Trillionths

In a review of Stephen Hawking's The Grand Design (subscription
required), physicist Steven Weinberg criticizes Hawking for concluding that "we
have no free will":

[Hawking] attributes the
illusion of free will to the fact that a human being contains about a thousand
trillion trillion particles, so that as a practical matter it is impossible to
predict what people will do.

This is a sign, says Weinberg, that Hawking
"overestimates the ability to answer deep philosophical questions." (Meanwhile,
practical souls may wonder how many particles will disappear in a good
weight-loss program--"I am down to 999 trillion trillion particles," etc.)