5 ms·

Suppose the gravitational attraction of particles, like spin, was signed, such that like attracts like, and unlike repels unlike? Because of the weakness of g

Suppose the gravitational attraction of particles, like spin, was signed, such that like attracts like, and unlike repels unlike? Because of the weakness of gravity, every other force would dominate at the local scale. But the prevalence of one or the other sign in a region (at the galactic scale) would vary - as there would have been a (very gentle, as gravity is weak) "sorting" in the early universe, as like signs attracted and unlike signs repelled. "Dark matter" would be variation in the prevalence of one sign or the other. How would one test such a model?

IanCal 9y ago
If I understand what you mean, then we would expect dark matter to not clump around "ordinary" matter, but that's what we find.
- thyrsus 9y ago
  Excellent. "ordinary" matter would be a 70%/30% mix of gravitational types, with dark matter being a 99%/1% mix (figures obviously pulled from nowhere) - but then one would see effects at the local scale, where an observable percentage of helium atoms would exhibit "anti-gravitational" effects. Surely, that would have been previously noticed, thus the model is refuted.
deleted 9y ago
[deleted]
dwaltrip 9y ago
On the galactic scale, my hunch is that the sorting dynamic would be very strong, and you would basically have g+ and g- galaxies. Which would be very interesting, but doesn't solve the dark matter issue. I think that this would also create a lot of other complex behavior that we don't see. For example, I think we would expect to see many cases of two galaxies or even two galaxy clusters pushing away from each other, because one is g+ and the other g-.
- thyrsus 9y ago
  Expansion does have the appearance of "pushing away". But, as noted, to explain "dark matter", one would observe "anti-gravitational" separations in inert gases at local scale, which has never been reported.
  - dwaltrip 9y ago
    Ah yeah nice idea. However, the expansion we see is stronger when things are farther away. Gravity gets weaker at a quadratic rate as distance increases, so I don't think opposite gravity signs could be contributing significantly to the observed expansion.
raattgift 9y ago
Sabine Hossenfelder has a slightly tongue-in-cheek FAQ on anti-gravitation, and from time to time blogs about it. https://fias.uni-frankfurt.de/~hossi/Physics/anti-gravity.html https://fias.uni-frankfurt.de/~hossi/Physics/anti-gravity.ht... You might find that interesting. The key constraints come from General Relativity; the successes of the Schwarzschild and Kerr(-Newman) metrics for physically plausible arrangements of matter need to be preserved if you try to add in a symmetry. If we use perturbation theory to capture deviations from the metric of a reasonable exact solution to the Einstein Field Equations, the structures can be represented as classical waves in the metric tensor. Quantizing these waves ("perturbatively quantized gravity") inevitably results in a massless spin-2 particle. Spin-2 interactions have a feature you wrote yourself: > that like attracts like, and unlike repels unlike (maybe more clearly put as: like charges mutually attract and unlike charges mutally repel). Note that this is backwards from the spin-1/2 of fermions. > "Dark matter" would be variation in the prevalence of one sign or the other. In the standard cosmology, dark matter is attractive. Ordinary matter falls into areas where dark matter is dense, as discussed in the "Unprecedently wide and sharp dark matter" phys.org article, or if you prefer, http://www.esa.int/Our_Activities/Space_Science/Planck/History_of_cosmic_structure_formation http://www.esa.int/Our_Activities/Space_Science/Planck/Histo... If you want a particle which interacts gravitationally with ordinary matter but which can carry a gravitational charge of opposite sign, you probably shouldn't call it "dark matter". However, you can certainly define such a thing with some rigour and test it. > How would one test such a model? Mathematically? After all, you need to generate reasoned (rather than guessed) observables that you can then look for. You would probably do like Noether and Hilbert and solve the equations of motion of your matter theory producing the canonical stress-energy tensor, and then improve it using a metric variational procedure. Forger & Römer is a good place to look: https://arxiv.org/abs/hep-th/0307199 https://arxiv.org/abs/hep-th/0307199 You can see how Hossenfelder does this in her anti-gravitation paper (direct link: https://arxiv.org/abs/gr-qc/0508013 https://arxiv.org/abs/gr-qc/0508013) in which her matter theory doubles the number of particles in the Standard Model, with the second set identical to the first except for the opposite gravitational charge); Forger & Römer is her reference [20]. Once you have a self-consistent and reasonably complete model you can consider areas where it generates identical observables to the standard cosmology where those are already being tested (the fine detail in the cosmic microwave background; gross structures like galaxies, clusters, and filaments; large-scale homogeneity and isotropy; the Hubble flow) and where your model makes predictions that differ from the standard cosmology.
posterboy 9y ago
This is funny, as I assume that spin is an effect of the force of gravity. Swinging and pendulum spin is just what happens in nonlinear dynamical systems. It's called ringing in sound engineering. You only need three bodies to simulate that. A binary pulsar will rotate. Crazy idea ... what if that's not a two star system of many neutrons, but just two neutrons moving really really fast, thus becoming heavy, bending space and thus appears to glow, because it act's as a lens for light. Is that the holographic universe?

