Unraveling the Universe's Expansion Mystery: A New Method Reveals a Surprising Truth
The universe is expanding, but there's a catch. When scientists measure its expansion rate using two different methods, they get two different answers, leaving everyone puzzled. Now, researchers at the University of Tokyo have developed a groundbreaking technique that provides compelling evidence for a real discrepancy, not just a measurement error.
For decades, astronomers have relied on distance markers like supernovae to measure the universe's expansion rate, known as the Hubble constant. These 'distance ladders' estimate the Hubble constant to be approximately 73 kilometers per second per megaparsec. Every 3.3 million light-years away from Earth, objects appear to recede 73 kilometers per second faster.
However, a different approach using the cosmic microwave background, an ancient radiation from the Big Bang, yields a different expansion rate of 67 kilometers per second per megaparsec. This discrepancy, known as the Hubble tension, is a significant concern because it might indicate unknown physics.
Project Assistant Professor Kenneth Wong and his team at the University of Tokyo's Research Centre for the Early Universe have taken a novel approach using time delay cosmography. This technique avoids traditional distance ladders and instead utilizes gravitational lensing, where massive galaxies bend light from distant objects behind them.
In ideal conditions, a single distant quasar can appear as multiple distorted images around the lensing galaxy. Each image takes a different path to reach us, taking varying amounts of time. By observing slight delays in these images, astronomers can measure the time difference between paths. When combined with estimates of mass distribution in the lensing galaxy, this method reveals the universe's expansion rate.
The team analyzed eight gravitational lens systems using cutting-edge telescopes, including the James Webb. Their findings showed a value consistent with the 73 kilometers per second per megaparsec figure from nearby observations, not the 67 from the early universe.
This new method is expected to remain unaffected by systematic errors in traditional distance ladders or cosmic microwave background analyses. The fact that it aligns with present-day observations rather than early universe predictions strengthens the argument that the Hubble tension represents real physics.
The current precision is around 4.5 percent. To confirm the tension definitively, researchers aim to improve this to 1-2 percent by analyzing more gravitational lens systems and refining mass distribution models for the lensing galaxies. The largest uncertainty arises from the unknown arrangement of mass within these lens galaxies, although researchers assume profiles consistent with observations.
This groundbreaking work is the result of decades of international collaboration between multiple observatories and research teams. If the Hubble tension is real, it could lead to groundbreaking discoveries in physics and a new era in cosmology, fundamentally altering our understanding of the universe's evolution.
Source: A speed camera for the universe (https://www.u-tokyo.ac.jp/focus/en/press/z0508_00434.html)
