This assertion is false in General Relativity. In GR, all of space-time exists forever. The past still exists and the future already exists. In GR time is kind of like space. My father died when I was young, but in GR, he's still there, just at a different location in time than I am. It's kind of like he's in California, only in time there's less freedom of movement than there is in space. So, while my father is alive and well in California (or actually 1969), I just can't get to California from where I am currently located.

In GR, I am not located below my feet or above my head, and likewise, I am not located before I was born or after I die. But I exist always between the bottom of my feet and below the top of my head and for the time between when I was born and before I die. — Douglas Alan

Let me be more clear with a more specific example. Let's say that we build or find a closed timelike loop. And now let's say that we have a million people traverse this timelike loop, but traverse it differently so that they all end up in different times in the past. And at each of these times, let's say that each of these million people is causally connected to billions of other people.

So, we now have a million different people who were here earlier today but are now spread across the past. Did they cease to exist? Or do only the locations surrounding these million people exist in spacetime? What about all the billions of people that are causally connected to them?

I'm sure that someone could come up with some crazy explanation for this which doesn't entail eternalism, but it sure to be ad hoc and completely violate Ockham’s razor. — Douglas Alan

I've presented a thought experiment where a million people use a closed timelike curve to all travel to different times. As far as I understand things, these types of thought experiments are generally taken by physicists to entail eternalism, assuming GR is true enough that closed timelike curves are actually possible.

Though even Special Relativity makes presentism difficult to defend. See the Stanford Encyclopedia of Philosophy for more details.

I went to a Philosophy conference at MIT filled to the brim with professional philosophers. In one of the talks, the moving spotlight theory was given a quick refutation as part of the argument. Here's a longer discussion. Though this author actually defends the moving spotlight theory as not being incompatible with Special Relativity:

https://web.mit.edu/bskow/www/research/timeinrelativity.pdf

There was Q&A after the talk. Not a single philosopher spoke up to question the implicit eternalism that was presented, nor to support the moving spotlight theory. My natural conclusion is that eternalism is not hugely controversial. Or at least not amongst the philosophers who might come to MIT for a conference.

In any case, eternalism is a simple and natural explanation for what happens in the thought experiment. It is also in my experience how virtually all scientists who talk about GR, talk about GR.

I consider eternalism prima facie true, assuming the thought experiment is actually possible.

I think that anyone who wants to reject eternalism without rejecting the possibility of this thought experiment has a lot of work to do! And I find it highly improbable that whatever theory is presented as an alternative would be widely accepted as more likely.

As for who is better equipped to address such questions, I don't consider philosophers better equipped than scientists. Particle physicists used to consider virtual particles just a mathematical convenience, rather than virtual particles being real. Now virtual particles are universally accepted as real. I don't consider philosophers to be better equipped than particle physicists to determine the metaphysical status of virtual particles wrt existence, and in the unlikely case that philosophers come to a different conclusion than physicists on this issue, I would most likely side with the physicists. — Douglas Alan

I've presented a thought experiment where a million people use a closed timelike curve to all travel to different times. As far as I understand things, these types of thought experiments are generally taken by physicists to entail eternalism, assuming GR is true enough that closed timelike curves are actually possible. — Douglas Alan

You have to be careful when you say "different times," unless they are all on the same worldline, which is not the case here. From what I gather (and I have to admit, I hadn't encountered this type of objection before; the most common objections from relativistic physics have to do with the relativity of simultaneity in Minkowski spacetime), closed time-like curves and some other other topologies that are theoretically allowed by GR are a prima facie problem for presentism because they cannot be foliated (i.e. you cannot slice spacetime along constant-time hypersurfaces). And even if we stay with one worldline, closed time seems to imply that there can be no objective "pastness" and "futureness," as the traditional A-theory requires. But it is still possible to recover a local surrogate of presentism even in a spacetime with time loops - see for instance Steven Savitt, Time Travel and Becoming (2005) and Phil Dowe, A and B Theories of Closed Time (2017). A more common response for a presentist though is to deny that such non-foliable spacetimes are (meta)physically possible, and that is a defensible position, since we don't know for a fact that they are.

Outside of closed time-like curves though GR - specifically, the GR of our universe - is said by some to be more hospitable to presentism than generic SR because its symmetries naturally lend themselves to defining special reference frames and privileged observers (e.g. the rest frame of local matter or the CMB), and those are said to be good candidates for defining objective now. (I don't think I buy this argument myself.)

