Is Time Static Like Other Dimensions?

[xantox]

There's no particular reason to think that the universe will ever 'rewind' or 'recollapse' (has it collapsed before? ).

This is simply completely unknown. There are no known fundamental reasons preventing "a priori" the possibility that the universe could recollapse. If that happens it would not mean something would rewind and people start becoming younger, but simply that the radius of the universe could no longer be considered a well defined clock. And if it does not recollapse, we can't be exactly sure that it is a global clock either, since the observed radius could be just a local feature.

I think that the list of possible candidates for a fundamental physical process is pretty short. The choice of the isotropic expansion of the universe certainly isn't an arbitrary one. Where would you look? The idea that the internal dynamics is shaped and driven by the force and energy of the expansion makes sense to me.

It is a mutual game, there is no "first engine" driving all the rest – all fields cooperate on the same footing to yeld the full dynamics of GR.

So, the idea is, there's a universal scale dynamic and all internal processes and properties (arrow of time, inertia, a limitation on propagational speed, gravity, em, etc.) are byproducts of, and circumscribed by that dynamic.

In my view, GR undermines any tentative to defend presentism intended as a condition on the realism of events based on clock readings. But other weaker forms of presentism may still remain compatible with GR (and this is why I said in the first post that there is no final word on the debate) in the case they are not relying on time intended as clock readings but on some other more fundamental eg quantum aspect. There are various proposals in that sense, though they are nowhere near the intuitive presentism based on clock readings, and they give rise to a more fine-grained spectrum of possibilities instead of the rough duality presentism/eternalism.

Of course, but 'spacetime' is a theoretical creation. It's part of the GR scheme for calculating length and time variables. Our sensory experience is used to determine how closely those calculations approximate measurements.

Our sensory experiences are also creations of some theoretical scheme encoded in our brains. When we deal about knowledge, everything is theoretical. Theories which make successful predictions encode knowledge of the same quality, as the only knowledge content of all theories, including sensory data, is in the fact that "they work". They could not work if they were just theoretical clouds of smoke or calculational tricks without significance. So "seeing is believing" is not satisfactory, if one wants to believe based on knowledge.

The universal spatial configuration that corresponds to 200 BC exists? What does that mean? Astronomers, astrophysicists and cosmologists who use GR don't seem to think along eternalist lines. They're always telling us that photographic images of galaxies depict those objects as they were many years ago -- that those objects no longer exist in those spatial configurations at the time that their light reaches us.

In GR there are no "global" spatial configurations, this is the fundamental point. In GR each event exists in some neighborhood of other events, without any "global" significance. So, events appear "eternally" written on a map of events, which contains the dynamics. The dynamics are already inside, and not coming from the outside.

Eternalism is sort of an 'extensio ad absurdum'. So is reification of spacetime curvature.

It may seem odd to extend the number of reified events instead of restricting it. Similarly as in MWI, where it may seem odd that the universe should split in copies. Similarly as in an infinite universe, where it may seem odd that there is all that redundant stuff. I had that same feeling, but I after found that the opposite idea is much more insane, too much weighted on terrestrial standards to be the basis of something as vertiginous as an ontology.

But sensory data IS how science evaluates ontological claims. The (GR) basis for eternalism, like the (QM) basis for MWI, rests on unwarranted assumptions about the correspondence to deep physical reality of basic constructs of those theories.

Well, we may take some concrete examples then. You enter a ship, travel one year, and when you come back, say ten years have passed on earth. Where is the missing time?

Also, there's observational evidence that tells us that eternalism (as well as MWI) is just bad metaphysics.

Tell me more about it..

How can ontological claims be separate from the only means that we have of evaluating their correspondence to physical reality? Objective reality is established and extended via operational definitions of objects whose existence is asserted.

They are not separated if we adopt a physical theory which had its own reality check.

Eternalism says that Plato exists. Presentism says that Plato does not exist. So far, presentism is correct and eternalism is wrong -- and I suspect that it will remain this way until ... the end of TIME.

Eternalism does not say Plato exists "for us". Eternalism say Plato exists "for the world", which is an entirely different concept, which has ontological significance because it is independent from particular observers. The first view is merely an effect of observer-dependence, just like an observer located in Bejing could consider by following the same logic that Florence "does not exist". I mentioned trees in the forest for the same reason, since they happen in a spatial region which we don't observe. However, no matter we look or not at them, the trees fall -objectively-, eg. "for the world". The ontology of the event "falling tree" is not dependent on -our- observation of it. In the same way, events in 200BC may be considered having an ontology even if -we- are not "there" to observe them.

