The 3D Earth doesn't move from t1 to t2; two different parts of the 4D Earth each exist at those times. — Luke

Exactly as I described. — Kenosha Kid

I never claimed that you said it; I said I thought that you agreed to it.

I'm perfectly happy with the description of the Earth moving through time. I am happy with that in an everyday, subjective, pseudo-presentist, practical sense. — Kenosha Kid

I'm happy with it too. I don't know what other sort of motion there could be.

The 3D Earth doesn't move from t1 to t2; two different parts of the 4D Earth each exist at those times. — Luke

Exactly as I described.
— Kenosha Kid

I never claimed that you said it; I said I thought that you agreed to it. — Luke

Okay, I was agreeing with the emboldened part. The first part does not enter an everyday, Gallilean idea of motion, which is the idea I've stuck with and that you said you were speaking of. In relativity, yes, objects have a fourth velocity component: temporal velocity. This is defined as the variability of temporal position within a reference frame with respect to the body's proper time (which is time in that body's rest frame). This has not entered any of my argumentation, not because I disagree with it (I lectured on it for years), but because it complicates descriptions and is not pertinent to an everyday definition of motion.

This movement through time is not a necessary condition for movement in space. Light, for instance, moves through space but has no proper time interval. Essentially, a photon cannot be said to move through time.

What I've been asking you to do is stick to one definition of motion and not change the definition as one moves from a presentist picture to an eternalist picture, or from an eternalist picture with a spotlight to one without, etc. You said you meant by 'motion' the typical, everyday, kinematic idea of different positions at different times: dx/dt, dy/dt, dz/dt for instance. Is this present in eternalism? Yes, because things exist at different positions at different times.

Switching to an Einsteinian/Lorentzian-type definition of motion that has a fourth coordinate to "move" within, is this present in eternalism? Yes, because again a continuous worldline through x, y, z, and t is defined, and so is the proper time T of the body under consideration. dx/dT, dy/dT, dz/dT and dt/dT are all there, and motion according to this definition is evident.

This T is not an other dimension, but a transformation of reference frame. Another way of moving through time might be, as SophistiCat suggested, to posit a second temporal dimension, call it ?. If this were true, then in the block representation of (x, y, z, t) one truly could expect the 4D object to move within the block, since particular values for (x, y, z, t) at one ? could differ from (x, y, z, t) at another ?. The lack of such movement of the 4D object within the block is what you've been describing as a lack of motion. But this is not any typical definition of motion. Neither in the Gallilean sense nor in the Einsteinian sense does motion depend on a higher-order variable ?.

Even a stoopid frog can figure out where a fly will be such that it can fire its tongue out and catch it. — Kenosha Kid

If it is moving, there is no place where it is.. That's contradictory, to say that it is moving, and that it is at a place. The frog intercepts the fly with another motion it does not figure out where the fly will be. Being bigger than the fly, that's an easy thing for the stoopid frog, it merely has to get in the fly's way.

Yes, but changes with time, i.e. has different positions at different times. I recall that the Moon was there. Now it is there. It has moved. — Kenosha Kid

No, motion is not having different positions at different times, that's having different positions at different times. Motion is what happens in between the different positions, how a thing gets from one position to the other. It is to be moving, which is very clearly not to have a position.

That's contradictory, to say that it is moving, and that it is at a place.
...
No, motion is not having different positions at different times — Metaphysician Undercover

It was to Zeno. It is not to kinematics, which accords with my everyday experience of motion: the thing is not where it once was. An assumption that motion is anything else would lead to a different argument and different behaviour. As I said to Luke, I'm not arguing against a different definition of motion: that's just the annoyance of using the same label for multiple meanings. If you define motion to be impossible, then I agree it is impossible. If you define it to depend on a presentist idea of an objective passing 'now', then I agree a universe without such a thing would not be in motion. But this is just me adopting your language. It does not change the fact that the derivative of position wrt time in an eternalist universe is not generally 0, i.e. that things move kinematically.

