Eternalism vs the Moving Spotlight Theory

I wanted to lay out my view of why Eternalism logically precludes motion.

Some members of this site, including SophistiCat and @Douglas Alan have previously claimed that Eternalism does not preclude motion.

In that case, my question is: when does motion occur according to Eternalism?

It cannot be at the present moment, because motion or temporal passage at the present moment implies the A-Theory, making it not Eternalism, but the Moving Spotlight theory instead. So, does Eternalist motion occur in the past or the future somehow?

"It cannot be at the present moment, because motion or temporal passage at the present moment implies the A-Theory, making it not Eternalism, but the Moving Spotlight theory instead. So, does Eternalist motion occur in the past or the future somehow?"
- Luke

There's the begging I smelled. Everything here are A-series references which assumes the conclusion you're trying to demonstrate.

At noon, the mug has coffee in it. At 1pm the mug is in the dishwasher. How is that not motion of the mug?

Please enlighten me as to the difference between Eternalism and the Moving Spotlight theory.

You seem to be implying that temporal passage is possible under Eternalism? How so?

You seem to be implying that temporal passage is possible under Eternalism? How so?

Moving spotlight (and pretty much the rest of your list) has a preferred moment. Eternalism does not.

The difference with presentism is mostly that an eternalist wants to say that the past and future are equally real as the now, whereas for a presentist only the now exists.

Presentism is not just about existence; it also entails the A-Theory and the reality of temporal passage.

What do you mean with the reality of temporal passage?

I disagree that presentism entails the reality of passage, because presentism might interpret the word "now" as being an indexical that cannot refer to the same set of affairs twice. If that is the case, then temporal passage cannot be referred to.

I tend to agree that a true presentist who rejects the existence of the past and future would be unable to judge which time is present. However, in reality, I think we are all able to ascertain this and can talk meaningfully about temporal passage. But this is not the focus of this discussion

For similar reasons I disagree that a denial of passage of time involves the denial of past and future, since "past" and "future" can similarly be interpreted as indexicals.

We can say that the state of the river has changed relative to the state of a photograph. But if the state of the river is also our notion of "the present", then we can no longer say that the river has changed relative to the present.

I believe that McTaggart was making a similar deflationary argument when he concluded the unreality of the A series.

See the OP section on The Passage of Time.

If B-theorist eternalist are right, and we are beings that only experience one moment in time, then we would experience the block-universe as passage of time.

You say that a denial of passage need not involve a denial of the past and future, but if "the state of the river is also our notion of "the present", then isn't this a denial of past and future? This seems to imply that we have no 'notion' of past or future states by which to judge that the present has changed.

But that passage is not real, right? Eternalist's don't believe that time really passes, right? So, I want to know how motion is supposedly accounted for under Eternalism (by those who believe that Eternalism admits of motion).

But the block-universe incorporates motion, in space and time? Isn't it a given that things change in space and time in a 4-dimensional block-universe?

If understood indexically, the past is always the past and the future is always the future, for yesterday is always yesterday, and tomorrow is always tomorrow....

How can it be, when B-theorist eternalists reject the reality of temporal passage?

What do you thing that dimension signifies otherwise?

Do you consider Eternalism and the Moving Spotlight theory to be equivalent?

But yesterday was a different day to today, just as tomorrow will be.
.

Existence only.

No, the moving spotlight theory give a special metaphysical status to the present

Yeah but existence in the block-universe is defined in four dimensions, that is probably what you are not realising?

What do you mean by 'special metaphysical status'? Is it any different to what you mean when you say "we are beings that only experience one moment in time"? When else can we experience things except in the present moment?

With 'experience of passage' or with 'passage that is real'?

it's derived from special relativity... and explains human experience after the fact.

Okay, and I am pointing out some problems with it.

That's fine, and i'm just saying I don't think they are really problems for the eternalist.

If B-theorist eternalist are right, and we are beings that only experience one moment in time

we are only privy to one moment and so experience it as passage of time.

The eternalist says that every point in time is equally real

Hate to butt in, however, these are all unproven theories?

If you perhaps fancy and have the time, could you explain in layman's terms. What differentiates eternalism from the moving spotlight theory?

Both have past, present, future.

Under eternalism, we beings are worldlines, and experience every moment along that worldline.

Hermann Weyl, Philosophy of Mathematics and Natural Science (1949):The objective world simply is, it does not happen. Only to the gaze of my consciousness, crawling upward along the life line of my body, does a section of this world come to life as a fleeting image in space which continuously changes in time.

I disagree that presentism entails the reality of passage

presentism can be understood as the following conjunction:

(PC) (i) Only present things exist,
&
(ii) What’s present changes.

Ouch. Under eternalism, we beings are worldlines, and experience every moment along that worldline.

If Presentism does not entail the reality of passage (i.e. the A-Theory), then are you arguing for the position of Presentism + B-Theory, i.e. that only present objects exist and that temporal passage is not real? I have never heard of this before. This is like the converse of the Moving Spotlight theory (Eternalism + A-Theory). I can only note this is at odds with the definition of Presentism given in most places, including the SEP article on Presentism:

presentism can be understood as the following conjunction:

(PC) (i) Only present things exist,
&

The reason why I call a perspectival interpretation of the B series "presentism", is due to the fact that tenses are treated as indexicals, where an indexical can be considered to be an act of pointing to something

All that is left to account for is the motion of one's consciousness crawling upward along the worldline.

Or alternatively we are stages which are located at a single instant and experience only that one instant of time while other counterparts experience the others. You know, cause experiencing every moment has the whole obviously wrong thing going on with us experiencing only one moment.

If that's how it works, it is still a form of presentism, with the consciousness (not part of the block) acting as the spotlight and defining a present.

It would be rather absurd to say that the 1997 portion of me is not conscious of the events of 1997.

How does that work if your consciousness is not crawling up a worldline?

The same way my thermostat turns on the heat in the winter despite the fact that it's warm in mid-May. No need for a 'measurment' spotlight to crawl up the thermostat's worldline in order to allow it to function.

Eternalism does not suggest that every state of a person along his worldline experiences every time in the worldline. That would be empirically quite different, wouldn't it?

OK, then it works the same way that my thermostat turns on the heat in the winter despite the fact that it's warm in mid-May.

I'm very sorry that you seem totally incapable of understanding an alternate point of view. I cannot help you with that. Not asking you to change your beliefs, but you have no argument for or against one side or the other of any philosophical issue if you don't have even a rudimentary understanding of both points of view.

Ouch. Under eternalism, we beings are worldlines, and experience every moment along that worldline. — noAxioms

Or alternatively we are stages which are located at a single instant and experience only that one instant of time while other counterparts experience the others.

Does this imply that there's a stage of you, e.g. tomorrow, that is having its experience now (from our perspective here today)? Or do we need to wait until tomorrow for that stage of you to 'light up', i.e. to have its experience?

You can think of stages like counterparts of yourself who experience their own moment parallel to yours. Since there are infinite instants in your life, then there are infinite versions of "you" so to speak.The stages don't light up, nor will you become those other stages via. the passage of time, for obvious reasons.

It's unclear why the stages are parallel to me. Aren't they stages of me?

Also, does this imply that each individual stage is on eternal repeat, replaying over and over again?

Is there an account of why we experience time sequentially instead?

Or alternatively that they just stay where they are. We are talking about a static view after all.

For the record, I only brought up the stage view as a way to account for the limited contents in our experience. Less accounting for what we do experience, but more about what we don't. I'll leave it to the eternalists in general to address that question.

A-Theory: Time passes; the passage of time is real
B-Theory: Time doesn't pass; the passage of time is not real

Okay, thanks for your responses. Unfortunately, there doesn't seem to be an account by the Eternalists of how we experience time the way we do. Except for those who simply assume (Presentist/A-theory) temporal passage within what is supposed to be a static block universe.

Imagine a transparent ball rolling along a table. People live in the ball and look out at the surface of the table (time) going by. But all of the table is there all of the 'time'. Just a thought...

If time is real and the future did not happen yet then the earth of tomorrow (or the earth in one second from now) does not exist. Likewise with the past. The earth of one second ago does not exist. This means the earth, and everything else, must be recreated every nanosecond???

The temporal passage thing is not the problem, the block is only static viewed from the outside.

So things change and we interpret that as time passing, though we never actually see a thing like time passing.

I don't think characterization as A-series or B-series explains anything by itself. It seems to be merely about the language we use to describe things, and so not about the nature of things.

(It is worth noting that some discussions of these issues employ terminology that is different from the A series/B series terminology used here. For example, some discussions frame the issue in terms of a question about the reality of tense (roughly, the irreducible possession by times, events, and things of genuine A properties), with A Theorists characterized as those who affirm the reality of tense and B Theorists characterized as those who deny the reality of tense.)

According to The B Theory, there are no genuine, unanalyzable A properties, and all talk that appears to be about A properties is really reducible to talk about B relations. For example, when we say that the year 1900 has the property of being past, all we really mean is that 1900 is earlier than the time at which we are speaking. On this view, there is no sense in which it is true to say that time really passes, and any appearance to the contrary is merely a result of the way we humans happen to perceive the world.

