On 2/20/2019 8:42 AM, [email protected] wrote:
On Wednesday, February 20, 2019 at 7:09:10 AM UTC-7, John Clark wrote:
>/Newton "explained" /
Why did you put explained in quotation marks? If you can predict
what something is going to do then you've explained it, the better
the prediction the better the explanation. I don't know what else
the word could possibly mean. And in science no explanation is
perfect, but some are less wrong than others.
*QM better illustrates the justification for quotes. Many
interpretations that make the same predictions. AG *
/> why a body at "rest" can start moving, via the application
of "force"/
And Einstein explained that a body moving in a geodesic through 4D
spacetime will take a path that is not a geodesic if a force is
applied. The Earth is moving in a straight line (aka a geodesic)
through curved spacetime; the reason Earth's orbit looks
elliptical to us is due to map distortion, the same reason that in
a flat map of the curved surface of the Earth Greenland looks
larger than South America and is almost as large as Africa. Except
that it's even worse, in one we're projecting the 2 D curved
surface of the Earth into the flat 2D surface of the map, but with
Einstein we're projecting a curved 4D volume into a flat 3D volume.
/> What does "rest" mean in GR /
In General Relativity moving in a geodesic is as close as you can
get to the traditional idea of rest, but as long as time passes
you're going to be moving through 4D spacetime.
*If you're at spatial rest in spacetime in the presence of a
gravitational source, how does GR explain the subsequent spatial
motion? AG
*
When you were at "spatial rest" you had a force applied to you. Removing
it allowed you to follow a geodesics path through spacetime....also
known as "falling".
Brent
/> what causes "motion" from that pov?/
Force, same as with Newton.
John K Clark
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