Being bigger than the fly, that's an easy thing for the stoopid frog, it merely has to get in the fly's way. — Metaphysician Undercover

It cannot do that if it only knows where the fly is now, and not where it is going.

Okay, I was agreeing with the emboldened part. — Kenosha Kid

To be clear, you disagree that "3D Earth doesn't move from t1 to t2"? That is, you believe that 3D Earth does move from t1 to t2?

The first part does not enter an everyday, Gallilean idea of motion, — Kenosha Kid

If you recall, I was saying that if you really want to take Eternalism seriously, then you should view objects as 4D rather than talking about them as though they are 3D objects which change temporal position. Of course this isn't a Gallilean or Presentist idea of motion; it's an Eternalist description.

Light, for instance, moves through space — Kenosha Kid

Light moves through space unlike everything else which simply exists in space? I'm happy to restrict the discussion to objects moving at less than c.

What I've been asking you to do is stick to one definition of motion and not change the definition as one moves from a presentist picture to an eternalist picture, or from an eternalist picture with a spotlight to one without, etc. — Kenosha Kid

Where have I been inconsistent on this?

You said you meant by 'motion' the typical, everyday, kinematic idea of different positions at different times: dx/dt, dy/dt, dz/dt for instance. Is this present in eternalism? Yes, because things exist at different positions at different times. — Kenosha Kid

But when I ask you to explain what the motion in your model represents, you can only do so in "pseudo-presentist" terms. If there is really motion in the Eternalist universe, then explain it in Eternalist terms. Otherwise, it's clear that motion only makes sense in Presentist terms. It's not like the (3D) Earth actually moves from one place to another over time, right?

Yes, because again a continuous worldline through x, y, z, and t is defined, and so is the proper time T of the body under consideration. dx/dT, dy/dT, dz/dT and dt/dT are all there, and motion according to this definition is evident. — Kenosha Kid

I think where we disagree is that you think the ability to calculate motion in your model therefore implies that motion is possible in an Eternalist universe, or implies that motion is consistent with actual 4D existence. You might be able to calculate motion, but how does that make it Eternalist rather than Presentist motion? Isn't it the same calculation? It appears to me that you are finding a value for a Presentist concept within an Eternalist universe.

Another way of moving through time might be, as SophistiCat suggested, to posit a second temporal dimension, call it ? — Kenosha Kid

Again, I've never suggested anything about a second temporal dimension. I'm okay with the fact that 4D objects don't move, whether that makes sense or not.

To be clear, you disagree that "3D Earth doesn't move from t1 to t2"? That is, you believe that 3D Earth does move from t1 to t2? — Luke

I am not making statements about my beliefs here. That motion is present in the eternalist universe if defined as per standard kinematics (or indeed relativity) is a fact independent of my belief. It may be demonstrated, and has been demonstrated. Belief is something that you might have that stops you accepting the demonstration. I am satisfied that, in Einsteinian motion, a body moves from one time to another. I am satisfied that, in Gallilean motion, this is not held. I am satisfied that Gallilean motion is merely an approximation to Einsteinian motion.

To assert something like "motion is impossible in an eternalist universe", you have to have some definition of "motion". We had agreed on the standard kinematic definition that accords with personal experience. I'm happy to take relativity into account or not, you choose. But you must have a consistent definition, and not say on the one hand that motion is e.g. Gallilean and on the other than, in the eternalist universe where by definition Gallilean motion is nonzero, that motion is not possible by definition.

...which change temporal position. Of course this isn't a Gallilean or Presentist idea of motion; it's an Eternalist description.
...
Where have I been inconsistent on this? — Luke

If "change temporal position" means, as it should, "is defined for more than one time", there is no inconsistency: that holds true in an eternalist universe. If it means "requires some objective driving thing that moves time along or moves something through time", then your idea of time is apparently presentist despite all protestations.

