I didn't make much of the 'timeless space' paper, — fdrake

Just briefly on this, my interest was less in the science itself than in the rhetorical moves made within it: the illigitimate jump from spatializing the 'fourth dimension' to declaring a timeless universe. It's illustrative of the 'scientific' instinct to do away with time, even when - perhaps especially when - there lacks any warrant to do so. Will come back to the big post later hopefully.

Well, in block universe, there is no motion, just worldlines, straight (inertial) or otherwise. The dimensions of those worldlines can be different depending on the choice of coordinates, but that change (the separation (interval) of any two events, say the event of some twin's departure and the event of his return) is a fixed value, and not frame dependent. — noAxioms

I think it's strange to say that there's no motion in special relativity, — fdrake

I meant nothing moves through the block of Minkowski Space time. Time is built in. This is about the block view, not SR or GR. Velocity is the slope of the worldline of some object. Relativity works in block or in 3D view, so the ontological difference is interpretation with no empirical difference. Relativity was born of the observation that the worldline of a photon has the same slope regardless of assignment of coordinate system. That fact is not a necessary property of Minkowski spacetime, so block universe is not necessarily relativistic.

A 3D model of the universe works, despite the 4D Minkowski spacetime model that SR suggests. — noAxioms

I really doubt this, since this trivialises space-time curvature. The Einstein and Riemann tensors are 4-tensors, and the metric derivatives and Christoffel Symbols they consist of interact to give 4 tensors., They need to maintain the number of indices they have so that they can be contracted through identification or multiplication by another tensor to derive the Einstein field equations. 4D space-time can't be removed from SR or GR without drastically changing their character.

But, if you have a reference or previous post on this, I'd be happy to read it. — fdrake

My post was using SR case, which admittedly has bunk to do reality except in a local sense, away from significant spacetime curvature. So perhaps the field equations do indeed require 4D spacetime.

The posts I refer to is not in this forum. Took a long time to figure out why I was in read-only mode here. Essentially I ran the train thought experiment in 3D absolute space and ran into no contradictions. At least one observer is simply wrong about his assessment of the simultaneity of certain events.

Just a side note in the convo: I remember SR being treated as a minor point to GR in my physics class. SR was the sort of thing which we learned to do in order to be able to accept GR, or understand it. We, however, did not delve into GR since it required mathematics beyond what the SR class required. I only mention this because my take away was that SR wasn't meant to be taken ontologically (from a scientific realist perspective), only GR was -- in some sense GR reduced to or was "in line" with SR. I wish I could say more than that but alas I was a chemist (interested in philosophy, I hope thats obvious) and not a physicist.

remember SR being treated as a minor point — Moliere

If the twin paradox was mentioned, that is not a minor point. However. If SR was treated as simply a measurement problem, with no ontology, then indeed it is minor.

I wasn't referring to anything like that. I suppose what I'm trying to say is that relativity doesn't necessitate a 4D block universe. It is certainly possible for us to view time in the traditional sense, as a 3D world that changes via. the passage of time though there are costs to that sort of view.

Yeah, I don't think a block universe is necessitated by the conceptual structure of relativity either. I spelled out what I thought were the ontological consequences of it in my reply to SLX. If you want to think of blocks because of space and time being conjoined, it relativises the blocks to individual motions - something I find pretty cool.

Velocity is the slope of the worldline of some object. Relativity works in block or in 3D view, so the ontological difference is interpretation with no empirical difference. Relativity was born of the observation that the worldline of a photon has the same slope regardless of assignment of coordinate system. That fact is not a necessary property of Minkowski spacetime, so block universe is not necessarily relativistic.

So you're saying that a block universe is neither implied by or implies either relativity? I think I agree with this, but I don't understand how you're using four-velocity in the presentation. Can you give me some more words please?

I'd also really like to see an abbreviated form of the post you made on another forum.

Just a side note in the convo: I remember SR being treated as a minor point to GR in my physics class. SR was the sort of thing which we learned to do in order to be able to accept GR, or understand it. We, however, did not delve into GR since it required mathematics beyond what the SR class required. I only mention this because my take away was that SR wasn't meant to be taken ontologically (from a scientific realist perspective), only GR was -- in some sense GR reduced to or was "in line" with SR. I wish I could say more than that but alas I was a chemist (interested in philosophy, I hope thats obvious) and not a physicist.

One of the minute-physics videos on special relativity highlights this. Special relativity isn't treated as a topic worthy of study on its own - despite showing up in particle physics. From memories speaking with physicist friends at university, its teaching was highly idiosyncratic and it's not presented in a general form.

