∆ Seconds and inches
tbc
Units of time are often compared to units of length, in that while we may describe a pencil as 4 inches long, we may also debate whether 'inches' really 'exist'. But such a debate is not really about reality. The pencil clearly has a length, and the inch is just an arbitrary and convenient subdivision of this length.
The problem arises if we see 'seconds' as arbitrary sub divisions of minutes (and so on). This is an issues because while in a sense it is true, it may also falsely give us the idea that seconds are as real as inches. While in fact we can show that distances, lengths etc can be seen to really exist, while 'time' need not. When for example we talk of a car travelling at 160 kilometres per hour, it seems as if cars, kilometres, motion and hours must all exist. In fact it may just be that cars, kilometres and motion exist.
in saying 160 km ph we are really just comparing the speed 'now' of the car to the speed of some other useful object 'now'. ) in this case the speed of the rotating earth).
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