The universe is expanding at a rate that has puzzled scientists for decades. Two distinct methods of measuring this expansion yield different results, prompting researchers at the University of Tokyo to explore a new approach. Their findings suggest that the discrepancy, referred to as the Hubble tension, could indicate a fundamental misunderstanding of physics, rather than just measurement errors.
Astronomers have traditionally relied on distance markers, such as supernovae, to determine the Hubble constant, which quantifies the universe’s expansion rate. This method indicates an expansion rate of approximately 73 kilometres per second per megaparsec. This means that for every 3.3 million light-years from Earth, objects appear to recede at an increasing speed of 73 kilometres per second.
A contrasting approach examines the cosmic microwave background, the remnant radiation from the Big Bang, to estimate the expansion rate. This method produces a significantly lower value of 67 kilometres per second per megaparsec. The difference between these two measurements has led to ongoing debate among cosmologists, as it raises questions about our understanding of the universe’s evolution.
Innovative Techniques Shed Light on Cosmic Discrepancies
Project Assistant Professor Kenneth Wong and his colleagues at the Research Centre for the Early Universe have introduced a novel technique known as time delay cosmography. This method bypasses traditional distance ladders entirely and leverages gravitational lensing, a phenomenon where massive galaxies distort light from objects located behind them.
When conditions align perfectly, a distant quasar can appear as multiple distorted images surrounding the lensing galaxy. Each image follows a different path to reach Earth, resulting in varying travel times. By observing slight changes in these images that occur out of sync, astronomers can measure the time difference between the paths. This information, combined with estimates of mass distribution within the lensing galaxy, allows researchers to calculate the universe’s expansion rate.
The research team analyzed eight gravitational lens systems, utilizing advanced telescopes, including the James Webb Space Telescope. Their measurements yielded a value consistent with the 73 kilometres per second per megaparsec figure derived from nearby observations, rather than the lower figure from early universe calculations. This independence from traditional methods strengthens the argument that the Hubble tension is a genuine phenomenon.
Future Research and Implications for Cosmology
The current precision of these measurements stands at roughly 4.5 percent. To definitively confirm the reality of the Hubble tension, researchers aim to refine this precision to between 1-2 percent. Achieving this goal will require further analysis of additional gravitational lens systems and improved models of mass distribution within the lensing galaxies. A significant uncertainty lies in understanding how mass is arranged within these galaxies, although researchers assume profiles that align with existing observations.
This work represents decades of international collaboration among various observatories and research teams. Should the Hubble tension prove to be a real effect, it could signify a paradigm shift in cosmology, potentially leading to new physics and a revised understanding of the universe’s evolution. The implications of such findings could reshape our comprehension of the cosmos and its underlying principles.
