in this video i want to talk about four theories of time all right so a theory of time usually involves three sub theories or three parts and i want to briefly talk about those but then i'll talk about them more in particular with respect to each one of the theories so what are the three parts of a theory of time well the first part is what's called a temporal ontology so your theory of time is going to state what times it thinks it exists and so another way of thinking about this is does the past present and future exist or is it just the present or is it just the past and the present or what combination of events in time exists another way of asking this question is does an object's position in time determine whether or not the object exists so if we said a particular object is in the future but you don't think the future exists then you would say that the object itself doesn't exist the second part of a theory of time concerns whether or not the time is an a theory or b theory and there's two ways of thinking about this one way of thinking about it is in terms of what kind of properties or relations do we need to suppose in order to structure the temporal order of the world in order to take various events and put them in some type of sequence now the a theorists will say that we can structure time in terms of a particular type of relation which is relations of earlier than and later then so we can talk about one event being before another event the atheist also says that reality is ordered by the past present and future and the ontological commitment of making this claim is at minimum said to involve a commitment to that there is a present moment in the world on the contrary bee theorists will say that this notion of being past present and future is simply perspectival it's a matter of how we see the world but it's not actually found in the world in other words there's no property of being present found in the world it's not a feature of events and it's not a feature found in the structure of time instead all of time can be organized in terms of these earlier than and later than relations the third part of a theory of time concerns temporal passage this involves whether or not you think time passes or another way of thinking about it is is there change in the world static theories of temporal passage say nah there's no change in the world time doesn't really pass it's just a again perspectival fact just like a large building looks small to you from a distance we know that this is a matter of your perspective not a matter of how things actually are on the other hand dynamic theories will say change is something that is found in the world that time really does pass and different dynamic theories will have different accounts of what type of change is found in the world so just a quick review a theory of time we'll talk about what times exist whether or not it's an a theory or b theory and then finally an account of temporal passage does time really pass or is again this just a matter of perspective so as i mentioned i want to talk really briefly about four theories i just want to introduce the theories without evaluating them or talking about their merit let's talk about the first theory which is presentism now presentism is a popular view because it's at least taken initially to be the most intuitive theory the present test says concerning the claim of temporal ontology is that only present events exist simplicitor so we'll talk about past events having existed and future events will existing but the only ones that simply exist are the things here and now in the present so the presidentist as we see acknowledges the a theory because they say that this distinction between past present and future is a real distinction and they're committed to the property of being present they think it's objectively real that events have this feature to them and it's not simply a matter of perspective concerning temporal passage the present test holds a dynamic ontological change view this sounds fancy but it's very simple the idea is that time passes because what is present the things that exist in the present change so in a prior present i did not exist different things existed but now you and i we are present and we are the things that exist but in the future unsadly you and i will no longer exist instead new things will exist and those things will be in the present in short reality is itself dynamic it is a feature of the world and what changes is what exists it's helpful to think of an illustration so take this particular illustration here where you have this four-dimensional block and that particular block signals all points in space time and any particular point in that block would be a particular event that occurs at a particular time and so the presenters would simply in trying to tell us what things exist would select a vertical plane from that block and say all the events which are here in this plane are all the events that are in the present and these are all the events that exist and when we want to figure out their view of temporal passage what we would ask the presidentist to do is to show us that with our their model and they would simply move the plane to the right a little bit more they'd move it towards the future let's look at another theory and this theory is similar to presentism in a lot of ways this particular theory is called the growing block theory now the growing block theory is similar to presentism but the only difference is that they say that it's not merely that the present events exist but also the past events exist and so they're also committed to the idea that future events do not yet exist and so the past and present events exist simply or simpliciter but these future exam events are or something like will exist this commitment to past entities existing is a counterintuitive feature of the growing block theory because think about what it's saying it's saying that the prior you that exists in the past still exists that is it doesn't simply exist in the past it exists just as much as you do here and now now in terms of whether it's an a theory or b theory since the growing block theory acknowledges the reality of past events