 

[baywax]

Eternalism does not say Plato exists "for us". Eternalism say Plato exists "for the world", which is an entirely different concept, which has ontological significance because it is independent from particular observers. The first view is merely an effect of observer-dependence, just like an observer located in Bejing could consider by following the same logic that Florence "does not exist". I mentioned trees in the forest for the same reason, since they happen in a spatial region which we don't observe. However, no matter we look or not at them, the trees fall -objectively-, eg. "for the world". The ontology of the event "falling tree" is not dependent on -our- observation of it. In the same way, events in 200BC may be considered having an ontology even if -we- are not "there" to observe them.

I agree. Although we can't say with objective realism that Plato existed "for" anything. We can only say his existence was and is a defining event for the whole world and even the universe. The same can be said for a forest or a sea cucumber.

 

[ThomasT]

This is simply completely unknown. There are no known fundamental reasons preventing "a priori" the possibility that the universe could recollapse.

The expansion is 'known' and certainly fundamental. There's no particular reason to think that the universe (or at least the expansion) didn't have a beginning. Assuming it did, then it follows that a finite (even if incalculable) amount of energy was imparted via this beginning event. It further follows that the expansion is dispersing and dissipating that energy.

It's logical to assume that the energy of the expansion is the dominant energy of the universe, and that all internal forms (including gravitational energy) are byproducts (ie., different manifestations) of it.

Given this scenario (which imho is the most plausible considering the multi-scale observational evidence and the efficacy of the classical and quantum mechanical wave models), then a 'big crunch' is physically impossible.

While perhaps a bit conceptually different, the conclusion about the ultimate fate of our universe implied by the above scenario is pretty much the same as the conclusion predicted by the standard cosmological model.

If that happens it would not mean something would rewind and people start becoming younger, but simply that the radius of the universe could no longer be considered a well defined clock.

Yes, I understand that. And even if the boundary of the universe is an expanding wave shell, there's no particular reason to think that it has to be an exactly spherical one. This boundary might be quite irregular for all we can ever know, and there might be variable internal and frontal expansion rates.

So, wrt what is known and what can be known (deduced from what is known) the radius of the universe will never be well defined in any physically verifiable sense. But I think that modelling along the lines that I suggested gives a conceptually more fundamental 'picture' than the 'picture' that one gets from reifying the GR geometrical representation.

And if it does not recollapse, we can't be exactly sure that it is a global clock either, since the observed radius could be just a local feature.

The radius of the observable horizon is almost certainly a local feature. Nevertheless, not knowing where we are wrt a possible universal boundary doesn't mean that the universe isn't bounded. Conceptually, the rate of expansion of the universal wave front would constitute a global or universal clock, of sorts.

It is a mutual game, there is no "first engine" driving all the rest – all fields cooperate on the same footing to yeld the full dynamics of GR.

Yes, well I think that current physics, insofar as it might be said to provide any sort of 'picture' of deep physical reality at all, provides an incomplete (and sometimes even misleading) 'picture'. I think it makes more sense to posit a "first engine", a fundamental dynamic, and proceed from there.

In my view, GR undermines any tentative to defend presentism intended as a condition on the realism of events based on clock readings.

You believe that the 'eternity' revealed by a 'spacetime map' is more, or just as, real as the reading on your clock?

But other weaker forms of presentism may still remain compatible with GR (and this is why I said in the first post that there is no final word on the debate) in the case they are not relying on time intended as clock readings but on some other more fundamental eg quantum aspect.

The general conception of TIME that I'm currently favoring has TIME as an index. Clock readings per se aren't necessarily involved. Indexes are generated by correlating sets of spatial configurations. This is happening in our brains wrt our uncommunicated or ambiguously communicated (subjective) and unambiguously communicated or quantifiable (objective) sensory stimuli and data.

There are various proposals in that sense, though they are nowhere near the intuitive presentism based on clock readings, and they give rise to a more fine-grained spectrum of possibilities instead of the rough duality presentism/eternalism.

I have a lot to learn about the development of, and the various issues involving, both presentism and eternalism. But I think that presentism is an intuitive, and basically correct, interpretation of the transitory nature of physical reality.

