 Hello, so I'm J.J. Joachim and welcome to this edition of Philosophy and What Matters, where we discuss things that matter from a philosophical point of view. Now, our topic for today is the philosophy of time. The great English philosopher Freddie Mercury once said, time waits for nobody. Well, he's not really a philosopher and you all know that, but many of us would still share his sentiment. Time seems to flow at a steady pace from the past into the future and it is indifferent to whatever our hopes and dreams might be. But what's the underlying philosophical idea behind this sentiment? And is it the right view to take on the matter? In the first place, why does it even matter to think about the nature of time? Now to guide us through the philosophy of time, we're joined by our good friend, Graham A. Forbes, head of the Department of Philosophy at the University of Kent. And we'll start. Hello, Graham. Welcome to our Philosophy and What Matters. So let's start with the question right away, what is time and to be precise, how do philosophers tackle the question about the nature of time? Well, kind of typically for philosophers, we break it down into lots of smaller questions that we might make a bit more progress on. So I find it really useful to think in terms of contrasts. So how is time different to space and how is the past different to the future? And then there's questions about is time something that maybe humans are responsible for or is it something that we're detecting in the world in some way? Is this something that's the same for everybody? So is it the case that some languages have a role for time that other languages don't? These sorts of questions are the kind of questions that we try and deal with. And hopefully, by being a bit more specific, we can make some progress on them. OK, so just to make some distinction here. So your your first point is that when philosophers tackle the philosophy of time, they're also tackling a question about space. Is time like space? So wouldn't that be a kind of nature question? What is the nature of time? Is it like space? Does it flow? Does it have a unique direction? Is that what's the thing going on here? Yeah, so the difference. So the sort with flow is that flowing seems to be a thing that time does in a way that space doesn't. Space doesn't flow. So if you think that there's any flow at all, there's got to be some respect in which time is different to space, where if you think that change over time is just like variation over space, you think that they're not different in that respect, that they're just sort of dimensions in a four dimensional manifold. So to get a grip on the question of the nature of time, we need to think about how it compares to to something with a somewhat similar nature. OK, you also mentioned about language we use to talk about this. So you distinguish between whether we experience those things and we do some language, describe them. Is this a kind of semantic question as well? Yes. And so. So historically, particularly in about the 1960s, people were very interested in this question of whether you can eliminate tense from language. So whether you could have a language that described everything, including the idea of being sort of now and and having stuff in the past and stuff in the future, whether you could capture all this without referring to a privileged now. And there was a certain level of work going, look, we found this language in Northeastern Canada or in Kenya. And in these languages, they don't have any time or they don't. And the debate has largely moved on since then, not to a question of what individual languages do, but to a question of how we make sense of and how we make sense of time sort of given any linguistic resources that we want to use. So we might use a formal language, like a formal semantics to sort of model what's going on. And so do we have a formal semantics that has a special role for now? Or do we have a semantics that says that now is just an indexical? It's just like here again, the analogy with space, like here, just pointing at the time we're at rather than the place we're at. But there's no sense of a changing now. So when you're using your language to describe your theory, it's important to work out what that language is committing you to. OK, so this are kind of privileging about the now. So is there a kind of ontological specialness about present or the now in this discussion? So there could well be. And so one way of viewing what we're doing when we do ontology is we're just working out what the commitments of our best theory are. So if we've got this language that we think is the language that best captures the world and that language privileges the now or says that there's a difference between the past and the future in that we've got some kind of commitment to the past and not the future or something like that. That's just going to create ontological commitments because according to a post-Quinian view of what ontology is, your your commitments to what exists are just whatever your best theory is committed to. So and so the question of ontology here is playing quite a special role in in committing you to something that's a consequence of your theory. A lot of the questions about the nature of time might be compatible with lots of different ways of catching out what exists because they're compatible with different ways of turning that into a rigorous formal semantics. OK, so why does it matter to ask the question about the nature of time? Why does it matter to ordinary people like ordinary laymen, lay persons? So I think I think that's an excellent question. I think that's one of the most important questions because if we lose sight of that, the formal semantics and the ontology doesn't seem to do anything for us. And the joke answer to that question I always have is, well, ask me again in five minutes. OK, we're stuck in time. So we're stuck in time in kind of two ways. So sometimes I find myself desperately wanting something to be over. You know, I quite like the global pandemic to be over and to get on. I don't I don't get a choice about that, particularly. I've got to wait it out, you know, I can go and visit a different place. Apart from quarantine restrictions, I can go and visit a different place. But I'm kind of stuck in the place in time I'm at. But not only am I stuck in time, I'm not stuck at the same time. If I want something not to change, if I think, well, I've got a deadline coming up, I really I'd like, you know, I'd like to stay here before I've missed the deadline. No, I'm going to get dragged despite my preferences into a future where I've missed the deadline unless I unless I work very hard. So there's this sort of double stuckness that we have. And not only is there that, but once we've had some time, we can't get it back. So, you know, my my hairline is rapidly retreating. I'm not I can get hair plugs or something, but I can't get my youth back. And if people don't care about that kind of thing, maybe they're not as middle aged, if people don't care about that kind of thing, I don't understand what they're asking when they say, but why should we care? I'm getting old and I'm never going to be young again. And there's nothing I can do about it. Yeah, so the issue about time really connects to us because we experience things in time. We are a temple beings as well. We have hope for the future and regrets about nostalgia for the past. But it's not just that we experience time. But we can't, you know, unless something's gone horribly wrong, we can't experience the world without experiencing it as a tiny one. So there's a sort of inescapability to time. Mm hmm. OK, so there are many theories of time in the philosophical literature. So you have here the A theory