Tuesday, April 03, 2018

Measuring time over long intervals

In this century we have been fortunate to find ways of measuring time over extremely small intervals, but we still are still lacking when it comes to measuring time over large intervals.

A common tool used by calendar makers across many civilization appears to be to use astronomical  precession cycles. The solar and lunar calendars are based on such ideas. These make sense as both bodies are unambiguously identifiable in the sky without the use of telescopes and their precession periods are small enough to be cross calibrated to earth based time keeping measures.  Even relatively crude systems like candles and water clocks can be built to keep a pace with the path of the sun through the sky.

Yet even these simple clocks (based on the Sun and the Moon) are not ideal for long time keeping. This is because the Earth's path around the Sun (and the Moon's path around the Earth) are not perfectly stable orbits and over time they undergo shifts due to the gravitational influences of nearby planets like Jupiter and Saturn. These perturbations are non-trivial over long timescales and any calendar we make using just the Sun and the Moon needs to be updated every 4 or so years.

We can use other stars and planets but we are exposing ourselves to several sources of error.

The further away the astronomical object, the harder it is to observe reliably. Some objects like constellations are relatively easier to identify in the sky, the time periods associated with their travel in the sky are large and the exact path across the sky is deeply correlated with the precession of the Earth's axis.

There are two components to the earth's precession axis and if you don't correct for both - you can assign the wrong time stamp to things.  Also if you aren't careful about your accounting - because these the typical approach is to look for coincidence or intersection of paths - you can have errors that propagate down the computation.

I am talking about things like this
Again this is nothing new - as real timekeepers go - this is all part of the job description. 

Calendar makers will refuse to make a calendar that doesn't have a run out date. It is physically impossible to make a calendar that is infinitely valid. At some point - the errors in your calculation propagate to the point where the prediction of the timestamp is worthless. (hint hint!! - that is why the Maya calendar runs out at a particular date). 

Archaeologists, geologists and historians - typically refrain from using stellar precession records as part of a dating scheme. The rationale behind this is very solid - the languages in which these records are made are difficult to interpret with certainty and little to nothing is known about the details of the coincidence events. Most of those events 

So these folks work with more definite chronological measures [1]. 

I agree this method is not always in agreement with myths which tend to take on a kind of timelessness but it is the only method that gives consistent and reproducible results. 

That may not sound like what people want to hear - but that is the only way science works. If you can't get consistent/reproducible results - you have nothing. 


At 8:22 AM, Blogger Ralphy said...

i'd like to see some carbon 14 dating correlation to some of these events......just sayin'....as it were.....


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