Been too busy to deal with this fairly unproductive line of discussion.

The Rindler horizon's similarity to the event horizon is only insofar as any light travelling from the negative x direction cannot reach the x=0 worldline. That seems to be the entire basis for your argument that the space the photon travels in does not exist in the Rindler frame. — Kenosha Kid

What light can or cannot do is irrelevant to my point. It is similar in other ways, which is why I brought it up. My arguments have not been based on light signals.

This is exactly the same as saying the car behind does not exist in the frame of the car in front because it can never reach it. It's the same argument.

Either car can say what the other is doing 'now', whether they can reach each other or not, so it is not the same at all. You continue to either not get my point, or you're deliberately evading it because its implications make you uncomfortable. So address the question I asked and not another:

A clock is dropped at Rindler event T=0 X=1. What are the Rindler coordinates of that clock when it reads T=1? When it reads T=2?

That's the question. There's no mention of light in it. I claim a lack of coherent answer, and conclude that Rindler coordinates are inadequate to the task of foliating all of spacetime. Similarly, inertial coordinates cannot foliate spacetime containing a black hole, and no coordinate system can foliate spacetime containing multiple black holes.

[At location x=0 in the ARF,] Time is infinitely dilated, and there is no light cone if there is zero time for light to get anywhere.
...
Nothing can ever get closer to it in its own proper frame. That's what I've been repeating in the last several posts.
— noAxioms

Yes, I know. And this is why your argument is incorrect. You seem to think that somehow, in the accelerating observer's frame, the distance from x=0 to x>0 is infinite in the proper frame because nothing from x<0 can reach x=0 — Kenosha Kid

I do not think this any more than I think the distance to a black hole EH is infinite because light from it will never reach an orbiting object. Pilot at x=1, RH at x=0. That's a constant finite distance of 1 (as I've said above), not an infinite distance as you suggest here.

akin to saying that if two cars were travelling in the same direction at the same speed, the car behind can't be represented in the rest frame of the car in front because it cannot reach it.

I never said one car cannot be represented in the frame of the other. That's partly because they're the same car, the front and rear bumper, moving by definition at the same speed in the rigid car's own frame. But the rear bumper must accelerate harder than the front one. The car on the other side of the RH is what cannot be represented in the Rindler frame of the accelerating car. It cannot be keeping up with the accelerating (but stationary) car in the ARF. (Please tell me if any of these acronyms are confusing. I tire of typing the full words).

For all finite accelerations within finite times, there is no infinite time dilation, no infinite length contraction, and any light approaching from the negative x-direction is getting closer, even if it cannot intersect the accelerating body's worldline in finite time. None of this is new: you can do all of the math in standard SR.

Yes, and the math says the acceleration cannot be finite at the RH, and which is why I said the length of my object extended almost 1 to the rear, but not all the way, because I wanted to avoid the infinite acceleration required there, with yes, infinite time dilation, just like at the EH of a black hole.

Do you accept that the accelerating object is always stationary in its own frame?
— noAxioms
If you'd read me carefully, I not only accept it, I asserted it.

Good. I wasn't sure given your posts.

This is all x=0 is in the rest frame of the moving body: a coordinate of the origin of that frame. It is not a singularity by any definition.

In the Minkowski frame, we know where the x=0 point is at t=0. It is at X=0, T=0, right? Think wiki picture if you don't know what I mean. Our object extends from X=2 back to X=0. It is effectively a long meter-stick in a rail gun, with a clock at each end and in the middle.

t is what's on the middle clock at the accelerating object at x=1. So at t=2, that clock is off the right side of the picture, but not far. Suppose we stop accelerating the entire object simultaneously (in the object frame) when that clock reads t=2. Where is x=0 in the object's frame? I contend that despite infinite acceleration there, it has gone nowhere and is still at X=0, T=0 (in the original Minkowski coordinates, which is not the object's frame) and not anywhere else on that picture. The clock at the rear of the object still reads zero. Do you agree with any of this? If not, where (in the original Minkowski diagram) is the left end of the object (simultaneous with, in the object's new frame, the cessation of acceleration at t=2 on the middle clock?

The problem is you don't understand the framework you're trying to use to make your point, so don't understand why your point is invalid.

You continue to make erroneous assumptions about what I'm saying, so of course you think I'm getting something wrong. No, I never claim a pair of cars following each other are not in each other's reference frames. You totally don't get my point if that's your take.

You have to do the legwork, not just try and jump to the crazy conclusions of some impossible edge cases and mistake that for the theory as a whole.

I'm asking you to do some legwork in the example above, to compute which event corresponds to the cessation of acceleration at the rear of the object, and where that event falls in the original Minkowski diagram. I can do the same mathematics if you like, but the picture already shows the event in question.
You seem to have been claiming that the RH somehow approaches the x=1 point in the ARF as the object accelerates, but in the object's ARF, the object is always stationary, so that can't be happening. It must remain a constant distance from x=1.

If the above is indeed your source, I hope this convinces you that it is the entire x=0 (or t=infinity) line that is the Rindler horizon, not the X=x=0 point. — Kenosha Kid

That's the same as the wiki picture, but with far less detail. Yes, in an arbitrary inertial reference frame as depicted in all these drawings, that entire line is the Rindler horizon. Under Rindler coordinate time (not shown in this new picture), the horizon is a coordinate singularity and is not comprised of a line like that. Time is infinitely dilated, and there is no light cone if there is zero time for light to get anywhere.

Of course, this is not the same as a black hole’s event horizon in two very important respects. Firstly, it’s always possible to stop the spaceship accelerating

Similarly, you can accelerate away from Earth to push the distant event horizon further away in the coordinate space of the thing accelerating away, but that just pushes it off. You can't turn off the acceleration of expansion like you can turn off the ship engine. Yes, I agree, the Rindler horizon exists for a continuously accelerating thing, and it ceases to exist when that condition goes away.

Secondly, there is nothing corresponding to a black hole’s singularity to do any actual damage to anything passing through the horizon.

Nothing is inherently damaged by free-falling through a black hole event horizon. Are you under the impression otherwise? As I said, a small black hole will 'damage' you before you even get to the event horizon, but that's not the event horizon doing it to you. Orbit close enough to a neutron star and you're dead, no event horizon needed at all.

This is not a real event horizon like the boundary of the universe or that of a black hole.

I was unaware of there being a boundary of the universe. In the ship case, yes, you have the option of turning off the acceleration. In the dark energy case, you do not, so no matter what you choose to do, there are points in space in no significant gravity well from which light can never reach you. This is not true in Minkowski spacetime.

