Time-Wasting Tip #9 for the Overworked Grad Student

Writer
Graduate Division

Got a long incubation time to kill? Waiting for your cells to spin? Bored in-between classes? In class?  This week take a break by checking out xkcd’s blog “What If?” at what-if.xkcd.com — a weekly treatise on how to estimate the answers to ridiculous, somewhat scientific questions.

Now, the webcomic xkcd deserves a time-waster of its own, but that’s for another time. In addition to posting comics every Monday, Wednesday and Friday, every Tuesday, xkcd answers questions, such as “From what height would you need to drop a steak to have it cooked when it hits the ground?” or “Can you make a jetpack out of downwards-firing machine-guns?” with what are called ‘Fermi approximations.

Apparently these are a big thing in engineering and physics — basically, in addition to being known for being a Nobel-winning physicist, Enrico Fermi was also very good at approximating values for complicated questions with limited data.

For example, he approximated the power of a nuclear detonation — and was off by only an order of two — while only knowing the distance that some pieces of paper drifted following the explosion. Fermi approximations aren’t necessarily accurate, but they’re a good way of identifying and consolidating variables, and getting an idea of the magnitude of whatever the ultimate answer is.

“What if?” demonstrates that they’re also good for finding out how much energy we’d save if cows were photosynthetic.

Check next week for another grad-student approved distraction — suggestions are welcome!