Here’s the effort:
Recently, theorists have been busy imagining new cosmic ingredients that, when added to the standard model, would rev up the universe’s expected expansion rate, making it match observations.
“Discovering anomalies is the fundamental way that science makes progress,” said Avi Loeb, a cosmologist at Harvard University and one of dozens of researchers who have proposed solutions to the Hubble tension.
These are some of the top ideas for what could be speeding up cosmic expansion.
Thomas Lewton, “What Might Be Speeding Up the Universe’s Expansion?” at Quanta
Lewton goes on to list and provide particulars for such contenders as decaying dark matter, inconstant dark energy, and modified gravity:
“We all know they are ad hoc,” Randall said of the proposals so far. “The amazing thing is that even with these ad hoc additions, it’s still very hard to accommodate the discrepancy.”
Thomas Lewton, “What Might Be Speeding Up the Universe’s Expansion?” at Quanta
Our physics color commentator Rob Sheldon comments,
Yet another example of “curve fitting”, adding free parameters whose only purpose is to get a closer fit to the data.
“What is big and red and eats rocks?”
“A big red rock-eater.”
The humor is that the name gives no further information. It’s a premise masquerading as a solution. In the same way, cosmologists “theories” are simply data masquerading as predictions.
This is why particle physics and cosmology has made no progress over the past few decades as Sabine Hossenfelder warns. No one even faintly understands what a theory is supposed to wear to Stockholm, much less accomplish for posterity.
Rob Sheldon is the author of The Long Ascent, Vol. 1 and The Long Ascent, Vol. 2.