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I think it is relevant to consider gravity from a more abstract standpoint as well by looking at Le Sage's theory and particularly Hyugens' comments. [1] Wheth

I think it is relevant to consider gravity from a more abstract standpoint as well by looking at Le Sage's theory and particularly Hyugens' comments. [1] Whether gravity is mediated by a graviton, and the intricacies that QM brings to bear, one interesting idea I took from the above hundreds of years of thought on the subject -- gravity may be a pushing force mediated by constant spherical wave emission (quantized as the graviton if necessary) from all mass/energy. Since every bit of mass-energy is releasing gravitons, the whole of space is rather isometrically filled with gravitons. The reason two objects would then appear to attract via Newton's inverse-square law is one of a shadowing effect. The graviton would apply a pushing force normally to any mass-energy it interacts with, and therefore any blockage/shadowing of one object by another, would end up looking like attraction. Le Sage's theory is more exacting and supposes gravitons are of similar substance to regular matter. I don't agree with most of these notions but what I said above is what I gained. 1] https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitation https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitat...

simpsond 9y ago
That’s a really interesting way of thinking about it. Gravity resists space.
Florin_Andrei 9y ago
This is one of the many kinetic theories of gravity. It's very old. No scientist nowadays believes that kinetic theories could really work in this realm. This is mostly of historic interest only.
- goldenkey 9y ago
  I'm aware of that-- but no one is sure about how the graviton operates. So though the kinetic part might not be very realistic or all that relevant anymore, the other parts still are.
  - Retra 9y ago
    The 'non-kinetic' parts are just geometry, which we already understand and incorporate into general relativity.
    - goldenkey 9y ago
      Just as there is a huge difference between Maxwell's laws and QED -- the same gap lies with relativity and the graviton. Knowing the gravitational field as full fidelity partial differential equations based on the stress energy tensors is a great achievement. But it alone does not tell the full story as to how that field is mediated. Just as EM is mediated via virtual photons, we wish to know more..
      - PuffinBlue 9y ago
        Not that i understood much of what you just said, but you're the first person I've seen say gravity is a push force, so i have a question. Does it me any sense to say mass repels spacetime? So imagine a spring on the surface of a massive sphere. Imagine that you compress the spring and release it. The spring would compress outwards, the sphere not moving (especially if an another antipodean spring was set up with a compression release cycle occurring at the same time). What if spacetime was like that spring, constantly being 'pushed' away or repelled from mass as it tries to return to an uncompressed state . The local effects would seemingly be the same, objects would travel the same curved paths through spacetime around the sphere as they would if mass was attractivly warping spacetime. Or perhaps we xould set up the conditions so that was so. Maybe ive misunderstood, but in most depictions of gravity its a point like a bottom of a well that's sort of stretched the 'rubber sheet' of spacetime. I know it's just an analogy but almost all layman explanations show spacetime elongating as it moves closer to the mass, the elongation depicting the 'warping' of spacetime. It's possible the real maths tells a more accurate story, but to me the more correct mental picture would be to think of circles around the mass spaced at distances where crossing between them takes time=1. For the outside observer it seems time slows as you draw nearer the mass, that would suggest the circles become 'closer' or you'd cross more space per unit time. It would also suggest the outside observer would see you eventually slow to a stop but locally you continue to accelerate along the curved spacetime, so it doesn't seem to violate special relativity. I'm not sure if mathematically space and time are treated separately, but if they're the same then thinking of mass as repelling spacetime 'outwards' from the surface of the mass seems to still work but might explain on larger scales where some of the expansion of space comes from - i.e. mass repels spacetime but the curvature this creates causes other mass to follow paths through spacetime that appear to make the two masses attract each other. I get that im no doubt wrong but ive not seen anyone adress this possibility (probably because it wrong!) but id be interested to hear where it breaks down, as i dont see it!
whatshisface 9y ago
There's no particular need for a special explanation of how particle exchange could produce an attractive force: as unlikely as it seems in classicical physics, it's how the forces (electromagnetic) arise in QED. The exchange of virtual photons can transport momentum any way you like.
- effie 9y ago
  'Exchange of virtual photons' is a metaphorical expression used to describe artifacts of perturbation theory, it is not necessarily a real process. There is no widely accepted model of what really happens on microscopic scales, we only have equations and those are often replaced by simpler perturbation scheme. So, explanations of attractive force are welcome, Le Sage - type models including.
  - whatshisface 9y ago
    >There is no widely accepted model of what really happens on microscopic scales, There's no experimental reason to come up with one - virtual photons work, which means anything else is at this point a matter of philosophy. That's not to cast off philosophy, of course.
    - effie 9y ago
      Virtual photons work in a very limited way (metaphorical language describing perturbation theory). Physics outside of applicability of perturbation QED (bound systems of charged particles, gravity) is not a matter of philosophy.
Taniwha 9y ago
Dumb question: how do you exchange gravitons with a black hole?
- ars 9y ago
  A graviton would have to be both massless and energyless. Thus it would be unaffected by gravity. It also means it can not have a "frequency" like light does (because lacking any energy there is no frequency to change). It must also always move at the speed of light, and could not exist at any slower speed. (Because to slow down, would imply a change in its energy, which it can not do.) But that means it can't interact in a way that is detectable, other than gravity. Because you can not give it energy, you can also never create it artificially. If you did, you would be creating gravitational force out of nothing, which is impossible because it violates conservation of energy, and you can not pay for that violation because you can not give it energy. It's pretty much the ultimate impossible to study particle.
  - Florin_Andrei 9y ago
    > A graviton would have to be both massless and energyless. However, gravitational waves do carry energy. Gravitons, whatever they are, must be some very tricky things.
  - auntienomen 9y ago
    This comment is almost completely wrong. It muddles together classical and quantum reasoning in any incoherent way. Gravitons are best understood as the quanta of the effective qft governed by the Einstein Hilbert action. This mathematical model is the universal low energy approximation to any quantum theory that reduces to general relativity. Gravitons need to be massless. They need not be zero energy. They can indeed be associated with frequency. They do couple to gravitational backgrounds and to other gravitons. You can crate them just like any other field quanta. The barrier to studying gravitons the way we do photons is that they couple very weakly to other systems.
    - ars 9y ago

simpsond 9y ago

That’s a really interesting way of thinking about it. Gravity resists space.

