The number 42 in Douglas Adams' The Hitchhiker's Guide to the Galaxy, is the number from which all meaning ("the meaning of life, the universe, and everything") could be derived.

The number 42 is manifest in our universe in many ways. It is:

* The angle at which light reflects off of water to create a rainbow is 42 degrees.
* Two physical constants in the universe are the speed of light and thediameter of a proton. It takes light 10 to the minus 42nd power seconds to cross the diameter of a proton.
* The sum of the ordinal alphabetic positions of the initials (SPG) for Stan (P.) Gibilisco, an oft-published science and technology writer, is equal to 42 (S=19, P=16, G=7).
* A barrel holds 42 gallons.


It is also the age the Elvis lived to. That in itself makes 42 an important number to remember.