Julian Barbour

(1937 -- )

Julian Barbour writes:

"I was born in 1937 and grew up in the village of South Newington in North Oxfordshire, England. As a boy I became very interested in astronomy. For this reason, I decided to study mathematics at Cambridge, after which I commenced a PhD in astrophysics in Munich.  However, at this time I became deeply interested in foundational issues in physics, above all the nature of time. I came to the conclusion that time itself does not exist. If we did not see objects move and things change, we could never say that time passes. Time is nothing but a measure of change. But physics had been developed under the assumption that time exists and flows independently of the objects in the world. I felt this was quite wrong and that physics must be recast on a new timeless foundation.
Since 1963 I have been working on this project and the closely related problem of the origin of inertia. I completed a PhD on the foundations of Einstein's general theory of relativity at Cologne in 1968 and then decided to become independent, fearing that an academic environment and the associated pressure to publish as many research articles as possible would deflect me from my long-term objectives. For 28 years I supported my family and research by translating Russian scientific journals. This left me free to develop, in collaboration with the Italian Bruno Bertotti, a theory of time and inertia. Another major topic of interest for me has been the implications of this work in quantum cosmology.
I also became very interested in the historical development of ideas about time and motion, the subject of my Absolute or Relative Motion?, Volume 1, The Discovery of Dynamics (now retitled as simply The Discovery of Dynamics and reprinted as a paperback, see writings). In 1996, I retired from my translating work and have since then concentrated entirely on my physics research and on writing. I have summarized my ideas about the non-existence of time for non-specialists in The End of Time, which has been published in hardback (1999) and paperback (2000) in the UK and hardback (2000) in the USA (with paperback to be published fall 2001). Articles about the main ideas in this book were published in The New Scientist in October 1999 and Discover (December 2000). For details about my main publications and ideas in physics, see writings and ideas.
My wife Verena comes from the Black Forest in Germany. We have one son and three daughters."

Quotations from the book The End of Time:

"Two views of the world clashed at the dawn of thought. In the great debate between the earliest Greek philosophers, Heraclitus argued for perpetual change, but Parmenides maintained there was neither time nor motion. Over the ages, few thinkers have taken Parmenides seriously..."

(Barbour: 2000, p. 1)

"Plato... taught that the only real things are forms or ideas: perfect paradigms, existing in a timeless realm. In our mortal existence we catch only fleeting glimpses of these ideal forms. Now each point - each thing - in these 'countries' I have asked you to imagine could be regarded as a Platonic form. Triangles certainly are. I shall call the corresponding 'country' Platonia. The name reflects its mathematical perfection and timeless landscape. Nothing changes in Platonia. Its points are all the instants of time, all the Nows; they are simply there, given once and for all."
(Barbour: 2000, p. 44)

"If, as I think they must be, things are properly considered in Platonia, Lucy never did leap to catch the swifts. The fact is, there never was one cat Lucy - there were (or rather are, since Lucy is in Platonia for eternity, as we all are) billions upon billions upon billions of Lucys. This is already true for the Lucys in one leap and descent. Microscopically, her 1026 atoms were rearranged to such an extent that only the stability of her gross features enables us to call her one cat. What is more, compared with her haemoglobin molecules the features by which we identified her - the sharp eyes, the sleek coat, the wicked claws - were gross. Because we do not and cannot look closely at these Lucys, we think they are one. And all these Lucys are themselves embedded in the vast individual Nows of the universe. Uncountable Nows in Platonia contain something we should call Lucy, all in perfect Platonic stillness. It is because we abstract and 'detach' one Lucy from her Nows that we think a cat leapt. Cats don't leap in Platonia. They just are."
(Barbour: 2000, p. 48-49)

"Now consider the dilemma God would have faced when he created the world. Since all places in absolute space are identical, God would face an impossible choice. Where would he put the matter? God, being supremely good and rational, must always have a genuine reason for doing something - Leibniz called this the 'principle of sufficient reason'... - and because absolute space offered no distinguished locations, God would never be able to decide where to put the matter. Absolute time, on the assumption that it existed, presented the same difficulty. Newton had said that all its instants were identical. But then what reason could God have for deciding to create the world at some instant rather than another? Again, he would lack a sufficient reason. For reasons like these, not all of them so theological, Leibniz argued that absolute space and time could not exist."
(Barbour: 2000, p. 64)

"(The Austrian physicist Ernst) Mach was interested in many subjects, especially the nature and methods in science. His philosophical standpoint had points in common with Bishop Berkeley, but even more with the ideas of the great eighteenth-century Scottish empiricist David Hume. Mach insisted that science must deal with genuinely observable things, and this made him deeply suspicious of the concepts of invisible absolute space and time. In 1883 he published a famous history of mechanics containing a trenchant and celebrated critique of these concepts..."
(Barbour: 2000, p. 65)

"(Considering Newton's bucket argument, Ernst Mach suggested) that it is not (absolute) space but all the matter in the universe, exerting a genuine physical effect, that creates centrifugal force... Mach's proposal boiled down to the idea that the law of inertia is indeed, as Bishop Berkeley believed, a motion realtive to the stars, not space. Mach's important novelty was that there must be proper physical laws that govern the way distant matter controls the motions around us. Each body in the universe must be exerting an effect that depends on its mass and distance. The (Newton's) law of inertia will turn out to be a motion relative to some average of all the masses in the universe. For this basic idea, Einstein coined the expression Mach's principle, by which it is now universally known (though attempts at precise definition vary quite widely).
Mach's idea suggests that the Newtonian way of thinking about the workings of the universe, which is still deep-rooted, is fundamentally wrong..."
(Barbour: 2000, p. 65)