I don't think this implies that it's not worthy of study or philosophical interpretation, especially since it's a less complicated form of general relativity - I think you get some interesting constraints on naturalistic metaphysics by trying to make it consistent with special relativity alone. But of course, it'd also be interesting to make it consistent with GR - more work too.

Velocity is the slope of the worldline of some object. Relativity works in block or in 3D view, so the ontological difference is interpretation with no empirical difference. Relativity was born of the observation <of fixed light speed>. That fact is not a necessary property of Minkowski spacetime, so block universe is not necessarily relativistic. — noAxioms

So you're saying that a block universe is neither implied by or implies either relativity? I think I agree with this, but I don't understand how you're using four-velocity in the presentation. Can you give me some more words please? — fdrake

Pictures are hard to post. Consider a simple spacetime of 2D, one of space, the other of time. Lots easier to visualize. Twins experiment requires only 1D of space for instance. So it can be done on 2D paper, preferably circular paper so there is no preferred orientation.

Draw a dot A somewhere, and B somewhere else. This represents 2 events, say the start and stop of a journey. Straight line between the two is its worldline, unaccelerated. A curved line denotes acceleration. So now superimpose a vertical axis S (space) and perpendicular horizontal axis T(time), with origin at A. If you orient the paper so the line is at an angle, the vertical space displacement of B is nonzero and the slope is the (positive or negative) velocity. If you assume a different frame and orient the paper so the T axis followsthe worldline, then the space displacement is zero, T is at a maximum value at event B. There is no motion in this frame since spatial displacement remains zero for the length of the worldline. Angle the paper a lot and the space displacement gets large and the T displacement starts to shorten, but regardless, the unitless separation between A and B (called the interval) remains fixed.
If there is a third event C which is directly above B at a certain orientation of the paper, then B and C are simultaneous, but only in that frame. Orient the paper different and the events become ordered differently.

All this is pretty much a description of flat Minkowski spacetime. At no point does something move across the paper, and orienting the paper different does not make any real change to what is drawn on it.

I'd also really like to see an abbreviated form of the post you made on another forum.

Found a bit of it: Context is the train experiment, where two lightning strikes occur, one at each end of the train, leaving a mark on the platform (and train ends) as it strikes. An observer on the platform and on the train each make their assessment of the simultaneity of the two lightning events.
----
Under the 4D model, the platform guy notices the two strikes at the same time, and after measuring the distance from where he was standing to each of the platform strike marks, determines that the two strikes were simultaneous. The train guy detects the strike at the front of the train first, and afterwards the rear strike. He also measures his distance to the two marks on the train, and is equidistant. He thus concludes that the front strike happens before the rear strike. Two frames, two different but valid ordering of events.

3D model, with 3D space and separate absolute time:
Two events are not ambiguously ordered. If one frame orders them differently, that frame is not the preferred one and it orders events incorrectly. Two events simultaneous in that frame are not in fact simultaneous, and thus there are no future events that exists. The frames that put you simultaneous with those future events are simply wrong about their designation of simultaneity.

So in my examples, I always pick the unintuitive stationary guy. So it turns out that the train guy is the one actually stationary. The platform observer is on the moving ground.
Lightning flashes go off, hitting the front of the train first, and the back later.
The train observer is midway between the two events, and records the front strike first. Being equal distant from the two events, the observer knows the front strike happens first.

The ground observer is moving towards the rear of the stationary train, and by the time the light from the two signals meet, he is at the point where they meet, so he measures the two signals as arriving simultaneously, but one has traveled further than the other, so this is expected. His clock also runs slow, but since he didn't use it, nobody cares.

The guy not actually stationary is incorrect in his assessment of two events being simultaneous. So the guy on the platform is basing his simultaneity assessment on the false fact that the two marks on the ground are where the lightning struck. Since the ground is moving, this is clearly not true. The marks are not the point in space where the strikes took place. The endpoints of the train are the actual spot where the strikes took place.

This is a description of the 3D scenario, and I hope is free of inconsistencies.

BTW, I also saved a post describing the twin experiment with only SR rules, no acceleration, and using a tag team. It is more for illustration purposes, and argues no philosophical points.

All this is pretty much a description of flat Minkowski spacetime. At no point does something move across the paper, and orienting the paper different does not make any real change to what is drawn on it.

Aha, I see what you mean. You're providing a demonstrative example of motion in 1 spatial dimension and 1 temporal dimension, not saying space and time can be thought of as physically 1 space 1 time in general.

The rest was just an example of the conservation of proper time.