It is an artificial horizon based on the decision of the ship to constantly accelerate away from everything else. Things effectively cannot reach it (cannot reach x=0) because it moves away from them. However, things can get closer to it (move toward x=0) in its own proper frame.

No. My bold. This is where you're wrong. Nothing can ever get closer to it in its own proper frame. That's what I've been repeating in the last several posts.

Maybe you could address my points instead of just repeating your own. The wiki picture shows the proper frames of the accelerating object, and since the picture is a different frame, it actually shows the distance increasing, but in the Rindler coordinates, the distance is constant over time. If it wasn't, there would be a test for absolute rest: when the distance to the rear of the ship is at a maximum. That would be a direct violation of Galilean relativity, the first of the SR postulates.

Because lightspeed is not observer-independent in non-intertial frames

No argument.

It is equivalent, in inertial motion, to saying that an object that is following me with the same speed as me doesn't reach me. Or, in my rest frame, an object to my left is not occupying the same space as me.

Do you accept that the accelerating object is always stationary in its own frame? I know it's not an inertial frame, but if you take any event on the ship (say the pilot at x=1 at time t=2, his clock), and you reference the one inertial frame in which the pilot is momentarily stationary at that event, then every location along the ship is simultaneously (relative to that IRF) stationary. In that frame, the Rindler horizon is still a distance of 1 behind the pilot, regardless of the time that has passed.
I typically imagine a ship of length almost 2 with the pilot in the middle and the rear just shy of the Rindler horizon, and the front at x=2.

The photon is still in the moving observer's coordinate system

Not the one at the rear. Time is stopped there in that coordinate system, and the photon makes no better progress than one at a black hole horizon trying to get out. A photon anywhere forward of that does indeed make progress and will eventually reach any part of the ship.

Follow that worldline to the edge of the diagram. Now, tell me, is it closer to the horizon or further away? — Kenosha Kid

The accelerating observer goes off the right side at about t=1.25, where proper distance to the horizon is still exactly x=1 behind him, unchanged. In another frame, the ship is moving, so of course the distance is length contracted, which would be true if the thing was accelerating or not. As I said, you don't need to wait for it's speed to change. Just do a Lorentz transform to a different arbitrary frame and you can contract that distance as much as you like, even at T=0.

Yes, the worldline is bending to the right (increasing X). But the horizon is always moving to the right more quickly

Only in a frame different than the ship frame. That frame is thus arbitrary, and irrelevant to our observer's measure of the distance to the event horizon.
Yes, I acknowledge that in a different frame, that distance is contracted. This seems to be your point,.

The Rindler horizon is not X=0. X=0 lies on the horizon at T=0.

It is a singularity, so this does not follow. Suppose the ship extends all the way back to the horizon. Where is the rear of the ship at t=1 (as measured by our observer at x=1)? Follow the t=1 line-of-simultaneity back to x=0 in the diagram. Where does it go? It goes to the same event where it was at t=0, the left-most event in the picture. That shows which event is approached as you move backwards in the accelerating frame. The actual event there is a singularity, with undefined time, so asking which horizon event is simultaneous with our observer at t=1.25 is meaningless, but I can point to the event in your arbitrary Minkowski frame that is approached.

So what you mean is that we choose a frame of reference where the acceleration is not simultaneous

Unclear what you mean by this. Acceleration is continuous, not something that is 'simultaneous'. At all times in ship frame, all parts of the ship are moving at the exact same speed, and thus the entire ship is always stationary in its own accelerating frame. The ship is said to be Born-rigid.
This implies that in a different frame (such as the Minkowski one in the pic), the various parts of the ship are not moving at the same speed. If they did, length contraction would contradict it, as shown by Bell's 'paradox'.

Your interpretation is still erroneous though, because you still think the Rindler horizon is a spatial horizon.

I don't 'think' that. It is a coordinate singularity, just like the one 16 billion light years away, and just like the event horizon of a black hole. The center of a black hole on the other hand is an example of a physical singularity. A coordinate singularity only exists in certain coordinate systems, and there's nothing actually physically weird going on at them. Hence people can drop into a sufficiently large black hole without really noticing any obvious immediate change, not even if they're looking out of the window. A small one of course will kill you before you get there.

The length of the ship may for all intents and purposes be infinite in the origin's rest frame.

Only to the right in this case, not the left. Can't go past x=0. For the same reason, I cannot have a rigid rod much longer than about 27BLY with us stationary at the midpoint. It is an interesting exercise to figure out how to position a rod of twice that length without strain. It can be done. I digress.

As you move to more rapid parts of the ship through one part's frame of reference, you approach but never reach the rapidity of photon emission

I assume 'more rapid' means higher acceleration (and associated rate of change in rapidity) and not high-speed since the ship is always stationary along its entire length in its own frame (the frame in which rapidity is meaningful), so there is no different frame of reference between one part and another. There is a variable rapidity change rate that is dependent on the different parts of the ship. Over at x=1, acceleration is 1, so the rapidity there is a function of how long it's been doing that between two times as measured by a clock there. At higher acceleration parts of the ship, the same time interval results in a greater rapidity change over the same interval on again a local clock. The rapidity of light is infinite, but I don't know what 'rapidity of photon emission' means.

You cannot map out an entire Minkowski space from the light cone of one event. That's fine because that's not what a Minkowski space is: it is a frame of reference containing all events, not just one.

It contains all events in the Minkowski frame, but in real spacetime, light should be able to get here from far away given enough time, but it doesn't in reality, so the Minkowski model fails to describe the large-scale structure of our universe. It is, and always has been, a model of local spacetime.

You cannot, by definition, "accelerate away from the Rindler horizon". — Kenosha Kid

Nonsense. Show me the definition that says this.

That horizon is an acceleration limit.

It is not. It, like any other event horizon, is a boundary in spacetime separating events that can have a causal effect on a given worldline and those events that cannot. So there is an event horizon currently about 16 billion light years distant beyond which no event can ever have a causal effect on Earth (the worldline in question here). This is due to the acceleration of Earth away from locations more distant than that. The only reason that is technically not a Rindler horizon is that Earth's acceleration is not constant, but is instead increasing.

Lemme dig out a pic to explain.

And you choose a picture correctly showing the worldline of our observer at X=1 (assuming we choose units where α is 1), curving to the right (positive acceleration AWAY from the Rindler horizon to the left at X=0. The text accurately says "If the observer is located at time T = 0 at position X = 1/α (with α as the constant proper acceleration measured by a comoving accelerometer), then the hyperbolic coordinates are often called Rindler coordinates with the corresponding Rindler metric."
X = 1/α (a positive location). α is positive, so acceleration is away from location X=0 where the Rindler horizon is. Your post contradicts your own assertions.

