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.

Aren't you simply defining temporal passage into existence? — Luke

This is not me defining anything. 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 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.

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

No, it does not say motion is impossible. You're saying that. Critics complain that it does not yield a passage of time. But motion does not depend on a passage of time, so is unaffected. That is, the geometry of an object in the block is not affected by whether it is growing, shrinking, or spotlit, beyond the fact that if it doesn't exist yet/anymore, it can't be said to have coordinates.

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?

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

The passage of time denotes some kind of now-ish thing moving from 'now' in the past to 'now' in the future.

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

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. Even the word 'already' is awkward in that sentence...

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

Fixed the definition. — ChatteringMonkey

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.

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. — ChatteringMonkey

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.

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. — ChatteringMonkey

: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.

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. — Kenosha Kid

Yes, and the eternalist idea that there is motion when nothing is moving, is contradiction, plain and simple. You can try to hide that contradiction behind claims, such as the notion that kinematic motion does not require that anything be moving, but that's smoke and mirrors. Kinematic refers to the effects of motion, and not motion itself, so all you are doing is talking about the effects of something which eternalism denies exists.

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. — Kenosha Kid

Agreed, this is also what I've been saying a couple of pages back... in less scientifically accurate terms anyway.

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. — Kenosha Kid

I agree with this too I think, and I've also been saying that you need to think about motion and change in eternalist terms if you want to apply them in that frame. 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.

: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. — Kenosha Kid

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.

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. — ChatteringMonkey

:up:

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. — ChatteringMonkey

I'd say necessary in any eternalistic viewpoint. Putting broader physics aside, if you have any idea of motion that does not depend on eternalism, the question is what does this specific behaviour look like in the eternalist picture? (My point was not that motion dependent on passage of time is unthinkable, but that it is different to conventional understanding of motion.) The problem here is an expectation that motion, if it exists, must be some kind of higher-dimension generalisation of everyday motion, or, as Metaphysician Undercover puts it:

the eternalist idea that there is motion when nothing is moving — Metaphysician Undercover

But that movement (or lack thereof) would not be what we call motion in an everyday sense or a kinematic sense. A ball moving through space(s) and time(s) in any physics is a "static" geometric object when laid out over all spaces and times. That's what objects look like. What does motion, in the everyday/kinematic sense, look like? Wiggles.

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?

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

The coordinates.

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

It's only isotropic in some reference frames. On Earth, if you point your spectroscope in different directions, you will get different temperatures of the black body radiation due to Earth's peculiar velocity relative to the rest frame of the CMB.

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 — Kenosha Kid

No frame is special in the narrow sense of violating the general covariance of relativistic laws, but frames can be special in other ways, such as yielding an approximately isotropic spectrum of the CMB, or zero average velocity of matter at large scales. The hypothetical hypersurface of simultaneity for the universal now defines yet another special family of reference frames. I am just saying that presentism is not unique in requiring 'special' reference frames. But unlike those other examples, there is no practical way to find this special frame - it's pure metaphysical conjecture.

The coordinates. — Kenosha Kid

What do they change from/to?

What do they change from/to? — Luke

That depends on the object. In the graphic employed by Huw Price over and over again in that video you posted (was it you? apologies if I misremembered), what is shown is the orbit of the Moon around the Earth. It is a block, it's longest side being time, the Earth is a cylinder, and the Moon is a helix spiralling around that cylinder.

Both the Earth and the Moon have geometry: they are continuous paths (worldlines) through the block. The path of the Earth (the cylinder) is a straight line parallel to the time axis in that picture, that is: if you choose any two points at random, the time coordinates of those points will be different but the spatial coordinates will be identical. This is a static body: its position is the same for all times (all times = all possible values for the time coordinate in the block), which allows us, indeed compels us, to say it is static in that frame.

If you take two points along the Moon's path (the helix) at random, their time coordinates will be different but their spatial coordinates will likely (since it's periodic) be different. This is a moving body: its position is different at different times. ("is" here in the sense of: "the thing is sometimes moving", not in the sense of "in the present".) So we can say that between these two times, the position changes, or more precisely: the path between point A and point B has a nonzero gradient. This is motion in the everyday and kinematic sense.

What they actually change from or to is a question about its geometry. Different objects have different geometries. This is the same as saying different objects have different motions.