"It would be much more natural to specify our distances to all objects. They define our position. This conclusion is very natural once we become aware that nothing is fixed. Everything moves relative to everything else.
Taking this further, thinking about the position and motion of one object is artificial. We are part of Mach's All, and any motion we call our own is just part of a change in the complete universe. What is the reality of the universe? It is that in any instant the objects in it have some relative arrangement."
(Barbour: 2000, p. 68)

"The proper way to think about motion is that the universe as a whole moves from one 'place' to another 'place', where 'place' means a relative arrangement, or configuration, of the complete universe...
It does not move in absolute space, it moves from one configuration to another. The totality of these places is its relative configuration space: Platonia...
... no Sun rises or sets over that landscape to mark the walker's progress. The Sun, like the moving parts of any clock, is part of the universe. It is part of the walker...
There is nothing outside the universe to time it as it goes from one place to another in Platonia - only some internal change can do that. But just as all markers are on an equal footing for defining position, so are all changes for the purposes of timing...
The history of the universe is the path. Each point on the path is a configuration of the universe. For a three-body universe, each configuration is a triangle. The path is just the triangles - nothing more, nothing less.
With time gone, motion is gone..."
(Barbour: 2000, p. 69)

"In modern theoretical cosmology, distance is absolute and the universe expands. For reasons that are not yet understood, it simultaneously becomes more richly structured. In a cosmology without both time and scale, this would correspond, in a realistic scale-free Platonia, to going from the bland centre to the more interestingly structured 'instants of time' situated between it and the frontiers. That is where the mist I introduced in Chapter 3 must collect most thickly - have the highest intensity - at time capsules structured so that they seem to record evolution from the symmetric centre. This would be a cosmology of pure structure..."
(Barbour: 2000, p. 75)

"Leibniz famously asked why, among all possible worlds, just one should be realized. He suggested, rather loosely, that God - the supremely rational being - could have no alternative but to create the best among all possible worlds. For this he was satirized as Dr. Pangloss in Voltaire's Candide. In fact, in his main philosophical work, the Monadology, Leibniz makes the more defensible claim that the actual world is distinguished from other possible worlds by preserving 'as much variety as possible, but with the greatest order possible'. This, he says, would be the way to obtain 'as much perfection as possible'."
(Barbour: 2000, p. 110-111)

"After it became clear to me that Platonia was the arena in which to formulate Mach's ideas, I soon realized that it was necessary to find some analogue of action that could be defined using structure already present in Platonia. With such an action it would be possible to identify some paths in Platonia as being special and different from other paths. In Leibniz's language, such paths could be actual histories of the universe, as opposed to merely possible ones."
(Barbour: 2000, p. 113)

"Each (point in Platonia) is a possible realtive arrangement, a configuration, of all the matter in the universe..."

(Barbour: 2000, p. 115-116)

"... a 'trial distance' d (between two triangles in Triangle Land)... is an arbitrary quantity, since the relative positioning of the two triangles is arbitrary. It is, however, possible to consider all relative positionings and find the one for which d is minimized. This is a very natural quantity to find, and it is not arbitrary. Two different people setting out to find it for the same two triangles would always get the same result. It measures the intrinsic difference between the two matter distributions represented by the triangles. It is completely determined by them, and does not rely on any external structure like absolute space...
Using the intrinsic difference... we can determine 'shortest paths' or 'histories' in Platonia...However, the intrinsic difference by itself does not lead to very interesting histories, and it is more illuminating to consider a related quantity. The potential energy of any matter distribution... is determined by its relative configuration, and is therefore already 'Machian'... Two nearly identical matter distributions have almost the same potential... To obtain more interesting histories we can simply multiply the intrinsic differences by the potential... This will change the definition of 'distance'..."
(Barbour: 2000, p. 116-117)

"Poincare's paper (1898) is very interesting. He identified two problems in the definition of time.
First he considered duration: what does it mean to say that a second today is the same as a second tomorrow? He noted that this question had recently been widely discussed... he then noted a second question, just as fundamental and in some ways more immediate, which has escaped close attention. How does one define simultaneity at spatially separated points? This was the question that Einstein posed and answered seven years later with such devastating effect. I read the subsequent history of relativity as follows. Einstein answered his question - Poincare's second - with such aplomb and originality that it eclipsed interest in the question of duration. It is not that duration plays no role in relativity - quite the opposite, it plays a central role. But duration is not derived from first principles. It appears indirectly."
(Barbour: 2000, p. 123)

"... Carl Neumann and Mach became aware of the need for new foundations of dynamics. In Poincare's writings of around 1900, one can see clear hints of how dynamics might have been developed further as the main stream of research. In particular, an explicit theory of the origin of the spatiotemporal framework might have emerged. That is more than evident from Poincare's 1898 paper on time and his 1902 comments...
All this was changed by Einstein's 1905 paper. Because of his quantum doubts, he distrusted explicit dynamical models ... (and) ... insight into the nature of time and duration was lost."
(Barbour: 2000, p. 136)

"It is impossible to understand relativity if one thinks that time passes independently of the world...
the important thing is to get away from the idea that time is something. Time does not exist..."
(Barbour: 2000, p. 137)