X here is position, T time in a Minkowski frame. The hyperbola are worldlines of bodies undergoing constant proper acceleration. t here is the proper time of the accelerating body.

The picture depicts the Rindler coordinates of one body, one worldline. Yes, other bodies to the left and right, at different accelerations, would trace those other worldlines, but their times would not correspond to the times plotted for the one object at X = proper distance of 1. The t= values are for that body and are not shown for any of the other worldlines.

As the body is accelerated for longer and longer, T and t increase. At infinity, they converge at the event horizon

After any amount of time, the proper distance between our accelerating body and the Rindler horizon remains 1. It is a constant. Sure, if you choose an inertial frame where this whole setup is moving fast, you can length contract it down to any size you like, but you don't need to wait a long time for that. Just choose a different frame. From the perspective of our constantly accelerating observer, the horizon remains at a fixed distance behind him (in the direction opposite his acceleration vector).

So it's difficult to make sense of what you're saying. I get that you're trying to simulate gravity here. If you have a long ship pointed radially outward from a black hole, the bottom undergoes more acceleration than the top. I can't envisage, in the absence of gravity, how you can make a single object do the same.

You are unaware of acceleration not being constant along the length of an accelerating rigid object? This is a simple consequence of special relativity. Read up on Bell's paradox (the two ships accelerating while attached by string). It illustrates most of the concepts involved.

Perhaps a fleet of ships would be better. Non-rigid bodies were among the original hypothetical objects of the equivalence principle for this very reason.

And connect them with string, yes. Unfortunately, the clock of only one of those ships will correspond to the times depicted in the picture above.

in the latter it is the coordinate approached by an accelerating body as t goes to infinity. — Kenosha Kid

What?? The body is accelerating away from the Rindler horizon. It's not approaching it. That's why I call the direction of it 'down'.

Thus I don't know what you mean by the wording here:

All accelerations lead to the horizon at eternity.

You have links where this wording is used? I'm trying to make sense of it.

The Rindler horizon can be reached one of two ways. As the worldline of a body undergoing acceleration, it is reached as that acceleration becomes infinite. — Kenosha Kid

Not sure what worldlines have to do with this. Yes, the (constant) proper distance to the Rindler horizon of a small object undergoing continuous proper acceleration is a function of the magnitude of that acceleration. An extended object such as I described doesn't have a worldline so much as a 'world-swath' of sorts (the accelerated coordinate system of which I spoke) since each part of the object traces different worldlines, none of which intersect the worldlines of other parts.

This is the light-line (e.g. photon creation).

Sorry, I'm unfamiliar with that term. Google was no help.

Why is your apparently infinitely long ship accelerating more the further away from x=0 you go?

Acceleration must be greater further 'down'. Less in the 'up' direction, so the 'ship' can be as long in that direction as required to serve its purpose as a coordinate system for an accelerated reference frame. It is somewhat equivalent to my weight being greater on the ground floor of a building than it is at a higher floor. Clocks run faster in the higher low-acceleration portions of the object than the clocks in higher-acceleration locations further down.

And why do you think it is infinitely accelerating one LY from x=0?

The product of the distance to the horizon and the inverse acceleration will equal c^2. So c^2 / 9.8m/sec^2 = ~9.2e15 meters which is not quite a light year.

If someone outside the hole applies the appropriate transformations to their forever-falling astronaut, they will find that form the astronaut's perspective the fall is finite.

If the astronaut applies the appropriate transformation, they will find that for someone outside the hoel the fall takes forever - or more.

I don't see any inconsistency. What did I miss? — Banno

Let me put it this way:

P1 Time is absolute. There is an absolute ordering of all events in all of spacetime.
C1: For any event in spacetime and a given (time-like, or at least not space-like) worldline, that event is simultaneous with exactly one event on the given worldline.
C2: If, from the perspective of any particular observer, the simultaneity of two events does not correspond to C1, then that perspective does not correspond with reality. It is merely an abstract perspective.

Notice that it isn't necessary for any observer to be aware of this absolute time. We're just supposing there is one, not that it can be known for sure. Problem is, no coordinate system I can think of meets the requirement of C1, and the lack of the existence of such a coordinate system contradicts P1.

My choice of the first event is the falling clock when it reads 1 second beyond what it did as it crossed the event horizon. The first worldline is the clock hovering near that black hole, and a second worldline is a different clock falling into a different black hole.
How might one assign a time that is simultaneous with that first event on each of those two worldlines. The coordinate transformations you speak of seem not to exist, and at best they only transform between an abstract relation to the one actual one. I don't see the purpose of considering the abstract one at all.

We can remove GR from consideration by application of the equivalence principle to remove all mass and gravity from consideration, and then use this to illustrate the lack of transformation from one coordinate system to another.

So acceleration is equivalent to gravity, so our space station hovering at 1g outside the black hole can be equivalent to the Rindler scenario where there is only acceleration and no significant mass/gravity anywhere in flat Minkowski spacetime, which can be described using SR rules.

So consider a coordinate system of a long rigid spaceship with meter markings on the sides that acts as our coordinate system. At the origin (the place marked zero), it is accelerating at a continuous 1g. Does this ship's coordinate system map all of spacetime? No, it does not. Acceleration of the ship is greater the further 'down' the length you go, until a limit is reached (about a lightyear from the origin in this case) at the event horizon (called the Rindler horizon).The ship cannot extend further back than this, but in can extend indefinitely in the 'up' direction. A clock dropped from the origin will fall past the ship and appear to freeze as it approaches that event horizon in the coordinate space of the ship. Light from events beyond this horizon can never reach any part of the ship, which means that while I accelerate at 1g, light from about a light year away will never reach me.

The events beyond that horizon do not exist (cannot be meaningfully ordered) in the coordinate space of the ship, and thus there exists no transform between them. Events there cannot be meaningfully placed on the timeline of the ship.

Of course, in the frame of the dropped clock, the rear of the ship passes it by without notice and the clock ticks on. Now from the perspective of the clock beyond the ship's event horizon, there is no event horizon at all. It is merely a coordinate singularity and not a physical singularity. Similarly, a black hole event horizon is a coordinate singularity. That means that from the perspective of beyond the horizon (the falling clock), the space on either side of the horizon can be mapped in a coherent coordinate system (that of the falling clock in this case). So there does exist a mapping between 'inside' and 'outside' so to speak, at least in the Rindler case, but only relative to an inertial (falling) reference. There is no physical singularity in the acceleration scenario, and there is one in the black hole case, and also there's the fact that no object can be falling into more than one black hole, so there seems to be no coordinate system that maps more than one of them.

