Atomic or Astrological time keeping. Nerds everywhere disagree. This raises all sorts of questions about the nature of time or if it can be accurately measured? Should time be measured by terrestial means (the decay of a radioactive isotope) or by astrological means (X-ray emmissons from pulsars)
A wish I had more to offer in this discussion but it has been about four years since my last philosophy class and about three years since I read A Brief History of Time.