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? — Luke
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. — Luke
Critics complain that it does not yield a passage of time. — Kenosha Kid
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? — Luke
The passage of time is whatever makes motion possible and what doesn't exist in B-theory eternalism. — Kenosha Kid
The passage of time is whatever makes motion possible and what doesn't exist in B-theory eternalism.
— Kenosha Kid
Fixed the definition. — ChatteringMonkey
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
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
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, 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
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
: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
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
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
the eternalist idea that there is motion when nothing is moving — Metaphysician Undercover
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? — Luke
I am no astronomer, but to my knowledge, the distribution is a uniform, isotropic black body spectrum. — Kenosha Kid
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
What do they change from/to? — Luke
I am just saying that presentism is not unique in requiring 'special' reference frames. — SophistiCat
you should seriously view any object, such as the Earth or the Moon, as a four-dimensional object — Luke
Instead, they are whole 4D objects which consist of different stationary 3D parts existing at different times. — Luke
The 3D Earth doesn't move from t1 to t2; two different parts of the 4D Earth each exist at those times. — Luke
It doesn't seem like taking it seriously to maintain that there is motion in Eternalism. — Luke
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
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
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
What does motion, in the everyday/kinematic sense, look like? — Kenosha Kid
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
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? — Luke
Motion, in the everyday sense, looks like something not having a determinable position — Metaphysician Undercover
We often describe it as what happens when a thing changes position. — Metaphysician Undercover
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? — Luke
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