Now' is an interesting concept, and it has been defined reasonably well for at least the last several millennia, but how well do we understand it, and what does it really mean?

Studies of brain function and perception have shown that there is a lag between stimulus and the brain's reaction to the stimulus. Such a lag is necessary, because impulses have to travel along nerves to the brain, and the electrolytic conduction of nerves is not instantaneous; it isn't even as fast as a current...