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Re: Is time an illusion?

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On 25.09.17 22.30, Daniele Futtorovic wrote:
> I'm trying to synchronise a process between two machines (actual, not
> virtual). I require sub-millisecond precision.

What is the distance between these two machines?

If they are far away there is not even a physical definition of the term 
"the same time" within the required precision. The theory of relativity 
prohibits this. The maximum theoretical distance for let's say 0,1ms is 
30km.
However, you can still make more precise assumptions about time 
differences under certain conditions.


> I have the impression that I'm seeing time drift in this process.
> Disregarding measurement errors, the differences between the clocks seem
> to increase over time.
>
> Q: Is this to be expected?

Yes.

> Are 10^9 nanoseconds on box A possibly not 10^9 nanoseconds on box B?

Exactly. They are not even the same when box A resides on a different 
location on earth.
But anything else depends on what you accept as "the same".

> If so, seriously, what the heck? I'm aware I might have stumbled on a
> very elementary truth here after so many years in the business, but I
> must say, the idea itself feels deeply unsettling.

Welcome to real world. ;-)

> Existential musings aside, would any of you have suggestions as to how
> tackle the issue?

Supply both computers with an atomic clock.
Reasonable Rubidium clocks are not that expensive. The most challenging 
task is to synchronize this clocks and, of course, avoid power failures 
after that.

A GPS clock might also be an alternative. They have very good long term 
precision - basically limited by the Caesium clocks of the sattelites -, 
but may suffer short term stability because of atmospheric effects or 
interference.

ntp, as recommended, is /not/ sufficient to synchronize within 
microsecond precision.


Marcel

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Thread

Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-25 22:30 +0200
  Re: Is time an illusion? Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-09-25 18:02 -0400
    Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-26 00:16 +0200
      Re: Is time an illusion? Jerry Stuckle <jstucklex@attglobal.net> - 2017-09-25 19:18 -0400
      Re: Is time an illusion? Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-09-26 15:37 -0400
        Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-27 01:13 +0200
          Re: Is time an illusion? Jerry Stuckle <jstucklex@attglobal.net> - 2017-09-26 21:00 -0400
            Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-27 04:26 +0200
              Re: Is time an illusion? Jerry Stuckle <jstucklex@attglobal.net> - 2017-09-26 23:32 -0400
                Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-28 10:58 +0200
                Re: Is time an illusion? Jerry Stuckle <jstucklex@attglobal.net> - 2017-09-28 12:50 -0400
            Re: Is time an illusion? Eric Douglas <e.d.programmer@gmail.com> - 2017-09-27 05:25 -0700
            Re: Is time an illusion? Arne Vajhøj <arne@vajhoej.dk> - 2017-09-30 22:57 -0400
  Re: Is time an illusion? Arne Vajhøj <arne@vajhoej.dk> - 2017-09-25 20:22 -0400
  Re: Is time an illusion? Marcel Mueller <news.5.maazl@spamgourmet.org> - 2017-09-26 20:18 +0200
    Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-27 01:30 +0200
      Re: Is time an illusion? lewbloch@gmail.com - 2017-09-28 10:52 -0700
  Re: Is time an illusion? Eric Douglas <e.d.programmer@gmail.com> - 2017-09-26 12:59 -0700
    Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-27 01:42 +0200
  Re: Is time an illusion? lewbloch@gmail.com - 2017-09-28 10:49 -0700
    Re: Is time an illusion? Robert Klemme <shortcutter@googlemail.com> - 2017-09-28 22:33 +0200

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