 Okay, so our next speaker is Etienne Lijoux, who will talk about fragmented visions of sterile relativity and the ontology of time more serious. Yeah, so yeah, so thanks everyone for coming. And so my talk is titled, as you said, from the vision of general relativity and the ontology of time. And basically, my goal is going to show that if you adopt a vision of general relativity where you are to consider just one formulation of the theory, this is what I call a fragmented vision. This is going to bias the ontology of time you are going to consider. And I think we shouldn't do that. So just to give a brief outline, first I'm going to give some brief reminder on the basic physics of ontology of time and how it works or not in a relativistic theory. And then I'm going on building on that to present an argument, a recent argument, by Romero. And the argument is based on the existence of an original way, basically. And then we are going to dive a bit more into the argument. And we are going to do that using two formulations of general relativity. And my point is going to be that the argument is wrong. And to see that, we are going to study it first in one formation and then in another. And so in doing that, we are going to see where Romero is mistaken. And using this example, I'm going to argue for a more general idea is that if you, like Romero, if you only use one formation of the theory, it will tend to suggest one thesis on the ontology of time. In that case. And I'm going to propose to conclude a solution to that. So first, so the ontology of time, it can be reduced to one question. What is the extension, or at least in my context, one question. Ontological extensionality of time. So right now we are in the present, but does that mean that only the present exists? Or do events in the past and in the future already exist? Also, even now? So there are two main phases on a more broad level. So intuitively, we have a presentism that says that only the event in the present exists. And then there is the opposite view that all the events exist even now. Like right now, the event in the future for me, they already exist. And it forms a sort of block. And of course, I say main phases because there are variations on that. But I just talked about the present. But as you know, in special and in general reality, the present, this doesn't mean anything. And this is because if you consider one observer, and let's say we have two events, E and E prime. And they are at the same time for this observer. Well, in special and general reality, we know that for another observer, they are not going to happen at the same time necessarily. And so we can say that because of that, the extension of the present is for independence. So the present doesn't make sense. And from there you could say, okay, so presentism is just wrong in special reality. And you could be very inclined to go to eternalism. And actually that's what many people do. But some disagree with that. And there is one phase which I'm going to focus on. So to be clear, I'm not going to defend presentism and this. I'm just saying that this is the ontology we are going to study. So this was done by Inge Cliff and Bourne, this proposal. So what they say is they say, okay, we present without many other things. But we can still define sort of presentism relative to the present of a certain frame. So a sort of relative size presentation, you could say. So just a bit of graphical explanation on that. If you have a certain observer and a frame, you can in his frame, you can always slice space-time events into slices, surfaces, special surfaces. We are going to represent the events at a certain time. So as you can see, they are at some time events. And as you go up, you progress into the future. And then what is surface presentism is going to say is that at present time t, only the event on the surface that's defining the present exists. And just a bit of technical precision. There are actually two kinds of surface present. So the first is you say this slicing and surface ID, it's relative to each observer. So the ontology is just a little bit dependent. But if you don't want to do that, you can say there is a frame, a metaphysically privileged frame that is not physically privileged, but it can be metaphysically. And so it's relative to this one that event exists or not. But actually for the argument we are going to study, it doesn't matter which kind of surface present we are going to, you consider each one. So now I come to the argument. So as I said before, it's based on the original way. And it starts from the following application of presentism, is that if presentism, and it implies surface presentism from now, then the ontological extension of the world is fundamental. The world is fundamental because you have just the special surface that contains the present. And from that Romero in the article I gave here in 2017, he proposed the following argument. So he says, and for now I'll just focus on the logical structure, not the term that I used. First, there are gravitational waves. We have detected a gravitational wave, and so Romero says we should incorporate a gravitational wave into our ontology. So we can ground this one, this premises. And then he says, gravitational waves have non-zero value, okay so I don't define this term but just take it for granted. And third premises, non-zero right curvature is only possible in four or more dimensions. And you can see that from a logical standpoint, if you combine the last two, you derive that if gravitational waves exist, well they have to live in a space that has four or more dimensions. But then if you come back to the presentist view, you see that this is not compatible because if surface presentism is true then the world is dimensional. And so for Romero, this is an argument that refutes this ontological position. Just before going a bit more about the gravitational wave argument, I just wanted to mention that there is another Mauritian argument by Marron and LeBion. And it's quite similar structurally, but it's based on black hole this time. If you want in the Q&A, I can come back to that, but I just don't have time to analyze it deeply. Okay, so for Romero's