Cycles of Time: An Extraordinary New View of the Universe

by Roger Penrose

The structure of life on this planet would run rapidly down were it not for a powerful low-entropy source, upon which almost all life on Earth depends, namely the Sun.

what the Sun does for us is not simply to supply us with energy, but to provide this energy in a low-entropy form, so that we (via the green plants) can keep our entropy down, this coming about because the Sun is a hot spot in an otherwise dark sky.

In a certain sense, what Minkowski did was to take the ‘relativity’ out of special relativity theory, and to present us with an absolute picture of spatio-temporal activity.

The contents of the universe, at extremely early times, would have consisted of effectively massless particles.

it would appear that rest-mass is a necessary ingredient for the building of a clock, so if eventually there is little around which has any rest-mass, the capacity for making measurements of the passage of time would be lost (as is the capacity for making distance measurements, since distances also depend on time measurements;

The location referred to as a ‘singularity’ in classical space-time descriptions should really be thought of as where ‘quantum gravity takes over’.

there is no agreement whatsoever as to what might actually be going on in ‘space-time’ at the Planck scale.