But from https://news.ycombinator.com/item?id=20666140, cited by sls:
> They're using "Big Bang" to mean the hot, dense, rapidly expanding state that is the earliest state of the universe for which we have good evidence. In models with inflation, this state occurs at the end of inflation, when "reheating" transfers all the energy stored in the inflaton field to the Standard Model fields (quarks, leptons, and radiation).'
Still trying to make sense of this dark matter subject besides the usual, no one is really sure...
Starting with analysis, measure theory, and I suppose the obligatory linear algebra should first if you don't already have those. Spectral theory and maybe group theory are probably next steps to having enough background to do the quantum and relativistic stuff. I glanced at the abstract for the source material for the HN post (https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.12...), and it almost certainly requires spectral theory.
I'm not an expert in this area, so a mathematical (or theoretical) astrophysicist might chime in and fill in the gaps.
This is referred to as the Cosmic Landscape, or, Eternal Inflation. In eternal inflation, the cosmological constant becomes a field in its own right, the Inflaton field, and our universe is a pocket of spacetime where that field has randomly adopted a value allowing nontrivial structure to form.
The big problem is that science is based on repeatable experiments, and it's very difficult to make a theory of what happens outside the observable universe that can be tested even in principle. If a theory doesn't make falsifiable predictions, then it isn't science. Until someone comes up with a prediction that can be tested, one might as well ask, "How do we know the world wasn't created by God?"
There are infinitely many things we don't know, the challenge is coming up with something we can know.
i will add though that from “it’s not science” it does not necessarily follow that “and therefore it’s not useful.”
the obvious example is that the idea of falsifiability as a criterion for what is and is not science is itself unfalsifiable — but very useful!
In a contemporary context, it would be similarly egotistical to assume that the whole of the universe began with the furthest event we puny humans are able to infer from our vantage point on this little speck of a planet. Context should teach us that we have no reason to assume that our local "big bang" is special or unique in any way.
Just because we can't see or infer any further out (and we might never be able to) gives us no right to declare the big bang to be any sort of beginning.
We have seen somewhat similar things before. Neutrinos interact very weakly with matter. A single neutrino needs to pass through a stack of lead that is an entire _light year_ in length just to have a 50% chance of hitting a single atom (yes, 1 actual light year).
And we have certainly have encountered unknown substances and particles before.
My layman's understanding is that no variation of MOND has managed to get that close to the comprehensive and robust scope of explanation provided by general relativity.
'Dark Energy' is physicist code for 'anti-gravitating non-stuff vacuum that we cannot see'.
It seems worth investigating.