The opponents of The B Theory accept the view (often referred to as “The A Theory”) that there are genuine properties such as being two days past, being present, etc.; that facts about these A properties are not in any way reducible to facts about B relations; and that times and events are constantly changing with respect to their A properties (first becoming less and less future, then becoming present, and subsequently becoming more and more past). According to The A Theory, the passage of time is a very real and inexorable feature of the world, and not merely some mind-dependent phenomenon.

What is "genuine change" as opposed to change that is merely things being different at different moments in time? What is this "temporal passage" that is supposedly absent from the B-series and essential to time?

The takeaway here is that B-theorists deny that time genuinely passes, so if you think it does, then you might not be one.

In 4d spacetime an object exists temporally extended, "wormlike" over time, but that doesn't mean it doesn't change, or that time doesn't pass... it does, per definition.

And that is not merely 'apparent change', change is part of the existing temporally extended object and just as real as change is in A-theory it seems to me.

I've read the things you referred to, and my question is still the same, what do you mean with genuinely passage of time and genuine change? I can't answer the question if I don't know what it means.

Tim Maudlin:The passage of time is an intrinsic asymmetry in the temporal structure of the world, an asymmetry that has no spatial counterpart. It is the asymmetry that grounds the distinction between sequences which run from past to future and sequences which run from future to past. Consider, for example, the sequence of events that makes up an asteroid traveling from the vicinity of Mars to the vicinity of the Earth, as opposed to the sequence that makes up an asteroid moving from the vicinity of Earth to that of Mars. These sequences might be ‘matched’, in the sense that to every event in the one there corresponds an event in the other which has the same bodies in the same spatial arrangement. The topological structure of the matched states would also be matched: if state B is between states A and C in one sequence, then the corresponding state B* would be between A* and C* in the other. Still, going from Mars to Earth is not the same as going from Earth to Mars. The difference, if you will, is how these sequences of states are oriented with respect to the passage of time. If the asteroid gets closer to Earth as time passes, then the asteroid is going in one direction, if it gets further it is going in the other direction. So the passage of time provides an innate asymmetry to temporal structure.

Per what definition?

You've introduced this talk of "change" rather than temporal passage. What changes about a space-time worm? Obviously, it has different parts at different times, but nothing about it changes.

As the SEP article notes, it's taking tense seriously, which means "the irreducible possession by times, events, and things of genuine A properties", which simply means that future events become present and then past. Genuinely! But I'm sure you already knew that.

The passage of time is an intrinsic asymmetry in the temporal structure of the world, an asymmetry that has no spatial counterpart. It is the asymmetry that grounds the distinction between sequences which run from past to future and sequences which run from future to past. Consider, for example, the sequence of events that makes up an asteroid traveling from the vicinity of Mars to the vicinity of the Earth, as opposed to the sequence that makes up an asteroid moving from the vicinity of Earth to that of Mars. These sequences might be ‘matched’, in the sense that to every event in the one there corresponds an event in the other which has the same bodies in the same spatial arrangement. The topological structure of the matched states would also be matched: if state B is between states A and C in one sequence, then the corresponding state B* would be between A* and C* in the other. Still, going from Mars to Earth is not the same as going from Earth to Mars. The difference, if you will, is how these sequences of states are oriented with respect to the passage of time. If the asteroid gets closer to Earth as time passes, then the asteroid is going in one direction, if it gets further it is going in the other direction. So the passage of time provides an innate asymmetry to temporal structure. — Tim Maudlin

This is the temporal passage that B-theorists reject.

Per what definition?
— Luke

The 4th axis of 4d spacetime.

The parts at different times are different right? Well, that simply is change. I don't know how to put it any other way really. Change is part of the thing that exists temporally extended.

You cannot expect the whole temporally extended object to change in yet another 5th dimension.

I get that if you think only the present exist, the future and past are ontologically different... And so yes you would take tense seriously. But that is just a question of what exist, which I agree is different in the two theories. I'm just not sure what the word "genuinely" is supposed to add to all of this.

I agree that the eternalist need to give an explanation for the apparent asymmetry of time, which unlike space, seems to move only in one direction. But, as I alluded to in an earlier post, I think they probably can with the second law of thermodynamics. Entropy only increases, and so that gives time an apparent direction, only one way.

As I keep repeating, what it adds is the difference between the A-theory and the B-theory, which is temporal passage. A-theorists think it's real; B-theorists do not. It is not "just a question of what exists" if temporal passage is something over and above everything that exists. If it's not, then there's no distinction between B-theory Eternalism and the Moving Spotlight theory, which would imply there's no distinction between the B-theory and the A-theory.

How would anyone know whether it's real? There is no possible source of information on that question.

Now now.

Is that a definition?

My concern, as presented in the OP, is with temporal passage and motion. I'm not sure whether "change" is really the same thing. Your use of this term seems to be a way for you to try and have both the A-theory and the B-theory.

I don't. I deny that "the whole temporally extended object" changes at all. However, this might depend on your definition of "change". I'm not all that interested in change unless it means the same as temporal passage or motion.

As I keep repeating, what it adds is the difference between the A-theory and the B-theory, which is temporal passage. A-theorists think it's real; B-theorists do not. It is not "just a question of what exists" if temporal passage is something over and above everything that exists. If it's not, then there's no distinction between B-theory Eternalism and the Moving Spotlight theory, which would imply there's no distinction between the B-theory and the A-theory.

I do not mean by it "that time is an independent metaphysical thing acting on the universe."

A direction to time assumes temporal passage, which B-theorists reject. Entropy won't help you. To provide an account of why temporal passage has a direction is to concede that temporal passage is real. The Eternalist doesn't need to account for the direction of apparent temporal passage, but for apparent temporal passage itself (i.e. for how and why apparent temporal passage is not real).

None of this implies the ontological truth of one theory or the other. In fact, it doesn't even imply that time has an ontological nature. It might just be an ordering principle in our minds.

In the case at hand, all you're doing if you move from the A-theory to the B-theory is abstracting from the individual observer to a hypothetical universal observer.

Because the universal observer has no individual position in time and space (physics being assumed to be uniform across both) "A-properties" necessarily disappear in the process, being replaced by "B-properties".

You at time x1 and you at time x2 are at different locations, so you move.

It doesn't make sense to say that 'the whole temporally extended object" doesn't move as a whole.

Now you say temporal passage is something that exists over and above everything else?

Temporal passage again eh,

But I give up, like noAxioms said, you seem to be incapable of entertaining another perspective

The Eternalist needs to account for how one moves from t1 to t2 if temporal passage is not real.

Look, you said that "In 4d spacetime an object exists temporally extended, "wormlike" over time, but that doesn't mean it doesn't change, or that time doesn't pass... it does, per definition". I've shown you that this is incorrect. B-theorists assert that time does not pass. You can always opt for the Moving Spotlight theory if you want to retain temporal passage.

It's a different type of existence compared to all other things which exist at a time.

You want me to entertain a perspective which is not the topic of this discussion?

You seem to think that there is something fundamentally different about an object existing over all the intervals of time (t1, t2, t3, etc) and the passage of time, I don't. Time passes just the same

As I understand it, there is a genuine dispute between A-theorists and B-theorists as to the nature of time, with the former affirming that temporal passage is real and the latter denying it.

I don't know of any B-theorists who claim that time actually passes and that temporal passage only "disappears" (or is not real) due to it being a more objective perspective. This seems contrary to the definitions I've posted and to what I've read on the subject. I'd welcome any information you have that says otherwise.

Do you believe that future events become present and then past? That's the passage of time; the thing you seem to have trouble to comprehend. If you believe in this, then you believe in temporal passage. This is what B-theorists do not believe. It's that simple.

Like I said I don't subscribe to any metaphysical theory of time.

In that case, my question is: when does motion occur according to Eternalism?
Somewhere between noon and 1 obviously (in my example). Every moment of it in fact, since at no time is any object actually stationary, what with Earth spinning and accelearting and all.

The fact that I don't subscribe to it, is evidence that I don't understand it?

Chattering Monkey:The temporal passage thing is not the problem, the block is only static viewed from the outside.

What is this "temporal passage" that is supposedly absent from the B-series and essential to time?

In 4d spacetime an object exists temporally extended, "wormlike" over time, but that doesn't mean it doesn't change, or that time doesn't pass... it does

Honestly, I have no idea whatsoever what you mean with temporal passage.

Temporal passage again eh, if only I knew what it meant

You seem to think that there is something fundamentally different about an object existing over all the intervals of time (t1, t2, t3, etc) and the passage of time, I don't. Time passes just the same

Time doesn't pass according to the B-theory. That's it's defining aspect. Temporal passage was the first thing I defined in the OP and the thing I have had to keep repeating to you throughout this discussion. It also marks the difference between Eternalism and the Moving Spotlight theory, which was the intended topic of this discussion. But you seem to have wanted to talk about something else.

Please enlighten me as to the difference between Eternalism and the Moving Spotlight theory. — Luke

Moving spotlight (and pretty much the rest of your list) has a preferred moment. Eternalism does not.

You seem to be implying that temporal passage is possible under Eternalism? How so?. - Luke

I implied no such thing. I said there is movement. I made no reference to temporal passage, which again is a term only meaningful to views that posit a preferred moment.

Time doesn't pass according to the B-theory. That's it's defining aspect.
— Luke

That's not its defining aspect, it's the lack of preferred moment, or a question of what exists.

Following from this and other discussions at this site, I wanted to lay out my view of why Eternalism logically precludes motion.

