Julian Barbour’s Time Capsules

[pood]

Someone else here (I believe it was Swammerdami) mentioned, in some context, Julian Barbour’s time capsules. I read his book The End of Time years ago, but no longer have the book. I still don’t quite feel I have grasped Barbour’s position. I understand the Minkowski block universe position that all moments in time exist in the same way all locations in space exist, and what we call “now” is an indexical.

Barbour denies that there is any time dimension at all, and claims all that exists are “nows” or “time capsules” in configuration space. We infer, falsely it would seem on his model, that there was a past, because our particular time capsules encode “records” of it, but if the past does not actually exist, it seems those “records” would have to be illusory, since there was no past according to Barbour’s metaphysics!

OTOH he speaks of “mutually consistent records,” so maybe he means all NOWS exist, including what we call “past” NOWS, in configuration space, so what we call the past definitely “happens” in these other Nows relative to us. But if that is what he means, how would that be any substantively different from the Minkowski block world?

In any event, Barbour also argues that the universe is completely static, and motion and change are an illusion, and it seems if that is right it would put an end to determinism and causality as well, rendering both as illusory. But then again many have said the same thing about the block universe.

Does anyone know enough about this to untangle my confuzzlement?

I put this in Natural Science because Barbour is a physicist, though his ideas strike me as mainly metaphysical. But then again, I don’t recognize a clear distinction between science and metaphysics, so there is that.

Plus, the man has a web site and an email, so maybe, if a discussion here ensues, I will simply invite him to join us.

 

[Swammerdami]

It was many years ago that I read that book by Barbour. I didn't understand it very well then, and my ignorance has only grown since. IIUC, Barbour provides his insights into the  Problem of time. But even understanding that Wiki page is above my paygrade. Its first paragraph is discouraging:

This article needs attention from an expert in physics. The specific problem is: this article has some interesting ideas in it, but some of it is wrong, and a lot of it reads like an attempt by someone without deep expertise to summarize half-understood stuff that they've read. WikiProject Physics may be able to help recruit an expert. (June 2015)

Nine years later and "WikiProject Physics" still hasn't recruited an expert?

Both that Wiki page and Barbour refer to the  Wheeler–DeWitt equation.

The End of Time book keeps things simple by supposing the universe has only three particles. Recently he has focused on the Arrow of Time, and he has a small 3-particle diagram to summarize his views on that. Lots of Google hits for Barbour, but I couldn't easily find that diagram. But here is the abstract to a paper:

Identification of a gravitational arrow of time
Julian Barbour, Tim Koslowski, Flavio Mercati

It is widely believed that special initial conditions must be imposed on any time-symmetric law if its solutions are to exhibit behavior of any kind that defines an `arrow of time'. We show that this is not so. The simplest non-trivial time-symmetric law that can be used to model a dynamically closed universe is the Newtonian N-body problem with vanishing total energy and angular momentum. Because of special properties of this system (likely to be shared by any law of the Universe), its typical solutions all divide at a uniquely defined point into two halves. In each a well-defined measure of shape complexity fluctuates but grows irreversibly between rising bounds from that point. Structures that store dynamical information are created as the complexity grows and act as `records'. Each solution can be viewed as having a single past and two distinct futures emerging from it. Any internal observer must be in one half of the solution and will only be aware of the records of one branch and deduce a unique past and future direction from inspection of the available records.

 

[pood]

Here is a review of Barbour’s book written about the time it came out, which appeared in the NY Times.

It still doesn’t clear up a couple of my main questions, but interestingly it argues that Barbour’s time capsules yield a solution for quantum gravity, but the solution eliminates time altogether. No solution for quantum gravity incorporating time has been found.

The author claims that Barbour’s time capsule yield the “deep structure” of general relativity but entirely without a time dimension.

The article discusses “the past” as being “records” that are somehow “encoded” in each time capsule, but I continue to grasp at the meaning of this. Since there is no past or future under this theory, only Nows, it continues to seem to me that Barbour is perilously close to saying that the “records” of the “past” in our time capsule are not records at all, because there was no past, and if that is the case, our personal pasts and the historic pasts would have to be some kind of illusions. I wondering if he is really saying this, or I am just not grasping what he is saying?

 

[pood]

Reading further, Barbour says “the cat that lands, is not the same cat that jumps.” So we have, let’s say, ten time capsules. These are “instants” that co-exist timelessly in a configuration space he calls Platonia. There are separate time capsules of the cat jumping, each static and unchanging, and in the first the cat prepares to jump, in the second he is frozen timelessly in the act of starting to jump, in yet a third he is frozen in a capsule in which he is a little ways off the table, etc., until in the last capsule he is frozen timelessly as having landed on the far table. So, like stills in a move. This is illustratively different from the world tubes of Minkowski spacetime, but I don’t really see how it is qualitatively different, since events in the block world have also been likened to movie stills.

 

[pood]

To continue contrasting the Minkowski block world with Barbour’s Platonia, in the former, the cat jumping from one table to another IS the same cat; but the cat has temporal parts, just like it has spatial parts. So the temporal part that lands on the second table, is different from the temporal part that jumps off the first table, but they are still the same cat, described by a world tube extended through spacetime. But in Platonia, the two cats apparently have nothing to do with each other.

 

[Bomb#20]

David Deutsch makes some similar arguments in The Fabric of Reality. He's a Many Worlds fan and proposes that other times are just a special case of parallel universes. Just as all the possible futures your current world might turn into are equally real and will all happen, likewise, all the possible pasts that could have turned into your current world are equally real and did all happen.