argument, first let's present the standard formulation of general relativity, which I think many of you know. So how do you do general relativity usually? You say that you want to determine the geometry of space-time and you say using what's called the Einstein equation, four-dimensional in that case, that the geometry of space-time is determined by the matter content of the universe, basically. And we do actually in the physics, write it in this way schematically, and you know the physics behind, you know that T here is the matter content, it's the stress energy tensor, and G, an object that characterizes geometry, this is the Einstein tensor, but for us you can just call it G and T. Okay, and I just wanted to remark about here, because we are adopting a sort of four-dimensional view, we have a global perspective, basically. We determine the geometry of the whole space-time. So you can do that with gravitational wave. So in general, in any space, gravitational wave, this is defined as a perturbation of the geometry that's due to the oscillation of gravitational force. So the basic example which empirically is how we know gravitational wave exists is that if you take two neutron stars or black holes that are orbiting one around another in what's called a binary system, they are going to attract each other and come closer and closer, and in doing so they are going to perturb the geometry and make it oscillatory, and that's how gravitational waves are emitted and reaches. So because they are perturbation of geometry, if you want to have a gravitational wave in a space, this space has to be curved. So for example, to give you a contra-example, sorry, in Minkowski's space there are no gravitational waves because the space-time is just a rigid structure that cannot be modified. And there is a mathematical general condition for any space mathematically of dimension D to be curved is that either the G-quantity we introduced earlier but adapted to the space is non-zero or another quantity that's called the vial curvature and we come back to the object in Romero's argument is non-zero. So to put it in another way, a space-time is flat if both of these quantities are zero and if one or both of them are non-zero, it's curved. So using that, we can treat gravitational waves in the standard formation and here I'm following what Romero is doing. So here we are sort of a hypnotic view, you could say, because we are just saying we are going to find a space-time where there are gravitational waves, not from time to time basically, which we are going to do later. So what you do is you say I'm going to put myself in a vacuum because gravitational waves usually they travel in the interstellar space where there is no matter basically. And if you come back to the inside equation I wrote earlier I said that G4 is equal to T4 because there is no matter you just put T4 is equal to zero and then you have this equation that G4 is equal to zero. But then using the condition of the existential gravitational wave the space-time of dimension 4, because you have G4 is equal to zero for it to be curved you need to impose that C4 is non-zero because if both were zero the space-time would be flat basically. So given that, so that was the first approach another more local approach you could say what you could say a snapshot view a description of the gravitational wave and intuitively we see how we think about it is that you are going to want to study how the spatial geometry of the universe will evolve from time to time. So this is really a shift of perspective because instead of considering the geometry of zero inter-space-time as a block that doesn't evolve and just creates a wave in it you want to start from a configuration and see how it will evolve basically and to give a graphical impression of that if you start from a spatial surface at some time what you want to know is how it will evolve given the matter on or its configuration and if there is no matter it just evolves because it has a certain spatial curvature. But that's now where the objection of Romo comes in is that the issue is that the vitality it vanishes in a lot of dimension and basically due to its symmetry I'm not going to prove that I'm just going to give an analogy so considering a standard Euclidean space of the dimension you can always define a vector so imagine that it has the components a1, tata, tata, until ad and we subject it to the following constraint the nature of the constraint is not important it's just an example and so you can see that you can define a in any dimension but as it turns out if you do that in d is equal to 3 it's very easy to show from this constraint that all the components are 0 and actually it's true for also d is equal to 2 and d is equal to 1 and on the contrary if you do that for d is equal to 4 or more it doesn't vanish so that's kind of the same idea basically it's too constrained in low dimension ok so with that let's come back to the older approach I was talking about and what's called actually the Frippes-1 formation of general relativity so the idea is that instead of looking at the spacetime and under hold you want to know the evolution of space in time so how do you do that technically what you do is you want to find the counterpart of Einstein equation but on the surface that you consider and what you find in doing that in projecting Einstein equation is that first you find two constraint equations which are really energy conditions it just states that if you have energy on the universe at some time it doesn't vanish at a later time which is kind of obvious and what you get is this equation and the thing I want to point out is that you do not get the kind of counterpart of Einstein equation the intuitive counterpart where you just change the dimension and that's because Einstein equations are nonlinear basically and so you get an additional term by nonzero and so the takeaway message is that on the surface the dynamics is not given by the same equation the same form for the equation as its version for dimension so with all that let's come back to Romero's argument so just a brief recall on the premises here and the issue actually one is that the second premise is not right and