I went to a Philosophy conference at MIT filled to the brim with professional philosophers. In one of the talks, the moving spotlight theory was given a quick refutation as part of the argument. Here's a longer discussion. Though this author actually defends the moving spotlight theory as not being incompatible with Special Relativity:

https://web.mit.edu/bskow/www/research/timeinrelativity.pdf

There was Q&A after the talk. Not a single philosopher spoke up to question the implicit eternalism that was presented, nor to support the moving spotlight theory. My natural conclusion is that eternalism is not hugely controversial. Or at least not amongst the philosophers who might come to MIT for a conference. — Douglas Alan

There is some truth to this, but if you haven't yet surveyed the extensive literature on the subject, then perhaps the review articles that I posted at the top will go some way towards disabusing you of the notion that this is a settled issue in philosophy.

Dean Zimmerman writes: "The A‐theory is almost certainly a minority view among contemporary philosophers with an opinion about the metaphysics of time." (He frames presentism as a variety of the A theory.) "Nevertheless, it has many defenders—Ian Hinckfuss, J. R. Lucas, E. J. Lowe, John Bigelow, Trenton Merricks, Ned Markosian, Thomas Crisp, Quentin Smith, Craig Bourne, Bradley Monton, Ross Cameron, William Lane Craig, Storrs McGall, Peter Ludlow, George Schlesinger, Robert M. Adams, Peter Forrest, and Nicholas Maxwell, to name a few." He notes further:

Although it seems that most philosophers who take a position on the matter are B‐theorists, nevertheless, A-theorists have made up a significant proportion of the metaphysicians actually working on the A‐theory–B‐theory debate during the past ten or fifteen years. We A‐theorists might be inclined to explain this as a case in which the balance of opinion among the experts diverges from that of the hoi polloi. There is an alternative explanation, however. I have the impression that there is a much larger proportion of incompatibilists (about free will and determinism) among those actually writing on free will than among philosophers more generally. A similar phenomenon may be at work in both cases: The B‐theory and compatibilism are regarded as unproblematic, perhaps even obviously true, by a majority of philosophers; they seem hardly worth defending against the retrograde views of A‐theorists and incompatibilists. Philosophers sympathetic to A‐theories or incompatibilism, on the other hand, are more likely to be goaded into defending their views in print precisely because they feel their cherished doctrines are given short shrift by most philosophers. — Dean Zimmerman, Presentism and the Space‐Time Manifold[/url], The Oxford Handbook of Philosophy of Time (2011)

Laying my own cards on the table, I am not a proponent of either A- or B-theory, eternalism, presentism or possibilism; rather, I suspect that there isn't a substantive difference between them. But I've only dipped my toes into this subject on occasion, so I haven't made up my mind.

As for who is better equipped to address such questions, I don't consider philosophers better equipped than scientists. — Douglas Alan

I do, in general. For one thing, scientists rarely consider the same questions as philosophers. Their approach tends to be instrumentalist; excepting those few who work on foundations (which is widely considered to be a philosophical subject among scientists, and thus widely discouraged), they favor questions that can be resolved empirically, rather than through conceptual analysis or other approaches employed by philosophers. Nearly all the literature on this subject that I have come across was written by philosophers, many of whom understand the relevant science very well (for such general questions the scientific underpinnings aren't that difficult or esoteric). And scientists who do opine on philosophical questions are subject to the same competence limitations as other laymen.

So a presentist walks into a spacetime bar, and the wormhole behind the counter asks: "Why so tense?"

This is a split of a side discussion in another thread (starting here), which I thought merits its own topic. I will just quote from some posts and continue here.

Some background: — SophistiCat

"We can't see this block, we're not aware of it, as we live inside the cement of spacetime. And we don't know how big the block universe we live in is: "We don't know if space is infinite or not. Or time - we don't know whether it has a beginning or if it will have an end in the future. So we don't know if it's a finite chunk of spacetime or an infinite chunk."

thats a quote from:
https://plus.maths.org/content/what-block-time

Time can never be measured exactly (or to be more precise, universally) because time is effected by the speed the measuring device is traveling at(clock). I read the book "a brief history of time". Because nothing ever exceeds speed C, to put it simply the various vectors of the whole of an object, slow down so that the combination of the vectors never exceed C.

