Is there really an invisible “mirror world” where particles interact with our world only through gravity, but are otherwise impossible to observe?
It’s a crazy-looking theory put forward by researchers looking for a solution to explain why the universe is expanding faster than it should.
Here’s what you need to know about “Hubble Tension” and why such bizarre theories are being offered by astrophysicists to help make more sense of the universe.
What is the Hubble constant?
It is the most wonderful number in nature. Describing the rate of expansion of the universe, it effectively contains within it where the universe came from and what will become of it in the future.
Arguably, the search for the expansion rate of the universe was the great holy grail of 20th century cosmology – and it continues to lead to incredible new theories and scientific discoveries.
The Hubble constant is named after an American astronomer Edwin P. Hubblewho not only discovered galaxies outside our own, but also observed in the 1920s (with Georges Lemaitre) that these galaxies are moving away from Earth, and the further away a galaxy is, the faster it appears to be moving away from us. Essentially, Hubble’s constant is the rate at which this happens – a calculation that also gives us the exact age of the universe.
In practice, the Hubble constant is not a constant, with different ways of measuring it leading to different answers. It is also known from change over time, so maybe should be called Hubble’s parameter.
How the Hubble Constant is Measured
To determine the rate of expansion of the universe, one must select anchors of light in the night sky, such as stars, galaxies and globular clusters. This is known as the cosmic distance scale. Astronomers start with nearby objects and then move further out into the universe. Local measurements tend to result in calculations of a larger Hubble constant – and therefore faster moving and therefore a younger universe: 73-74 kilometers per second per megaparsec.
However, when distant objects are measured, such as the cosmic microwave background (the residual radiation from the Big Bang and strong evidence of it) was made by the European Space Agency Planck’s Satellite— the Hubble constant is smaller, which means a slower and therefore older universe: 67-68 (more or less 0.5) kilometers per second per megaparsec.
Why the disconnect between the expansion rates of the local universe and the early universe?
The “Hubble tension”
The discrepancies between estimates of the rate of expansion of the universe – and therefore of its age – are called the “Hubble tension”. It’s so statistically significant that it suggests astronomers may need a new interpretation of the fundamental properties of the universe. A new cosmological model, even?
No, says a new theory, which reveals a previously unnoticed mathematical property of cosmological patterns – scale symmetry – that could allow for a faster rate of expansion. But the full explanation gets pretty weird.
The “mirror world” theory
The new research published in the Physical examination letters by a team of astrophysicists from the University of New Mexico and the University of California, Davis, suggests an unseen dark sector of the “mirror world” of new particles that are all copies of known particles that exist alongside ours and interact with our world only through gravity.
“In practice, this scale symmetry could only be achieved by including a mirror world in the model, a parallel universe with new particles that are all copies of known particles,” 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 new paper. “The idea of the Mirror World first emerged in the 1990s, but was not previously recognized as a potential solution to the ongoing Hubble problem.”
This “mirror world” could explain the phenomenon of black matteror be an exotic form of it, it could be a way to resolve the Hubble tension.
It’s an extraordinary theory that lacks extraordinary evidence – and any mention of a parallel universe should invite extreme caution– but it’s still interesting. A variant of the theory has been published in 2018 with scientists claiming that an “anti-universe” extends through time, a mirror image of our own, which helps explain dark matter.
What is “dark matter”?
Dark matter is invisible, emitting neither light nor energy, so it is undetectable. It is therefore also hypothetical, although it is nevertheless believed to represent about 85% of the matter in the universe. This is one of the great discoveries that has been a by-product of researching the expansion rate of the universe. The same goes for “dark energy,” an unknown repulsive force that seems to be accelerating the expansion of the universe.
“It could be more than just collisionless dark matter and dark energy– two different and quite indescribable things – but many components of the dark sector, just as complicated as the light sector that we have studied so well in laboratories on Earth,” said Lloyd Knox of the Department of Physics and Astronomy at the ‘UC Davis, and a co-author of the new article.
“Mirror worlds” come from particle physics
Yes, it sounds crazy at first glance, said Cyr-Racine. “But these mirror worlds have a vast physical literature in a completely different context, because they can help solve an important problem in particle physics,” he said. “Our work allows us to connect, for the first time, this vast literature to an important problem in cosmology.”
Indeed, they propose a modification of the current cosmological model to explain discrepancies in measurements of the Hubble constant which, crucially, must involve an exotic form of dark matter.
The new theory isn’t perfect, incorrectly predicting the amount of deuterium and helium in the early universe, but it’s a smaller problem for scientists to solve than “Hubble stress,” claims- your.
What happens next?
In terms of cosmic mile markers, Cepheid variable stars — stars that brighten and darken in predictable ways — are the gold standard for local measurements. To calculate much larger distances, astronomers use explosive stars called type Ia supernovae.
Mid-2020s NASA to launch the Nancy Grace Roman space telescope, which will explore the value of the Hubble Constant through cosmic time by collecting more data on new Type Ia supernovae, as well as Cepheid variables and red supergiant stars. It is hoped that the data will enable astronomers to fundamentally improve distance measurements to near and distant galaxies.
I wish you clear skies and big eyes.
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