On 2/21/2019 4:05 PM, [email protected] wrote:
On Thursday, February 21, 2019 at 1:35:17 PM UTC-7, Brent wrote: On 2/21/2019 5:27 AM, [email protected] <javascript:> 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.
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