"We are, each of us, finite beings in a universe which, so far as we can know, is infinite. Whether the universe had a beginning and an end we are not sure - but we are certain we had a beginning and we all know we will have an end. There is a limit to the time during which we can learn things - and there are far too many things to learn for any of us ever to be sure we are an authority except - at best - in small and limited ways."

from here