If someone outside the hole applies the appropriate transformations to their forever-falling astronaut, they will find that form the astronaut's perspective the fall is finite. — Banno

No such transformation exists since the astronaut never crosses the event horizon, so there can be no transformation of events beyond that from either frame to the other.

If the astronaut applies the appropriate transformation, they will find that for someone outside the hoel the fall takes forever - or more.

He cannot apply the transformation, which is what is meant by events that cannot be consistently assigned a spot on the outside observer's timeline. His events do not exist at all on that outside timeline.

That is a limitation of inertial frames, not of the physical universe. — Kenosha Kid

Exactly, which is why I say that inertial frames do not describe the universe.

Also, you seem to think that if we see light from a star 13.4B LY away, there must have been a time when that star was very close to us. That is not right. It didn't have to "move 13.4 BLY away and then send a signal back". Stars did not emerge from the big bang.

The material/energy from which they are comprised very much did.
Cosmologists estimate that the light we see now from GN-z11 was emitted when the universe was around 0.4 BY old, and was emitted at a proper distance from here of about 2.8 BLY at the time, which is closer than the emission distance of other galaxies with somewhat lower redshift. Light from a galaxy with redshift z=2 for instance was emitted at a proper distance of around 5.8 BLY away. That has the unintuitive effect that the more distant galaxy (the one receding faster) appears larger (greater angular measure) than a similar size object that is closer. Were the same two objects to be viewed in a Minkowski inertial universe, the angular measure of the higher redshift object would be smaller.

the current inertial frame of Earth won't do: There are objects beyond our event horizon (events from which light can never reach us even in infinite time).
— noAxioms

I don't see why an absolute coordinate system would be obligated to propagate that the speed of light. — Banno

A coordinate system doesn't propagate. You mean light propagates at c in a coordinate system. This is more or less true for an intertial coordinate system, with variation on speed due to changes in gravitational potential. So light from another star often gets to us at slightly greater than c due to most of the trip taking place in space at higher gravitational potential than we have here.
Light in an inertial coordinate system can get from any location to any other in a time dependent on the separation of the two locations. This does not describe our actual universe.

Hence, those events that are beyond our event horizon nevertheless might have a particular position in an absolute coordinate system.

They do in some coordinate systems, but they don't have a particular position in our inertial frame.

The answer to your question seems to me to be that any coordinate system might be set up as absolute; relativistic physics specifies how we translate from any frame to any other frame, so calling any frame of reference absolute becomes simply irrelevant.

No coordinate system works. That's been my point. Every choice leaves parts of spacetime unordered. As Enai puts it: There are always events that cannot be consistently assigned a spot on any choice of objective timeline.

Worse, at the event horizon, time dilation becomes so extremely that, from the perspective of the outside observer, events there do not ever occur- not even after an infinite amount of time has passed. — Enai De A Lukal

I need your opinion then. OK a foliation based on the perspective some outside observer cannot account for events beyond the event horizon, and thus seems to not to be a viable candidate for an objective foliation of all of spactime. Is there some other coordinate system that is actually up to the task? If not, is this a valid falsification of objective space and time such as is proposed by Lorentz Ether Theory? This is not even including those interpretations that additionally posit a preferred moment in time.

So you drop an absolutist into a black hole, then ask him, what's your brother doing now? His inability to give a coherent answer seems to falsify his view, but then until we drop him in like that, I suppose he's free to deny the interior events altogether, which seems to be the only recourse.

could multiverse theories be an attempt to explain causation prior to the Big Bang? — 3017amen

There are at least six kinds of multiverses discussed. Tegmark enumerated them as Level 1 (other Hubble spheres), Level 2 (other bubbles in eternal inflation theory), Level 3 (other quantum worlds), and Level 4 (other unrelated structures). There is also the Smolin evolutionary thing where the interiors of black holes are considered to be other universes. If Level 1 is our universe but spatially 'not here', then there should be a Level 0 which is our universe but temporally 'not now'. That's six at least.
Of those, it is probably the Level 2 multiverse that most qualifies as an attempt to explain causation of the Big Bang. It is also the model that explains the fine-tuning argument.
The Smolin evolutionary thing also seems to attempt this, but each universe created is of infinitesimal magnitude (matter and energy and such) compared to its parent, so it's hard to see how that can continue for enough generations for evolution to be effective.

As a very rudimentary example, what in theory, would exist outside of the block universe?

Whether it is interpreted as block or not seems immaterial. Look into eternal inflation theory. Wiki has a terse entry on it. I found a more comprehensive description in Tegmark's Mathematical Universe with some illustrations that help with visualization. There are other 'universes' that have different number of spatial and temporal dimensions, and the vast majority of them cannot produce complex physical states.

The wiki site says it was emitted 13.4 billion years ago, but it could not have got far enough away in only 400M years for light to take that long. Of course, wiki isn't using inertial coordinates when making that statement, so kindly describe the situation in those terms. Where is the emission event?
— noAxioms

Right. So, first, there was a supposed stupendous inflation period in the early universe that cannot be described by any inertial frame. — Kenosha Kid

GN-z11 is about 2/3 of the way to the edge of the visible universe. Immediately after inflation, the size of the visible universe was anywhere from a grain of sand to a city block, depending on your model. A 1 meter head start isn't going to get that object (or rather, the material that would eventually become it) out far enough to be 13.4 GLY away when that light is emitten only 400 MYr later

Second, it is unexpected that the galaxy would have formed 400M years after the big bang

OK, you're allowed to give it more time, but how long do you want? It's going to take 13.4 billion years to get far enough away, at which point there's no time left to send the light back to us here.

i.e. it is a cosmological and astronomical mystery but a) that doesn't stop it being 13.4 billion light years away from us when it did form

Actually it does stop it. It's not a mystery, it's a physical impossibility in an inertial coordinate system for something to move 13.4 BLY away and then send a signal back, all in 13.8 BYr. Waving your hand around and spreading 'I don't know/it's a mystery' dust all over the place isn't a viable model.

I take it you're not familiar with the comoving coordinate system (which does foliate spacetime to any distance) or the FRW models of the universe (from which that 13.4 BY figure comes). I'm not here to debate the viability of an inertial coordinate system to describe the universe. Trust me, it isn't a candidate. I'm here to discuss my argument against absolute time, with people who know their physics sufficiently to comment productively on it. This is not that discussion.