as opposed to the B theory. You also have the C theory, R theory, then the series and so on. So can you disentangle these things for us? I can certainly have a go. So I think we start off with a debate about change or about the moving now. They might be two slightly different debates. They're often treated as the same debate. I'm going to the simplicity to the same debate. So you need to think, as I said earlier about, whether now works in the same way as here or whether there's a difference. So A theories or tense theories or dynamic theories, these are more or less different terms for roughly the same debate and claim that there is some special changing nature to now. Whereas all the other theories deny that pretty much all the all the non dynamic theories, the static theories, the tens of theories, the B or C or R theories, all deny that there's some special nature of change. So if you think that there's this special kind of change, change in what time it is, you then have a debate about the direction of time, whether there's a difference in the past and future. Whether there's a difference in the past and future. Is there an arrow of time? So C theorists claim there is no arrow of time. And the reason it seems like there's a difference between the past and future is actually there's an entropic gradient that's given by the second law of thermodynamics. So physics creates this difference that makes it seem like a difference between past and future, but maybe this difference is local and perhaps contingent. It's not the difference in time, it's just the difference in entropy. So where the B theorist or the R theorists or indeed the A theorists think there's some kind of difference between earlier and later, the C theorist thinks that that's just entropy. So you've got this question about change, then this question about the arrow of time. And then thirdly, you finally get onto the temporal ontologies, the ones that start talking about existence. So these are models of how we think about time in terms of what exists and changes potentially in what exists. So presentism claims that only the present exists or nothing that isn't present exists. The grown block view claims that the past exists and the future doesn't. The moving spotlight claims that past, present and future all exist, but there's a sort of changing now that moves along. The shrinking tree is the view that not only do the past and the present exist, but all the future possibilities exist. So you've got this sort of branching structure where the branches drop off as they seem to be possible. And then eternalism is generally the view that past, present and future all exist, but there's no distinctive now. They're all equally real and not distinguished in any ontological way. So often these temporal ontologies presuppose some answers to the previous questions about whether there's an arrow of time or whether time passes. So they tend to come sort of stirred in the order of operations as it were. Okay, so I'm trying to make sense of the distinction here. So the A theories will be theories which are dynamic. They respect tensed languages in a way. Then you have the B theories which are static theories. They're tenseless theories. Then you have the C theories and the R theories as well. So those questions are about the nature of time, whether time has a direction, whether time flows, whether time is like that. Then you have the ontological theories or temporal ontologies. You have the present systems and the growing block which shared the A theory commitment. On most ways of understanding the A theory, yeah, certainly they're both dynamic. So what they disagree about is when I say things like Julius Caesar was assassinated, is that true because there's a bloke Julius Caesar and he was assassinated? Or is that true? Or is that not true? Or is that true? Because there used to be a bloke but there isn't any longer. And they put it in terms of existence. So a lot of this is a question of how you turn your dynamic theory into a sort of a rigorous and precise formal theory that has particular commitments. The presentist is committed to certain possibly exactly the same sentences being true as the growing block view. But disagrees on how they're made true. Okay, then you have the moving spotlight and the shrinking tree view which has... Yeah, so Stores McCull defended this in about 1994. So this view is a bit like a moving spotlight that thinks that there are multiple ways the future could go and these future possibilities cease to exist as they cease to be possible. So you can imagine a tree-like structure with the branches disappearing and the trunk being like the past. Okay, so but that's still a dynamic view of time as well. Still a dynamic view, yeah. So of these theories here, the temporal ontologies here, which do you prefer? So I defend the growing block view. So I think that the past exists and the future doesn't. Oh, surely the past and the present exist for you. Well, it depends what you mean by the present. So there's a sense in which I think there's no time like the present. So I don't think the present is like a moment of time which is neither past nor future. I think that events are present. This conversation is present because part of it exists, but it's still ongoing. So the reason I get to this view is essentially I've got two ontological statuses exists and doesn't exist. And I've got three tenses and there's a problem of how you get the three tenses into two ontological statuses. And so the best way of thinking about it I found is to think of the present in some senses being partially existing but having this potential for more to happen. So the bit of it that exists is just recent past. There is no bit of it that doesn't exist because you can't have bits of things that don't exist. So it's the idea that there's stuff that's started to happen but is ongoing. That's roughly the idea with the present. We'll get into your view some more later. But for now let's talk about some time puzzles. So philosophical literature has interesting puzzles about time. Yeah, let's start with the problem of change. What is this problem all about? So I've touched on it a little already. It's a problem that really we get from a kind of 1920s University of Cambridge where they're trying to work out what it is for something to change. And they come up with this criterion which is if you have a proposition that's true at one time and false at another. Or two propositions which are exactly the same except one is about one time and one is about the other and one's true and one's false. You can do it either way depending on what you do. This idea you have propositions where there's the only difference between them is the time but there's a change in truth value. That gives you an account of change. It just gives you a really terrible account of change because it means that I can change you by moving my chair back. So now you are different with respect to your distance to me. And so you get what's called Cambridge change which is just this very general account of change that doesn't pick out the kind of features of change we're interested in. And mere Cambridge change which is those changes that aren't the changes we're interested in but still satisfy this notion of Cambridge change. And so you had two sort of more specific views of change. One associated with Bertrand Russell and also known as at-at change where change just is an analog of variation over space. So it's things are one way at one time and another way at another time hence at-at change. So it's just you describe things at different times if they're not the same at different times they've changed. Whereas the British idealist philosopher also at Cambridge John MacTaggart, Ellis MacTaggart, yes he