Orders of Magnitude Fermi Estimates and Understanding Numbers This was my idea of a Fermi Question: Turn every experience into a question. Can you analyze it? If not, you'll learn something. If you can, you'll also learn something. - Philip Morrison, Ph.D.

Enrico Fermi ( ) Born in Italy Earned Ph.D. in physics at the age of 21. Received Nobel Prize in 1938, for work on “Artificial Radioactivity Produced by Neutron Bombardment”. Emigrated to U.S. in 1938, mostly to escape the fascist regime of Mussolini. Lead work in Chicago which resulted in the first controlled nuclear reaction. –This ultimately lead to the development of the atomic bomb. In 1944 became an American citizen. Died in Chicago in Today the Fermi National Accelerator Laboratory in Batavia, IL is named after him. Sources: %20at%20Trinity,%20July%2016,% pdf

Time and Distance

"How many piano tuners are there in Chicago?"piano tunersChicago To start you have to make some reasonable guesses. –Approximately 5,000,000 people living in Chicago. –On average, there are two persons in each household in Chicago. –Roughly one household in twenty has a piano that is tuned regularly. –Pianos that are tuned regularly are tuned on average about once per year. –It takes a piano tuner about two hours to tune a piano, including travel time. –Each piano tuner works eight hours in a day, five days in a week, and 50 weeks in a year. From these assumptions we can compute that the number of piano tunings in a single year in Chicago is: Source:

Sources: N. Angier, The Biggest of Puzzles Brought Down to Size, The New York Times, Weinstein and Adam, guesstimation, 2008

1 mile ~ 1.6 km Need: Diameter of golf ball. Circumference of earth. 1 inch ~ 2.5 cm The diameter of golf ball is ~1.5 inches or ~4 cm The circumference of the Earth is a little more tricky. If you can remember it or the Earth’s radius great, but I never do. But I do remember that it is about 3,000 miles from the east coast to the west coast and that is about 1/8 the distance around the earth. So the circumference is ~ 24,000 miles or ~40,000 km

~33 km or ~ 20 mi