[One's] inability to invalidate your hypothesis is not at all the same thing as proving it true.

If we can't think for ourselves, if we're unwilling to question authority, then we're just putty in the hands of those in power.

The prediction of nuclear winter is drawn not, of course, from any direct experience with the consequences of global nuclear war, but rather from an investigation of the governing physics.

But the fact that some geniuses were laughed at does not imply that all who are laughed at are geniuses. They laughed at Columbus, they laughed at Fulton, they laughed at the Wright Brothers. But they also laughed at Bozo the Clown.

In all our searching, the only thing we've found that makes the emptiness bearable is each other.

Some 5 billion years from now, there will be a last perfect day on Earth... then the sun will begin to die, life will be extinguished, the oceans will boil and evaporate away.

Except in pure mathematics, nothing is known for certain (although much is certainly false).