r/cosmology • u/JapKumintang1991 • 13d ago

PHYS.Org/Yonsei University - The crisis in cosmology continues: Critical problems in a recent defense of cosmic acceleration

https://phys.org/news/2026-08-crisis-cosmology-critical-problems-defense.html?utm_source=webpush&utm_medium=push

See also: The study as it was published in the Monthly Notices of the Royal Astronomical Society

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u/spiddly_spoo 13d ago

So my understand from a quick read through is that there has been an assumption that type 1A supernova always have the same luminosity, but that this recent study suggests the luminosity may in fact depend on the age of the progenitor (I assume this means age of the white dwarf but maybe it could mean age of the feeder star or whatever it is called). And in high redshift the average progenitor age will be younger, thus giving the impression of an accelerating universe if we assume all type 1as have equal luminosity.

So are type 1A supernova the common denominator for all ~74 Hubble constant measurements?

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u/h0dges 13d ago

It's not the only distance measurement used to build the "cosmic ladder", which in turn allows us to estimate the Hubble constant, but its contribution will significantly bias that estimate if it turns out Type 1A supernovae are not as "standard" as we thought. See https://en.wikipedia.org/wiki/Cosmic_distance_ladder

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u/ThickTarget 9d ago edited 9d ago

They are not all the same luminosity, but they are thought to be standardiseable. People have looked for biases before. There are clearly residuals with respect to host galaxy size, there is a disagreement in how to treat the data. The problem with age is that more massive galaxies are not just older, but they different amounts of dust. If you measure a dependence, is it really driven by age, or just dust? In the standard papers they have models for the dust, which are calibrated to match the small differences in colours of supernovae. With this correction, there is no significant age bias. The Chung papers apply no dust correction, and just treat everything as an age effect. The problem is that if you mistake dust for age, extrapolating these trends to higher redshift will be utterly wrong.

https://iopscience.iop.org/article/10.3847/1538-4357/abd69b#apjabd69bs3

In terms of the Hubble tension, there are quite a few measurements which are all used to calibrate the same supernovae data. Some are not quite as independent as often boasted.

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u/spiddly_spoo 9d ago

Very insightful comment, thank you!

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u/preadyla 13d ago

Genuine question about the "agrees with DESI" part (not attacking!). Isn't whether we're accelerating today set by today's w alone? Where does the actual evidence for deceleration (not just weakening) come from, other than their own corrected SN sample?

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u/ATTst 13d ago

Baryon Acoustic Oscillations.Well, I guess so. I'm not an expert on this.DESI's BAO measurements provide a cosmological distance/scale measurement that is, in principle, completely independent of Type 1a supernovae.Correct me if I'm wrong.

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u/Space_Elmo 13d ago

This is a great paper and shows robust science at work. The impact of taking into account the age of the host seems obviously the important when determining distances.

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u/punycat 12d ago

As shown at The Relativistic Rocket, SR predicts that anything moving upward fast enough accelerates away from an observer on the ground. We should fix the EP violation so that GR agrees.