But when I ask you to explain what the motion in your model represents, you can only do so in "pseudo-presentist" terms. — Luke

That is made up. I have said a ridiculous number of times that motion in a 4D or eternalist universe looks like a geometric path that is not always parallel to the time axis. I have asked you to explain how such a path could be possibly said not to describe a standard kinematic definition of motion. You have, so far, not attempted this.

You might be able to calculate motion, but how does that make it Eternalist rather than Presentist motion? — Luke

The definition of motion you claim to ascribe to is the same whether the universe is eternalist or presentist. There is no feature in that definition that depends on whether future or past times exist or not.

Again, I've never suggested anything about a second temporal dimension. — Luke

As I quite clearly stated in the quote, SophistiCat suggested this. But actually, to all intents and purposes, yes you have suggested it. Your claim that nothing moves in an eternalist universe is based solely on the fallacy that motion in the eternalist universe would be something equivalent to the motion of a 4D object with respect to the block. This makes no sense if all times are already defined in the block. You would need at least one other time to propagate through so that you could see the motion of the object in the block. Whatever that is, that's an additional time dimension. This is the mistake you make whether you're aware of it, or whether you accept it, or not. You generalise a 3D + time view of motion to 4D + time, note that that "+ time" isn't in the eternalist universe, and claim that motion is impossible. But there is still time in the eternalist universe: it is one of the four dimensions. The consistent thing to do would be to ask: "what does this 3D + time definition of motion look like in straight 4D?" As said, it looks like geometric paths in a block that are not parallel to the time axis.

I'm okay with the fact that 4D objects don't move, whether that makes sense or not. — Luke

If you're happy not to make sense, go right ahead. I'm not the police. :rofl:

It is not to kinematics, which accords with my everyday experience of motion: the thing is not where it once was. — Kenosha Kid

I think that's ridiculous. My tea cup is sitting on the table right now, and it used to be on the counter. So you say my cup is in motion because it's not where it used to be. That's ridiculous the cup was in motion, and that's why it moved from one position to another, but being in a new position, it is no longer in motion. My OED defines motion as the act or process of changing position. To say that motion is being in a new position, is nonsense. Nobody uses "motion" like that. Nor is it consistent with anyone's experience of motion.

If you define motion to be impossible, then I agree it is impossible. — Kenosha Kid

I don't define motion to be impossible. But I think it is ridiculous to define motion as being in a different position, because no one in conventional English usage uses the word that way. To be in a position is not to be in motion, the two are contradictory. To be in motion is to be changing position. Do you not understand what it means to be active?

It cannot do that if it only knows where the fly is now, and not where it is going. — Kenosha Kid

Sure it can, because it's bigger than the fly. A big thing doesn't need to know where the small thing is going, to get in the small thing's way.

I am satisfied that, in Einsteinian motion, a body moves from one time to another. I am satisfied that, in Gallilean motion, this is not held. — Kenosha Kid

In Gallilean motion, a body does not move from one time to another?

But you must have a consistent definition, and not say on the one hand that motion is e.g. Gallilean and on the other than, in the eternalist universe where by definition Gallilean motion is nonzero, that motion is not possible by definition. — Kenosha Kid

I can't say that motion is impossible by definition, but you can say that motion is possible by definition? That's hardly sporting.

If "change temporal position" means, as it should, "is defined for more than one time", there is no inconsistency: that holds true in an eternalist universe. — Kenosha Kid

What "is defined for more than one time" in a 4D universe? Once again, in Eternalism you don't have a 3D Earth that changes from one temporal position to another - that's Presentism. Instead, you have one part of 4D Earth existing at one temporal position and another part of 4D Earth existing at another temporal position. No two parts are the same, i.e., no part is "defined for more than one time". Therefore, no part changes temporal position.

In Gallilean motion, a body does not move from one time to another? — Luke

Correct. There's no concept of having a temporal velocity through time in classical kinematics. It does not preclude the possibility, it's just an irrelevancy, since there's no rotation possible from time to space directions or vice versa in Galilean motion.

