I discuss Julian Barbour's Machian theories of dynamics, and his . The other two criticisms both concern 'the end of time'; the first from a. universe presented in The End of Time . Instead, using a few elementary equations and some new arguments, I wish to strengthen the case. Read "The End of Time The Next Revolution in Physics" by Julian Barbour available from Rakuten Kobo. Sign up today and get $5 off your first download.
|Language:||English, Spanish, French|
|Genre:||Fiction & Literature|
|ePub File Size:||26.39 MB|
|PDF File Size:||14.20 MB|
|Distribution:||Free* [*Sign up for free]|
I discuss Julian Barbour's Machian theories of dynamics, and his proposal that a Machian perspective enables one to solve the problem of time in quantum geometrodynamics (by saying that there is no time!). I concentrate on his recent book, The End of Time (). I discuss Julian. Julian Barbour, a theoretical physicist, has worked on foundational issues in physics for 35 years. He is responsible for a radical notion of "time capsules which. Richard Feynman once quipped that "Time is what happens when nothing else does." But Julian Barbour disagrees: if nothing happened, if nothing changed.
Not in United States? Choose your country's store to see books available for download. See if you have enough points for this item. Sign in. Richard Feynman once quipped that "Time is what happens when nothing else does. For time is nothing but change. It is change that we perceive occurring all around us, not time.
This is relevant because quantum theories are generally arrived at by starting from a classical picture and performing something which is called quantization. For non — physicists it's a rather difficult thing to grasp. But you can see where the idea of a timeless universe will come from if you consider the way quantum wave mechanics was discovered by Schrodinger in In classical Newtonian physics, if you have three particles they will always be at definite positions at definite times.
They will form some triangle, and the center of mass of the triangle will be somewhere and it will have some orientation. Now what quantum mechanics says is that, until observations are made, for all these quantities, there are no definite values, but only probabilities, all of which change in time. The reason that Schrodinger could create a picture of quantum mechanics like that is because he was using the Newtonian concepts of absolute space and time. The framework that they create makes it possible to give probabilities for the triangles formed by three particles to be in different positions and for the probabilities to change in time.
There's an independent time which is nothing to do with the contents of the universe. But if you are trying to construct a universe where you say there's no external framework of space and time in which the contents exist, then you can't give probabilities for the particles to be in certain overall positions in the universe and have some overall orientation, because there's no meaning to that.
And nor can the probabilities change in time, because there isn't any time in which they can change. The most simple — minded attempt to reconcile quantum physics with the idea that there's no invisible framework holding up the universe — and that idea is made very plausible by the 'Platonic structure' of general relativity — leads you to a picture in which there are just probabilities given once and for all for the relative configurations of the universe.
So if we had a three — particle universe the probabilities would just be for where the three particles are relative to each other, say, two close together and one further apart.
That's the complete story — static probabilities for static configurations, which are what I identify with Nows. Thus, quite a simple argument leads to a picture where you just have possible Nows, and the Nows are defined by how the things in the universe are arranged. That's all you get out of the theory. In fact this picture, which Dirac helped to create, crystallized something over 30 years ago. It is described by an equation called the Wheeler — DeWitt equation.
John Wheeler prodded Bryce DeWitt into its derivation. If it really turns out to be the equation of the universe, the episode will be a rerun of the way Hooke badgered Newton into his solution of Kepler's problem.
People found it very difficult to make sense of the static universe that seemed to emerge. However, I find the arguments that lead to it are strong.
There is support for it in the structure of Einstein's theory and in the structure of quantum mechanics. The equation would never have been found if that were not the case. So I take the picture seriously and try and make sense of it, and ask how can we nevertheless recover from it a picture of our world; how can it be that I can sit here and see my own hands moving, yours too, if the world is completely static? Suppose we accept the quantum universe is static and timeless.
How can we reconcile that with actually seeing motion and remembering the past? In fact, besides the direct sensing of change of one kind or another, the only direct evidence we have for time and the past comes from records, which include memories. Now records, either natural like fossils or man made, are so ubiquitous we can easily forget how remarkable their existence is according to the current understanding of classical mechanics.