To my limited understanding, Einstein based his theory of Relativity on the idea that we live in a block universe. I don't know if this belief has changed alot in the past 100 years or not. Nor do i even know if that first statement in this paragraph is valid. I'll read those 3 articles later.

Laying my own cards on the table, I am not a proponent of either A- or B-theory, eternalism, presentism or possibilism; rather, I suspect that there isn't a substantive difference between them. But I've only dipped my toes into this subject on occasion, so I haven't made up my mind. — SophistiCat

I tend to towards the threshold of eternalism (to my understanding of eternalism). However i see the universe as just a collection of objects and particles (with a "web" of emotions going through it to put it overly simple). When particles move the only way to measure that movement accurately (in terms of speed as opposed to angles and geometry) is within a small subset of the universe (a given area of space). The only way to go back in time is to place each particle back in the same position only relative to the other particles as it was in that remembered time in the past. The vectors or paths of motion also have to be exactly the same. Our memories are extremely rough notions of what the past really was given all the variables involved in solidying exactly what the past was.

I do, in general. For one thing, scientists rarely consider the same questions as philosophers. Their approach tends to be instrumentalist; excepting those few who work on foundations (which is widely considered to be a philosophical subject among scientists, and thus widely discouraged), they favor questions that can be resolved empirically, rather than through conceptual analysis or other approaches employed by philosophers. Nearly all the literature on this subject that I have come across was written by philosophers, many of whom understand the relevant science very well (for such general questions the scientific underpinnings aren't that difficult or esoteric). And scientists who do opine on philosophical questions are subject to the same competence limitations as other laymen. — SophistiCat

This is wishful thinking on your part. People like to watch movies but the reason Physicists typically stick to very slowly (using software) finding a more precise number to attach to an important variable, is that alot of the "fun" stuff ended with Einstein. Einstein was a genius but as time progresses, the type of work that has to get done in a given field of study changes.

My stance on this topic is well known. While an eternalist, I've started an advocatus diaboli thread on the old PF defending presentism. There's no falsification test for it, and thus relativity theory doesn't demonstrate the topic one way or the other.

OK, you didn't say 'demonstrate', but it very much suggests it anyway. The vast majority of non-religious physicists that know their relativity (many (most?) probably don't) hold a block view. The view is semi-incompatible with the promises of major religions, and thus meets significant resistance without actually admitting the reason driving the resistance.

OK, you didn't say 'demonstrate', but it very much suggests it anyway. The vast majority of non-religious physicists that know their relativity (many (most?) probably don't) hold a block view. The view is semi-incompatible with the promises of major religions, and thus meets significant resistance without actually admitting the reason driving the resistance. — noAxioms

But what's the relationship between the block universe (a physical model) and the metaphysical interpretation of time? It seems to me that there are two different "natures" of time: how time operates in our best predictive models, and what this means. Those two shouldn't be mixed.

To my limited understanding, Einstein based his theory of Relativity on the idea that we live in a block universe. — christian2017

No, relativity does not assume any of the questions that are at issue, such as whether the present is in some sense more "real" than the past or the future, or whether past, present and future tenses are objective properties and not merely indexical. Some argue that relativity makes anything but the block universe untenable, but not because that is already assumed by the theory.

To be clear, "block universe" in this context is not merely a visualization of the spacetime continuum (in Newtonian physics you can also visualize the space and time dimensions as a single block). Here it is a synonym for the B-theory of time or for eternalism, which are metaphysical positions.

But what's the relationship between the block universe (a physical model) and the metaphysical interpretation of time? — Echarmion

Yes, that is a question that is often glossed over. Scientists in particular often implicitly assume the stance of scientific realism when talking about time, i.e. that all and only those things that are posited by our best scientific theories are real (or something like this) - which is natural, since methodological realism, which we assume when doing science, and metaphysical realism are easily confused. But whatever the merits of this position, it is a philosophical position and must be acknowledged and defended as such.

It is uncontroversial that physics in general, and relativistic physics in particular does not endorse presentism or the A series. But what conclusions are we warranted to make from that fact?

In what sense do virtual or real particles live outside the mathematical equations?

I mean also unicorns, dragons and God/s can be real in some sense...

But what's the relationship between the block universe (a physical model) and the metaphysical interpretation of time? — Echarmion

Sorry, but I consider them to be the same model, both metaphysical interpretations of space and time.

