Rethinking Time

(Geoffrey Edwards) #1

I came across the work of Carlo Rovelli recently and started to delve into the background behind his ideas in order to understand them better. That took me on a rather roundabout path - I ended up reading one of his books for the layperson about time (Reality is Not What It Seems - The Journey to Quantum Gravity) and a good chunk of his textbook on Loop Quantum Gravity (Quantum Gravity) - the latter not for the lay person - and I have been circulating around his most recent book, The Order of Time, but have not actually purchased it (I am trying to keep my book purchases down to a ‘reasonable’ level). There is also this particularly good lecture he gave on the subject (see below) - he is a very good pedagogue. I know this because I understood the main argument of the first chapter of his textbook and I’m pretty sure this was primarily the result of good writing.

I also reviewed the conversation held here on Synchronicity and Modeling Time. I was going to append these ideas to that conversation, but I think these are sufficiently general to justify a separate thread. This is also related to the Rosen paper on the relation between Taoism and Quantum Gravity, which I likewise “read” - well, not completely, I read the first half and the bit about string theory, which I also have some background in, but I skipped the details of his particular approach.

Here are my notes extracted from my readings and listenings of Rovelli’s ideas. It should be noted that Rovelli is one of the leading physicists in the world, having made major contributions to the development of Loop Quantum Gravity which is the primary focus of these documents. Loop Quantum Gravity is a different approach that that of string theory which Rosen uses as his reference in his paper.

  1. Rovelli makes the argument that within the emerging theories of Quantum Gravity, time as a variable has disappeared. He points out that this has been true for some time (since the late 1960s with the emergence of the Wheeler-DeWitt equation), but that, at first, the significance of this was not understood. In both Quantum Mechanics and General Relativity, time variables are present, but when the two are combined, the time variable disappears. In the emergent understanding of modern physics, time appears to be, uh, irrelevant, although there is still controversy around this idea (Rovelli addresses this in the clip above). The argument Rovelli makes is that the idea of time as an independent variable was first introduced by Newton as a convenient reference to understand how variables relate to each other, and that clocks embody the concept. However, clocks themselves are merely physical systems which vary themselves in a broad variety of ways and the new unification focuses on the relation between processes and systems rather than between processes and any external time variable.
  2. There is no well-defined present, no shared present - each entity (physical system) has its own (proper) time and these are never comparable (whether the comparison is made with clocks or bodies or something else). Rovelli makes an extended explanation of this in the talk I cited above which I find compelling but I’m not sure everyone will. He does make the point, however, that this is scientific consensus, that there are no real dissenters to this point of view.
  3. The so-called flow of time from future to past seems to be a product of the interactions between the brain as a memory system and the world - there are indications that outside this relationship, time does not flow. This dovetails with ideas such as Whitehead’s process philosophy. Rovelli is careful to point out that this is his own hypothesis, but that it is consistent with what is accepted knowledge among scientists. It is also a very interesting idea.
  4. Loop Quantum Gravity does away with space-time altogether : This is another major innovation of the theory (which is, to be clear, incomplete) - it is called a background free theory, but this is what it means. The argument goes like this : General Relativity developed the idea that space-time and gravitational fields are equivalent. This is widely understood to mean that matter and gravity is what causes space-time to curve, but it is actually more “tautological” than that - gravity fields are space-time, they don’t “cause” space-time. Put another way, without gravity, there would be no space-time - empty space-time is a misnomer, an impossibility. Loop Quantum Gravity does not presuppose a space-time substrate within which matter resides, rather, space-time is constructed from “quanta of space” which are inextricably associated with gravity (and hence matter). These quanta of space are of two types - volume quanta and area quanta. Volume quanta are associated with the nodes of a lattice structure (think spider web) while area quanta are associated with the links between the nodes (the web strands). Space-time (i.e the gravitational field) is constructed by superimposing many different lattices (called “spin networks”) in a way that parallels how electromagnetic fields are constructed by superimposing photons (light quanta). The theory requires the presence of loop integrals (hence its name) that are analogous to the Faraday loop integrals one uses to understand electromagnetic fields. However, within the loop integrals, both time and space are absent, even when considering so-called dynamic fields. The dynamics come from the relations between other physical parameters without evoking either space or time.
  5. Space-time is hence granular at the Planck scale (10**-33m - this is very, very small, however) - that is, it is a discrete lattice. In essence, space-time is “constructed” by gravity.
  6. In Loop Quantum Gravity, there are no ultraviolet catastrophes (resulting from 1/(x-y) when (x-y) becomes very small) because space-time is granular (1/(x-y) cannot become arbitrarily small) - this was a problem with earlier formulations of Quantum Gravity. If I understand this correctly, it also means the Big Bang probably didn’t involve a singularity in the mathematical sense.
  7. In Loop Quantum Gravity, physical amplitudes are expressed as “correlation probability amplitudes”, W(s), “associated with the outcome s in a measure of geometry” - in comparison to Quantum Mechanical probability amplitudes W(x,t,x’,t’) for a particle in space ; the spin network “s” folds in both “x” and “t”, so time is not well-defined, but the physics are well-defined. For a really, really good, lay person’s explanation of probability amplitudes, see Feynman’s amazing book, QED: The Strange Theory of Light and Matter - I reread this little book often because it has such a clear exposition of modern quantum ideas. Essentially, Quantum Field Theory replaces discussions of the movement of particles through space and time with the probabilities of the movements of particles, and these probabilities must take into account all possible movements between the start location and time and the end location and time. However, the theory allows one to eliminate most of the possible movements as contributing too little probability to the final calculations, and only a few trajectories need be included. Physicist Richard Feynman developed a very elegant diagrammatic method for figuring these things out, today called “Feynman Diagrams”.
  8. Transition probabilities W(s,s’) are provided by Feynman sums-over-paths and hence by modified Feynman Diagrams (see the QED reference I cited above) - these modified diagrams describe what are called “spinfoams” where links are labelled by areas and nodes by volumes. In spinfoams, the world-histories of links form faces, the world-histories of nodes form edges, and edges intersect at vertices, which correspond to the individual actions of the Hamiltonian. The Hamiltonian is an “action operator”, that is, a way of updating the spinfoams based on induced changes. The spinfoam is therefore the world-history of spin networks (i.e. of the lattices that make up space-time).
  9. The theory of Loop Quantum Gravity is still incomplete - although it provides an elegant portrait that reconciles General Relativity and Quantum Mechanics, it is only just beginning to yield predictions that could be tested and there are still many technical issues to be resolved. It is also only one approach among several. However, it appears that some of the lessons learned from the work done in Loop Quantum Gravity may apply to other approaches and hence may have more general applicability. In particular, the new ideas about time may be of particular importance.

