The universe is expanding, but a significant discrepancy in its expansion rate remains unresolved. Researchers from the University of Tokyo have introduced a new method for measuring this rate, providing compelling evidence that the difference between current measurements and earlier calculations is not merely due to errors. This issue, known as the Hubble tension, has puzzled astronomers for years and could indicate new physics.
Traditionally, astronomers have relied on distance markers, such as supernovae, to calculate the universe’s expansion rate, known as the Hubble constant. This method estimates the expansion rate at approximately 73 kilometres per second per megaparsec. For every 3.3 million light-years from Earth, objects appear to recede at this rate. However, when scientists employ a different approach—examining the cosmic microwave background radiation from the Big Bang—the calculated expansion rate drops to 67 kilometres per second per megaparsec.
This discrepancy raises vital questions about our understanding of the universe. The recent study led by Project Assistant Professor Kenneth Wong and his colleagues at the University of Tokyo’s Research Centre for the Early Universe offers a fresh perspective by introducing a technique that bypasses traditional distance measurements entirely.
Innovative Measurement Technique
The team’s method relies on gravitational lensing, a phenomenon where massive galaxies bend light from objects situated behind them. When conditions align perfectly, a single distant quasar appears as multiple distorted images surrounding the lensing galaxy. Each image travels along different paths to reach Earth, resulting in varying travel times.
By observing these images for slight changes occurring at different intervals, astronomers can measure the time difference between paths. This information, when combined with estimates of mass distribution within the lensing galaxy, reveals the expansion rate of the universe.
The research team analyzed eight gravitational lens systems, each featuring a massive galaxy distorting light from a distant quasar. They utilized data from advanced telescopes, notably the James Webb Telescope. Their findings yielded a value consistent with the 73 kilometres per second per megaparsec figure derived from nearby observations, thus supporting the current understanding and challenging the earlier calculations from the early universe.
Implications for Cosmology
The results are significant because if systematic errors affect traditional distance ladders or cosmic microwave background analyses, this new approach should remain unaffected. The alignment of the new measurement with present-day observations rather than early universe predictions strengthens the notion that the Hubble tension may represent genuine physics, rather than simply a measurement error.
Currently, the precision of this new method sits at approximately 4.5 percent. To definitively confirm the existence of Hubble tension, researchers aim to refine this precision to between 1 and 2 percent. Achieving this will require analyzing additional gravitational lens systems and improving models for mass distribution in lensing galaxies. The primary challenge lies in accurately determining how mass is organized within these galaxies, although researchers generally base their profiles on existing observations.
This research reflects decades of international collaboration involving various observatories and research teams. If the Hubble tension proves to be a real phenomenon, it could lead to groundbreaking advancements in our understanding of cosmology, fundamentally altering how scientists perceive the evolution of the universe.
