1 00:00:00,330 --> 00:00:04,830 Hello and welcome to this series on physics and philosophy from the University of Oxford. 2 00:00:06,200 --> 00:00:14,510 Time is an illusion. Lunchtime doubly so. As Douglas Adams famously wrote, Time is a concept that has always fascinated us. 3 00:00:14,960 --> 00:00:18,890 It can flow like a river or trickle like a stream. On a busy day. 4 00:00:18,890 --> 00:00:23,390 It seems to rush past us. Yet as we wait for a bus a it can take forever. 5 00:00:24,320 --> 00:00:25,730 But what exactly is time? 6 00:00:26,570 --> 00:00:33,470 Is it an absolute flowing entity, or is it simply a relation between when you put bread in the toaster and when a toaster pops out? 7 00:00:34,580 --> 00:00:39,110 How we view time has profound philosophical impacts on the way in which we approach science. 8 00:00:40,090 --> 00:00:41,350 I am anti-Taliban. 9 00:00:41,560 --> 00:00:48,610 And I'm speaking to Professor Frank on seniors Sir Peter Strawson, fellow and professor of philosophy at University College, Oxford. 10 00:00:49,360 --> 00:00:55,690 Professor, aren't seniors holds undergraduate degrees in both physics and philosophy and a Ph.D. in the philosophy of science. 11 00:00:56,410 --> 00:01:00,130 His research interests are in the philosophy of physics and decision theory. 12 00:01:00,790 --> 00:01:05,500 His book Space Time and Stuff was published in early 2012. 13 00:01:06,100 --> 00:01:09,910 In this, he discusses a number of ideas about the structure of space and time. 14 00:01:11,520 --> 00:01:18,450 So was that time before the universe started, for example, with the Big Bang, or did time come into existence with the universe? 15 00:01:19,500 --> 00:01:25,020 So my answer is basically no. There was no time before the Big Bang started, but it depends on the details of general activity that answer. 16 00:01:25,470 --> 00:01:30,690 One could in principle have something like a big bang theory set in a Newtonian space time. 17 00:01:31,320 --> 00:01:37,320 So it could be that there was one point in time in which everything was concentrated well near to a point, 18 00:01:37,320 --> 00:01:40,020 and then it exploded out and was bigger and bigger. 19 00:01:40,980 --> 00:01:45,990 In a Newtonian theory, well, there is just because of what the determining theory is, there's always space and time. 20 00:01:45,990 --> 00:01:49,440 It doesn't come to an end. So there would have been time for the Big Bang occurred. 21 00:01:49,950 --> 00:01:56,819 But generative it is quite different because it says that the structure of space and time depends on the matter that there is they are interrelated, 22 00:01:56,820 --> 00:02:01,410 in particular this curvature where there's matter and in particular if you look at general activity, 23 00:02:01,410 --> 00:02:10,230 at how presence of matter affects the structure of space time, what you find is then that as you go back closer and closer to the big bang, 24 00:02:10,620 --> 00:02:14,850 the matter gets closer and closer together and produces a stronger and stronger curvature. 25 00:02:15,000 --> 00:02:20,730 And in fact, the more closely you get to the big bang, the curvature gets bigger and bigger. 26 00:02:21,210 --> 00:02:29,580 And then if you then try and extrapolate it backwards to this moment at which the Big Bang occurs, you find that the curvature goes to infinity, 27 00:02:30,120 --> 00:02:34,139 which really means it makes no sense that to say there couldn't have been a 28 00:02:34,140 --> 00:02:38,550 spacetime fabric that satisfied the standard equations of general activity, 29 00:02:38,850 --> 00:02:43,679 plus all the matter in the universe concentrated at a single point because the curvature at that point would have been infinite. 30 00:02:43,680 --> 00:02:49,079 That makes no sense. So the answer with good reason to believe that there was no sense to be made of space 31 00:02:49,080 --> 00:02:53,010 and time at the moment that supposedly all of the matter was literally at that point. 32 00:02:53,010 --> 00:02:59,220 So it's wrong to think of the Big Bang starting at the point. Rather, the right way to think of it is spacetime has a finite size. 33 00:03:00,300 --> 00:03:04,110 There just is no spacetime at the moment at which the Big Bang Singularity occurs to. 34 00:03:04,140 --> 00:03:10,310 But in another way you cannot well satisfying the equations general tivity extend spacetime beyond the big bang. 35 00:03:10,710 --> 00:03:17,460 So with good reason. If there was no space and time, it's not that it makes no philosophical sense is that the details of the physical 36 00:03:17,460 --> 00:03:20,580 theory tells you there couldn't have been space and time before the Big Bang. 37 00:03:21,950 --> 00:03:26,899 But I have to also say that this kind of inference based on classical general relativity, 38 00:03:26,900 --> 00:03:32,180 so not using quantum mechanics, we don't have a decent here combining quantum mechanics and general tivity. 