[nostrebored]

Dark matter is overfitted. This isn’t some comparative advantage it has. The number of parameters you set manually in many of these models is insane.

We are fundamentally missing something. Thankfully it’s just not all that important for us right now.

[empyrrhicist]

I mean, we already know about existing "dark" matter particles. The Neutrino comes to mind, though it's not massive enough to explain the gravitational phenomena. LCDM really isn't that weird or unexpected, since it's a lot like what we already observe, and we already think more particles should exist.

[denton-scratch]

Hypothetical "dark matter" doesn't interact with ordinary matter, except gravitationally. Neutrinos do interact with ordinary matter; otherwise we wouldn't be able to build neutrino detectors. Therefore neutrinos are not an example of dark matter.

[consilient]

> "dark matter" doesn't interact with ordinary matter, except gravitationally.

It's possible that this is the case, but particles that also interact with the weak force (hence WIMPs: weakly interacting massive particles) are generally considered better candidates.

[arbitrage]

Neutrinos aren't dark matter.

[mr_mitm]

They are, because they have mass and don't interact electromagnetically. They are just not cold dark matter, because their mass is so low they behave more like radiation than matter, i.e. the scale as a^4 instead of a^3, where a is the scale factor. A sterile neutrino, if it existed, could still be a dark matter candidate.

[MichaelZuo]

Can you give examples of these parameters that must be set manually?

[kelseyfrog]

These are the free parameters of the Standard Model https://en.m.wikipedia.org/wiki/Standard_Model#Construction_...

[btilly]

Every one of those parameters is associated with a field that does symmetry breaking. Every one of those fields has a particle associated. Every one of those particles has been observed, studied, and found to have properties in line with what would be required for the fields to have the values that we measure.

So yes, that's a lot of free parameters. But they are intrinsic to the theory. And we have considerable experimental evidence that they represent something real.

For those who don't know what symmetry breaking is, the Standard Model has a lot more symmetries than the observed universe. For example the theory does not specify that electromagnetism is long range while the strong nuclear force is short range. Or that the muon weighs more than the electron. But for each symmetry in the theory that we don't see in practice, there is a field that specifies the value of the observed asymmetry. Each field is carried by a particle. Each particle has properties that reflect the value of all of the fields. Every particle has been found and almost all have the predicted properties (to within measurement error).

The last particle found was the Higgs boson. The Higgs field determines the relative masses of different particles.

The "almost all" is the fact that the neutrino has 3 versions and oscillates between them in flight. Also the neutrino is not massless. While the Standard Theory can adapt to match this, this isn't what was originally predicted.

[kelseyfrog]

Right, and some physicists have a nagging feeling that the addition of another symmetry would result in the reduction in free parameters. "We've done it before, so why shouldn't it work again?" is their thought process. So they devise a model which replicates the standard model in observable ranges and to make it testable, doesn't replicate the standard model outside of the observable range. This is an attempt to make the model falsifiable and thus scientific. Then they advocate for expensive accelerators to falsify the model.

[cld8483]

You'd be hard pressed to derive a model for the coarse structure of the universe from the Standard Model, considering the Standard Model can't describe gravity. Maybe this is part of the problem..