On 5 February 2014 12:07, meekerdb <[email protected]> wrote:
> On 2/4/2014 2:35 PM, LizR wrote:
>
> You said we don't need a coordinate system at all, we can just use
> 4-momenta and 4-intervals - so using those doesn't imply or define a 4D
> coordinate system?
>
> Sure they imply that a 4D coordinate system is possible, in fact many
> different ones. This is just like map surveyors who measure a lot of
> distance and angles between points can infer that they're on a spheroid and
> hence can introduce a consistent coordinate system. But the distances and
> angles are more fundamental, i.e. operational, than the coordinate system
> which has a lot of arbitrariness in it. But we don't say we know we live on
> a spheroid because of the relativity of latitude.
>
Well if you want to be picky we don't know that either, we only have those
blooming buzzing sense impressions from which we assume the assume
surveyors extracted their assumed conclusions. I was just operating at a
particular level of description, which let's face it is fairly common when
trying to explain something. ("Today we will be discussing philosophy, but
first we need to discuss what we mean be "we", "discuss", "philosophy" and
"today"...amongst other things.")
>
> The point only makes a difference when people are asking things like does
> SR mean that the block universe is really real. I think even the phrase
> "relativity of simultaneity" is kind of misleading. It seems to imply that
> distant events are simultaneous with local ones relative to some frame.
> But in general it's only that given two spacelike events there exists a
> frame in which they are simultaneous. If you add a third event then there
> may not be any frame that will make the three simultaneous. So I'd rather
> say there is no such thing as simultaneity for distant events.
>
Well, we don't know if *anything* is really real. I wasn't intending to
discuss metaphysics on this thread; if you want to do that, maybe you could
start another one. All I'm arguing is that SR (and to some extent NM) imply
a block universe as the simplest explanatory framework (via the usual
application of Occam), plus throw in a few points about the circularity of
competing explanations. If that's wrong then I will go out into the garden
and eat worms, but I don't think that anything you're saying actual
conflicts with that.... as far as I can tell. But then I'm not sure what
point you're trying to make, unless you're just to take apart everything I
say in order to make me look and feel stupid (which, you know, I can do
quite well myself).
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