"It is often said that relativity destroyed the concept of Now... In Newtonian physics ... there is a unique sequence of instants of time, each of which applies to the complete universe. This is overthrown in relativity, where each event belongs to a multitude of Nows. This has important implications for the way we think about past, present and future.
Even in Newtonian theory we can picture world history laid out before us. In this 'God's-eye' view, the instants of time are all 'there' simultaneously. The alternative idea of a 'moving present' passing through the instants from the past to the future is theoretically possible but impossible to verify. It adds nothing to the scientific notion of time. Special relativity makes a 'moving present' pretty well untenable, even as a logical possibility."
(Barbour: 2000, p. 142)

"...(in relativity) there are just point-like events in space-time and no extended Nows. At the psychological level, Einstein himself felt quite disturbed about this... (and) the philosopher Rudolf Carnap wrote: ... So he (Einstein) concluded 'that there is something essential about the Now which is just outside the realm of science'."
(Barbour: 2000, p. 143)

"I am not claiming that the description of space-time given by Einstein or Minkowski is wrong. Far from it - they got it right, but they described the finished product, and the complete story must also include the construction of the product."
(Barbour: 2000, p. 145)

"In the... (Newtonian worlds), past, present and future are defined throughout the universe, and present is a single simultaneity hyperplane. In the... (Einsteinian worlds), they are defined separately for each event in space-time, and the present is much larger."
(Barbour: 2000, p. 150)

"It is the implications of the BSW paper (see in the references the article by Ralph Baierlein, David Sharp and John Wheeler) that I discussed with Karel (i.e. Karel Kuchar) in 1980. They can be quickly summarized. The basic problem that BSW considered was what kind of information, and how much, must be specified if a complete space-time is to be determined uniquely. This is exactly analogous to the question that Poincare asked in connection with Newtonian dynamics, and then showed that the information in three Nows was needed. As we have seen, a theory will be Machian if two Nows are sufficient. What BSW showed is that the basic structure of general relativity meets this requirement.
In fact, the all-important Einstein equation that does the work is precisely a statement that a best-matching condition between the two 3-spaces does hold. The pairing of points established by it is exactly the pairing established by the orthogonal struts (Barbour's figure 30 on page 175). In fact, the key geometrical property of space-times that satisfy Einstein's equations reflects an underlying principle of best matching built into the foundations of the theory. I think that Einstein, with his deep conviction that nature is supremely rational, would have been most impressed had he lived to learn about it."

(Barbour: 2000, p. 176)

"We have reached a crucial stage, and a summary is called for. In all three forms of classical physics - in Newtonian theory, and in the special and general theories of relativity - the most basic concept is a framework of space and time. The objects in the world stand lower in the hierarchy of being than the framework in which they move. We have been exploring Leibniz's idea that only things exist and that the supposed framework of space and time is a derived concept, a construction from the things.
If it is to succeed, the only possible candidates for the fundamental 'things' from which the framework is to be constructed are configurations of the universe: Nows or 'instants of time'. They can exist in their own right: we do not have to presuppose a framework in which they are embedded. In this view, the true arena of the world is timeless and frameless - it is the collection of all possible Nows..."
(Barbour: 2000, p. 177)

"We need to consider the 'official line', known as the Copenhagen interpretation because it was established by Heisenberg and Bohr at the latter's institute in Copenhagen shortly after the creation of quantum mechanics...
... It is a basic Copenhagen tenet that the probabilistic statements reflect a fundamental property of nature, not simply our ignorance. It is not that before the measurement the particle does have a definite momentum and we simply do not know it. Instead, all momenta in the superposition are present as potentialities, and measurement forces one of them to be actualized. This is justified by a simple and persuasive fact. If we do not perform measurement but instead allow * to evolve, and only later make some measurement, then the things observed later (like the two-slit fringes) are impossible to explain unless all states were present initially and throughout the subsequent evolution. Outcomes in quantum mechanics are determined by chance at the most fundamental level. This is the scenario of the dice-playing God that so disturbed Einstein."
(Barbour: 2000, p. 202-203-204)

"If anything, the second cardinal fact disturbed him even more. There seems to be a thoroughgoing indefiniteness of nature even more radical than the probabilistic uncertainties. As we have seen, one and the same state can be regarded as a superposition of either momentum or position eigenstates. It is the way this mathematics translates into physics that is startling. The experimentalist has complete freedom to choose what is to be measured: position or momentum. Both are present simultaneously as potentialities in the wave function. The experimentalist merely has to choose between set-ups designed to measure position or momentum. Once the choice is made, outcomes can then be predicted - and one outcome is actualized when the measurement is made. In fact, the indefiniteness is even greater since other quantities, or observables as they are called, such as energy and angular momentum, are also present as potentialities in psi (sorry that there are no Greek fonts for the letter psi).
Only one experiment can be made - for position or momentum, say, but not both. Every measurement 'collapses' the wave function. After the collapse, the wave function, which could have been used to predict outcomes of alternative measurements, has been changed irrevocably: there is no going back to the experiment we opted not to perform. It is a very singular business. Whatever observable we decide to measure, we get a definite result. But the observable that is made definite depends on our whim. The many people who, like Einstein, believe in a real and definite world find this immensely disconcerting. What is out there in the world seems to depend on mere thoughts that come into our mind...
The fact that in quantum mechanics one can choose to measure one but not both of two quantities was called complementarity by Bohr. Pairs of quantities for which it holds are said to be complementary."
(Barbour: 2000, p. 204)