If 1) B-theories are defined by the absense of the passage of time, and 2) Eternalism is a B-theory, but 3) the passage of time is not a meaningfull thing to talk about in eternalism… then maybe something is off with the whole qualification sceme.

instead of insisting on using the qualifications and definitions you set out in the OP, and God forbid trying to logically proof something from them about eternalism, maybe you should be asking the question if they make sense to begin with.

I don't know what you mean by "the passage of time is not a meaningful thing to talk about in eternalism".

However, if "Eternalism is a B-theory" and the B-theory is defined by "the absence of the passage of time", then time does not pass in Eternalism. Therefore, I argue, there is no motion in an Eternalist universe. That's what I'm arguing for here and what this discussion was supposed to be about.

It's not meaningfull because it assumes there is a present moment. If there is no present moment what could passage of time possible mean?

But this is all per definition. The conclusion is allready assumed in the definitions, so what's there to talk about?

I wouldn't call it an assumption; it's how we experience the world. Nonetheless, there is no passage of time under B-theory Eternalism, so the assumption of a present moment is equally absent. I don't understand how this is problematic or meaningless.

What I think you should say instead is something like this, 'in an eternalist view passage of time is replaced by things existing at different times' and motion is therefor re-defined as 'an object existing at different spaces and times'. This all a bit crudely formulated, but I'm just trying to get the point across.

What I think you should say instead is something like this, 'in an eternalist view passage of time is replaced by things existing at different times' and motion is therefor re-defined as 'an object existing at different spaces and times'. This all a bit crudely formulated, but I'm just trying to get the point across.
— ChatteringMonkey

The passage of time is not "re-defined" under B-theory Eternalism. Time does not pass according to the B-theory. You seem to want to retain temporal passage in Eternalism, just as a different way of looking at it. No: If time passes, it's A-theory; if time doesn't pass, it's B-theory. You can't have it both ways.

The conclusion is allready assumed in the definitions, so what's there to talk about?

There is an notion of time (nevermind the passage of time) in eternalism, right?

So what i'm saying is that you should take that notion and how it's used in eternalism (and not the presentist notion) into account when you speak of stuff like motion in that view. That seems pretty uncontroversial to me.

I thought you agreed that there is no motion because time does not pass, and that this conclusion is already contained in the definitions?

Yes if motion is defined in presentist terms of passage of time, then yes that conclusion follows logically.

I'm saying there is something wrong with the premisses, not with the validity of the argument.

What's wrong with the premisses?

The passage of time is not "re-defined" under B-theory Eternalism. Time does not pass according to the B-theory.

They apply to a presentist view only, and you are using them to arrive at a conclusion about motion in eternalist view.

I'm not even sure 'passage of time' the way you use it, is even essential to motion in a presentist view.

I'm not even sure 'passage of time' the way you use it, is even essential to motion in a presentist view.

The terms A and B theory are sometimes used as synonyms to the terms presentism and eternalism, but arguably presentism does not represent time being like an A-series since it denies that there is a future and past in which events can be located.

The motion of a body is observed by attaching a frame of reference to an observer and measuring the change in position of the body relative to that frame.

Here is what an eternalist might say: There is neither passage of time nor motion. Simply different spatio-temporal locations. Your mind simply apprehends temporal locations as a series of events, rather than as a region of coordinates, and this creates the appearance of motion.

The soul, as an eternal unchanging being

In either case, a mysterious power is required to produce the perception of movement.

How does a mind work if there is neither passage of time or motion? How does the human body work? What becomes of our understanding of beating hearts, circulation, respiration, vision, and all the rest?

Please don't bring religion into this discussion.

Couldn't you argue that Presentism presumes that same power, it just names it "time"?

How the mind works is the more interesting question. Given my description, it'd have to be outside the space-time block. That may be the reason Metaphysician Undercover called it a "soul".

The human body would be less of a problem, since what we know about it is based on perception, and thus would simply be subject to the same construction.

In case you haven't yet noticed, religion offers the most intelligent understanding of time.

I don't know what "subject to the same construction" is supposed to mean.

I don't follow how this is not problematic just because our understanding of physiology is "based on perception". I get that it's not a problem if there is passage of time and motion, but how is it supposed to work if there isn't?

The core idea here is that "everything you think you know is false" or more specifically: It is possible that the metaphysically objective world is entirely different from the physical world. One of these differences could be that time isn't what we think it is, that our concept of time is a construct of the human mind.

It could simply be that the relations of events in the time dimension are not fundamentally different from the relations of things in the spatial dimension. There'd still be a continuum where changes occur, just like there is a point where your desk ends and a wall begins. Just the specific appearance of a unidirectional passage of time would be just that - an appearance rather than an ontological reality.

Either there is motion or there is not, unless you know of a third option. I thought you had already accepted that there is no motion or no "continuum where changes occur" in an Eternalist universe. I'm not buying your "never mind the details" argument

As to your question, objects are arranged in space in an orderly way. Their arrangement can be described without referring to "passage of space" or some equivalent of motion. You can start your description at any point in the coordinate system and move in any direction, look at subsets in arbitrary order etc.

The same thing could be true for time. This wouldn't mean that events are no longer connected to each other. There'd still be the same laws that describe how one event (a region of time) is connected to another.

Motion only appears because you're traveling that web in one direction, seemingly getting events that follow another.

I'm not here for a lesson on Eternalism, unless it involves an explanation of how anything is supposed to work in a motionless universe, including the supposed illusion of temporal passage.

Nothing is travelling.

And I'm not here to serve on your whim. I have already spend time trying to give you an example, if you don't care for it then I guess I'll just leave you to it.

Motion only appears because you're traveling that web in one direction.
— Echarmion

Nothing is travelling.
— Luke

It's a metaphor.

Not interested. Please take it elsewhere.

You dismiss eternalism because it requires religion to make sense of time passage.

This is like saying you dismiss salt because it requires religion to make sense of pepper.

Huh? I thought you didn't want to discuss this. Why make such a strange analogy?

You dismiss eternalism because it requires religion to make sense of time passage.

What I meant, is that you dismiss eternalism, because accepting eternalism requires that you also accept religion in order to understand the passage of time.

You have been harping about how eternalism makes the passage of time unintelligible, and I explained how if you accepted a religious principle (the soul), you could make sense of time passage in an eternalist framework.

This must be some sort of illusion, although nobody has offered any explanation of what type of illusion it is, or how the illusion of temporal passage in a static universe works.

That's because I don't think it really requires much additional explanation once you accept the basic premisses of eternalism, namely that all moments in time have the same 'existence'. If you accept that, you already assume that we don't see the entire picture, but only a slice of it at a time... and so you already accept that the way we perceive things is limited or 'illusionary'. That is the big one, and then it doesn't take that big of a leap that, given that assumption of limited perspective, we would experience things as moving through time.

This also strikes me as backward. You're not making an inference that this is how we should expect to experience things; this is how we experience things, regardless of any metaphysical theory.

So now you are claiming that when you originally said that I dismiss eternalism because it requires religion to make sense of temporal passage, what you meant was that I accept eternalism because it requires religion to make sense of temporal passage. Except this doesn't make sense, because I don't accept eternalism either.

The Moving Spotlight theory already makes sense of temporal passage in an eternalist framework so no "religious principle" is required.

So you accept that all moments in time have the same existence and you accept that our perception of this is limited or 'illusionary'. But how do you get from there to the inference that we should expect to "experience things as moving through time"?

So we only experience one slice or one moment of time, at a time. But we also have a memory, we remember some of those experiences of moments at a time. And then there is also entropy always increasing, giving the appearance of directionality, (the textbook example being layered coffee and cream always tending towards totally mixed cream-coffee, but not the other way around).

4d existence is not static, it has time and movement included in existence.

Under eternalism, we beings are worldlines, and experience every moment along that worldline. So iff I define 'me' to be my worldline, then I am present at some event in 1995 and also 2021, and I experience those events and all others. There is none of this 'privy to one moment', which again smacks of a preferred moment.

The spotlight defines a present (preferred) moment, which makes it presentism, just like all the other variants described in the OP. Eternalism asserts the lack of a present,

Do you agree or disagree with noAxioms earlier statement that "Under eternalism, we beings are worldlines"?

Do you agree or disagree with noAxioms earlier statement that "Under eternalism, we beings are worldlines"?
— Luke


To expand on this, if you exist at every moment of your worldline as a "space-time worm", i.e. you exist at every moment from your birth to your death, then what sense can it make to talk of moving through time from one moment to the next? Your physical existence, at least, exists as a four-dimensional object. What requires explanation in this scenario is why we have the conscious experience of time that we do; experiencing only one moment at a time in sequence, as though we are three-dimensional beings moving through time, and as though time actually does pass.

if we assume a limited perspective (which is what the assumption of eternalism entails)

if you exist as a static four-dimensional object

If we assume that time does not pass and that motion is not real,

This is what I'm objecting to. There is nothing static about a four-dimensional object, it's dynamics by virtue of it existing in a 'four'-dimensional space-'time'. It's can only be considered static when viewed from outside the time-dimension of 4d space-time, in relation to some other imaginary fifth time-dimension.

The B-theory of time is the name given to one of two positions regarding philosophy of time. B-theorists argue that the flow of time is an illusion, that the past, present, and future are equally real, and that time is tenseless. This would mean that temporal becoming is not an objective feature of reality.