why is that it's because on the spatial surface you consider in the surface presentism this surface can be curved even though C3 is equal to 0 and to see that let's come back to the general condition of that space is curved so remember that all we have to impose is that either G or C is nonzero so if G is 0 you have to impose that C is nonzero but so this is the case in for dimension but notice that in free dimension in the surface when you put the material content to 0 you don't get G3 is equal to 0 actually you get another term which is nonzero is equal to 0 so this means that G3 is nonzero and so you see that you can have a curved space because G3 is nonzero and so the fact that C3 is 0 is not a problem actually so can you go back just to be slightly before yeah just because I yeah it's fine that's fine okay so let me come to the last part so the thing I want to point out is that of course you are you can choose to work with either of the formulation I have talked about and actually there are more formulation of general utility which I am not going to evoke but this doesn't mean that you have to restrict yourself to 1 and that's why I am pointing out relative to Rommel's argument is that for him what I have called the external formation this is how you define the general utility and you have no other way basically this is the general utility and I don't think that's right I don't think you should think that way and that's why I called the bias metaphysics because in thinking that the external formation is the only way to do metaphysics in this theory you conflate two things you conflate the fact that presentation is a compatible general utility which is what Rommel wanted to prove but actually this is not what his argument shows what he shows is that external formation because you take a sort of global view it's not apparently suggestive of a presentation but that doesn't mean that it's not inscribable so the overarching point I could say is that when you have this fragmented view where you consider only one formation you get a confusion between the specifics of the formation you are considering and the physical core what's common to the formation and I think this can lead us astray because if you identify the theory with the formation you consider then you would tend to use concept outside of that reach and this is what Rommel was doing because when he said that basically his argument implicitly stated that the form of the Einstein equation is the same on the surface that it is on the four dimensional universe but as we saw that's not the case and so if you do that the apparent inequality of the formation you are considering with a particular ontology view which is okay in appearance it doesn't seem to suggest some ontology but you can conflate that with the fact that it's a real incompatibility to illustrate that you can say it's true and Rommel and other people are defining that that the four dimensional perspective on the general entity this does not suggest a more eternalistic view and conversely if you take the local time from time perspective you could say this seems to suggest presentism but what I want to point out is that because you can do either actually you should be careful that when you say that it proves that some ontology is right or at least that some are wrong and the solution for me is that you should accept basically all the formulation and so I propose to adopt a sort of holistic stance where you say metaphysics I should consider or at least not one formulation and then general entity is going to be defined not with respect to one formation but with respect to all of them at least several okay so I come to my conclusion so what we affirm I mean on the more basic level is that you cannot refute surface presentism with Rommel's so okay so where is that but why it's interesting to refute it I think is that the mistake of the argument is very interesting basically because I think Rommel is in that case is showing that or is mistakenly saying that the manifest feature of the standard formation this is the core of the theory basically and so I think that the lesson from metaphysics should be that it is important as to not draw ST on its conclusion to keep in mind that the specific features of one formulation they may not be enough so for example the fact that you have a global view in the standard formation is not there in the 3 plus 1 formulation and just to come back to the title of the conference so should we go from science to metaphysics I don't have an answer to that but just wanted to point out that if you want to do that consider all of the formulation of the theory and just to extrapolate a bit on that not only should you consider several theory but maybe you should because they are certainly really see that what is physical what is the core of the theory is only what is common to them so for example you cannot say that generality is an interesting theory because it's not there in our formation it's still a lot of time for discussions so yeah oh thank you that was really interesting so I have a couple of questions maybe the last one first so yeah so basically I wanted to know why do you think that the 3 plus 1 formulation of general relativity suggests presentism to me it might also allow for a view like moving spotlights so it's not so the 3 general well the standard formulation seems to suggest eternalism the 3 plus 1 just leaves the possibility it doesn't suggest a specific yeah maybe that was not well formatted by me but I only wanted to say when I say it suggests presentism I should maybe I say it does not subject eternalism because in this talk yeah it's kind of maybe they call to me but it's not but I would say it's very it's not you have some that is in many other phases so I just wanted to clarify this okay so well that wasn't a real question yeah so so my question and this one might be naive but I really not very knowledgeable about the physics why is there a specific reason why the 4 dimensional formulation is the standard one as opposed to 3 plus 1 like is there a specific physical reason or historical reason so first it was the first that was formulated historically I call it standard because it's the one that