It's perfectly appropriate for that: that's just light further outside the light cone. It being further away just means its further away. Minkowski spacetime is not appropriate for gravity, though. — Kenosha Kid

You don't comprehend my explanation, so I'll try to comprehend your vision.

Perhaps you can explain a distant galaxy then using this coordinate system. Gravity at very large scales is negligible, so space is effectively flat so long as we're not noticing lensing effects and such.
So take GN-z11, a very distant thing with redshift of over 11.
Using your coordinate system, where (and when) is the event when the light was emitted that we see of it today? The wiki site says it was emitted 13.4 billion years ago, but it could not have got far enough away in only 400M years for light to take that long. Of course, wiki isn't using inertial coordinates when making that statement, so kindly describe the situation in those terms. Where is the emission event? If it vanishes today, will we ever see that from here if we wait long enough?

I don't see how that is a consequence of a global inertial frame. Light may not reach us for other reasons unrelated to it, one of which is the cosmic expansion of the universe being faster than light. — Mr Bee

There is no cosmic expansion under inertial spacetime. There is only an explosion of stuff from a point, with nothing moving at faster than c.

If there is a boundary to an inertial frame, then event outside that boundary do not exist in that frame.
— noAxioms

You seem to be mixing up the boundary of the observable universe with the "boundary" of an inertial frame, the latter of which I don't really understand. They are both not the same.

They are indeed not the same. The boundary of our inertial frame is much less than the 47 BLY radius of the observerable universe, and even less than the ~16 BLY distance to the event horizon. The current radius of our inertial frame must be 13.8 BLY because nothing outside that radius could have come from the big bang without moving faster than c, and nothing moves faster than c in an inertial frame.

My understanding is that it is mainly spacetimes with closed timelike curves that preclude the existence of global hypersurfaces, but I haven't heard anything about black holes doing the same.

Your understanding here is fine. Nobody is proposing a closed timelike curve. Any foliation, objective or not, would preclude that.

I got lost at:

The [clock] is dropped from a hovering location outside, which shines light down on the dropped clock.
— noAxioms

It's not clear what frame of reference we're in here. — Kenosha Kid

First of all, I meant dropping a clock, which seem more useful than dropping a glowing rock. I used a rock at first and neglected to change them all to 'clock'. But it moves like the rock: not under propulsion or anything.

The light shines from the hovering station. It can be light from the clock displaying the time if you will. The time is the proper time of the hovering space station that maintains a constant distance from the black hole. We can build a shell around if you like it so we don't need to expend fuel to stay indefinitely at that location.

From the perspective of an observer outside the event horizon (with some magic blackholescope), the clock will accelerate toward the singularity and run slower and slower. Any photons emitted from the rock (which is getting further and further away from the clock) will still travel at the speed of light and catch up with the clock, because the clock cannot move at the speed of light.

I've caused confusion. The rock and the dropped clock are the same thing. The space station can watch it fall in, but if it reads time T when it crosses the event horizon, then the space station will never see the clock read anything after T. It will appear from the space station to slow and approach but never reach T. Event B is that clock when it reads T+1.

From the rest frame of the clock, it is in perpetual free fall. Eventually the rock will simply recede so far into the distance it cannot be detected.

Again, they are the same thing, so the clock indeed will eventually reach the abrupt end of time and tick it's last, so to speak. This is assuming the clock is a point device that isn't destroyed by excessive violence like tidal forces before it gets to the singularity.

If you want to describe a clock and a rock dropped say at separate times, you need to lay out the scenario. I never meant for there to be two things falling like that.

So your perspective is more psychological and related to our conscious experiences. Is this a Berkeley or Kantian strategy you are gleaning from in treating spacetime as a fundamental psychological process but nothing more? — substantivalism

I said it is a psychological choice when I decide what components comprise a system or not. The physics of the relationalism has zero to do with this choice.

I get that this philosophical viewpoint is not emprically well-founded and never could be (it would be consistent with any personal experience) but it always felt relatively possible. — substantivalism

I find the acquisition of new information to be a contradiction in the solipsistic idealist view. Say you find a tomb full of Egyptian writing and spend years trying to decipher it. You've memorized every character and could reproduce it at will from memory, yet you cannot read it. After years of study, you finally break the code and learn the language, and suddenly there is information that was always there, but suddenly is meaningful to you. That implies there is something out there that didn't come from you. I cannot dream of a coherent language that I don't yet understand. Something else has to have produced that tomb, which contradicts your experience being more fundamental than the noumena. That contradiction sinks the view in my opinion.

Two quick questions:

1. Does black hole time travel increase or decrease Time ( I can't remember)?
2. Do black holes contribute to Multiverse theories at all? — 3017amen

Time slows (is more dilated) when deep in a gravity well, So clocks on Earth for instance run objectively slower than say GPS clocks (which are very high up and not moving fast). Those GPS clocks are slowed due to their orbital motion, but the gravity effect is greater at that altitude. Clocks on the ISS run slower than the ones on the ground due to minimal gravitational potential difference in low orbit, coupled with significant dilation from the higher orbital velocity. So at an altitude of 1.5 R (R being Earth's radius), the two effects cancel out and orbiting clocks can be synced indefinitely with those on the ground.

Similarly, from the PoV of the distant observer, a clock falling into a black hole freezes on the event horizon. It doesn't just appear to freeze. Coordinate time slows and actually stops there.
From the PoV of the observer falling in, he sails right in without a hitch, and the universe behind him appears to speed up, but not infinitely so. There's definitely a time outside the black hole beyond which is not part of his past light cone, and thus is not observable.

About the multiverse thing, I think there are theories that a black hole in one universe is a white hole from the perspective of the interior spacetime. I think we're possibly supposed to be in such a white hole in some of these theories, except I don't see how we could be expanding then. There's no singularity (big crunch) at the end of time like one would expect from a geometry with an abrupt cessation of time like that.

Thanks for your initial responses.

I've been in discussion about this on physics sites, but they don't care so much there about the metaphysical implications to absolute time interpretations.

As you can see, any event can be located in an inertial frame, but only those events within our past light cone can be detected by us now. Events outside that cone are still in the reference frame but cannot influence us. — Kenosha Kid

You've drawn flat Minkowski spacetime (with arbitrary inertial frame) in which light from any spatial location will reach any other location. That makes it an inappropriate model of the large scale universe where light that is currently say 17 GLY away will never get here, not in 17 billion years or ever.
Earth has an event horizon, and Minkowski spacetime does not. The universe cannot be foliated with such a coordinate system.