"Contrary to the impression given in many books, quantum mechanics is not about particles in space: it is about systems being in configurations - at 'points' in a Q, or 'hybrid Platonia'. That is something quite different from individual probabilities for individual particles being at different points of ordinary space. Each 'point' is a whole configuration - a 'universe'. The arena formed by the 'points' is unimaginably large. And classical physics puts the system at just one point in the arena. The wave function, in contrast, is in principle everywhere.
This is what I mean by saying that Schrodinger opened the door onto a vast new arena..."
(Barbour: 2000, p. 210)

"... The simplest possible illustration is given by two particles moving on a single line;... together they have a two-dimensional configuration space...
...Many different kinds of prediction can be made, but they are often mutually exclusive. In a very essential way, the predictions refer to the system, not its parts.
... The important thing is that a single point in Q corresponds to positions of both particles. Anyone who has not understood this has not understood quantum mechanics. It is this fact, coupled with complementarity, that leads to the most startling quantum phenomena."
(Barbour: 2000, p. 211)

"... innumerable interference phenomena indicate that, in some sense, the (two) particles (in entangled states or quantum inseparability) are, before any measurement is made, simultaneously present whenever * extends. Since there is no restriction on the distance between the particles, any causal effect on the second particle after the first has been observed would have to be transmitted instantaneously..."
(Barbour: 2000, p. 217)

"Relativity absolutely prohibits the transmission of information faster than light. But, curiously, wave-function collapse does not transmit information. When information about particle 1 has been obtained by an experimentalist, he or she will know immediately what a distant experimentalist can learn about particle 2. But there is no way such information can be transmitted faster than light. There is no conflict with the rules of relativity, though many physicists are concerned that its 'spirit' is violated."

(Barbour: 2000, p. 218)

"... if the position of one particle was measured, the position of the other particle could be immediately established with certainty because of the perfect correlation. Since the second particle, being far away, could not be physically affected by the measurement, but it was known for certain where it would be found, EPR (i.e., Albert Einstein, Boris Podolsky and Nathan Rosen in formulation of their EPR paradox in 1933) concluded that it must have had this definite property before the measurement on the first particle .
... Finally, the choice between momentum or position measurement is a matter of our whim, about which the second particle can know nothing. The only conclusion to draw is that the second particle must have possessed definite position and momentum before any measurements were made at all. However, according to the fundamental rules of quantum mechanics, as exemplified in the Heisenberg uncertainty principle, a quantum particle cannot possess definite momentum and position simultaneously. EPR concluded there must be something wrong - quantum mechanics must be incomplete.
Niels Bohr actually answered EPR quite easily, though not to everyone's satisfaction. His essential point was that quantum mechanics predicts results made in a definite experimental context. We must not think that the two-particle system exists in its own right, with definite properties and independent of the rest of the world. To make position or momentum measurements, we must set up different instruments in the laboratory. Then the total system, consisting of the quantum system and the measuring system, is different in the two cases. Nature is holistic: it is not for us to dictate what Nature is or does. Quantum mechanics is merely a set of rules that brings order into our observations. Einstein never found an answer to this extreme operationalism of Bohr, and remained deeply dissatisfied.
I feel sure that Bohr got closer to the truth than Einstein. However, Bohr too adopted a stance that I believe is ultimately untenable. He insisted that it was wrong to attempt to describe the instruments used in quantum experiments within the framework of quantum theory. The classical world of intruments, space and time must be presupposed if we are ever to talk about quantum experiment and communicate meaningfully with one another..." 

(Barbour: 2000, p. 218-219)

"Despite the sofistication of all his work, in both relativity and quantum mechanics, Einstein retained a naive atomistic philosophy. There are space and time, and distinct autonomous things moving in them. This is the picture of the world that underlies the EPR analysis. In 1949 Einstein said he believed in a 'world of things existing as real objects'. This is his creed in seven words. But what are 'real objects'?
To look at this question, we first accept that distinct identifiable particles can exist. Imagine three of them. There are two possible realities. In the Machian view, the properties of the system are exhausted by the masses of the particles and their separations, but the separations are mutual properties. Apart from the masses, the particles have no attributes that are exclusively their own. They - in the form of a triangle - are a single thing. In the Newtonian view, the particles exist in absolute space and time. These external elements lend the particles attributes - position, momentum, angular momentum - denied in the Machian view. The particles become three things. Absolute space and time are an essential part of atomism."

(Barbour: 2000, p. 220)

"Strong confirmation for quantum mechanics being holistic in a very deep sense was obtained in the 1960s, when John Bell, a British physicist from Belfast, achieved a significant sharpening of the EPR paradox. The essence of the original paradox is the existence of correlations between pairs of quantities - pairs of positions or pairs of momenta - that are always verified if one correlation or the other is tested. By itself, some degree of correlation between the two particles is not mysterious. The EPR-type correlated states are generally created from known uncorellated states of two particles that are then allowed to interact. Even in classical physics, interaction under such circumstances is bound to lead to correlations. Bell posed a sharper question than EPR: is the extent of the quantum correlations compatible with the idea that, before any measurement is made, the system being considered already possesses all the definite properties that could be established by all the measurements that, when performed separately, always lead to a definite result?
Bell's question perfectly reflects Einstein's 'robust realism' - that the two-particle system ought to consist of two separate entities that possess definite properties before any measurements are made. Assuming this, Bell proceeded to derive certain inequalities, justly famous, that impose upper limits on the degree of the correlations that such 'classical' entities could exhibit (tighter correlations would simply be a logical impossibility). He also showed that quantum mechanics can violate these inequalities: the quantum world can be more tightly correlated than any conceivable 'classical world'. Aspect's experiments specifically tested the Bell inequalities and triumphyntly confirmed the quantum predictions..."
(Barbour: 2000, p. 220-221)

