Metaphysics of Time: McTaggart's Argument Explained

[00:00:02]hello everyone so my plan is to use the handout that the extended hound outlets on Moodle to use as a base for what will be I guess a sort of lecture on the topic of the metaphysics of time so I'll basically talk through the hand now hopefully elaborate a bit especially on difficult points in an effort to make them clearer the the handouts together with hopefully this lecture and the readings on the topics of the metaphysics of time will provide you with a solid grounding in the topic so so for the most part we so far in this sort of interrupted course we've focused on space and then latterly the nature of space-time so thinking about the relation of time to space and the integration of time within special relativity theory now we're going to focus more on time specifically in its own right and in order to do that we're going to examine to start with one of the most famous philosophical arguments and certainly I think the most influential philosophical argument that's been advanced concerning the nature of metaphysics of time which is due to McTaggart and we'll see that actually McTaggart thinking and arguments although generally they're rejected have never less help to frame a lot of the debate on philosophy of time since because different people disagree on which part of McTaggart argument ought to be rejected and that's come to define a lot of interesting positions in time so why focus specifically on time rather than just talking about space-time well one one reason is that time seems to have some interesting features that the spatial dimensions lack right so it's not just the math that seems like it's not just another dimension right so a dimension that happens to be labeled team and cough tsuki space-time diagrams it seems to have sort of rather different features from that the three spatial dimensions so specifically we normally think of time as directed so we think that there's very symmetry between past and future we'll talk more about what that is an asymmetry might amount to in in the way in which there are some analogous spatially symmetries so the the difference between and up and down according to one spatial dimension there's nothing doesn't seem to be really thing really metaphysically fundamental about its sort of arbitrary relative to a point of reference you know such the earth you might find up and down relative to our position on the earth you know might be there are differences between what lies above me to what lies below me but that all looks very contingent just to do with the contingent arrangement matter whereas you might think there's something more metaphysically fundamental about the difference between future and past and well that's something we'll come back to another difference is that time at least many people seems as reasonably thought to have a flow to it so we often speak of the passage of time or the flow of time you might hear and analogies drawn between time and a river or something like that which also seems to have a flow to it whereas doesn't seem to be any obvious analogous flow to the spatial dimensions so it's a little bit weird to talk about the flow of space or something like that so again this suggests that there might be something metaphysically interesting maybe physically interesting about the time dimension it just doesn't straightforwardly apply to a three spatial dimensions so questions have been asked by philosophers and that will touch upon our what accounts for the apparent asymmetry of time what if anything accounts for that what if anything accounts for the apparent flow of time or is the flow of time just something like an illusion what exists in time so do any present things exist or the future and past events and objects exist and these are some of the questions we'll touch upon but first look like some MacTaggert so McTaggart I suppose his argument is one that naturally has drawn a lot of attention and actually continues to despite the fact that it was published over a hundred years ago and partly that's because of the very surprising conclusion them Kosmic tag argues that time is unreal now that's weird we'll see a bit more about what it means and as I say most most people probably have have rejected it but they did do to an interestingly different ways so McTaggart starts off by claiming that events in time or moments in time so you can think of a moment in time I suppose especially if you think times absolute it might be like a particular position in space or a space time point or something but a sort of exposure I think about how many time is a sort of point among that along the T dimension this so that moment is an event is a sort of thing that might occupy a moment in time or might have past occupy moments in time so friends it's regular events like the football match my occupy multiple moments of time I'd be extended in time maybe they have a part corresponding to each moment in time so McTaggart claims the events can be distinguished in in two different ways as they exist in time so the first is that events can be distinguished according to what he calls their a properties so a and B are just labels quite boring labels but they're just labels Montag gives to these things they're arbitrary labels so the a properties he says a properties like being past being present being future as well as more specific properties like being two days past been 20 years whew so we can distinguish events according to those properties one difference between I suppose Henry gates and Prince William's great great grandchildren is their one lies in the past whereas the other lies in the future or something like that another way we can distinguish them is according to what he calls their B relations so B relations relations like is earlier than is later than is simultaneous with is during and also more specific ones like his two days prior to his thirty years posterior to and so on so for instance we as well as same Henry 8th is in the past whereas Williams great-great-grandchildren or in the future we presumably can say that Henry the 8th is earlier them the eggs are objects I should talk about their lives maybe because those would be things that were event so the life of Henry Hayes is is it is not only past but its earlier than the lives of Prince William's great-great grandchildren okay so we have this two sort of ways of distinguishing events in time hunt away properties are going to be relations now McTaggart points out that B relations are permanent right so if one event is earlier than another so for instance the first world war is earlier than the second world war then it's always the 10 so is the case that the first event silly ii said that if it's sure one time that the first world war is over the second world war then it's always going to be the case that the first world war is the second world war a properties different they're impermanent so something that was once future you know at some point of time they