I couldn’t possibly comment on Rosen’s paper in any kind of detail as I don’t understand the physics well enough to do so intelligently. What I can say, however, is that Rosen seems to be going for a different way to deal with the problem of reconciling Quantum Mechanics and General Relativity by focusing on the subject-object unification implicit in quantum mechanics and using that as the basis for integrating general relativity (although I don’t fully understand how). While this approach has obvious interest, it is a “maverick” approach - not an argument against it, but it means that fewer scientists will be looking to make progress in this area. I think it probably is a worthwhile avenue of exploration, but I think the way Loop Quantum Gravity deals with time also has major implications for our understanding of the world, and our “place” within it, to use a space-time metaphor.

I know most people’s eyes will glaze over when they read “probability correlation amplitudes” - the argument seems to get very “physicsy” at that point, but I do think these things are not so difficult to understand if they are presented in the right way and that understanding these things has bearing on the philosophical and, indeed, life practices we are investigating here (e.g. think of Philip K. Dick’s ideas about multiple parallel universes overlapping with humans, so that we do many things at once - see the Wierd Science podcast on this). The idea that time can be broken down into many distinct ideas (as Rovelli does in his presentation), and that many of these ideas have been revealed to be fictitious is exceedingly suggestive. The idea that there is no “shared present” is radical. That flow of time may be a feature of a cognitive system also. The idea that space-time may be granular has been around for a while, but it is not fully realized what this means - it means the world is not continuous. Not ever. And that geometry is not fundamental, either (sorry Aristotle!). Events are real - in Rovelli’s list, events are the only idea about time that survives intact.