I can't say that motion is impossible by definition, but you can say that motion is possible by definition? That's hardly sporting. — Luke

I didn't say that. You can say eternalist motion is impossible by definition. As I said to MU, if that's your definition, then I will agree with you that eternalist motion is impossible, a truism. But then you're not talking about everyday kinematics in which motion is positions changing with time, and your entire argument is then circular.

What "is defined for more than one time" in a 4D universe? ... Instead, you have one part of 4D Earth existing at one temporal position and another part of 4D Earth existing at another temporal position. — Luke

You have answered your own question: the geometry of the Earth. There is still time in 4D, it is just a dimension, the other 3 of those 4 dimensions being spatial. The spatial coordinates of an object are defined for a continuum of temporal coordinates, i.e. the geometry of a 4D object is a path through 4D space.

What "is defined for more than one time" in a 4D universe? ... Instead, you have one part of 4D Earth existing at one temporal position and another part of 4D Earth existing at another temporal position.
— Luke

You have answered your own question: the geometry of the Earth. There is still time in 4D, it is just a dimension, the other 3 of those 4 dimensions being spatial. The spatial coordinates of an object are defined for a continuum of temporal coordinates, i.e. the geometry of a 4D object is a path through 4D space. — Kenosha Kid

Does this imply that the 4D Earth moves? But that would reintroduce the problem that a second temporal dimension is required.

Does it also imply that you can only measure the motion of the entire 4D object and not any of its parts? That's not what we've been discussing.

Edit: ...that is, if "change temporal position" means "is defined for more than one time" and if this can only refer to the 4D object, not to any 3D part.

I think that's ridiculous. My tea cup is sitting on the table right now, and it used to be on the counter. So you say my cup is in motion because it's not where it used to be. — Metaphysician Undercover

Well there's a couple of ridiculous things there. The first is the straw man that changes in position between different times in the past describe a velocity that must still hold true now, i.e. that there are no forces.

The second ridiculous thing applying this straw man to: "My tea cup is sitting on the table right now, and it used to be on the counter" to imply that it did not move.

My everyday experience of something moving now is based on recent and current sense data on the positions of the thing. If the positions change, it is in motion. How the positions change allow me to estimate its velocity. The true motion might be qualitatively and quantitatively different from that estimate. However all I have to is wait a moment and I'll build a better model of its motion. In short, I build up a model of the thing's motion by building up time series of its positions and analysing their differences: kinematics!

To be in a position is not to be in motion, the two are contradictory. — Metaphysician Undercover

I didn't say it was, but their not contradictory. Unless knowledge stalled millennia ago.

Sure it can, because it's bigger than the fly. A big thing doesn't need to know where the small thing is going, to get in the small thing's way. — Metaphysician Undercover

Now that IS ridiculous. In the thing's way... no clue there? :rofl:

Does this imply that the 4D Earth moves? But that would reintroduce the problem that a second temporal dimension is required. — Luke

No, because motion is differences of spatial positions over corresponding differences in temporal positions, and both spatial and temporal positions are present in 4D. It just doesn't look like a moving thing in 3D. It looks like a wiggly or slanted line.

Refer again to the image used by Huw Price. This is, in our everyday sense, a static image: the image does not appear to us to move. But it is an image of the Moon moving around the Earth. That motion is represented in the picture (a helical 4D Moon).

Also, since in 4D time is just another dimension, I do encourage you to consider the mountain analogue. A mountain's slope is a spatial gradient just as motion in 4D is a spatial gradient. The only real difference is that the former is a gradient with respect to another spatial dimension. Would you say that the mountain is flat? This is analogous to saying that 4D worldlines are also flat, which is what the absence of motion in 4D looks like (viz. the Earth in Huw's picture).