genuinely has MacTaggart twice in one name. So I think it was something that he had to change his surname to get a legacy or something but he already had the middle name as a family. So he's got this example of a poker in the sense of a bit of metal that Bertrand no one is familiar with anymore but he used it for a fire. His thought is this bit of metal that's hot at one end and cold at another varies over its length but that's different from it being hot on Monday and cold on Tuesday. That there's some disanalogy between varying over the length of the poker and changing between Monday and Tuesday and so there must be something about change over time that's different to change across space and whatever that changes that's characteristic of the passage of time, the change between the poker on Monday and the poker on Tuesday. So it's probably bound up with how things persist. Do they persist simply by varying across their parts or do they persist by having properties and then having different properties. So that's the kind of problem of change. Are we thinking about change in Russell's kind of attack sense or change in the sense that McTaggart wants which I started to call McChange just to clarify it's change in the McTaggart sense. If you do it properly the T gets pronounced McChange. Change, okay I like that. Okay so speaking of McTaggart he has this famous paradox. So what is this paradox all about? So given that McTaggart thinks that for time to pass you need this sense of change he then also thinks that time couldn't possibly pass because nothing could change in the relevant sense. So he's got this strong view of what changes as a kind of positive thesis and then this negative thesis nothing could change in that sort of way. I've spent a lot of time wrestling with this argument and in the end I agree with C.D. Broad also Cambridge philosopher that it's a philosophical howler that it's an absolutely terrible argument. But I also know lots of people who I really respect and are very clever who think the argument really works and it's an excellent argument and indeed it's the view that I'm entirely wrong about in ancient time. So it's a weird position and quite a common one for a philosopher but the weird position to be utterly convinced this argument is terrible but also to be aware that I've got really good evidence by very clever people who I respect that I must be wrong about how terrible it is. So I've got a bit of an interesting relationship with this argument. The argument is essentially that you need change in an irreducible sense but any attempts to describe time will require that you explain how this change works and in order to explain how this change works you've got to sort of have a description that doesn't change but then you've either lost how the change works or you've described multiple incompatible properties to things. So you're saying well things were this way and now they're that way but to say that they were this way is to say that there's a true description of the universe according to which those things are present and one according to which these things are present and they can't both be present and so there's some kind of contradiction. My favorite paper on this is by David H. Samford in the 60s who basically argued that McTaggart's argument is like a reductio and absurdum where you've forgotten you're allowed to assume the thing in the first place to generate the contradiction. So if you accept that there's this weird sort of change where you can't describe it once and for all because it keeps changing on you there's no paradox you've just accepted that there's this this irreducible change that has no spatial animal on the problem comes with thinking that this this McChange has to be reduced down to a theory where you describe it in a static way like your theory of the universe is going to have to change because the universe is changing and if you accept that there's no paradox but lots of people think that that's a terrible thing to accept or an incoherent thing to accept. Okay so I'm trying to make sense of this. Yeah it's very difficult. Yeah so what I learned about McTaggart's paradox is that the first premise will be every event is past present future because it goes through the flow time okay so it was Yeah apart from the first event in the universe and the last event all of them are going to be past present in the future yeah. Okay then the second premise will be no event will be past present future because you can't have incompatible temporal location okay. Things can't both be past and not be past like. So the conclusion will be well it's incoherent to have those two things in your metaphysics. So your solution is at least some people would say well we drop premise two or we drop premise one we can't have both. Yeah there's a kind of dilemma that you either think not everything is past present in future if you go for that dilemma you might be attracted to presentism just the view that only the present exists. This isn't going to help you in the end. People think that that in some way helps you can set the problem up again just talking about things being present but having incompatible things being present. So presentism is not going to help but some people have argued that way. The other thing is to say let's drop the requirement for change if we just have changes being temporal variation things don't have incompatible properties because they just are the way they are at each time. So the very idea of having change over time being different to variation over space just leads to incoherence so we should drop it. So that's the kind of dilemma that people like MacTaggart set up. Now let's go to another puzzle. So this one is a more recent code and code 60s puzzle by Sidney Shoemaker. It's time without. So how does it work? So it's kind of quite an odd argument and it's important to remember what the argument is an argument for because people often seem to forget this. He's trying to show that it's possible that there could be a situation in which we can have evidence that time has passed with no change during it. So he's not actually arguing that there could be time without change. He's arguing that there could be circumstances under which we could have evidence that there could be time without change. So maybe there couldn't be time without change around here but there are some situations in which we could have reason to believe that that was. So he imagines the the universe is divided exclusively and exhaustively into three regions and so the entire universe is made up of three reasons and every now and again we notice that the other regions kind of become inaccessible for a bit and then about a year, just put a number on it, about a year these regions become inaccessible and then after a year we notice that apparently nothing has happened since they were last accessible and they have different periods during which they have these freezes and these periods of inaccessibility and the periods are related in such a way that we think hey, if we also had freezes which occasionally the other regions support and report us doing, there'll be some point in time where we all have such a freeze at the same time and we can make sense of the sort of regularity if say every 60 years each region freezes it would just it would mean that we could say that region A freezes every three years region B freezes every four years and region C freezes every five years if once every 60 years they're all frozen at the same time just nice regular pattern that we would get. So if we were in such a scenario we would have reason to believe that the entire universe freezes for about a year and every 60 years. Now the problems with this argument tend to come when we explain why the freezes stop because