Gravitation can't be accurately described by inertial frames but require curvilinear coordinate systems. — Kenosha Kid

You can still foliate reasonable gravitation in 'bent' Minkowski spacetime, but not black holes. So for instance, a device measuring absolute time here on Earth would run apparently faster than one on the surface of Saturn due to the lower gravitational potential here on Earth. The same device on a ship with relativistic absolute speed would similarly appear to run faster (than the clock next to it) than it would if the ship had low peculiar velocity.

I don't get this. Why would they have to reach us? — Mr Bee

There's no requirement for light to reach any location from any other since there are very much cases where that does not occur. My point was that in an inertial frame, light can reach location X from Y given enough time, and thus such a model is not a model of our universe.

The light will never reach us because of cosmic expansion, so the fact that we don't see them doesn't mean they don't exist.

If there is a boundary to an inertial frame, then event outside that boundary do not exist in that frame. An inertial frame does support cosmic expansion, but it does not support acceleration of that expansion. So given no such acceleration, there would be no event horizon and light will eventually get from location X to Y given time. And even locally, an inertial frame cannot foliate the interior of black holes, so it fails twice.

I'm not sure about that. As far as I know, any spacetime that doesn't allow for closed timelike curves is open to being sliced into global hypersurfaces.

There are indeed ways to do it with a single black hole, but you must assume the black hole is at some kind of privileged location. So consider 3 events: A clock is dropped into a black hole. Event A is that clock 1 second (measured on that clock) after passing the event horizon. The black hole is big enough that it survives at least one second. The rock is dropped from a hovering location outside, which shines light down on the dropped clock. At some point the last light is emitted from this location that will catch up to the dropped clock before it hits the singularity. Event B is that hovering location 1 second after that last light goes out.
Event C is at the location of the former black hole after it has evaporated.
Yes, you can come up with various schemes to order these three events, but do any of those schemes order all of spacetime? OK, C occurs after B since it is in the future light cone of B. That's easy. Not so easy with event A.


I'm not suggesting retrocausality anywhere. Event A is not causally connected with either B or C, so no objective ordering scheme is going to produce a contradiction unless B is in A's future but C is in A's past.

I mean no disrespect — substantivalism

None perceived. I agree with your comment that there is a general aversion to solipsism among philosophers, and I was just pointing out that the aversion itself is a poor reason to reject any view. I personally find the view self contradictory, and reject it for that reason.

We see eye to eye on the geocentrism and anthropocentrism of view points as I also find metaphysics which make us highly centered in the grander scheme of things likewise also highly suspect.

Yes, but again, I identify that as a personal bias, and therefore not good grounds for rejection. Who knows, maybe the universe is made for us. That possibility must be considered, but positing such doesn't seem to explain anything better than more plausible views.

It's like a sorites problem of sorts to attempt to specify where you end and the greater worldly environment begins.

Where I end (spatially, not temporally) is an interesting problem. It seems to be a purely abstract thing. The guy in the sci-fi show straps a time travel device to his wrist and it takes him and his clothes and briefcase to some other time, but doesn't take the nearby shrubbery. How does the device know what's you and what's not? It's intuitive to us, but in trying to tell a device how to do it, it turns out it isn't obvious at all.
Where does a mountain stop? Most of them don't sit nicely on an otherwise flat surface that gives an obvious boundary delimiting mountain from the surface on which it rests.
All these things are part of exploration of identity, but not particularly important to relationalism, which cares not so much what one defines as a 'system' or not.

Yeah, solipsism really makes a philosopher run for the hills doesn't it. — substantivalism

Just because it's distasteful doesn't mean it's wrong. But I think there are serious logical problems with the solipsistic view, coupled with a personal bias against any sort of geocentrism, anthropocentrism, or any other view asserting us having a privileged status.

It was just the words being used by you such as 'me' that made me think you were taking a sort of idealist direction for you metaphysics but I was wrong there.

If I want to be formal, I had to find a definition of 'me' that didn't violate the law of identity, and it pretty much makes a hash of the way 'me' is used in everyday language. Language is littered with unstated premises, all of which I question (hence my user name), and most of which I cannot justify.

Under RQM, experiencing something has nothing to do with it being real. There simply needs to be a relation, especially a measurement. So the apple exists relative to the rock iff the rock measures the apple in some way. The rock having conscious experience of the apple has nothing to do with it. That kind of thinking leads to solipsism. Think Wigner interpretation, which many people hold without knowing it, but even Wigner himself abandoned it due to the solipsism thing.

I don't do polls, but I'm a relationist is probably far more ways than the one you describe.

Yes, time has no meaning without regular change to define it. Space has no meaning without at least three locations so that it can be meaningfully expressed that A is closer to B than is C. Without physical objects to anchor those locations, they're just abstract geometry to us. I consider our reality to be 'real' only because it relates directly to me, however I might care to define 'me'.

As for relational interpretations of special relativity, yes, I tend to favor RQM (Rovelli).

I think I read your post wrong, because upon re-reading it, I agree.

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.

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

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.

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

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. Dualism doesn't fit well at all with eternalism under which the entire worldline of a person is conscious. It would be rather absurd to say that the 1997 portion
of me is not conscious of the events of 1997.

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. — Mr Bee

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?

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

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

Ouch. 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 eternalist says that every point in time is equally real — ChatteringMonkey

I'd say 'has equal ontological status'. There's a difference to us non-realists.

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

They're interpretations actually, despite all the literature referring to them as theories. No, neither interpretation can be falsified since they do not make distinct empirical predictions. All attempts to discredit one or the other proceed along logical grounds, not scientific ones.

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

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,and doesn't seem to have so many variants.

Both have past, present, future.

Under eternalism, such words are only relations, like Earth, 1927 is in the future of Earth, 1925.

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?

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.

The mug moves probably by me carrying it there. That's probably not the answer for which you're looking, but I don't know what else you might be asking with that question.

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

I smell a begging argument coming on. You did this fairly large post, but then never actually get around to this point until the last couple sentences.

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

You can add me to that list. At noon, the mug has coffee in it. At 1pm the mug is in the dishwasher. How is that not motion of the mug?

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.

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?

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

Firstly, I don't know if communication per se is an indication of consciousness meant here as the existence of an inner life - what is it like to be something. — TheMadFool

I don't think there's anything 'being' me, so does that mean I shouldn't consider myself conscious?

