There would seem to be nothing more obvious, more tangible and palpable than the present moment. And yet it eludes us completely. All the sadness of life lies in that fact. In the course of a single second, our senses of sight, of hearing, of smell, register (knowingly or not) a swarm of events and a parade of sensations and ideas passes through our head. Each instant represents a little universe, irrevocably forgotten in the next instant.