Clarke's First Law:
When a distinguished but elderly scientist states that something is possible he is almost certainly right. When he states that something is impossible, he is very probably wrong.
Clarke's Second Law:
The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
Clarke's Third Law:
Any sufficiently advanced technology is indistinguishable from magic.
Corollary to Clarke's Third Law:
Any technology distinguishable from magic is insufficiently advanced.
For more information about the man behind these quotes, see Arthur C. Clarke.