Theory Group of INFN, Sezione di Torino, and Dipartimento di Fisica Teorica, Università di Torino

... what is limited is not limited in relation to anything.
Aristotle - Physics, Book III

Wheeler's first moral principle: "Never make a calculation until you know the answer". Make an estimate before every calculation, try a simple physical argument (symmetry! invariance! conservation!) before every derivation, guess the answer to every paradox and puzzle. Courage: No one else needs to know what the guess is. Therefore make it quickly, by instinct. A right guess reinforces this instinct. A wrong guess brings the refreshment of surprise. In either case life as a spacetime expert, however long, is more fun!
E.F. Taylor and J.A. Wheeler, Spacetime Physics, W.H. Freeman and Company, New York, 1992,
Second edition, p.20

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