IanCal 9y ago

If I understand what you mean, then we would expect dark matter to not clump around "ordinary" matter, but that's what we find.

thyrsus 9y ago
Excellent. "ordinary" matter would be a 70%/30% mix of gravitational types, with dark matter being a 99%/1% mix (figures obviously pulled from nowhere) - but then one would see effects at the local scale, where an observable percentage of helium atoms would exhibit "anti-gravitational" effects. Surely, that would have been previously noticed, thus the model is refuted.

deleted 9y ago

[deleted]

dwaltrip 9y ago

On the galactic scale, my hunch is that the sorting dynamic would be very strong, and you would basically have g+ and g- galaxies. Which would be very interesting, but doesn't solve the dark matter issue. I think that this would also create a lot of other complex behavior that we don't see. For example, I think we would expect to see many cases of two galaxies or even two galaxy clusters pushing away from each other, because one is g+ and the other g-.

thyrsus 9y ago
Expansion does have the appearance of "pushing away". But, as noted, to explain "dark matter", one would observe "anti-gravitational" separations in inert gases at local scale, which has never been reported.
- dwaltrip 9y ago
  Ah yeah nice idea. However, the expansion we see is stronger when things are farther away. Gravity gets weaker at a quadratic rate as distance increases, so I don't think opposite gravity signs could be contributing significantly to the observed expansion.

raattgift 9y ago

Sabine Hossenfelder has a slightly tongue-in-cheek FAQ on anti-gravitation, and from time to time blogs about it. https://fias.uni-frankfurt.de/~hossi/Physics/anti-gravity.html https://fias.uni-frankfurt.de/~hossi/Physics/anti-gravity.ht... You might find that interesting. The key constraints come from General Relativity; the successes of the Schwarzschild and Kerr(-Newman) metrics for physically plausible arrangements of matter need to be preserved if you try to add in a symmetry. If we use perturbation theory to capture deviations from the metric of a reasonable exact solution to the Einstein Field Equations, the structures can be represented as classical waves in the metric tensor. Quantizing these waves ("perturbatively quantized gravity") inevitably results in a massless spin-2 particle. Spin-2 interactions have a feature you wrote yourself: > that like attracts like, and unlike repels unlike (maybe more clearly put as: like charges mutually attract and unlike charges mutally repel). Note that this is backwards from the spin-1/2 of fermions. > "Dark matter" would be variation in the prevalence of one sign or the other. In the standard cosmology, dark matter is attractive. Ordinary matter falls into areas where dark matter is dense, as discussed in the "Unprecedently wide and sharp dark matter" phys.org article, or if you prefer, http://www.esa.int/Our_Activities/Space_Science/Planck/History_of_cosmic_structure_formation http://www.esa.int/Our_Activities/Space_Science/Planck/Histo... If you want a particle which interacts gravitationally with ordinary matter but which can carry a gravitational charge of opposite sign, you probably shouldn't call it "dark matter". However, you can certainly define such a thing with some rigour and test it. > How would one test such a model? Mathematically? After all, you need to generate reasoned (rather than guessed) observables that you can then look for. You would probably do like Noether and Hilbert and solve the equations of motion of your matter theory producing the canonical stress-energy tensor, and then improve it using a metric variational procedure. Forger & Römer is a good place to look: https://arxiv.org/abs/hep-th/0307199 https://arxiv.org/abs/hep-th/0307199 You can see how Hossenfelder does this in her anti-gravitation paper (direct link: https://arxiv.org/abs/gr-qc/0508013 https://arxiv.org/abs/gr-qc/0508013) in which her matter theory doubles the number of particles in the Standard Model, with the second set identical to the first except for the opposite gravitational charge); Forger & Römer is her reference [20]. Once you have a self-consistent and reasonably complete model you can consider areas where it generates identical observables to the standard cosmology where those are already being tested (the fine detail in the cosmic microwave background; gross structures like galaxies, clusters, and filaments; large-scale homogeneity and isotropy; the Hubble flow) and where your model makes predictions that differ from the standard cosmology.

posterboy 9y ago

This is funny, as I assume that spin is an effect of the force of gravity. Swinging and pendulum spin is just what happens in nonlinear dynamical systems. It's called ringing in sound engineering. You only need three bodies to simulate that. A binary pulsar will rotate. Crazy idea ... what if that's not a two star system of many neutrons, but just two neutrons moving really really fast, thus becoming heavy, bending space and thus appears to glow, because it act's as a lens for light. Is that the holographic universe?