RE: SUO: RE: A proposed SUO content outline
(This is reply is quite delayed because of interruptions. Still, I wanted
to get on the record.)
Pat,
We (probably) aren't as far apart as I thought. See embedded comments
below.
Regards,
John Velman
>
>Subject: RE: SUO: RE: A proposed SUO content outline
>
>
>
>>Pat,
>>
>>Pat Hayes wrote
>> >
>> >John Velman wrote:
>> >>I've snipped most of the following, and left only the snippet I want to
>> >>comment on
>> >>just now.
>> >>
>> >>It seems to me that it is fundamental that things don't have locations.
>> >>They only
>> >>have locations _relative_ to other things.
>> >
>> >Why do you think so? This idea doesn't conform to normal geographical
>>
>>I guess this highlights two different senses of "where" (a "where"
>function
>>was proposed in the part of previous message that I edited out.) Or
>>perhaps to my use of the word "location" (the context that I didn't snip
>>out refered to a function from things to their locations).
>>
>>Why do I think so? Because of many years of starting an analysis with
>>words to the effect: "Assume a coordinate frame with origin at the center
>>of the earth, X axis oriented positively toward the vernal equinox..", or
>>"Coordinates are given relative to the Clarke Ellipsoid of 1866 ". In
>>other words, specifying the locations of things relative to some agreed
>>upon identifiable standard (although only specified with the precision
>>necessary for the purpose).
>
>Ah, yes: but reference to a coordinate frame precisely ISNT reference
>to another "thing". Is it? (If you think so, then I simply
>misunderstood you, and withdraw my comment. )
Ahhh! I was guilty both of sloppy thinking and sloppy expression of my
thinking. Here is a rough (but hopefully better) expression of where I
seem to stand :-)
I think coordinate systems are abstract (but are encoded in physical
objects in some way, in order to be useful). However, I think coordinate
systems themselves are, let me say, "anchored" by identifiable aspects of
physical things. So when I said that "it is fundamental that things don't
have locations. They only have locations _relative_ to other things." I
was speaking very loosely (blush), and the dependence may be rather
indirect through a chain of abstractions.
I know this is stated roughly, and is going to take some time to work out.
Probably should be deferred till we start dealing seriously with
measurements and coordinate systems.
>
>>On the other hand, your reference to geographical intuition is a clue to
>>another sense, I guess. "Where is Taksim Square?" "In Istanbul." I'm
>>not so sure, however, that it is possible to specify where something is
>>_except_ in terms of its spacial relationship to something else, either
>>explicitly or implicitly. ("Where is Istanbul? On the Bosphorus. Where
>>is the Bosphorus? Between the Black Sea and the Sea of Maramara, a long
>>ways from California.") Perhaps my geographic intuition has been spoiled
>>over the years. Or perhaps I'm still missing your point.
>
>I was thinking precisely of the use of coordinate frames, rather than
>dead-reckoning locations from 'landmarks, as being counter to your
>claim.
Yes. See above on coordinate systems.
>
>> >intuition, it isn't supported by Newtonian physics and it isn't even
>> >strictly true in General Relativity. I believe the only person who
>> >seriously believed this was Ernst Mach.
>>
>>This is also a puzzle. As far as I recall, Mach claimed that inertial
>>properties of matter were due to the distribution of mass in the universe
>>(roughly speaking).
>
>Right, so location is defined by reference to *things* (with mass,
>and rather a lot of them, but things for all that.) Mach believed
>that there would be no inertia in an empty universe, contra Newton
>(for whom absolute location was simply a property of space).
>
>> Inertial properties have to do with accelerations, not
>>with absolute locations.
>
>But in Newtonian mechanics, acceleration is defined to be the second
>temporal derivative of (absolute) location. A single particle in an
>otherwise empty universe can still be accelerated, which is *why* it
>will feel inertia. So empty space has to be 'real', which indeed
>Newton admitted was very puzzling.
>
>>Both the mass distribution in the universe, and
>>accelerations of individual bodies are properties concerning relative
>>locations. Of course Newton thought space was absolute in the sense of
>>inertial properties of matter. But I don't think his spinning bucket
>>experiment has anything to do with locations per se. If you have a
>>reference otherwise, I'd be most grateful.
>
>I believe Newton himself used it as an argument for the absolute
>nature of space, did he not? I think the argument is in Principia, in
>fact, but I don't have the page reference. The distinction between
^^^^^^^^^^^^^^ Nor do I. I only know this
as reported in textbooks and other recent writings.
>space as location and space as the vessel for inertial properties is
>(I think) a more modern reconstruction; but I may be out of my
>historical depth here.
>
>>As I recall, general relativity implies frame dragging, and some other
>>things that go a little way toward Mach's principle, but not all the way.
>
>GR refers gravity to essentially geometric properties of
>spati(otempor)al coordinates rather than to relative locations of
>other material things. That was widely cited as its chief beauty over
But interestingly, the geometric properties depend on the distribution of
physical things.
>Newtonian 'action at a distance', I gather. There is no action at a
>distance in GR; things just go along minimum-action paths, determined
>locally by the locally curved spacetime.
>
>>I also recall that Einstein relied extensively on simultaneity (as John
>>Sowa's http://www.bestweb.net/~sowa/ontology/causal.htm reminded us).
>>This clearly depends on a relationship between two events in space-time.
>
>Those are used in his intuitive account of special relativity, which
>is indeed wonderfully convincing. But the point there is really only
>to infer the equations of the coordiante transformations. Once those
>are determined, there is no need to then refer all measurements to
>other events or other 'things': space-time itself has a geometry.
>(However, as Ive emphasised before, space-time with the Minkowski
>metric is a very different beast from the nice orthogonal Newtonian
>4-d spacetime that Matthew West and I like to use for ontological
>reasoning. I really don't think we should base a practical ontology
>on Minkowski space; I don't want to have to be always thinking about
But we may have to provide room for it. I recall thinking some time ago
that the modeling the problem of communicating between two "far apart"
objects with laser beams was easier to formulate in spacetime with the
Minkowski metric. I don't recall if it was really easier, or whether it
was just a tool I wanted to learn to use.
>Lorentz contractions.)
>
>>Perhaps I'm looking at things in a totally different way than you
>>are, but I can't see how one can talk about the location of one thing
>>without at least implicitly referring it to another thing (or event, in 4
>>D).
>
>Well, look at Einstein's equations.
>
>Pat Hayes