Monday, December 20, 2021

What If?

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. 

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