The Wonky Physicist

A short story, one of my favorites. In a physics test at the University of Copenhagen the examiner gave the following question to the students: “Describe how to determine the height of a skyscraper with a barometer.”

One student replied: “You tie a long piece of string to the neck of the barometer, then you lower the barometer from the roof of the skyscraper to the ground. The length of the string plus the length of the barometer will equal the height of the building.” An undeniably correct answer but one that angered the examiner and the student was failed.

The student appealed, claiming that his answer was factually correct. The university referred the case to an independent arbiter who ruled that the answer was indeed correct but did not reflect a passable knowledge of physics. Still a conundrum, the university decided give a retest. He was allowed six minutes to give a verbal answer to the question. For five minutes the student stared out the window until the examiner shook him out of his reverie. This time he answered:

• “First, you could take the barometer up to the roof of the skyscraper, drop it over the edge, and measure the time it takes to reach the ground. The height of the building can then be worked out from the formula H = 0.5g x t squared. But bad luck on the barometer.”
• “If the sun is shining you could measure the height of the barometer, then set it on end and measure the length of its shadow. Then you measure the length of the skyscraper’s shadow, and thereafter it is a matter of proportional arithmetic to work out the height of the skyscraper.”

He carried on:

• “If you wanted to be highly scientific about it, you could tie a short piece of string to the barometer and swing it like a pendulum, first at ground level and then on the roof of the skyscraper. The height is worked out by the difference in the gravitational restoring force T = 2 pi square root (l/g).”
• “If you want to be orthodox, of course, you could use the barometer to measure the air pressure on the roof of the skyscraper and on the ground, and convert the difference in millibar into feet to give the height of the building.” (The answer the examiner was looking for).

Then the student added:

• “But since we are constantly being encouraged to think in practical terms, if the skyscraper has an outside emergency staircase, it would be easy to walk up and mark off the height of the skyscraper in barometer lengths and then add them up.”

The student was Niels Bohr who later became famous for proposing that the electrons of an atom are, like the planets in our solar system, orbiting around the nucleus. Bohr would be the first Dane to win the Nobel Prize for Physics in 1922 and the element bohrium was named after him. 

Bohr shows there are often many answers to a question which are correct but may not fit the existing paradigm. Isn’t this the essence of creativity: to think outside of an existing mind frame and look at a problem from many angles?

Bohr’s final solution to the barometer problem: “Knock on the janitor’s door and say to him: “If you would like a brand new barometer, I will give you this one if you tell me the height of the skyscraper”. Simple, original and solves the problem.

This story of Niels Bohr is based on urban legend and is not necessarily true. 

But then, being a story, does it really matter?