Re: [ontolog-forum] Looking for some pragmatic guidance on modeling rela

["Matthew West" <dr.matthew.west@xxxxxxxxx>]

Dear Steve,

You said:

 

One thing that’s nagging me is that a satellite clock isn’t just a clock that happens to be ticking more slowly – time itself is passing more slowly in space than on earth.

[MW>] More particularly when you are travelling at higher speed than on earth.

So if you took the earth-bound clock and put it into orbit, it would also slow down. So the tick rate is not (only) a property of the clock, but also on the depth of the gravitational well the clock happens to be in at any given time.

 

These kinds of issues are why I was hoping somebody had already modeled all this…

[MW>] The big thing is that time is not absolute, so you can be sure that any ontology that has time set by a single clock will not work for these purposes.

In ISO 15926 (and generally in 4D) a point in time is a plane in space time across all space, but from some reference point. Different reference points have different speeds, so give different planes. As John said, time is just a metric scale, and is specific not just to a clock, but what reference point it has. If that reference speeds up or slows down, then the clock appears to do the reverse.

Event horizons are another consideration. You don’t know what happened at the same time as you are at until sometime later when light from that event arrives.

I recommend doing only what you need, but without imposing constraints that may later be incorrect.

 

Regards

 

Matthew West

http://www.matthew-west.org.uk

+44 750 338 5279

 

 

 

 

- Steve

 

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

 

From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of John Bottoms
Sent: Wednesday, April 08, 2015 6:01 PM
To: ontolog-forum@xxxxxxxxxxxxxxxx
Subject: Re: [ontolog-forum] Looking for some pragmatic guidance on modeling relativistic time events

 

There is also an issue about reconciling (or not) times when contexts cross or merge.
This may already be addressed in current context processing such as crossing the International Dateline and time zones.

For most of these issues there is a standard time such as GMT or sidereal. Those are with respect to the Earth. Maybe there is a need for a more cosmic time standard. We are a long way from that point, but there are issues associated with planetary exploration. Recently, the rotation rate of Venus was used as a reference, and it was recently discovered that it is changing quite rapidly. As a result, targeted landing spots are out of place by as much as 20 km.

National Geographic: Venus Spinning Slower Than Thought—Scientists Stumped

http://news.nationalgeographic.com/news/2012/02/120214-venus-planets-slower-spin-esa-space-science/

-John Bottoms

On 4/8/2015 8:14 PM, John F Sowa wrote:

On 4/8/2015 6:29 PM, Steve Ray wrote:

I didn't see anything specifically talking about different rates

of time passing

A clock can be any process that you believe is sufficiently

regular that it is can be adopted as a standard.  Galileo

used his heartbeat to time experiments.  That is sufficient

to establish a partial ordering.

If you want to relate the ticks of different clocks, then you need

to find or assume some ratio (or other function).

John

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