The Flow of Time
Roger Penrose : I think there's always something paradoxical about the way we seem to perceive time to pass and the way physics describes time. And partly it's a question of is there a clear temporal order of things in our perceptions or do we somehow put lots of things together and form pictures of things in which temporal order is all part of one thing..and I think we see this most clearly in Music where music is something which has a fundamentally temporal character and it's just nothing without the passage of time, that's a crucial part of what music is. And yet there is something of a whole there which you grasp as a whole, and there's something of the paradox of how time on the one hand seems to pass and each moment is an independent thing yet there is a kind of wholeness about it which we don't see in our present picture.
Faun Flynn (composer): We only know about time by the things that happen in it. We're conscious of the occurrence of events. We're not conscious of time in any other way.
Narrator : In our world, time flows, but never from old age to youth. Every age has tried to understand how our time on this world fits with the larger workings of eternity, and has tried to explain the flow of time with the intellectual tools it had to hand. In the Medieval period these tools were religion and Music.
Faun Flynn : The difference between the Medieval view of time and our view of time is quite considerable. If you consider the way that the Medieval world was, one of the most controlling and powerful forces in the Medieval world was the church. They actually saw that Music is directly connected to our perception of time. They liked Plainsong; music that just had one theme that was sung by everyone. To them, the idea of a single line of music, they equated this directly with the idea of the eternal, of God.
Narrator : To the Medieval world, there were two kinds of time:God's and our's. For God, all eternity, past and future was laid out. Only for us does time flow.
Bishop at Durham: God is in fact outside time (Fact? -TC) so there's no 'before' for God. He's present with each bit of our temporal story, and so he has a different way of knowing what's going to happen. Aquinas has the image of God standing on a hill overlooking a valley and we think of the history of this world as a caravan of travellers going through the valley. And God is related to that caravan whatever point it happens to be in its progress through the valley. The caravan moves but God doesn't and God has full awareness of everything happening in the valley but has so without having to alter his position.
Faun Flynn : In the Christian view of the world(up to about the 17th century) one very much gets the view that heaven is a world that time is not experienced in the way that it is experienced on earth. Those poor mortals who live on earth have to undergo the vagaries of worldly mundane existence.
Narrator : Before the scientific revolution, time was deemed an inexplicable part of God's purpose. An unknowable flow which cuts us off from the changeless perfection of eternity.
Bishop : This world is a place of trial for human beings. There's a degree of pessimism about the way the world is, and I can find that reflected in the language of the prayers used in the medieval monastery, that was here before the reformation. Every night before they went to bed the last prayer that was said in that service asked God to protect them through the silent hours of the night, so that we who are wearied by the changes and chances of this fleeting world may rest upon thy eternal changelessness.
Narrator : Medieval man's divided attitude to time is summed up in their cathedrals. They were built as monuments to the changelessness of eternity; yet it was recognised that time would inextricably grind even them away.
Bishop : Durham cathedral is a bit like a forest of oaks saying "here is the permanence of God". The huge thickness of the pillars emphasise solidity and permanence, in dramatic contrast to our fleeting world.
Narrator : Medieval architecture and music were a celebration of Gods permanence, but the study of these things, particularly music, began the transformation of the Medieval mind-set.
Faun Flynn : If you consider that the people who were commissioning the building of the cathedrals were the same people who were commissioning music, they very much wanted to elicit the same emotional response from people with both these things. They wanted a sense of awe. They were meant to be monuments to eternity. One is permanence in motion, one is permanence at rest.
Narrator : Just as architecture required the ability to unfold a structure in space, so music required the ability to unfold a structure in time. Music was one of the places where the mathematical and scientific understanding of time began.
Faun Flynn : If you consider what every educated man was expected to know, it consisted of the classical quadrivia, which was constituted of geometry, arithmetic, music and astronomy . So you can see that these are very important things and they all go together.
Narrator : The medieval study of time in music and then in Geometry influenced the fledgling sciences of mechanics and astronomy.