Sorry, but I consider them to be the same model, both metaphysical interpretations of space and time. — noAxioms

If that's the case, why is it of particular note what the majority of physicists thinks?

I think the philosophical preference of a physicist, one who knows what he's talking about, typically has better grounding than a similar opinion from someone less familiar with the physics involved.

I for one know my physics enough to know that I've never seen an empirical falsification of either interpretation, and hence any logical argument must proceed from non-empirical assumptions. I've done that process and concluded what I conclude, but my stance keeps changing as I learn more, so the odds that my current favored view corresponding to 'the way that it actually is' (if there is such a thing) is pretty minimal.

In what sense do virtual or real particles live outside the mathematical equations? — MathematicalPhysicist

In what sense do chairs live outside the mathematical equations?

|>ouglas

No, relativity does not assume any of the questions that are at issue, such as whether the present is in some sense more "real" than the past or the future, or whether past, present and future tenses are objective properties and not merely indexical. Some argue that relativity makes anything but the block universe untenable, but not because that is already assumed by the theory.

To be clear, "block universe" in this context is not merely a visualization of the spacetime continuum (in Newtonian physics you can also visualize the space and time dimensions as a single block). Here it is a synonym for the B-theory of time or for eternalism, which are metaphysical positions. — SophistiCat

oh ok. I don't have a strong opinion at this point. To put it simply, i believe whatever form of block universe we live in, that scientific determinism determines all of our actions. Any future decisions are based on what we learned from our own actions or what we observed in the past. Some would say the past present and future exist all at one time, however i would say that all depends on "how big you are". This guy you are talking to exists now. Perhaps there are others on this forum who are "bigger".

There is some truth to this, but if you haven't yet surveyed the extensive literature on the subject, then perhaps the review articles that I posted at the top will go some way towards disabusing you of the notion that this is a settled issue in philosophy. — SophistiCat

I take it that nothing is ever settled in Philosophy. But I've also noted that if you swim against the tide, the onus then is usually on you to make a very strong case, and if you swim with the tide, you need say little to defend your position.

Does this make the tide necessarily right? Of course not. Tides change from time to time, and philosophical debates can rage for thousands of years. But if we are to believe that Philosophy is of any use at all, other than just as a means of honing one's ability to think and argue well and coherently, it seems that one must be committed to the belief that following the tide is the path that is generally most likely to lead to knowledge.

I did some skimming of the references you provided that were actually available to me. One thing I noted that was of interest is that in a closed timelike curve, there can be no consistent entropy gradient that gives time its forward arrow. If there were such a gradient, you couldn't return in the loop to the same point in space-time, since that point must have the same entropy, and consequently it wouldn't be a closed curve. It seems that this would make traveling around one unpleasant. But, I suppose if it were large enough, you could refrain from going all the way around the loop, and I suppose there could be a gradient that does not change direction in the part that you stay on. Well, this is probably neither here nor there for this discussion, but I found it an interesting worry.

So, I've been thinking about time-traveling wormholes instead. Let's say that you enter a wormhole headed for the past. Your lovely wife died and you are heartbroken. You wish to be with her again. While you were with her, she mentioned that she had had a wonderful boyfriend in the past who was a lot like you, only older. Unfortunately, he eventually died in a freak gardening accident, but they had been very happy together for many years while he was alive.

You decide that you must have been/will be this man, and so you enter the wormhole and begin your new life as your dead wife's sugar daddy. Only she's no longer dead from your new location in time.

So what is happening here with respect to existence? We already know the eternalist view, so I will elide that. But there are two other possibilities that I can think of:

(1) When you enter the wormhole, reality splits in two, and now there are two presentist universes. Though they are both on deterministic rails. Such a split happens every time someone enters the wormhole. Oh, but wait? What about random particles that enter the wormhole. Do they cause a myriad of forking realities?

I find this view to be highly unsatisfying.

(2) Presentism is correct and the only existing point in time is now. When you enter the wormhole you cease to exist. I.e., you die. You committed suicide. It's really very tragic.

But to soften this tragedy, there was a time in the past when there were two of you. Unfortunately, one of you just appeared without any cause or history, and so this mysteriously appearing version of you is not really you at all, but rather a weird clone of you made by space and time out of nothing but random particles and energy.

