Taiwanese scientist WunYi Shu made some waves last month with a mathematical model that challenges the dark energy driven model of cosmology. Here's a quote from the Technology Review blog:^{1}
"Shu's idea is
that time and space are not independent entities but can be converted
back and forth between each other. In his formulation of the geometry
of spacetime, the speed of light is simply the conversion factor
between the two. Similarly, mass and length are interchangeable in a
relationship in which the conversion factor depends on both the
gravitational constant G and the speed of light, neither of which need
be constant.
So as the Universe expands, mass and time are converted to length and space and vice versa as it contracts."
The first paragraph says nothing new, but the second may have some interesting implications. He uses this idea (in a somewhat controversial manner) to predict redshifts that closely match those observed in the late 1990's, as shown in the graphic (from the paper). The data represent the effective peak magnitude of Type Ia supernovae in the Bband spectrum (688 nm) against redshift.
Shu claims that, if correct, his model eliminates the need for dark energy. There is a heavy price to be paid, though  both the universal constants c and G must be variables, i.e. they must be changing over cosmological time. It did not take long for other scientists to find holes in Shu's theory. The most readable critique that I found was on Sarah Kavassalis' Blog "This Week in the Universe".^{2}
As far as I can see, her main point is that changing c and G requires a complete redo of Einstein's field equations (EFEs). The EFEs require those values to be what their names say: constants. According to Kavassalis, Shu changed the EFEs in an arbitrary manner, yielding them invalid and in a way meaningless.
She also claims that such a good fit to the observed data can be achieved without doing proper science. Her final words in the blog article are revealing: "Yes, if you pick and choose what physics to ignore you can arrive at meaningless equations."
I am less dismissive, because I like alternatives that show at least some promise. Maybe one of them will one day be refined to properly explain redshift observations in a more palatable way than dark energy.
What do you think?
Jorrie
1. Big Bang Abandoned in New Model of the Universe
2. "Cosmological Models with No Big Bang" review

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