Physicist : There'd been astronomy been investigated the heavens , the heavens are cyclical and perfect, they don't change. On earth though everything changes and it was thought that many things on earth were not susceptible to scientific analysis. And Galileo changes that. Galileo was one of the first people to make an adequate attempt to mathematize nature and whereas the entire science of change, the entire understanding of the world that we lived in came under the general heading of 'Motion' (you know from chicken to egg and so on) ; what Galileo Does is he creates a mathematized science of motion, so he mathematizes the fall of a body, and shows that one can mathematize it in a parabolic trajectory. And Newton just just goes way beyond that.
Narrator : Where the Medieval Man saw permanence, the Renaissance man now saw change.
Physicist : He (Newton) thinks of a curve as a point being drawn out through time and when the point moves across it marks out a line. Curves, as it were, have their own velocity. You can express any curve in terms of the rate at which that curve is changing with respect to time. It's absolutely the most significant contribution to science that there has been.
Narrator : Our lives are an infinite series of present moments, moments which Newton used to calculate motion. Time, the agent of dying and decay, in Newton's hands becomes the agent of motion and progress.
Physicist : The triumph of Newton is to link the celestial and the terrestrial . He shows that the Law of Universal Gravitation applies to things happening down here on Earth as much as they explain the orbits of planets around the sun and that is a remarkable achievement.
Narrator : Newton's science of motion and his mathematics of time underlay the technological revolution that propelled humanity forwards. Newton's idea that space and time together formed a simple rigid framework dominated all thinking until the very last years of the 19th century. Then a problem occurred: scientists, experimenting with light found that no matter what they did to it, they could never alter the speed at which it travelled. This, and other anomalies, eventually led Einstein to his Theory of Relativity in which he said that the speed of light is the only absolute constant, and that space and time are variable.
Physicist : Einstein's Theory of Relativity was really the death-knell for the old concepts of space and time. Einstein showed that Absolute Space and Absolute Time could not exist any longer.
Narrator : According to the Theory of Relativity, space and time were no longer a rigid framework but were instead a fabric which could be stretched and distorted.
Physicist : Einstein in fact had 2 theories of relativity. In one he showed that time can slow down if you travel very fast, close to the speed of light. That was in his Special Theory of Relativity. In general Relativity, he showed that time can slow down if you sit in a strong gravitational field.
Narrator : Just as a magnet creates a magnetic field, so all massive objects create around themselves a gravity field , and just as a magnetic field affects objects within it, so a gravitational field affects not just objects, but light and even time; bending, stretching or compressing it. The more massive the object, the greater the field it creates, and the more it bends space/time.
Physicist : Imagine you approach a massive star. The closer you get to the star's gravitational field,the slower your clock will run. Even your biological clock, your whole concept of time will be running more slowly than it did when you were further away from the star. [I doubt that it affects the biological clock,gravity affects photons and thus the nature of "an event",if the actual brain's capacity to perceive time is affected too,then I don't see how -LB]
Narrator : The by-product of time slowing down is time-travel to the future.
Physicist : Both Einstein's Theories of Relativity say that travelling to the future is allowed; in fact we've proven it experimentally. One way is to travel very fast, so you head off in a rocket,close to the speed of light and come back again. Because you've travelled very fast your clocks will have run more slowly and so if you've been away for one year according to your clock, maybe ten years have gone by on earth; so, in essence you've travelled 9 years into the future. Another way to travel to the future is to orbit a massive star. If you do it for a year, again, you may come back to find again that ten years have elapsed on earth. So either way time travel to the future is possible.
Narrator : This is a fact that we've got to deal with. Satellites orbiting the earth do travel minutely in time; because of the speed they travel their on-board clocks gain milliseconds relative to clocks on earth.
Physicist : Time travel to the past however is a bit more tricky. Despite that, Einstein's Theory of Relativity. says that it is allowed. It was shown half a century ago in fact that there are solutions to Einstein's equations; the mathematics shows that time travel to the past is possible.