Our sensory experiences are also creations of some theoretical scheme encoded in our brains. When we deal about knowledge, everything is theoretical. Theories which make successful predictions encode knowledge of the same quality, as the only knowledge content of all theories, including sensory data, is in the fact that "they work". They could not work if they were just theoretical clouds of smoke or calculational tricks without significance. So "seeing is believing" is not satisfactory, if one wants to believe based on knowledge.

Of course GR is an improvement on preceding attempts to understand the nature of large scale behavior. But it's an intermediate step toward a deeper conceptual understanding of nature. Spacetime curvature is an improvement over some mysterious invisible 'force', toward some sort of complex wave mechanical theory that renders the deep nature of any scale behavior in terms of the same conceptual apparatus.

In GR there are no "global" spatial configurations, this is the fundamental point. In GR each event exists in some neighborhood of other events, without any "global" significance.

I consider that to be a conceptual shortcoming of GR.

So, events appear "eternally" written on a map of events ...

Again, a conceptual shortcoming of GR.

... which contains the dynamics. The dynamics are already inside, and not coming from the outside.

In my view, the dynamical precedence is from the top --> down, not the other way around. And the 'top' isn't gravitational behavior, it's the isotropic expansion of the universe.

It may seem odd to extend the number of reified events instead of restricting it. Similarly as in MWI, where it may seem odd that the universe should split in copies. Similarly as in an infinite universe, where it may seem odd that there is all that redundant stuff. I had that same feeling, but I after found that the opposite idea is much more insane, too much weighted on terrestrial standards to be the basis of something as vertiginous as an ontology.

There's no particular reason (and it might be considered insane ) to believe that different scale phenomena are the result of different fundamental dynamics. The idea that the deep nature of reality is wave mechanics and that there is a fundamental dynamic governing behavior on any and every scale makes a lot of sense to me. Not at all insane. Nature reveals some of her essence in all her various guises -- a hierarchy of media with disturbances in those media governed by the same fundamental dynamic.

I think I have a better understanding of why one might choose to believe in Eternalism or MWI. But they seem to me to be based on faulty primary assumptions.

Well, we may take some concrete examples then. You enter a ship, travel one year, and when you come back, say ten years have passed on earth. Where is the missing time?

There's no 'missing time'. The periods of oscillators are affected by accelerations.

Wrt a common clock, say revolutions of the Earth around the sun, I'll have counted the same number as you on landing back on earth, but my accumulator will have been incremented at a different rate. My ship's atomic clock will show a different elapsed time for the trip than your earthbound clock, and I'll have aged less.

They (ontological claims) are not separated if we adopt a physical theory which had its own reality check.

I'm not sure what you mean by this. Aren't 'reality checks' basically the same wrt any theory, ie., we make positional measurements and compare them to a theory's physical predictions?

Eternalism does not say Plato exists "for us". Eternalism says Plato exists "for the world", which is an entirely different concept ...

What does "Plato exists for the world" mean then? Better yet, just give me your definition for the word EXIST. I've already mentioned that its ordinary language and scientific usage is as a synonym for operational definition -- that is, a set of directions for accessing sensory stimuli corresponding to the object or event whose existence is asserted.

... which has ontological significance because it is independent from particular observers.

Something has ontological significance because it can't be observed by particular observers?

The first view is merely an effect of observer-dependence, just like an observer located in Bejing could consider by following the same logic that Florence "does not exist". I mentioned trees in the forest for the same reason, since they happen in a spatial region which we don't observe. However, no matter we look or not at them, the trees fall -objectively-, eg. "for the world". The ontology of the event "falling tree" is not dependent on -our- observation of it. In the same way, events in 200BC may be considered having an ontology even if -we- are not "there" to observe them.

200 BC no longer exists because we can't go to it. Florence and Bejing, and forests and trees (both upright and fallen) exist because we can go to them.

If we live in an expanding evolving universe (and the evidence suggests that we do) then spatial configurations are transitory. If spatial configurations are transitory, then our experience referred to as NOW has a special significance and is the basis for verifying assertions and answering questions about our world. If so, then eternalism should be rejected.

Just because something is obvious doesn't mean it isn't also a gateway to a deeper understanding of reality. Of course, what's obvious to you might not be obvious to me, and vice versa.

 

[ThomasT]

I agree. Although we can't say with objective realism that Plato existed "for" anything. We can only say his existence was and is a defining event for the whole world and even the universe. The same can be said for a forest or a sea cucumber.