you find it more like it's predominant you could say and also it's you know it's a kind of feedback loop that most people are taught this formulation first because it's maybe more it's easier then they they can't be taught all of the relations so if you there is no intra-interdictionary textbook on generality that would not stop from being done so that's why I call it that no but I mean is there like a debate in the physics at which formulation is? oh okay so yeah something I mentioned is that each of these two foundations can be useful in center context and not so useful in all so for example suppose you have a very symmetrical situation like a spherical star then the standard formation will be very useful because it's very good at solving very symmetrical IELTS case but now suppose you don't have you don't want analytical solution but you want to do numerical computation well then the four dimensional case it's useless basically so you will take the purpose one to do the incrementation on the computer quantum and actually to take the example of gravitational wave to the table of gravitational wave we have to model or to start colliding one and two and over and there is not analytical solution to that and so you have to resolve two so you have to so you can choose either in this context no because in this context there is no in this context you have to do numerical simulations so you have to do the purpose one the standard one no three percent yeah I want to come back to what you just raised at the very beginning so the previous one could just as well work with moving slope light to you and I think it is actually so I mean I think you are fully right that remember sorry but against present but I would make your conclusion even stronger I don't think it's the case that given any interpretation of in this case general relativity a clear ontology of mind follows yeah and I think it's even stronger than that even within a certain general relativity you can't compute what the correct ontology of time is the ontology of time is going to remain undetermined by any interpretation of general relativity or special relativity I wouldn't think that just wrong I would go I would go to the science of physics I am digging more of a statistic you can get to the methods I think you are just for science yeah, here I didn't want to make a statement as strong as that but I just wanted to point out that you should not consider formulation, but I agree that, yeah, the moving spotlight theory is, physics is a good example that even in one you cannot decide, or at least along those lines. But really, this talk was about a trend that says that aims to show that, tries to show that geneticity shows that some are wrong. But yeah, you could infer the inverse statement that actually no physics can be inferred. This just was not the precise aim. I agree with your conclusions completely. Maybe I'm not sure that the 3 plus 1 and the four-dimensional formulations really are just two different formulations of the same theory, I think maybe we agree maybe on that. Okay, so maybe it's worthwhile just like get the reasons out of the open, right? So not all, the models of gender relativity can be decomposed in this 3 plus 1 way, and the way that you decompose them requires the addition of a structure that is a bit analogous to the preferred frame you started with in the case of special relativity. Choice of shift and lapse functions. We don't have to go into details about that. So one could have a response to like these are just two formulations in the same way that one could have a response to claims that special relativity versus special relativity plus a preferred frame such as like the Lorentzian theory, right, are equivalent formulations because one has strictly more structure. Now for those reasons one might say there's actually an argument for preferring the one over the other. To be clear I agree with your final conclusions so I think that even but I think that I have some hesitation in this particular case about these two being equivalent formulations. Well, yeah something I didn't have time to, yeah actually I had time. It was that when you do the slicing into a surface, this is specific to one observer and a different observer will do, will get announced slicing, but the important thing is just that they agree on the prediction basically, like true they will not have the same but they will, at the same space I mean they will do the same thing. And even in the formational case you could say okay there is the global view but you still have to choose a frame when you do physics I mean, when you do the physics of, well I mean at least in practice you always choose a frame in a cocoon or something else. Yeah but I would say that has to do with the fact that when we want to do experiments it's because we want to see like what is this device going to predict and so then you have to it's convenient to model things in that way. I don't think we have a disagreement about that but there's a question about whether or not the contingent features about this physical device add like a special ontological status above say that device or that device. Yeah thanks. I'd like to come back to the suggestion you made in the very end. Yeah right, all of the fibrillations of this theory are relevant for its physical core and then I take it only the physical core is like relevant for metaphysical inferences, right? Sorry. For metaphysical inferences, so if you want to learn about metaphysics then we have to protect the physical core, right? I was wondering whether, I don't know what I understand correctly but wouldn't that mean that I have to find just one formulation that is incompatible with a certain metaphysical view to show that the physical core is incompatible with this metaphysical view and in this case it seems like the argument against present to them would go through because we have this one from the relation that's incompatible. Maybe I will reverse the idea that what I call the physical core is basically the physical prediction that do not vary from the information because if they would vary it would just be different theory. For example, if I put a clock on the surface of the earth and