Anonymous writes: 
Via ScientificAmerican.com: Cosmology Has Some Big Problems /By Bjørn Ekeberg on April 30, 2019
The field relies on a conceptual framework that has trouble accounting for new observations
Credit: Thanapol Sisrang Getty Images
What do we really know about our universe?
Born out of a cosmic
explosion 13.8 billion years ago, the universe rapidly inflated and then
cooled, it is still expanding at an increasing rate and mostly made up
of unknown dark matter and dark energy ... right?
This well-known story is
usually taken as a self-evident scientific fact, despite the relative
lack of empirical evidence—and despite a steady crop of discrepancies
arising with observations of the distant universe.Advertisement
In recent months, new
measurements of the Hubble constant, the rate of universal expansion,
suggested major differences between two independent methods of
calculation. Discrepancies on the expansion rate have huge implications
not simply for calculation but for the validity of cosmology's current
standard model at the extreme scales of the cosmos.
Another recent probe found
galaxies inconsistent with the theory of dark matter, which posits this
hypothetical substance to be everywhere. But according to the latest
measurements, it is not, suggesting the theory needs to be reexamined.
It's perhaps worth
stopping to ask why astrophysicists hypothesize dark matter to be
everywhere in the universe? The answer lies in a peculiar feature of
cosmological physics that is not often remarked. For a crucial function
of theories such as dark matter, dark energy and inflation, which each
in its own way is tied to the big bang paradigm, is not to describe
known empirical phenomena but rather to maintain the mathematical
coherence of the framework itself while accounting for discrepant
observations. Fundamentally, they are names for something that must
exist insofar as the framework is assumed to be universally valid.
Each new discrepancy
between observation and theory can of course in and of itself be
considered an exciting promise of more research, a progressive
refinement toward the truth. But when it adds up, it could also suggest a
more confounding problem that is not resolved by tweaking parameters or
adding new variables.
Consider the context of
the problem and its history. As a mathematically driven science,
cosmological physics is usually thought to be extremely precise. But the
cosmos is unlike any scientific subject matter on earth. A theory of
the entire universe, based on our own tiny neighborhood as the only
known sample of it, requires a lot of simplifying assumptions. When
these assumptions are multiplied and stretched across vast distances,
the potential for error increases, and this is further compounded by our
very limited means of testing.
Full article: https://blogs.scientificamerican.com/observations/cosmology-has-some-big-problems/