Two events are not ambiguously ordered. If one frame orders them differently, that frame is not the preferred one and it orders events incorrectly. Two events simultaneous in that frame are not in fact simultaneous, and thus there are no future events that exists. The frames that put you simultaneous with those future events are simply wrong about their designation of simultaneity.

I don't think this is true. If it were legitimate to axiomatically posit a preferred frame of reference with which to define all motion relative to, it'd be a consequence. I think the absence of a preferred reference frame is an implication of the equivalence principle - what would be the point in stressing the transformability of motion to equivalent forms if the only purpose was to index all motion again to an arbitrary origin point? Why should any one ordering of events be more true than another?

In other words, nothing changes about relativistic computations if there is a preferred reference frame for any given motion, so there being a preferred reference frame is something out-with the influence of the theory. An arbitrary decision about space-time should not structure how we think about it.

Your post takes the view that a predicate equivalent to 'is the true reference frame' is something that can be appended to a reference frame, this is something SR and GR prohibit from having any ontological import.

If I've understood you and it, anyway.

Aha, I see what you mean. You're providing a demonstrative example of motion in 1 spatial dimension and 1 temporal dimension, not saying space and time can be thought of as physically 1 space 1 time in general. — fdrake

No, ours is 3+1, but the concepts are the same. The coordinate system (all four axes) can still be oriented any way, so long as they stay perpendicular. Radial systems sometimes work better for the cosmological scale where SR is completely irrelevant.

The rest was just an example of the conservation of proper time.

I don't think this is true. If it were legitimate to axiomatically posit a preferred frame of reference with which to define all motion relative to, it'd be a consequence. I think the absence of a preferred reference frame is an implication of the equivalence principle - what would be the point in stressing the transformability of motion to equivalent forms if the only purpose was to index all motion again to an arbitrary origin point? Why should any one ordering of events be more true than another?

Undetectable is what the equivalence principle states, no?. Just because something is undetectable doesn't mean it isn't there. Hey, I'm not arguing for it, just against this being a proof against it. I personally favor a block view, and no ontology to it at all.

In other words, nothing changes about relativistic computations if there is a preferred reference frame for any given motion, so there being a preferred reference frame is something out-with the influence of the theory. An arbitrary decision about space-time should not structure how we think about it.

Correct. Something undetectable makes no difference to what is an empirical theory.

Your post takes the view that a predicate equivalent to 'is the true reference frame' is something that can be appended to a reference frame, this is something SR and GR prohibit from having any ontological import.

If I've understood you and it, anyway.

No GR prohibitions anyway. SR perhaps not, but it describes a flat massless spacetime that doesn't correspond to reality. I.E. no inertial reference frame foliates the universe, so none can be the correct one. Inertial frames are local, and the universe is not. There are objects that can actually be seen that do not exist in our inertial frame since they are, in our frame, simultaneous with a time before the big bang. Talking about stuff near the edge of the visible universe that "has since" (<-- questionable use of verb tense) passed beyond the Hubble Sphere which confines events even remotely valid in our reference frame. Hence the curved foliation with is not a reference frame at all, but covers all the universe.

Undetectable is what the equivalence principle states, no?. Just because something is undetectable doesn't mean it isn't there. Hey, I'm not arguing for it, just against this being a proof against it. I personally favor a block view, and no ontology to it at all.

I don't think an undetectable in principle difference should be elevated to a difference in practice.

No GR prohibitions anyway. SR perhaps not, but it describes a flat massless spacetime that doesn't correspond to reality. I.E. no inertial reference frame foliates the universe, so none can be the correct one. Inertial frames are local, and the universe is not. There are objects that can actually be seen that do not exist in our inertial frame since they are, in our frame, simultaneous with a time before the big bang. Talking about stuff near the edge of the visible universe that "has since" (<-- questionable use of verb tense) passed beyond the Hubble Sphere which confines events even remotely valid in our reference frame. Hence the curved foliation with is not a reference frame at all, but covers all the universe.

I'm assuming 'foliates' here means, essentially, 'providing a coordinate system for'. And the way in X foliates Y is always done differentiably (my differential geometry-fu isn't particularly strong). So I'm thinking of a foliation as the thing which describes the rate of change of an application of a coordinate system to a locality with respect to infinitesimal shifts in its origin.

There are objects that can actually be seen that do not exist in our inertial frame since they are, in our frame, simultaneous with a time before the big bang.

So at time t they were in the Hubble volume, and at some time t' they expanded out of it? That's the picture?

Hence the curved foliation with is not a reference frame at all, but covers all the universe.

