Earth and the rest of the Milky Way could be floating in a billion-light-year-wide cosmic void, according to new research.
By looking at the echoes left by the ‘soundwaves' of the Big Bang, a team of astronomers discovered that our corner of the Universe could be far emptier than we first thought.
If true, the theory could answer one of the biggest problems in cosmology, known as the Hubble Tension – the fact that how fast our Universe is expanding changes depending on how you measure it.
Astronomers have long battled with this issue. When they measure the expansion rate by looking at the distant Universe, it’s markedly slower than the value they get from examining our local corner of the cosmos.
“A potential solution to this inconsistency is that our Galaxy is close to the centre of a large, local void,” said Dr Indranil Banik, from the University of Portsmouth, who shared the findings at the National Astronomy Meeting in Durham.
This is because the regions around the void would have a higher density of galaxies, and their gravitational pull would slowly coax galaxies inside the void to the edge, slowly emptying the region over time.
“As the void is emptying out, the velocity of objects away from us would be larger than if the void were not there,” said Banik. In other words, it would make the local Universe appear to be expanding faster than it actually is.
To be responsible for the Hubble Tension, the void would need to be around one billion light-years wide, with a galaxy density 20 per cent lower than the Universe’s average.
Life in the void
The idea that we might be living in a void has been around for a while but determining whether it’s true or not has been difficult.
For one, it’s very hard to tell the shape of something from within – imagine trying to work out the shape of a house when you’re stuck in a room inside it.
Our current understanding of cosmology also suggests the Universe should be uniform over large scales, so shouldn’t have enormous holes lying around the place.
Banik’s team, however, were able to find evidence of a local void by looking at baryon acoustic oscillations (BAOs). These are the fluctuations caused by the pressure waves created during the Big Bang that were frozen in time early in the Universe’s history.
Over billions of years, these oscillations have grown, shaping the distribution of galaxies in the Universe around them. If the Galaxy were in the middle of a void, it would distort the pattern of BAOs near to us.
The study looked at measurements taken over the last 20 years, and found they all supported the theory that we truly are living in a void.
The true test will come from when people investigate how living in a void might affect other aspects of the Universe around us, but it could be that our corner of the Universe is a lot lonelier than we first thought.
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