we can explain why region A stops freezing because there could be some kind of causal trigger from one of the other regions and so on for each individual region sorry each individual region. Coming up with a reason for the entire universe to unfreeze that doesn't involve some little tiny change happening over like a little countdown timer or something going right well it's now 10 months till we unfreeze and don't don't cause the don't cause the unfreeze for another 10 you know what mechanism is going to cause this to stop it looks like we'd have reason to think that there was some changing mechanism that was counting down till the unfreeze so the argument maybe doesn't work in the end but it is a really interesting way to get us to think about what kind of things would count as evidence for views that on the surface look like they're empirically equivalent the views that look like there couldn't be any any kind of physical difference between. I remember this one so Aristotle once said that you can't have time without change so I think this the shoemaker argument tries to give well some empirical sorry let's not have empirical some epistemic reasons to think that well it's possible that time without change but the counter argument is well there's still some change there if you think about how the unfreezing happens every year so often. I mean we should always be a bit cautious attributing stuff to Aristotle and so Aristotle said something like time is the number of change so the word chronos in Greek is used to measure durations as opposed to the other word for time in Greek chyros which is used to think about opportunity so when is the right moment fraction so it may be that he was distinguishing between time as measured and time as moments for action and it's unclear whether he was thinking about kind of this metaphysical question at all but certainly we've attributed this interview to him that there couldn't be time without change and I mean I'm not I'm not clear that he ever actually like thought about anything quite this abstract okay fair enough I mean I'm not an Aristotle scholar I'm just enough of a and enough of a non-Aristotle scholar to know that every time I talk to Aristotle scholars about this stuff they go whoa whoa whoa why do you think Aristotle said that okay so the kind of the Aristotle that the metaphysicians like to talk about thought that but I encourage people to get into the Aristotle because there's a lot of interesting stuff there that makes you think okay speaking of time with regard to action so there's so another sort of puzzle concerning time bias or temporarily bias attitudes one such time bias is feature bias right so how does it work this this program so Megan Sullivan has an absolutely fantastic fairly recent book on on time biases which I recommend if you want to get into this and so so we seem to have a couple of biases so one of them is the kind of near bias so we tend to be more interested in in recent things or things in the near future and then there's a future bias where and we'd rather have pain in the future sorry we'd rather have pain in the past rather than the future so if I wake up a bit sort of drugged up and I'm not sure whether I've just had an operation and can't remember it or I'm just about to have an operation and I've got confused about this and the operation the drug the drugs I'm on only remove my memory they don't remove the experience so that if I've had the operation it was horribly painful and I can't remember it and if I'm about to have the operation I'll experience everything but then forget it afterwards so in this situation the thought is and this argument's from Derek Parfit the thought is that we'd rather have the operation over and done with we'd rather we'd rather have the pain in the past rather than the future and so then if you get into decision theory which I'm going to try and avoid doing today but you get into decision theory and you're thinking right so I want to to maximize expected utility I want to have and utility is just your measure of what you think is good and the expected bit is just how likely that you think it is we want to have something that we think will give us most of the good stuff if I think past pain is is less bad than future pain or or future goods are more good than past goods someone can trick me into a situation where I keep having pain because I don't care about past pain so as soon as the pain's past I'm prepared to trade off more past pain by doing things that will will mean that I I keep you know I keep being in a situation where I make choices to trade off past pain against future pain so more of my pain is in the past and and you can you can mess with the numbers so you get structures like this and so these are pain pups where you can just have a situation where you have way more pain in the end than you would have on some other situation but at each moment you choose your maximizing expected utility because you've got this distinction between past pain and future pain and and so that looks totally irrational in the long run and so Sullivan and Green Sullivan in other papers they've done argue that we shouldn't have any bias between past and future when it comes to these decision theoretic calculations because if we have bias we end up in these irrational situations and I think these arguments are really interesting but I think a lot of the work is being done by being utilitarian about it by thinking that there are you know quantities of goods at certain times and what we're doing when we act is just to try and work out where in time we want these quantities of good right and I think we can make much more sense of how our different attitudes towards the past and future work if we don't think of it as just distributing quantities of goods but think about the kind of relationships we have for instance so my relationship to my grandfather is very different to my relationship to my grandchildren why is this well my grandfather's dead but I remember happy childhood memories of being with him I I don't have any memories of my grandchildren because not only do I not have any grandchildren I don't have any children it's really unclear that I'm talking about anybody at all and Elizabeth Harman has a really nice argument that captures this quite well in which you consider as a teenage mother who accepts that their life would have gone better in every way that matters if they hadn't had a child when they were 15 nonetheless they actually do have a child whom they love a lot and they wouldn't trade this actual child which they care for for an alternative life in which they waited and had possibly a nicer child who was better brought up and happier and the whole family would have been wealthier but trading the actual child for a potential alternative seems kind of incompatible with how loving relationships are supposed to go so there seems to be a difference between actual loving relationships and nearly potential relationships where we can't trade the actual for the potential so I think the difference between the past and future here might be a difference between actual and potential which trading potential past pain to potential future pain doesn't really capture so so I think we're making sense of the difference between past and future when it comes to kind of affect to how we feel about it Sullivan's going to be right that we shouldn't just trade off and shouldn't prefer in the abstract pains to be past rather than future we should think about how our relationships to things we're we're actually acquainted with relationships of nostalgia of hope of love and of various things like that and work in terms of the actual and the potential but of course perhaps you can do these things where um where I've got an