A ‘ghostly mirror world’ could be causing our universe to behave in ways we don’t understand

Mysterious symmetry could help resolve problem with the expansion of the cosmos

Andrew Griffin
Friday 20 May 2022 16:38
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<p>Lyrid meteor shower set to delight stargazers (Owen Humphreys/PA)</p>

Lyrid meteor shower set to delight stargazers (Owen Humphreys/PA)

A hidden “mirror world” of particles that are only evident through gravity could help answer the strange behaviour of our universe, scientists say.

It could be the answer to the difficulties of the Hubble constant – which measures the expansion of our universe – and the fact that it does not seem quite as constant as researchers expected.

When scientists predict the rate of expansion using the standard model of cosmology, and then compare it with precise measurements, the two numbers are different. In recent years, those precise measurements have become yet more precise – and has only made it more clear that the problem is not the result of another problem, such as measurement errors.

As yet, there is no explanation for why that is, and the answer is likely to require a fundamental rethink of our understanding of the cosmos.

Now a team of scientists say they have found a new mathematical property of cosmological models that could allow that problem to be resolved – since it allows for the universe to be expanding more quickly without changing the model in ways that would prove problematic elsewhere.

The discovery suggests that there might be a universe, very similar to ours, that remains almost entirely invisible. But it can be seen in the evidence in the gravitational impact on ours, the researchers say.

Such mirror world theories have been around since the 1990s – but they have not been suggested as a solution to this problem, before, scientists said.

“This might seem crazy at face value, but such mirror worlds have a large physics literature in a completely different context since they can help solve important problem in particle physics,” said Francis-Yan Cyr-Racine, assistant professor in the Department of Physics and Astronomy at The University of New Mexico, and one of the authors of the research.

“Our work allows us to link, for the first time, this large literature to an important problem in cosmology.”

A paper describing the findings, ‘Symmetry of Cosmological Observables, a Mirror World Dark Sector, and the Hubble Constant’, is published in the journal Physical Review Letters.

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