When you entered the wormhole, you were hoping for a continuity of consciousness. You expected to be traveling into the past. But nothing could be farther from the truth. You died. Nothing more. And it just so happens that someone else just like you, but not you, was brought into existence, at precisely the time and place you wished to travel to. Not only is your suicide a tragedy, but it is compounded by the fact that in the distant past some imposter got to spent all this wonderful time with the woman of your dreams.

I also find this view to be highly unsatisfying.

|>ouglas

In what sense do virtual or real particles live outside the mathematical equations? — MathematicalPhysicist

We get a sense that some theoretical entity is more than a mathematical contrivance if it does not go away when we change the model, i.e. if we find it indispensable. Our sense of the reality of the thing also strengthens when we find more independent ways of probing it with empirical tests. However, these criteria are not so solid and there is room for much ambiguity in edge cases. Physicists do not usually obsess over questions of whether something is really real or somewhat real or not quite real.

General Relativity does not depend on block time, it merely depends on mathematically treating it in a manner analogous to spatial dimensions. That it should be treated this way does not establish this as ontological.

It's often said that Relativity entails the block universe, or eternalism, or the B-theory of time (whatever you call it), but that's a common misconception, as much as the idea that Quantum Mechanics entails indeterminism.

In the latter case, indeterminism only holds for the most widely adopted interpretation of QM, the Copenhagen interpretation, but there are others. For instance, one can preserve determinism by incorporating some form of non-locality, as in Bohmian mechanics. One can also introduce multiple parallel universe as in Many Worlds as well. They're all equally valid ways of understanding QM as far as the scientific theory goes.

Though less well known (perhaps on account of the fact that Relativity isn't notorious for having 100 different interpretations unlike QM) the same goes for both SR and GR. One can introduce a preferred frame (or foliation) to designate an absolute sense of time, and that'd be compatible with the scientific theory so much as it doesn't make any differing empirical predictions. In fact, one of the predecessors to SR was an empirically equivalent model that included an absolute frame called the Lorentz Ether Theory. With respect to GR, there are also alternative formulations like Shape Dyanamics which incorporate an absolute time in exchange for absolute scale.

Of course there are questions about whether we should introduce such additional structure in the first place to account for our traditional sense of time, but that's a question of metaphysics, not physics.

Some background:

Kristie Miller, Presentism, Eternalism, and the Growing Block, A Companion to the Philosophy of Time (Wiley, 2013)

David Ingram, Presentism (Stanford Encyclopedia of Philosophy)

Steven Savitt, Being and Becoming in Modern Physics (Stanford Encyclopedia of Philosophy)

Dean Zimmerman, Presentism and the Space‐Time Manifold, The Oxford Handbook of Philosophy of Time (2011) — SophistiCat

A Physics Forums Insights article I've found useful is The Block Universe – Refuting a Common Argument.

Essentially:

(1) Relativity of simultaneity + all observers' 3D worlds (surfaces of simultaneity) are real at every event = block universe

The point of contention is generally the second premise. However experimental results that demonstrate relativity of simultaneity can only be communicated at the speed of light, and all such communicated events are in the observer's past light cone. So the second premise is unnecessary - the following is sufficient to account for our observations:

(3) All events in the past light cone of a given event are real (i.e., fixed and certain) for an observer at that event.

Since the second premise is unnecessary, Relativity does not imply a block universe (at least on that argument).

As David Mermin puts it:

That no inherent meaning can be assigned to the simultaneity of distant events is the single most important lesson to be learned from relativity. — David Mermin, It's About Time

I did some skimming of the references you provided that were actually available to me. One thing I noted that was of interest is that in a closed timelike curve, there can be no consistent entropy gradient that gives time its forward arrow. If there were such a gradient, you couldn't return in the loop to the same point in space-time, since that point must have the same entropy, and consequently it wouldn't be a closed curve. It seems that this would make traveling around one unpleasant. But, I suppose if it were large enough, you could refrain from going all the way around the loop, and I suppose there could be a gradient that does not change direction in the part that you stay on. Well, this is probably neither here nor there for this discussion, but I found it an interesting worry. — Douglas Alan