What implications do you draw from this? I've said previously that there are still things which can be said about spacetime in general with respect to increasing time - like the expansion of space when the metric tensor is an increasing function of time. I interpret foliations as ways of setting up for questions like this - they will provide a system of coordinates in which the evolution with respect to some variable, probably time in this case, can be indexed.

I don't think this makes length contraction or time dilation go away, but it does implicate some notion similar to universal time in the pre-theoretic sense. Regardless, how would you think of this time without destroying the relativisation of time/space through motion? I doubt the right answer is through an assertion against the relativisation of simultaneity (which screws with time = the succession of events), or against the way space expands/contracts relative to motion (which screws with its identification with pure extension).

I don't think an undetectable in principle difference should be elevated to a difference in practice. — fdrake

What difference can an undetectable thing make to practice? In what way is the latter 'elevated'?

I'm assuming 'foliates' here means, essentially, 'providing a coordinate system for'.

It is an ordering of events, and not otherwise specifying full coordinates. This event is simultaneous with that one, and prior to that third one over there. A foliation of the universe must order all events, not just local ones like an inertial reference frame does.

And the way in X foliates Y is always done differentiably (my differential geometry-fu isn't particularly strong). So I'm thinking of a foliation as the thing which describes the rate of change of an application of a coordinate system to a locality with respect to infinitesimal shifts in its origin.

Foliation specifies no origin. Just relations, and only temporal relations at that.

So at time t they were in the Hubble volume, and at some time t' they expanded out of it? That's the picture?

Pretty much yes. Time t' would be the event of that thing increasing its proper distance from us at the speed of light. Like from beyond the Hubble Sphere can still reach us by crossing back and eventually getting here. So maybe the image of it we see is one already outside that Sphere. There is an event horizon beyond which objects are undetectable from here even in infinite time.

About t', I speak of proper distance. In reality, time is frozen for it in our frame, and t' is unexpressible in our reference system, so t' represents the local time of both here and there when the contracting Hubble Sphere no longer includes that distant place. Something like that.

What implications do you draw from this? I've said previously that there are still things which can be said about spacetime in general with respect to increasing time - like the expansion of space when the metric tensor is an increasing function of time. I interpret foliations as ways of setting up for questions like this - they will provide a system of coordinates in which the evolution with respect to some variable, probably time in this case, can be indexed.

Well, IF presentism is true, AND the foliation suggested by GR happens to match the geometry of this 'present' boundary, then there is an actual velocity and location of all things. So from what I read, this 4D metric tensor means in part that the distance between two events is path dependent, and none of the paths is straight or obviously the actual separation. In 3D, a lot of that falls away, and two events need to be simultaneous to have a defined spatial separation. Not sure how much I'm addressing your question, or if I'm being accurate here.

I don't think this makes length contraction or time dilation go away, but it does implicate some notion similar to universal time in the pre-theoretic sense. Regardless, how would you think of this time without destroying the relativisation of time/space through motion? I doubt the right answer is through an assertion against the relativisation of simultaneity (which screws with time = the succession of events), or against the way space expands/contracts relative to motion (which screws with its identification with pure extension).

Of course this 3D view still works under relativity. The twin comes back younger because time progresses slower if you move faster. Clocks do not measure time in that view since there is no way to know if it is stationary. So they just measure local process rates. Relativity of simultaneity is an illusion then. As I said, the platform guy is using incorrect data to determine the two events were simultaneous. They're simultaneous in his frame, which is all he cares about. He cares not that his frame is not actually stationary, since that distinction makes zero difference.

What difference can an undetectable thing make to practice? In what way is the latter 'elevated'?

I was meaning something like the following: the equivalence principle in SR is essentially that motion is always relative motion - which introduces coordinate transforms - constrained by a cosmic speed limit -which introduces the scaling factors. In GR the equivalence principle is essentially between gravitation and an accelerated (that is curvilinear) coordinate system, and that intrinsic curvature is introduced by mass.

One of the motivating examples for the equivalence principle is the elevator thought experiment. Someone in an elevator could not tell the difference between the elevator moving down with constant acceleration due to a cord and the elevator moving down with constant acceleration due to a gravitational field. If you ignore tidal forces, there's nothing the person in the elevator could do to see if their acceleration is cord based or gravitation based.

In SR, this kind of thing manifests in equivalence between a rocket moving away from a planet with constant speed and the planet moving away from the rocket with constant speed.

I was trying to say that the undetectability of the difference between the relata in any equivalence principle should not be interpreted as an epistemic property, the equivalence in descriptions should be interpreted to be as real as its consequences - such as the relativity of simultaneity and length contraction. These things really happen and are not mere artefacts of coordinate system choice.

