On 2/21/2019 10:47 PM, [email protected] wrote:
On Thursday, February 21, 2019 at 8:38:12 PM UTC-7, Brent wrote:
On 2/21/2019 4:05 PM, [email protected] <javascript:> wrote:
On Thursday, February 21, 2019 at 1:35:17 PM UTC-7, Brent wrote:
On 2/21/2019 5:27 AM, [email protected] wrote:
On Wednesday, February 20, 2019 at 7:50:51 PM UTC-7, Brent
wrote:
On 2/20/2019 1:23 PM, [email protected] wrote:
On Wednesday, February 20, 2019 at 12:16:31 PM UTC-7,
Brent wrote:
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
*So it seems that GR doesn't explain motion; rather, it
assumes motion is a natural state of things. AG
*
So called "standing still" is just motion in the time
direction only...in Newtonian and special relativity as
well. Just as there is no absolute motion, there's no
absolution motionless either...it's called "relativity"
for a reason.
Brent
*Other than gravity, the remaining known forces are
moderated, or shall we say "caused by" particles. Doesn't GR
remain an exception; that is, wouldn't it preclude the
existence of a graviton? TIA, AG
*
Gravitons, the weak-field limit quanta of the gravitational
field, aren't precluded. They are implicit in string-theory;
which is why string theory is a candidate for the quantum
theory of gravity. The problem is there's no mathematically
consistent way to extend the graviton, weak field, picture to
the strong field limit and predict what happens in a black
hole where GR predicts a singularity.
Brent
*ISTM that gravitons would be inconsistent with GR, which derives
gravitating motion from geometry, not mediating particles. AG*
It is conceptually inconsistent, just as GR is conceptually
inconsistent with Newtonian gravity. But that doesn't mean the
theories make detectably different predictions in the domain where
we can test them. Notice how difficult it was to test GR vs Newton.
Brent
*Even if gravitons are detected, and they account for "force"
consistent with the other three forces, wouldn't there remain the task
of changing the form of gravity to make it covariant? *
Gravitons, as quanta of the metric field, are already relativistic
particles and covariant.
*Would that require tensors? AG*
Dunno. But it would have to reduce to GR in the weak field statmech
limit, so it would have something that reduced to tensors in that limit.
Brent
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