The history of exploration across nations and across time is not one where nations said, 'Let's explore because it's fun.' It was, 'Let's explore so that we can claim lands for our country, so that we can open up new trade routes; let's explore so we can become more powerful.'

Facts are true whether or not you believe them.

Passion is what gets you through the hardest times that might otherwise make strong men weak, or make you give up.

The theory of evolution, like the theory of gravity, is a scientific fact.

For all we know, the aliens have already done this and unwittingly concluded that there was no intelligent life on Earth. They would now be looking elsewhere. A more humbling possibility would be if aliens had become aware of the technologically proficient species that now inhabits Earth, yet they had drawn the same conclusion.

Our entire universe emerged from a point smaller than a single atom. Space itself exploded in a cosmic fire, launching the expansion of the universe and giving birth to all the energy and all the matter we know today. I know that sounds crazy, but there’s strong observational evidence to support the Big Bang theory. And it includes the amount of helium in the cosmos and the glow of radio waves left over from the explosion.

Publicly and among themselves biologists rightly celebrate the diversity of life on Earth... At the end of the day, however, their confession is heard by no one: they work with a single scientific sample-life on Earth.