Narrator : One candidate for how time travel to the past might be physically possible was via one of the University's more exotic features: Black holes.
Physicist : Normally we think of a black hole, a collapsed star, as being a point of zero size and infinite density surrounded by what's known as the event horizon, the point of no return. But most stars actually spin, and when they collapse they will begin to spin more rapidly. And the spinning star that becomes a spinning black hole doesn't have a point, a singularity in the centre; its singularity looks like a ring, a dough-nut. One possibility was that maybe we could travel into a black hole, avoid the singularity, and travel through the middle and come out the other side. Because space and time were linked, you would not only have to come out in another point in space, but in time as well. This sounds like it would be the ultimate freedom for us that we can time travel; Einstein gives us this wonderful freedom of moving back, changing history, going to the future, seeing what things are like and coming back again, finding what mistakes we might make and then avoid them. This would imply that the past, present and future all exist. There is no present moment to distinguish past from future. All times co-exist, time just is. And so the future is already out there. The only way to understand this was to link the 3 dimensions of space with the one dimension of time to what became known as 4-dimensional space/time.
Roger Penrose : Space-time is certainly different stuff from space because its 4 dimensional instead of 3-D (RP larfs!) which is a big diff. Time really has to be brought into the picture; this one thing which is space/time.
Physicist : Just imagine what this might be like: 3-D space implies a volume, and you can move any where in that volume. Once you add time as a 4th dimension, another axis, then this block of space/time would contain within it past, present and future, all at once. Time is frozen, all times exist together; so just as you can say "over here, over there" in 3-D space, you can talk about "over then", in 4-D space/time.
Roger Penrose : It's a way of looking at things if you like which physically we seem to be forced into. I say physically from the point of view of what the theory of rel. tells us. And Relativity is remarkably well tested, I mean, 14 places of decimal, its just incredible. So we know that this theory does describe the universe to an extraordinarily precise degree, so we have to take it seriously. And that theory tells us that we have to regard space and time as one thing, its all out there, its one thing. In the same sense that space is out there, time is out there.
Narrator : Like the Medieval God's-view of time, Einstein's physics says that the future is already out there. The moments of our lives are just waiting for us to step into them.
Roger Penrose : But there's no more problem about the future being out there than saying that space is out there. You say, "Mars is out there", but why is that more comprehensible than saying "next week is out there"? Its just as far away in a certain sense.
Physicist : If you take this block of 4-D space/time literally, it means you have to abandon free will. It means not only is the future pre-ordained, but its already there, its already happened. There's no point in making any decisions, whatever you do has already happened. If I choose to drop this stone into a pond, I think of it being my own free choice, but of course in 4-D space/time I had no choice in dropping the stone ; the splash is already there in the future and so we lose all free will. If time travel was possible, you can imagine people coming back from the future to visit us; its no good us saying, "you cant exist - you haven't happened yet".They've come from a time which they consider to be their 'now' and for them we're in their path.
Roger Penrose : So this means that in a sense, the present past and future are out there, and that also gives us a very deterministic view of the world. We have no control of what happens in the future because its all laid out. I think the trouble that people have with this idea is that you think the future is under your control, to some degree, and so this means that if the future's laid out then in a sense its not under your control.
Physicist : Personally I'm very uncomfortable about the block universe idea. Now this may be just a gut feeling or just irrational, but can't accept the future's already 'out there'. I don't accept that I don't have any free will.
Roger Penrose : I think there is a positive side to this picture of space and time being laid out there as 4 dimensions, because it tells you that all times are there once and it can affect the way one thinks about people who have died. I mean, I remember thinking in this kind of way when my mother died. In some sense she was still there because her existence is still out there in space/time although in our time she is not alive. A colleague of mine had a son who died in tragic circumstances and I presented this idea to him and it helped his understanding also. This was before I heard that Einstein had a colleague died and he wrote to the man's wife that Bessa was still out there, and that somehow this was reassuring. I certainly think this way often, that space/time is laid out and that things in the past and things in the future are out there still.
