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Expansion of the universe: what if we were in a giant bubble of different density?

A new study of the speed at which the universe is expanding seems to resolve, at least in part, the divergences that physicists and cosmologists have achieved by trying to measure it. The new study, published in Physics Letters B, does so without resorting to any “new physics”.

Currently there are two methods used to measure this speed: the first is based on the cosmic microwave background and the data provided in particular by the Planck space mission. According to this first method we obtain a value for the so-called “Hubble constant” of 67.4 (km/s)/Mpc. That is, the universe is expanding 67.4 km/s faster every 3.26 million light years.

The second method is based on supernovae that appear sporadically in distant galaxies. Measuring these strong light events gives a Hubble constant value of 74.
Lucas Lombriser, researcher at UNIGE’s Faculty of Science, says: “These two values have continued to become more precise for many years while remaining different from each other. It didn’t take much to trigger a scientific controversy and even raise the exciting hope that perhaps we were facing a ‘new physics'”.

According to Lombriser, perhaps these differences are due to the fact that in the end the universe is not as homogeneous as it has always been claimed. It has always been difficult to imagine, for example, fluctuations in the average density of matter calculated on volumes thousands of times larger than a galaxy.

This is precisely why Lombriser, in his new study, theorized the existence of a gigantic bubble, 250 million light years in diameter, in which our galaxy is also present and in which the density of matter is significantly lower than the density known for the entire universe.

Such a thing would have an impact on the calculation of Hubble’s constant because this same bubble would include the galaxies that are usually referred to when measuring distances.

So, by establishing that this huge bubble exists and establishing that the density of matter inside it can be 50% lower than that of the rest of the universe, we would obtain a value for the Hubble constant that would converge with the one obtained using the first method, that of the cosmic microwave background: “The probability that there is such a fluctuation on this scale ranges from 1 in 20 to 1 in 5, which means that this is not the imagination of a theorist. There are many regions like ours in the vast universe”.