the first world war was future then it became present and then it became past so these eight properties i don't like to be relations seem to change now matenda points out there corresponding to the eight properties and the relations of events there are two ways in which we can order events in time or think about them being ordered in time so you can think about them being ordered in terms of their a property so for instance how distantly past they are when they're present how distantly future they are or we could think about them as being ordered according to their be relations so the idea is with order events in this series which is called the b-series as opposed to the a series according to whether that event was earlier than or later than others and how how much earlier it was or later was than others now these sort of two ways of ordering presumed to be equivalent right so I guess the most distant past events come earlier than all of the subsequent ones today the a series is going to wind up producing the same order as the the B series but it's just two ways of thinking about that order okay so targets argument metalia draws upon this notion of the a series that is the way of ordering events according to the a properties and the B series that is the way of ordering events in time according to their B relations in giving his argument that time in fact doesn't exist so how does the McTaggart so I can go well it's laid out on the handout and the first premise is that there could be no time without change soma Taggart thinks that change is essential to time we'll go into this premise shortly and explain think about why will my believe premise one secondly he argues that the a series or the a properties are necessary for change so they're essential if there's gonna be change he then says the VA series is contradictory and he draws from the premise three their premise that the user is contradictory the intermediate conclusion ulema the VA series doesn't exist and you know that seems if premise three is true then it seems that this intermediate conclusion that I've laid but lemma one must be true right so it doesn't seem that anything that's contradictory could exist he then draws another intermediate conclusion which is that there's no change right so he said that the a series is necessary for change which is premise two and he says that the a series doesn't exist but if the e series doesn't exist and yet the a series isn't necessarily change that it seems that it can't be any change so that's the intermediate conclusion or lemma two and follows from premise two 1 and lemma 1 and then the overall conclusion of the argument is that time doesn't exist and this follows from lemma 2 namely that there's no change together with premise 1 which says there couldn't be no time without change premise 1 there can't be time without change we've inferred already that there is no change so it seems to follow logically deductively that time doesn't exist now it seems that this is a vow arguments so buy valid I mean in the the narrow Philosopher's sense that if the premises are true then the conclusion has to be true so the conclusion deductively follows from the premises saying that an argument is valid doesn't imply anything in this sense about whether the premises are in fact true and many people would argue that one or more of the premises is false but if we ground the premises it seems difficult to avoid the conclusion it seems that the arguments valid so what's McTaggart justification for the premises well when it comes to premise 1 there can't be any time without change he thinks it's more or less self-evident so he thinks that a universe with nothing at all that changed would be a timeless universe now I suppose you could sort of try to get a grip on this I suppose by try to imagine a universe where nothing changed and you might sort of think well you could kind of imagine that see you sort of I suppose if I try to do it at least I sort of imagine myself staring out at a scene maybe the last scene of galaxies and so on in which nothing changes right so there's there's there's I don't observe anything to change at all you know maybe I'm viewing this I'm getting increasingly bored because nothing's going on to interest me now I might think ok yeah so sometimes elapsing nothing's changing that seems possible but what's really going on there is I'm sort of supposing that my mental states are changing so you know I'm looking out at this scene thinking about - getting increasingly bored and so we at least still have some change in this universe but if I sort of try to imagine I genuinely changeless universe where no no physical objectives changing no mental state of any observer or anything is changing then then maybe this becomes increasingly hard so this is a sort of motivation that megataiga has for premise one many people accept that couldn't be time without change but it's definitely not completely uncontroversial so if you're interested in the debate about that premise then the papers by shoemaker and Laporte even on the further reading list for this topic the shoemaker argues that the can be in fact the time time without change and the point of aim is a response to Schumacher but let's let's grant it for the sake of argument what about premise two premise two is the a-series is necessary for change so McTaggart does provide a extended justification for this the justification is that the be relations are as is observed permanent and unchanging so if world will once earlier than World War two then it's always earlier than World War two there's no point in time at which that temporal ordering reverses or something like that so thinks it's only a properties that could change right so it's the properties of past nurse present as Futurity are the sorts of things that can change the eight properties now you might think that you don't actually need the a properties for change because you might think that regular properties can change so you might say well look an apple could go from being green to being red to being brown as it ages [Music] so Bissell is changing in its color properties not these fancy a properties of past Nespresso most Futurity but the response that McTaggart will make to this would be to say that this change in regular properties is in fact nothing more than a change in a properties so in other words what he'd say is that the green state of the Apple goes from being present past the red state of the Apple goes from being future to present to past and the brown state of the Apple goes from being future to presence and so on so basically in order to understand change in ordinary properties he will faint or he will claim that we have to appeal to a properties so what makes an object change in its ordinary properties is that the state of its exhibiting those ordinary properties changes from whether it's past present or future okay so this premise that the a properties are necessary for change is definitely controversial in spite of