Narrator : But almost at the same time that Relativity was gaining universal acceptance a radically different picture of the universe was emerging.
Physicist : The way out if you don't want to accept the block universe idea is quantum mechanics.Now, Quantum Mechanics is the second great discovery of the 20th century physics and that states that the future isn't predetermined and preordained.
Narrator : Quantum Mechanics was born out of a series of experiments whose results even today have no satisfactory explanation. Relativity works at the large scale where it provides exact predictions as to what will happen next. But when physicists started looking down at the atomic and sub-atomic level, the familiar laws failed. At this level, there were no certainties, only probabilities. How can the future of the universe be already out there if the future of a single molecule is so utterly unpredictable?
Physicist : Before we look to see what the atom is doing, not only is there a gap in our knowledge, the atom itself has not decided what to do. It had an infinite number of choices to make, it will be doing all those choices all at once, and its only when we look to see what is happening do we force it to make a choice. In Quantum Mechanics the future is not determined, and so Quantum Mechanics in a sense rescues us and rescues free will.
Roger Penrose : In a sense you don't have the future laid out in Quantum Mechanics So Quantum Mechanics. is basically different in the way we look at it. You do have this indeterminacy about the future and a necessary feature of this is its incompatibility with Special Relativity. So we have these 2 great theories, both of which are extremely accurate, tell us something about how the world operates, something very insightful and profound and accurate, but they're incompatible with each other. So there's no doubt there's something missing here. How important it is to how we 'feel' the passage of time is I think very important.
Narrator : The tragedy of modern physics is that it explains so much of the objective universe but at the cost of what we subjectively feel; about our conscious free will and our feeling that time does flow.
Faun Flynn : I very much think there's a flow to time. If you consider what music would be like if there was no flow to time. You couldn't have music if you didn't have memory, or if you didn't have an expectation generated by that memory. You'd have an isolated note in the 'now'. Music unfolds in time in such a way that we have a memory of what we've heard, and this memory conditions to what we expect. This of course is something that everybody is familiar with, because if you hear ( 7 note scale played on piano) you have a very strong expectation that the next note will be (plays final octave note of scale) . Music is a distillation or a side-effect of that mental faculty we employ to perceive time, and things changing in time.
Roger Penrose : The question of the passage of time is something the scientists have rather set aside, and taking the view that its not really physics, it's a subjective issue; and subjective questions are not part of science. Now when you start talking about phenomena like one's own perception of the passage of time, then that is a subjective thing. And that's almost a taboo subject for science because it's subjective. The physical world at least according to Relativity, is out there, and there is no flow of time, it's just there; whereas our feeling (we have this feeling of the passage of time) are intimately connected to our perceptions.
Physicist : We have this subjective feeling, that time goes by, but physicists would argue this is just an illusion.
Roger Penrose : Yes I think physicists would agree that the feeling of time passing is simply an illusion, something that is not real. It has something to do with our perceptions.
Narrator : Illusion or not, our perceptions emerge somewhere between the cosmic scale of Relativity where the flow of time is frozen and the quantum scale, where flow descends to uncertainty.Our world is on a scale governed by a mixture of chance and necessity.
Roger Penrose : My view is that there is some large scale quantum activity going on in the brain.Physics does not say that Quantum Mechanics takes place in small areas, but also take place over larger areas. I think this has to do with the consciousness. I think we need a new way to look at time, not either Quantum Mechanics or Relativity.
Narrator : If Quantum Mechanics is taking place in the
brain then the same randomness of outcome and unpredictability might explain
our ability to make sometime random choices. Opening up the future to the
possibility of change would provide the first step of restoring to physics
the flow of time it currently denies.
Physicist : I don't think time flows, I feel that time flows, but I feel we can only understand this if we have a better understanding of how consciousness works. I think human consciousness probably has the secrets as to how and why we think of time as going by.
Roger Penrose : I don't think we have the tools, I don't think we have the physical picture to accommodate these things yet. We're not very close to it.