Knowing it — knowing it's true is one thing, but believing what you know... well, there's the tough part.

Most people like to believe something is or is not true. Great scientists tolerate ambiguity very well. They believe the theory enough to go ahead; they doubt it enough to notice the errors and faults so they can step forward and create the new replacement theory. If you believe too much you'll never notice the flaws; if you doubt too much you won't get started. It requires a lovely balance.

It takes a certain amount of courage to tackle very hard problems in science, I now realise. You don't know what the timescale of your work will be: decades or only a few years. Or your approach may be fatally flawed and doomed to fail. Or you could get scooped just as you are finalising your work. It is very stressful.

I am often asked what it is like to be a scientist and how one goes about being a scientist. I find such questions uncomfortable because I know of no nicely potted answers to them. It is necessary to dig deep into one’s own experience to produce anything like a worthwhile assessment. And this is to risk the perils of autobiography, usually so fascinating to the narrator and so boring to the reader.

At the heart of science is an essential balance between two seemingly contradictory attitudes - an openness to new ideas, no matter how bizarre or counterintuitive, and the most ruthlessly skeptical scrutiny of all ideas, old and new. This is how deep truths are winnowed from deep nonsense. The collective enterprise of creative thinking and skeptical thinking, working together, keeps the field on track. Those two seemingly contradictory attitudes are, though, in some tension.

At the heart of science is an essential balance between two seemingly contradictory attitudes — an openness to new ideas, no matter how bizarre or counterintuitive they may be, and the most ruthless skeptical scrutiny of all ideas, old and new. This is how deep truths are winnowed from deep nonsense.

The scientist has a lot of experience with ignorance and doubt and uncertainty, and this experience is of very great importance, I think. When a scientist doesn't know the answer to a problem, he is ignorant. When he has a hunch as to what the result is, he is uncertain. And when he is pretty darn sure of what the result is going to be, he is still in some doubt. We have found it of paramount importance that in order to progress we must recognize our ignorance and leave room for doubt. Scientific knowledge is a body of statements of varying degrees of certainty — some most unsure, some nearly sure, but none absolutely certain.<P> Now, we scientists are used to this, and we take it for granted that it is perfectly consistent to be unsure, that it is possible to live and not know. But I don't know whether everyone realizes this is true. Our freedom to doubt was born out of a struggle against authority in the early days of science. It was a very deep and strong struggle: permit us to question — to doubt — to not be sure. I think that it is important that we do not forget this struggle and thus perhaps lose what we have gained.

I take it you're not a believer, Meroka?" "Are you?" "I don't believe." He paused theatrically. "In anything. I question. I doubt. I doubt and I doubt consistently and systematically. It's called thinking scientifically." "I hope you understand what the fuck that means," Meroka said, because I sure don't." "I wouldn't expect you to, my dear. The world isn't exactly conducive to scientific thinking. Not in its present condition. But it's changing, and so must we. Those of us who can, anyway.

There are no forbidden questions in science, no matters to sensitive or delicate to be probed, no sacred truths. That openness to new ideas, combined with the most rigorous, skeptical scrutiny of all ideas, sifts the wheat from the chaff. It makes no difference how smart, august, or beloved you are. You must prove your case in the face of determined, expert criticism. Diversity and debate are valued. Opinions are encouraged to contend–substantively and in depth.

The constant questioning of our values and achievements is a challenge without which neither science nor society can remain healthy.

I’m talking about a specific, extra type of integrity that is not lying, but bending over backwards to show how you’re maybe wrong, that you ought to have when acting as a scientist.

Once you start doubting, just like you’re supposed to doubt, you ask me if the science is true. You say no, we don’t know what’s true, we’re trying to find out and everything is possibly wrong.

One thing being a scientist has taught me is that you can never be certain about anything. You never know the truth. You can only approach it and hope you get a bit nearer to it each time. You iterate towards the truth. You don't know it.

Anybody who has been seriously engaged in scientific work of any kind realizes that over the entrance to the gates of the temple of science are written the words: Ye must have faith. It is a quality which the scientist cannot dispense with.