what Montag it says and what we'll see is that it's rejected by a US of school or tradition of philosophers of time who have become known as B theorists right B theorists normally agree with McTaggart the a series doesn't exist or is problematic but they rejects McTaggart conclusion that time doesn't exist and that's because they reject his premise that the a series is necessary for change they claim that in fact the be seriousness is is efficient on its own for change in time what about premise three so the a series is contradictory so McTaggart in order to justify this says well the a properties of past nurse present nurse and future nurse of Futurity are incompatible right so nothing can be past present and future but ii suppose the basis exists is to suppose that every event has all of them so the first world war has the property of being past being present and being future which is contradictory so supposing that events have a properties and stand in the series because it implies that these events have all of the a properties results in a contradiction so everything the result everything results in a contradiction can't be true so they can't really be a properties and then a series and given these a properties are necessary to change and change this or for a time he thinks at time is unreal okay i should caveat that right so i suppose if there's a first on last moment in time there may be some events that occur at the first moment of the universe only have the properties of being present and past and never have the property of being future whereas events in the last moment of time have the properties have been future and present and therefore the property you can past but is there any event in the a series has at least two of the three broad a properties now you might think that look McTaggart just made a mistake here a basic mistake here and actually a serious and contradictory doll at least he hasn't shown it to be McTaggart AG anticipates that the reader might think he's made a mistake here and he talks about the natural objection that the reader might have right so the the natural objection to his claim that the a-series is contradictory is to point out that it's just not true that some any event has two or more of the a properties at the same time right so what would be contradictory is the first world war say to be past present and future at the same time we can't have all those properties at once but of course no one wants to say norm claims then they have all of these properties at once right so what it would be natural to say is that the first world war had the property of being future prior to 1914 it had the property of being present during the years 1914 to 1918 and has had the property of being past subsequent in 1918 so there's no contradiction right it's perfectly coherent that's something that was future should now be present and should be going to be past that's the natural objection the contradiction would only be in supposing an event house all of these properties simultaneously now McTaggart anticipates this and responds that surely the natural objection involves a vicious circle or a regress in that it presupposes the existence of time in order to explain the compatibility of the aid properties so the idea is there we need to presuppose time if we're going to save that actually there's no contradiction because the first world war doesn't have the properties of past present and future us at the same time it's when we say at the same time that we presupposed the existence of time and we might say in the past it was future and then present and now it is is past but again we're talking about past and what's true past and what's true now so we presupposing these a properties he would say with presupposing the property of being past when we explained how it could be that the boodle was future and present we're presuppose in the property of present nurse when we say well it's now the case the first world war was past so he thinks were often or something like a vicious circle or a vicious or a grass in having to presuppose time and therefore the a-series in order to explain how the a series is not contradictory so looked at it thinks that there's some no refuge from this this parent problem with a series now not everyone's convinced still so in particular theorists who are now known as a theorists reject McTaggart premise 3 they reject the idea that the a series involves a contradiction and hence they reject my tenets argument that times and real so atheists normally believe they're well they do believe that there are are a properties and normally they would take those nè properties to be necessary for changing therefore time now ok so how do they resist McTaggart response the natural objection so how do you resist this claim that we use when we try and explain the coherence of the a properties we have to fall back on appeal to time itself for the a properties themselves and so off on a a vicious circle or a vicious or a grass or something similar well the natural a reasonable response that they might appeal to is to say something like the eight properties in the a series are something like basic or primitive and can't be explained in terms of or reduce to anything else so they might say it's just a brief fact that it's consistent for an event to be present to be going to be past and to be to have been future and you can't explain this consistency in other terms so this seems a kind of a reasonable points if you're going to take the a properties to be basic then it it it's quite natural to think that you're not going to be able to explain them without appealing to those very properties themselves so in other words explain them in other terms for instance I mean by analogy suppose that we take space to be basic it's gonna be very difficult to explain what space is without appealing to that that very notion and the same applies to things like causation and other philosophically interesting notions so some people think these can be reduced to other things but many people think that they're somehow irreducible and so the best they can do in giving an account of these things is giving a a non reductive account so they might explain some causal relations in terms of other causal relations or something like that but you can never get away from that concept of causation if you're a if you think that that's a a basic notion so there's there's a sort of there's a big issue in position you can take namely that these are primitive that doesn't make it that surprising that you can explain these in other terms and the fact that you can't explain them in other terms doesn't necessarily mean that a notion is incoherent as McTaggart seems to be claiming but just that it's basic right you can't define it away in in terms of something else okay but let's return for now to Montag excitement so he thinks obviously that changes needed for time the a series is needed for change the a series is incoherent and the a series doesn't exist