Cosmos Café: Integrating Science, Art, and Time [6/5]
(john davis) #2

I appreciate that you refer to the Models of Time presentation from the Cafe. After watching Rovelli’s lecture I reviewed the Cafe conversation and sense that there are some odd resonances happening. As time is more fluid and our models of time quite unique it may be possible to create new relationships for a more collaborative time. I have a funny feeling we have been here before! Perhaps in another pluriverse?

(Geoffrey Edwards) #3

I agree, Johnny. In particular, I was struck by how the models of time developed by each participant were largely focused on memory and hence dovetails with the ideas about how flow of time may be a side effect of cognition. Also, the abandonment of other ideas about time may intersect with some of our explorations into Aurobindo’s ideas, among others. I do find that understanding how modern physics views these things can lead to new insights - physics frames the ideas in very precise ways which can be a boon…

(john davis) #4

I recently viewed this video from the Helix Center which in some ways compliments the Rovelli conversation. As we are in the midst of a transdiscipinary shift in our culture, I hope we laypersons can find ways of articulating our questions in more artful ways. I so appreciate your willingness, Geoffrey, to share your expertise! Perhaps we can start to imagine how we can develop a program on someone we both admire, Gregory Bateson? More maps and more territories to explore. Maybe we can do this on a future Cafe? I think this could be a lively conversation.

(Geoffrey Edwards) #5

I’d like to finish The Minor Gesture, but I think this might be a good follow-up conversation, although Whitehead would also be a possibility for that (maybe conversation #3?). What would be nice would be to find a “post-Batesonian” perspective which remains true to Bateson’s understandings of the world and yet which modernizes some aspects of his ideas which may need to be updated.

(john davis) #6

I love that idea, Geoffrey. And let’s have more Whitehead, too!

(Geoffrey Edwards) #7

I had seen this interview before, but I replayed it as it is still quite an enthralling exchange, even though they don’t actually seem to arrive at any kind of consensus! The exchange is essentially a kind of epistemological recapitulation of the main arguments concerning the relationships between the different branches of science, with a little place given to philosophy as well, but ultimately I think our discussions here go well beyond what is considered to be legitimate inquiry in this context.

(Geoffrey Edwards) #8

I’ve been taking a look at Nora Bateson’s book, Small Arcs of Larger Circles. Perhaps we could use that book as a modern anchor and then bring in Bateson the father (and Mary Catherine, the sister) as seems appropriate. It seems Nora also did a film about her father called An Ecology of Mind - I haven’t seen it, but if we can get ahold of this, it might also enrich the discussion.

(john davis) #9

Excellent idea. I love the Nora Bateson book.

(Geoffrey Edwards) #10

The film appears to be available for download (1,9 Gb) at vimeo :

(Ed Mahood) #11

Thank you immensely for this, dear sir. It is exceedingly helpful because it is understandable.

OK, OK … an eye or two will roll with the probability-correlation-amplitudes punch, but as you point out, no one has to climb a mountain to start getting a bit of a grasp on what’s being described. Not only is Feynman’s QED accessible to the informed layperson, his other texts are well worth the (relatively small amount of) time that must be invested to get a good strong feel for what he’s talking about. But, your notes also help keep the notions well grounded.

In particular, I was taken with your notes points 1-4. Much of what I here you saying is what I believe Gebser is pointing to in his own inimitable way. In particular points 2 and 3 are resonant of what I think he is trying to “describe” by his use of the term “achronon” (the one free of time, time-freedom), but also “atemporal”. Point 4 corresponds well with what I hear him saying when he talks about the “supersession of space and time”. (A while back we were looking for instances of Gebser’s “integral structure of consciousness” and the notions behind what Rovelli is telling us seem to be pointing in that direction as well.

And my eyes perked up when I read the the following remark:

As you note, our explorations of Sri Aurobindo may shed more light on some of the reality that is involved, but I believe that this is consonant with what I’ve been uncovering in my own kabbalistic searches and it is certainly something that Stan Tenen has been pointing toward in his Meru work. The ways of describing it are, unsurprisingly, far removed from the (lovely) precision of physics, but I’m convinced they’re all describing the same phenomenon (in the truest sense of that word).

There’s so much more to come, that’s for sure, but I’m really glad you opened up this thread (or can of worms, or … we still love our perspectives). It’s another breath of fresh air in this well-ventilated, sometimes drafty, but never dull little Cosmos of ours. Thanks again.