By exploring other worlds we safeguard this one. By itself, I think this fact more than justifies the money our species has spent in sending ships to other worlds. It is our fate to live during one of the most perilous and, at the same time, one of the most hopeful chapters in human history.

Imagination will often carry us to worlds that never were. But without it we go nowhere.

Avoidable human misery is more often caused not so much by stupidity as by ignorance, particularly our ignorance about ourselves.

Science is an attempt, largely successful, to understand the world, to get a grip on things, to get hold of ourselves, to steer a safe course. Microbiology and meteorology now explain what only a few centuries ago was considered sufficient cause to burn women to death.

In science it often happens that scientists say, "You know that's a really good argument; my position is mistaken..."

On the day that we do discover that we are not alone, our society may begin to evolve and transform in some incredible and wondrous new ways.

The universe forces those who live in it to understand it.