If you wish to make an apple pie from scratch, you must first invent the universe.

Chlorine is a deadly poison gas employed on European battlefields in World War I. Sodium is a corrosive metal which burns upon contact with water. Together they make a placid and unpoisonous material, table salt. Why each of these substances has the properties it does is a subject called chemistry.

Those who seek power at any price detect a societal weakness, a fear that they can ride into office.

We can't help it. Life looks for life.

I also wish that the Pledge of Allegiance were directed at the Constitution and the Bill of Rights, as it is when the President takes his oath of office, rather than to the flag and the nation

In more than one respect, the exploring of the Solar System and homesteading other worlds constitutes the beginning, much more than the end, of history.

When you make the finding yourself - even if you're the last person on Earth to see the light - you'll never forget it.