Don't you see an important difference between the phrases "Plato exists" and "baywax exists"? If so, what's the difference?

 

[xantox]

I'll answer to part of your points as I don't have much time now, I hope I'm addressing the main ones.

The expansion is 'known' and certainly fundamental.

According to current cosmological models and observations, the universe is expanding, but this does not imply we know it will -always- continue expanding.

It's logical to assume that the energy of the expansion is the dominant energy of the universe, and that all internal forms (including gravitational energy) are byproducts (ie., different manifestations) of it.

Cosmology says something different here: what is currently dominant is vacuum energy – which does not in itself causes the expansion, but rather its acceleration. In the early universe, radiation energy was dominant.

Given this scenario (which imho is the most plausible considering the multi-scale observational evidence and the efficacy of the classical and quantum mechanical wave models), then a 'big crunch' is physically impossible.

No, if the lambda-cdm model is true, and since we do not know the equation of state of dark energy, then a big crunch cannot be excluded (eg have a quintessence field and make it vary in the good way).

Yes, well I think that current physics, insofar as it might be said to provide any sort of 'picture' of deep physical reality at all, provides an incomplete (and sometimes even misleading) 'picture'.

I'm not questioning that it's not incomplete, but affirming that it's the best picture we have.

You believe that the 'eternity' revealed by a 'spacetime map' is more, or just as, real as the reading on your clock?

I believe this: since for relativity space and time are on the same footing, then if we consider that two events on a spacelike interval both "exist" then we also consider that two events on a timelike interval "exist". It's as simple as that.

The general conception of TIME that I'm currently favoring has TIME as an index. Clock readings per se aren't necessarily involved.

Then what do you mean by time if it is not a clock reading?

I'm not sure what you mean by this. Aren't 'reality checks' basically the same wrt any theory, ie., we make positional measurements and compare them to a theory's physical predictions?

I mean that once a physical theory had his check with reality and stands still upon that check, then it has a strong word to say on some ontological questions.

What does "Plato exists for the world" mean then? Better yet, just give me your definition for the word EXIST. I've already mentioned that its ordinary language and scientific usage is as a synonym for operational definition -- that is, a set of directions for accessing sensory stimuli corresponding to the object or event whose existence is asserted. [..] Something has ontological significance because it can't be observed by particular observers?

"Plato exists for the world" means that the world contains an equivalence class of observers all agreeing on the observation of a Plato system. If you and me are not part of this class that has no ontological significance.

200 BC no longer exists because we can't go to it. Florence and Bejing, and forests and trees (both upright and fallen) exist because we can go to them.

But then very distant space locations could exist that we can -never- reach them, so do they exist or not?

 

[ThomasT]

xantox, good points, I'll respond this afternoon. One thing I can say quickly is that I don't think that the fate of the universe is relevant to our primary discussion.

 

[ThomasT]

xantox, sorry for the delay ... New Year's Eve, etc.

Cosmology says something different here: what is currently dominant is vacuum energy – which does not in itself causes the expansion, but rather its acceleration. In the early universe, radiation energy was dominant.

We'll never know what initiated the expansion or if the apparent acceleration is a local or universal or temporary (like some mini-inflationary period) phenomenon, but wrt the nature of time it doesn't matter. Dark energy is still expansion energy. There's no reason that I know of to think that the rate of expansion should necessarily be constant wrt either space or time. Anyway the fact that there is an expansion is what matters wrt the nature of time.

I believe this: since for relativity space and time are on the same footing, then if we consider that two events on a spacelike interval both "exist" then we also consider that two events on a timelike interval "exist". It's as simple as that.

Space and time aren't exactly the same thing, even though it all has to do with spatial configurations. Spacelike and timelike intervals have different physical meanings. The spatial dimensions are positional variables, and the time dimension is an index of measurements of the spatial dimensions. The traversing of both spacelike and timelike intervals is constrained by the universal expansion -- but in different ways. Travelling to some distant solar system is limited by the fact of a universal speed limit. Traveling to some distant TIME is limited by the fact that the spatial configurations defining the recorded past and the possible future of our universe simply don't exist. Alpha Centauri probably exists wrt the NOW of our local earthbound clocks (maybe not, of course, but it seems like a reasonable assumption), but the human race will probably never develop the capability to go there. On the other hand, traveling to 200 BC isn't just a technological problem. The universal spatial configurations defining 200 BC are not the universal spatial configurations which define January 1, 2009 AD.

