Our part of the universe is different from the whole universe

A research team led by Dr. Prabhakar Tiwari from the National
Astronomical Observatories of Chinese Academy of Sciences
(NAOC) has found that superhorizon modes could explain the
observed Hubble tension (https://phys.org/pdf562845717.pdf).
It is generally believed that the universe is isotropic and
homogeneous on large distance scales. This hypothesis forms
the basis of the standard Big Bang cosmology, called the
cosmological principle (CP). CP does not follow from the laws
of fundamental physics and has to be conjectured as an independent
hypothesis.  The principle appears to be observationally valid to
a good approximation. However, detailed
observations reveal small but significant deviations from isotropy.
The matter distribution is found to be higher in one direction
compared to the others.
Although a part of this can be attributed to our motion with respect
to the cosmic frame of rest, this
does not seem to be the whole story. Interestingly, there is another
anomalous observation. The observed Hubble constant, which is
a measure of the rate at which the universe is expanding, also
indicates that the local universe is special and not the same as the
universe elsewhere.
Essentially, its value extracted from nearby galaxies seems to
deviate from that measured globally. The latter would be the
expected mean value over the entire universe. This deviation is
called the Hubble tension and at present is one of the most pressing
problems in cosmology. It has been suggested that the observed
deviations from isotropy can be explained if we consider cosmic
perturbations or fluctuations with wavelengths larger than the size
of the horizon.
Horizon is the maximum distance light could have traveled since
the origin of the universe. These are called superhorizon modes. It
is assumed that for very large wavelengths, these modes are aligned
along the same direction. Hence these do not obey CP.
"Miraculously, these modes can explain the observed Hubble tension,"
said Dr. Prabhakar Tiwari. "The new finding connects the two most
crucial issues of modern cosmology. Furthermore, as the redshift
is a crucial observable in cosmology, its corrections due to
superhorizon modes would be of fundamental interest."

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