The coordinates. — Kenosha Kid

What do they change from/to?

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

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

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

It's not critics who complain about it; that's just what B-theory states. According to the SEP article on Time regarding the B-theory: "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."

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

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

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. — Kenosha Kid

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

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. — Kenosha Kid

Aren't you simply defining temporal passage into existence? You're saying it's impossible that an object could not change its temporal position. That is, you're saying the B-theory is false by definition. But this is just an assumption of your model (or by users of the model). I sense we are talking past one another. You seem to only be talking about "the block" as a model in physics, whereas I wish to discuss the metaphysical concept of Eternalism as defined in the OP.

"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. — Kenosha Kid

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.

What I am arguing is this:
Eternalism has no passage of time. I believe we agreed to this earlier.
Passage of time means that time passes, or that objects pass through time, which means that objects change their temporal position (in a given direction, if you prefer).
Without passage of time, then objects do not change their temporal position.
If an object does not change its temporal position, then it cannot change its spatial position, and therefore it cannot move. Since this applies universally, then there is no motion in the block universe.

Thank you all for helping me to clarify my argument that the block universe precludes motion:

The block universe (or B-theory Eternalism) has no temporal passage - that's just the B-theory
Temporal passage is (typically sequential) change in temporal position - no passage = no change
Motion is change in spatial position over change in temporal position - no change = no motion

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. — Kenosha Kid

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

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!!! — Kenosha Kid

Why does a 3D universe need a time axis? You seem to be imagining a stationary ball that does not change its spatial position over time, but which still changes its temporal position.

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? — Kenosha Kid

Unless I've misunderstood you here, you seem to be talking about a ball that changes or doesn't change its spatial position, despite all the while changing its temporal position.

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. — Kenosha Kid

I'm not disagreeing with this definition of motion or suggesting any "non-kinematic definition" of motion. However, what I believe Eternalism entails is that there is not "anything [that] exists whose...time position changes". Eternalism posits a universe in which all things (commonly thought of as being past, present and future) have equal existence. That is, everything exists at all times. This implies that all things have a four-dimensional existence and therefore nothing moves through time. Instead, everything exists at its own (fixed) temporal location. The block universe in this case is not a model along which you can trace time with your finger, but the actual universe in which nothing changes its spatiotemporal location.

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. — Kenosha Kid

Okay, but the Presentism/Eternalism debate is a metaphysical, ontological concern, in which it is argued that the nature of time and existence is best described by one (or a hybrid) of either Presentism or Eternalism. To say that Eternalism precludes motion means that there is no motion in reality. You're saying that motion is no more than tracing out a line on a map? What does the map represent?

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

If Eternalism implies that motion is impossible in the universe, how can it be that motion is "already encoded in the worldline"? Isn't that just an assumption - an assumption which is contradicted by Eternalism?

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". — Kenosha Kid

What do you mean when you say "as we move along the time axis"? Do you mean simply tracing out a path on a map, or is it that we actually pass through time?

But you are presenting MST for consideration. — Kenosha Kid

I presented the MST mainly for comparison with the block universe. Perhaps that was an error on my part. It was intended to demonstrate that if you want Eternalism with temporal passage, then the MST appears to be the only available option (rejected by most Eternalists), unless someone can present an alternative option. Otherwise, you must acknowledge that Eternalism (i.e. the block universe) does not contain temporal passage - that is, if you didn't already believe the definition.

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? — Kenosha Kid

Yes, these are all well documented problems for Presentism. My concern in this discussion, however, is with whether or not Eternalism precludes motion.

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

Great! I hope you can help to clarify some of these matters (particularly if I am wrong about all of this).

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 — Kenosha Kid

You find it problematic that MST reintroduces a passage of time? Does this imply that you acknowledge and find it unproblematic that Eternalism (i.e. the block universe) has no 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. — Kenosha Kid

I get that it could be viewed and used like a model in that way. But are you referring here to Eternalism (i.e. the block universe)? 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?

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

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.

The whole point of spacetime is that it is invariant. — Kenosha Kid

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.