A natural prohibition on time travel is a necessary byproduct of an expanding evolving universe.

Then what do you mean by time if it is not a clock reading?

An individual clock reading is a subset of a time index. Time indexes are a subset of all indexes. Indexes are ordered sets of correlations of spatial configurations. The order of spatial configurations in time indexes is determined by the evolution of the universe (as opposed to the order defined by, say, the Dewey Decimal System of indexing).

Both the subjective (psychological) and the objective meaning of TIME have to do with ordered sets of correlations of spatial configurations.

I mean that once a physical theory had his check with reality and stands still upon that check, then it has a strong word to say on some ontological questions.

Aren't the predictions of a theory ontological statements? How do we check them? If a theory is interpreted as predicting that 200 BC exists, but can't direct us to any spatial configurations that correspond to 200 BC except those that correspond to the interpretation itself, then what are we to conclude? That such interpretive statements aren't part of or necessitated by the physical theory? That they aren't saying anything about nature?

"Plato exists for the world" means that the world contains an equivalence class of observers all agreeing on the observation of a Plato system. If you and me are not part of this class that has no ontological significance.

Ok, so what sort of ontologically significant data encodes the "observation of a Plato system"? An interpretive extension of a mathematical model that, without the interpretive extension, produces accurate predictions of positional measurements. And, when an interpretation (of a theory which produces ontologically significant statements about the physical universe) produces statements which have no ontological significance, then what do we do with the ontologically insignificant statements? We discard them as being physically meaningless. And, how do we regard an interpretation that produces such statements? We regard it as metaphysics.

A metaphysical interpretation of a physical theory isn't necessarily a bad thing. If the metaphysics is on a solid enough foundation, then heuristics arising from it might be useful in the development of better theories of nature. But, equating timelike and spacelike intervals is, imho, clearly a faulty interpretation of the physical meaning of the geometrical constructs of GR. They're both related to each other and to Nature of course, but they refer to somewhat different things. The difference SEEMS clear to me, although articulating it takes some effort -- partly because we often use terms like NOW and THEN to refer to indexes of configurations as well as individual configurations (indexes of positions).

How would you express it?

Also, there's overwhelming physical evidence that we are part of an evolving universe, and that universal spatial configurations are transitory, fleeting phenomena (even though persistent physical objects, bounded wave structures that are ponderable by us, do appear in more or less the same form across a range of configurations defining a temporal interval).

Our historical records and our experience tell us that Bejing and Florence and forests and trees (upright and fallen) and the year 2009 exist NOW, and that Plato and the year 200 BC don't. The path that leads to an obfuscation of these evident truths of Nature is, I think, a metaphysical road to nowhere.

But then very distant space locations could exist that we can -never- reach them, so do they exist or not?

We have no way of knowing what's beyond our observational horizons, though we can make some reasonable speculations. The current astronomical horizon is about 14 billion light years. I don't know what the current estimates of the size of the universe are, but it's reasonable to assume that our universe has a much larger volume than we can see -- that our universe exists, now, beyond our observational horizon.

Anyway, we'll never reach our closest galactic neighbor, but we can be pretty sure that it exists in more or less the same form as it appears in photos of it -- for reasons that I assume you're aware of. We can be more sure, I think, that the exact galactic and universal configurations corresponding to our photos of it do not exist.

 

[xantox]

xantox, sorry for the delay ... New Year's Eve, etc.

Yeah, happy new year to you and all readers too.

We'll never know what initiated the expansion or if the apparent acceleration is a local or universal or temporary (like some mini-inflationary period) phenomenon, but wrt the nature of time it doesn't matter.

I offered this argument re the possibility of considering the expansion as a well-defined clock, which is therefore not possible since we don't know if the expansion is monotonic.

Space and time aren't exactly the same thing, even though it all has to do with spatial configurations. Spacelike and timelike intervals have different physical meanings.

I'm not opposing that, the point is that the slicing in space and time can be done in all sort of ways – arbitrarily. So -how- do you define the "universal spacelike present", since there is not a single one?

Travelling to some distant solar system is limited by the fact of a universal speed limit. Traveling to some distant TIME is limited by the fact that the spatial configurations defining the recorded past and the possible future of our universe simply don't exist.