therefore there's no change therefore there's no time now actually because McTaggart thinks that the a series doesn't exist he also thinks that the b series doesn't exist either so why is that obviously this is going to be claimants rejected by B theorists who themselves believe in the existence of the B Series but normally reject the a series mukha targets claim is that we need the a series to make sense of the distinction between earlier than and later them so this is the the B relations so for instance it's only by supposing with E is present but F is past or years future but F is present or is future but F is past and so on that we can make sense of EB later than F and likewise for F's being earlier than these things only in terms of their having different properties of past us and present us that we can make sense of future future aarati that we can make sense of the notions of earlier that and later that that as I said to be theorists will contest this and we'll come back to that okay now what doesn't target exactly so let's have it's completely the time is unreal but it's worth being some a bit careful about exactly what he means by that what is Hicks is I sure know the words and what he doesn't take it show so what he doesn't take it to show is that there's no fourth dimension right so nothing that would label T I suppose in a spacetime diagram what he does take it to show is that this fourth dimension doesn't have the characteristics that would make it something that we could properly call a temporal dimension so it's kind of more a now I guess to a spatial dimension if anything rather than a distinctively temple by mention and that's because there's a lack of change so there's no real passage or maybe direction of time 7th dad will tell it does indeed seem to think there is a fourth dimension so he calls it the CSeries so essentially that's what's left of the B's series when we do away with the distinctions of past and future right so once we get rid of the eighth series this undermines a b series but there's some sort of residue left of the b series so the C series basically has there's an order to it but there's no kind of direction right there's no past future distinction and therefore no earlier than later than distinction so for instance in the natural numbers 1 2 3 and so on have an order there there's no real privileged direction in which they're ordered I'll explain this in a second so so yeah I mean so consider so we might we might not try to make sense of this ordering in terms of a betweenness relation when it comes to to this C series of this this fourth dimension so one thing we could say is we could appeal to the notion of between us that doesn't suppose nearly as a no later than distinction for instance one might say that World War Two was between World War One and the Vietnam War in this fourth dimension just as we can appeal to between us when distinguishing points in space so we could say something like London is between Paris and Edinburgh I mean that might not be exactly true but we do that in a more precise way so so the analogy is supposed to be that we could we could appeal to between us World War 1 is sorry World War 2 is between World War 1 and the Vietnam War and also for instance World War 1 is between the American Civil War and World War 2 and this get this doing this sort of thing gives us an ordering so we have the order in could be American Civil War World War 1 World War 2 vet now war so in this order in World War 1 and World War 2 lie between the American Civil War and the Vietnam War well the one lies between World War two in the American Civil War and World War two lies between World War one and the Vietnam War but notice that we don't have an asymmetry here in the sense of a sort of privileged early then and later them distinction so there's nothing to privilege this this or during American Civil War World War One World War Two there now war over the one that sort of goes in Reverse Vietnam War World War to World War one American Civil War right so just as when we appeal to betweenness to order Edinburgh London and Paris there's nothing privileged to an ordering that says an ordering that says something like Paris London Edinburgh for one that says Edinburgh London Paris there's no some sense in which Edinburgh is prior to Paris objectively or Paris's prior to Edinburgh all we have is is this sort of symmetric ordering and so the claim would be that it did this goes the the fourth dimension too okay so MacTaggert still I think house bit of experience new so even if we accept all of this we might say well look we experienced the passage of time we experienced change so how's it out for that if there is no change and if there is no time now McTaggart spaces we can argue that Timon changed passage of time change are in fact illusory so he does this by arguing that our impressions of time actually just couldn't correspond to anything objective so they must be something wrong with them they must be losery so specifically pills the facts or the notion of the experiential present that is the set of all things that are experienced by an individual as being present now it's well known from psychological experimentation and I guess even was reasonably well known in McTaggart stein that the experiential presence isn't an instant but rather an interval so for instance you can do psychological experiments where a sound or two sounds were emitted from the same at the so distance from an agent and they're not absolutely simultaneous but rather one is emitted slightly before the other and nevertheless the agent will experience them as being simultaneous so present at the same time there's even experiments that show that in some cases you can actually get the the agents experience is of the sounds to be reversed from one we might want to say the objectively are in times so the earlier one is experienced as later and vice versa that's even though they're emitted at the same distance from the agent there's also empirical psychological evidence of time dilation or psychological time dilation and contraction not to be confused with the special relativistic phenomenon basically you can sort of most of us have had some sort of experience of this so time seems to pass very slowly when you're bored maybe but it also seems to pass slowly when you're in danger than if you've ever had this experience but somehow you sort of perceive a higher resolution or something when you're in danger so it seems as though that time sim see that that time time slows down you know and we've all heard the sort of sort of folk expressions like time flies when you're having fun but there is actually some serious psychological research that shows that we we're subject to these temporal illusions now so McTaggart basically takes phenomena like this and says look what reason do we have to believe in a flow of time and [Music] something like an objective presence if there's just no systematic relation between this and the experiential