 

[pood]

David Deutsch makes some similar arguments in The Fabric of Reality. He's a Many Worlds fan and proposes that other times are just a special case of parallel universes. Just as all the possible futures your current world might turn into are equally real and will all happen, likewise, all the possible pasts that could have turned into your current world are equally real and did all happen.

In fact, Barbour merges his time capsules with many worlds and renames it the Many Instants interpretation of QM.

 

[bilby]

So, is Barbour's hypothesis that time (or spacetime) is quantized? Is he proposing that spacetime is a grid of static cells each a Planck length on a side, and a Planck second in duration?

Or am I as thick as two short Plancks?

 

[pood]

So, is Barbour's hypothesis that time (or spacetime) is quantized? Is he proposing that spacetime is a grid of static cells each a Planck length on a side, and a Planck second in duration?

Or am I as thick as two short Plancks?

He is proposing that there is no time dimension. Reality consists of a vast and perhaps infinite number of these “time capsules” that co-exist in a configuration space, and the only reason we have “memories” of a non-existent past is because we have “records“ stored in our individual time capsules. The records, I guess, presumably refer to real events as instantiated by different time capsules, but that appears to be sheer luck, I guess, since from what I can tell the different capsules have no relation to one another: The cat that lands on one table is not the same cat that jumped from the other table.

 

[bilby]

So, is Barbour's hypothesis that time (or spacetime) is quantized? Is he proposing that spacetime is a grid of static cells each a Planck length on a side, and a Planck second in duration?

Or am I as thick as two short Plancks?

He is proposing that there is no time dimension. Reality consists of a vast and perhaps infinite number of these “time capsules” that co-exist in a configuration space, and the only reason we have “memories” of a non-existent past is because we have “records“ stored in our individual time capsules. The records, I guess, presumably refer to real events as instantiated by different time capsules, but that appears to be sheer luck, I guess, since from what I can tell the different capsules have no relation to one another: The cat that lands on one table is not the same cat that jumped from the other table.

So, last Thursdayism, writ small.

OK. Sounds highly implausible to me, but there's no way to prove it false, so it's also valueless.

 

[pood]

So, is Barbour's hypothesis that time (or spacetime) is quantized? Is he proposing that spacetime is a grid of static cells each a Planck length on a side, and a Planck second in duration?

Or am I as thick as two short Plancks?

He is proposing that there is no time dimension. Reality consists of a vast and perhaps infinite number of these “time capsules” that co-exist in a configuration space, and the only reason we have “memories” of a non-existent past is because we have “records“ stored in our individual time capsules. The records, I guess, presumably refer to real events as instantiated by different time capsules, but that appears to be sheer luck, I guess, since from what I can tell the different capsules have no relation to one another: The cat that lands on one table is not the same cat that jumped from the other table.

So, last Thursdayism, writ small.

OK. Sounds highly implausible to me, but there's no way to prove it false, so it's also valueless.

I think he claims it can make testable predictions, and that it offers a route to quantum gravity. I am still looking into it.

 

[bilby]

So, is Barbour's hypothesis that time (or spacetime) is quantized? Is he proposing that spacetime is a grid of static cells each a Planck length on a side, and a Planck second in duration?

Or am I as thick as two short Plancks?

He is proposing that there is no time dimension. Reality consists of a vast and perhaps infinite number of these “time capsules” that co-exist in a configuration space, and the only reason we have “memories” of a non-existent past is because we have “records“ stored in our individual time capsules. The records, I guess, presumably refer to real events as instantiated by different time capsules, but that appears to be sheer luck, I guess, since from what I can tell the different capsules have no relation to one another: The cat that lands on one table is not the same cat that jumped from the other table.

So, last Thursdayism, writ small.

OK. Sounds highly implausible to me, but there's no way to prove it false, so it's also valueless.

I think he claims it can make testable predictions, and that it offers a route to quantum gravity. I am still looking into it.

If time is not a dimension, but is instead a number of closed 'capsules' that contain 'records' that appear to be of the past, although the past does not exist, then the present does not influence the future, and so there is no such thing as a prediction.

Nor any way to test one, if it could exist.

 

[pood]

So, is Barbour's hypothesis that time (or spacetime) is quantized? Is he proposing that spacetime is a grid of static cells each a Planck length on a side, and a Planck second in duration?

Or am I as thick as two short Plancks?

He is proposing that there is no time dimension. Reality consists of a vast and perhaps infinite number of these “time capsules” that co-exist in a configuration space, and the only reason we have “memories” of a non-existent past is because we have “records“ stored in our individual time capsules. The records, I guess, presumably refer to real events as instantiated by different time capsules, but that appears to be sheer luck, I guess, since from what I can tell the different capsules have no relation to one another: The cat that lands on one table is not the same cat that jumped from the other table.

So, last Thursdayism, writ small.

OK. Sounds highly implausible to me, but there's no way to prove it false, so it's also valueless.

I think he claims it can make testable predictions, and that it offers a route to quantum gravity. I am still looking into it.

If time is not a dimension, but is instead a number of closed 'capsules' that contain 'records' that appear to be of the past, although the past does not exist, then the present does not influence the future, and so there is no such thing as a prediction.

Nor any way to test one, if it could exist.

I read his book The End of Time some 20 years ago but never grasped it, though I got bits and pieces of it. The reason I started this thread is to see if others can help me make sense of it. I am tempted to invite Barbour himself to participate. He has an email. I doubt he would join, but who knows? I’ve done that in the past and it worked.