This is the problem of the extraordinarily low entropy of the universe. It was emphasized a century ago by Boltzmann. In the modern context of general relativity, Roger Penrose keeps on pointing out what a huge problem it is. All statistical arguments based on classical mechanics suggest the universe ought to have a vastly higher entropy and exist in a state in which records simply cannot form. Penrose wants to explain the low entropy and the arrow of time by a new physics which is explicitly time asymmetric and comes with a built — in arrow of time and forces the universe to begin in a highly uniform state.
My own view is that, paradoxically, the arrow of time may be easier to explain in a theory in which there is no time at all. I suggest that our belief in time and a past arises solely because our entire experience comes to us through the medium of static arrangements of matter, in Nows, that create the appearance of time and change.
Geologists certainly deduced that the earth has an immensely long history from structures frozen in rocks. That is, evidence for time and motion in static form. Our long — term memories must also be hard — wired in the patterns of the neural network in our brains. Again, we have mutually consistent records in static form. It is even possible that when we see motion the material counterpart of the phenomenon is a pattern of neuronal connections that codes several different positions of a moving object at once, and the appearance of motion arises from their simultaneous presence in one brain configuration.
As I have no expertise in neuroscience, I do not want to push this idea hard. I merely want to suggest that the appearance of time arises exclusively from very special matter configurations which we find can be interpreted as mutually consistent records of processes that unfolded in a past in accordance with definite physical laws that involve time.
I call such configurations time capsules and take the perfectly conventional realist view that they do exist in an external world. However, I think they may arise in a lawful manner that does not involve time at all. If we take the Wheeler — DeWitt equation at its face value, this is what must happen. I'm more optimistic and I am by no means completely alone in thinking that the appearance of time can arise from an essentially timeless universe. There is a quite long — standing regular research program involving at least twenty recognized physicists devoted to the problem.
One of Hawking's main papers contributed to it about 15 years ago. The aspect of the problem that most excites me is that it might abolish the dichotomy between laws of nature and the initial conditions that you have to add to them before you can make any predictions.
The really interesting thing about quantum cosmology is that it should be in a position to make predictions about the universe which can't be made within classical physics. Classical physics as it exists now has laws and it has initial conditions. If quantum cosmology really is static, there's no initial conditions.
There is no time. You can't set conditions at an initial time. In my view, this means that quantum cosmology is potentially much more predictive. It should be able to predict phenomena like the arrow of time and the low entropy of the universe that in classical physics you would just have to attribute to initial conditions, and just say, well the Big Bang happened to take this form rather than a different form.
This is where I think the strongly asymmetric structure of any Platonia that we use to describe the universe could be highly significant. This possibility does not seem to have occurred to other physicists, but I think it must be relevant. If the universe really is governed by something like the Wheeler — DeWitt equation and we interpret it as determining the relative probabilities for the various different possible configurations of the universe to be realized, or experienced, then a major factor in determining how those probabilities are distributed must be the overall shape of the arena on which it acts.
But that is some Platonia, in which there is always a distinguished point Alpha, from which the complete arena opens up somewhat like a flower.
Surely this structure must put a rooted bias into the game. My conjecture is that this static bias in the structure of the arena funnels the higher probabilities onto the special configurations that are time capsules, which, being more probable, are the ones that we are most likely to experience.
The overall structure of the arena is reflected in the experienced configurations and interpreted by us as time and a past. This may seem fantastic, but I think the arguments for a timeless universe are quite strong. If we accept them, then we must look for something really radical and powerful that does put the appearance of time into the universe.
The difference between past and future is a massive asymmetry. I believe that it can only arise from some other massive asymmetry, which I find in the structure of Platonia.
I cannot as yet see any direct experimental way of testing this particular idea. What is needed above all is development of the mathematics. In my view, quantum cosmology is rather like the quantum physics of the stationary states of huge molecules, and the development of ideas used in atomic and molecular physics might help.
Quite a lot of work has already been done in this direction in the program I mentioned earlier. But in principle predictions can be made in the context of the Wheeler — DeWitt equation. However, nearly all of them at this stage are rather difficult because of the mathematics.
You're dealing with complicated systems, you don't know how to find the solutions; there's a whole lot of issues there. Another issue is that cosmology is a special subject because it's dealing with a unique thing. There is only one universe. There's a philosophical question: Have you ever considered that the world is an invention, and there's not an a priori existence before discoveries of people like yourself? Isn't this a kind of naive materialism? Wallace Stevens addressed the idea that the words of the world are the life of the world.
