The Earth, Solar System, as well as the entire Milky Way and a few thousand galaxies in our vicinity move in a large ‘bubble’ that is about 250 million light-years in diameter, while the overall density of matter is half as massive as for the rest of the Universe.
This is an assumption delivered by a theoretical physicist from the University of Geneva (UNIGE) to address a conundrum that has been dividing the scientific community for more than ten years now, namely the accurate speed of the expanding of the Universe.
Sporadic Supernovae or Cosmic Microwave Background?
Until now, at least two separate calculation techniques have resulted in two different values that vary by about 10 percent with a deviation that is numerically irreconcilable. This new concept, which has been published in the journal Physics Letter B, gets rid of the divergence without using any ‘new physics.’
The Universe has been expanding since the Big Bang explosion, which took place about 13.8 billion years ago, according to the Belgian canon and physicist Georges Lemaître. It was later demonstrated by the American astronomer Edwin Hubble.
Further research helped the Hubble-Lemaître law, as well as the Hubble constant (H0), which refers to the Universe’s rate of expansion, to rise, with the best H0, estimates currently being around 70 (km/s)/Mpc.
The issue is that there are two opposing methods of calculation. The first is founded on the cosmic microwave background, and the second is based on supernovae that appear sporadically in faraway galaxies. The first calculation resulted in a value of 67.4 H0 using Einstein‘s theory of general relativity, and the second has made it possible for researchers to determine a value of 74 for H0. The results are quite different, as can be seen.
A Massive ‘Bubble’
Lucas Lombriser, a professor in the Theoretical Physics Department in UNIGE’s Faculty of Sciences, explained: “These two values carried on becoming more precise for many years while remaining different from each other. It didn’t take much to spark a scientific controversy and even to arouse the exciting hope that we were perhaps dealing with a ‘new physics.'”
To close this gap, professor Lombrisier considered the idea that the Universe is not as uniform as claimed, a theory that may seem clear on relatively low scales. The fact that that matter is divided differently inside a galaxy than outside one is definitely accurate, but it is more challenging, though, to image variations in the average density of matter measured on volumes a lot larger than a galaxy.
“If we were in a kind of gigantic ‘bubble,’ added professor Lombriser, “where the density of matter was significantly lower than the known density for the entire universe, it would have consequences on the distances of supernovae and, ultimately, on determining H0.”
“The probability that there is such a fluctuation on this scale is 1 in 20 to 1 in 5, which means that it is not a theoretician’s fantasy. There are a lot of regions like ours in the vast Universe,” he explained.