Sunday, September 30, 2007

The timeless universe of Julian Barbour

Bookshops and public libraries are powerful attractors in my life: hardly a day passes by without a fleeting visit to these cornucopias of information and dreams. Friday was no exception: I was at Borders loafing about, and I ended up in the Physics section. My trained eye spotted an interesting title within seconds: The End of Time, by Julian Barbour. I had vaguely heard of the fellow before, through some readings on the interpretation of Quantum Mechanics and on Quantum Gravity. Barbour, I seemed to recall, does not believe in Time. He in not alone, mind you: Melissus, Nagarjuna, Plotinus, McTaggart, and numerous others were also vocal disbelievers. But there is a difference: Dr. Barbour is a theoretical physicist, and physicists (with some notable exception, such as the Loop Quantum Gravity folks) assume space-time as the background where physics happens.

What kind of universe does Barbour envision? His world, which he cleverly christened Platonia, is a world of Nows (by the way, Platonia is also the name of his web site). Each Now is a possible configuration of the entire universe, complete in itself, and static (think of a single photo snapshot). How are Nows concatenated to one another? They aren't. Quite simply, there is notion of similarity describing how far apart two Nows (i.e. two universe's configurations) are. Some photos look similar, others do not. By arranging a list of contiguous Nows, one gets a factitious timeline, a bit like arranging photo grams one gets a movie (notice that you could arrange the deck in more than one manner).

All right, but how come we do experience the flow of time? Here is a clever move by Barbour (as matter of fact, a few others, like Emanuele Severino in Destino della Necessita', had a similar argument, albeit from a different angle). It is called time capsule. A time capsule is a special type of Now, containing some data that appear like traces of other Nows, or fragments of recorded history. Thus, in his view, there is no flow whatsoever, only we (you and I) are inside the same time capsule that suggests the existence of past & future.

Crazy? Not really. After all, what do we know about past and future? Only what our memory and our imagination tell us. No more, no less.

Summing up, Julian Barbour brings us back to the number 3 instead of the Minkowskian 3+1 =4. Space is real, time is not (*). Instead of increasing dimensions, like String theorists do, he reduces them by one. He kills Time.

Allow me to add a coda here, before quitting. I like all of the above, so much so that in my book on Time a section will be dedicated to charting the charming land of Platonia. However, I have a gut feeling that this is a great start, but not the entire story. Perhaps space too is not that real after all. Perhaps we live in a space-time capsule, and the entire vast expanse of this universe is no more than a mad game of mirrors within mirrors. Perhaps the basic ingredients of reality are not Nows, but a multiplicity of Here-And-Nows, hic et nunc. Perhaps....

(*) A note for the math-savvy: I hope my sentence above hasn't mislead anyone into believing that Barbour's universe is R^3. It is not; his kosmos is the so-called configuration space, whose dimension depends on how many entities there are. For instance, if there were only 3 particles, our physical universe would be the manifold whose points are the different configurations of a three-body system. As you can see, it is a pretty roomy house...

PS After coming back home, I chased Barbour all over the net. He appears in a riveting 1/2 hour video, which I truly liked. It is called Killing Time: enjoy.

19 comments:

andrew said...

If you imagine that there's a universe out there for every possible configuration of every possible particle, then our histories, presents, and futures would all be represented in that array, and then some.

There's also a Planck unit of time (5.39121 × 10^−44 seconds), so the universe could be said to have a "frame rate" and his "snapshots" would indeed exist (and, incidentally, Zeno's arrow paradox would have a possible solution).

But I'm curious how he strings together these snapshots in a model that seems to necessarily obliterate cause and effect. At this "moment" (I'm forced to use the term loosely as there is an astronomical number of snapshots between even the emergence of two individual memories) I experience that my recollections are limited to events leading up to my present state. But without cause and effect a configuration of particles in which my brain contains a memory of tomorrow, next year, or the 84th century is equally as possible as any other. Isn't it odd that in this moment I don't have a single memory that continuity says I shouldn't have?

Extrapolated further, it's difficult to see how consciousness could even exist in the first place.

I'm sure he has an answer to this (you mentioned a time capsule). If I don't get to read his book soon, at least summarize the explanation for me when you do.

Polymathicus said...

Andrew, thanks for your interesting comment!

As for Planck's unit of time, I suspect it plays no direct role in Barbour's scheme, because he denies time altogether. To him, if I understand him at all, change is the basic notion, and time is a derived (and illusory) one. Here change means that different Nows are somehow comparable, shape-wise.

