Carlo Rovelli quotes
The new coherent picture is not yet available. With all their immense empirical success, G(eneral)R(elativity) and Q(uantum)M(echanics) have left us with an understanding of the physical world which is unclear and badly fragmented. At the foundations of physics there is today confusion and incoherence.
Carlo Rovelli
But it isn't absence that causes sorrow. It is affection and love. Without affection, without love, such absences would cause us no pain. For this reason, even the pain caused by absence is, in the end, something good and even beautiful, because it feeds on that which gives meaning to life.
Carlo Rovelli
A handful of types of elementary particles, which vibrate and fluctuate constantly between existence and non-existence and swarm in space even when it seems that there is nothing there, combine together to infinity like the letters of a cosmic alphabet to tell the immense history of galaxies, of the innumerable stars, of sunlight, of mountains, woods and fields of grain, of the smiling faces of the young at parties, and of the night sky studded with stars.
Carlo Rovelli
The notion of time familiar to us may... be reconstructed in special physical situations, or within an approximation, as... the "surface of a liquid" disappears ...[at] the atomic level, or "temperature" ...makes sense only in certain physical situations and when there are enough degrees of freedom.
Carlo Rovelli
While non-relativistic time is the observable quantity measured (or approximated) by physical clocks, in general relativity clocks measure s along their worldline, not t. The relativistic... t is a freely chosen label with no direct physical interpretation. ...The physical content of a solution of Einstein's equations is not in its dependence on t, but ...in what remains once the dependence on t (and x) has been factored away.
Carlo Rovelli
The way evolution is treated in general relativity, is... subtle... Change is not described as evolution of physical variables as a function of a preferred independent observable time variable. Instead, it is described in terms of a functional relation among equal footing variables... as... (T1,T2)... In general relativity, there isn't a preferred and observable quantity that plays the role of independent parameter of the evolution... General relativity describes the relative evolution of observable quantities, not the evolution of quantities as functions of a preferred one. ...[w]ith general relativity we have understood that the Newtonian "big clock" ticking away the "true universal time" is not there.
Carlo Rovelli
The thermal time hypothesis. In nature, there is no preferred physical time variable t. There are no equilibrium states ρ0 preferred a priori. Rather, all variables are equivalent; we can find the system in an arbitrary state ρ; if the system is in a state ρ, then a preferred variable is singled out by the state of the system. This variable is what we call time.
Carlo Rovelli
