How to coordinate the clock when dual-booting with Windows

Peter Silva peter at
Sun Dec 10 19:43:45 UTC 2017

There is nothing special about UTC, any more than there is anything
special about Greenwich, or Earth. One just needs to select a known
reference in order to compare times in different frames.  This is the
entire reason the metric system was invented.  When every local area
could have it's own units of measure, commerce over large distances
was difficult because amounts of anything were very difficult to
compare. It is the normal and general solution for everyone to agree
on a standard unit, folks convert from their locally convenient unit
to the reference and vice versa.

Without that sort of convention, how would you suggest to arrange a
meeting of 10 spacecraft initially travelling at different velocities
in different directions at a given location, velocity and direction,
at a given time?  They need to agree on a common measure of time, and
it doesn't matter what it is, but it has to be common.  To do anything
else would do extreme violence to Ockam's razor.

On Sun, Dec 10, 2017 at 12:26 PM, Xen <list at> wrote:
> Peter Silva schreef op 10-12-2017 18:00:
>> If you don't know your timezone, then you don't know what time it is.
> Then you don't know what time it is, because you don't know the time with
> respect to the rest of the universe.
>> This relative/absolute dichotomy is a red-herring, because time isn't
>> only used within one frame of reference.
> The frames are relative to one another.
>> Time is very often use to co-ordinate things among people who aren't
>> in the same frame of reference.   It's just like timezones, only worse
>> with Einstein because now time doesn't even run at the same speed.
>> How do you schedule a meeting between someone on earth and someone
>> orbiting at a speed where relativity is an issue?
>> You need a means to map the various relative times to the standard
>> one, and then communicate in the standard time reference.   This isn't
>> at all academic.  All (LEO) navigation satellites are built to
>> account the fact that the atomic clocks on board are running slower
>> relative to the earth because of their relative velocity to their
>> users.
> So they translate their local frame to the earth frame, which is really only
> sensible if you are going to move information to earth.
> Now of course you suggest that they "keep up" their time by adding a
> multiplication and thus make sure they always have Earth time, right?
> Thus they keep UTC time at all times.
> But they can do this because they are orbiting a planet and thus the planet
> is the frame of reference.
> Effectively they don't "know" what UTC time is, it is just a time they've
> been set to and try to "keep up", if they lose it, they can't magically
> rediscover UTC time, except by measuring the physical properties of the
> Earth relative to the Sun or something like that.
> We also don't know what our time is with regards to daylight savings, but
> that is a warp regardless.
> If you move into space, it is said, you lose a sense of up/down, left/right.
> I don't discount that hierarchy forms part of the universe, ie. moons belong
> to planets, planets to suns, and so on.
> Yet would you advocate keeping time locally on Earth in the central time of
> some higher-up central sun that you were part of?
> Even supposing these translations would be simple, how are you going to keep
> Earth time in the time frame of some planet with 30 hour days?
> Would you seriously consider adopting a 30 hour day calendar just so you can
> speak the "same language"?
> And then call everything else "insane"? :).
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