This also brings up another relevant question: does the coordinate time of a mathematical model (in this case the theory of relativity), physical time (time that is measured by physical clocks) and metaphysical time always coincide? I am more than a little skeptical of the metaphysical time (as distinct from the other two), although some A-theorists find themselves more-or-less forced to assume it in order to rescue the hypothesis. But as for mathematical vs. physical time, hypothetical time loops in GR spacetime may be one of the instances where they pull apart. And they highlight a problem with relativity as a model of time: relativity does not have a concept of the arrow of time. Sure, the coordinate time has two opposite directions, but there is no fundamental distinction between them; the designations of "future" and "past" are purely conventional in the model. If what you are saying about closed timelike curves is correct, it appears that even as the physical time reverses its flow, the coordinate time does not notice the fact, merrily ticking along. (Another interesting question is what happens after the heat death or, in some models, at the Big Bang, where physical time may effectively disappear, even as coordinate time goes on. But that is a discussion for another time, as it were.)

Relativity does have the concept of the passage of time, and notably it admits differential rates of time, when the duration of proper time is shorter along some future-directed worldlines than others, as in the twins paradox - in effect giving us future time travel. The way we, as empiricists, can know that this really does capture at least some aspects of the flow of time is that this is something that has observable physical consequences: the differential rates of time's passage can actually be marked and recorded by physical clocks in properly conducted experiments. But the question remains: are there limits to the fidelity of this model when it comes to describing time?

I am not yet sure what to make of past time travel. Not surprisingly, there is plenty of literature on this issue as well, including discussions of causality paradoxes (see for instance SEP articles on time, or Kutach's article in A Companion to the Philosophy of Time, or Smeenk and Wüthrich's article in The Oxford Handbook of Philosophy of Time). But I think I'll leave this can of worms for another time...

Well, if there is no such thing as simultaneity then how does a presentist, who, it seems, depends on the notion of a present/now, make her case? The concept of the present/now turns on that of simultaneity or so it is claimed.

In spatial terms the matter of events occurring in the same place (the "now" of space) appears to be nebulous; as the "size" of the space varies, the number of events occuring in the same space (the "now" of space) also varies. The rule of thumb seems to be that as the space available is increased the number of events that are spatially "simultaneous" also increases and upon downsizing the space, the number of events that can occur in that region also decreases until, it seems, at a single point in space only ONE event can occur.

For time the situation is quite different. Yes, increasing the time-period results in an increase of the number of events in that zone of time but, unlike space, reducing time down to a single instant doesn't limit the events possible down to ONE: many, possibly an infinite, number of events can occupy a single moment in time.

The "now" of time is not limited in the same way as the "now" of space. Simultaneity is simply the temporal concurrence of events at a single instance of time. It maybe obvious that moving along the time axis we may have an infinite number of events at a single point in space. Does this mean that moving along the space axis we can have an infinite numner of events at a single point in time? Yes.

My concern is how simultaneity defines the present/now? Is the idea of spatial "simultaneity" critical to the definition of a spatial "now"? When I speak of such a thing as the same spot, do I depend on events having taken place at that particular spot? Not really, right? A location/spot is defined in terms of a frame of reference which even if arbitrary has nothing to do with events at all. In other words, while different events may occur at the same spot, that they do has nothing to do with the notion of a location/point in space.

Likewise, a temporal spot, the present/now, shouldn't be predicated on the notion of simultaneity which is basically events that occur at a particular moment. The now/present, like a location in space, is defined, not by any feature of events like simultaneity, but by a frame of reference and how any particular point, spatial or temporal, exists in relation to that frame of reference.

I guess I don't see the relevance of simultaneity to the definition of the present/now on the basis of some kind of symmetry between space and time.

However, it can be said that there is no ONE "now" in time and that is demonstrated by the difference in the set of simultaneous events as the frame of reference varies.

a problem with relativity as a model of time: relativity does not have a concept of the arrow of time — SophistiCat

I think you're just saying that relativity doesn't entail an arrow of time, nor is it dependent on there being one. Nevertheless, relativity is consistent with there being an arrow of time. Relativity is not a theory of everything.

As always, it's impossible to tell when someone claims to represent opponents' arguments made elsewhere, whether they are doing it accurately. Anyway, the arguments as presented sound pretty confused, which doesn't inspire one to follow their refutation, especially since the refutation is pretty confused as well.

