131–140 of 193 posts
> In fact, MOND’s constant equals the speed of light squared, divided by the radius of universe. That does not sound like a coincidence. Did the constant change when the universe was smaller? Or does the light speed depend on the size of the universe?
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I've also been in the same boat, preferring the intellectual idea of modified Newtonian dynamics, primarily based on the fact that the only real checks we have on gravity are based on relatively short distances cosmologically. AIUI, assuming that gravity tends to 1/r at galactic distances "solves" the dark matter problem, for galactic rotation at least. The problem is that there are other phenomena that involve invok…
Also assuming gravity tends to 1/r at galactic distances makes no god damned geometric sense and would require like extra dimensions with funny topology for gravity to be traveling though.
Why? I think I can use simple force formula such as F=k/r without any idea of extra dimensions or topology.
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Except that electrical/magnetic forces are vastly more powerful than gravitational forces. Any such force that's noticeable at the cosmic scale would be powerful enough at the object scale (star, planet, even galaxy) to tear them apart or cause them to collapse. Lets suppose the Earth and the Sun were both positively charged sufficiently that their repulsive force was enough to noticeably affect the orbit of the Eart…
I don't think this is true. Let's assume every matter is our solar system is actually not neutral, but slightly positively charged. For Sun-Earth, let's say this reduces the effective force by 1%. Since both Coulomb and gravitational attraction has the same power law, this fixes the change everywhere, or in other words, you could absorb the change into the gravitational constant. Same goes for making everything 1% le…
We've measured the charge of base particles, we know their charge to 8 decimal places. (e.g. for electrons).
There is simply no way for the force of electromagnetism to be different at the scale of solar systems.
Even MOND is a tiny modification to Newtons laws, and only a modification in extreme circumstances.
There is another possible explanation instead of dark matter and that is electric charge and currents (plasma flows). Electric force is many orders of magnitude stronger than gravity. So, if the objects in the universe are charged, the repelling force between them could account for the expansion acceleration in a very simple way.
The electromagnetic force still follows the inverse square law. So if objects in the universe are charged, the effects end up being similar to the force of gravity.
i.e. it's still an inverse square law, and it's still linearly related to the observable mass.
The only way something else is happening is if you use either the dark matter / energy theories, or MOND.
The shorter explanation is that it's naive to think that "off the cuff" ideas from amateurs are better than ideas from experts in the field who have devoted decades of their life to the subject.
Just would loved more current criticism on his theories.
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Shouldn't there be a big lump of dark matter at the center of every planet, moon, and star? If we were to hollow out an asteroid, would there still be a blob of intangible dark matter inside of it?
I like to look through the lens of quantum field theory instead of 'dark matter particles'. Dark matter may be some field or interaction of existing fields that we don't understand yet.
What you are saying is the exact same thing.
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I like to look through the lens of quantum field theory instead of 'dark matter particles'. Dark matter may be some field or interaction of existing fields that we don't understand yet.
Particle is an excited state of a field. What you are saying is the exact same thing.
Particles aren't exactly the same idea because they don't explain the coupling between fields, or things like 'virtual particles' which don't "count" as real particles but have important real behaviors of the field itself.
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> Evidence for atoms and protons was already there before they were "invented". Right, and there is also evidence for dark matter.
I think arenaninja is saying that the theoretical models predicted those things, then empirical experiments later confirmed them. (I don't know if this is actually the case) This gives the theories credibility as being predictive. In this case we have a theoretical mode, but we later notice our empirical data doesn't match this. Both MOND and dark matter are an attempt to patch up our existing theory to explain what…
There have been several independent observations that are explained by dark matter, and it's not like the theory for dark matter was specifically changed to accommodate those observations. The most well-known is around gravitational lensing, as the amount of observable mass in clusters of galaxies does not match the amount of distortion that we observe. There are however several others. This kind of independent validation of a theory from other angles is a textbook case of how theories are validated - they are proposed to explain one thing, but turn out to also explain other things.
MOND meanwhile has a much tougher time explaining the other observational evidence. It has had to be extensively patched to fit the other cases. Additionally, as noted elsewhere in the comments, neutrinos are not dissimilar to dark matter. Both are forms of matter that it do not interact electromagnetically, making them all but impossible to detect directly. Theorizing that there is more than one such type of particle is not very much of a stretch. Taking that into account, MOND seems to be a much more complex solution than just having another type of matter with properties similar to those we have already seen.
Almost all of the skepticism around dark matter comes from outside of the scientific community, and I think both the name and it being lumped in with dark energy (which is just a placeholder, not an actual validated theory) are part of what contributes to this. While obviously the consequences of this skepticism are significantly less dire, the reasons for it seem pretty similar to those of climate change skeptics - primarily tied to human intuition.