Cosmology Has Some Big Problems

Scientificamerican

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.

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.