No, because motion is differences of spatial positions over corresponding differences in temporal positions, and both spatial and temporal positions are present in 4D. — Kenosha Kid

Rght, but aren't you talking about the motion of some thing; an object? You've established that "change in temporal position" means "is defined for more than one time". I've argued that no 3D part is defined for more than one time. You've replied that what is defined for more than one time is the 4D whole.

This implies that the 4D whole is what changes temporal position. You can't measure just a part of that whole to derive a value for motion, because the part is neither defined for more than one time nor what changes temporal position. That was our agreed definition of motion. So either the 4D whole moves or nothing does.

I've argued that no 3D part is defined for more than one time. — Luke

Right, I think I see what you're saying. If the path of the 4D object could be written as something like P(x,y,z,t), i.e. whether the object is present at a given spatial+temporal 4D position, you're saying that essentially P(x,y,z,t)=P(x,y,z), i.e. time is irrelevant in 4D. This would be like the Earth in Huw Price's picture. If every object were like this, this would be a 3D universe with a pointless fourth dimension added with no purpose. It would not correspond to motion as we perceive it or mean it in a Galilean sense.

You've replied that what is defined for more than one time is the 4D whole. — Luke

Yes, exactly. And if it is also defined for more than one position, it is moving, i.e. "it is at some times moving".

You can't measure just a part of that whole to derive a value for motion, because the part is neither defined for more than one time nor what changes temporal position. — Luke

You're right to say I can't measure motion in a 4D object at a time without considering times before and/or after. In fact, to fully and accurately assess the motion of an object at a given point of time, I have to consider the object at all times, i.e. it is a field property of the 4D object, not a point on the object. I have been part of disagreement as to whether this means that something like velocity at some time t is a property of the 4D object at time t (local), the vicinity of t (semilocal), or the entire object (ultra-nonlocal).

The way I measure it in 4D is semilocal, but nature is thankfully not confined to human approximations of it. The way I experience it subjectively is also semilocal, that is: in determining which direction a bird is flying in, I need only consider the recent positions of the bird, not the bird's entire history.

Irrespective of how we calculate it, and irrespective of whether we can say that, at a given time, the velocity of an object is a property of that object at that point in time, we can say that, at that point in time, the object has velocity, and therefore is in motion at that time, i.e. velocity, however we get to it, is a time-dependent as well as spatially-dependent concept.

That was our agreed definition of motion. — Luke

If I agreed that velocity is undefined at a particular time, I did so in hideous error. I believe the definition of motion I stuck to that of kinematics, for which motion at a given time is well-definable.

Right, I think I see what you're saying. If the path of the 4D object could be written as something like P(x,y,z,t), i.e. whether the object is present at a given spatial+temporal 4D position, you're saying that essentially P(x,y,z,t)=P(x,y,z), i.e. time is irrelevant in 4D. This would be like the Earth in Huw Price's picture. If every object were like this, this would be a 3D universe with a pointless fourth dimension added with no purpose. It would not correspond to motion as we perceive it or mean it in a Galilean sense. — Kenosha Kid

That's not quite right. I like it, but it's not really what I'm getting at. This is what I mean:

We define motion as change in spatial position over change in temporal position.

Furthermore, change in temporal position means "is defined for more than one time".

If a 3D part cannot be defined for more than one time (per Eternalism), then change in temporal position cannot be calculated and neither can motion.

The second ridiculous thing applying this straw man to: "My tea cup is sitting on the table right now, and it used to be on the counter" to imply that it did not move. — Kenosha Kid

I agree that to have changed position implies that something has moved. But motion is defined as. and the word is used to refer to, the activity of moving, not the effects of moving. That's the problem with your kinematic definition, kinematics deals with the effects of motion, not motion itself.

My everyday experience of something moving now is based on recent and current sense data on the positions of the thing. — Kenosha Kid

You seem to have a sense apparatus which is completely different from mine. When I see a thing moving, such as a car going past me on the road, I see it as moving. I do not see it as having been in one position, and now in another position. But I don't believe that you really experience motion in this way. So I think you are either lying about how you experience motion, for the sake of supporting some metaphysical position, or you haven't ever really thought about how you experience motion, and so you are just fabricating this claim.