39 00:03:32,570 --> 00:03:37,250 And it may very well be, as a lot of people have speculated, that what's actually happening is that you have a. 40 00:03:38,660 --> 00:03:43,520 A bouncing balloon type universe where before the Big Bang there was another period of expansion. 41 00:03:44,390 --> 00:03:49,190 Then before our Big Bang, there would have been space and time, maybe multiple space times, 42 00:03:49,400 --> 00:03:53,030 that are disconnected through this quantum version of a singularity. 43 00:03:53,180 --> 00:03:56,290 But if you look at classical general tivity, then the answer is no. 44 00:03:56,300 --> 00:04:00,740 There wasn't space and time before the Big Bang. But who knows what will happen when you apply quantum mechanics of that? 45 00:04:00,740 --> 00:04:06,480 That's hard to say. Could you please explain the difference between absolute time and relational time? 46 00:04:08,010 --> 00:04:14,940 Relational time is the idea that there is no such thing as space and time as an 47 00:04:14,940 --> 00:04:20,670 object that separate from matter and fields that live in this space and time. 48 00:04:21,030 --> 00:04:25,080 All there is are relations between events of the form. 49 00:04:25,470 --> 00:04:32,730 This event was 5 seconds later than that event, or this event was five metres distant from that event. 50 00:04:33,120 --> 00:04:36,779 But. One should not understand on the relational view. 51 00:04:36,780 --> 00:04:39,930 When I say this event occurred 5 seconds after that time, 52 00:04:40,170 --> 00:04:46,050 I shouldn't think that that's true in virtue of the locations in time that they occupied, because there is no such thing as time. 53 00:04:46,410 --> 00:04:55,170 There are merely relations between events. Just like there could be a father son relationship without there being a space in 54 00:04:55,170 --> 00:04:59,879 which these things occupy the father position and the son position at first sight. 55 00:04:59,880 --> 00:05:02,940 It seems like a bit of a strange debate to non philosophers, 56 00:05:03,300 --> 00:05:07,320 even though I've said to given to explain what the distinction between the two you might think. 57 00:05:07,320 --> 00:05:10,720 I have no clue what this guy is talking about. What is the distinction? 58 00:05:10,770 --> 00:05:14,100 He's saying that there is space and time or saying that there's merely relation between events. 59 00:05:14,550 --> 00:05:18,180 But here's a way in which you can understand the distinction. 60 00:05:18,180 --> 00:05:26,130 And let me talk now about the relational view of space. If you thought that all spatial relations between, let's say, objects at a particular time, 61 00:05:26,910 --> 00:05:30,690 like a particular distance, were due to the positions in space that they occupy, 62 00:05:31,020 --> 00:05:37,919 then there would be a big difference between the world that is the way it is now and the world, which is just like the current world, 63 00:05:37,920 --> 00:05:42,510 except that everything is shifted five metre to the right because they would occupy different positions in space. 64 00:05:42,930 --> 00:05:47,100 The distance between everything will be the same if you shift everything five metres to the right, 65 00:05:47,520 --> 00:05:51,360 but the locations that you occupy in space will be different. So it will be a different universe. 66 00:05:51,750 --> 00:05:54,300 On the other hand, on this view that are called relational, 67 00:05:55,090 --> 00:06:00,270 there will be no difference between the two because when the relational view is all, there is a spatial relations between things. 68 00:06:00,270 --> 00:06:04,140 There is an energy in the space where objects occupy locations in space. 69 00:06:04,440 --> 00:06:10,290 So those two worlds would kind of the same. So in that way you begin to get a bit of a grip. 70 00:06:10,290 --> 00:06:13,080 You can get an even better grip if you think about the following question. 71 00:06:14,160 --> 00:06:18,330 Think of the issue as to whether it could be that the entire universe is rotating in space. 