According to The B Theory...there is no sense in which it is true to say that time really passes, and any appearance to the contrary is merely a result of the way we humans happen to perceive the world.

Or put in another way, you cannot simply treat a 4d object the same as a 3d object, in the sense that the entire 4d object has to move in time, like a 3d object does. The movement happens within the object because the time-dimension is already included in its existence.

Eternalism...is sometimes referred to as the "block time" or "block universe" theory due to its description of space-time as an unchanging four-dimensional "block", as opposed to the view of the world as a three-dimensional space modulated by the passage of time.

And I think this assumption is not a good way to go about categorizing theories of time, because for this category it is already assumed that it cannot work. Why have a category for something that is impossible? I think, rather, we should only be looking at theories of time that could possibly fit our experience. Eternalist claim that the theory could fit our experience, I'm not entirely sure yet, but that is not because I think motion or passage of time are impossible under it... or assumed to be impossible even.

Eternalism...is sometimes referred to as the "block time" or "block universe" theory due to its description of space-time as an unchanging four-dimensional "block", as opposed to the view of the world as a three-dimensional space modulated by the passage of time.

According to The B Theory...there is no sense in which it is true to say that time really passes, and any appearance to the contrary is merely a result of the way we humans happen to perceive the world.

It seems as though we are at an impasse

Or put in another way, you cannot simply treat a 4d object the same as a 3d object, in the sense that the entire 4d object has to move in time, like a 3d object does. The movement happens within the object because the time-dimension is already included in its existence.

Okay, maybe that is how some view the block-universe, I can't speak to how they view it of course. But still, I think using words like 'unchanging' or 'static' to describe the block-universe is misleading because it assumes a perspective from outside the 4 dimensions.

There is no movement within that 4d object because there is no passage of time.

See, you're on the right track here. Now, do you see how your statement above, "movement happens within the object because the time-dimension is already included in its existence", is inconsistent with this? You cannot say that "movement" happens within the object, because it's a word classed with those others, "unchanging", and "static", which assumes something outside the four dimensions.

I think using words like 'unchanging' or 'static' to describe the block-universe is misleading because it assumes a perspective from outside the 4 dimensions.

I think it's not so much that time doesn't pass in the sense that there are different moments of time, but that it doesn't flow in any particular direction.

If one says the block-universe is static or unchanging, one is looking at the whole picture, all the 4-dimensions, and says the 'line' or 'worm' in the eternalist graph as a whole doesn't change (thereby imagining another 5th dimension where that change would have to take place, i.e. 'viewed from the outside').

So I've been told, over and over again, but I don't see why there is something fundamentally different about something existing at time t1, t2, etc ... and time passing (aside from the direction and the ontology which I already agreed with). The moments of times associated with past, future and present all exist in eternalism, but not at the same time, right? That's what the 4th dimension indicates.

No it precisely doesn't assume something outside the four dimensions, that's the whole point, that one should adjust the concept of movement to the 4d frame.

Again I'm not a metaphysician and I don't assume words to have fixed meanings... but if you want to insist that the word movement doesn't apply, fine, then i'll have to invent another word with basically the same meaning for things changing position over time.

If one says the block-universe is static or unchanging, one is looking at the whole picture, all the 4-dimensions, and says the 'line' or 'worm' in the eternalist graph as a whole doesn't change (thereby imagining another 5th dimension where that change would have to take place, i.e. 'viewed from the outside').

(An odd but seldom noticed consequence of McTaggart's characterization of the A series and the B series is that, on that characterization, the A series is identical to the B series. For the items that make up the B series (namely, moments of time) are the same items that make up the A series, and the order of the items in the B series is the same as the order of the items in the A series; but there is nothing more to a series than some specific items in a particular order.)

In case you haven't yet noticed, religion offers the most intelligent understanding of time.

You dismiss eternalism because it requires religion to make sense of time passage. That says a lot about you.

Time flows but not "in any particular direction"?

That's not what the B-theory is. This would imply that time flows when "viewed from the inside", but then it would be no different to the A-theory.

What does that have to do with anything...?

Hmm ... what is motion but a spatial path in spacetime anyway?

It's just that no particular time is considered (a special privileged indexical) now, hence the block-verse model is incomplete.
But wasn't that the idea in the first place, that a t parameter can represent any now, any time, on equal footing? That any direction only is implicit in the ordering and nothing else?

It's not that block-verse does not model motion as such (mentioned path with all of time internal to the model), it just sacrifices the special for general (non-indexical) descriptive prowess.

What might a complete model look like anyway?

I'm thinking that both duration and simultaneity would be part thereof, which seems to suggest dimensionality of some sort.

there is no direction of time... so the word flow doesn't apply

Again past and future existing and a direction to time is different... But ok fine, if you want to talk about theories that clearly don't apply to the world I or everybody else experiences, be my guess, but I have nothing to say about that.

You said in your last post that time flows but has no direction. You seem undecided?

Otherwise, I'd welcome an explanation of B-theory Eternalism which allows for temporal passage and motion and/or an explanation of motion without temporal passage.

I said time doesn't flow in any particular direction

But a lot of scientists believe in eternalism, and I'm pretty sure very few of them believe that there can be no motion under it. Are they just all that stupid for not realizing that motion is impossible under eternalism, or doesn't it have to entail that and the presupposed qualification sceme is simply misguided? I'm guessing the latter.

I was talking more about the fact that two days ago you said time flows (but not in any particular direction), whereas yesterday you said "the word flow doesn't apply".

And you seem to think that the definitions I've provided from the SEP and Wikipedia articles on the subject are incorrect. Do you have any support for your claims?

Definitions can not be correct or incorrect, it's a decision, you can define something however you want in principle.

They can be more or less useful though, and I'm saying they don't seem to be very useful if they only apply to a theory of time that can't be the case and that nobody believes in.

But a lot of scientists believe in eternalism, and I'm pretty sure very few of them believe that there can be no motion under it. Are they just all that stupid for not realizing that motion is impossible under eternalism, or doesn't it have to entail that and the presupposed qualification sceme is simply misguided?

I don't see that there is anything in eternalism per se that precludes motion, unless you define it as such.

... objects are arranged in space in an orderly way. Their arrangement can be described without referring to "passage of space" or some equivalent of motion.

I don't think anybody claims that these theories of time are complete physical theories. The way I see it that they are merely theories about time that could possibly fit our experiences. And my point is that I don't see that there is anything in eternalism per se that precludes motion, unless you define it as such.

Nothing in eternalism "precludes" motion

Criticisms of Presentism just seem to be much more prevalent.

I think that's because the criticism is of a different order, not merely definitional. A universal now or present has been shown to be a problematic idea in relativity. So either you say relativity is wrong, which will be a hard sell because it has been tested over and over again, or you adjust presentism and maybe you could save some sort of universal now or present that accounts for relativity. Or you bite the bullet of relativity entirely and adjust the theory so that it only allows for local nows, which gets you close to some kind a solipsism.

Unless you are talking about the Moving Spotlight theory (which I consider to be a hybrid of Eternalism and Presentism/A-theory, rather than true Eternalism), or unless you can provide an explanation for how motion is possible under B-theory Eternalism (i.e. without temporal passage), then I think it is clear that Eternalism does logically preclude motion.

Maybe ChatteringMonkey is right that nobody really believes in this extreme, pure version of Eternalism, and the same probably applies at the other end of the spectrum, too, but I think it's worth pointing out what those extremes entail. Criticisms of Presentism just seem to be much more prevalent.

The point was that eternalism does not make motion impossible, because all you have to do is add more premises, like your spotlight theory does. Therefore we cannot say that it precludes motion.

what is motion but a spatial path in spacetime anyway?

Even if the start of the 4D object is at position x1 at t1 and the end of the 4D object is at position x2 at t2, it still would not have moved from x1 to x2, because this would be to treat the four-dimensional object as a three-dimensional object ("modulated by the passage of time") instead.

Because what is motion other that something changing position over time, that is literally the definition of motion.

You seem to assume that existence at all points is the same as moving from one point to another.

And yes why not split a 4d object up into 3d objects...

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?

I'm not really concerned with it. I'm interested in the logical implications of the concepts.

So what moves? Whatever part of the 4d object that changes position over time.

In eternalism, what word would you use to differentiate between a 4d object that only exist at one place and 4d object that exists over multiple positions?

In eternalism, I see no need to differentiate between them. To what end?

So 3D parts of the 4D object change position over time, despite the fact that the 4d object as a whole does not change position over time. Isn't this just smuggling in Presentism and/or the A-theory?

To our ends of course, as human beings. Even if eternalism is true, we would only experience part of it, and things existing over multiple positions over time presumably would be still of interest to us.

So 3D parts of the 4D object change position over time, despite the fact that the 4d object as a whole does not change position over time. Isn't this just smuggling in Presentism and/or the A-theory?
— Luke

No I don't thinks so, you need another concept of movement, like I said earlier.

You "need another concept of movement" for what?

Put simply, 3D objects move; 4D objects don't.

?Luke
I'm done with the thread, I said what I have to say.

But at this point i'm starting to repeat myself again.

You need to adjust the concept of motion to the 4D frame,

... saying a 4D object doesn't move, doesn't make sense because there is no 5th dimension in relation to which it could move. The term movement just doesn't apply, because motion is change in position over time. There is no 'over time' for a 4D object as a whole.

