Dark energy doesn’t exist? Scientists propose radical rethink of cosmic expansion

CHRISTCHURCH, New Zealand — Dark energy has been modern physics’ most successful placeholder, a theoretical force invented to explain why galaxies seem to be racing away from each other at ever-increasing speeds. Now, after analyzing light from over 1,500 exploding stars, researchers have reached a startling conclusion: this mysterious force might not exist at all. Instead, the answer may lie in how time itself flows differently across the cosmic landscape.

While not definitively disproving the existence of dark energy, the research presents compelling evidence for an alternative explanation that could reshape fundamental cosmology.

The concept of dark energy can be traced all the way back to the early 20th century. In 1917, Albert Einstein added a term called the “cosmological constant” to his equations of general relativity, essentially proposing a force that would prevent the universe from collapsing under its own gravity. When Edwin Hubble discovered in the late 1920s that the universe was actually expanding, Einstein abandoned this idea, which he reportedly later called his “biggest blunder.”

But in 1998, two independent teams of astronomers made a shocking discovery while studying distant supernovae. They found that very remote galaxies appeared to be moving away from us faster than predicted by the known laws of physics, suggesting the universe’s expansion was mysteriously accelerating rather than slowing down as expected.

To explain this puzzling observation, physicists revived Einstein’s cosmological constant in a new form — dark energy, a hypothetical force that works against gravity, pushing the cosmos apart. This mysterious energy was calculated to make up roughly 68% of the universe’s total energy content, dwarfing the contributions of normal matter (5%) and dark matter (27%).

The scientists who discovered this apparent acceleration, Saul Perlmutter, Brian Schmidt, and Adam Riess, were awarded the 2011 Nobel Prize in Physics for their work — even though the fundamental nature of dark energy remained, and still remains, unknown. In an ironic turn of scientific history, the cosmological constant that Einstein had rejected became a cornerstone of modern cosmology.

In this latest study, a team of researchers from the University of Canterbury in New Zealand propose an alternative explanation that might eliminate the need for dark energy entirely.

Their theory, known as “timescape cosmology,” suggests that what we perceive as cosmic acceleration might actually result from how we measure and interpret cosmic distances. This new perspective takes into account something the standard model largely ignores: the universe isn’t smooth like soup, but rather “lumpy,” with galaxies clustered together and separated by vast empty voids.

The research, published in Monthly Notices of the Royal Astronomical Society, analyzed data from the Pantheon+ catalogue containing 1,690 supernova observations, representing 1,535 unique stellar explosions. These supernovae serve as cosmic “standard candles,” allowing astronomers to measure vast distances across space. The team developed new statistical methods specifically designed to avoid assumptions tied to traditional cosmological models.

Modern cosmology rests heavily on Einstein’s theory of general relativity and assumes that space is uniformly distributed on large scales. However, anyone who has looked at pictures from powerful telescopes knows that matter in our universe is actually clumped together in a cosmic web of galaxies and voids. The timescape theory takes this inherent lumpiness into account, proposing that these structural variations affect how we perceive cosmic distances and time itself.

Instead of assuming uniform expansion throughout space, timescape cosmology suggests that different regions of the universe expand at different rates. Imagine a cosmic landscape where galaxy-rich regions experience time and space differently than the vast empty voids between them. This varying expansion rate could create an illusion of acceleration when viewed from our particular vantage point in the cosmos.

By analyzing the light from distant supernovae using a sophisticated statistical approach, the researchers found evidence supporting this alternative view. Their analysis revealed patterns in the data that align better with timescape predictions than with the standard model, particularly at certain cosmic distances.

Most intriguingly, the study identified a specific scale — roughly equivalent to 75% of the way to cosmic structures like the “Great Attractor” — where the universe begins to show signs of statistical homogeneity. This scale, larger than previously thought, might represent a fundamental transition point in how cosmic structure influences our measurements.

What makes this research particularly timely is its potential to resolve the “Hubble tension” – a significant discrepancy between different methods of measuring the universe’s expansion rate. Recent observations from the Dark Energy Spectroscopic Instrument (DESI) have revealed that the standard cosmological model doesn’t fit observations as well as previously thought, particularly when considering how dark energy might evolve over time.

The implications of timescape cosmology are profound. According to the research team, a clock placed in our Milky Way would tick approximately 35% slower than an identical clock positioned in the vast cosmic voids between galaxies. Over billions of years, this time difference would allow for greater expansion of space in void regions, creating what appears to us as accelerating expansion when these enormous empty regions come to dominate the universe’s volume.

“Our findings show that we do not need dark energy to explain why the universe appears to expand at an accelerating rate. Dark energy is a misidentification of variations in the kinetic energy of expansion, which is not uniform in a universe as lumpy as the one we actually live in,” explains Professor David Wiltshire, who led the study, in a statement.

“The research provides compelling evidence that may resolve some of the key questions around the quirks of our expanding cosmos,” continues Wiltshire. “With new data, the universe’s biggest mystery could be settled by the end of the decade.”

Looking ahead, several major astronomical projects, including the Euclid space telescope and the Vera C. Rubin Observatory, will provide unprecedented amounts of data to further test these ideas. These observations could definitively determine whether timescape cosmology truly offers a better description of our universe than the standard model.

The European Space Agency’s Euclid satellite, launched in July 2023, and the upcoming Nancy Grace Roman Space Telescope will be crucial in gathering new data. According to Professor Wiltshire, “With new data, the Universe’s biggest mystery could be settled by the end of the decade.” However, testing these competing theories will require at least 1,000 high-quality supernova observations.

While this research doesn’t definitively resolve all questions about cosmic expansion, it offers a compelling alternative to dark energy that aligns with both Einstein’s general relativity and our observations of the universe’s structure. As more data becomes available from new telescopes and surveys, we may find that the greatest mystery in modern cosmology isn’t why the universe’s expansion is accelerating, but rather how our perception of time and space across cosmic scales affects our measurements of that expansion.