72 00:06:19,110 --> 00:06:24,450 On the absolutist view, well, there's a real fact of the matter. Are these things moving through space or are they not moving through space? 73 00:06:24,450 --> 00:06:27,060 If they are moving through space, they could be rotating through space. 74 00:06:27,480 --> 00:06:31,590 On the other hand, the relational view, it makes no sense for the entire universe to be rotating, 75 00:06:31,890 --> 00:06:35,670 because if the entire universe is rotating, all the distance would be preserved. 76 00:06:36,150 --> 00:06:42,970 So if you somehow thought that it makes no sense at all to speak of the entire universe being rotating or not. 77 00:06:42,990 --> 00:06:48,990 If you think that's a completely illegitimate and understandable, silly question, then you're probably a relation ist. 78 00:06:49,230 --> 00:06:54,809 If, on the other hand, you think, well, it could be that the universe is rotating, I'm not quite sure how I would know it, but it could be. 79 00:06:54,810 --> 00:06:59,250 The universe is rotating. Then you have an absolutist view of space. 80 00:06:59,640 --> 00:07:06,000 So that's a way of explaining, trying to get across what the difference is between those two views. 81 00:07:06,030 --> 00:07:11,549 One consequence of absolutism is it makes sense for the universe to rotate a consequence of the relationship, 82 00:07:11,550 --> 00:07:17,810 which make no sense to say the universe is rotating. So what are the arguments for the idea of absolute time? 83 00:07:17,960 --> 00:07:20,300 And what are the arguments for the idea of additional time? 84 00:07:21,080 --> 00:07:26,780 For a long time, it's a tradition in physics and in philosophy was to believe that there is such a thing as space. 85 00:07:26,780 --> 00:07:32,269 When Newton talked about motion, he made motion through space. He didn't mean change in relative position, change of distances. 86 00:07:32,270 --> 00:07:35,749 He meant motion through space. On the other hand, knits. 87 00:07:35,750 --> 00:07:38,120 But he didn't have many followers thought that no. 88 00:07:38,120 --> 00:07:43,910 All there was was a distance between things, and it didn't make any sense for the entire universe to be rotating. 89 00:07:44,480 --> 00:07:49,070 And the Newton responded to life needs by saying, Well, look, but we can tell where the things are rotating. 90 00:07:49,070 --> 00:08:00,050 Not if you spin water in a bucket. You'll see that it's rotating by the curvature on the water surface, but it's not moving relative to the bucket. 91 00:08:00,320 --> 00:08:06,080 It must be that the reason why the water has this curved surface is that it's moving relative to space for you. 92 00:08:06,080 --> 00:08:09,350 Listening to it doesn't believe there is such a thing as space. This makes no sense whatsoever. 93 00:08:09,350 --> 00:08:12,799 So clearly you're just wrong because there is a difference between a rotating 94 00:08:12,800 --> 00:08:16,040 bucket and a non rotating bucket and we can see it in the curvature of the water. 95 00:08:17,150 --> 00:08:23,180 Mark responded to that by saying, Yes, that's right. But what matters is not the rotation of the water relative to the bucket. 96 00:08:23,180 --> 00:08:25,940 I agree that there is no relative motion between the water and the bucket, 97 00:08:26,480 --> 00:08:30,530 but the reason why the water surface is curved because it's rotating relative to the stars. 98 00:08:31,550 --> 00:08:35,890 So my maintained a relation is view. Einstein, by the way, was very much influenced by this, 99 00:08:35,900 --> 00:08:39,710 even though later on it turned out his theory wasn't really a relationship theory, his theory of general activity. 100 00:08:41,490 --> 00:08:48,540 What is really interesting is that ultimately somebody here in Oxford called Julian Barber and collaborators have developed a relational 101 00:08:48,540 --> 00:08:57,269 theory that makes quantitatively precise marks idea about the curvature of water being due to rotation relative to the stars, 102 00:08:57,270 --> 00:09:06,870 or rather the other objects in the universe. What is really interesting and rather surprising fact is that Barbara has pointed out is that. 103 00:09:08,660 --> 00:09:16,780 We can even make sense of the universe as a whole, rotating or not. Roughly speaking, if you take a water balloon and rotate it just like the earth, 104 00:09:16,780 --> 00:09:25,120 it will expand along the equator because of the centrifugal forces, or rather the centripetal forces that are needed to keep the water in place. 