ahhhh!” said Sommerfeld. “But of course that is even easier to explain.”
The story appears to be apocryphal. I’ve heard many versions of it associated with various famous scientists. The source quoted is a collection of jokes, with very low veracity. Additionally, there are no independent versions of the story anywhere on Google. By the way, the quoted date of Sommerfeld’s death is also incorrect. I wonder if there even were (unpowered) ceiling fans in Munich’s trolleys during that time.
I wonder if there even were (unpowered) ceiling fans in Munich’s trolleys during that time.
I’m not much of an engineer, but based on my understanding of their design from the description given, I can’t see how they would even contribute to their alleged purpose.
It’s an interesting story, but it might not be as silly as it sounds if one considers “ease of explanation” as a metric for how much credence one’s model assigns to a given scenario. (Yes, I agree this is a hackneyed way of modeling stuff.)
Well, the world is a complicated place and we have limited working memory, so our models can only be so good without the use of external tools. In practice, I think looking for reasons why something is true, then looking for reasons why it isn’t true, has been a useful rationality technique for me. Maybe because I’m more motivated to think of creative, sometimes-valid arguments when I’m rationalizing one way or the other.
Devine and Cohen, Absolute Zero Gravity, p. 96.
So, uh, what’s the explanation?
The story appears to be apocryphal. I’ve heard many versions of it associated with various famous scientists. The source quoted is a collection of jokes, with very low veracity. Additionally, there are no independent versions of the story anywhere on Google. By the way, the quoted date of Sommerfeld’s death is also incorrect. I wonder if there even were (unpowered) ceiling fans in Munich’s trolleys during that time.
Good point. Effects that don’t exist don’t need to be explained.
I’m not much of an engineer, but based on my understanding of their design from the description given, I can’t see how they would even contribute to their alleged purpose.
Perhaps because pressure is (approximately) constant, for every molecule going into the car, one must leave it (on average)?
Trolleys have open windows in summer.
It’s an interesting story, but it might not be as silly as it sounds if one considers “ease of explanation” as a metric for how much credence one’s model assigns to a given scenario. (Yes, I agree this is a hackneyed way of modeling stuff.)
Unfortunately, this seems to be the default way humans do things.
Well, the world is a complicated place and we have limited working memory, so our models can only be so good without the use of external tools. In practice, I think looking for reasons why something is true, then looking for reasons why it isn’t true, has been a useful rationality technique for me. Maybe because I’m more motivated to think of creative, sometimes-valid arguments when I’m rationalizing one way or the other.