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Gravitons? are they a real thing? If spacetime really is curved (the marble on a sheet of rubber analogy) there isn't any need for gravitons as the marble just sits at the lowest point.
So does anyone know just what gravity is??
But nobody has ever come up with a mechanism as of yet
It seems 'gravity' and 'field' and 'graviton' etc are terms like 'dark energy' - place holder words almost - which don't have any 'real' meaning at all.
Quote from: johnspannenburg on 08/01/2013 08:04:48It seems 'gravity' and 'field' and 'graviton' etc are terms like 'dark energy' - place holder words almost - which don't have any 'real' meaning at all. Why stop there, on fundamental levels... What's a particle? what is charge? ect ectOn another thread somewhere on these boards I once mentioned the model of particles being waves or oscillations in fundamental fields, and said itís fields all the way down.Well, you could say of science and its study of the physical worldÖ itís models all the way down. How and When will we know we have the truth of anything fundamental and not just a Ďveryí good model? And just how do you link to posts on other threads..
http://www.laboratoryequipment.com/news/2013/01/scientists-find-evidence-speed-gravity This says nothing about what gravity is, but it is related and interesting.
I'm still skeptical; I think gravity propagates many times faster than light. If gravity propagates at light speed, the Sun's gravity should accelerate Earth in the direction where we see the Sun, not the direction where the Sun is now. If you put that "correction" into Kepler's laws of planetary motion, the planets would all be dragged into higher and higher orbits until they escape from the Sun's gravity, all together.
The popular belief is that the warp of Minkowski space-time is the CAUSE of gravity. That's putting the cart before the horse. The definition of meters and seconds is the cause of the warp, and the question of what causes gravity is swept aside as a frivolous pursuit of ontology.
Even if you thought of gravity as being a static field around the sun. It would still be like the Earth was always moving uphill on the gravity gradient as everything in space is moving.
Would this also apply if you thought of gravity as being just a distortion of spacetime?
The distortions in spacetime that you mention here are tidal gradients in the gravitational field. Since its concievable to have gravitational fiels without tidal gradients it wouldn't make much sens to think of gravity as a distortion in spacetime.
Pmb, I would like to understand you but you are a little over my head sometimes.
Sorry to put it like this but I'm puzzled. I'm certainly not trying to catch you out, i'm trying to lean ( yes, I know I shouldn't expect to lean on forums).
Do you agree that mass/energy alter space in their vicinity ? Yes or no
Or, do you agree that mass/energy alter spacetime in their vicinity? Yes or no
Would an interstellar rock that by chance enters the solar system and starts to accelerate, would you say that acceleration has something to do with the sun's mass/energy
Yes or No?There are no forces in GR, Ö
so how does the sun 'transmit' this effect of its mass/energy to the nearby passing rock?
A quickie... Are you saying gravity distorts space or spacetime and not the other way round i.e. distorted space or spacetime gives rise to gravity?Sorry to put it this way.. Here's an apple sir.
Iím sorry but that does not have a yes/no answer to it. The answer is that matter ďcanĒ alter change space near it but it need not. Whether it does or not depends on the particular distribution of matter. But just because space is altered near an object it doesnít mean that the spacetime is curved near the matter.
Some distributions of matter curve the spacetime near then and other donít, it all depends on the distribution of matter.
Letís consider an example of matter which generates a gravitational field
Quote from: lean beanso how does the sun 'transmit' this effect of its mass/energy to the nearby passing rock? Just like all interactions in physics. Objects generate a field and that field exerts forces on objects in the field
That is a common misconception. In GR there most certainly are gravitational forces.
So, in the above two quotes are you saying the sun does alter space or spacetime around its vicinity? Yes or NoÖ
But itís also possible in the event of an evenly distribution of matter for there to be a mutual cancelling-out and so no curvature results? Is that whatís happening here?
Sorry to put it like that almost repeating you, but I wanted to be specific.
What is matter or the sun doing to generate a gravitational field, are they altering space or spacetime around them, so that a smaller interstellar rock passing, by chance, close by would have its path altered?
Or, are we talking of a Newtonian force and nothing to do with space or spacetime around the sun?
Again,do you mean like the force which Newton postulated or is it something to do with being in the space or spacetime near matter?
Will read the rest of your post when I have time, thanks for your link...even distribution of matter and cancelling out in a cavern in a sphere.
Question: I assumed that you knew what tidal forces were when I wrote all of that. Perhaps I shouldnít have made that assumption. Do you know what the definition of ďtidal forces/tidal gradientsĒ is?
The potential energy of a body in such a field is given by Phi = mgz. The tidal gradients in such a field is zero even though there is a gravitational acceleration. Since the tidal gradients are zero the spacetime curvature is zero. This is an example of a gravitational field with no spacetime curvature.
What do you mean by ďhereĒ? In the case of the sun, no. In the case of the cavity that I explained, yes.
I think I do now after your post hereÖ
So, I would say tidal forces are the strength/ potential at different points of a gravitational field. If the field is uniform the accelerations are the same anywhere in the field. If the field has tidal gradients, then you would have different accelerations at different points of the field?
What do I mean by a Newtonian force? All I can say really is that he never involved altering space/spacetime in his ideas. Didnít he say it would be an insane person that could describe the mechanism?
Thanks for answering. I feel I may have more questions, but I will digest your posts and link more now, the answers may be thereThanks again for time.