actual child whose future I have great ambitions for versus a possible relative but I don't know if I'm really related to them and you know maybe I am related to James Kea Hardy maybe I'm not we're not really sure because um other relatives that lost contact with their family and so so maybe it's not going to be totally a past future distinction I don't know but it might be the stuff that's that's creating the the worry about our different relationships between past and future is to do with how how relationships to actual and potential work rather than just where we want pains to be no I like that uh understanding so on the one hand this puzzle is generated the bias is generated because of quantitative thinking about goods pains and stuff things and so on now you're suggesting or at least some people are suggesting like yeah Preston Green and Sullivan are suggesting that perhaps you could have a qualitative view of what's going on there qualitative relationships not just assigning some value but more of the qualitative um you know how the quality of your relationship is with the thing that you're thinking about be it in the past or the future or be an actual or potential now on to the last puzzle so this one generated a lot of discussions in the 70s but we have I think most of us even our general audience would have an inkling of what this is so these are the paradoxes of time travel so what are the paradoxes okay so in terms of time travel um a lot of the problems you kind of don't need much time travel for and and when I say time travel I'm going to assume we mean time travel to the past um as Van Imwagen famously said this chair is the limiting case of a time machine if you sit in it for 70 years you'd have traveled 70 years into the future so when we talk about time travel like we're all the easiest thing in the world we're all doing it but um but there's a sense in which we like time travel to the past this creates a situation where things that are future in some sense are also past in some sense so they might be in your personal future and and also in your personal past and and that creates some problems but a lot of the problems might be problems that we would get anyway so in English when we say that something will happen we usually rule out the possibility that something else could happen or we're just expressing an intention that we want something to happen which isn't quite the same as predict but if we're predicting say no no I predict this will happen we're ruling out that something else might happen um if we try and change something in the past um the fact that it's in the past might make us think well we know it will happen because it has happened we can we can go from the fact that something has happened to the fact that it will happen because the past and the future are just the same um here nonetheless it looks like we can do things in the future and we can bring about things and we have lots of capacities to do things so I have the capacity to press buttons if if there's a situation in the past where my grandfather could be killed by my pressing a button and it and I'm in the past and I'm confronted with this button it seems like I could just press the button and that pressing that button would kill my grandfather um but I know that my grandfather will not be killed because he was not killed because I'm here um so so there's a kind of trick here of how we make sense of on the one hand our having this apparent capacity to do a really straightforward thing and our knowledge that we don't do it so one thought here which is a thought that kind of comes via Elizabeth Lanscombe that we just can't intend things that we think are impossible because if we intend something we we plan to do it and we can't plan to do things that we think are impossible we can plan to do things that we don't know are impossible we can't succeed but we can certainly plan um so if the future isn't really different to the past if you've got a static view an eternalist view on which past future past present and future all kind of on a par there's no real difference between the difficulty of killing your grandfather and the difficulty of killing your grandchildren I mean you probably shouldn't do any of these things and there's a question about whether you do um but that question whether you know what or not is is settled so so the question about what our capacities to do things are just comes apart from whether they happen and so what you can do comes apart from what you will do and given how I think about the past time travel to the past is ruled out already um because I think the difference between the past and future is the future is potential and the past is actual and saying can't be both potential and actual uh well if not in the same way like things that are potential and actual are present according to me but they can't the same the same bits can't be potential and actual like the start of this conversation is actual and the future is potential but the future of this conversation can't both be actual and potential because that would be incoherent so I've already ruled out the possibility of standing in front of a button that will kill my grandfather and so the paradox doesn't get going but um but if you think if you think you can travel to the past that's a bit like thinking that future's already there and so whatever you say about the past you'll also have to say about the future so this isn't just interesting because you know we all like sci-fi stories it's interesting because if you don't think there's a difference between the past and future you need to explain why these puzzles about affecting the past don't also affect the future you know okay so let me try to get a handle on this yeah so famously there's the grandfather paradox so you mentioned that yeah so the question is can you kill your grandfather in the past so if you go back to the past and suppose that he died actually died in 2000 then you went back to 1950s and killed can you kill him at that time I think that's the then some philosophers would say you can't do that because that's changing facts in the past but we can't change the past some other philosophers would say yes you could change the past but that's another way of oh that's another could or can your view so far as I understand it is that well you can change the past but it's forever there it's a potential but it's not an actuality am I getting your view no so I think that you can't change the past and if you were going to be and indeed lots of people who think time travel is possible think that you can't change the past they think that you have a loop where you can't change the past but you can't change the future either I mean I don't think you can change the future because I don't think there's a future there to change but I so yes there's a couple of distinctions that are useful so one is whether you can change what happens at a certain time another is whether you can affect what happens at a certain time so for me if something has happened at a certain time you can't change that it's happened it's actual it can't go from the actual to not be actual and and so that's why I don't think the future exists because if it did exist it would be actual and you wouldn't be able to change and you wouldn't be able to change it if you would be stuck with it and we would just be kind of a node in this this network of counterfactual dependence we wouldn't actually be doing it people who think um the past and future both exist they they don't need to think that you can change them and they just need to think that you can affect them that is that you can causally influence them and the difference between them and me is I think that you need more than counterfactual dependence to cause the influence