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[ontolog-forum] Rethinking Time in Distributed Systems

To: "'[ontolog-forum] '" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: John F Sowa <sowa@xxxxxxxxxxx>
Date: Sun, 02 Mar 2014 08:05:19 -0500
Message-id: <53132C8F.6090209@xxxxxxxxxxx>
The subject line is the title of a talk that Paul Borrill presented
at Stanford a few years ago.  It's important for many issues about
time that have been discussed in Ontolog Forum.    (01)

In particular, he emphasizes the complexities of time, the difficulty
of defining time, and the disasters that have been caused by treating
time as a Newtonian linear sequence.    (02)

The talk:  http://www.youtube.com/watch?v=VKkGqNRlUJM    (03)

The slides:
http://www.stanford.edu/class/ee380/Abstracts/091111-RethinkingTime.pdf    (04)

The slides are useful for an overview, but the talk is much richer.
It's packed with examples and stories that aren't on the slides.    (05)

Three of many examples:    (06)

  1. For a multi-core chip, each core maintains its own clock. The time
     delays for signals passing across the chip make it impossible to
     keep the clocks exactly synchronized.    (07)

  2. For GPS, even special relativity is not sufficiently accurate.
     People on earth are sitting in a deep gravity well compared to the
     satellites.  GPS requires the corrections of general relativity.    (08)

  3. The disaster of the Challenger space shuttle, for which he was
     on the engineering team.    (09)

Borrill's conclusion:  Simultaneity is a myth.  Except for a single
local observer, don't assume a linear time.  In a distributed system,
never depend on clocks to serialize anything.    (010)

I also like the slogan of his company:  "Radical simplicity."
That is his recipe for designing reliable systems.    (011)

His final slide is a quotation by Leonardo da Vinci:
"Simplicity is the ultimate sophistication."    (012)

John    (013)

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