Wednesday, July 14, 2021

Is Dark Energy Just Systemic Error?

The authors of this pre-print argue that the redshift estimated age of supernova which is the most important means by which the acceleration of the universe's expansion attributed to "dark energy" is determined may actually be a product of systemic error that does not take into account that the age of the stars that go supernova influences how bright they become. 

If their very plausible analysis is correct, there should be no "dark energy" and the cosmological constant may be zero. 

Supernova (SN) cosmology is based on the assumption that the width-luminosity relation (WLR) and the color-luminosity relation (CLR) in the type Ia SN luminosity standardization would not vary with progenitor age. Unlike this expectation, recent age datings of stellar populations in host galaxies have shown significant correlations between progenitor age and Hubble residual (HR). It was not clear, however, how this correlation arises from the SN luminosity standardization process, and how this would impact the cosmological result. Here we show that this correlation originates from a strong progenitor age dependence of the WLR and the CLR, in the sense that SNe from younger progenitors are fainter each at given light-curve parameters x1 and c. This is reminiscent of Baade's discovery of two Cepheid period-luminosity relations, and, as such, causes a serious systematic bias with redshift in SN cosmology. Other host properties show substantially smaller and insignificant differences in the WLR and CLR for the same dataset. We illustrate that the differences between the high-z and low-z SNe in the WLR and CLR, and in HR after the standardization, are fully comparable to those between the correspondingly young and old SNe at intermediate redshift, indicating that the observed dimming of SNe with redshift is most likely an artifact of over-correction in the luminosity standardization. When this systematic bias with redshift is properly taken into account, there is no or little evidence left for an accelerating universe, posing a serious question to one of the cornerstones of the concordance model.


neo said...

the cosmological constant may be zero.

good news for string theory ?

andrew said...

@neo At this point I take it as evidence that the value of the cosmological constant (or equivalently, the aggregate amount of dark energy) is much less precisely known that commonly credited to be (even then, not very precise), because there are ill understood systemic issues with the measurement.

neo said...

based on 1 paper ?

measurements of the cosmic microwave background radiation give a similar value

andrew said...

This is one of several well reasoned papers in recent years making the suggestion of serious systemic error, and is notable because it is by an independent group of authors

neo said...

does the one of several well reasoned papers also apply to
measurements of the cosmic microwave background radiation

Fab said...

@neo Measurements of the cosmic microwave background radiation [alone] don't give [directly] the value of lambda

andrew said...

The CMB pattern has much more to do with dark matter assumptions of LambdaCDM than it does with the dark energy assumptions. At the time that the CMB arose, the proportion of dark energy in the universe of a share of the total mass-energy budget in LambdaCDM was much, much lower.

Dark energy is proportional to the volume of the universe. On a length dimension (and length is proportional to the age of the universe) the universe was about 4% of its current size then. But, since volume is proportional to length cubed, the amount of dark energy in the universe was smaller by a factor of about 15,625 then.

Right now, according to LambdaCDM, dark energy is about 70% of the total stuff in the universe (plus or minus), but at the time that CMB was formed was about one part per 6700 of the mass-energy of the universe, which wouldn't impact the CMB very much at all.