You question is good, but I venture a possible explanation: there maybe other Andrews out there in Platonia who do not experience continuity. The reason why YOU do experience continuity NOW is because you happen to be part of a "lucky" Now (or unlucky, depending on your taste) where "memory" arises (the infamous time capsules). The Nows are not stringed together at all.
Quite simply, there are many paths in Platonia, a few of them looking like time lines.

At all events, I may be way off: I have only skimmed Barbour's book. I''ll probably post a follow-up when I''ll know more.

il sindaco said...

Polymathicus, you are a really bookworm! Don't give up the fight!

Dirk Roorda said...

Your remark that space might not be as real as we think, triggers a continuing thought I have: space, time, matter, fields, they all are not hardware but software.The laws they obey are software that do not say anything about their ultimate reality. Somewhere there is a machine, or computer, that instantiates our universe and runs it.
Why do I think this? It is an extrapolation of the experience that everything that was once rock solid has appeared to be an illusion, created by a reality at a more abstract level.

Polymathicus said...

Hi Dirk, thanks for you comment.

I share your feelings, and, as it turns out, we are not alone. One recent shift in the foundational studies of physics is the central role that information plays (see for instance the work of Carlo Rovelli or David Deutsch).

Information, not energy, matter, fields, etc. is the "ultimate stuff of this world".

NOTE: If the foregoing were true,instead of thinking of the Eternal as the Grand Architect, as Plato suggested long ago, we may perhaps update the old label to Grand Software Architect.

W7MJR said...

Perhaps Planck length is a more fundamental unit in Platonia, Plank time being an artifact? One Now cannot differ from the next by any less than a Planck length leading to a discrete but infinite(?) number of configurations starting at the vertex ("alpha").

And perhaps the time capsule we seem to share at this moment is yet another manifestation of the anthropic principle (or paradox if you prefer). It is a trajectory (or bundle of trajectories) resulting in what we call evolution and consciousness---in essence, a mechanism to carry an (imperfect) memory of past nows. Cause and effect, as we see it, is a consequence.

I read The End of Time last year (not without some effort) after reaching a similar impression about time. I would like to see more mathematical treatment on the subject. I'm not sure how Barbour is tackling the problem, but one based on information theory would be quite interesting and pertinent. I wonder how it fairs with respect to the holographic principle?

I struggle with whether or not Platonia is a cop out, but who am I to say? Is it anymore outlandish than relativistic or Newtonian space-time? Barbour's ideas do seem consistent at a basic level with relativity and quantum physics (hence some interest within the study of quantum gravity).

For now, Platonia seems like metaphysics, but maybe it will lead to testable experiments in causality or something. Or perhaps we'll be "chasing out tails" for the rest of our history trying to make sense of it all.

Anonymous said...

Please all are wrong on time issue.
Time is man made and based on the fact it takes apprx 24hrs for 1 complete revolution.What about if the earth did not rotate? apart from the gravity problem how would we measure time and conduct experiments. Thats where we are going wrong.. we assume as humans that time is the same everywhere.. it is not.
Example.. two planets next to each other one turns one is static what is the speed of light on the static planet ? how can they measure it, when they dont have seconds to deal with?. This is my point man has created a means to measure his own time. This is not a universal constant.
The universe is Timeless only in the fact that it is impossible to say the universe is 13 billion earth years old.. reason is simply you cannot determine the age by measuring the oldest light from the furthest star. What about all the stars that have died before the earth came into existance. Its like an alien coming to this planet finding the oldest person alive and stating that the earth is 97 earth years old. No the universe is timeless.. it could be several times the age we think it is.. we need to look in the right place to find the age, and we are not doing it. You dont look at the residents to establish the age of the enviroment.
Time is a name given by man to the recording of events and should not be used to calculate experiments outside earth.
example.. 2 people each on different planets . Events will be viewed differently by each person so how can time be universal. It must be Timeless.

amrit said...

yes, universe is timeless

see

http://atemporaluniverse.blogspot.com/2008/07/atemporal-universe-enlarged-article.html

amrit said...

yes universe is timeless, time is run of clocks

yours amrit

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Anonymous said...

Think of it this way...

Time as being represented by a fence on a hilly landscape. As we drive by in our car we experience the fence going up and down, when in reality the fence is just there, not doing anything.

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Collin said...

Time is not man-made. On the contrary, man is time-made. People, as well as all life, are the result of a sequence of species progressing through evolution.

It's often said we can't assume time exists because we can't observe it. But if the irreversible processes we see all around us aren't enough evidence, there is also dark matter, which seems to pass through ordinary matter without interacting. All interactions between material substances involve an exchange of torque. A manifestation of the passage of time would be a perfect gradient, incapable of carrying torque, so dark matter fits the bill perfectly.

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