Saturday, August 05, 2017

Rovelli 4: Time Does Not Exist

This is my fourth post on Carlo Rovelli's new book, Reality Is Not What It SeemsThe first three posts were:
1. Chapter 7 is getting closer to theology. I have always been sympathetic to the medieval view that God is outside time. God immanent goes through time with us. God transcendent sees all of time in an eternal now. This construct provides a helpful way around the "Does omniscience imply determinism" debate.

I had the thought while reading this chapter, "God is quantumly entangled with the entirety of his creation." Quantum entanglement is the sense that when two paired particles go their separate way, their states remain connected. In Quantum Gravity, Smolin suggests that this connection can apply to particles inside and outside a black hole.

So I was playfully musing of God knowing every quanta of the universe from its connectness with him at the moment of creation. It's not a suggestion or completely satisfying. After all, this musing does not clearly relate to the future. It would only suggest an exhaustive knowledge of the present and the past.

2. One of the implications of general relativity is that "every object has its own time, running at a pace determined by the local gravitational field" (178). If I am traveling close to the speed of light and you are not, I will age much slower than you will. If you live on a planet with a much greater gravitational field than earth, you will age more slowly than me back on earth. In fact, someone who spends their whole life in Tibet will be a fraction of a second older than me, living my whole life at the Dead Sea, even if we were born at the same exact moment somewhere.

"Time" does not pass at the same rate everywhere.

One thing Rovelli has already mentioned is that, in some of the fundamental quantum gravity equations (e.g., Wheeler-DeWitt), there is no time variable. How is that possible? It gets back to a principle he has stated in his chapter on quantum mechanics. Reality is relational.

Quanta of gravity do not change "in time." Time is simply a counting of the interactions of quanta of gravity. The world is not something that changes "in time," for time does not exist. There is only process after process. "There is no longer space that 'contains' the world, and no longer time 'during the course of which' events occur" (183).

I am hoping I will have a better sense of what I am saying by the end of the book. :-)

3. So an event does not take place in spacetime. Rather, spacetime is part of the event. The event is a process with an initial and final state. And there is a boundary for the event.

"If quantum space has the structure of a spin network, what structure will spacetime have?" (186). Spacetime is the history of a spin network. This history of a spin network is apparently what Loop Quantum Gravity (LQG) physicists call "spinfoam."

I don't really like this word. The idea seems to be that the area of the node foams up to the beach of the line between nodes. And that beach is a spin line. I'm sure I'm massacring it.

"To compute the probability of a process, one must sum up over all the possible spinfoams within the box that have the same boundary in the process. The boundary of a spinfoam is a spin network and the matter on it" (187). This is what Feynman did to calculate the probability of a particle's trajectory.

4. So to sum up the chapter. "Space is a spin network whose nodes represent its elementary grains [of gravity], and whose links describe their proximity relations" (192). What we call spacetime is the transformation of these spin networks into and apart from one another, and the history of these spin networks is called "spinfoam."

So all reality is variations on quantum fields, fields one on top of the other. Another name for these are "covariant" quantum fields. These are, in Rovelli's mind, the fundamental reality that connects spacetime with quantum fields.

More to come...

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