105 00:09:25,660 --> 00:09:29,080 Similarly, if the entire universe were rotating, and if the entire universe, 106 00:09:29,080 --> 00:09:33,490 or at least a matter in it, had a roughly spherical shape it would bulge at the equator. 107 00:09:33,730 --> 00:09:42,550 Now, the universe doesn't consist of a bunch of radically distributed matter, but the analogy in general is if it can be tested. 108 00:09:43,000 --> 00:09:46,540 And it turns out that if you do that experiment that within a very, 109 00:09:46,540 --> 00:09:50,710 very large degree of accuracy, we have evidence that the entire universe is not rotating, 110 00:09:51,190 --> 00:09:57,280 which a lot of people claimed supports this relational view because after all relation it says it doesn't make any sense for the universe to rotate. 111 00:09:57,280 --> 00:10:01,720 So no surprise that the entire universe is not bulging at the equator or the analogy of that in general activity. 112 00:10:03,150 --> 00:10:09,930 But I don't think this is a telling objection since the substantive list or the absolutists can also explain this. 113 00:10:10,260 --> 00:10:14,160 In any case, the upshot of it is, is that it's still an unresolved issue. 114 00:10:14,790 --> 00:10:17,400 I happen to be a substantively or an absolutist, 115 00:10:18,450 --> 00:10:23,429 but I think it would take a bit long for me to explain why I'm an absolutist, but suffice it to say that is still alive. 116 00:10:23,430 --> 00:10:28,920 Debate amongst philosophers and physicists as to whether the relational view is right or whether the absolutist view is right. 117 00:10:30,110 --> 00:10:34,830 And do you think that time can exist without events occurring? 118 00:10:34,850 --> 00:10:38,090 But we do. We need things to be happening to measure time around it. 119 00:10:38,420 --> 00:10:42,580 I am actually an absolutist, so I don't think the time is merely metaphor of change. 120 00:10:42,590 --> 00:10:46,040 I think there is time and even if there were no events, there could still be time. 121 00:10:46,460 --> 00:10:50,450 But let me give you an interesting argument. You might think how on earth could give evidence for that? 122 00:10:50,750 --> 00:10:56,990 So there's an interesting argument by the philosopher Sidney Shoemaker that imagine the following thought experiment when people said. 123 00:10:57,900 --> 00:11:02,820 How on earth could you ever have evidence that there's time without events happening? 124 00:11:03,750 --> 00:11:05,640 He gave the following thought experiment says, Look. 125 00:11:05,750 --> 00:11:12,930 Supposing you live in the following universe, admittedly rather bizarre universe, the universe is divided into, let's say, into three different parts. 126 00:11:13,470 --> 00:11:18,370 And the following bizarre thing happens. For a period of one year. 127 00:11:19,980 --> 00:11:27,990 Let's call them regions A, B and C in region A ten year stuff happens like normal, and then one year all the events freeze. 128 00:11:27,990 --> 00:11:36,240 Nothing happens. Things stay exactly in their position. In Region B, this happens every 13 years and in Region C it happens every 17 years. 129 00:11:36,570 --> 00:11:42,570 So if you're in Region B, you see every ten years you see region eight freeze for a year and then move again. 130 00:11:43,380 --> 00:11:47,430 Similarly, you see in region see everything freeze every 17 years. 131 00:11:48,900 --> 00:11:55,000 You don't, of course, know this anything. In the 13th year when you're freezing because you're also frozen, nothing happens. 132 00:11:55,000 --> 00:11:56,590 But the people in 17 or in ten. 133 00:11:56,830 --> 00:12:02,020 So you freezing or if you think, oh, I don't want to be frozen, you move from region B to C, then you C, region B freezing. 134 00:12:02,230 --> 00:12:07,390 Okay. So we clearly have evidence that this is the case. It's a bizarre world, but good evidence that that is the case. 135 00:12:07,810 --> 00:12:12,379 But once we know that eight freezes every ten years, B freezes every 13 years, 136 00:12:12,380 --> 00:12:19,060 C freezes every 17 years, we can immediately figure out that once in every ten times, 13 times 17, 137 00:12:19,060 --> 00:12:24,280 which is, I think 391, it doesn't really matter what if you multiply ten by 13 by 70, 138 00:12:24,490 --> 00:12:30,610 we can figure out that every whatever it is, 1391 or so years, the entire universe will be frozen. 