something you actually need to bring things about bring them into existence so I've just got this much richer notion of causation and that's where the disagreement comes in but sure there's a sense in which there's nothing stopping you having a counterfactual dependence between you and your grandfather such that if you hadn't traveled back in time your grandfather wouldn't have died the problem is that you also counterfactually depend on your grandfather not dying right right because he has to conceive your parents and your parent has to conceive you in order for you to show up and now you might think what about a case where it's just contradictory in that case it doesn't look like however you came into existence was caused by that thing that you affected that there as it were branches one of which you're on and one of which your grandfather gets killed on but the branch on which your grandfather get killed isn't your past it's somebody else's past or nobody's past or something you know and so that's not really changing the past that's just creating this extra branch which doesn't affect you is it well do you consider that as time travel no okay no that's dimensional travel or something yeah that's good so we're clear that's not time travel here that's not time travel yeah so back to the future isn't a time travel film and unfortunately for you guys okay and I mean whereas um I'm trying to think Bill and Ted's excellent adventure is excellent like seriously Bill and Ted's excellent adventure is one of the best time travel movies ever it's totally consistent yeah I agree I agree um sometimes people stupidly think that 80s comedy films can't be philosophically deep but they're wrong um so so yeah so we've got this idea of can you affect the past there seems to be no reason why you couldn't have the right kind of counterfactual dependence apart from that you generate a loop and that loop seems to be inconsistent um but the mere fact that it would be inconsistent doesn't seem to affect anybody's sort of physical capacities so you either have the kind of banana skin approach where there's nothing to stop you know you can have all the capacities they will just fail for just various kind of coincidental non-causal reasons you'll just slip on a banana skin just as you're about to press the button and then fail but you've got the capacity right step on the button and of course capacities here aren't very modally rich they're just descriptions of um abilities thing of yeah descriptions of abilities um in terms of of impossibility of things that could could be possible with each other whereas when I talk about capacities I'm thinking of things that can generate effects and bring effects into existence and so that rules out the very possibility of time travel so it's a difference between a kind of humane approach to causation um where you just think um causes are are just kind of descriptions of non-accidental regularities of some kind or or counterfactual dependencies whereas I think that there's something kind of productive or as they say in Australia biffy there's some biffiness or and where something makes the other thing happen there's that there's a connection a modal connection between the two and given how I think that works you're not going to get time travel to the past going because you can't make sense of that kind of causal connection all right so there's another argument here that's interesting the nowhere argument are you what is that argument all about so it's another time travel uh it's against time travel right so I'm not I'm not sure I know this argument under that description so the nowhere argument so how can you travel to somewhere or some wind that does not exist so if you are oh yeah yeah no I yeah I'm fairly with you yeah I mean of course it always exists when you get there right and yeah so so I um I did a nice talk on this in Birmingham a few years ago actually um so it depends I mean again this looks like it creates a problem just for normal views of time right so on my on my growing block view and I think the present is being created as you go you know like it's and it's always present when you get there but it wasn't present I mean it didn't exist until you got there and it's um it's you're being created as much as it's being created and so on so you have to have some story about how that works in my case it's a kind of causal story but um it's not just that when I'm playing pool and I have one billiard ball bashing into another billiard ball that the causal impulse goes from one to the other but the the pool table that gets brought into existence and you at each moment by causation as well that there's this sort of causal fizz and of of creating the next spacetime atoms and and whatever properties they have so in the case of time travel you've kind of got a problem of how there can be action at a distance so how something over here can cause something to come into existence over there even if you're going into the past you can think of it like um an old kind of vcr where you're recording over the vcr like how can you how can you have the equivalent of the the erase head and then the the right head kind of sweeping through the past you've got to have some kind of mechanism for doing that if it's causation how can causation happen across this distance if it's something else how can that work um in this way how does it know when to go couldn't you have like a horrible problem where you travel to one time but the rewriting happens at a different time you just get stuck in this moment and then there's always change happening in what previously was passed but going forward so so this kind of challenges you to have some account of what's happening when time passes normally and to work out how that account can account to travel to somewhere else and and yeah i'm i'm very skeptical that whatever good account you have of what what is for time to pass normally what it is for the for one present to become another present that that's going to make sense if you try and do it for like a distant time okay so we've been talking about your view but let's try to make it more explicit so you and your co-author Ray Briggs defended a version of the growing block or growing universe view so yeah let's first distinguish that from cd broad's growing block yeah okay um so cd broad um for one thing didn't think that there were any truths about the future so certainly with my work with Ray we were interested in in understanding how there can be truths about the future so the general idea for the growing block view is that the the past exists and the future doesn't and and the passage of time is stuff coming into existence or cd broad would put it becoming so so far we agree with with cd broad we've got past exists future doesn't and there's becoming absolute becoming so it's not merely becoming from my perspective it's it's becoming without further qualification and as i've kind of gestured too earlier the reason we care about existence is that stuff that exists is in a position to make sentences true so we've got sentences about Julius Caesar Julius Caesar was assassinated i think that's true and i think it's true because of something involving Julius Caesar and and some knives and Brutus and the point is i seem to be talking about someone and saying of him that he was assassinated if i compare him to a fictional character like or Elena snow from the hunger games doesn't really seem in the same way that i'm talking about anybody i might pretend i'm talking about somebody but it's not like i can point at the person and go you know i'm talking about that i can point at the actor but that's not quite enough um so so that's the reason for thinking the past exists and broad has a fantastic explanation of why we