The past history of human belief is a cautionary tale. We have killed thousands of our fellow human beings because we believed they had signed a contract with the devil, and had become witches. We still kill more than a thousand people each year for witchcraft. In my view, there is only one hope for humankind to emerge from what Carl Sagan called "the demon-haunted world" of our past. That hope is science.

Kids didn't have huge backpacks when I was their age. We didn't have backpacks at all. Now it seemed all the kids had them. You saw little second-graders bent over like sherpas, dragging themselves through the school doors under the weight of their packs. Some of the kids had their packs on rollers, hauling them like luggage at the airport. I didn't understand any of this. The world was becoming digital; everything was smaller and lighter. But kids at school lugged more weight than ever.

In order not to be misunderstood, I want it perfectly clear that I believe it is incumbent on us to conduct our lives in a way that takes into account all the consequences of our actions, including the consequences to other people, and the consequences to the environment.

Right now, scientists are in exactly the same position as Renaissance painters, commissioned to make the portrait the patron wants done, And if they are smart, they'll make sure their work subtly flatters the patron. Not overtly. Subtly.

Human beings are so destructive. I sometimes think we're a kind of plague, that will scrub the earth clean. We destroy things so well that I sometimes think, maybe that's our function. Maybe every few eons, some animal comes along that kills off the rest of the world, clears the decks, and lets evolution proceed to its next phase.

In other centuries, human beings wanted to be saved, or improved, or freed, or educated. But in our century, they want to be entertained. The great fear is not of disease or death, but of boredom. A sense of time on our hands, a sense of nothing to do. A sense that we are not amused.

The work of science has nothing whatever to do with consensus. Consensus is the business of politics. Science, on the contrary, requires only one investigator who happens to be right, which means that he or she has results that are verifiable by reference to the real world. In science consensus is irrelevant. What is relevant is reproducible results. The greatest scientists in history are great precisely because they broke with the consensus.