This is likely my ignorance, but the MST seems to imply a privileged history.

The whole point of spacetime is that it is invariant.

The passage of time for a woman flying to a neighbouring solar system at 0.1c is not that of her Earthbound twin, and no objective duration for comparison is necessary or possible.

So either the MS adds nothing, or it adds something that makes a nonsense of the world around us.

Or does every observer have her own spotlight?

why would that be smuggling in religion?

MST is a hybrid of Presentism and Eternalism. Presentism does indeed entail a "privileged history". However, I'm not here to defend Presentism, but to point out the nature of the (block) universe according to (B-theory) Eternalism, which, by definition, contains no temporal passage.

I'm not sure whether that's the "whole point of spacetime", but the laws of physics are considered to be invariant in spacetime, yes.

That only makes sense if there is a passage of time.

when does motion occur according to Eternalism?

My point was that there is no concept of absolute simultaneity. There is no "now" that you and I share, unless we're co-moving.

But you are presenting MST for consideration.

My point was that there is no concept of absolute simultaneity. There is no "now" that you and I share, unless we're co-moving. So I was wondering how a spotlight illuminates "now" across many bodies moving at different speeds. Is there a basis for choosing?

It absolutely is. (I used to teach this stuff at uni, so I'm not totally pulling this out of the air.)

That only makes sense if there is a passage of time.
— Luke

Yes, that's the problem. The MST seems to reintroduce a passage of time

Simplest of kinematics is velocity: change in position / change in time. This, and all higher orders of motion, are retained in four dimensions. It's just that "change in time" is not special. Let's say you're due south of the summit of a mountain. As you move toward the summit, you're moving north. But you're also moving upwards as you ascend. There's a relationship there: the gradient change in altitude / change in latitude. "Motion" in the usual 3D+1 way of thinking is now just equivalent to that.

I presented the MST mainly for comparison with the block universe. Perhaps that was an error on my part.

Does this imply that you acknowledge and find it unproblematic that Eternalism (i.e. the block universe) has no passage of time?

If so, then how do you answer my question of what it is that changes position over time if 4D objects (and/or their subdivided 3D parts) remain fixed at their spatiotemporal locations according to Eternalism?

According to the principle of relativity, laws of physics don't privilege any reference frame. But that doesn't mean that a reference frame cannot be privileged in some other sense - like in the sense of indicating the absolute now. The absolute now would not be part of the known laws of physics if it existed; it would come as an extra fact about the world. But that's old news - it was as true for Galileo and Newton as it is for Einstein.

When you say "changes... over time", in the block universe that means "what changes in the rest of the worldline as we move along the time axis in a particular direction".

Do you mean simply tracing out a path on a map

Yes, just this. It would be easier if I could draw it, or write equations. But if you can imagine it, groovy. The question is: what changes (other than the time coordinate) as you follow the path of the helix? The answer is the spatial coordinate of the helix.

To anticipate the follow-up question, or the similarity of what I'm suggesting to the spotlight, it is not necessary to do this for the "change" with time to be there.

It's merely a means of illustrating that the change is already encoded in the worldline.

Motion is conventionally defined as change in position wrt time (which also works for presentism). Motion exists in the block (if anything exists whose spatial position changes as its time position changes). The answer is inevitably geometric, since the block universe is geometric, and inevitably kinematic given the (imo only sensible) kinematic definition of motion.

That is, everything exists at all times.

The block universe in this case is not a model along which you can trace time with your finger

To anticipate the follow-up question, or the similarity of what I'm suggesting to the spotlight, it is not necessary to do this for the "change" with time to be there. It's merely a means of illustrating that the change is already encoded in the worldline.

The block universe in this case is ... the actual universe in which nothing changes its spatiotemporal location.

Caveat to follow, but: everything exists at all times, but not necessarily at the same place at all times. This variance of position with time is motion.

Imagine a 3D universe consisting only of an eternal stationary ball. In the block universe depiction, this is a straight line parallel to the time axis. Now boost to a frame of reference in which the straight line now has a gradient. i.e. is no longer parallel to the time axis. There's your motion: I just moved the whole universe for you, Luke, and you're still not happy!!!

The ball has motion, though. Informally, the ball "is moving", i.e. if instead the worldline of the ball is sometimes parallel to the time axis and sometimes not, I could say "the ball is sometimes moving" and you'd understand me, right?

You still seem to be presuming that an object can change its temporal position (i.e. move through time). Eternalism rejects this.

Taking the broader point, I agree that the existence of things that cannot even be indirectly observed is possible. I'm less convinced that it's meaningful to talk about them. Which I guess is what I was saying earlier: what is the explanatory power of the spotlight? If we accept that a) it is a privileged frame, not shared by all of us, and b) makes no difference to observable phenomena, it can't explain, say, the psychological passage of time, which is subjective, i.e. relative.

An "absolute now" is not a concept that makes sense to me though. "Now" now is not "now" exactly a year ago: it is not absolute. But a privileged moment (e.g. 13.7 billion years ago) wrt which "now" can be referred and seen to change would be absolute and sensible, even if it has no obvious descriptive power.

"change in t" does not mean "some passage of some objective present moment from the first value of t to the last".

That does not mean that the worldline itself, which we may write as a function of (z,y,z,t) is moving with respect to some other time t2.

While relativistic laws are reference frame invariant (up to coordinate transformation), the same cannot be said about those things that the laws do not fix, such as the distribution of matter and radiation in the universe.

If we take those other things into account, we can identify reference frames that are special in some way, such as the frame in which the cosmic microwave background radiation has the same energy profile in all directions.

All the same,the need for a privileged frame is not fatal to presentism, although as you point out, no observation can help us identify this frame.

You seem keen to saddle me with Presentist assumptions. I have not mentioned an objective present moment or a second time dimension. I am using the same definition of motion as you.

Motion is a gradient of position over time. Position exists in the block. Time exists in the block. As long as objects are a) continuous and b) not parallel to the time axis of the block, you get motion from that and that alone. There's nothing else needed, it's there in the geometry of the object.

Aren't you simply defining temporal passage into existence?

This is the definition of velocity in classical kinematics. This is what I mean when I say: if you insist on no motion in the block, necessarily you insist on a new or obscure definition of motion.

This is not me defining anything either. It's known as the B-theory in philosophy of time.

Critics complain that it does not yield a passage of time.

But motion does not depend on a passage of time, so is unaffected.

What is the difference between passage of time and change in temporal position?

The passage of time is whatever makes motion possible and what doesn't exist in B-theory eternalism.

The passage of time is whatever makes motion possible and what doesn't exist in B-theory eternalism.
— Kenosha Kid

Fixed the definition.

But in Luke's defense if we take eternalism seriously as a metaphysical theory of time, and not merely as a description, then there does seem to be somewhat of a tension between change in temporal position and saying things already exist at all moments of time.

Where I seem to come down on all of this is that word 'what exist' or what is 'real' is in some way tied to our experience, and therefor presentism.... and rather then denoting something about metaphysical reality, it usually is used to differentiate between things that can have a direct effect on us. Or put in another way we invented those words because they has some utility to us. And so the problem is ultimately with the word 'real' or 'exist' really. Saying that something in the distant future and distant past exists doesn't seem very useful to us... whatever the metaphysical reality may be.

The idea that no motion cannot occur because there is nothing moving along the time axis or moving along the worldline or moving within the block is in itself a presentist notion.

Yes, that's precisely what I've been saying all along: any definition of motion that requires a passing 'now' differs from the standard kinematic definition of motion. I assume this integral-like definition yields the same actual velocities as kinematics, but mechanically relies on a 'now' moving from time A to time B, i.e. it is some kind of propagator.

I would strongly disagree. If you take eternalism seriously, then take it seriously with both feet and think about things like motion and change in eternalistic terms. The idea that no motion cannot occur because there is nothing moving along the time axis or moving along the worldline or moving within the block is in itself a presentist notion.

:up: Yes, totally. In this case a problem appears to be with the word "change", which is why I suggested a more precise terminology. Motion in eternalism depends on geometry: differences between coordinates at different points on the object. It's totally understandable that subjective, everyday, presentist-like experience would affect one's language when talking about time, motion, change, etc. I've just been working in 4D for so long that the habit has largely been superseded.

I guess my point was that the confusion comes from thinking about things "existing", which kind of implies an "already', or in other words 'at the same time'... and so it's hard to make sense of something changing position then. But the point is that they exist at different times in eternalism.

Agreed, it's useful in physics to think in those terms, maybe not so much in everyday life... not as long as we don't start venturing into space at relativistic speeds anyway.

the eternalist idea that there is motion when nothing is moving

A change in temporal position is two different values of t on two different events on the same worldline.

Change in temporal position is the existence of a pair of values? What changes?

I am no astronomer, but to my knowledge, the distribution is a uniform, isotropic black body spectrum.

Since the point of relativistic physics is that phenomena are invariant even if the way we denote them is wrt coordinate systems, it's difficult to imagine what special universal features might be yielded simply by judicious choice of inertial frame. Moving to non-inertial frames, if, say, the universe was found to have net spin, you could call the frame it which it doesn't 'special'. A very novel physics explaining pseudoforces would be required

The coordinates.

What do they change from/to?

