For periodicity to be conceived, a relationship of regular repetition must be able to be observed which can be continually compared to the memory of a previous configuration. The most primordial cycles of the solar day, the lunar month and the sidereal year, can be established as periodicities in the memory of a single awareness and hence eventually invoke the concept of time. It is seductively tempting to suppose that change alone is sufficient to enable conceptualizing time, but this is not the case. Our conscious awareness is so intricately accustomed to the pulse and beat of the biological processes sustaining us, that they become entirely taken for granted, so that when we observe change, we also attribute a passage of time. But an effort of introspection seems to suggest, that if every periodicity was purged from either conscious or unconscious perception, then a sense of time would be inconceivable.

Beyond the lifespan of individuals, longer periodicities are more difficult to establish. The first comet to be identified as a periodically returning celestial entity... and not a random mystical portent of some significant event... was one which was recognised when historical records were checked. The period of about seventy-six years makes it a once in a lifetime experience for most humans, although several tortoise can recall the last two or three apparitions quite clearly.

Although it is the stored-remembered evidence of periodicity that engenders the concept of time in an awareness, the cosmos retains... and so in a sense 'remembers'... evidence of its own cyclic evolution. Complexification in the composition of stars, the chemical and physical structure of rocks, and the fossil remnants of biological life, etc., ensures that there is indeed a sense in which it can be asserted that time 'exists' independently of an individual awareness thinking about it.

Time is not absolute but relative to the periodicity chosen. It is probable that no periodicity is absolute, but is effected by motion and the strength of gravitational fields and various of the perturbations intrinsic to the universe. Time as measured by one particular periodicity is variable when compared to a different periodicity. The oscillations of anything... including the nine thousand one hundred and ninety two million, six hundred and thirty one thousand, seven hundred and seventy cycles per second of a Caesium atom... will not be independent of the chaos of the universe. If time is a concept which depends upon periodicity, and the periodicity is observed in diverse circumstances, then there will in all probability be discrepancies. This is no different from any other quantity we wish to measure. If we want a reference standard to measure our perceived dimension of time, then we simply set up the standard in defined conditions just as we do for all the other dimensions we choose to try and measure. The supposition that time is some sort of intrinsic cosmic-independent parameter, that forms a constant and invariable eternal background to existence, is really not sustainable or helpful. The constancy or otherwise of a measured velocity... of light say... which is the ratio of the two separate quantities length and time, could well be a function of the variability of periodicity.

It is meaningless to interpolate minuscule durations of a present standard periodicity... like 'seconds'... to a putative primordial phase of a cosmic singularity, if there was no periodic change intrinsic to that phase. There would be no periodicities to compare. To speculate that a supposed initial phase of an expanding universe 'lasted' for a time equivalent to one second divided by ten to the power of forty-three, is an academic extrapolation of cosmic proportions.

It is only when things come round that time is unwound. Periodicity is the property of a physical system. Deciding what existential factors influence any specific periodic phenomenon is one of the great challenges facing scientific simplification.