"The quanta of gravity, that is, are not in space; they are themselves space. The spin networks that describe the quantum structure of the gravitational field are not immersed in space, they do not inhabit a space. The location of single quanta of space is not defined with regard to something else, but only by the links, and the relation these express.
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Space is a spin network whose nodes represent its elementary grains, and whose links describe their proximity relations. Space-time is generated by processes in which these spin networks transform into one another, and these processes are described by sums over spin foams. A spin foam represents a history of a spin network, hence a granular spacetime where the nodes of the graph combine and separate. This microscopic swarming of quanta, which generates space and time, underlies the calm appearance of the macroscopic reality surrounding us. Every cubic centimeter of space, and every second that passes, is the result of this dancing foam of extremely small quanta.
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In the world described by quantum mechanics there is no reality except in the relations between physical systems. It isn’t things that enter into relations but, rather, relations that ground the notion of ‘thing’. The world of quantum mechanics is not a world of objects: it is a world of events. Things are built by the happening of elementary events: as the philosopher Nelson Goodman wrote in the 1950s, in a beautiful phrase, ‘An object is a monotonous process.’ A stone is a vibration of quanta that maintains its structure for a while, just as a marine wave maintains its identity for a while before melting again into the sea."
- Carlo Rovelli (1956 - )
