In article , Steve Willner
writes:

In article ,
Phillip Helbig---undress to reply writes:
LCDM is not a theory in the classical sense.

That took me aback. I think what you mean is that the exact
constituents of the Universe aren't predictions of any theory.

Right.

That's correct: the various densities and a few other things are free
parameters. If you put specific values for these parameters into GR
and known baryon physics, you can predict lots of observables.

Many people use "LCDM theory" to refer to GR+baryon physics+a
specific set of free parameters. That last doesn't mean specific
values, only the list of parameters. The era of "precision
cosmology" means that each of the parameters is now measured with
multiple observations.

Right.

Dark matter is
something which is observed (or, rather, not observed, but the existence
of which is inferred from observations).

In particular, a non-zero density for non-baryonic dark matter is
inconsistent with observations. One set of such observations is the
CMB fluctuations. Another is the cluster velocity dispersions
combined with the nucleosynthesis upper limit on baryon density.

Right.

To be more precise, LCDM is not a theory derived from first principles
like, say, Newtonian physics or GR. Rather, it is strongly motivated by
what is observed, in the same way that particle physics is. That
doesn't mean that it is not a theory at all; it is, and can make further
predictions which don't depend on observational input and some of these
have been confirmed.

In particular, LCDM does not "predict non-baryonic matter" because the
idea of non-baryonic matter is an observational input.