What If? Serious Scientific Answers to Absurd Hypothetical Questions by Randall Munroe
This book was a lot of fun to read. Randall is a cartoonist with a popular web
page, google XKCD, where people often ask all kinds of questions involving science, engineering
and technology. Many are wild and
fanciful. For example, the question was
asked whether if everyone on earth had a laser pointer and directed it at the
moon, could the reflection be seen from earth?
The way he sets up the answers are always instructive. He lays out assumptions and starting
scenarios. For this one, he makes the
reasonable assumption that the world’s population would have to congregate in a
suitable location on the same side of the earth. And at night of course. He suggests placing everyone in the the
Arabian peninsula, and at a time when the moon is three quarters dark. There would have to be enough moonshine to
know where to point. Laser pointers are usually
about 5 milliwatts each. But, several
billion such eye safe laser pointers striking the moon would be too faint to
see. So he ratches up to a more powerful
laser, by 200 times. It is possible to
buy a 1 watt handheld laser. It is not
recommended. That is enough power to
ruin an eye and can catch things on fire.
Even if each person directed a 1 watt laser accurately to the lunar
surface, the reflection would not be visible on earth. What if every person had an IMAX projector
with a pair of 30,000 Watt lamps? Well
yes, finally, it would be visible.
He answers fifty such questions in a similar way. Often throwing in all kinds of wonderful
factoids.
This is a great way to learn.