Florin_Andrei 9y ago

This is one of the many kinetic theories of gravity. It's very old. No scientist nowadays believes that kinetic theories could really work in this realm. This is mostly of historic interest only.

goldenkey 9y ago
I'm aware of that-- but no one is sure about how the graviton operates. So though the kinetic part might not be very realistic or all that relevant anymore, the other parts still are.
- Retra 9y ago
  The 'non-kinetic' parts are just geometry, which we already understand and incorporate into general relativity.
  - goldenkey 9y ago
    Just as there is a huge difference between Maxwell's laws and QED -- the same gap lies with relativity and the graviton. Knowing the gravitational field as full fidelity partial differential equations based on the stress energy tensors is a great achievement. But it alone does not tell the full story as to how that field is mediated. Just as EM is mediated via virtual photons, we wish to know more..
    - PuffinBlue 9y ago
      Not that i understood much of what you just said, but you're the first person I've seen say gravity is a push force, so i have a question. Does it me any sense to say mass repels spacetime? So imagine a spring on the surface of a massive sphere. Imagine that you compress the spring and release it. The spring would compress outwards, the sphere not moving (especially if an another antipodean spring was set up with a compression release cycle occurring at the same time). What if spacetime was like that spring, constantly being 'pushed' away or repelled from mass as it tries to return to an uncompressed state . The local effects would seemingly be the same, objects would travel the same curved paths through spacetime around the sphere as they would if mass was attractivly warping spacetime. Or perhaps we xould set up the conditions so that was so. Maybe ive misunderstood, but in most depictions of gravity its a point like a bottom of a well that's sort of stretched the 'rubber sheet' of spacetime. I know it's just an analogy but almost all layman explanations show spacetime elongating as it moves closer to the mass, the elongation depicting the 'warping' of spacetime. It's possible the real maths tells a more accurate story, but to me the more correct mental picture would be to think of circles around the mass spaced at distances where crossing between them takes time=1. For the outside observer it seems time slows as you draw nearer the mass, that would suggest the circles become 'closer' or you'd cross more space per unit time. It would also suggest the outside observer would see you eventually slow to a stop but locally you continue to accelerate along the curved spacetime, so it doesn't seem to violate special relativity. I'm not sure if mathematically space and time are treated separately, but if they're the same then thinking of mass as repelling spacetime 'outwards' from the surface of the mass seems to still work but might explain on larger scales where some of the expansion of space comes from - i.e. mass repels spacetime but the curvature this creates causes other mass to follow paths through spacetime that appear to make the two masses attract each other. I get that im no doubt wrong but ive not seen anyone adress this possibility (probably because it wrong!) but id be interested to hear where it breaks down, as i dont see it!

whatshisface 9y ago

There's no particular need for a special explanation of how particle exchange could produce an attractive force: as unlikely as it seems in classicical physics, it's how the forces (electromagnetic) arise in QED. The exchange of virtual photons can transport momentum any way you like.

effie 9y ago
'Exchange of virtual photons' is a metaphorical expression used to describe artifacts of perturbation theory, it is not necessarily a real process. There is no widely accepted model of what really happens on microscopic scales, we only have equations and those are often replaced by simpler perturbation scheme. So, explanations of attractive force are welcome, Le Sage - type models including.
- whatshisface 9y ago
  >There is no widely accepted model of what really happens on microscopic scales, There's no experimental reason to come up with one - virtual photons work, which means anything else is at this point a matter of philosophy. That's not to cast off philosophy, of course.
  - effie 9y ago
    Virtual photons work in a very limited way (metaphorical language describing perturbation theory). Physics outside of applicability of perturbation QED (bound systems of charged particles, gravity) is not a matter of philosophy.

Taniwha 9y ago

Dumb question: how do you exchange gravitons with a black hole?

ars 9y ago
A graviton would have to be both massless and energyless. Thus it would be unaffected by gravity. It also means it can not have a "frequency" like light does (because lacking any energy there is no frequency to change). It must also always move at the speed of light, and could not exist at any slower speed. (Because to slow down, would imply a change in its energy, which it can not do.) But that means it can't interact in a way that is detectable, other than gravity. Because you can not give it energy, you can also never create it artificially. If you did, you would be creating gravitational force out of nothing, which is impossible because it violates conservation of energy, and you can not pay for that violation because you can not give it energy. It's pretty much the ultimate impossible to study particle.
- Florin_Andrei 9y ago
  > A graviton would have to be both massless and energyless. However, gravitational waves do carry energy. Gravitons, whatever they are, must be some very tricky things.
- auntienomen 9y ago
  This comment is almost completely wrong. It muddles together classical and quantum reasoning in any incoherent way. Gravitons are best understood as the quanta of the effective qft governed by the Einstein Hilbert action. This mathematical model is the universal low energy approximation to any quantum theory that reduces to general relativity. Gravitons need to be massless. They need not be zero energy. They can indeed be associated with frequency. They do couple to gravitational backgrounds and to other gravitons. You can crate them just like any other field quanta. The barrier to studying gravitons the way we do photons is that they couple very weakly to other systems.
  - ars 9y ago