present or the experience is present or the the flow that we seem to experience so he thinks there there you a reason we could have of believing an objective present an objective flow is because of our experience which seems to be of a present and a flow but actually this experience couldn't represent anything objective so there's no reason to believe in the objective phenomenon now of course you sort of might try to resist attend its argument so you might think that well these psychological experiments actually sort of presuppose an objective an objective present an objective flow of time so for instance in describing the one involving the sounds you know I said well the sounds are emitted at the same time sorry at different times one earlier than the other there are either experienced by the agent simultaneous so as Co present or it's the case that the earlier ones experienced by the agent as later than the later one so if saying things like that I'm kind of falling back upon the sort of notions of present us and past nurse or at least there the B relations of early event and later them that tagging is trying to reject and so in general in explaining how people are subject temporal illusions where so falling back on the idea that there's an objective passage of time that they're somehow misrepresenting so you might sort of think that even this talk of illusions presupposes an objective passage of time so Montag it can't escape that that easily okay in any case so mo philosophers as I've suggested think there was something wrong with me targets argument so hardly anyone wants to accept that time isn't real even in McTaggart sense in which there's perhaps a fourth dimension but it just isn't distinctively a temporal dimension now since we've seen McTaggart segment appears to be valid these philosophers have got to reject one of its premises and philosophers are divided over which to reject so we've already seen that a theorists tend to reject or do reject premise three so they reject the idea that the a series is incoherent they accept the existence of a properties they think that event change with respect to these eight properties and that this change in a properties corresponds to the passage of time which they take to be a real objective feature of the world does not a loser II and normally they'll take the eight properties to be primitive you can't reduce them to anything else and this as I said allows them to escape something like the net with a natural objection that Montagnard most certainly Taggarts responds to the natural objection that is circular on the other hand B theorists reject this series but they think that actually don't need the a series to make sense the B Series and they will normally think that the B properties alone are enough for change in their for time so they reject premise to amend its arguments so some of them also reject premise one so they - you don't think you need change genuine change for time yeah so so beef there is so that's one question is how do you make sense of the relationships of earlier than and later that if you don't have the a properties so a is early than B if for instance a is in the past of B's in the future where has a it's later than B if for instance a is and the future of beers in the past so how could make sense of later than earlier though if we don't avail ourselves in that way of the distinctions of past present and future us the a properties in other words well I mean basically the sort of strategy that's often appeal to is a strategy that gives a notion in which the temporal dimension is asymmetric but doesn't rely on the series to give that asymmetry so one of the most well known accounts of the direction of time or the symmetry of time appeals to a notion of entropy increase associated with the second law of thermodynamics so the idea is sir entropy is a measure of roughly speaking a measure of disorder if you're interested in this by the way you can look at I think it's the second last topic on Moodle there's some reading some of their action of time or might be the last I think it's the last time potentially but you'll be able to find them fully straightforwardly reading some on the direction of time now okay so if you believe in this sort of reduction of the direction of time to entropy increase or in other words disorder increase then you can just say that well the earlier times are the ones where disorder is lower or entropy is lower and the later times the one where entropy is higher or disorder is higher and so you can make sense fairly than later that without actually having to invoke past as present and future nurse so now that's the sort of thing that move that the B theorist is liable to make we'll talk more about this when we talk about time travel that's our next topic okay anyhow so so that's the the sort of be theorist approach now although they reject the idea that there are kind of a properties of past mr. president's and futures they still want to kind of make sense of our usual ways of speaking so I usual ways of speaking invoke things like you know we talked about the past or we talked in tensed ways you know we said World War happened we don't say it's happening or we say that we will go to the supermarket tomorrow again a future temp statement so they want to make sense of this sort of apparent talk as though there are eight properties without actually invoking eight properties and so actually what they'll do is they'll try and reduce this talk to be relations so this is this point here on the handout so they take that the this sort of talk to be a kind of indexical talk so it's analogous to spatial expressions like here or one mile away so whether it's true that Bloomsbury is here when someone says that depends upon the person's relation to Bloomsbury at the time of utterance and what whether it's true when someone says the BT tower is one mile away it depends upon the location of the speaker at the time of utterance again so the B theorists idea is that analogously a statement like World War two is passed actually is sensitive to the location in there B series that the speaker occupies the speaker's utterance of that of the sentence occupies so when they say world war two is passed that's going to be true if world wat who bears the earlier than relation that is B relation to their utterance of the sentence World War two has passed and likewise when I say that 20:21 is future then according to the B theorists that's going to be true because my utterance of that sentence bears the relation the B relation of being earlier than to the year 2021 so you could say they offer a reduction of temps to be relations although reduct real for a reduction of talk about a properties to be relation so they won't make sense of our talk without saying literary there are eight properties okay so what okay so the that's the eighth in the B theory outlined but what do we think about them so which is preferable if either so atheists will normally argue that their theory