Brown noted that nature isn't created But I don't know of any notable physicists today who are seriously concerned with the role that language plays in the creation of reality. The words are meaning something. What impresses me is that, despite what you say, the rules of the game of science have stayed amazingly constant, despite the fantastic changes in how we see the world.
Basically, the assumption has always been that that there are material things that move around subject to the constraints of geometry. There is change subject to order. Science — or at least physics — has been about establishing how those changes take place and describing them mathematically. Every now and then they lead to a dramatic new way in looking at the world, but the rules of the game have always been the same really, going right back to geometry and ancient astronomy.
I personally believe the world is still probably very much richer than we imagine, and that we still may well be only just scratching the surface of it. If you climb a mountain range you get different views as you go up.
When you've got to the top you can understand what you could see lower down, but you couldn't understand it properly when you were lower down. I see the progress of science being like that, that suddenly completely new vistas are opened up, and you find new ways to think about it. I do think we are discovering the world, not inventing it. But John Wheeler sometimes seems to suggest that we create the universe.
He thinks that by insisting on finding a consistent description of it we conjure it up by a kind of conspiracy. He illustrates the idea by a variation of the game of twenty questions in which there is no object at the start of the questioning. Instead, each answer that is given must be consistent with all those already given. Eventually, there emerges some object that matches the answers. As it happens, this is about an issue very closely related to quantum cosmology.
What is the meaning of general covariance? Empson is arguing that it is a tautology. I think he is right in that but not in the claim that all law becomes the assumption of the description. Tensors relate different things and bring them into lawful connection.
Let's consider a great experience I just had. I witnessed the total eclipse of the sun in France on August 11th. I remember vividly reading as a boy that there would be this eclipse in , the first one visible in England in a long time — actually I went over to France to see it. Now there isn't any doubt about an eclipse; either you see an eclipse or you don't. The astronomers predicted that it would be seen as total in the medieval town of Senlis just north of Paris, and sure enough we did see it total.
That's pretty impressive. I don't think there's anything to do with inventing there — the impression of actually seeing the sun totally eclipsed is quite unambiguous.
My memories of reading about the eclipse as a boy and my memory of the actual eclipse are not tensors but they are real different things that match up. That's why I believe there's something real out there in the world and that we are getting our hands on it. Your theories appear to be bumping up against the ideas of many of your colleagues? Who might be sympathetic? The string theorists will probably not take it very seriously, because I'm tied to a certain approach to attacking the problem and they will perhaps just say well he's doing the wrong thing.
But I don't worry too much about that, because certain approaches can become unpopular for a long time and then come back in again. There are certainly people who do think about the fundamental issues of how you describe the world and these very basic questions of what is motion and so forth; they should be sympathetic to my approach.
The people who will not like me are the people who don't want to take the many — worlds interpretation of quantum mechanics seriously, and who are trying to modify quantum mechanics so as to banish that specter. I don't think Roger Penrose would take it very seriously, because he doesn't like any form of the many — worlds interpretation of quantum mechanics. Stephen Hawking might be quite sympathetic, because he's been basically working along those lines for many years now. Other people who I would not expect to be sympathetic are Murray Gell — Mann, Jim Hartle, and several others who have developed the so — called consistent histories approach to the interpretation of quantum mechanics.
They start out by taking a complete history as being a fundamental concept, whereas for me the Now is the starting point. They start with a string of Nows. Lee and I are great friends, and we've talked a lot and we've developed ideas together — we don't follow exactly the same line now, but we share a lot in common.
We are both very interested in structure, and in thinking that the way things are structured is the really important thing.
That relates to this basic issue of whether the world exists in some all — powerful background or whether the world is really just an interaction between the things that are in it.
We share that view very much. The people who commented tended to be the people who know about the so — called problem of time, that time seems to disappear altogether when you try to make a quantum universe in this particular approach. Basically they were fairly sympathetic to my viewpoint.
First of all, I'm working on some ideas which try and take scale out of physics.
This is analogous to the issue of duration: You can also ask, how can you say that an inch here is the same as an inch on the Andromeda nebula? That's also a very deep question, and I think I've made some progress with an Irish colleague in working on that.
