The amount of visible matter only accounts for 4% of the cosmic microwave background.
The CMB is extremely smooth, but visible matter is highly clumped up. This can only be explained by a huge amount of matter that doesn't clump up ie non-baryonic.
The ratio of deuterium to hydrogen rises based on the density, since there's more pressure from gravity. There's way more deuterium than can be explained by visible matter, so there must be some extra compression happening.
Galaxies have more kinetic energy than they can have given their visible matter and how fast it's moving. This implies a huge amount of invisible mass.
Gravitational lensing around the edges of galaxy clusters indicates a halo of invisible mass.
Colliding galactic clusters show their mass splits into two parts: one that clumps up into a bright, dense blob, and another that has much higher inertia and continues past the bright blob as if it didn't interact with it in any way besides gravity.
We can map variations in empty space where there is more mass than is expected, in a way that can't be explained by a self-consistent theory of gravity but can be explained by invisible mass.
Dark matter as a theory hasn't changed for 80 years and every single one of these discrepancies is solved exactly by using the measurements of dark matter that already existed. They all agree with each other perfectly. There is no theory that even competes with dark matter. Nobody has come up with another idea that explains all of those or even most of those problems.
This is not correct. Datk matter's presence is inferred from the CMB anisotropy not because it doesn't "clump up" but because it does not interact with photons (EM field). Inflation is responsible for excess smoothness. In fact dark matter drives regular matter to "clump". See eg:
https://physics.stackexchange.com/questions/61239/how-the-cm...
>every single one of those discrepancies is solved exactly
This is quite an oversell as far as I know. The margins of error on these calculations are often large.
In particular the version with a slightly modified gravity field and smaller amounts of unobserved regular matter is not too outlandish. What would be needed to exclude this is a proof that the amount of unobserved matter cannot be reduced significantly by modifying G, which has not been written yet.
Could you explain what do you mean by 'accounts for 4% of the cosmic microwave background'? How is one supposed to account for CMB by matter density, when its spectrum is almost equilibrium one (thus consistent with almost any value of matter density)?
Why would there be a relation between CMB temperature and amount of (visible+invisible) matter? I suppose the CMB temperature decreases in time. Would`s the relation you talk about imply that the mass or density of mass of the Universe then has to decrease as well?
Just be careful. Dark matter distributions are highly paramterized quasi-continuous functions, so getting measurements to match exactly is a function of their definition, not an emergent property. While we do feel confident that there could something reasonable there, a priori exactitude cannot be evidence because that's begging the question and also possibly over fitting parameters.
The closest we have come to direct evidence are the independent calculations of the properties if it's a self-annhilating particle that agree with a certain set of observations. Even so that seriously breaks a conservation rule, because if there's no proposed way to create dark matter, the universe makes no sense.
Secondly, many other areas of physics have worked this out. The prime example of Quantum Field Theory and the Standard Model, which has been incredibly successful in predicting the existence of new types of particles from purely mathematical equations and theories (and trust me that stuff is pretty damn abstract, even compared to General Relativity)
It is of course a possibility, although you make it sound somewhat obvious, as if physicists just haven't bothered to question that the widely-regarded theories might be wrong. I assure you this is not the case; there are no politics involved in this kind of research which is stopping people presenting questions such as "are we sure our current models are correct?"
In cases like this, it is safe to assume that researchers have already explored any ideas you could come up with, especially the particularly simple ones...
While it might not be true in this case, you couldn't be further from the truth. there is an EXTREME amount of politics. people's careers are based on entire assumptions, thesis', papers, and work could be all for not if based on false assumptions.
Dismissing a theory that is (now known to be) right is not necessarily political; it can be just a mistake. There are certainly cliques that are invested in believing the orthodoxy, but there are ways in the hard sciences of absolutely disproving that orthodoxy; and, though they are subject to fierce scrutiny, as they should be, they can be, and have been, accepted after surviving that scrutiny.
it would take a great deal of hubris to say 'yes, all other sciences and research suffer from the human condition, but not physics!'
I don't think that aspect of the theories is in dispute? Newtonian physics well enough at certain scales, but breaks down at others. The question is if there's something better out there and if we adopt something better, would it remove the need for all this "dark matter".
> Secondly, many other areas of physics have worked this out. The prime example of Quantum Field Theory and the Standard Model
Wait, what? Quantum Field Theory suggests the existence of dark matter?
I'm not sure about this, personally I don't know enough about quantum gravity to comment on that. Dark energy is a tricky question though because it is somewhat explainable within our current theories, and it is unobservable.
> Secondly, many other areas of physics have worked this out.
I don't know why I put this. I meant to put that QFT is an example of a theory which predicts many more phenomena than it was originally invented to describe.
A thing we can't detect or see or have any other evidence of ... other than our equations and theories need that thing there for them to work?
> In other words situations where we see twin images of a very distant galaxy
It's entirely possible our equations do not function well on those scales.