One of science’s biggest mysteries is dark energy. For the past century, astronomers have maintained that the Universe has been expanding in all directions. They used the idea of dark energy as a stand-in for physics they could not comprehend, but this hotly debated theory has always had its share of issues.
A group of physicists and astronomers from the University of Canterbury in Christchurch, New Zealand, are now challenging the conventional wisdom by demonstrating that the Universe is expanding in a more diversified or “lumpier” way using enhanced light-curve analysis of type Ia supernovae.
According to the research team, there is no dark energy. The new discoveries support the so-called “timescape” hypothesis of cosmic expansion. Since the differential stretching of light results from our calibration of time and distance rather than from a speeding universe, dark energy is not required in this paradigm.
Time passes quicker in such empty space than in a galaxy because gravity slows time.
According to the model, a clock in the Milky Way would run roughly 35% slower than one at an average location in vast cosmic gaps, indicating that billions more years would pass in those voids. The expansion appears to accelerate because the more expansive the empty void that extends in the Universe, the more space it yields for expansion.
Professor David Wiltshire, who led the study, said: “Our findings show that we do not need dark energy to explain why the Universe appears to expand at an accelerating rate.
New precise measurement of the universe’s expansion 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 live in.”
He added: “The research provides compelling evidence that may resolve some of the key questions around the quirks of our expanding cosmos.
“With new data, the Universe’s biggest mystery could be settled by the decade’s end.”
Dark energy accounts for about two-thirds of the Universe’s mass-energy density and is generally believed to be a weak anti-gravity force that operates independently of matter.
Dark energy is necessary for the mainstream Lambda Cold Dark Matter (ΛCDM) model of the Universe to account for the observed acceleration in the cosmos’ expansion rate.
Measurements of the distances to supernova explosions in far-off galaxies, which seem farther away than they should be if the Universe’s expansion were not speeding, serve as the basis for this conclusion.
New observations keep challenging the present expansion rate of the Universe.
On the one hand, the evidence from the Big Bang afterglow- the so-called cosmic microwave background- uprightly contradicts the “recent expansion” of the Universe, an anomaly summed up in the phrase “Hubble tension.”
Professor Wiltshire added: “We now have so much data that in the 21st century, we can finally answer the question – how and why does a simple average expansion law emerge from complexity?
“A simple expansion law consistent with Einstein’s general relativity does not have to obey Friedmann’s equation.”
The researchers say that the European Space Agency’s Euclid satellite, launched in July 2023, has the power to test and distinguish the Friedmann equation from the timescape alternative. However, this will require at least 1,000 independent, high-quality supernovae observations.
They say the new data now provides “strong evidence” for timescape. It may also point to a compelling resolution of the Hubble tension and other anomalies related to the expansion of the Universe.
Furthermore, the Dark Energy Spectroscopic Instrument (DESI) has analyzed additional high-precision data and discovered that models in which dark energy is “evolving” throughout time instead of staying constant fit better than the ΛCDM model.
In models that employ Friedmann’s equation, a simplified version of the 100-year-old cosmic expansion rule, it is challenging to resolve both the Hubble tension and the surprises uncovered by DESI.
This presupposes that the Universe expands uniformly on average, as though all cosmic structures might be blended into a featureless soup without any complex structures. In reality, though, the current Universe comprises a complicated cosmic web of galaxy clusters that encircle and thread enormous empty spaces in sheets and filaments.
Journal Reference:
- Antonia Seifert, Zachary G Lane et al. Supernovae evidence for foundational change to cosmological models. Monthly Notices of the Royal Astronomical Society: Letters. DOI: 10.1093/mnrasl/slae112