Instead, we physicists use observation and experiment, together with a hard-to-describe intuitive mathematical sensibility, to guide us toward particular physical laws. We then analyze the laws mathematically to determine which environmental conditions in the earliest moments of the universe, if any, would have sparked the rapid expansion of space. Upon finding, happily, that there are such conditions, we postulate that they held near the big bang and we use the equations to determine what subsequently would have happened.