If you really want to take Eternalism seriously "with both feet and think about things like motion and change in eternalistic terms", then you should seriously view any object, such as the Earth or the Moon, as a four-dimensional object. You keep talking about them as though they are 3D objects which change their spatiotemporal positions or which have a "path" over time. However, they are not whole 3D objects that change their spatial and temporal positions (i.e. that move). 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. You can call it that if you want, I suppose, but it seems like more of a Presentist (3D+1) notion.

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

Oh sure, I'm not saying it's unique. It could have lots of bad company :) However, any idea that requires a special frame, the logical questions to ask (indeed, the questions I did ask) are: can it exist, can it explain anything if it does, can we justify it if it does? The special frame in question that obeys relativity of simultaneity cannot be constructed (except maybe, as you say, with the addition of a limitless supply of other temporal dimensions to wind through); the one that that can that dispenses with SR needs to explain the seeming existence of SR; the universes it could explain (e.g. the Newtonian universe, or a frame-dependent 'now') are redundant.

[Edited for clarity. Twice. Crappest answer ever, I'm disappointed in myself :( ]

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

Exactly as I did, and as Huw did, in treating them as 4D objects like (in Huw's reduced picture), the cylinder and the helix. (Strictly hypercylinder and hyperhelix.)

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

Exactly as I described.

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. And further, the spatial coordinates may be different at those times, which is motion.

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

Then, once again, you are defining motion to be presentist, and ignoring the kinematic definition of motion which holds well and unmolested in eternalism. I sense you will always do this, because you're specifically after the conclusion that motion does not exist in eternalism. But this is a circular definition of motion, having nothing to do with kinematics or everyday experience.

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.

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. — Kenosha Kid

Yes, the maths can still be done in the model; you can continue to subtract the value at t1 from that at t2. 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.

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. — Luke

It's not, and certainly is not shown. Is d(altitude)/d(radial) undefined for a mountain in good ol' fashioned 3D-land? No. It would be a mammoth achievement to show that dx/dt no longer makes sense in 4D, which is equivalent to saying, at the least, all 4D objects are straight lines parallel to the time axis. I have invited you to demonstrate it a number of times, rather than assume such a strange assertion has already be justified.

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.

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. — Luke

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.

He's been stuck on this point for years.

↪Kenosha Kid He's been stuck on this point for years. — SophistiCat

I guess he's right then :rofl:

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

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. It's what happens between a thing being in one place and that thing being in a different place, it moves.

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. — Kenosha Kid

Okay, let's say I agree to the definition of kinematic motion, and I agree that motion can be calculated in your physical model.

Earlier you appeared to agree when I stated:

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

So there is motion, even though the Earth doesn't move? Then what does the motion in your model represent?

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

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.

The mistake is in generalising 'movement' to some higher-order equivalent in which, in the block reprentation, the Earth (its worldline) moves through the block such that its presence or absence at a given coordinate (x, y, z, t) is not fixed. This would not be movement in any typical sense, but some kind of hypermotion.

The presentist equivalent of that mistake would be Zeno's paradox: right now the Earth is at (x, y, z). That coordinate is fixed in that present moment, therefore movement is impossible.

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

Not having a determinable position is a stretch. Even a stoopid frog can figure out where a fly will be such that it can fire its tongue out and catch it. Clever humans have built science and astronomy and technology on the observation that figuring out where something will be in the future is straightforward. If you let go of a bowling ball from the top of the tower of Pisa and halfway down it turned left, that would be a shock.

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

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.

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. — Kenosha Kid

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

Or are you saying that it doesn't really move in the block universe? If it doesn't move in the Presentist sense, then in what sense does it move? That is, I still don't understand what the motion in your model represents.

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

You said that, not me. It will be harder if you cannot remember which of us has which opposing argument. 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. And I am happy with that as an interpretation of even a straight line parallel to the time axis of the block.

[EDIT] But that sort of "movement" is not what we mean by "motion" in an everyday or kinematic sense. I'm satisfied with that description from a study of special relativity, in which the 4D velocity of a body "at rest" points along the time axis. In that sense, and I am happy with that sense, it does "move through time". However this is no longer everyday kinematics. It is not v = dx/dt. It is relativity theory.