Dark Energy Controversies

In a recent post titled “Recent discussions on dark energy” I discussed various speculations on the nature of dark energy assuming dark energy is real. It never occurred to me that the data analyses of 2 independent teams lead by Saul Perlmutter (Supernova Cosmology Project) and Brian P. Schmidt and Adam G. Riess (The High-z Supernova Search Team) who were awarded the 2011 Nobel Prize in Physics could be wrong. Besides, the official history of the discovery is very convincing.

Oxford physicist Subir Sarkar and 3 co-authors recently published a paper challenging the conclusion of the Nobel winners. Nobel winning analyses were done 20 years ago using 110 supernovae. Subir Sarkar and co-authors used 740 supernovae from the JLA catalogue. You can read Sabine Hossenfelder’s summary of their paper here. In the comments section of Hossenfelder’s post, Subir Sarkar and co-author Mohamed Rameez respond to  comments. Mohamed Rameez also wrote a guest-post explaining their findings.

David Rubin and Jessica Heitlauf published a rebuttal titled “Is the expansion of the universe accelerating? All signs still point to yes“. Subir Sarkar and co-authors published a rebuttal of the rebuttal immediately.

In addition to Hossenfelder’s post, Quanta article by Natalie Wolchover titled “No Dark Energy? No chance, Cosmologists Contend” is a good place to learn about the discussions.

Rocky Kolb’s views on dark energy.

Edward (Rocky) Kolb became the director of the Kavli Institute for Cosmological Physics at the University of Chicago in 2019. He succeeded Michael S. Turner as director. Michael S. Turner is the person who coined the term “dark energy”. Kolb and Turner have been working very closely over the years at FERMILAB and the University of Chicago. It is interesting that Rocky Kolb has a contrarian view on dark energy.

Rocky Kolb has a presentation titled “Taking Sides on Dark Energy” which is a summary of his paper “Backreaction of inhomogeneities can mimic dark energy“. Interestingly, this paper was published in 2011 the same year the Nobel Prize was given to the dark energy discovery.

“In the standard approach to cosmology, the evolution and observations associated with an inhomogeneous universe with density \rho (\vec{x}) are modeled by employing a homogeneous cosmological model of density \left\langle \rho (\vec{x}) \right\rangle, where lang⋅⋅⋅rang refers to some sort of spatial average. While there is broad agreement that since general relativity is a nonlinear theory, this procedure cannot strictly be correct, there is less agreement that the effect of backreactions can be significant. Some have proposed that effects usually attributed to dark energy may be due to the backreactions of inhomogeneities, and there is no dark energy and the universe is not accelerating (at least, not in the usual sense). Here, I present a critical analysis of the standard dark-energy approach and discuss the proposal that the backreaction of inhomogeneities on scales much less than the Hubble radius mimics dark energy.” – Rocky Kolb

Rocky Kolb’s presentation titled “Taking Sides on Dark Energy” is very educational. I highly recommend it.

Regardless of contrarian views and data analyses, the supernova evidence for dark energy is strong. The graph below cannot be ignored.

image credit

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