I am just saying that presentism is not unique in requiring 'special' reference frames.

you should seriously view any object, such as the Earth or the Moon, as a four-dimensional object

Instead, they are whole 4D objects which consist of different stationary 3D parts existing at different times.

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

It doesn't seem like taking it seriously to maintain that there is motion in Eternalism.

At the end of the day, unless you can demonstrate that dx/dt is everywhere zero or meaningless in the eternalist picture, velocity, and therefore motion, will assert itself. Asserting to the contrary is your prerogative, but it is not an argument.

But dx/dt is inconsistent with the static 4D nature of the universe as described by Eternalism, as there is no actual change in position over time.

If all objects are 4D, then they don't change over time. I'm not here to convert things to your physics model. I'm here to discuss metaphysics.

?Kenosha Kid He's been stuck on this point for years.

What does motion, in the everyday/kinematic sense, look like?

As I said, if you're abandoning kinematics (e.g. v = dx/dt), fine. If you're making claims about kinematics though ("no kinematic motion can exist in a 4D that has x and t"), they can be rejected on kinematic grounds.

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.

So there is motion, even though the Earth doesn't move?

Motion, in the everyday sense, looks like something not having a determinable position

We often describe it as what happens when a thing changes position.

The Earth does move, though, in the same way we mean in our everyday, subjective, presentist definition of movement: the Earth has different spatial coordinates at different times.

I thought you agreed that "The 3D Earth doesn't move from t1 to t2"? Now you're saying that it does?

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.

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.

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.

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

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.

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

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

Okay, I was agreeing with the emboldened part.

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

Light, for instance, moves through space

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.

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.

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

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?

...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?

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

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

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.

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

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

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

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.

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.

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.

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

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

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.

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.

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.

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

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.

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

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

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.

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.

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.

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.

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

no clue there?

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

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.

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

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.

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.

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.

To consider it the same object is a Presentist notion.

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.

...so cannot change temporal position.

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".

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

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?

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?

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.

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

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.

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.

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.

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.

Yes, iirc I did ask for clarity on "3D part", I wasn't sure if you meant the body or its spatial coordinates. Continuity is what makes it the same object. Although, the ship Theseus and all that.

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.

Yes, iirc I did ask for clarity on "3D part", I wasn't sure if you meant the body or its spatial coordinates. Continuity is what makes it the same object. Although, the ship Theseus and all that.

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.

The mountain at the summit is the same mountain as the one at the foot. What is it then that changes spatial position?

It's not my definition, blame Galileo!

An effect of the motion of the teacup is that it is now on the floor.

my everyday experience of motion: the thing is not where it once was.

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.

What is it then that changes spatial position?

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.

What is it then that changes spatial position?
— Kenosha Kid

In Eternalism? Nothing. That's what I'm arguing. Nothing moves; nothing changes.

Forget eternalism. Just a mountain at a given moment in time, an aerial photograph of you will. The summit is in one place. The foot is far away from it. It exists in more than one position.

The summit is in one place. The foot is far away from it. It exists in more than one position. By your argument, radius is impossible because what changes spatial position?

Irrelevant. For which object are you measuring the motion? The mountain. So you need to measure the change in its temporal position. This will require that the same mountain (edit: object) is "defined for more than one time". And then see my argument.

I can calculate the gradient of the mountain at any point by measuring the "change" in altitude with "change" in radius. These are not changes over time, these are merely lengths. Not does that gradient depend on me measuring it.

The same goes in 4D, where I can measure motion as "change" in spatial position with "change" in temporal position: these are lengths. And the motion is there whether I measure it or not.

The gradient of the mountainside is not a change in the spatial position of the mountain, as you implied earlier. The mountain hasn't moved.

Precisely, and yet it has spatially-dependent altitude (a gradient).

What object has changed its spatial location? Please tell me.

Nor does that gradient depend on me measuring it.

You do not need to "change" spatial location

Are you trying to "change" the subject? I thought the subject of our disagreement was whether there is motion in Eternalism. I've given my argument for why there isn't. You may need to clarify how this response addresses that argument.

In short, your counter-argument is equivalent to saying that, at a given moment, a mountain must be flat because there is nothing "changing" position to allow its altitude to vary with position.

I'm not going to argue with you by analogy. There is no long-standing debate about whether altitude of a mountain can change with position. This is about time and motion.

This seems to be par for the course: every opportunity I've suggested to consider how motion is possible in eternalism, you have given some excuse to look away. It all comes down to dx/dt being well-defined in eternalism as d(altitude)/d(radius) is defined for a mountain at any given time, and that the geometry of a 4D object is not dependent on how we calculate it, just as the geometry of a mountain is not dependent on how we calculate it.

Oh my god. Your argument is little more than motion is possible in Eternalism by definition. The least you could do is address my argument if I'm so obviously wrong.

Show me where I've used a different definition of motion.

Your argument is little more than motion is possible in Eternalism by definition.

Motion is change in spatial position over change in temporal position.

"Change in temporal position" means "is defined for more than one time".

Therefore your argument is nothing more than: "motion is impossible in Eternalism by definition".

My argument is based on these definitions.

I've actually presented an argument. Where's yours?

Then motion is possible by definition, since the time-dependence of an object's position is retained in the eternalist picture.

Your responses have amounted to circular arguments, contradicting yourself, and refusing to ever consider any point that would resolve the argument when offered

What does "the time-dependence of an object's position" have to do with either of the definitions that we previously agreed to?

a 4D object's position depends on time

This is an example of taking the time to explain oneself.

What does "depends on time" mean?

Motion is change in spatial position over change in temporal position.

I've taken great pains to explain myself and present my argument, which you continue to ignore.

What does "depends on time" mean?
— Luke

It means:

Motion is change in spatial position over change in temporal position.
— Luke

i.e. that where something is depends on when.

I have answered every question you have asked. You have not done the same.

What comes before and after the "i.e" is not equivalent. Motion is not defined as merely having a spatiotemporal position.

Did you have questions? I thought you were just telling me what's what.

What is it then that changes spatial position?
— Kenosha Kid

In Eternalism? Nothing. That's what I'm arguing. Nothing moves; nothing changes.
— Luke

No. What is it that changes position at all? Forget eternalism. Just a mountain at a given moment in time, an aerial photograph if you will. The summit is in one place. The foot is far away from it. It exists in more than one position. By your argument, radius is impossible because what changes spatial position?

I'm not going to argue with you by analogy. There is no long-standing debate about whether altitude of a mountain can change with position. This is about time and motion.

...the spatial part of the spatiotemporal position depends on the temporal part, that is: for each time, the object has a position. Assuming continuity.

What is it that changes position at all? Forget eternalism. Just a mountain at a given moment in time, an aerial photograph if you will. The summit is in one place. The foot is far away from it. It exists in more than one position. By your argument, radius is impossible because what changes spatial position?

Is this different for Presentism?

However, if what you mean by "exist in more than one position" is to have a part of the mountain existing at one spatial position and another part of the mountain existing at another spatial position, then I agree that different parts of the mountain "exist in more than one position".

If you are happy that a 4D object exists at more than one time

And if you're happy with time intervals in 4D, and you are happy that the spatial position at one end of the interval may be different to that over the othet end, you are presumably happy that a 4D object's position changes with with respect to time, i.e. it's position at one time (x, y, z, t) maybe different at another.

There is the kinematic definition of motion

I have no qualms with saying that different parts of the 4D object have different spatial positions at different times. I disagree that the 4D object as a whole has different spatial positions at different times.

There is the kinematic definition of motion
— Kenosha Kid

Following your reasoning above, this would imply that the 4D object as a whole moves.

The gradient of the mountainside is not a change in the spatial position of the mountain, as you implied earlier. The mountain hasn't moved.

Do you agree that even a part of a 4D object, such as an atom in the window of a car, has different spatial positions at different times?

A body at a spatial coordinate (x,y,z) at time t may have a different spatial coordinate (x',y',z') at time t' (a path). This does not mean that the body at coordinate (x,y,z,t) moves. That is not shown, nor is it sensible.

you are presumably happy that a 4D object's position changes with with respect to time

The gradient of the mountainside is not a change in the spatial position of the mountain, as you implied earlier. The mountain hasn't moved.
— Luke

It may help to imagine a pipe going down the mountainside. The answer to where the pipe is on the 2D surface of the Earth depends on which altitude you’re asking about: the pipe changes 2D location with altitude. If the pipe is on the east aide of the mountain, for instance, it gets further east the lower down the mountain it goes. It’s not moving over time, but the relevant segment of it at a given altitude is further east the lower the altitude. Yet at every altitude, it is still the same pipe.

Do you agree that even a part of a 4D object, such as an atom in the window of a car, has different spatial positions at different times?
— Kenosha Kid

I get the sense this could be a trick question, but yes, I think so.

I didn't claim that it wasn't the same mountain.

Fine fine fine. Not a trick at all. We only need consider an atom. This is also kinematic motion: different spatial positions at different times, i.e. time-dependent positions.

I didn't claim that it wasn't the same mountain

Sorry, I don't understand what you're getting at. I didn't claim that it wasn't the same mountain.

Hold on. You said the atom was "part of a 4D object", not a 4D object. It depends on Presentism or Eternalism whether this remains the same object at different times.

What difference will continuity make?

However, different objects exists at these two locations in Eternalism - the different parts of the 4D object.

