Physicists have proposed a revolutionary model that could rewrite our understanding of the universe’s expansion, suggesting that dark energy—a key component of the standard cosmological model—might not exist.
At a glance:
- Researchers challenge the existence of dark energy, proposing a “timescape” model to explain the universe’s expansion.
- The timescape model argues that variations in time and space calibration, not dark energy, account for perceived cosmic acceleration.
- New findings could resolve anomalies like the “Hubble tension” and discrepancies in expansion data.
- Advanced observations from space telescopes may confirm or refute this groundbreaking theory by the end of the decade.
For decades, physicists have theorized that dark energy, a mysterious force making up two-thirds of the universe’s energy, is driving its accelerated expansion. However, researchers at the University of Canterbury in New Zealand argue that dark energy is unnecessary to explain cosmic acceleration.
Their findings, published in the Monthly Notices of the Royal Astronomical Society Letters, introduce the “timescape” model, which suggests that the apparent acceleration is due to differences in how time and space are calibrated across the universe.
“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,” explained Professor David Wiltshire, who led the study.
A “lumpy” cosmos changes the equation
Traditional models assume a uniform expansion of the universe, but the researchers emphasize the importance of the universe’s complex structure, characterized by galaxy clusters, filaments, and voids.
The timescape model accounts for how gravity slows time differently in varying cosmic regions. For example, clocks in the Milky Way would tick about 35% slower than clocks in vast cosmic voids. Over billions of years, this discrepancy could make voids appear to expand faster, mimicking the effects of dark energy.
Challenging the standard model
The standard Lambda Cold Dark Matter (ΛCDM) model relies on dark energy to explain supernova observations showing distant galaxies receding faster than expected. Yet, new analyses highlight inconsistencies in the ΛCDM model, including:
- Hubble tension: A discrepancy between the early universe’s expansion rate (measured via the Cosmic Microwave Background) and its current rate.
- Evolving dark energy: Observations by the Dark Energy Spectroscopic Instrument (DESI) suggest that dark energy may not remain constant over time, conflicting with ΛCDM assumptions.
Professor Wiltshire contends that these anomalies can be resolved without dark energy. “A simple expansion law consistent with Einstein’s general relativity does not have to obey Friedmann’s equation,” he said, referring to the century-old equation underpinning the standard model.
A new era of cosmic exploration
The study leverages an improved catalog of 1,535 supernovae, offering “very strong evidence” for the timescape model. However, further observations are needed to validate these findings.
Upcoming missions by the European Space Agency’s Euclid satellite and NASA’s Nancy Grace Roman Space Telescope aim to collect the high-quality data necessary to distinguish between the Friedmann equation and the timescape model.
“If successful, these findings could resolve some of the key questions around the quirks of our expanding cosmos,” said Wiltshire, adding that a resolution to these mysteries may come by the end of the decade.
This breakthrough challenges our understanding of the universe and raises profound questions about the true nature of cosmic expansion, potentially transforming cosmology as we know it.
