Scientists out there, what are the best physical constants or material properties to have memorized for back-of-the-envelope calculations? [more inside]
posted by SBMike on Jul 17, 2007 - 25 answers

Is there any evidence that physical laws have changed, or could possibly change over time? For example, has the speed of light - since the beginning of the universe - been the same, and will it always remain the same into the future? [more inside]
posted by extrabox on May 31, 2006 - 23 answers