The great Albert Einstein postulated that the velocity of light is constant at approximately 300,000 km/h. This one postulate and maybe a few more is the allegedly the foundation of his theory of relativity, a theory that has withstood many attempts at disproof. So far so good. — TheMadFool

It's 300,000 km/sec. It's a speed, not a velocity.
The postulate of SR is that that speed will be measured regardless the reference frame used. It doesn't actually posit that the speed actually IS frame invariant, just that it will be measured that way.

Consider 2 cars, A and B, moving on the same practically straight freeway.

1. Situation 1: A is moving at 20 km/h north and B is moving 60 km/h north. The relative velocity of B with respect to A is 60 - 20 = 40 km/h.

Per Einstein, no. Close, but not exactly 40. For instance, scale up the speed to say 0.2c and 0.6c, and the relative velocity of B with respect to A becomes 4/9 c, not 0.4c.

What then of the postulate that the relative velocity of light with respect to an object is "constant"? If I'm travelling in a spaceship with a given velocity, the relative velocity of light with respect to my spaceship will be 300,000 km/h. If I were then to alter my velocity, doesn't the velocity of light have to change accordingly so as to ensure that the relative velocity stays at a constant 300,000 km/h?

Unintuitive, but no. Light speed (not velocity) remains at c relative to anything. This works out if you use the velocity addition formula instead of straight addition like you're doing all through the OP.

Several of the questions presuppose the idea that minds can exist separated from the body. — Harry Hindu

Well yea, since the OP opens with: "If the mind is immaterial:"
The post asks to explore the viability of the alternate POV where there are two separate things, or where matter supervenes on mind. Given the wording of the post, I'd say more the former of those two.

I ask, "What is the point of a mind separated from a body?"

Or the point of a mind not consisting of a body?

All the above post seems to be about the mind being a function/process of the brain (or larger self), and sure, I am on that side of the fence, but I think the OP was asking about the opposite, where the body is a byproduct/purposeful-extension of the mind. The body seems to poorly implement such a purpose.

I've stayed out, and I find the arguments by unenlightened to be on point.
Nevertheless, the discussion seems to have turned to how materialism explains itself, and the original purpose of the OP seems to have been lost.

I think most of the relevant replies came from Wayfarer, but much of that was dropped. The Lusthaus quote was interesting but does not seem to address the question at hand. OK, it seems that it is a mistake to model the relationship as 'mind as an object'. We instead work with ideas and purpose, and the physical world is derivative from it. But then suppose it was my idea to take my purpose of needing an vehicle to animate my need for getting around and experiencing the world. Given that purpose, why would I imagine a vehicle with zero controls, that goes where it wants, when it wants. That's pretty useless for my purposes. I'd give it pedals and a steering wheel so that I could exert my will upon it. A physical being seems to have no pedals and such. It doesn't seem to be the product of the sort of purposeful ideas posited by this non-primary-material model.

What I'd like to say about that, is that both mind and matter are idealisations or abstractions. There is neither mind as a 'substance' (in the philosophical sense), nor matter per se because all matter has particular attributes and characteristics which define its type.

So whilst I agree that there is no 'immaterial object', I'm also inclined to believe that there are no 'purely material' objects either. — Wayfarer

I actually agree with this. On that point:

And then you've still got three ducks but now you've got a row as well. Assume the ducks are material. — unenlightened

If the row isn't 'new stuff', then neither are the ducks, being themselves just more arrangement of stuff that was already there. At what point is there actually stuff? It seems the scientists have never found it, and hence the unstable foundation of what is typically exemplified as 'materialism'.

Anyway, I was hoping to see more discussion on this original intent of this thread.

Near as I can tell, you mean something like 'coordinate time' when using the phrase 'relativistic time'. Coordinate time and physical (proper) time is the same thing for an inertial worldline with the time axis of the coordinate system aligned with said worldline.

Sure. But as you note later, proper time can be well-defined even in the absence of anything to mark its passage, and that is where I see a problem. You could have a relativistic spacetime with nothing else, and formally it would still have time of every description. But would it be physically meaningful? — SophistiCat

No, time without change is meaningless, as is say motion of an object in the absence of other objects. The words might as well be invisible pink unicorns.

Of course, here we run into the more general question of the nature of the physical law. Are laws ontologically prior to things and events that are subject to them? Do they describe potentialities (like what would happen if that empty spacetime did have something in it to demonstrate its relativistic properties)? Or do laws serve only to connect the dots, describe the regularities in our observations? In the latter case - and only in the latter case - it would be unjustified to talk about time in the absence of anything that is time-like. I think I lean towards the Humean regularity view.

I seem to be in the latter camp. Spacetime with nothing in it doesn't have relativistic properties.

The reason we came up with the theory of relativity in the first place was to give a better account of clock-based time (among other things). Without clocks what is the point of relativity?

Can there be time without clocks? Surely there are primitive people and animals with an awareness of time, but they also arguably have clocks, however inaccurate. If the speed of light was a lot slower, its properties could be more apparent and intuitive to primitive beings who may not have developed accurate measurements for it yet. Similarly, our intuitive perception of time as flowing is only there because that perception makes us more fit, not because time necessarily flows.

An empty, flat spacetime with a positive cosmological constant is an interesting case.

Meaningless. If it has stuff, I don't think it can be flat. If it were, an inertial frame could foliate the space, and it cannot.

relativistic time is not identical to physical time (the time that physical clocks measure) — SophistiCat

Actually, you never really defined what you mean by 'relativistic time'. You say physical time is that which clocks measure. I think physics would say that a clock measures proper time, a frame independent property of any timelike worldline. Clocks, not being confined to a single point, cannot be perfect, just like the exact length of a curving road is ambiguous because the road has nonzero width.
I digress. What do you mean by relativistic time? You said the two are usually the same except after heat death, but that doesn't tell me what you mean by the term, especially since a clock cannot exist in heat death conditions. It seems that time in general (both duration and direction) fade to meaninglessness along with most other physical concepts.

If I take a cube, and divide it in half, and then again, ect to infinity and then line them all up biggest to smallest, what is the smallest? ...
You might say "there is a limit". — Gregory

I might not. You're the one making the suggestion and then driving your own assertions to obvious nonsense conclusions.

So we have a huge paradox here.

Exactly so. So maybe try it without positing a last term in the infinite series.

Does the series go off into the physical horizon forever?

Physical now? A physical cube-shaped object has a finite number of particles in it and can only be divided so many times. There is a smallest part at the end of the sorted line and it has a color if you're going to abstractly assign colors to the even and odd ones.