What I really hope for is to build up more and more evidence for my overall picture of what the universe is like. You never can tell whether you're on the right line, but I just can't stop thinking about these things. If you look in the history of physics, you very often see that before a definite breakthrough is made, there's some sort of qualitative idea appears, and then gets made more precise, more mathematical.
I would hope that I'm making some contribution to such a development, not only with qualitative ideas like Platonia and time capsules but also in simplified models as in my work with Bertotti. Some have said if your theories are correct our perception of the world will change dramatically. Certainly if I, or other researchers, are on the right track, there's definitely got to be a different overall view of the world. But it's very hard to predict exactly how it would change things.
How could Copernicus know what would come out of his proposal? What I feel for myself is that by concentrating on the things that we know are in the world, it makes one think about the actual world more, and I would say cherish it and value it more, and perhaps take a more relaxed attitude toward life and sit back and enjoy it more.
This is actually happening to me personally — maybe it's just because I'm getting older and don't want to miss things, but certainly I'm aware of savoring the moment more than I when I was young. And it's partly influenced by my idea that really the universe is static, and the only things that are real are Nows, in one of which we now are.
Some years ago, I heard Dame Janet Baker interviewed on radio. She was asked if she ever listened to her recordings and, if so, what were her favourites. She said she hardly ever listened to them. For her, every Now was so exciting and new, it was a great mistake to try to repeat one.
In her singing, she made no attempt at all to recreate earlier performances and do the high points in the same way as the night before. Again and again she spoke with the deepest reverence of the Now and how it should be new and happen spontaneously. I thought it was the perfect artistic expression of how I see timeless quantum cosmology.
Well, you are clearly into the big questions. Does anything less than everything mean nothing to you? I'm nothing if not ambitious in that way. How well I succeed is another matter, but it keep's me happy trying. Absolutely not. No, I'm human emotion through and through, but I love the universe too.
I would love to show that the universe is as rich as it appears to us through our senses and not rather drab as it appears in science. For me one of the great miracles is colors, and different sounds and sensations. The primary qualities, related to geometry, shape, and motion, are believed to exist in the material world while colours and sounds exist only as mental states.
Scientists work happily with the division of qualities and the conjectured relationship between them. I am proposing that motion should cease to be a primary quality and become a secondary one. I do not think this is necessarily so. A theory like mine must propose structure in the physical world that is correlated consistently with experience.
If I have in front of me simultaneously two snapshots showing a football match with the players and ball in slightly different positions, I can work out from that static information how each player and the ball have moved between the two snapshots. As an example, you write: All the things I see, hear, smell and taste are knit together in a whole. The End of Time, op. One can argue that all concepts in theoretical physics, including the most abstract ones in quantum mechanics, are suggested by experience.
Close your eyes and open them for about half a second before closing them again. You do experience something very like seeing a snapshot. In the theoretical concept, geometry plays a decisive role; it holds the world together.
For me the key notion is of a plurality within a unity a deeply suggestive expression often used by Leibniz. As I employ it, the notion comes from direct experience but is honed by abstraction to a precise theoretical concept.
Astronomers take account of the speed of light to correct apparent positions and obtain instantaneous positions in some particular frame of reference.
The spacelike surface is in fact a 3D curved Riemannian space. Though others might not agree, I do not see how either theory can survive if it is not retained in some form or other. Thus, when I speak of itches and sounds experienced simultaneously with images of objects, that is only to get across the idea of an instantaneous plurality within a unity.
In order to even qualify as a candidate theory, is it not required that the would-be theory make novel and testable predictions? Think of Copernicus: The motion of the sun across the sky and the retrograde motions of the planets relative to the stars are empirical conditions and were used by Copernicus Time, Reality and Experience Cambridge: Cambridge University Press, , ; cf.
Oxford University Press, , esp. Ultimately, science is not really about prediction but explanation and confirmation. Geologists, for example, developed a theory of the deep past without making any experiments.
All their conclusions were drawn from present data. Cosmologists are currently developing an account of cosmology in the same way. Even experiments at the LHC are ultimately interpreted by theoreticians from data sets acquired from the experimentalists. Records are always a vital part of the story. Information is all of the same kind; we divide some of it into effects and some into records. A present memory of a correct experiment having been performed should be associated with a present memory of a correct result having been obtained.