For example, after extensive paraphrasing, the blogger ends up with the following thesis:

(1) Relativity of simultaneity + all observers’ 3D worlds are real at every event = block universe

I take it from the context that "observers" here are not meant literally, but rather as virtual probes that could potentially be dropped anywhere within the spacetime block. Oh, wait. Well, he does go on to state the obvious: that the second premise already presupposes the conclusion. But then for some reason he backtracks and adds that the first premise is needed as well, although he doesn't explain why.

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. — Kristie Miller, Presentism, Eternalism, and the Growing Block, A Companion to the Philosophy of Time (Wiley, 2013)

I appreciate that Presentism has many problems of its own, but it always amazes me that proponents of Eternalism so readily accept the static, motionless nature of their own temporal landscape. I'm no scientist, but much of science appears to be reliant on a dynamic world involving rates of change, momentum, spin, acceleration, velocity, etc.

Yes, it's difficult to square what appears as a very dynamic universe with block structure. All the mathematics I dabble in involves patterns of movement, so I am biased. :cool:

If what you are saying about closed timelike curves is correct, it appears that even as the physical time reverses its flow, the coordinate time does not notice the fact, merrily ticking along. (Another interesting question is what happens after the heat death or, in some models, at the Big Bang, where physical time may effectively disappear, even as coordinate time goes on. But that is a discussion for another time, as it were.) — SophistiCat

This is more evidence for eternalism if you ask me. E.g., why is it that "metaphysical time" just happens to agree with the arrow of time placed by the direction of increased entropy? What a fortunate coincidence, since it would be a crazy world otherwise.

For eternalism, there is no problem here.

On the other hand, I guess presentists could just say that the world had a 50/50 chance, and fortunately, it came up heads.

|>ouglas

P.S. Or maybe presentism is true, but metaphysical time is actually reversed from the direction of increased entropy. Maybe we are constantly hurtling forward into the past without even knowing it!

This is more evidence for eternalism if you ask me. E.g., why is it that "metaphysical time" just happens to agree with the arrow of time placed by the direction of increased entropy? What a fortunate coincidence, since it would be a crazy world otherwise.

For eternalism, there is no problem here. — Douglas Alan

Except that an arrow of time assumes a dynamic world?

For example, after extensive paraphrasing, the blogger ends up with the following thesis:

(1) Relativity of simultaneity + all observers’ 3D worlds are real at every event = block universe

I take it from the context that "observers" here are not meant literally, but rather as virtual probes that could potentially be dropped anywhere within the spacetime block. Oh, wait. Well, he does go on to state the obvious: that the second premise already presupposes the conclusion. — SophistiCat

The argument is simply that relativity of simultaneity isn't sufficient by itself to imply a block universe. An additional premise is required, which is that all events to the past of any observer's surface of simultaneity are fixed and certain.

Observer is just being used in its common physics sense - an inertial reference frame. But the specific example referenced - the Andromeda Paradox - has sentient observers.

The "paradox" says that the alien invasion launch is already fixed for one of the people on Earth (since it is in the past of their surface of simultaneity). But this conclusion assumes the above additional premise. Moreover, the alien launch is not in the past light cone of anyone on Earth, it's in a spacelike separated region. So there is no reason to conclude from Special Relativity that the alien invasion is fixed for observers on Earth.

BTW the Physics Forums thread for that article is at:
https://www.physicsforums.com/threads/the-block-universe-refuting-a-common-argument-comments.843000/

But then for some reason he backtracks and adds that the first premise is needed as well, although he doesn't explain why. — SophistiCat

Well if relativity of simultaneity is rejected, i.e., simultaneity is absolute, then every observer has the same surface of simultaneity which then doesn't imply a block universe. So both premises are needed to imply a block universe.

As always, it's impossible to tell when someone claims to represent opponents' arguments made elsewhere, whether they are doing it accurately. — SophistiCat

Case in point:

it always amazes me that proponents of Eternalism so readily accept the static , motionless nature of their own temporal landscape. I'm no scientist, but much of science appears to be reliant on a dynamic world involving rates of change, momentum, spin, acceleration, velocity, etc. — Luke

I don't think the typical eternalist would assert a motionless landscape. An object is here at time zero, and over there at time 1, thus there is motion, spin, acceleration, velocity and all that.

Except that an arrow of time assumes a dynamic world? — Luke

The block view does not lack dynamics. The arrow of time kind of assumes that view since I don't see how you can draw an arrow in a direction that is posited not to exist.