"In 1957, Hugh Everett, a student of John Wheeler at Princeton, proposed a novel interpretation of quantum mechanics. Its implications are startling, but for over a decade it attracted little interest until Bryce DeWitt drew wide attention to it, especially by his coinage many worlds to describe the main idea. Everett had used the sober title 'Relative state formulation of quantum mechanics'. One well-known physicist was prompted to call it the 'best-kept secret in physics'. So far as I know, Everett published no other scientific paper. He was already working for the Weapons System Evaluation Group at the Pentagon when his paper was published. He was apparently a chain smoker, and died in his early fifties."
(Barbour: 2000, p. 221-222)

"Everett noted that in quantum mechanics 'there are two fundamentally different ways in which the state function can change': through continuous causal evolution and through the notorious collapse at a measurement. He aimed to eliminate this dichotomy, and show that the very phenomenon that collapse had been introduced to explain - our invariable observation of only one of many different possibilities that quantum mechanics seems to allow - is actually predicted by pure wave mechanics. Collapse is redundant.
The basis of Everett's interpretation is the endemic phenomenon of entanglement. By its very nature, entanglement can arise only in composite systems - those that consist of two or more parts. In fact, an essential element of the many-worlds interpretation as it is now almost universally understood is that the universe can and must be divided into at least two parts - an observing part and an observed part. However, Everett himself looked forward to the application of his ideas in the context of unified field theories, 'where there is no question of ever isolating observers and object systems. They are all represented in a single structure, the field'..."
(Barbour: 2000, p. 222)

"The measurement problem of quantum mechanics is this: how does the entangled state of many possibilities collapse down to just one, and when does it happen? ... You can go on asking quantum mechanics again and again to say when collapse occurs, but it never gives an answer... All that the Copenhagen interpretation can say is that collapse occurs at the latest in the perceptions of the experimentalist. When it happens no one can say - it can only be said that if collapse does not happen we cannot explain the observed phenomena.
But must it happen? Everett came up with a simple - with hindsight obvious - alternative. Collapse does not happen at all: the multiple possibilities represented in the entangled state continue to exist. In each possibility the observer, in different incarnations, sees something different, but what is seen is definite in each case. Each incarnation of the observer sees one of the possible outcomes that the Copenhagen interpretation assumes is created by collapse."
(Barbour: 2000, p. 224)

"Everett's proposal raises two questions. If many worlds do exist, why do we see only one and not all? Why do we not feel the world splitting? Everett answered both by an important property of quantum mechanics called linearity, or the superposition principle. It means that two processes can take place simultaneously without affecting each other.  Consider, for example, Young's explanation of interference between two wave sources. Each source, when active alone, gives rise to a certain wave pattern. If both sources are active, the processes they generate could disturb each other drastically. But this does not happen. The wave pattern when both sources are active is found simply by adding the two wave patterns together. The total effect is very different from either of the individual processes, but in a real sense each continues unaffected by the presence of the other. This is by no means always the case; in so-called non-linear wave processes, the wave pattern from two or more sources cannot be found by simple addition of the patterns from the separate sources acting alone. However, quantum mechanics is linear, so the much simpler situation occurs.
As a result, quantum processes can be regarded as being made up of many individual subprocesses taking place independently of one another... Each subprocess is, so to speak, aware only of itself. There is a beautiful logic to this, since each subprocess is fully described by the quantum laws. There is nothing within the branch as such to indicate that it alone does not constitute the entire history of the universe. It carries on in blithe ignorance of the other branches, which are 'parallel worlds' of which it sees nothing. The branches can nevertheless be very complicated..."
(Barbour: 2000, p. 225)

"Any scientific theory must establish a postulate of psychophysical parallelism: it is necessary to say what elements of the physical theory correspond to actual conscious experience..."

(Barbour: 2000, p. 226)

"... quantum mechanics is doubly indefinite. First, if states of a definite kind are chosen, any state of a composite system is a unique sum of states of its subsystems. For position states... (the) probability distribution is spread out over a huge range of possibilities in which one particle has one definite position and the other particle has one definite position. Positions are always paired together in this way. Everett resolved the apparent conflict between our experience of a unique world and this multiplicity of possibilities by associating a separate and autonomous experience with each. However, he did not address the second indefiniteness:: the states shown as positions... could equally well be represented by, for example, momentum states. Then pairs of momentum states result. Depending on the representation, different sets of parallel worlds are obtained: 'position histories' in the one case, 'momemntum histories' in the other. One quantum evolution yields not only many histories but also many families of different kinds of history.
It was surprisingly long before this difficulty was clearly recognized as preferred-basis problem: a definite kind of history will be obtained only if there exists some distinguished, or preferred, choice of the basis, by which is meant the kind of states used in the representation. The preferred basis problem is the EPR paradox in a different guise. Everett may have instinctively assumed that the position basis is somehow naturally singled out, but there is little evidence in his paper to confirm this.
The first question that must be addressed is surely this: what is real? Everett took the wave function to be the only physical entity. The price for this wave-function monism is the preferred-basis problem. Because the wave functions of composite systems can be represented in so many ways, the application of Everett's ideas to different kinds of representation suggests that one and the same wave function contains not only many histories, but also many kinds of history. It leads to a 'many-many-worlds' interpretation. Some accept this, but I feel there is a more attractive alternative. "
(Barbour: 2000, p. 226-227)