In later comments on Everett John S. Cambridge University Press, , For my part, I am not a solipsist and retain virtually all the ontology of impeccable realists — except that ever-elusive time. We are clearly learning a great deal about the workings of the brain, but how anything ultimately comes into consciousness is, to my knowledge, still a complete unknown. However, let me make this comment: This implies that the brain compares two structures and on the basis of the structures alone decides which is later and presents it to us later in consciousness.
My view is hardly different; in fact I am not sure if it is in any way different. I am merely saying that they can be put naturally in that order solely using their intrinsic structure; in the process of presenting the stored information to us in consciousness, the brain does not need access to an externally supplied time-order.
It constructs it from the information available in one instant. I put such arguments in The End of Time, especially Chapter Two, and still think they are reasonable, despite what George says. I would answer that, when it comes Ought we take this as a kind of avowal, then, that you are indeed suggesting that the mind in some way transcends the physical world?
I certainly grant that very exciting advances are being made in the study of the relationship between brain activity and conscious experience. But this always leads to the recognition of correlations. Kepler remarked long ago that if certain phenomena are invariably correlated, this may occur for two reasons: Thus, it is not necessarily the case that the correlations now being found explain the conscious state. Your example of motor control shows that complex automata can and do exist, but I do not think that understanding of the control mechanism could ever suggest that an automaton is self-aware.
Suppose that there were a machine so constructed as to produce thought, feeling, and perception, we could imagine it increased in size while retaining the same proportions, so that one could enter as one might a mill.
On going inside we should only see the parts impinging upon one another; we should not see anything which would explain a perception. Everyman, , Thus, I believe one should keep an open mind about the true connection between the brain and experience.
I do not see how one can get more dualistic than that. Moreover, the precise connection between these two remains obscure because of the profound interpretational problems in quantum mechanics. Of course, the dualism I have just mentioned is not between mind and matter, but it is still a fundamental dualism. I note that when talking about the way in which the psychological impression of time and motion is created a moment ago, you spoke about the brain rather than the mind doing all the work, and thus seem to accept that conscious- ness is indeed subserved by neurobiological mechanisms.
This is more or less correct. If I use the word mind, it is inadvertently except in idioms. But I would say correlated with, not subserved by. The position that I adopted in The End of Time is conventional: The only role of the wave function that I attributed to experience is to make it the wave function determine the probability of particular experiences.
But these are all tentative ideas. The only difference between my view and the conventional one is that I remove motion from the overall state of the physical world with which I propose experience to be correlated.
This contrasts with the standard view that correlates experience with positions and motions. Position is clearly much more fundamental than motion, for motion is change of position. I may also mention that there are people with what is said to be a neurological malfunction that makes them see the world as a succession of snapshots. I know one such person; she is currently cured of the problem, but it was so extreme in her case that she would sometimes experience the snapshots in the wrong chronological order, so that crossing a road was life threatening.
She contacted me having read my book and found that my concept of Nows resonated deeply with her experience. This suggests to me that deepest-level experience may be snapshot-like and that continuous experience is a higher-level phenomenon. One might wish to maintain, in quasi-Kantian terms, that time is only a mode of intuiting reality rather than something pertaining to the world as it is in-itself.
No, I would not advocate that. A French man did write a whole book without using the letter e, but writing one using only the verb to be does not appeal to me. It may help to note that for millennia theologians and millions of believers have been happy with the idea that God is eternal, unchanging, and omniscient and therefore presumably self-aware.
I believe I am part of a universe far larger than myself; I know I am self-aware; ergo I conclude that the universe is self-aware. So self awareness resides in eternity. What, after all, could these experiences be good for? We are talking about such big issues, we must take one thing at a time. It is based on a quantum theory of the universe from which the appearance of a classical universe can in principle arise.
Although my book has clearly attracted much interest because of its denial of time, virtually no one has commented on this idea. Thus I think I can provide the broad framework needed for evolution to be represented in eternity. In principle, that is enough to have evolution emerge. Could you provide examples? What would testing your theory involve? I am hesitant to say that my theory makes any predictions at the moment because it is as yet more in the nature of an outline of a theory.