can't talk about the future and it's not really an argument it's just uh a kind of nice nice analogy and you can't talk about the future for the same reason that prevents you from robbing a highlander of his bricks so for those of you and not familiar with Scottish culture and those from the highlands are famous for not wearing trousers or beaks but for wearing kilts so you can't take the the bricks off a highland man because he's not wearing any so you can't talk about the future for the same reason that stops you wearing um from stealing the trousers off someone wearing a kilts there just aren't any trousers to steal so that idea that our ability to talk about my grandchildren or fictional characters isn't the same as my ability to talk about historical characters even though in the case of Caesar he's also a fictional character in Julius you know Shakespeare's Julius Caesar but we can go look Shakespeare you've got Caesar wrong that's that's made up that didn't happen you know the the events of your play are massively compressed to compare to what happened you can have a little entry on Wikipedia that says historical accuracy this is inaccurate in the following you know um so so we've got that sort right so given we've got that sort Ray and I were really concerned to work out how we can make sense of all the truths it looks like we know about the future it looks like we know that coronavirus isn't going to be finished next week okay like it looks like I'm really going to plan my life around that like it's not it's not just like well you know I've kind of got this feeling like I think I've got really good evidence as much as I've got evidence for stuff I know about the past you know um so we need some account of future truth but our idea is we should be able to generate this this account of future truth in terms of what's already happened and whatever it is that constrains how the future goes so the laws of nature or or whatever um whereas Broad just says that there aren't any truths about the future and that's kind of odd because as we've just said really looks like there are lots no going back to the the issue about the past so when we talk about the past there's something concrete at least a historical past so we can talk um there are truths about the past okay yeah you might have evidence about it but if you are going for the growing block view isn't that inconsistent because from the point of view of past people the historical due to Caesar we are in his future so for him we should not exist or we don't exist how how do you handle that okay so there's no internal incoherence here okay unless we accept McTaggart's argument I mean so basically that this objection is um and and Craig Bigborn actually specifically said this is a version of McTaggart's argument and so so that's the first thing but that's that's not that's not an argument yet that's just me denying that there's a incoherence like right right I refuse you that so the second thing to note is that Caesar doesn't have a point of view like one of the most famous things about Caesar is that he's dead okay right that's a fact yeah dead people don't have points of view I'm kind of assuming here um so so I think the mistake here comes and it's a natural mistake for lots of people to make um it comes from thinking of the growing block as being like a static block but with the end missing so you've got all these people who are present at each time that they they exist and then there's this other moment which in some other sense is present and there's some sort of causally stuff going on here and then there's a gap um that's not how you should think about the growing block view but it's not that they really disagree with the static views about what present this is so look I think the Caesar exists because I think there are all these truths about Caesar but I don't think he's kind of wandering around I don't think he's doing anything kind of present continuous apart from maybe decaying but that's as it were Caesar's corpse or something it's not Caesar anymore okay so um the past in some sense is like the present in the they both exist modulo the stuff I said about the existence of the present being slightly tricky um but stuff like living seems to require not merely having some some matter but the matter being engaged in various processes so respiration metabolism digestion um having a point of view seems to require processes too for example living but you know perceiving thinking lots of things ending in ing so the thought is stuff that's past that isn't ongoing um like this conversation is ongoing like stuff that's past isn't engaging in any of these processes it's it's it's spent it's it's causal fizz it's now just a series of states at times but of course these states are times that are such that if they were present we know what kind of processes they would be involved with because we know we know about the change from potential to actual that you get when these kind of states and the laws of nature meet the potential of the future but they kind of they've not got any potential anymore they've used it all for good or ill and and they're just kind of statically there now in a much more you know in the static sense which i think all static views are committed to but static defenders of static views in i but there's nothing happening there's no kind of creation of effects there's no one going there's just a pattern of states spread across time we can use this pattern of states to to get truths about what did happen but it's not happening anymore and so seiza has no point of view he's not living he's not in a position to criticise us of course back when he was present he was um succeeded by no times just by potential and had all this potential and was turning potential and potentiality into actuality he wasn't in a position to say hey you guys are future because you have no idea who we were but he was in a position to think hey you know there's a load of future there but that'll probably be different from this and probably you know maybe we'll read plays about me after i'm gone and maybe horribly mischaracterise me he was in a position to think that but that was ages ago right that's that's not happening anymore that's the past no there's always kind of two senses of past here the past is the once present and the past as no longer you know of what was no you made the distinction i think that's important here so you're talking about the past as states so you have past yeah but they're not events they're not happening now i mean there are events in the sense the events are just there filled regions of spacetime so like coin talks about events in that way so i tend to distinguish between processes and events and there are no processes but the literature is really confusing and events means all sorts of different things in different places so the way i'm using it if we use events as coin did for the filled regions of spacetime loads of that but no processes no no change you know changing unfolding activities so the past has those events or states yeah they're not moving they're not processing they're processed in the past yes exactly they're processed but not processing yeah so we are processing right now and the future for you is what what potential potential so we are in the process of coming up with the future or making yeah actually raising the potential yeah yeah so but you're saying that there are future to there are truths about the future so oh what's your story about the future contingent so to the extent that there are any truths about the future they are constrained by some what ray and i call and some element of the nomological package so there's some some some kind of causal or modal thing and could be the laws of nature could be