Physicists say the universe could be explained without dark energy. 

New work by a team of New Zealand physicists has cast serious doubt on the theory of dark energy, a concept long used to explain the accelerating expansion of the Universe.

Dark energy is a mysterious force thought to be driving the Universe's accelerating expansion, making up about 70 per cent of its total energy. 

The Lambda Cold Dark Matter (ΛCDM) model is the most widely accepted theory in cosmology, explaining the Universe's structure and growth using dark energy (Λ), cold dark matter, and ordinary matter.

The research, which revisited data from exploding stars known as Type Ia supernovae, proposes a more nuanced understanding of the Universe’s growth, suggesting it is not uniform but instead uneven or “lumpy”. 

The findings challenge key assumptions of the ΛCDM model, which has dominated cosmology for over two decades.

Using refined methods to analyse supernovae light curves, the researchers argue that the Universe’s expansion can be explained without invoking dark energy. 

The alternative framework, called the ‘timescape cosmological model’, suggests that variations in gravitational energy across cosmic structures, such as voids and filaments, drive the observed changes in expansion.

The timescape model replaces dark energy with kinetic gravitational energy and its gradients to explain the expansion of the Universe. 

The study used a model-independent statistical approach to analyse the Pantheon Type Ia Supernovae data set, the largest such collection to date. 

Unlike earlier analyses, this method avoided assumptions that might bias the results. 

It instead focused on empirical comparisons of the standard ΛCDM model with the timescape cosmology. 

The findings offered “very strong evidence” in favour of the timescape model, even when limited to high-redshift supernovae, where data is often considered more reliable.

One of the study’s strengths lies in its rejection of conventional simplifications used in earlier analyses. 

Previous studies assumed uniform distributions for certain supernovae parameters, which newer research shows to be flawed. 

By accounting for these complexities, the team identified features in the data that align better with the timescape model.

The timescape cosmology departs from the standard ΛCDM framework, which assumes a smooth, average expansion of the Universe. 

Instead, it incorporates the effects of cosmic inhomogeneities - differences in matter distribution - on gravitational energy. 

These variations, the study argues, create localised differences in expansion rates that, when averaged over large scales, mimic the effects previously attributed to dark energy.

This approach builds on a principle known as the backreaction of inhomogeneities, which considers how smaller-scale structures influence the overall evolution of the Universe. 

According to the researchers, this mechanism resolves longstanding inconsistencies in the ΛCDM model, particularly at smaller scales where traditional assumptions break down.

The findings carry significant implications for cosmology and astrophysics. 

If confirmed, they may eliminate the need for dark energy, reshaping our understanding of the Universe's expansion and its governing principles. 

The researchers anticipate that ongoing data collection, particularly from higher-resolution supernovae surveys and cosmological simulations, will provide further clarity in coming years.

The results also underscore the importance of exploring alternative models. 

“Regardless of what model cosmology is to be the standard in future, exploring more than one model is important,” the researchers say.

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