I didn't say it was, but their not contradictory. Unless knowledge stalled millennia ago. — Kenosha Kid

To have a position means to have a particular, and determinable spatial location. To be in motion means to be actively moving from one spatial location to another. So yes, the two are contradictory. And if this implies that knowledge stalled out millennia ago, then so be it. It's people like you make quantum uncertainty into acceptable physics. The particle was there, and now it's here, but who cares what happened in between. We know that it moved, and for us that's what constitutes "motion" Big problem, that's not really what constitutes motion, you are deceiving yourself, and you really haven't a clue what motion is.

no clue there? — Kenosha Kid

.It's becoming very clear, you really haven't got a clue as to what motion is.

That's not quite right. I like it, but it's not really what I'm getting at. — Luke

Okay, sorry.

If a 3D part cannot be defined for more than one time (per Eternalism), then change in temporal position cannot be calculated and neither can motion. — Luke

Ignoring the parenthetical, sure, yes. I assume by "3D" part you mean spatial coordinates. This is the same as saying "All positions of all objects are fixed". I would agree that, assuming that, motion is impossible. But eternalism does not say this. It says that all of positions of all objects, past, present, and future, exist. It does not follow that the position of an object at a point in the future must equal the position of the object at a point in the past. Any difference is motion, even just judicious choice of reference frame.

That's the problem with your kinematic definition, kinematics deals with the effects of motion, not motion itself. — Metaphysician Undercover

It's not my definition, blame Galileo! :rofl: But there is no problem. It does not describe effects of motion, it describes motion. An effect of the motion of the teacup is that it is now on the floor. The motion of the teacup was the variation of its position with time.

When I see a thing moving, such as a car going past me on the road, I see it as moving. I do not see it as having been in one position, and now in another position. — Metaphysician Undercover

That's quite the strangest thing I've heard in a while. I will refer you to yourself:

But I don't believe that you really experience motion in this way. So I think you are either lying about how you experience motion, for the sake of supporting some metaphysical position, or you haven't ever really thought about how you experience motion, and so you are just fabricating this claim. — Metaphysician Undercover

If that's your level of argumentation, we cannot trust that each other are trying their best to explain what seems true to them. Further discussion would be pointless. I'm not having a go; you've described exactly how I feel about everything you have said. I just would have persevered and tried to reconcile our different experiences of motion, or perhaps got a consensus on another thread.

It does not follow that the position of an object at a point in the future must equal the position of the object at a point in the past. — Kenosha Kid

It's not the spatial position which is at issue but the object itself. The same temporal part of a 4d object cannot be "defined for more than one time", so cannot change temporal position.

It's not the spatial position which is at issue but the object itself. — Luke

This difference in the spatial position at different temporal positions is movement though. It has to be at issue!

The same temporal part of a 4d object cannot be "defined for more than one time", so cannot change temporal position. — Luke

I see. Yes. The temporal coordinate at one time is fixed. That is a truism. So what?

...so cannot change temporal position.

Edit: It's not the same 3D part or "object" at both t1 and t2, so it is not defined for more than one time and so it cannot change temporal position. To consider it the same object is a Presentist notion.

To consider it the same object is a Presentist notion. — Luke

Nothing stays the same from one moment to the next, as in identical... the law of identity X=X. Even in presentism X is not X anymore a moment in the future, so technically there is in fact no X that can be said to have changed position.

The law of identity and logic is a useful convention, so we can abstract away from the world and try to infer things from that, but it should not be confused with the world itself.

To borrow @Kenosha Kid's definition, to change temporal location means "is defined for more than one time". This makes sense in Presentism where the same 3D object moves through time from t1 to t2. It does not make sense in Eternalism where different 3D parts exist at t1 and t2.