"... in classical relativity, space-time represents all reality - the complete universe. In contrast, a quantum state by itself has no definite meaning until the strategic decision - say, to measure position or momentum - has been taken. The state acquires its full meaning only in conjunction with actual measuring apparatus outside the system. The system must interact with the apparatus to reveal its latent potentialities. At present, its interaction with an apparatus - essentially the rest of the universe - is not fully understood. The quantum state by itself is only part of the story. It may be premature to draw conclusions about the quantum universe from incomplete quantum descriptions of subsystems of it."
(Barbour: 2000, p. 227-228)

"... quantum mechanics as presently formulated needs an external framework. Indeed, the most basic observables, those for position, momentum and angular momentum, all correspond to the 'lent' properties mentioned in the discussion of the EPR paradox. They could not exist without the framework of absolute space, and Mach's principle suggests strongly it is determined by the instantaneous configurations of the universe. Time, moreover, plays an essential role in quantum mechanics yet stands quite outside the description of the quantum state. But ... time is really just a shorthand for the position of everything in the universe, so the configurations of the universe can be expected to play an essential and direct role in a quantum description of the universe... This is what leads me to the dualistic picture of Platonia, the collection of all possible configurations of the universe, and the completely different wave function, conceived of as 'mist' over Platonia. In the language of Everett's theory, this introduces a preferred basis. In answer to the question 'what is real?', I answer 'configurations'.  My book is the attempt to show that they explain both time and the quantum - as different sides of the same coin."
(Barbour: 2000, p. 228)

"... two equations (that) Schrodinger discovered in 1926... (according to Dirac)... explained all of chemistry and most of physics ...
....in every instant we experience creation directly. Creation did not happen in a Big Bang. Creation is here and now, and we can understand the rules that govern it. Schrodinger thought he had found the secret of the quantum prescriptions. Properly understood, what he found were the rules of creation.
... In quantum mechanics, this (the wave function psi) is all that does change. Forget any idea about the particles themselves moving. The space Q of possible configurations, or structures, is given once and for all: it is a timeless configuration space. The instantaneous position of the system is one point of its Q. Evolution in classical Newtonian mechanics is like a bright spot moving, as time passes, over the landscape of Q. I have argued that this is wrong way to think about time. There is neither a passing time nor a moving spot, just a timeless path through the landscape, the track taken by the moving spot in the fiction in which there is time."
(Barbour: 2000, p. 229)

"In quantum mechanics with time... there is no track at all. Instead, Q is covered by the mists... (illustrating the notion) of wave functions and the probabilities associated with them. The red and green mists evolve in a tightly interlocked fashion, while the blue mist, calculated from the other two, describes the change of the probability. All that happens as time passes is that the patterns of mist change. The mists come and go, changing constantly over a landscape that itself never changes.
One of the equations that Schrodinger found governs this process. If psi is known everywhere in Q at a certain time, you know what * will be slightly later. From this new value, you can go on another small step in time, and another, and so on arbitrarily far into the future. The role played here by the red and green mists, the two primary components of psi, is quite interesting: the way the red mist varies in space determines the rate of change of the green mist in time, and vice versa. The two components play a kind of tennis. This equation is sometimes called the time-dependent Schrodinger equation because time features in it. This is not in fact the first equation that Schrodinger discovered.
The first one he found is now usually called the stationary or time-independent Schrodinger equation. This determines what happens in certain special cases in which the two components of psi, the red and green 'mists', oscillate regularly, the increase of one matching the decrease of the other. This has the consequence, as we have already seen for a momentum eigenstate, that the blue mist (the probability density) has a frozen value - it is independent of time (though its value generally changes over Q). Such a state is called a stationary state. This explains the name given to the second equation - its solutions are stationary states. The standard view is that the time-dependent equation is seen as a special case derived from it...
There are intriguing hints that in the quantum mechanics of the universe the roles of these two equations are reversed. The stationary equation (or something like it) may be the fundamental equation, from which the time-dependent equation is derived only as an approximation... "
(Barbour: 2000, p. 230)

"All solutions of the time-dependent equation can be found by adding stationary solutions with different frequencies. Each stationary solution on its own has regular oscillations of its red and green mists, but a constant - in fact static - distribution of its blue mist. But as soon as stationary states with different energies, and hence frequencies, are added together, irregular oscillations commence - in particular in the blue mist, the touchstone of true change. All true change in quantum mechanics comes from intereference between stationary states with different energies. In a system described by a stationary state, no change takes place."
(Barbour: 2000, p. 231)

"If the Machian approach to classical dynamics is correct, quantum cosmology will have no dynamics. It will be timeless. It must also be frameless."

(Barbour: 2000, p. 232)

"(Schrodinger's) stationary equation determines the structures - indeed, creates the structures - of all these amazing atoms and molecules that constitute so much of the matter in the universe, our own bodies included. The equation does it by determining which structures are probable. But I mean creation not only in this sense of the structure of atoms and molecules, but in an even deeper one..."

