But now think about what I would have to do to prove to you that I had no cockroaches living in my house. I'd have to be able to observe every cubic inch of my house: the floors, the ceilings, the walls, the furniture, the cabinets; every cubic inch of my house--all at the same time, because cockroaches move. Simultaneously I'd have to examine every cubic inch of my house to prove to you that there were no cockroaches living in it. So it's a difficult thing to prove a negative, and so it is with god.
Science is agnostic when it comes to the existence of god, and it has to be. You can't apply the scientific method to this question. And so if you were to ask me if I believed in god, since I am a professional scientist I would want to give you two answers. In my capacity as a professional scientist I would have to--I would be required to--be agnostic on the subject, since I couldn't say with scientific certainty that there is a god, and I couldn't with scientific certainty say that there isn't'.
But if I were allowed to respond just as a regular non-scientist, and if you allowed me to take the very same indulgences that all other non-scientists are allowed to take--and that is I'm allowed to reject the training I received as a scientist that taught me--that drilled into my head--not to except anything as fact that can't be scientifically proven, but instead I'm allowed to do what many others do and profess to know something, and profess to believe it in the complete absence of facts, then I would have to say (just as a regular schmo) that my very strong faith--my very very strong belief--is that there is no god.
On this level, my belief is perfectly equivalent to religious belief; we're both doing the same thing. So when a scientist says: "the charge on an electron is 1.602 x 10-19 coulombs," that is not an expression of belief or faith; that is an established fact. It's based on many, many Galileo-type experiments following the format that was established by Galileo four hundred years ago. It is not at all equivalent to religious belief.
But when a scientist says there is no god, and he's acting in the capacity of a scientist, he is not giving you a scientific conclusion on the subject. He is at that moment expressing a personal belief and opinion. Now it may be that to some that's an opinion that carries more weight, because after all it's coming from a person who's been trained in examine things using the principles of logic, using induction, using detection and so on, and it's coming from a person who's trained to withhold final judgement until all the facts are in. But nonetheless it can only be an opinion. And in this case, it is as I said an opinion that could be put on a par with religious belief, because both are expressed in the absence of evidence.