Science is about natural law, while religion is about ethics. As long as you keep these two separate, Kaku says, there’s no problem at all. Problems arise, however, when the natural sciences begin to “pontificate upon ethics” and when religious people begin to pontificate about natural law.
Albert Einstein believed in the “god of Spinoza”—not a personal god, but one who has set order and harmony in the fabric of the universe. “You can put the laws of physics as we know them on a simple sheet of paper—amazing! It didn’t have to be that way,” says Kaku.
The existence of God is not testable because such a review is not reproducible or falsifiable, as most scientific investigations are. In this sense, Kaku says the question and answer whether God exists rests outside the “normal” boundaries of science.