Couldn't sleep.

"different objects exists at these two locations in Eternalism" is such a assumption. My counter would be that this is not generally held to be true by eternalists, nor is it a component of any typical definition of eternalism, i.e. this is now a special kind of eternalism.

Just as I am not happy that a 3D object exists at more than one space (the object fills the space), I am equally not happy that a 4D object exists at more than one time (the object fills the time). And just as I agree that different parts of a 3D object exist at more than one space, I agree that different parts of a 4D object exist at more than one time.

A body at a spatial coordinate (x,y,z) at time t may have a different spatial coordinate (x',y',z') at time t'

That said, motion may still be recovered in this eternalism, even if we assume the object at t' to be different to the object at t, so long as there exists another continuity connecting the objects at t and t'. This is at least sensible: we do not see an object disappear then be replaced by a different but indistingushable object.

Which is a complicated way of changing some labels at the end of the day.

Eternalism says that if you could somehow step outside of our normal space and time, you would see thing still in it like that line.

The 4D object can be broken into its constituent parts, just like a mountain can.

If the 4D object is the entire spatiotemporal existence of the mug, and if the 4D mug is made up of its constituent parts, then how are the two parts you mention above not different and co-existing parts?

In that case, how do you intend to calculate your Eternalist motion between one part and another? You will need to pick out these two different parts in order to do so.

And this has been your mistaken assumption all along: that the existence of time automatically implies the existence of motion.

But that's exactly the difference between Presentism and Eternalism.

Eternalism is a motionless existence.

Moving to QM, you don't even need time to have momentum: it is a purely spatial geometric feature.

They are, but now we can consider the 4D geometry of the part, see that it has one, and motion again falls out.

You'd need some information about what parts exist where and when. This would replace a history of one object in 4D with a history of different 3D objects transforming into one another, building up the worldline that you say is not one object but different parts at different times.

You can have an eternalist universe without motion, but then the temporal dimension would be redundant.

No, it doesn't. It says time is really static (inside spacetime).

A 3D part in Eternalism is equivalent to a 3D object at a time in Presentism. Both describe the mug on my desk at time t.

the Eternalist part at t and the Eternalist part at t' cannot be considered to be the same part (by Eternalists)

But they are nevertheless still parts of the same object.

Are you wanting to argue that the 4D object moves?

Moves with respect to what? Time is one of the four dimensions.

An object moving in three dimensions with respect to the fourth will just look like a 4D object to you, though.

You're arguing against something that nobody is defending.

Eternalists don't think that the universe is motionless.

They think motion has to be with respect to something. 3D objects move with respect to a fourth dimension of time, tracing out a 4D shape as they do so.

not the motion of 4D objects with respect to... what exactly?

This underlies my whole view of the matter (although somewhat vaguely): that Eternalism is all position and Presentism is all momentum.

Motion implies that the same object moves from t to t'. This is a Presentist assumption which makes no sense in Eternalism.

I don't understand your use of the word "redundant" here.

Motion implies that the same object moves from t to t'. This is a Presentist assumption which makes no sense in Eternalism.
— Luke

As defined, yes.

Wait... Are you saying you are satisfied that Eternalism logically precludes motion (according to our agreed upon definition of motion)?

Eternalists don't think that the universe is motionless.

There is something that turns the cup at t into the cup at t'.

Motion still falls out: dx/dt = (dx/dc) x (dc/dt)

So as long as x, c, and t are continuous, i.e. so long as objects don't disappear then later reappear, motion is still possible.

Space is present in both, so therefore momentum is possible in both.

If motion were impossible, then x(t) = x, which a constant. We could write a position as (x, y, z, m, n, t). But since (x, y, z, t) fully determine position, i.e. (m, n) don't do anything, this is merely describing a 4D something in a 6D space for no reason: it is still 4D. Likewise if nothing moved, (x, y, z) cannot change thus those coordinates define everything.

1) Eternalism does not say that the cup at time t is a different cup at time t', so the above is unnecessary

2) Is still yields motion, just via an additional variable.

There is something that turns the cup at t into the cup at t'.

Momentum requires only space?

Eternalism logically entails that the cup at time t and the cup at time t' both co-exist as separate objects/parts. They exist as different 3D parts of the same 4D cup, but always as different parts. You can call them the same cup if you like, but you can also say that time passes if you like.

The additional variable is motion? That is, what is this "something"?

The momentum of a quantum mechanical body at a particular time is a feature of its wavefunction's geometry at that time. Precisely, it is, in a given direction, proportional to the number of wave peaks per metre in that direction. It is still related to time, but indirectly, via something called the dispersion relation, which is energetics not kinematics.

If it is irrelevant in eternalism whether consider the cup at time t' to be the same cup as the cup at time t, then it cannot form part of your argument one way or the other. (So here we agree.)

No, just whatever it is that connects the cup at t' to the cup at t. It's not something I postulate.

I know the cup at t' is the same as the cup at t, that they are different cross sections of the same 4D object. But if you want to postulate they are not, then there needs to be some explanation for why, if I stare at a cup for a given interval of time, the cup at the end not only appears indistinguishable from the cup at the start, but appears continuously.

If you want to refer to them as the same part, then you are ignoring the Eternalist reality and may as well be a Presentist

An Eternalist can just reject that and attribute it to something else with an identical effect?

What you need to account for as an Eternalist, which you have simply assumed here, is how you, or your consciousness, moves from one temporal cross section to another.

There's no "you" to get from one point to the other (presentism).

So it's the same cup from t to t', but not the same you?

No you don't, that is precisely what the eternalist viewpoint doesn't need. You don't need to account for how you get from an event at time t to one at time t', because it's all just laid out there and real. The continuity of 4D objects purely as geometric objects is sufficient, and that geometry is sufficient for motion.

Unless you main one must account for the subjective human experience of presentism in an eternalist universe. But understand that is not needed for motion: motion is geometric in 4D just as shape is in 4D.

"there needs to be some explanation for why, if I stare at a cup for a given interval of time, the cup at the end not only appears indistinguishable from the cup at the start, but appears continuously"

The impression of presentism when you are laid out in 4D is a different question that does not bear on whether or not motion is possible.

The continuity of 4D objects purely as geometric objects is sufficient, and that geometry is sufficient for motion.

Or are you saying that "history is laid out there and real" somehow provides this motion? If so, how?

If you're just going to assume that motion is possible because it's "in the model", then I suppose there's nothing to discuss. I guess your model contains no assumptions.

Why is it sufficient?

As I've said before, motion is the geometry of the 4D object. Any point on that object will have a coordinate (x, y, z, t). If two points (x, y, z, t) and (x', y', z', t') on the same 4D object have different time coordinates (t' != t) but the same spatial coordinates (x'=x, y'=y, z'=z), the object is not in motion. Otherwise it must be by definition, since its position is different at different times

Motion in 3D + time = geometry in 4D.

doesn't the very concept of motion assume that a 3D object moves from t to t' in some fashion akin to temporal passage?

the concept of motion is based on Presentist assumptions, I would argue.

What is motion in 3D? How does that work without time?

Motion in (3D + time) = geometry in 4D.

To support this thought, they define "motion" in very strange ways, as Kenosha has demonstrated. This makes the thing described as "motion" something completely different from what we commonly refer to as motion.

doesn't the very concept of motion assume that a 3D object moves from t to t' in some fashion akin to temporal passage?
— Luke

No, it just depends on position being a continuous function of time. What you're talking about is a kind of propagator. That can be made consistent with kinematics, but not derived from it.

Isn't such a "propagator" being implicitly assumed when you talk about deriving motion from the geometry?

No, not at all, as per the mountain example. You don't need a hiker to have a gradient. You don't need a temporal hiker to have a gradient either.

We ordinarily talk quite readily of motion or change with respect to a dimension other than time as we usually experience it. Hence the mountain that gets smaller with altitude even though it stays the same size with time; the pipe along its side that gains altitude as it moves westward, even though it’s not moving with respect to time; the abstract line that moves in a y-ward direction over the x-ward direction, even though it too doesn’t move with respect to time.

Would you not say that a cone is smaller at the point than at the open end?

Is that really such a weird way to speak to you?

Hence the mountain that gets smaller with altitude even though it stays the same size with time; the pipe along its side that gains altitude as it moves westward, even though it’s not moving with respect to time; the abstract line that moves in a y-ward direction over the x-ward direction, even though it too doesn’t move with respect to time.

Allow me to fix the ambiguity:

Motion in (3D + time) = geometry in 4D.

Some measure in the first n-1 dimensions changes over the last dimension. In the case of the mountain it’s diameter over altitude.

In the case of the mountain it’s diameter over altitude. In the case of me it’s height over time.

I am an eternalist, I've read the views of other eternalists plenty, and none of us deny that change or motion happen.

How can you give the diameter of a mountain without specifying at which altitude you mean? The mountain has different diameters at different altitudes.

You (and MU) seem to think that that sign is lying. "The road doesn't actually get narrower.

And I'm asking what justifies your assumption that such change/motion does happen?

You've been talking about a change in altitude/diameter.

I don't deny that it "gets" narrower over time

That I see it happen, and nobody's presented a good reason to doubt that. I remember things being different at earlier times than they are now. That's what change over time is.

A change in diameter over altitude.