I put a clock far into space, I know that the clock at surface of the earth would go far in the slower relative to the other one and this temporal delay is even quantitatively is the same in any formulation, right? So you could calculate that in 3 plus 1 or in the standard or any other we are also for those who know that, like the quantitative spin-to approach to general utility which is completely different but also you could calculate the same thing and that's why I call the physical core basically the prediction that are invariant in between formations and what change between formation is basically how you articulate measurable quantities but not the value you could say. Okay, many thanks. I absolutely agree with the conclusion so many thanks for this. Just one very question about what you think, would you extend your view to other physical theories? I mean think about quantum mechanics or other views in which there are a little bit of physical discussion and everything again everything seems to be depending on, okay formulation is a probably tricky word and probably is not the right way to say it but in any case you have different views right and there are different claims and they claim to reject different things but okay so at some point we should do something and also in quantum mechanics there is this people doing what they call neutral quantum mechanics or the overlapping strategy and they seem to be in this direction at at least some point which we should focus on the agreements between neutral agreements but so I want to know if you if you would be happy to extend this view to other. Yeah actually this I think I would because this is a general worry area that we tend to be trapped into the version of theories we know and sometimes we forget in doing so we forget that some part of the structure of the formulation of the sets of the conceptual framework can be changed and it wouldn't change anything. And so yeah I think I think a similar in quantum mechanics could be rather than like yeah but the maybe thing you could object or be worried about my my proposal is that all of the formulation what does it mean because for example probably there are formulation of general utility that we don't know yet but we'll be finding sometimes from now on. Yeah I don't think I know this one but I agree with you mostly so so of course if you want to think about time at a very abstract level you look at different version of version I don't know if version for me there are different theories but at least different theories of general utility compatible with stuff that we believe good but it's exactly like Aristotle thinking okay let's think about time and change time depends change but there's another part in Aristotle is that we don't live in this general universe we live in a particular universe compatible with these principles so would you say okay we have to check for every version of general utility but also every cosmological model that is compatible with the specific observation we have because we don't live in the world of general utility we live in a certain cosmos that is compatible if these theory of truth of course compatible with the equation so would you add a cosmological systematic studies do you mean like a cosmological metric? Yeah the kind of model that are compatible with with our universe big band model well you can you you can do you can find metrics in either formulation for the universe yeah but you see you see you see maybe it's because of my history Aristotle spends a long time to say that you know time is strictly dependent on change so time is a little stuff but the cosmological model he has there's this customer's time that just percolate to so he has a tension between time in general super time contingently necessary in yeah us so in general utility you have the equation of general utility that are real more metaphysical abstract let's say level and there's the specific model representing our cosmos yeah and you with nothing that we should be careful to explore systematically also time more locally or we're just interested in his present is and seems to be to be not just at the highest level of physics but do you mean locally like in like not to consider the universe at the bigger scale but just here I don't know I don't do that I'm asking you I'm not sure I understand the question I understand the question because let me start again so you have general utility it's like pure formalism we say metaphysical stuff about that okay and we are we have quantum things in our world which are not just not just governed by quantum mechanics in general by specific conditions yeah and we do metaphysics at the looking at the space but it's not impossible that some particular stuff yeah contribute also to our our reflection about metaphysics so you did a very convincing arguments that we have to be careful if you look just at the 40 level general theory because there's also other variation that could be important but you never you talk of general duty I need to be independent of the universe with it yeah well like it's a it's a it's a metaphysics of all the possible world where general duty is true yeah and I worry that in our specific universe there's maybe contingent condition that will make your exploration of what is time okay well what you're asking I think is ready to the questions for example when once you have the answer to the question this doesn't in itself give you prediction because you have to set a model so for example you are going to say the matter is distributed in this way in our universe and this implies geometry but then it's just a question in general of if I have a set of physical law we in general in general physical law how do we apply then how do we choose the condition of the sets of the configuration that applies in our universe but I think this is not specific to general entity like it's it's the same thing is in Maxwell equation okay so what is the distribution of charge in the universe well I'm test on models and see if it but I don't worry about the ontology of Maxwell equation I don't worry about time I'm not sure everything about time is captured at the highest abstraction level especially direction of time okay