does a better job of accounting for the passage of time of a change they'll argue kind of animal Taggart in way that really the b-series doesn't provide enough for time because of the be relations are permanent so then they're unchanging so just because one state of the world is earlier than another state of the world doesn't really give a sense in which the first state of the world changes into the second state of the world because it's just this is just a permanent relation of earlier them whereas if we say that the the the earliest state goes from being present past of the future to present to past then this provides genuine sense in which there's change in the world so you can sit at the the Apple example that we used earlier so it's green state is earlier than it's red state is still in its brown State but this doesn't really provide a sense of change at least the Atheist will say so because it's always the case that the brown State is certain the green stoats sillier than the red state is earlier than the brown State what we'd actually need in order for genuine change they claim is fully the green states to be present and then past and the red state to be future them present then past and for the brown state to be future them present the past and that will give us genuine change so that's an object ssin the be theorists might so that they'll they'll normally try to respond to this there they might say such things as well that we talk about rivers changing over their course now maybe a rivers a bad example but there is a sense of which rate of the flows but like time flows that's analogous used that is only analogy but we might say for instance the river changes from being narrow to wide so it might be narrow near its source and wide at its mouth and yet we don't need to appeal to anything analogous to an a property in order to make sense of what it is for the river to change over its course it's changing over its course is just a matter of its having one property at one point on its course namely narrowness and other points at another point of its course namely wideness and likewise the B theorists might say well what it is for for instance the Apple to change is just for it to have one property the property of greenness and in earlier points than its property of a redness so they'll say that's that's just what change is just like change for the river whereas the DA theorists will say well you know this is enough for real change right there that the river ism isn't really changing it's just in a figurative sense that it changes and changes and they'll say that that the B theorist has only really provide a figurative sense in which the Apple changes but then I mean there are objections the a theory too so one might wonder about whether you can really make sense of the passage of time right so according to the a theorist I'm genuinely passes and that's marked by the transition of events from future to present to past but we really make sense of the the notion of time passing so one might say well if time passes then it surely follows logically that there's a rate at which it passes but then is it really coherent to speak of a rate at which time passes right what would we say it passes at one hour an hour second a second this hasn't really seemed to make clear sense or isn't really sort of seemed to be meaningfully meaningful talk now if you were genuinely to make sense of the the rate of which time passes you might need an external reference points maybe a second stream of time with which to measure the first stream of time just like if you wanted to measure the amount of time it takes for a clock to register a change of a minute it seems that you need a second clock and well you might be skeptical of there's a second stream of time to make sense of the notion of passage from the first string of time another objection to the a theory and this is what it's worth maybe if you're interested especially if you're thinking right now soundless topics it's also worth taking a look at the readings for next week's topic and the handout that I've taught Moodle there is is because as sort of an object of to the a theory from the special theory of relativity so the problem for the a theorist is that the present so they believe there's such a thing as a present and the pretty objective present is supposed to correspond to a set of points in space-time that are all simultaneous right what else could we mean by the prep the objective present if it's not a point a set of points in space-time that are simultaneous but the trouble is that as we've seen in special relativity minkovski space-time really there's no unanimity on simultaneity so in particular simultaneity is relative to a choice of reference frame which corresponds to a position and the velocity or a velocity of an observer so okay I think we can just you know we can get a grip on the notion of simultaneity being reference frame relative but does it really make sense to talk about present nurse being reference frame relative certainly it seems that the a theorist might have to concede that in light of the special theory of relativity so so that I mean this sort of problem is that it it kind of now looks perspectival exactly what's present what's past and what's future looks relative relative wise to reference frame and he might wonder whether this can be sort of reconciled with the view that there are fundamental facts about what's present past and future next week's handout contains some more elaboration or the next topics on that I should say about this issue so it's worth a read okay so the 8th here in the be theory which we've looked at so far can be thought of as different theories of the nature of time there's also an interestingly different in some senses related debates in metaphysics about what exists in time and the main positions there are known as present his eternalism and the growing universe theory now present ism is the thesis the only temporarily present objects events and times exist right so according to the present issed Aristotle doesn't exist World War one doesn't exist and the year 2018 doesn't exist because these are all past objects events or times also according to the present ists my grandchildren the year 2020 the inaugurate a seriously 2021 or the inauguration of the 46th president the United States don't exist and that's because they're their future objects events or times so eternal ISM by contrast thinks they're or claims that present and future objects events and times exist just as present objects that sometimes exist so all those things that I mentioned exist so Aristotle exists my grandchildren exists exists and presuming I will have some and the inauguration of the 46th president the United States exists so these things all exist just as present objects and events exist so the aterna list conceives of reality as a kind of four-dimensional space-time structure sometimes referred to as the block universe seem I think actually Minkowski space-time