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. — Kenosha Kid

That only makes sense if there is a passage of time. However, there is no passage of time according to B-theory Eternalism. Furthermore, if the absence of temporal passage implies the absence of motion, as I am arguing, then nothing - including light - can travel.

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

That's a little hyperbolic. A common criticism of Presentism is that it is inconsistent with special relativity. I don't claim to have the answers on how to make Presentism consistent with special relativity. Maybe light is travelling at the leading edge of the present moment and everything else is travelling relative to it. At least, this seems to make more sense to me than everything at all times (including all past and future times) somehow being in motion. Anyway, I'm merely trying to point out the logical implications of Eternalism, such as its preclusion of temporal passage and motion.

Or does every observer have her own spotlight? — Kenosha Kid

According to special relativity, I think so.

Do you have anything of substance to add - any argument for motion in a block universe - or just hand waving and eye rolling?

To recap:

- Motion is defined (by you) as change in position over time
- 4D objects don't change position over time - because this would require a higher dimension
- 3D parts of a 4D object don't change position over time - because each 3D part exists at its own fixed spatiotemporal position

So where is the motion? What changes position over time? Anyone?

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

What is this adjustment?

... 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. — ChatteringMonkey

Exactly. This supports my claim that B-theory Eternalism precludes motion. All objects are 4D in Eternalism, whereas motion only makes sense with 3D objects.

What changes position over time? You seem to be saying that it's not a 4D object, but a 3D part of it. But no 3D part actually moves; there's one 3D part at one position and another 3D part at another position. It's not the same 3D part moving through time or changing position over time. So again: what changes position over time?

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. — ChatteringMonkey

You "need another concept of movement" for what?

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

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. — ChatteringMonkey

It seems like you want me to say that one moves and one doesn't, or that one contains motion and one doesn't, except, in eternalism, neither moves and neither contains motion.

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? — ChatteringMonkey

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

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

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?

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

Because then you'd be talking about Presentism and/or the A-theory instead of B-theory Eternalism.

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

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

What "they"? Is it a 3D object or a 4D object? You don't get to assume it's a 3D object as an Eternalist, so how can it move through time? What moves?

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

What "something" are you are talking about here? Is it a 3D object which starts at t1 and moves to t2? Or is it a 4D object which exists at t1, t2, and all points in between? You seem to assume that existence at all points is the same as moving from one point to another.

what is motion but a spatial path in spacetime anyway? — jorndoe

To reiterate my argument against this general assumption by the Eternalists: Assume a four-dimensional object exists at every point between t1 and t2. What moves? 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.

You said that Eternalism doesn't preclude motion "because all you have to do is add more premises, like your spotlight theory does". The Moving Spotlight theory (which is not mine) is a hybrid of Eternalism and Presentism; it is as much a form of Eternalism as it is a form of Presentism. I'm not sure what "premises" you are referring to. Regardless, I don't think that any of the Eternalists here are willing to accept the Moving Spotlight theory as their form of Eternalism. I'm happy to refer to it as B-theory Eternalism or the block universe theory, as I did in the OP, to avoid any ambiguity. Like most Eternalists, I'm quite sure this is what the Eternalists in this discussion are arguing for anyway.

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. — Metaphysician Undercover

Do you agree that the Moving Spotlight theory is a hybrid of Eternalism and Presentism/A-theory? If so, then it's not Eternalism.

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. — ChatteringMonkey

Yes, I wasn't asking for a repeat of the criticism. Do you acknowledge that Eternalism logically precludes motion, or do you have any further defence to offer?

Nothing in eternalism "precludes" motion — Metaphysician Undercover

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.

As evidenced in this thread, there are Eternalists who will complain, with some saying that nobody really believes in this form of Eternalism. However, these same folk reject Presentism, while simultaneously wanting to retain the temporal passage and motion that belongs to Presentism. Do these folk allow the same concessions to Presentists when pointing out the shortcomings of Presentism? Perhaps. 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.

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

Again: they're not my definitions.

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. — ChatteringMonkey

You seem to imply that nobody believes in the B-theory of time, that time does not flow. Do you have any support for this claim?

I said time doesn't flow in any particular direction — ChatteringMonkey

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".