It is an ordering of events, and not otherwise specifying full coordinates. This event is simultaneous with that one, and prior to that third one over there. A foliation of the universe must order all events, not just local ones like an inertial reference frame does.

A foliation of space-time is a lot different from a foliation of time, you were referring solely to the latter? I don't understand how this is possible, given that in some reference frames event A can happen before B and in some event B can happen before event A - and there can be no strict total order (like <) with this property. How would you construct a foliation to produce a time which obeyed this?

One possibility would be to say that if there exist two events A and B, that they occur at the same time if and only if there exists a coordinate system in which they do occur at the same time. Or that there exists a coordinate system in which A is before B and B is before A. Of course coordinate systems exist in which B can be said to have occurred any time before A or B by adopting the frame of a particle with a particular motion (you can solve the Lorentz equations for v). But I think that this conception of time inappropriately quantifies over reference frames, and destroys the relativity of simultaneity. That is to say, simultaneity in SR is simultaneity in a reference frame, and the solvability of the Lorentz transform for arbitrary t shows that the ordered pairs of events in any such order are incompatible with a total order; unless time is trivialised in the sense that all events occur at the same time (which isn't presentism or a block universe).

So, the question is whether an order produced by such a foliation would resemble anything like a universal time. I'm not convinced that there is such an ordering, could you provide some references for where you're getting this from? I think you're losing too much detail when thinking of foliations as an order.

I hope you don't exhaust yourself in this quest. There are better things to do in life then try to make sense out of a theory that a) really has been of very little use other than fodder for sci fI stories b) contradicts itself c) creates more paradoxes and problems than it solves d) is on the way out.

Definitely a useful thread in demonstrating that Relativity is an ontological mess, with some nominal usefulness as simple transformation equations that no one really understands. Bergson analysis was spot on and Ellis, reluctantly, is going down that path. No block time, only frozen (memory) time.

I was meaning something like the following: the equivalence principle in SR is essentially that motion is always relative motion - which introduces coordinate transforms - constrained by a cosmic speed limit -which introduces the scaling factors. In GR the equivalence principle is essentially between gravitation and an accelerated (that is curvilinear) coordinate system, and that intrinsic curvature is introduced by mass.

One of the motivating examples for the equivalence principle is the elevator thought experiment. Someone in an elevator could not tell the difference between the elevator moving down with constant acceleration due to a cord and the elevator moving down with constant acceleration due to a gravitational field. If you ignore tidal forces, there's nothing the person in the elevator could do to see if their acceleration is cord based or gravitation based. — fdrake

Right. Tidal forces is effectively a non-local experiment. Make the box big enough and the mass close enough, and tides can be felt. In SR, it doesn't matter if one of the frames is special since that special nature is undetectable, and thus moot just like it doesn't matter to the elevator guy how the force being applied to his box is linear acceleration or bent space. Either way he holds his cup this way to prevent the drink from spilling. That's my point, that the reality behind the experience doesn't matter. It makes no useful predictions either way.

I was trying to say that the undetectability of the difference between the relata in any equivalence principle should not be interpreted as an epistemic property, the equivalence in descriptions should be interpreted to be as real as its consequences - such as the relativity of simultaneity and length contraction. These things really happen and are not mere artefacts of coordinate system choice.

I find myself resisting this. Is my length really contracted if in my frame, it's the length of everything else that's contracted? Seems like an artifact of of choice. On the other hand, the twin really does come back younger, despite the stay-home twin aging slower during both legs of the journey, from the frame of the rocket-twin. No mere arithmetic games can do that.

A foliation of space-time is a lot different from a foliation of time, you were referring solely to the latter?

Don't know what the latter is. Events are points in spacetime, not in time. Not trivial to order them, but it would be trivial to order moments in time.

I don't understand how this is possible, given that in some reference frames event A can happen before B and in some event B can happen before event A - and there can be no strict total order (like <) with this property. How would you construct a foliation to produce a time which obeyed this?

Different frames foliate space differently. That's what frames do. They specify an ordering, but not otherwise a coordinate system or an origin. An actual present would imply an objective foliation instead of a relative one, but SR is all about the physics in relative terms and isn't affected by a possible objective foliation.

One possibility would be to say that if there exist two events A and B, that they occur at the same time if and only if there exists a coordinate system in which they do occur at the same time.

