John,
This is very helpful perspective - thanks for that. I didn't see
anything specifically talking about different rates of time passing, but for
my purposes I can just think of my satellite clock as Clock A and a
terrestrial clock as Clock B. Nothing in what you references says they have
to tick at the same rate, so I think I'm OK. I'll just have to allow for a
"rate" factor (which is actually built in to the clocks on the satellites
anyway). (01)
- Steve (02)
Steven R. Ray, Ph.D.
Distinguished Research Fellow
Carnegie Mellon University
NASA Research Park
Building 23 (MS 23-11)
P.O. Box 1
Moffett Field, CA 94305-0001
Email: steve.ray@xxxxxxxxxx
Phone: (650) 587-3780
Cell: (202) 316-6481
Skype: steverayconsulting (03)
-----Original Message-----
From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
[mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of John F Sowa
Sent: Wednesday, April 08, 2015 12:24 PM
To: ontolog-forum@xxxxxxxxxxxxxxxx
Subject: Re: [ontolog-forum] Looking for some pragmatic guidance on modeling
relativistic time events (04)
Steve, (05)
Carl Adam Petri and his colleagues have been working on related ideas for
years. He developed his widely used net theory in his PhD dissertation in
1962, and he headed a group at a research center in Bonn (GMD) for many
years. (06)
His general principle is that clock time is an abstraction that uses one
kind of process (called a clock) as a standard for defining a metric for
timing other processes. But the choice of clocks, the assumptions about
their reliability, and the assumptions about synchronizing them are
problematical. (07)
Petri noted that a metric-free theory of time is both more general and more
appropriate for a wide range of phenomena. For metric time, the most
general ontology is to assume that (08)
1. Every clock is a process that measures time in linearly ordered
units called ticks. (Since the clock itself is the standard,
it's meaningless to ask questions about its accuracy -- except
in comparison to some other clock. Note the joke about the man
with two watches.) (09)
2. For any two processes timed by a given clock, their times
can be compared to a resolution of one tick of that clock.
Those ticks are called the _local time_ for those processes. (010)
3. For a global system with multiple clocks, the most general
assumption is that clock time is partially ordered. (011)
4. When different local times are compared, it's important to
to determine how and when (according to each clock's local
time) they were synchronized. (012)
For a brief summary of the issues and ontologies for time, see (013)
http://www.jfsowa.com/ontology/process.htm (014)
For a more detailed discussion of issues related to time and causality, (015)
http://www.jfsowa.com/ontology/causal.htm (016)
For a 50-year assessment of Petri's research, (017)
http://www-dssz.informatik.tu-cottbus.de/publications/materials/silva-2013-5
0years-of-pn.pdf (018)
For more references, google the keywords 'Petri', 'time', 'metric-free', and
'asynchronous' -- in various combinations. (019)
John (020)
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