The earth, the solar system, the entire Milky Way and the few thousand galaxies closest to us move in a vast "bubble" that has a diameter of 250 million light years, where the average density of matter is half than that of the rest of the universe.
This is the hypothesis put forward by a theoretical physicist from the University of Geneva (UNIGE) to solve an enigma that has divided the scientific community for a decade. If the universe is expanding (and it looks like it is at the moment) how fast is it expanding?
Until now, at least two independent calculation methods have come to two different values of about 10% with a statistically irreconcilable deviation.
This new approach, published in the journal Physics Letters B, cancels this divergence without resorting to any "new physics".
The expanding universe
The universe has been expanding since the Big Bang occurred 13,8 billion years ago. It is a theory first formulated by the Belgian physicist and canon Georges Lemaître (1894-1966), and first demonstrated by Edwin Hubble (1889-1953).
In 1929 the American astronomer discovered that every galaxy is moving away from us and that more distant galaxies are moving faster. This suggests that there was a time in the past when all galaxies were in the same spot, a time that may correspond to the Big Bang.
This research gave rise to the Hubble-Lemaître law, including the Hubble constant (H0), which indicates the expansion rate of the universe. The "problem" is that to calculate the expansion of the universe there are two conflicting methods of calculation.
Two methods, two different results
The first is based on the cosmic microwave background: this is the microwave radiation that reaches us from everywhere, emitted when the universe has become cold enough to allow light to circulate freely (about 370.000 years after the Big Bang). Using the precise data provided by the Planck space mission and assuming that the universe is homogeneous and isotropic, we obtain a value of 67,4 for H0 using Einstein's theory of general relativity to walk through the scenario.
The second calculation method is based on supernovae that appear sporadically in distant galaxies. These very bright events provide the observer with very precise distances, an approach that allowed to determine a value for H0 of 74.
Lucas Lombriser, professor at the Department of Theoretical Physics of the UNIGE Faculty of Sciences, explains: “These two values have continued to become more accurate for many years while remaining different from each other. It didn't take long to spark a scientific controversy and even to raise the exciting hope that perhaps we were facing a "new physics". "
To narrow the gap, Professor Lombriser formulated the hypothesis that the universe is not as homogeneous as claimed, a hypothesis that may seem obvious on relatively modest scales.
Next another: after the idea that you are part of an immense holographic projection and what you do part of an immense quantum computer, here's another study. The nice thing is that everyone has their own dignity and a statistical possibility of existing.
There is no doubt that matter is distributed differently within a galaxy than it is outside. It is more difficult, however, to imagine fluctuations in the average density of matter calculated over volumes thousands of times larger than a galaxy, also considered the intimate connection between them.
The "Hubble bubble"
"If we were in some sort of gigantic bubble", continues the professor Lombriser, where the density of matter is significantly less than the known density for the entire universe, “There would be consequences on the distances of supernovae and, ultimately, on the determination of H0”.
This "Hubble bubble" should be large enough to include the galaxy that serves as a reference for measuring distances. By establishing a diameter of 250 million light years for this bubble, the physicist calculated that if the density of the matter inside were 50% lower than the rest of the universe, a new value would be obtained for the Hubble constant, which would therefore agree with that obtained using the cosmic microwave background.
"The likelihood of such a fluctuation on this scale is 1 in 20 to 1 in 5," says Professor Lombriser, which means it is not a theorist's fantasy. “There are many regions like ours in the vast universe. "
In short, I would like to say that it is not a bubble. Not soap, I mean.
References: Lucas Lombriser. Coherence of the local Hubble constant with the cosmic microwave background. Physics Letters B, 2020; 803: 135303 DOI: 10.1016 / j.physletb.2020.135303