Actually, under relativity, there exists a frame such that any two (reasonably local) events are simultaneous with only spatial separation, are at the same location with only temporal separation, or right on the edge between the two (on the edge of each other's light cone) in which case separation is 0/0 or undefined. From event A, all events outside its light cone are the first sort, all inside are the second sort. There can be no two points that don't meet one of those 3 cases. This is pure relativity, and has nothing to do with 3D space or absolute time.
So as for your comment above, no, A and B are not simultaneous just because some frame exists where they are. They're only simultaneous in that frame, and not in some other frame where they're ordered A first or B first. One can rotate the paper at will to put C above or below B in the time dimension (my events B and C were potentiall simultaneous in my paper example. A and B were inside each other's light cones and B is unambiguously after A).

Or that there exists a coordinate system in which A is before B and B is before A. Of course coordinate systems exist in which B can be said to have occurred any time before A or B by adopting the frame of a particle with a particular motion (you can solve the Lorentz equations for v). But I think that this conception of time inappropriately quantifies over reference frames, and destroys the relativity of simultaneity. That is to say, simultaneity in SR is simultaneity in a reference frame, and the solvability of the Lorentz transform for arbitrary t shows that the ordered pairs of events in any such order are incompatible with a total order; unless time is trivialised in the sense that all events occur at the same time (which isn't presentism or a block universe).

All true. Presentism just says that there is an objective correct answer as to which of A or B happens first. Relativity supplies frame dependent answers, not objective ones.

So, the question is whether an order produced by such a foliation would resemble anything like a universal time. I'm not convinced that there is such an ordering, could you provide some references for where you're getting this from? I think you're losing too much detail when thinking of foliations as an order.

Comoving time is such an ordering. Essentially, for every event in spacetime, the actual time there is the age of the universe in the frame that maximizes that age, or in which the red shift of distant objects (most notably the CMB) is isotropic. Same thing. That age is an objective one, and provides an objective ordering of all events.

So that's the 'frame' referenced when they say our galaxy is moving at about 0.2%c. Our solar system is on the side that cancels out some of that, so we're actually cruising at about 0.12%c. I put 'frame' in quotes because it is not an inertial reference frame, and is different for every point in space due to expansion.

Right. Tidal forces is effectively a non-local experiment. Make the box big enough and the mass close enough, and tides can be felt. In SR, it doesn't matter if one of the frames is special since that special nature is undetectable, and thus moot just like it doesn't matter to the elevator guy how the force being applied to his box is linear acceleration or bent space. Either way he holds his cup this way to prevent the drink from spilling. That's my point, that the reality behind the experience doesn't matter. It makes no useful predictions either way.

I think we agree on this. So long as you're not going to say that from the equivalence of motions we should posit one reference frame as privileged. I think you agree that such a decision has no consequences, and it doesn't mean anything to index motion to one privileged reference frame. The procedure for doing that is also antithetical to the logic of SR and GR.

Don't know what the latter is. Events are points in spacetime, not in time. Not trivial to order them, but it would be trivial to order moments in time.

It's trivial to order them within a given reference frame, not trivial to order them when multiple are being considered. Think it's impossible to provide a total order of events consistent with all motions, I saw you agreed with my argument that this is the case, so I don't think we need to discuss a total order without respect to a reference frame more.

All true. Presentism just says that there is an objective correct answer as to which of A or B happens first. Relativity supplies frame dependent answers, not objective ones.

Do you conclude that relativity thus refutes presentism?

So as for your comment above, no, A and B are not simultaneous just because some frame exists where they are. They're only simultaneous in that frame, and not in some other frame where they're ordered A first or B first. One can rotate the paper at will to put C above or below B in the time dimension (my events B and C were potentiall simultaneous in my paper example. A and B were inside each other's light cones and B is unambiguously after A).

Great, this is another convergence in how we see it. I think, anyway.

Comoving time is such an ordering. Essentially, for every event in spacetime, the actual time there is the age of the universe in the frame that maximizes that age, or in which the red shift of distant objects (most notably the CMB) is isotropic. Same thing. That age is an objective one, and provides an objective ordering of all events.

Comoving coordinates are those in which the expansion of the universe is uniform in every direction. So a measure of proper time between particles tagged to comoving frames would be a time measure with respect to the expansion of the universe. This makes good sense as a vantage point with which to define cosmological time. So when people speak about the age of the universe, we're speaking about it with respect to the history of intrinsic changes to its space.

However, there's nothing saying that this perspective must be adopted for all phenomena, and it does not remove the shenanigans relativistic motion induces on temporal orderings of events. The age of the universe is certainly a relevant parameter with respect to cosmic expansion, but it renders other motions untouched. That is to say, the sense of time derived from considering comoving frames must be conceptually consistent with the ability to induce changes in event orders by motion. There are real trajectories with which the expansion of the universe looks different.