representations lend themselves to a kind of a journalist picture although it's not absolutely clear that we can really just read facts about what exists of some representation of space-time rights that's actually a philosophical move B might think that sort of somehow eternalism naturally compliments present physicalist think sorry present thinking in physics about space and time we'll go into that in a moment the the grain universe theory is a third major theory on what exists in in time and it's sort of a halfway house between present ISM and eternal ISM so going to the growing universe theorists the past and present exists but the future doesn't exist correspondingly past and present objects and events exist for the future objects and events things don't exist so the Big Bang Aristotle and so on exist this again should save thee from the hand out the year 2021 my grandchildren and so on don't exist so the growing universe theorists again regards the universes dimensional space-time structure but it's sort of to speak figuratively it's not as big as the one that the journalist believes in because it doesn't include the future so it's a a structure that increases in size as more things come into existence in other words as time passes so more stuff is in the past so why would you be a growing universe theorist well one or probably the main motivation is that we sort of have an intuition that the past is settled while the future is open so the growing universe theorist accommodates this intuition by saying that the past is settled in the sense that it exists whereas the future is open in the sense that it doesn't yet exist okay so let's go into a bit more though some motivation and the evaluation of these various positions about what exists in time so now you might say well look eternalism sounds very weird and to some extent the growing universe theorist does because it just says sounds very weird to say things like dinosaurs exist that place the growing universe theorist has to say that just as well as the eternal is because I committed the existence of past object know that saying dinosaurs exist is equivalent saying there are some dinosaurs no that's weird right it's weird say there are some dinosaurs if someone said it to you I think you probably think what they said was false and maybe a bit crazy likewise the eternalists seems committed to say that my grandchildren exist or there are some people who are my grandchildren which is is logically equivalent and yet I deny that I have grandchildren so they seem to be weird and counterintuitive consequences now the journalists and the growing universe theorists fortunately have responses to to this and they they argue that the apparent oddity of these claims have to do with what's known as quantify restriction domain restriction some of you that those of you have done first order logic will have hopefully come across this so the analogy that they might give is as follows suppose that I'm driving around a full car park be driving around for ten minutes can't find a space anywhere and my passenger says to me there's a free parking space now I'd be like ah all excited where's the free parking space and suppose they said well there's this car park suppose I've been driving around a car park in London they're like well there's a car park in Paris that's got a space free look I just googled it presumably I'm not gonna be very impressed by that statement right and in fact their initial statement is a free parking space sounded quite wrong even though there's a sense in which they're right that is somewhere in all of reality there's indeed a free parking space so what's going on in this parking space example is there's a variability in asturias quantify restriction so the natural way of understanding my passengers claim that there's a free parking space is it claim about things in this car park right so Clayton that's a free cup parking space in this car park in other words their existential claim there exists or there is a free parking space is naturally understood by me or interpreted by me to be restricted to the domain of things in the car park relative to that restricted domain they're they're claims false however relative to an entirely unrestricted domain the domain of all things that exist in reality and not just this car park that claims true so the eternalists in the growing universe theorists are going to make it analogous appeal to quantify restriction and they'll say that the claim that there are dinosaurs there are some dinosaurs and likewise more generally claims that there exist past objects events and in the case of the eternalists there are future objects and events are true relative to a totally unrestricted domain of quantification so when I say there are dinosaurs that's true relative to a completely unrestricted domain but the reason it sounds odd is because normally someone who hears me say that will interpret me as making a claim about more in some more restricted domain for instance the domain of objects that exists in the present rather than throughout of reported reality so in other words when I say there are dinosaurs well there are some dinosaurs I might be now naturally interpreted as meaning there are some dinosaurs exist in the sir there are some dinosaurs in the present which of course is false but they'll say all they mean is that they're dinosaurs is true relative to most unrestricted domain in other words what there isn't all of reality ok so the so that's a discussion about eternal is what about the growing universe theorist so we've seen one advantages that they provide a sense in which the past is settled on the future is open enough and we think about the universe in this way but the growing universe theorist has some problems too and and actually one of them or maybe there may be the key one is very similar to an objection to a theory which is that so the a theory seems to want to account for the passage of time or seems to imply there exists the passage of time and then it makes sense if time genuinely passes to ask what rate it passes out but it seems to me no sensible answer to that question likewise with the growing universe theorist if the universe is growing we might think it seems that it's sensible to ask what rate is growing out but all the answers to that look kind of absurd and so maybe makes a question absurd and given that the growing universe theorists him seem severe he seems to suggest that that questions legitimate maybe it casts doubt in the growing universe theory so we might say well you know what rate the universe possibly be grown an hour per hour of trillion objects now it seems you know those answer seems will seem weird but moreover there's another objection related which is that if the growing universe theorist is going to talk about the rates of growth then they're going to have to appeal on to the passage of time so they don't have to say them when they can out per hour or trillion objects per hour but that I suppose undermines