Search for Dark Matter

exchemist said:
Does MOND bugger up general relativity, as well as Newtonian gravitation? Big G, or a constant equivalent to it, appears in GR, if I’m not mistaken.
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This is far more reaching than all the previous papers IIRC. The recent focus was all on wide binary data from Gaia. This if correct explains a whole lot more.
 
DaveC426913 said:
Explain this. How does a "larger particle" equate to a longer wavelength?
Or better yet, how does contraction of space result in smaller particles?

Are we talking photons? Atoms? How do these things shrink?



How does larger mean closer? i thought they were larger because they were more spatially extended, so no more mass - and in fact, less attraction (inverse square law of gravity)
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Sorry for the duplicate but I didn't see the reply button so I clicked it to make sure you get notified of my reply.

"To me, contraction means contraction of space, as in "contraction of the space between galaxies" for instance instead of "expansion". The difference with expansion is that if the particles are contracting, then things made of particles are contracting too, and it's the light emitted by the particles that guides them, so it must not contract. When we look at the sun, we would see it as it was eight minutes ago, so larger than it is now, and its light would have a longer wavelength - or slower frequency if you prefer - so the earth would have to move towards the sun to increase the apparent frequency of its particles by doppler effect, which would cause gravitation. The general idea is that particles would move to stay synchronized and they would use the light they exchange to do so. If they would perceive blueshift, they would move away from the source to nullify the blueshift by doppler effect, and if they would perceive redshift, they would move towards the source to nullify it by doppler effect too. Of course, they couldn't nullify the contraction completely even if they were adjacent to one another, like two atoms of the same molecule for instance.

I'm not sure I'm large enough to look closer though, if I may say. :0)"

Larger means closer if the number of particles is the same. The same object looks larger if you get closer to it. It's a parallax issue. By the way, what Pinball just posted is consistent with the idea that, from the point of view of stars, the core of a galaxy would appear closer if they had contracted while light from the core was reaching them.
 
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exchemist said:
Does MOND bugger up general relativity, as well as Newtonian gravitation? Big G, or a constant equivalent to it, appears in GR, if I’m not mistaken.
Click to expand...
Mond doesn't tend to explain some relativistic effects, but those effects (gravitational lensing and waves, some cosmic background radiation properties and colliding clusters of galaxies.) I would suspect that's not an issue as those first effects are not part of a galactic gravitation explanation, they are already explained by Newton or GR. The colliding clusters most likely require yet another explanation. Maybe that's the way gravity works, it requires it's own explanation in quantum mechanics, another for large objects (GR), another for galaxies and maybe another for clusters and so on. Perhaps when each one becomes clear, they can work on tying them all together with one simple explanation. Or, maybe not.
 
(Q) said:
Mond doesn't tend to explain some relativistic effects, but those effects (gravitational lensing and waves, some cosmic background radiation properties and colliding clusters of galaxies.) I would suspect that's not an issue as those first effects are not part of a galactic gravitation explanation, they are already explained by Newton or GR. The colliding clusters most likely require yet another explanation. Maybe that's the way gravity works, it requires it's own explanation in quantum mechanics, another for large objects (GR), another for galaxies and maybe another for clusters and so on. Perhaps when each one becomes clear, they can work on tying them all together with one simple explanation. Or, maybe not.
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Actually what I meant was whether MOND can be made compatible with GR, or rather whether GR can be made compatible with MOND. But I suppose it may be just a question of altering some parameters in GR, or replacing constants by suitable variables. Since GR is amply confirmed, I can only think MOND would have been ruled out long ago if it can't be harmonised with GR in some way.

As I read it, MOND can be treated either as a modification to F=ma or to F=GmM/r².
 
exchemist said:
Actually what I meant was whether MOND can be made compatible with GR, or rather whether GR can be made compatible with MOND. But I suppose it may be just a question of altering some parameters in GR, or replacing constants by suitable variables. Since GR is amply confirmed, I can only think MOND would have been ruled out long ago if it can't be harmonised with GR in some way.

As I read it, MOND can be treated either as a modification to F=ma or to F=GmM/r².
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The point I was trying make is that Mond may or may not be harmonized in GR, but that there may be different explanations that can't work together. Perhaps, GR can explain one large object while another explanation may be required for multiple objects together such as stars/black holes in a galaxy.
 
(Q) said:
The point I was trying make is that Mond may or may not be harmonized in GR, but that there may be different explanations that can't work together. Perhaps, GR can explain one large object while another explanation may be required for multiple objects together such as stars/black holes in a galaxy.
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Hmm, I see. Well that would be a huge deal, if GR had to be reworked too.
 
exchemist said:
Hmm, I see. Well that would be a huge deal, if GR had to be reworked too.
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I believe that Mond suggests via the second law where a force exerted on an object is proportional to the acceleration, wherein the accelerations here are very small, matches the data they're seeing on the outer regions of the galaxy and within its galactic center. It would seem that due to the billions of stars in one place causes the outer regions gravity to decay less than predicted. Most likely then, GR would indeed need to be reworked.
 
exchemist said:
Hmm, I see. Well that would be a huge deal, if GR had to be reworked too.
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I had a read some Milgrom today, I was in work so I need another.
Lambda CDM is from GR which is geometric and has DM as a component, MOND does not and is based on forces, a 'nought' in F=ma

It's like a fiddle factor but then again Lambda was too right?

Mcgaugh is claiming MOND predicted early large galaxy formation but Lambda CDM did not. This is a lot more than all that wide binary data from Gaia.

As a lot of the physics here is quite difficult (GR, Lambda CDM, MOND derivation) I am hoping a YouTube scientist will put this all together and into perspective. I'm not lazy and I am trying but I am still working full time!
 
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