(Barbour: 2000, p. 235)

"... we found an alternative definition of 'distances' that works in the purely relative configuration space - in Platonia - and owes nothing to absolute space. They are defined by the best-matching procedure, which uses relative configurations and nothing else. In classical physics, this makes it possible to create a purely relative and hence self-contained dynamics. We also found that a sophisticated form of best-matching lies at the heart of general relativity. Best matching would appear to be a basic rule of the world. "

(Barbour: 2000, p. 236)

"What ... is curvature? For any given curve, it is the rate at which its slope changes. But the key thing about a rate of change is that it is with respect to something. That something is all-important. It is a kind of 'distance'. The ordinary quantum-mechanical 'distance' is simply distance in absolute space (times the mass of the particle considered). To eliminate absolute space in classical physics, we replaced it by the Machian best-matching distance. There is no reason why we should not do the same in quantum physics.
... the wave functions that satisfy the Schrodinger conditions in this Machian case are precisely the eigenfunctions of ordinary quantum mechanics for which the angular-momentum eigenvalues are zero. This exactly matches our result in classical mechanics - that the best-matching condition leads to solutions with angular momentum zero...
The quantum counterpart of Machian classical dynamics is a static wave function * on Platonia. The rules that govern its variation from point to point in Platonia involve only the potential and the best-matching 'distance'. Both are 'topographic features' of the timeless arena. Surveyors sent to map it would find them. They would see that the mists of Platonia respect its topography. It determines where the mist collects. "

(Barbour: 2000, p. 237)

"... many people came to the same conclusion: there is a time, but it is hidden in the three degrees of freedom.
According to this insight, the basic framework of quantum mechanics could be preserved, but the time it so urgently needed would be taken from the 'world' to which it was to be applied. Putting it in very figurative terms, one-third of space would become time, while the remaining two-thirds would become two true quantum degrees of freedom. Because time was to be extracted from space, from within the very thing that changes, the time that was to be found was called intrinsic time. The notion of intrinsic time was - and is - a breathtaking idea. But there was a price to be paid, and there was also a closely related problem to be overcome: which third of space is to be time?
... The price and the problem are one and the same. They presented the quantum theoreticians with a head-on collision between the basic principles of their two most fundamental theories - the need for a definite time in quantum mechanics and the denial of a definite time in general relativity."

(Barbour: 2000, p. 245-246)

"At an international meeting on quantum gravity held at Oxford in 1980, Karel Kuchar, concluding his review of the subject, stated that the problem of 'quantum geometrodynamics is not a technical one, but a conceptual one. It consists in the diametrically opposite ways in which relativity and quantum mechanics view the concept of time'."

(Barbour: 2000, p. 246)

"... There has to be different way to think about time.
I believe it was found, perhaps unintentionally, by Bryce DeWitt in 1967. John Wheeler had strongly urged to find the fundamental equation of quantum gravity. It was Wheeler's high priority to find the Schrodinger equation of geometrodynamics...
Dirac's method makes it possible to treat all parts of space on an equal footing, and simply defers to later the problem of time. DeWitt used Dirac's method to write the fascinating equation that, as Kuchar noted, he himself calls 'that damned equation', John Wheeler usually calls the 'Einstein-Schrodinger equation' and everyone else calls the 'Wheeler-DeWitt equation'.
... The Wheeler-DeWitt equation is telling us, in its most direct interpretation, that the universe in its entirety is like some huge molecule in a stationary state and that the different possible configurations of this 'monster molecule' are the instants of time. Quantum cosmology becomes the ultimate extension of the theory of atomic structure, and simultaneously subsumes time.
We can go on to ask what this tells us about time. The implications are as profound as they can be. Time does not exist. There is just the furniture of the world that we call instants of time."
(Barbour: 2000, p. 246-247)

"I believe in a timeless universe for the childlike reason that time cannot be seen - the emperor has no clothes. I believe that the universe is static and is described by something like the Wheeler-DeWitt equation... I believe that it leads to the rules of creation...
According to many accounts, in both mainstream science and religion, the universe either has existed for ever or was created in the distant past. Creation in a primordial fireball is now orthodox science - the Big Bang. But why is it supposed that the universe was created in the past rather than newly created in every instant that is experienced? No two instants are identical. The things we find in one are not exactly the same as the things we find in another. What, then, is the justification for saying that something was created in the past and that its existence has continued into the present? "
(Barbour: 2000, p. 251)

"A classical theory that treats time in a Machian manner can allow the universe only one value of its energy. But then its quantum theory is singular - it can only have one energy eigenvalue. Since quantum dynamics of necessity has more than one energy eigenvalues, quantum dynamics of the universe is impossible. There can only be quantum statics...
Neither Newton's nor Einstein's equations tell us why the universe has its present form. They have to be augmented by information about a past state. We could invoke a deity in the way Einstein was wont, who goes through two steps in creating the universe. First, laws are chosen, then an initial condition is added...
The stationary Schrodinger equation is quite different in this respect. It obviously cannot have initial conditions, either..."

(Barbour: 2000, p. 253)

"There are no laws of nature, just one law of the universe. There is no dichotomy in it - there is no distinction between the law and supplementary initial or boundary conditions. Just one, all-embracing static equation. We can call it the universal equation.... it attaches a ranking - a greater or lesser probability - to each conceivable static configuration of the universe.
... the density of the blue mist can be used to create a collection of configurations in a bag, a heap even, from which the most probable atomic configurations can be drawn at random. Configurations - which are structures - are created as more or less definite potentialities to the extent that the stationary Schrodinger equation tells us to put more or less into the heap. Like the individual structures within it, the heap is static. It is carefully laid up in a Platonic palace, which, since probabilities play such a mysterious role in quantum mechanics, is a kind of 'antechamber of Being'."
(Barbour: 2000, p. 254)

"DeWitt already clearly saw... the crass contradiction between a static quantum universe and our direct experience of time and motion - and hinted at its solution in 1967.... (The key idea of his paper) is that the static probability density obtained by solving the stationary Schrodinger equation for one fixed energy can exhibit the correlations expected in a world that does evolve - classically or quantum mechanically - in time. We can have the appearance of dynamics without any actual dynamics..."
(Barbour: 2000, p. 257)