one seeming virtue of the growing universe theorists which was that we might have hoped that it would provide an account of the passage of time in terms of the growth of the universe so he might have hoped that you know if we're gonna appeal to this notion of the growth of the universe then maybe we can understand the passage of time in terms of the universe's growth but this actually look might look circular if if if we then have to appeal again to the passage of time in order to explain the rate of the universe's growth so so better I mean like it I suppose at worst the problem is that if the universe is grown then it should make sense to be a rate at which it's grown and that it doesn't really make sense because ants like an hour per hour or trillion objects per hour really sensical at best the the objection is just one advantage or or apparent had vanished the growing universe theory namely that it seemed able to provide an account of the passage of time is actually undercuts because we need announced this question what rate is it growing out and in order to account for what rate it's growing out we need to appeal in a sort of circular manner to the passage of time okay what about present ISM so I think present ISM maybe has some sort of intuitive pull so you you know you might think beyond the point about the weirdness of saying there are some dinosaurs and beyond there the eternalists defense against that worry you might think this is some intuitive sense in which the dinosaurs have gone out of existence right so they just don't exist anymore and you might think even more so this may be an intuitive sense in which my grandchildren don't exist they don't they don't exist yet and and they're not part of reality right so so you might have one is some Diggy Hills in against the the eternal list and say look you know they really in are not part of reality right it might have been that they were part of reality or they will be part of reality but they're they're just not part of reality as it is so that's that's probably appeal but there are also worries about present ISM so there are a few we'll go through three key ones so there's an objection about causation so consider the claim Trump's election victory caused him to be US president that seems like a plausible claim but the trouble is that Trump's election victory was in the past so according to the present test it doesn't exist B might say well how could an event that doesn't exist cause one that does namely he's present he's currently being president it doesn't doesn't seem to make any sense to talk by events that don't exist causing ones that do in a similar vein there's an objection to do with language an objection from reference so it seems that I can refer to non present objects like Shakespeare so I might say Shakespeare is a playwright and I normally think I'm referring to somebody when I say Shakespeare is a playwright namely Shakespeare B might wonder how I can refer to objects that don't exist so this is sort of difficult so you might think well you know there's a sense in which I can refer to fictional objects that don't exist maybe unicorns maybe Harry Potter maybe father Christmas but the story about how I refer to them or in what sense I refer to them might be sort of complex and a bit controversial so it might might we might think there are sort of fictional entities that you can refer to we might think you don't literally refer to an entity but you sort of refer to some feature of a fiction now okay so you might be able to give some story that how are your furtive sort of non-existent some non-existent namely fictional entities but what do we want to reduce our account of how your third Shakespeare - the same thing as how we were to father Christmas it seems that there's a greater reality we might say to Shakespeare the Father Christmas so maybe our story about reference should be the same and maybe the absolute pushes in that maybe pushes in the direction of eternalism so I think the way in which I refer to Shakespeare is more like the way in which I refer to Queen Elizabeth the second thing is like the way I refer to father Christmas now finally and again it it'll be worth for those interested in particularly those writing on this topic to take a look at some of the details from next week on the extended hand out the reading because there's a sort of objection from the special theory of relativity which again is developed in more detail in the next topics reading and obviously kind of interesting and in light of the themes of the course and the the issue is that it seems that there's a tension between present as' and the special theory of relativity in a way analogous to the sense in which there's a tension maybe between the eighth year in the special theory of relativity so the 8th year of course says that there's a property of present nurse an objective property but what is it for a set of points in space-time to be present well it's presumably at least they have to all be simultaneous they also have this property of being present now the trouble was that simultaneity is relative to a reference frame and so in other words a velocity according to the special theory of relativity so it becomes difficult to make sense of an absolute notion of present nurse now this problem is potentially from deeper for the present test than it is for the Atheist and the reason is that the present is thinks that what's present is what's real where's the Atheist don't mess we have to deny that non present objects exists but merely say that present objects have a special property of present nurse but if you say that what's real what exists is what's present and yet what's present is relative to a velocity then does that mean that we have to say that what's real is relative to a velocity now that's quite peculiar and will give a sense in which maybe what's real for me traveling at one velocity is different from what's real for you traveling at a different velocity and we might really wonder about the clearance of this notion of reality for me or reality for you in any case the Zuma challenge for the the present issed in trying to give a coherent picture of what it is they're claiming is real that's compatible with the relativity of simultaneity and therefore relativity of present nurse that the special theory of relativity seems to imply so as I say if you'd like more details on that but it's well worth taking a look at some of next week's readings and also the handout that ok but we will leave it there and I'm sorry this hasn't been as enjoyable as a hopefully seminar would be because for instance it hasn't allowed for Q&A or any sort of discussion but hopefully you've got something out of there and as I say between between the the handout my discussion and that the readings that are on Moodle you'll be in pretty good shape if you've if you've read through all of those okay thank you and I will produce another one of these for the next week's topic so have fun and stay healthy