The last sentence in point 2 of my previous message should have be:
"To keep the time which is displayed by our watches
more or less connected to earth rotation, one can easily adopt
the zone time."
What I mean is the following: Today, Central European Time (CET) is
UTC + 1 h. When UTC differs from UT1 by nearly 1 second (usually
UT1 is behind UTC), UTC clocks are practically stopped for a second
("leap second"). When there will be no leap seconds any longer,
after some 5000 years or so UTC will be ahead UT1 by about 1 h.
Instead of stopping UTC clocks for one hour ("leap hour"), one
may adopt zone time, so that CET = UTC. Great Britain will have
a zone time of UTC - 1 h, etc. We practice this twice each year
with summer time: Our watches have to be re-set by 1 h - but UTC runs
without any change! The same may be after 5000 years: UTC clocks
do not have to be re-setted, just our normal watches. Who cares about
UTC in every-day life? Our watches run in parallel to UTC
and normally do not display UTC. But the existence of a continues
time scale for technical and scientific purposes is very important.
There is no need to keep UTC connected to UT1.
When there will be no leap seconds, UTC is practically the same as
atomic time TAI, except for a shift. One could switch to TAI
as a continous time scale, but this would mean that the time scale
would be discontinous (the difference of UTC and TAI is 32 seconds
at this moment, next year it will be 33 seconds).
Wolfgang Dick
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