dispositions or powers we're not really too bothered which you pick plug in your pet one but it's going to be realist it's going to be constraining in a way that a communion picture where it's just a mosaic of different things and this constraining modal thing i'm just going to use laws because it's a nice short word and there are these laws and then there are these states in the past and present that create the kind of initial conditions for the laws and the laws might be chancey that's fine but whatever truths there are about the future are just the truths that are generated by the combination of the laws of nature and the states that they're already up and yeah so and if there are multiple opportunities you know multiple different possibilities and we provide three different semantics for dealing with those but the super valuationist one is kind of the most straightforward and if every way the future can go there'll be a sea battle tomorrow then it's true that there will be a sea battle tomorrow if on none of the ways the future can go there'll be a sea battle tomorrow then it's false that there'll be a sea battle tomorrow and if on some of it some of the ways the future can go there will be and on some of the ways the future will go there won't be then it's neither true nor false that there will be a sea battle tomorrow and in fact in our more recent paper you can potentially put like a number on this and say it's 0.8 true that there will be a sea battle tomorrow i'm not so committed to the the degrees of truth thing and i'm happy to call it like it's 0.8 likely it's it's more likely than not that there'll be a sea battle tomorrow but it's not true that they will and it's not true that they won't be okay so let me figure out the semantics here so there's a super valuationist semantics on the one hand yeah where some truths will be super true some future truths will be super true or super false and some others will be true or false some others will be neither true nor false and but you're not going for the fuzziness the the degree so to why is that because i reckon that i mean so officially rey and i do go for the the degrees of truth i'm i'm happy to talk to that you know talking that way uh-huh for the purposes of a plane i'm not sure i know what a degree of truth is unless it turns out to be something like a likelihood yeah probability right probably yeah um but but officially that's how we talk um so and so mainly i don't want people to get put off by this degrees of truth thing oh that's really weird and i mean it's essentially just committing to there being a way of having some gradation between the thing that's definitely gonna happen the thing that's definitely not gonna happen like we can we can say how likely something is and it's kind of quite straightforward theoretically to have a truth value of one a truth value of zero and then truth values in between right you don't like if you put off by that just don't talk like that i think rey is thinking about uh decision theoretic language as well because you could plug in your decision matrix and so i'm using this language okay so finally so we had a question come up on what would mean for the future to be probabilistic so and maybe i can clarify that so literally the for the future to be probabilistic is just for the laws not to determine exactly what happens um but perhaps to make and so it could be that there's like a 50 50 chance and it could be that the laws um actually give you particular probability probabilities i mean it could be that there are situations where we can't put numbers on it and there's no you know there's no way of over-signing probabilities but it could be that something genuinely random um i've got this you know atomic you know particle with a half life there's a 50 50 chance um that it's going to decay in a certain time period half the possible futures that we're we're kind of imagining in our model are going to be ones in which it decays after the months and so that's how we get the 50 50 probability but it's going to be whatever in the laws of nature makes it the case that this atomic particle has a half-life that's doing the work here okay so before we entertain the questions from the audience uh last so both of us are part of the new generation of academic philosophers so what's your advice for people who may want to get into a career in academic philosophy okay so i've been thinking about this a bit um academic careers are quite tricky to get into like one of the rudest things my sister has ever said to me was that once she takes early retirement from her career in business she might become an academic it's not a hobby you know like like it's actually a really difficult career to get into right and takes a lot of work and involves a lot of career uncertainty and so for myself um i was it was about seven and a half years from finishing my phd before getting any job security you know before having like a permanent job that's kind of not not unusual some people are a bit quicker some people take a bit longer some people never get careers at all um that's that's something that you need to go in with your eyes open about we would be misleading you if you we didn't warn you of that nonetheless you know if an idiot like me can can make it there's there's going to be some hope for you guys um i think so my tips are it's much more of a team game than it often appears so a big mistake i made when i first finished my phd as well my supervisors aren't getting paid to supervise me anymore so i mustn't bother them and i mustn't you know i just have to sit in a room by myself and tap away at my computer and produce excellent philosophy that's not a good recipe for producing philosophy i mean they can't mediate and meditated in this you know pot-melod stove and produce the meditations and they're terrible um he's totally wrong you know end up worrying about demons that might be deceiving you and stuff no and actually having a network of people that you talk to attending events like this you know bouncing ideas off people that's really important um it's also important to have a life outside of philosophy so if you get a rejection which um all of us often do um very frustratingly a lot um not your entire you know self-esteem is hanging on that you've got you've got something we go no i've got a nice life um i'm going to go for a walk with my friends and we're going to complain about and then come back and have another shot at it um one of the other final tips that i want to give is like any loving relationship the love of wisdom can require work from time to time to rediscover what it is you love about it um and like any loving relationship sometimes love isn't enough um you need to put the work in you need to you need to rediscover what what makes you love what you do but you also need to be lucky and and you need to have the right kind of situation and some jobs aren't worth having um have you know own the decisions you make like either love the job you're in or look for another one and lots of people it turns into a competition where i just have to get an academic job so i've i've won and they end up accepting a job in a really toxic place that i hate and i'm just miserable but i won and i i myself you know turn down the opportunity of a permanent job because i couldn't see myself being in that institution for for a long period of time and then was very lucky to land the job that i got now um so um yeah take take ownership of it love what you do but you're not alone and try and try and look after each other and support each other okay so thanks again graham for sharing your time with us yeah join me again for another episode of philosophy and what matters where we talk about things that matter from a philosophical point of view thanks