It's interesting to still see so little attention to some details in favor of others.
In Aug, 2018, 78% of the IAU vote changed the Hubble Constant to the Hubble-Lemaitre Constant. None of these articles, however, respect the new term.
Some of the articles, at least one, talks about Hubble in his work to demonstrate expansion. Edwin Hubble never once argued for an expansion, surprisingly. To him that claim was for theorists, not him.
But, and my very cursory views of the articles, seem to treat the "Hubble Constant" as a constant, but we know it's not. The expansion rate is non-linear. Lemaitre applied Einstein's cosmological constant in his original theory that gave us the Big Bang. Further, he (and Eddington, IIRC) disagreed with Einstein that his cosmological constant should be removed.
It was in 1998, as we have discussed recently, that an acceleration component is needed for the "constant".
So, what am I missing? Is the constant a term that has great utility even if it lacks accuracy? Given our margin of errors for distance, etc. aren't fantastic, perhaps so.
Naming is a conventional issue. If peer reviewers do not catch the problem, it will remain for a while among astronomy papers. Cosmology is a partly different area, and IAU has no power over all of them.
I think you are confusing the initial observation of an apparent linear expansion of the universe - which was called the "Hubble constant" - with modern cosmology measurements of the expansion parameter - which is called the "Hubble parameter". There is a century of advance between those different things, including the discovery that the expansion rate depends on the inner state of the universe. The expansion is modeled by the scale factor [link below].
If we start with the universe as a classic newtonian gravity system and the era of matter domination some time after the hot big bang happened, cosmologists describe distant galaxies as a thrown mass object so at the time their distancing looked like a parabola. When radiation, which is stretched by expansion (redshift) dominated the era before right after hot big bang the universe expanded like a so called hyperparabola. And when inflation dominated before that as well as now as dark energy dominates the inner energy state of the universe, their constant vacuum energy means that the universe expand exponentially. It is the value of the exponent *now* that is identified with the Hubble parameter H0.
More precisely there is currently a 70/30 proportion dark energy – which constant energy density is what drives the expansion towards an exponential – and the rest. So the exponent that it approaches is changing (in fact decreasing) [
https://en.wikipedia.org/wiki/Scale_factor_(cosmology) ]. “Current evidence suggests that the expansion rate of the universe is accelerating, which means that the second derivative of the scale factor {\displaystyle {\ddot {a}}(t)}{\ddot {a}}(t) is positive, or equivalently that the first derivative {\displaystyle {\dot {a}}(t)}{\dot {a}}(t) is increasing over time.[5] This also implies that any given galaxy recedes from us with increasing speed over time, i.e. for that galaxy {\displaystyle {\dot {d}}(t)}{\dot {d}}(t) is increasing with time. In contrast, the Hubble parameter seems to be decreasing with time, meaning that if we were to look at some fixed distance d and watch a series of different galaxies pass that distance, later galaxies would pass that distance at a smaller velocity than earlier ones.”
Note that the possible constant in Einstein's equations were initially put there by Einstein when he believed the universe was static, before Hubble's results became known, and on the metric curvature tensor side. Later it was removed, and it was long thought the vacuum energy - the use of the constant on the energy-stress tensor side - was either zero (consistent with then cosmology) or naturally Planck energies (the highest energy density of quantum field theory as well as general relativity itself). It was in the late 90s that dark energy expansion was observed and the parameter became useful as expression for vacuum energy density and got an observed value.
Since we are on that subject, I'm happy to note that Weinberg's selection bias ("anthropic multiverse") is no longer too controversial not to be among the two listed candidates for explanations in the BOSS paper -and it is the simplest one [
https://arxiv.org/abs/2007.08991 ].
"Nevertheless, the observed consistency with flat ΛCDM at the higher precision of this work points increasingly towards a pure cosmological constant solution, for example, as would be produced by a vacuum energy finetuned to have a small value. This fine-tuning represents a theoretical difficulty without any agreed-upon resolution and one that may not be resolvable through fundamental physics considerations alone (Weinberg 1989; Brax & Valageas 2019). This difficulty has been substantially sharpened by the observations presented here."
It seems if H0 is not a constant but perhaps a variable that changes with distance from Earth and perhaps dark energy acceleration, those cosmology calculators, e.g.
https://ned.ipac.caltech.edu/help/cosmology_calc.html, may need some tweaking or revision to accurately show the *true age* of the universe
No exactly, but note that you can either use them with defaults as rough estimates, or put in the latest values if that is what you wish. These sites or apps do not need to modify the code, based on the LCDM model, yet.
as far as I am concerned, none of the *true age* claims tossed around are scientific fact. They may have some good arguments supporting, but areas that remain untested too, e.g. the radius of the universe from Earth out some 46 billion light years or more.
These are different problems. It is true that some works derives an age of the universe based on their work, but we don't have to accept that. The age is a rather precise fact, with no tension between data.
The only remaining tension is on the value of expansion rate parameter H0. [I have already commented on that tension and possible solutions in my earlier comment.]
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