139 00:12:30,610 --> 00:12:36,589 So there are no events. But we also have good reason to believe that time will continue because in part, 140 00:12:36,590 --> 00:12:39,620 a freeze is not as if time stops because things keep happening everywhere else. 141 00:12:39,620 --> 00:12:44,550 When we can be freeze is not as if time stops. It seems that we have at least some reason to believe now. 142 00:12:44,570 --> 00:12:53,299 It's not like time stops when events everywhere stop. It's just that once every 1391 years, the entire universe comes to a standstill. 143 00:12:53,300 --> 00:12:59,780 So there are no events, but time doesn't stop. So he said, this is how we could have empirical evidence that there can be a flow of time, 144 00:12:59,780 --> 00:13:03,980 even when there are no events occurring because everything is frozen. That's merely a thought experiment. 145 00:13:04,340 --> 00:13:07,210 The reason why I believe that in fact this is true of our universe, 146 00:13:07,220 --> 00:13:13,510 even though I also believe that in fact there never will be a moment if we are no events occurring is a bit more complicated. 147 00:13:13,520 --> 00:13:19,569 Has to do with these arguments for absolutism. But surely against this zone A, B and C argument, 148 00:13:19,570 --> 00:13:27,100 you could argue that the only reason we know that time stops for a year end zone is because there are things happening in zone B and C. 149 00:13:27,280 --> 00:13:29,990 So you have those observers to note that everything is frozen. 150 00:13:30,010 --> 00:13:36,890 Surely if in the 1390 first year, if everything was frozen, then what would it mean if at time to go on? 151 00:13:36,940 --> 00:13:40,089 So clearly, what kind of direct evidence for this? 152 00:13:40,090 --> 00:13:43,810 Because we are assuming that everything is frozen, that means that we're not gathering any evidence. 153 00:13:44,740 --> 00:13:51,130 So here's where philosophy begins to matter a bit for how you solve these kind of problems. 154 00:13:51,220 --> 00:13:56,160 So how do we think in general you solve problems like that? There's lots of things that we don't directly observe. 155 00:13:56,170 --> 00:13:59,790 We don't directly observe electrons. We don't directly observe genes. 156 00:13:59,980 --> 00:14:04,930 We don't directly observe very distant parts of the universe, but we have theories about it. 157 00:14:05,260 --> 00:14:10,300 So in general, we solve problems like that, and we have to do this in science all the time. 158 00:14:10,750 --> 00:14:13,600 We have to form opinions about things that we don't directly observe, 159 00:14:13,900 --> 00:14:19,650 can't directly observe or haven't observed by forming a theory and confirming or confirming theories. 160 00:14:19,660 --> 00:14:24,670 How do we do that? Well, the general strategy is we believe that the simplest explanation of those things 161 00:14:24,670 --> 00:14:28,330 that we have observed is likely to be true or is likely to be approximately true. 162 00:14:28,930 --> 00:14:39,490 And the simplest theory in that little example, the simplest theory, it seems to me, about the ABC region universe is that time keeps flowing. 163 00:14:39,880 --> 00:14:46,840 It's just that once every 191 years, 30, 191 years, the entire universe comes to a halt. 164 00:14:46,840 --> 00:14:50,530 But that doesn't mean the time stops. It will be a bit of a strange theory that says. 165 00:14:51,750 --> 00:14:55,020 Oh, yeah. Some of the time little bits of the universe come to a halt. 166 00:14:55,380 --> 00:15:01,980 But the entire universe never comes to a halt, though. Just once every 3091 years, something really strange happens to time. 167 00:15:01,980 --> 00:15:07,560 It just sort of. It's not that the universe freezes, it's just the time comes to a standstill and then it starts to pick up again. 168 00:15:08,160 --> 00:15:11,910 In fact, it doesn't even start and pick up again. It just flows through continuously. 169 00:15:11,910 --> 00:15:18,750 But once every 391 years, we get an exception to the theory that says once every 13 years this region comes to hold, 170 00:15:18,750 --> 00:15:20,490 once every 19 years this comes to a halt. 171 00:15:20,850 --> 00:15:27,840 So generally you give such answers, it seems to me, by looking at what the best theory is of the things that we have observed and that can very often. 172 00:15:28,970 --> 00:15:33,640 Give us good reason to believe certain things about things that we haven't observed, including that there is time when no events occurring. 173 00:15:34,370 --> 00:15:36,410 Thank you very much, Professor Owens, on youth.