[ExI] physics

John Clark johnkclark at gmail.com
Mon Apr 25 16:38:14 UTC 2016


On Mon, Apr 25, 2016  William Flynn Wallace <foozler83 at gmail.com> wrote:

​> ​
> In the standard general relativity view there is a patch of spacetime
> there, with its own properties (curvature).
>

​If "real" means something that's invariant then curved spacetime is not
real because it looks different for different observers. If you're far away
looking at somebody falling toward a planet you'd say he's moving in a
straight path through spacetime that is curved due to the mass of a planet
that is nearby, and that's why he's accelerating. Unless somebody is
accelerating they always take the shortest path through 4D spacetime, and
in curved spacetime the shortest path is a curve not a straight line. But
if you're the guy who's actually falling you'd say you are moving in a
curved line through flat spacetime, and in flat spacetime the shortest path
is a straight line not a curve,  so you'd say your acceleration is due to
gravity.

Both would agree that you're not taking the shortest path through
spacetime, but one would say it's because you're following a curved path in
flat spacetime and the other would say it's because you're following a
straight path in curved spacetime. Both are correct so curved spacetime
isn't invariant and isn't real.

 John K Clark

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