Experts confirm that global universe expansion is still accelerating

An international research coalition has successfully verified that the expansion of the universe is accelerating. The study refutes a controversial claim that cosmic growth is slowing down, preserving the widely accepted theory regarding dark energy

The new paper directly addresses a study published by a South Korean research team.

That previous study claimed the expansion of the universe had entered a deceleration phase because the influence of dark energy, which acts as a repulsive force against gravity, was weakening over time.

Universe expansion: Resolving a cosmological dispute

The debate threatened to disrupt established models of modern cosmology. However, the international rebuttal, published in the Monthly Notices of the Royal Astronomical Society, demonstrates that the previous claim was the result of a scientific misunderstanding rather than a fundamental flaw in cosmic measurements.

Tracing the supernova measurements

The standard model of cosmic acceleration is based on the study of Type Ia supernovae, which are highly luminous explosions of white dwarf stars.

In 2011, scientists Adam Riess, Brian Schmidt, and Saul Perlmutter won the Nobel Prize in Physics after using these predictable stellar explosions to determine that more distant cosmic objects move away from Earth at faster speeds.

The South Korean paper challenged this framework by claiming that Type Ia supernovae exhibit different maximum brightnesses as the universe ages. It argued that these changing brightness levels had tricked astronomers into perceiving acceleration where none existed.

Identifying the calibration error

The investigation, led by Dr Phil Wiseman at the University of Southampton alongside Nobel Laureates Riess and Schmidt, reviewed the data and identified a critical calibration error in the South Korean study. The original paper assumed that the age of an exploding white dwarf star was identical to the overall age of its host galaxy.

Furthermore, the South Korean team failed to apply standard cosmological corrections that account for the specific mass of host galaxies. When the Southampton-led team properly calibrated the supernovae data to account for different host environments and star populations, the mathematical evidence for an accelerating universe remained completely stable and consistent.

Refocussing on dark energy

By proving that the historical measurements are correct, astrophysicists can move past questioning whether cosmic acceleration exists and focus instead on determining the true nature of dark energy.

While the challenging theory turned out to be incorrect, researchers noted that the review process provided a valuable opportunity to double-check their core assumptions. The process has opened up more precise ways of thinking about how white dwarf stars explode, which will ultimately help astronomers measure the properties of universe expansion with greater accuracy.