The following is a link to a moderated 40-minute discussion among
Roger Penrose, Sean Carroll and Laura Mersini-Haughton, about what
"universe" and "beginning of the universe" actually mean.
All agree the universe is expanding, which necessarily means that in
the past, the universe was smaller and hotter than it is now. Applying
only General Relativity, this reasoning necessarily leads to a
singularity of infinite density and temperature. This violates
principles of Quantum Mechanics and contradicts observed evidence,
like the average background temperature of the CMB.
In part to resolve these issues, it's hypothesized there was a prior
period of exponential Inflation, of at least 60 doublings, lasting
about 10^-36 seconds, where spacetime ballooned from subatomic scales
to about the size of a grain of sand. As spacetime Inflated, it also
cooled, which ended Inflation and precipitated the fundamental forces.
Cosmic Inflation is the bang of classic Big Bang.
Roger Penrose doesn't like Cosmic Inflation. He argues that the
conditions required for it are too unlikely, on a scale of 1 chance in
10^124 times for it to happen. Instead, Penrose proposes a cyclic
cosmos, separated by eons, where the end of one universe spawns the
beginning of another.
Setting aside for the moment the veracity of Penrose's calculated
probability, his hypothesis requires a consideration of what is the
most likely outcome of the end of our universe, sometime around 10^100
years. All stars will have long since winked out. All black holes
will have long since evaporated from Hawking radiation. All particles
of matter will have long since decomposed into energy. All energy
will have long since distributed itself uniformly throughout the
universe. This is the classic Heat Death of the universe.
I freely confess I had previously argued that such conditions don't
allow anything to happen, nevermind spawn a whole new universe.
However, as I listened to Penrose in the cited video, it occurred to
me that the conditions at the end of our universe are similar to the
conditions of the false vacuum which are presumed to have borne Cosmic
Inflation. In both cases, the presumption is of a random quantum
fluctuation precipitating a subatomic energy state lower than the
background, which then exponentially Inflates into equal amounts of
positive attracting matter, and negative repulsive energy. So since I
allow the possibility of Cosmic Inflation, then to be
epistemologically consistent, I must also allow the possibility of
You're entitled to your own opinions.
You're not entitled to your own facts.