The mountain isn't changing its altitude. Over the dimension of altitude, the mountain changes its diameter.

You believe that temporal passage is real? Perhaps you are a Moving Spotlight Theorist instead of an Eternalist.

The virgule was intended to signify "or", not division.

So nothing actually changes? It's merely comparative?

Moving Spotlight is nonsense; if something "moved" to give the perception of time, it would have to be over time, and so would appear static from a perspective outside of time

Nothing moves through time, and time itself doesn't move past anything. Saying that either of those things happens is nonsense. Things move through space over time.

They can also move through one dimension of space over another dimension of space, without bring time into anything at all.

All change is comparative. Something changes in one dimension with respect to another dimension. The road to my house changes its altitude in respect to its latitude (it gets higher the further north it goes).

What does a gradient have to do with motion? It's just an assumption that there is motion in the gradient.

I was shorter as a child than I am now. That child and the adult I am now are the same person. How can one person possibly be shorter or taller than themselves? The same way a mountain can be smaller at the top: we’re talking about an n-1 dimensional section of an n-dimensional whole. Some measure in the first n-1 dimensions changes over the last dimension. In the case of the mountain it’s diameter over altitude. In the case of me it’s height over time.

You may think it’s a weird way of talking, but understanding that way of talking is necessary to understand what eternalists mean, and if you don’t, then you’re not talking about the same thing as them at all.

It is the definition of velocity in kinematics. If position depends on time, position has a gradient with respect to time in the exact same way altitude has a gradient with respect to radius (and angle, for non-isotropic mountains :) ). In eternalism, position does depend on time, et voila: motion.

Firstly, thank you for taking the time to try and clarify this matter for me.

I think that my argument is really more to do with the change in time that underpins motion. I don't understand what difference there is between the change in time found in Eternalism and the temporal passage of Presentism.

You didn't answer the question: do you believe that temporal passage is real?

Kinematics holds in eternalism and presentism. That is, it doesn't care how you conceive of a change in time, whether it's a length or an evolving 'now'. Eternalism is more general and complete insofar as it both allows for and does not require motion forward in time to have motion in space. Presentism has a more tenuous position because it does need such a thing, be it a spotlight or whatever.

position has a gradient with respect to time in the exact same way altitude has a gradient with respect to radius

neither does the temporal position of the object change

What would a "change in temporal position" even be

No I'm pretty sure Kenosha Kid will deny as much as I do that objects change their temporal position.

You just don't understand what motion means

A "change" in temporal position, as referred to by myself, meant nothing more than an interval of time over which we can consider different positions of the same object, i.e. it is a length of a section of the 4D object. It is not something the object does in classical kinematics.

However, in relativistic kinematics, an object does have a velocity in the temporal direction and so can be thought of, at any given time, as changing temporal position in a reference frame with respect to temporal position in its own rest frame. This is true at all times and requires no particular 'now'. Nor does motion completely depend on it, since photons have no temporal velocity and yet move pretty nippily.

We have been discussing the former, but happy to discuss the latter, or QM.

Doesn't the interval of time represent some change of temporal location?

I don't see what difference it would make to my arguments, but I'm happy to discuss them.

Does a distance represent some change in spatial location? It's the same thing.

A "change" in temporal position, as referred to by myself, meant nothing more than an interval of time over which we can consider different positions of the same object

It can, can't it?

does something need to change temporal location in order for us to have a concept of duration?

I'm trying to understand. You said that "change in temporal position" is only a length and "not something an object does." So is an object's change in spatial position, or its motion, at different times also "not something an object does"?

So is an object's change in spatial position, or its motion, at different times also "not something an object does"?
— Luke

Yes.

I see. So you concede that, in terms of classical kinematics at least, objects do not move?

Okay you kinda edited out the bit that was clearly talking about lengths.

Yes. We might colloquially say that a ruler goes from one end to another, but nothing is really going anywhere: it just occupies that space.

You're still left with v = dx/dt, and as long as you have that, you have motion.

Well, either "dt" represents a length/duration for comparison purposes only (is "not something an object does"), or else it represents a change in temporal position. You can't have it both ways.

Well, either "dt" represents a length/duration for comparison purposes only (is "not something an object does"), or else it represents a change in temporal position. You can't have it both ways.

This seems more an objection to terminology than the necessity of motion arising from 4D geometry.

Motion is a Presentist notion.

From "outside of time", viewing time as just another dimension like space, that looks like an object that spans time and space, geometrically, changing where it is in space over time.

If you're looking at a 4D object, where one of the four dimensions is time, then you're standing outside of time, and there is no dimension that seems timelike to you in which for the 4D object to move.

An object moving in three dimensions with respect to the fourth will just look like a 4D object to you, though.

If you stare at a clock for one minute, you will have changed your temporal location by one minute. Of course, you don't need to stare at a clock in order to change your temporal location, you can do whatever you like. You only need to age and experience life as you always do. Apparently, you have no choice but to do this. Taking this (literally) everyday aspect of the experience of time's passing to be reflective of something real in the world, this is known as temporal passage (aka the passage of time, time passing, etc.).

How can anything move through time if there is only one time, the present?

However, if an object does not actually change its temporal position, then it cannot actually change its spatial position either. And if an object does not actually change its spatial position, then it doesn't actually move. According to the above definition of motion, that is.

It is not a condition in eternalism that a 4D object need move within a 4D space to have motion, since that would be a new kind of motion (hypermotion, I guess) in an even higher-dimensional space that would be hard to conceive of.

I've only ever been talking about the motion of 3D objects in the 4th dimension; that is, 3D parts of the 4D object.

If so, are you satisfied that a 3D part at time t' may differ from the 3D part a time t?

Yes, representing a change in temporal position of the object. That is, the object has changed its temporal position.

And you've agreed that the object has moved from t to t'.

Either the object moves from t to t' and there is temporal passage (not B-theory).
Or the object does not move from t to t' and there is no motion.

Then your definition of motion depends on temporal passage, which kinematics does not.

If you are happy with a ruler having length without changing position, you have no reasonable objection to a 4D object having duration without changing temporal position.

If time is continuous, what else could change in temporal position of the object mean except that the object moves from one time to the next , i.e., temporal passage?

If time is like a ruler, as per Eternalism, then there is no motion.

Again, if you're arguing that time passes "inside" of time but not "outside", then you're saying that temporal passage is real.

the motion of 3D objects in the 4th dimension

Motion is an inevitable consequence of the geometry of 4D objects.

Things change in space with respect to time.

3D object move in three dimensions OVER a fourth (time). They’re not moving THROUGH a fourth

our attention is the only thing changing spatial position there

but you and I agree that the object is not changing its location in time, which is what Luke means by a change in temporal position.

3D object move in three dimensions OVER a fourth (time). They’re not moving THROUGH a fourth

car travelling from point A to point B. But let's say that the car is already at point A and at point B simultaneously, with the same car also at every point in between. You wouldn't then say that the car could move from point A to point B, would you?

A real car moves from spatial point A to spatial point B over time. It's not at both points at the same time:

In order for something to move through time, there must be some hyper-time for that motion to occur over.

No, this "hyper-time" would be required for the 4D object to move through, but we are talking about a 3D object (potentially) moving through/over the fourth dimension of time.

Every kind of motion is through one dimension over another dimension.

If you want to be a stickler for that sort of usage, then fine. Take any of my former uses of these words to mean the same thing.

Take any of my former uses of these words to mean the same thing.
— Luke

Which thing?

Only if you assume it is.

2. 'Change in temporal position' means the object does not move from t to t' (there is no motion)
...
You need to explain how 3 can make sense.

It's a direct consequence of its kinematic definition: dx/dt.

Again, only if you assume motion in the first place. Otherwise there is no change. Which is what you keep saying.

Actually motion we get fir free.

Namely, how does {change in temporal position from t to t'} not mean exactly the same thing as {the object has moved from t to t'}?

I guess you're not going to address this question then:

Namely, how does {change in temporal position from t to t'} not mean exactly the same thing as {the object has moved from t to t'}?
— Luke

In translating phenomena from an eternalist viewpoint to that of subjective experience

I'm just asking you to explain the difference between {change in temporal position from t to t'} and {the object has moved from t to t'}.

Because motion in 4D is not given by a time duration, it is given by the geometry of the 4D object over that time duration. If the 3D position of the object varies, it is moving. If it does not, it is not.

If the 3D position of the object changes ("varies") from t to t', then it moves from t to t'.

However, you continually deny that the 3D position of the object changes from t to t',

No. It moves from position to position. In classical kinematics, a body at rest is not said to move from t to t'.

No, I attest that it does, i.e. its position is time-dependent. I deny that this necessitates something moving from t to t' in order to do so.

But in order for it to move, it needs to change both spatial and temporal position.

A moving body's position changes with respect to time: that is the very gradient that tells us it is moving.

As I understand it then, according to 4D geometry, a 3D body changes spatial position with respect to temporal position only, but it does not actually change either spatial or temporal position. And despite not actually changing either spatial or temporal position, the 3D body still moves (or there "is" motion). Have I understood that correctly?

Have I understood that correctly?
— Luke

Not completely. The gradient in 4D may be with respect to other spatial dimensions just as it can in 3D.

However, your position is that a 3D body moves without changing either its spatial or its temporal position. That's quite a magic trick!

But nothing's moving along the time axis; it's all just laid out.