"... if the universe as a whole is described by a stationary Schrodinger equation and time does not exist at all, how does a Schrodinger equation with time arise?...
... Two static wave patterns (in a space of arbitrarily many dimensions) can, under the appropriate conditions, be interpreted as an evolution in time of the kind expected in accordance with the time-dependent Schrodinger equation. The appearance of time and evolution can arise from timelessness."
(Barbour: 2000, p. 258-259)

"... Schrodinger's enigmatic psi (wave function) covers Platonia. Mist hovers over the eternal landscape. The static mist is a well-behaved solution - an eigenfunction - of the Wheeler-DeWitt equation. There is nothing here an unsuspecting bystander could say looks like time. You have seen mist on a landscape. Did it enter your head that such a thing could explain time? But it can, in principle. The static wave function, simply by its well-behaved response to the landscape it finds, may be induced into a regular wave-like pattern. If so, time can 'emerge' from timelessness... "
(Barbour: 2000, p. 260)

"When... I find myself in Plato's cave and see his demesne of Platonia laid out before me, I can, using my vivid memory of the kingfisher between the banks of the stream where I stood, identify the instant in which death took me. By 'identify the instant', I mean recognize the configuration of riverbank, sunlight and shadow, rippled water and kingfisher's wings - all frozen in the position I last witnessed. As always, I insist that instant of time simply means configuration of the universe..."

(Barbour: 2000, p. 265-266)

"All interpretations of quantum mechanics face two main issues. First, the theory implies the existence of far more 'furniture' in the world than we see. I have suggested that the 'missing furniture' is simply other instants of time that we cannot see because we experience only one at a time. The other issue is why our experience suggest so strongly a macroscopic universe with a unique, almost classical history...."

(Barbour: 2000, p. 268)

"In the 1820s and 1830s, William Rowan Hamilton... established a fascinating and beautiful cennection between the two great paradigms of physical thought of his time - the wave theory of light and the Newtonian dynamics of particles..."
(Barbour: 2000, p. 268)

"Hamilton's work in the 1820s showed... that there are two seemingly quite different ways of explaining the behaviour of light and the functioning of optical instruments...
This insight led to the distinction between wave optics and geometrical optics which uses light rays. Innumerable experiments show that only wave optics, in which light is described by waves, can explain certain phenomena. The earlier theory of light rays simply fails under these circumstances. Equally, there are many cases in which geometrical optics, with its Keplerian light rays, functions perfectly well. We see here the typical situation that arises when a new theory supplants an old one. The new theory invariably uses very different concepts - it 'inhabits a different world' - yet it can explain why the old theory worked as well as it did and why it is that it fails where it does. Where the wave pattern becomes irregular, geometrical optics ceases to be valid."
(Barbour: 2000, p. 270)

"Geometrical optics shows how theories that explain many phenomena impressively and simply can still give a misleading picture..."

(Barbour: 2000, p. 271)

"... in a strict wave theory the rays are not really 'there', but they are present as theoretical constructs. And many phenomena can be explained rather well by assuming that particles really are there. As John Wheeler would say, one has 'particles without particles', or even 'histories without histories'.
In fact, work that Hamilton did about ten years after his optical discoveries shows how apt such a 'Wheelerism' is...
Working entirely within the framework of Newtonian dynamics, Hamilton introduced something he called the principal function...  it is like the mists on configuration space: at each point of the configuration space, it has a value (intensity), the variation of which is governed by a definite equation."
(Barbour: 2000, p. 272)

"I certainly find it difficult to believe that there is a material world in which we currently find ourselves, and some other, quite different, immaterial world we enter after death. Apart from anything else, modern physics suggests very strongly that so-called gross matter - the clay from which we are made - is anything but that. It is almost positively immaterial."

(Barbour: 2000, p. 327)

"You cannot travel back into the past and kill your parents before your conception. In quantum cosmology, you can travel back to a parallel universe, and there kill your parents before they conceive you. However, we have to be careful about the use of 'you'. The person who 'travels' to these other worlds is not exactly you now.
... I find the idea of time travel boring compared with the reality of our normal existence. Each time capsule that represents an experienced Now reflects innumerable other Nows all over Platonia, some of them vividly. In a very real sense, our memories make us present in what we call the past, and our anticipations give us a foretaste of what we call the future. Why do we need time machines if our very existence is a kind of being present everywhere in what can be? This is very Leibnizian. We are all part of one another, and we are each just the totality of things seen from our own viewpoint."
(Barbour: 2000, p. 329)

"... I wonder if, at root, there is that much difference between the Heraclitan and Parmenidean schools, representing 'verbs' and 'nouns' respectively. If my definition of an instant of time is accepted, it becomes hard to say in what respect those two great Pre-Socratics might differ. The two best-known sayings attributed to Heraclitus are 'Everything flows' (Panta rei) and the very sentence which, entirely unconsciously, I used to clinch the argument that the cat Lucy who leapt to catch the swift was not the cat who landed with her prey: 'One cannot step into the same river twice'. There is always change from one instant to another - no two are alike. But that is just what I have tried to capture with the notion of Platonia as the collection of all distinct instants. Heraclitus argued that the appearance of permanence, of enduring substance, is an illusion created by the laws that govern change..."
(Barbour: 2000, p. 330)

Go to Julian Barbour's official home page

Site Map
Best Excerpts
Index of Articles
Picture Gallery