Except that there is actually no motion according to Eternalism. I would imagine that it's much easier to explain why we perceive motion if there actually is motion than if there actually isn't. My point, again, is better expressed by Kristie Miller:

For the eternalist, the key challenge lies in explaining temporal phenomenology and in explaining the apparent directionality of time. There has been significant work in this area, but questions still remain: why do we have such a different relationship with the future than with the past: why is it that effects typically precede their causes when the laws of nature are symmetric: why do we remember the past, but not the future: why does the present seem to us to have a particularly salient quality that other moments lack; what are the cognitive apparatuses that underlie our experience of
temporality and how do they function to create temporal phenomenology; what is the evolutionary significance of the phenomenology of temporal flow and to what extent is the phenomenology of temporal flow essential for agency.
— Kristie Miller — Luke

I think I'm up to that explanation, which, from a physicalist point of view, can be explained through entropy and evolution, but almost nobody actually accepts physical monism deep down. I think I have but it was a multi-year struggle to shake off the biases put there by a very proficient liar.

So the story from the dualist POV (there is an (physical or spiritual, doesn't matter) identity 'I' that consistently experiences the life of physical body X. The analogy here is that physics is like a first person Harry Potter movie and the experiencer is the guy in the cinema. Eternalism is the same thing, except no cinema, no entity watching the show, and especially no projector.

Under presentism, the present is whatever frame is currently being projected. Normally the film runs front to back, but if it were run back to front, the experiencer in the cinema would notice the difference but Harry would not. The movie would end with the guy in the cinema knowing Harry's life story (the future) but Harry wouldn't even know that he's a wizard at the end. Harry obviously has different memories than the guy in the cinema. So the movie always runs forward because we'd be able to tell if it didn't.

Hence it being totally unintuitive to such a dualist to conceive of eternalism, which requires the lack of the experiencer (the definer of the present), and he interprets the description (the word 'static') as the experience of a stuck projector. The view is anything but that.

The eternalist view has no experiencer. It doesn't even have Harry (as an identity). It only has the individual frames in the film and one can talk about the experience of that frame, and yes, the experience of any given frame is one of motion of the passing car. One is forced to use B-series language to express what each frame experiences because there is no preferred frame defined by a projector, and A-series requires that preferred reference. By 'frame' here, I'm talking a frame of film (the local state of things at a particular time), and not relativity's reference frame.

The subjective flow of time is an illusion, illustrated empirically with the twins scenario in relativity. If people could detect the actual flow of time, then they'd be able to detect movement due to the subjective slowing of clocks when they're moving fast, whereas if it were an illusion, any traveler would notice no difference.
— noAxioms

It's unclear to me what the illusion is that you are referring to. What 'movement' is going undetected? What 'movement' would be detectable if "people could detect the actual flow of time"? — Luke

Not movement. I refer to the rate at which the present moment progresses into say a moment one second hence. No device measures this, and the subjective experience of a human is no exception to this. If there was, one could design an objective clock that would stay in sync with any other objective clock regardless of where it was or how much it has been accelerated around.

How to interpret data is subjective. The sole thing Einstein noticed was the observation that external motion changes the size and some of the rate of change within the object. That's it. — Gregory

This is totally wrong. The sole observation from which Einstein did his SR work was the apparent constant speed of light. From that, all the things above were predicted, not measured ahead of time.

Since he didn't do the experiments, he probably didn't even come up with that.

Indeed, he didn't do them himself.

Do you deny that it is unintuitive to be able to divide something finite a literal infinite amount of times? — Gregory

For one, 'infinite' is not an amount, and 'literal infinite' is no different than 'infinite'.

I would instead find it unintuitive to suggest that there would be a limit to it, a pair of non-identical points for which there is not a location between them. To assert otherwise is to assert that two non-equal numbers A and B can be found such that (A+B)/2 is equal to either A or B or both. You have weird intuition.

So I would say that a finite segment can be divided without limit, and yes, this is intuitive to me.

This is not true of any discreet system. For instance, in the domain of integers, the finite segment from 20 to 6051 can be divided, but only so many times. There is no integer between 21 and 22, and (21+22)/2 does not define a new integer, nor is the answer necessarily equal to either 21 or 22. It might be, depending on how the divide operator is defined for the discreet set in question.

According to the Kristie Miller article cited in the OP, the difference between Presentism and Etetnalism is not only their differing views on existence, but also their staticity/dynamism. — Luke

Miller writes this:

Thus eternalists endorse the following pair of theses:

Eternalist Ontological Thesis (EOT): Past, present, and future times and events exist.

Static Thesis (ST): The present does not move: which moment is the present moment does
not change. — Miller

Now either Miller has no understanding of the position, or she's talking about something completely different. The view denies the existence of a preferred moment called 'the present' and hence the ST part is nonsense. I've actually heard of such a view, which is presentism without the movement, but Miller doesn't seem to be talking about that since she correctly states that all events at all times exist equally, which is not true of a model with a present that stays put like that.

Anyway, I'd never accept these points as worded. The first isn't totally wrong, but past/present/future are all relations like < = >, and not objective states like negative, zero, and positive, and the wording makes it sound like the latter.

Then I take it you agree with all of the following:

Eternalists, then, hold that the world as a whole is static in two senses: which events
exist does not change, and there is no sense in which the present moves. — Luke

I'd say there is no 'the present' to do any moving. 'The present' would be just any event's self reference, and that, by definition, cannot move.

Eternalists accept what is known as the B-theory of time. This is the view that the
world is a static block of events ordered by the earlier than, later than, and simultaneous
with, relations. [1]

Also known in physics as 4-dimensional spacetime. 3D Space and time are separate under presentism.

Presentists endorse the A-theory, since they hold that it is a genuine feature of a
presentist world which moment is present, and that this fact changes over time so that
different moments are present at different times. To say that a view accepts the A-theory
is really to say that it endorses the dynamical thesis, and to say that it endorses the
B-theory is to say that it rejects the dynamical thesis.

I haven't seen the dynamical thesis, but this seems right.

Eternalism, on the other hand, is a static view that rejects temporal flow. Since it certainly
seems to many that there is temporal flow and change, this is a cost to eternalism.
At the least, the eternalist owes us an account of why it s

The subjective flow of time is an illusion, illustrated empirically with the twins scenario in relativity. If people could detect the actual flow of time, then they'd be able to detect movement due to the subjective slowing of clocks when they're moving fast, wheras if it were an illusion, any traveler would notice no difference. This of course isn't easy to test given the cost of the experiment, but it is there.
No, it isn't a proof of one view or the other, just a demonstration that the flow of time is a subjective illusion.