PRIDE CHEKERAis a metric in which coordinates are stretched apart, and what
caused this was unknown.
The universe must have started from a bang
In 1927, German priest named Georges Lemaitre discovered a
solution to EFE, basing on Friedman expanding metric and the
time reversal symmetry of the metric tensor.
In that solution, he found that if there is a spatially expanding
metric, applying time reversal symmetry of general relativity
there must exist a contracting model of the universe, in which
coordinates fall into each other finally merging into an infinitely
dense region, in which space-time is undefined, and from which
the cosmos was given birth, the so-called cosmic singularity.
According to Lemaitre that moment of existence of the universe
from such an infinitesimally small point, he called a 'primeval
atom' is well known as the Big Bang.
Was it really a bang?