John Barrow is a British cosmologist, mathematician and science writer who wrote New Theories of Everything.
Quotes by John Barrow in Time One
In more conventional quantum mechanical terms, we would say that the Universe is the result of a quantum mechanical tunneling process, where it must be interpreted as having tunnelled from nothing at all.
If the expansion did have a beginning then we are faced with further questions: is this ‘beginning’ merely the start of the expansion of the Universe that we see today or is it the Beginning, in every sense, of the entire physical Universe?
The search then began for a natural process … which would insure that if the universe began with, say, nine space dimensions all expanding equally, six of those dimensions would remain trapped …. How this trapping might occur is still an unsolved problem.
Whereas most physicists regard the second law of thermodynamics as a reflection of the improbability of certain types of initial conditions, there are others who regard it as a far more fundamental idea that is prior to the laws of nature themselves.
There is one qualitative aspect of reality that sticks out from all others in both profundity and mystery. It is the consistent success of mathematics as a description of the workings of reality and the ability of the human mind to discover and invent mathematical truths.
As we try to reconstruct the past history of these cosmologies, we encounter a striking feature. If matter and radiation continue to behave as they do today, and Einstein’s theory continues to hold, then there will be a past time when the expansion must have encountered a state of infinite density and temperature.
One of the most puzzling properties of our universe is that it is now expanding at a rate very close to the critical divide separating the ever-expanding universes from the recollapsing ones. It is a puzzle because as the universe expands it tends to deviate steadily from the critical divide because of the attractive force of gravity. In order that we be as close to the divide as is observed today, the universe must have begun expanding extraordinarily close to the divide originally.
The conventional Big Bang model held to a picture of the Universe in which it expanded from some initial state at a finite time in the past. This [conventional] expansion is forever decelerating after the start because of the retarding pull of gravity.