It seems like human understanding of space can be no clearer than our understanding of time. I still don't understand time. On the one hand it is a discrete interval; but it is also continuous and infinite. All our science is based on an understanding of this time concept and its constructions. Is there a solid understanding of time out there? What is it? Much like PI is an irrational number (perhaps because it represents the relationship between the continuous length of a circle and the discrete length of its diameter) so it seems that time may also be irrational in our minds. If so, how could space-time be any different? Why don't scientists spend more time explaining time? And why is the art of science in its attempt to describe the world we live in defined as being "time-invariant"?