To borrow Kenosha Kid's definition, to change temporal location means "is defined for more than one time". This makes sense in Presentism where the same 3D object moves through time from t1 to t2. It does not make sense in Eternalism where different 3D parts exist at t1 and t2. — Luke

Why not though? My position is, from the beginning, that existing at t1 and t2 and moving through time is the same, except for existing only in the preferred moment and the direction. It don't think 'temporal passage' really adds something fundamentally in relation to movement, hence my repeated questions about it.

Edit: You say 'different parts' exist at different times, but in presentism what will exist in the future is also not identical to what exist now. The different 3d parts at different times in eternalism are just as different as some object will be compared to the future object in presentism.

To repeat @Kenosha Kid's definition, to change temporal location means "is defined for more than one time". As I've repeatedly asked: what is it that changes temporal location? It has to be considered the same object to meet the definition "is defined for more than one time". You can't determine the change of temporal location of an object if it's not the same object that changes temporal location. To compare Presentism and Eternalism we need to talk about 3D objects, which is what motion typically deals with anyway. Eternalism doesn't have 3D objects so we need to use 3D parts of a 4D object instead. It is quite clear that, in Eternalism, the 3D part existing at t1 is not the same as the 3D part existing at t2. You wouldn't say that the 3D part at t1 moves to t2; clearly not: a different part exists at t2. However, in Presentism it is considered to be the same object that changes temporal location from t1 to t2.

You may wish to argue that it is the same object in Eternalism: the 4D object. But this would imply that it is the 4D object which moves or changes temporal location, and that makes little sense.

...so cannot change temporal position. — Luke

Of course. That is true of spatial positions too. If a spatial coordinate is fixed, it by definition cannot be changed. That does not mean that an object cannot have length, for instance. Other spatial coordinates exist too.

As I've repeatedly asked: what is it that changes temporal location? — Luke

I think you need to reword the question then. I can't make sense of something "changing temporal location" beyond "existing at multiple times". They means the same thing to me. Can you differentiate them for us?

It has to be considered the same object to meet the definition "is defined for more than one time". — Luke

However, in Presentism it is considered to be the same object that changes temporal location from t1 to t2. — Luke

Yes but it is not the same object, even in presentism. And as I said in previous posts what is considered 'the same object' is something we decide and somewhat arbitrary.

Language and logic is not the world itself. So you seem to be merely making a point about the language we use, and not about the nature of reality.

Why would you think that lines that are arbitrarily drawn by us humans, that the language we choose to use, would have consequences for the nature of reality? — ChatteringMonkey

As I've repeatedly asked: what is it that changes temporal location?
— Luke

I think you need to reword the question then. I can't make sense of something "changing temporal location" beyond "existing at multiple times". They means the same thing to me. Can you differentiate them for us? — Kenosha Kid

Why would I? I agree to your definition.

As I've repeatedly asked: what is it that changes temporal location? It has to be considered the same object to meet the definition "is defined for more than one time". You can't determine the change of temporal location of an object if it's not the same object that changes temporal location. — Luke

Yes but it is not the same object, even in presentism. — ChatteringMonkey

A presentist would disagree.

It has to be considered the same object to meet the definition "is defined for more than one time". You can't determine the change of temporal location of an object if it's not the same object that changes temporal location. — Luke

Oh, I think I understand. But that is satisfied by continuity. The mountain at the summit is the same mountain as the one at the foot. What is it then that changes spatial position? A presentist-esque answer might be a hiker moving from the foot to the summit. But this is not necessary for the mountain to occupy the space at the summit and the space at the foot. What's required is continuity: the geometry of the mountain.

Same goes for 4D objects. The Moon at some future event is the same as the Moon at some past event: both events are points on the Moon. What makes it the same Moon is continuity. It has length along the temporal axis. No temporal hiker, or spotlight, or objectively passing 'now' is required for it to have that length.



The length in time is evident in both the Earth (the cylinder) and the Moon (the helix). Both have spatial lengths (the thicknesses of the paths), but only the Moon has motion (wiggles).