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. — ChatteringMonkey

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?

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

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

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. — ChatteringMonkey

Hey, I didn't invent these concepts. You seem eager to be an Eternalist but you also seem reluctant to commit to the B-theory. There's always the Moving Spotlight theory (Eternalism + A-theory) instead. 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.

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

The traversing of that path. Or, at least, that's what I'm asserting/challenging in the OP: doesn't motion require temporal passage?

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? — jorndoe

Is this Eternalism? According to what definition?

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. — jorndoe

When you say "block-verse", do you mean B-theory Eternalism? Would you care to address the OP?

What might a complete model look like anyway? — jorndoe

The Moving Spotlight theory? Depends what you mean by "complete".

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

So?

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. — ChatteringMonkey

Time flows but not "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'). — ChatteringMonkey

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.

You're talking about Presentism and Eternalism rather than A-theory and B-theory.

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. — ChatteringMonkey

Just to try and address this objection, what difference do you perceive there to be between the A-theory and the B-theory? You seem to be saying that the A-theory and the B-theory are identical with regard to temporal passage from within time, and that they differ only with regard to temporal passage outside of time. That is, you seem to say that time passes for the A-theory both inside and outside of time, and that time passes for the B-theory inside of time, but not outside of time. My question, then, is why you believe that these two theories which purport to be about the nature of time itself are about something external to time instead?

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. — ChatteringMonkey

It seems as though we are at an impasse. I can only reiterate that Eternalism assumes the B-theory unless you are talking about the Moving Spotlight theory. The static nature of time according to Eternalism is not something that only applies, as you say, "when viewed from outside the time-dimension of 4d space-time":

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. — B-theory of time - Wikipedia

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. — SEP article on Time

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. — ChatteringMonkey

I don't expect a 4d object to move in time like a 3d object. Instead, B-theory Eternalism rejects the idea that 3d objects move through the 4th dimension of time:

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. — Eternalism (philosophy of time) - Wikipedia

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. — ChatteringMonkey

Perhaps motion is possible under Eternalism, but there seems to be few explanations forthcoming for how it is possible. It certainly seems impossible, unless one sneaks in temporal passage, but then it's no longer B-theory Eternalism.

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

Without getting too bogged down in details, I should spell out my belief that conscious experience, i.e. the mind, is produced by the brain/body. Furthermore, I believe that our collective knowledge includes at least some understanding of how the body and mind works, and that this understanding is based on the presumption that time passes and motion is real.

If we assume that time does not pass and that motion is not real, then, based on our current understanding of human physiology, I don't see how it could be possible to have conscous experiences at all. In other words, if you exist as a static four-dimensional object, then this includes your brain states. A four-dimensional brain doesn't move or function; it merely exists. If your synapses aren't firing, due to the lack of motion, then you can't be having any conscious experience either. The only thing that can get you from one state to the next (both physically and mentally), and which injects motion into this picture, is temporal passage. The perspective is not just limited under Eternalism; it is absent.

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 in time from your birth to your death, then what sense does 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.

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). — ChatteringMonkey

I responded to this earlier. Entropy explains why there is a directionality to time. However, such an account presupposes that temporal passage is real ("time passes, but why is it only in one direction?"). Whereas what is required is an explanation of our experience given that temporal passage is not real. You can't invoke an explanation which presumes temporal passage in order to account for why we have the experiences we do without temporal passage.

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

4D existence has time, but there seems to be no "room" for any movement. As I said earlier, "Motion seems to make sense for a three-dimensional object travelling through the fourth dimension; I just can't make sense of the possibility of motion with four-dimensional objects." Do you agree or disagree with @noAxioms earlier statement that "Under eternalism, we beings are worldlines"?


I'll also just note here my disagreement with the rest of his statement:

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. — noAxioms

He states that he experiences and is "present at" each and every event on his worldline, but then he rejects any preferred moment. However, the preferred moment is the present moment. As he stated elsewhere in the thread:

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, — noAxioms

I guess he could reject the existence of an actual present moment, but no account is given of how we can possibly experience time in this way without temporal passage.