However, I do have the clear proposal that there is a static wave function of the universe that concentrates its associated probabilities In principle, this suggestion could be supported or clearly disproved by mathematics. At the beginning of The End of Time you compare your theory of the non-existence of time to the Copernican revolution in cosmology in the following terms: Copernicus, Galileo and Kepler taught us that the earth moves and rotates while the heavens stand still, but this does not change by one iota our direct perception that the heavens do move and that the Earth does not budge.
Our grasp of the interconnections of things was, however, eventually changed out of recognition in ways that were impossible to foresee. Now I think we must, in an ironic twist of the Copernican revolution, go further, to a deeper reality in which nothing at all, neither heaven nor Earth, moves. Stillness reigns. I hope you will be able to change from a way of thinking to which we have been conditioned by the fact that we evolved on the stable surface of the Earth to a more abstract way of thinking that would have been forced upon us had we evolved from creatures that roamed in space between objects moving through it in all directions.
Is it really possible that a creature whose imagination and cognitive capacities evolved, as you say, on the stable and reassuring surface of the earth, could ever be capable of coming to terms with the implications of such a revolution in anything more than the most purely abstract way? Cambridge University Press, , 30, 34 and Chapter Two passim. They can be thought of as like snapshots that a child can pick up and examine.
The other half of my ontology comes from quantum mechanics and will be easy for physicists, if not children, to grasp: I regard quantum mechanics as a theory that explains structure. Close and open your eyes for a second; you see a structure, a snapshot.
The fundamental law is a law of structure selection in which structures are favoured by virtue of their structure and nothing else.
It is not totally unlike a child selecting the most interesting snapshots among a large collection. To make the connection with experience I propose that awareness is correlated with single snapshots which can be arbitrarily complex and contain, as it were, snapshots within snapshots. It is easy to show that the speed part of this initial condition is redundant if one considers the whole universe.
History is then not a path traversed as some speed but merely a path. This can be done in a timeless fashion that is precisely analogous to the way That is impossible to answer. All I can say is that life could be less hectic and more contemplative.
People in the parts of Platonia where my theory is accepted should cherish the Now more than in this overworked region.
To go back to what I said about theology: In the Middle Ages busy kings still spent hours in daily prayer because they believed deeply in eternity and its primary importance. Today, many would reject their beliefs. However, mathema- ticians have rational grounds for believing in eternal math- ematical truths.
Indeed, it can hardly avoid doing so, since it uses mathematics, and mathematics that is only occasionally true is not much use. Lee Smolin, for example, to whom you introduced Leibnizian and Machian ideas when he was visiting Oxford in , and with whom you subsequently collaborated in an attempting to formulate Leibnizian monadological ideas in precise mathematical form, has gone on to develop, along with Carlo Rovelli and In this way, in the form of Loop Quantum Gravity and Relational Quantum Mechanics, ideas of distinctly Leibnizian inspiration stand at the very cutting-edge of contemporary theoretical physics.
This led me to ask myself seriously: What is time?
What is motion? By I had worked out the framework of a Machian theory of time and motion in classical physics. This has since been elaborated but not fundamentally changed. What I found exciting in Leibniz was a deeper intellectual under- pinning of my scheme. Indeed, reality is variety.
Leibniz also has this wonderful conjecture that the actually realized universe is more varied than any other conceivable universe. It has generated a fair amount of interest, but as of now does not seem to have any obvious applications in physics. As regards differences between my approach to quantum gravity and the present approach of Smolin and Rovelli, they concern the antithesis of the discrete and the continuous.
When Lee met me, he was already convinced that at the deep microscopic level space must be discrete. This was a formative experience to which I had not been exposed. I was initially sympathetic to the idea that the continuum of experience should emerge from a discrete foundation, but rather soon came to the conclusion that the problems to be overcome were great and probably insur- mountable.
In this respect, Lee and I continue to differ, but we are each inspired by relational examples drawn from Leibniz: There seems to be a general feeling abroad amongst those searching for that veritable Holy Grail of contemporary physics — that is, a workable theory of quantum gravity — that something fundamental is missing, a common erroneous assumption which needs to be rooted out, and that this erroneous assumption very likely concerns the nature of time. Norton eds , The Cosmos of Science Pittsburgh: