#time reborn

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The one ancient philosopher who did speculate about the paths taken by falling bodies – Aristotle – proposed an answer that was easy to disprove but nonetheless was blindly believed for more than a thousand years

Time Reborn: From the Crisis of Physics to the Future of the Universe by Lee Smolin

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The Evolution of the Laws of Physics

The Evolution of the Laws of Physics - Lee Smolin (SETI Talks)

SETI Talks archive: http://seti.org/talksProf. Lee Smolin of the Perimeter Institute in Waterloo, Canada, author and theoretical physcist, w

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"To rebel against the precariousness of life, to reject uncertainty, to adopt a zero tolerance to risk, to imagine that life can be organized to completely eliminate danger, is to think outside time. To be human is to live suspended between danger and opportunity."

— Lee Smolin, Time Reborn

Lee Smolin is a theoretical physicist who has been since 2001 a founding and senior faculty member at Perimeter Institute for Theoretical Ph

[kakitunder]

John Archibald Wheeler used to write physics equations on the blackboard, stand back, and say, “Now I’ll clap my hands and a universe will spring into existence.” Of course, it didn’t. Stephen Hawking asked, in A Brief History of Time, “What is it that breathes fire into the equations and makes a universe for them to describe?” Such utterances reveal the absurdity of the view that mathematics is prior to nature. Math in reality comes after nature. It has no generative power. Another way to say this is that in mathematics conclusions are forced by logical implication, whereas in nature events are generated by causal processes acting in time. This is not the same thing; logical implications can model aspects of causal processes, but they’re not identical to causal processes. Logic is not the mirror of causality. Logic and mathematics capture aspects of nature, but never the whole of nature. There are aspects of the real universe that will never be representable in mathematics. One of them is that in the real world it is always some particular moment. So one of the most important lessons that follow once we grasp the reality of time is that nature cannot be captured in any single logical or mathematical system. The universe simply is — or better yet, happens. It is unique. It happens once, as does each event — each unique event — that nature comprises. Why it is, why there is something rather than nothing, is probably not a question that has an answer — save that, perhaps, to exist is to be in relation to other things that exist and the universe is simply the set of all those relations. The universe itself has no relation to anything outside it. The question of why it exists rather than not is beyond the scope of the principle of sufficient reason. What form are the discoveries of cosmology to be expressed in, if not in a single timeless mathematical law acting on a timeless space of initial conditions? This is a question on which the future of cosmology depends. With a little thought, some possible answers emerge. The examples I have given, such as cosmological natural selection and the principle of precedence, demonstrate that we can conceive of testable scientific theories that go beyond the Newtonian paradigm. It is good to reflect on the fact that in the history of science there are many hypotheses that don’t need to be stated mathematically. And in some cases mathematics is not needed to work out their consequences. An example is the theory of natural selection; aspects of it have been captured in simple mathematical models, but no single model captures the whole variety of mechanisms by which natural selection acts in nature. Indeed, new mechanisms of evolution may emerge at any time, as new species are born. To be scientific, hypotheses must suggest observations by which they could be verified or falsified. Sometimes this requires expression in mathematics; sometimes it doesn’t. Mathematics is one language of science, and it is a powerful and important method. But its application to science is based on an identification between results of mathematical calculations and experimental results, and since the experiments take place outside mathematics, in the real world, the link between the two must be stated in ordinary language. Mathematics is a great tool, but the ultimate governing language of science is language.

Lee Smolin: Time Reborn

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A star can be characterized as a system driven far from equilibrium by a steady flow of energy through it. The energy comes from both nuclear and gravitational potential energy, which is slowly converted into starlight in a range of frequencies. The starlight then illuminates the surfaces of planets, like ours, driving them into far-from-equilibrium states of their own. This is an example of a general principle: Flows of energy through open systems tend to drive them to states of higher organization. (“Open systems,” recall, are any bounded systems that can exchange energy with their surroundings.) We can call this the principle of driven self-organization. If the principle of sufficient reason is the paramount explanatory principle in nature and the identity of the indiscernibles her prince, the principle of driven self-organization is the good angel who does the detailed work in myriads of stars and galaxies to ensure a diverse, complex universe. [...] A ubiquitous feature of such self-organizing systems is that they are stabilized by feedback mechanisms. Any living thing is an intricate network of feedback processes that regulate, channel, and stabilize the flows of energy and material through it. [...] Patterns in space and time are formed when different feedback mechanisms compete to control a system. When a positive-feedback mechanism competes with a negative-feedback mechanism but they act on different scales, you may get patterns in space. [...] [O]ur present universe is characterized by structure and complexity on a wide range of scales, from the organization of molecules in living cells to the organization of galaxies into clusters. There is a hierarchy of self-organizing systems, driven by energy flows and stabilized and shaped by feedback processes. [...] What do we see when we look back? We see a universe evolving from less to more structured, from equilibrium to complexity. [...] [I]f we consider the solar system as an isolated system, the fact that parts of it are undergoing self-organization is compatible with an overall increase of its entropy. The system as a whole is trying to come to equilibrium and will increase its entropy where it can. The second law is doing its best to drive the solar system to equilibrium, but as long as there’s a big star radiating hot photons into cold space, that equilibrium is postponed. While it’s postponed, molecules can ride the energy flow to greater and greater states of organization and complexity. And stars burn for billions of years, so there’s lots of time for complexity to proliferate. The existence of stars has much to do with why the universe is far from equilibrium almost 14 billion years after its formation. But why are there stars? If the universe must tend toward entropy and disorder, how is it that stars, which drive the universe away from equilibrium, are ubiquitous? To put this another way: If the universe is to be Leibnizian, something like stars must exist. What features of the laws of nature guarantee that they do? The physics of stars relies on two unusual features of the laws of nature. The first is incredibly fine tuning in the parameters that govern physics. These fine tunings include the masses of the elementary particles and the strengths of the four forces. They make nuclear fusion possible, so the hydrogen gas comprising a star does not behave as it would in the absence of nuclear forces. Rather than just moving around randomly, the hydrogen atoms jammed together at the center of a star can interact in a new way. They fuse to make helium and a few other light elements. It’s as if you were trapped in a cell, day after day, in the same boring equilibrium. Every hour is like every other. Then all of a sudden a door opens where there was none before, and you escape into a whole new world. The laws of thermodynamics applied to generic atoms would never predict nuclear fusion and the possibilities it gives rise to. The second unusual feature has to do with the behavior of systems held together by the force of gravity. Very simply, gravity subverts our naïve ideas about thermodynamics. An everyday observation, which is also a consequence of the second law of thermodynamics, is that heat flows from hotter bodies to colder bodies. Ice melts. Water on the stove boils. Heat stops flowing when the temperature of the two bodies is the same; they have reached the state of equilibrium. Normally when we take energy out of a body, its temperature goes down, and when we put energy into a body, it heats up. So when heat flows from a hotter body to a colder body, the latter heats up and the former cools down. This goes on until they’re at the same temperature. This is why the air in a room is at a single temperature. If it weren’t, energy would flow from the warmer side to the cooler until they reached a common temperature. This behavior makes the system in equilibrium stable against the effects of small fluctuations. Suppose, by a small fluctuation, one side of a room became a bit warmer than the other. Energy would flow from the warm side, cooling it, to the cooler side, warming it, so that soon the temperature is uniform again. Most systems work in this intuitive way. But not all. Imagine there’s a gas that works the other way, cooling down when you add energy to it and heating up when you take energy away. This may seem counterintuitive, but there are such gases. They have to be unstable. Suppose you start off with all of this kind of gas in a room at the same temperature. A little fluctuation moves a bit of energy from the left side to the right. Then the left side heats up, while the right side cools down. This causes more energy to flow from the left side, the hot side, to the cold side. As it does, the left side won’t cool down; rather, it gets even hotter. And as more energy flows into the cool right side, that side gets even cooler. Soon you have a runaway instability, in which the two sides of the room are driven to continually increase their temperature difference. Now let’s look at just the hot side and repeat the scenario. Suppose another fluctuation appears, cooling the center of the hot side a bit. The same phenomenon acts as positive feedback to further cool the center and further heat the region around it. As time goes on, the little fluctuation grows into a feature. This can happen again and again. Soon you have a complex pattern of cold and hot regions. A system that works this way naturally drives itself to form complex patterns. It’s hard to predict where such systems will end up, because there are a huge number of heterogeneous, patterned configurations it might evolve toward. We call these anti-thermodynamic systems. The second law still operates in them, but because putting energy into a region cools it down, the state in which the gas is uniformly distributed is highly unstable. Systems held together by gravity behave in this crazy way. Stars, solar systems, galaxies, and black holes are all anti-thermodynamic. They cool down when you put energy into them. This means that all these systems are unstable. The instabilities drive them away from uniformity and stimulate the formation of patterns in space and time. This has a lot to do with why the universe is not in equilibrium 13.7 billion years after its origin. The increasing structure and complexity that characterize the universe’s history are largely explained by the fact that the gravitationally-bound systems filling it, from clusters of galaxies to stars, are anti-thermodynamic. It’s easy to understand why such systems are anti-thermodynamic. Two basic features differentiate gravity from the other forces: The gravitational force is (1) long-range and (2) universally attractive. Consider a planet in orbit around a star. If you put energy in, it will move to an orbit farther from the star, where it moves slower. So putting energy in decreases the speed of the planet, and this lowers the system’s temperature — because temperature is just the average speed of things in the system. Conversely, if you take energy out of the solar system, the planet must respond by falling closer to the star, where it moves faster. Hence, taking energy out heats up the system. We can compare this with the behavior of an atom, which is held together by the electric force between charges. Like gravity, the electric force acts over long distances, but it differs by being attractive only between opposite charges. A positively-charged proton will attract a negatively-charged electron, but once the electron is bound to the proton the resulting atom has no net charge. The force is said to saturate, and the atom does not attract any other particles to it. A solar system works the opposite way, because when a star attracts some planets, the resulting system is even more attractive to passing bodies than the star alone would have been. So here’s another instability — a gravitationally-bound system will attract still more bodies to it. This anti-thermodynamic behavior manifests itself in the devolution of star clusters. If a star cluster were to act thermodynamically, it would reach equilibrium — in this case, a state in which all its stars had the same average speed and stayed clustered forever. Instead, what happens is that a star cluster slowly dissipates. This happens in an interesting way. Every once in a while a star comes close to a double star — that is, two stars in orbit around each other. A close approach can result in a narrower orbit for the double star. This orbital shrinking releases energy, which is imparted to the third star. The third star now has enough energy to escape the cluster, and it begins a journey off into space. After a long time, little is left of the star cluster except some double stars in close orbits and a cloud of fast-moving stars streaming away from the cluster. This does not contradict the second law, only a naïve interpretation of it. The law that entropy should usually increase just codifies the truism that the more ways there are for something to happen, the more likely it is that it will. Normal thermodynamic systems end up in the single, boring state of uniform equilibrium; gravitationally-bound, anti-thermodynamic systems end up in one of a large number of highly heterogeneous states. So the fact that our universe is interesting has a threefold explanation: The principle of driven self-organization acts over a myriad of subsystems and scales, from the molecular to the galactic, evolving them to states of ever increasing complexity. The engines driving that process are the stars, which exist because of a combination of the fine tuning of the fundamental laws and the anti-thermodynamic nature of gravity. But these forces can produce a universe filled with stars and galaxies only if the initial conditions of the universe are strongly time-asymmetric.

Lee Smolin: Time Reborn

[kakitunder]

Shape dynamics was created by following a chain of thought proposed by Julian Barbour, whose timeless quantum cosmology was discussed in chapter 7. Barbour is a great advocate of the relational philosophy, and the road to shape dynamics began with his insistence on making physics as relational as possible. Many of the key steps were taken by him over the last decade, with Niall Ó Murchadha and several young collaborators, but the final pieces were put in place in the summer and fall of 2010 by a trio of young people working at Perimeter Institute: graduate students Sean Gryb and Henrique Gomes and a postdoc, Tim Koslowski. Once you know the basic ideas of relativity theory, it’s easy to understand shape dynamics, because that theory is a natural next step. Let’s recall some aspects of simultaneity: It’s meaningful to talk about two adjacent events occurring simultaneously. We can also order them in time, and it makes sense to do so, because one event could be the cause of the other. But when we try to order events that are far from each other, we find there is no absolute ordering that all observers can agree on. For some observers, the two events may be simultaneous; for other observers, one event may appear to be in the past of the other. Barbour tells us that size behaves the same way. If we have two adjacent objects, it makes sense to order them by size: If you can put a mouse into a box, it makes sense to say that the mouse is smaller than the box. If you have two soccer balls, it makes sense to say they have the same diameter. These comparisons make physical sense, and all observers will agree about them. But now let’s ask if the mouse here is smaller than a box in the next galaxy. Does this question still make sense? Does it have an answer all observers will agree on? The problem is that because they’re far away from each other, you cannot put the mouse into the box to see whether it fits. To answer the question, you can move the box to where the mouse is and see if the mouse fits inside. But this answers a different question, because now the box and the mouse are in the same place. How do we know there’s not some physical effect expanding everything we move into our galaxy, so that a box the size of a mouse’s eye becomes, en route, large enough to enclose the mouse? We might leave the box where it is and instead send a ruler to it. But how do we know that the ruler doesn’t suffer the reverse effect, shrinking as it travels from mouse to faraway box? This is one line of thought that led Barbour and friends to propose that it’s not sensible to compare the sizes of objects distant from one another. What you can do is compare shapes, because shapes are not subject to the same kind of arbitrary modification. The one exception to the relativity of size is that the volume of the whole universe at each moment of time must remain unchanged. It’s not easy to explain this in nontechnical language, but what it means is that if you shrink everything at one place, there must at the same time be somewhere else where you compensate by enlarging everything by the same amount, so the overall volume of the universe doesn’t change. The volume can still of course change in time as the universe expands. Although shape dynamics is radical when it comes to sizes, it’s conservative when it comes to time. There’s a single rate at which time flows. It’s the same throughout the universe, and you aren’t allowed to alter it. General relativity is more or less the opposite. Sizes of objects are fixed and remain fixed when you move them around, so it’s meaningful to compare the sizes of distant things. What general relativity is flexible about is the rate of time. It is not meaningful to ask whether a clock distant from us is running fast or slow with respect to a clock near us, because the speeding-up and slowing-down of distant clocks are among the funhouse changes that observers will disagree about. Even if you synchronize your watch with a distant clock, they can go out of sync, because there’s no physical meaning to their rates staying the same. In a word, in general relativity size is universal and time is relative, whereas in shape dynamics time is universal and size is relative. Remarkably, though, these two theories are equivalent to each other, because you can — by a clever mathematical trick that isn’t necessary to go into here — trade the relativity of time for the relativity of size. So you can describe the history of the universe in two ways, in the language of general relativity or the language of shape dynamics. The physical content of the two descriptions will be the same, and any question about an observable quantity will have the same answer. When that history is described in the language of general relativity, the definition of time is arbitrary. Time is relative and there’s no meaning to what it is at distant locations. But when the history is described in the language of shape dynamics, a universal notion of time is revealed. The price you pay is that size becomes relative and it becomes meaningless to compare the sizes of objects far from one another. Like the wave/particle picture of quantum theory, this is an example of what physicists call a duality — two descriptions of a single phenomenon, each of which is complete yet incompatible with the other. This particular duality is one of the deepest discoveries of contemporary theoretical physics. It was proposed in a different form in 1995 by Juan Maldacena in the context of string theory and has since become the most influential idea in that field. As of this writing, the exact relationship between shape dynamics and Maldacena’s duality is unclear, but it seems likely that there’s a correspondence.

Lee Smolin: Time Reborn

[kakitunder]

The best thought-through approach to making sense of the quantum cosmology framed by the Wheeler-DeWitt equations has been proposed by the British physicist, philosopher, and historian of science Julian Barbour, who described it in his 1999 book, The End of Time. Barbour’s idea is radical but not difficult to explain in words. He asserts that all that exists, fundamentally, is a vast collection of frozen moments. Each moment has the form of a configuration of the universe. Each configuration exists — and is experienced by any beings caught in that configuration — as a moment of time. Barbour calls the collection of all the moments “the heap of moments.” The moments in the heap don’t follow each other, one after the other. There’s no order to them. They simply are. In Barbour’s metaphysical picture, nothing at all exists except these pure moments of time. You may object, “But I experience time passing.” Barbour says you don’t. All any of us experience, he insists, is moments — snapshots of experience. Snap your fingers — that was one snapshot, one moment in the heap. Snap your fingers again — that’s another moment. You have the impression that the second followed the first, but that’s an illusion. You think so because in the second moment you have a memory of the first moment. But that memory is not an experience of time passing (which Barbour says never happens); it’s just that the memory of the first moment is part of the experience of the second moment. All we experience — and all that’s real, according to Barbour — are the individual moments in the heap. However, there’s one bit of structure in the heap. Moments can be represented more than once. You can then speak of the relative frequency of moments; one moment may be present a billion times more than another moment. These relative frequencies of moments are what the probabilities given by the quantum state refer to. Two configurations have a relative probability to appear in the heap, given by their relative probability in the quantum state. That’s all there is. There’s one quantum universe, described by one quantum state. That universe consists of a very large collection of moments. Some are more common than others. Some, indeed, are vastly more common than others. Some of the common configurations in the heap are boring. They describe a moment of time in a universe filled with a gas of photons, or a gas of hydrogen atoms. Barbour asserts that in the actual quantum state of the universe, most of these boring configurations have small volume. Hence he predicts a correlation between being small and being boring. If we assumed the existence of time, we would say that the universe was boring when it was small. Barbour says it is enough to say that being small and being boring are highly correlated properties of moments in the heap. Other configurations in the heap are interesting — full of complexity, with living beings like ourselves living on planets orbiting stars in galaxies, which are themselves arranged in sheets and clusters. Barbour asserts that in the right quantum state, the property of being full of complexity and life correlates with a large volume. Thus many, and perhaps most, of the configurations in the heap with large volumes will have living beings in them. Furthermore, Barbour asserts that in the right quantum state, the most common configurations have structures that refer implicitly to other moments. These references are what Barbour calls “time capsules.” They are memories, books, artifacts, fossils, DNA, and so on. They tell a story open to interpretation in terms of a sequence of moments in which things happened that built on each other, leading to complexity. That is, the time capsules support the illusion that time is passing. According to Barbour’s theory, causality, too, is an illusion. Nothing can be the cause of anything, because in actuality nothing is happening in the universe. There’s just a vast pile of moments, some of which are experienced by beings like ourselves. In reality, each experience of each moment is only that — unconnected to the rest. There are moments, but there is no ordering of them, no passage of time. But the Wheeler-DeWitt equations do allow approximate notions of order and causality to emerge, so that there are correlations among the most common moments — correlations that make it appear as if there were a succession of moments in time, between which causal processes could operate. To a high degree of approximation, the story of a succession of moments can be helpful for explaining the structures that occur in the moments. But it is not a fundamental story, and when looked at closely enough, there is no order and no causality, just a pile of moments. [...] Barbour’s version of timeless quantum cosmology offers palpable consolation for our mortality. I can feel it. I wish I could believe it. You experience yourself in a collection of moments. According to Barbour, that’s all there is. Those moments always are, eternally. The past is not lost. Past, present, and future are with us, always. Your experience may figure in a finite set of moments, but those moments never go away or cease. So nothing comes to an end when you come to your last day. It’s just that now you are experiencing a moment that has all the memories you will ever have. But nothing ceases, because nothing ever started. The fear of death is based on an illusion, which in turn is based on an intellectual mistake. There’s no flow of time running out, because there’s no flow of time. There are just, and always are, and always will be, the moments of your life.

Lee Smolin: Time Reborn

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Throughout history, the idea that time is an illusion and that the laws of physics are fixed or ‘eternal’ has been a religious, philosophical and scientific commonplace...