Do you conclude that relativity thus refutes presentism? — fdrake

Again, no.
Relativity says the math works with or without the existence of magical invisible pink unicorns, but it doesn't refute said unicorns. Presentism is such an addition: Something irrelevant, undetectable, and unrefuted.

There are real trajectories with which the expansion of the universe looks different.

Yes, but I think that from any such trajectory, the universe appears younger than it would if it were a comoving object, and an observer on that trajectory would be aware of the deviation from the local mean.

All true. Presentism just says that there is an objective correct answer as to which of A or B happens first. Relativity supplies frame dependent answers, not objective ones.

And you don't think that simultaneity is a frame dependent phenomenon refutes the idea of there being an objectively correct answer to whether A is before B? Why or why not?

Oh I see the point of this thread now. You want to discuss the fact that relativity refutes presentism. Why didn't you just say that in the op?

"I don't want to discuss the question of whether relativity refutes presentism, I want to discuss the fact that relativity refutes presentism."

No, I just don't trust you or Rich to have anything I would find worthwhile to say on the topic.

Why not put that in the op then? Instead of a convoluted list of rules, simply state "Metaphysician Undercover, Rich, and any others who do not agree with the ontological implications of relativity, need not reply."

No, I just don't trust you or Rich to have anything I would find worthwhile to say on the topic — fdrake

Well, we did hear from Ellis (no slouch) and other physicists on the subject. But your quest is a noble one. To do what Einstein couldn't do, which is to make Relativity compatible with quantum theory. I believe your approach is probably better, just ignore quantum theory and build your block universe anyway. That is what you are desperately trying to preserve, isn't it? A block universe in a universe defined by quantum theory indefiniteness. Tough job, but heroic nonetheless.

Well, if you're happy to adopt the rules and stay on topic, I would've at least read your responses.

I gave you the consequences of trying to preserve the block universe. You can't without ignoring quantum theory. Ellis's attempts are more in track, but while he is reluctant to say so (he describes it as a revision), he just dismantled the block universe and Einstein's determinism.

So do you wish everyone to pretend that Relativity's block universe ontology is fine and quantum theory is all wrong? Just say so. Say you would like us all to ignore the elephant in the room.

I never broke rule 2. I never referred to any of the things listed in rule 2. I referred to the arbitrariness of "proper time", which ought not even be considered as a "deficiency of measurement", arbitrariness is just a standard feature of measurement. Your accusation was unfounded and just an excuse to disregard the points I was making.

You are assuming that relativity is true, and asking how this affects the ontology of time. The obvious answer is that "proper time" is completely arbitrary, meaning that there is no true, or real thing anywhere, which corresponds to this notion. It's like assuming a "metre", with no physical standard anywhere, to refer to. Do you accept the truth of this, concerning "proper time", or does it somehow break rule 2, and fall into the category of things you don't wish to discuss?

And you don't think that simultaneity is a frame dependent phenomenon refutes the idea of there being an objectively correct answer to whether A is before B? Why or why not? — fdrake

Your question can be interpreted different was, so I pick this one: Time as used in physics equations is what simultaneity is about, and relativity describes that. The second definition of time is from presentism, which is the rate of advancement of this 'present', which has no units, not even seconds per second since the two are different things. So I will say that presentism posits a different definition of simultaneous altogether, and there is no refutation of any part of the presentism because presentism is irrelevant.

That's the key word: irrelevant. It is an invisible pink unicorn, and not refuted for the same reason.

Answer number two:
Relativity is a scientific theory born of empirical observations. Presentism is a metaphysical interpretation of time, not a scientific theory at all. It has zero falsification tests, as do all interpretations. If such a test (a difference between 4D block and 3D universe) could be proposed and performed, then it could be elevated beyond interpretation and one or the other could be falsified. Meanwhile, relativity would stand because it works the exact same way in both interpretations.

Relativity is a scientific theory born of empirical observations. Presentism is a metaphysical interpretation of time, not a scientific theory at all. It has zero falsification tests, as do all interpretations. If such a test (a difference between 4D block and 3D universe) could be proposed and performed, then it could be elevated beyond interpretation and one or the other could be falsified. Meanwhile, relativity would stand because it works the exact same way in both interpretations.

I don't see how these two things can be compatible:
(1) There is a unique order of events induced by the idea of the present in presentism.
(2) Events A and B can be ordered differently depending on the motion of a particle.

I don't understand how you can say 'presentism is independent because it's metaphysics', when one of its implications is negated by how time works in SR.

I don't see how these two things can be compatible:
(1) There is a unique order of events induced by the idea of the present in presentism.
(2) Events A and B can be ordered differently depending on the motion of a particle.