and present events it acknowledges a distinction between these events and future events that the past and the present are found in the world the theory is an a theory they're saying that the past and present is something that is objectively real and not simply a perspectival fact the last component of the growing block theory is its view on temporal passage or whether or not their time passes or there's change in the world and just like the present test it asserts that reality itself is dynamic time does pass and there is real change in the world and it also asserts that time passes because what exists changes but there is one slight difference i think between the present test and the growing block theorist and it's worthwhile to look at our visual model to understand it so the growing block theory will assert that the past events exist and present events exist when we thought of presentism we thought of this horizon this vertical plane moving along the four dimensional block and whatever is found in that particular plane is what exists in this case we are simply adding on to the block and so the present moment simply refers to the latest entities that have been added to all the things that exist so in this sense it differ from presentism which seems to assume that events that exist no longer exist as the time passes where the growing block theory asserts that we're simply adding on to the universe one cool implication of the growing block theory is when you apply it to your own life not only do you exist here and now but you also exist at times before this time and so rather than existing holy present in a single moment instead you are spread out in time and you are also growing in time the next theory to look at is eternalism and i think this is kind of the coolest theory even if it strikes many as the most implausible this theory says in a rough way that past present and future events all exist everything that ever existed exists or will exist exists eternally or permanently another way of thinking about this idea is that whether or not something exists it doesn't depend upon its location in time so whether or not an object is past present or future that has no bearing on to whether or not that thing exists provided it's found in our four-dimensional model of space-time if it's found in the model then it's a thing that exists just like you and i exist here and now the second portion of eternalism is the fact that it is a b theory this means that it's asserting that being past being present and being future are merely perspectival facts these are not features that are part of reality or found in the world as i mentioned a properties like a moment being in the present are simply a matter of perspective they are like when you're looking at a building far away and it looks small or the property of being north there's nothing in reality that has this property of being north instead what b theorists assert and what the eternalists assert since their be theorist is that reality is structured in terms of relations so some events occur before other events and some events occur after other events and there is some notion of two events occurring at the same time or being simultaneous with each other but there's no notion of being present being past or being future this is not something we can look to the world and say ah this particular occurrence or event is in the past or is in the present or in the future the last feature of eternalism is its view on temporal passage and concerning temporal passage it asserts that time does not really pass that things do not change that we live in a static universe now many eternalists will say that you know maybe things look like they pass this is simply a matter of our perception is a perspectival fact that we think things change things actually though don't change so since the eternalist doesn't really say that there is an objective past present or future instead says that there's only earlier events and later events we can point to the four-dimensional model of space-time and say any event in the time itself is an event that exists and if this is all the events that ever have existed and ever will exist then those are the events that do exist the last theory i want to look at is the classical moving spotlight theory there's some new versions of the moving spotlight theory but i want to present the original formulation or understanding of this theory and if you're interested i can provide some resources in the description below about the more updated versions of this theory in terms of temporal ontology the ontology the things that the moving spotlight theorist says that exist is the same as what the eternalist says that exists so the past the present and the future entities these all all these entities exist another way of putting it and i think it's a little bit more clearer this way everything that ever exists existed or will exist simply exists where the moving spotlight theory is different from eternalism though is the fact that it posits an a theory rather than a b theory remember that the eternalist says that there's only these relations of earlier then and later then there's no real past present and future the moving spotlight theories disagrees they say that there really is in the world a property of being past present and future this is a feature of things it's objectively real that there is a present moment and it's not simply a matter of your perspective concerning temporal passage what the moving spotlight theorist proposes is a property change dynamic theory and what that means is that reality itself is dynamic in a sense but what exists does not change what exists stays constant what does change however are the events that have the property of being present so the metaphor for this theory is that the property of being present passes over the events that already exists and lights them up in a sense and that the events that already exist will exist and do exist the only change that occurs are which ones are in the present moment nothing else in fact changes so the idea is that all events exist at their respective locations in time but events come to take on the property of being present as time passes