I don't understand how you can say 'presentism is independent because it's metaphysics', when one of its implications is negated by how time works in SR. — fdrake

IMO, presentism explicitly rejects (2) cause it has to reject the relativity of simultaneity as you have noted. That doesn't mean that it rejects the science of relativity though. More specifically, you can accept the mathematical models and the empirical predictions of the theory without accepting the relativity of simultaneity itself (essentially privileging one order of events over the others). Similarly we can accept the science of QM without accepting that indeterminism is true (as in the copenhagen interpretation) or that multiple parallel universes exist (like in the MWI). That is the reason why we call them "interpretations" instead of "theories", "metaphysics" instead of "physics". In that sense presentism is "independent" from both SR and GR. Do you agree with this?

I certainly think it's possible to think that there is a real unique ordering of events by rejecting relativity. But I don't think it's possible to think that there is a real unique ordering of events while accepting relativity.

Adopting a specific reference frame, or class of reference frame, can be useful in inducing an order of events relative to a process - like picking coordinate systems in which the expansion of the universe is spherically symmetric for probing the age of the universe - but this doesn't negate anything from SR.

I think the more interesting endeavour, rather then debating whether presentism is true or not, or accepting or rejecting SR based on previously held principles, is to try to make sense of its implications in a naturalistic metaphysics, and what constraints they place on metaphysics of space and time.

I'd draw the following conclusions from SR and GR:

(1) Space, time and motion are distinct but inseparable, no two should be taken as a derivative category or combination of the other.
(2) Time cannot be thought of as a unique succession of events, as this is contradicted by the real motion of objects.
(3) Despite of (2), time can be immanently defined within a process to study its history. Perhaps different coordinate frames can be thought of as immanent definitions of space and time with respect to motion or mass.
(4) Space cannot be considered as an unconditioned field of pure extension, since motion doesn't just happen through it over time, motion and mass change space itself.
(5) The behaviour of space and time is induced by motion and mass, the former being extrinsic properties of space/time and the latter giving intrinsic properties of space/time.
(6) Different metaphysics may be appropriate depending on whether SR or GR are in play or not, SR isn't very relevant for slow moving objects or intrinsically curved space, GR isn't very relevant when there is no intrinsic curvature to space.

Methodologically, there are some interesting implications of (6): different domains of things (in the broadest sense) may require different ontologies. This is why I posted previously in terms of regional ontologies of SR and GR.

I see it as intellectually lazy to posit metaphysics as independent from science, much more interesting to attempt a naturalistic metaphysics which is informed by current scientific theories. Rather than, say, dogmatic adherence to Aristotelian physics or New Age Quantum Woo.

I certainly think it's possible to think that there is a real unique ordering of events by rejecting relativity. But I don't think it's possible to think that there is a real unique ordering of events while accepting relativity. — fdrake

Maybe you can define what you mean by "relativity" for me cause I think we are using the term differently.

To me, when I speak of "relativity" and "quantum mechanics" I am referring to them as scientific theories through and through. That is, the postulates, the mathematical formulas, and the predictions that we derive from them. Everything else isn't relevant. This is why I say that presentism is compatible with SR and GR, because as far as a physicist is concerned on the matter, it isn't an idea that has been falsified. It has the same status with respect to relativity as does determinism to QM.

I see it as intellectually lazy to posit metaphysics as independent from science, much more interesting to attempt a naturalistic metaphysics which is informed by current scientific theories. Rather than, say, dogmatic adherence to Aristotelian physics or New Age Quantum Woo. — fdrake

I agree with this. I am certainly not suggesting that we shouldn't base our metaphysics in part on our scientific theories. By "independent", I just meant that it cannot be falsified via. the scientific method. If a metaphysical theory such a presentism or eternalism could be falsified in such a manner then they would no longer be metaphysical theories.

I don't see how these two things can be compatible:
(1) There is a unique order of events induced by the idea of the present in presentism.
(2) Events A and B can be ordered differently depending on the motion of a particle. — fdrake

The first speaks of objective ordering, and the latter means that the observer is free to order events differently, and physics will still work without detectable differences, rendering any potential objective ordering undetectable. The latter is about empirical observation, not about an interpretation of what actually is. And #2 should be "depending on the reference frame", not depending on particle motion. Motion.

I don't understand how you can say 'presentism is independent because it's metaphysics', when one of its implications is negated by how time works in SR.

Presentism doesn't comment about how time works in SR. Presentism was around well over a century ago, and SR was not in any way suggested by it. Not sure when the term was coined, since the interpretation is far older than the name needed to distinguish it from alternative interpretations.