You're using as argument the very conclusion which you're supposed to derive from it. In all the post you're formulating different arguments which are clearly variants on a single deduction where you're -postulating- this idea that "there is a universal present space configuration". This idea is for you an axiom without needs of justification whatsoever since it looks fine with everyday perceptions, no matter which arguments relativity can offer to show that it is a wrong assumption. The good way of arguing against eternalism would be to start where relativity leaves us, and going ahead to possibly show how a sudden turn could restore presentism, or make both wrong, but not side-stepping relativity entirely and using perceptual axioms of the same category as "earth is flat".

If a theory is interpreted as predicting that 200 BC exists, but can't direct us to any spatial configurations that correspond to 200 BC except those that correspond to the interpretation itself, then what are we to conclude?

Either we postulate, "200BC does not exist" - so that we don't need any other justification for this belief. Either we use scientific models of physical reality to support this at least in part, and in this case, relativity invites us to abandon the idea of an absolute present.

Ok, so what sort of ontologically significant data encodes the "observation of a Plato system"? An interpretive extension of a mathematical model that, without the interpretive extension, produces accurate predictions of positional measurements. And, when an interpretation (of a theory which produces ontologically significant statements about the physical universe) produces statements which have no ontological significance, then what do we do with the ontologically insignificant statements? We discard them as being physically meaningless. And, how do we regard an interpretation that produces such statements? We regard it as metaphysics.

The fact that an equivalence class of observers agrees on the observation of a Plato system is here an operational -definition- of Plato existence, nothing non-significant here. It's not even linked in itself to a physical theory, it's more or less the same way of forming the concept of existence as when as childs we play with boxes or hear stories about Santa.

But, equating timelike and spacelike intervals is, imho, clearly a faulty interpretation of the physical meaning of the geometrical constructs of GR. They're both related to each other and to Nature of course, but they refer to somewhat different things. The difference SEEMS clear to me, although articulating it takes some effort -- partly because we often use terms like NOW and THEN to refer to indexes of configurations as well as individual configurations (indexes of positions).

It's a relative, not absolute difference, as it depends on each observer. Two different observers can consider the SAME interval to be timelike and spacelike, so is it timelike or spacelike? All this would be far clearer if we would move in our everyday life at speeds of 0.99c.

 

[Charlie G]

The arrow of time is just an illusion caused by physical systems moving from lower entropy to higher entropy( eg. eggs breaking, carbon dioxide nicely packed in your soda to being spread about the room randomly, ice melting) under normal cicumstances most physical systems do not go from high entropy to low, giving us an illusion that time has an arrow, most physical laws do not make a distinction between past and future and can work either way.

 

[baywax]

The arrow of time is just an illusion caused by physical systems moving from lower entropy to higher entropy( eg. eggs breaking, carbon dioxide nicely packed in your soda to being spread about the room randomly, ice melting) under normal cicumstances most physical systems do not go from high entropy to low, giving us an illusion that time has an arrow, most physical laws do not make a distinction between past and future and can work either way.

I had no idea a physical law was capable of making a distinction in the first place.

Since this thread is still in the Philosophy section it should be noted that "illusions" and "distinctions" are the results of anthropocentric perception and that beyond that, the phenomenon of "perception" is limited to living organisms. Physical laws are neither able to "perceive" a "distinction" nor to "create" an "illusion". In fact I'd go so far as to say that without human "perception" there would be no "physical laws".

 

[ThomasT]

The arrow of time is just an illusion caused by physical systems moving from lower entropy to higher entropy( eg. eggs breaking, carbon dioxide nicely packed in your soda to being spread about the room randomly, ice melting) under normal cicumstances most physical systems do not go from high entropy to low, giving us an illusion that time has an arrow, most physical laws do not make a distinction between past and future and can work either way.

The fact that an equation of motion can describe movies of our world run either forward or backward has nothing to do with the fact that the movies themselves are asymmetric wrt time reversal. That is, if you run the movies backward, they look ... wrong.

It isn't an illusion that the New York of 1900 looked a lot different than the New York of today. It really was different. The past looks different than the present.

That there is an arrow of time, a preferred direction wrt the evolution of our universe, and any process within it, is a fact of Nature. The problem is that there's no fundamental dynamic in the current formulation of physics that accounts for this.

 

[ThomasT]

Yeah, happy new year to you and all readers too.

Thanks and same to you.

I'm not opposing that, the point is that the slicing in space and time can be done in all sort of ways – arbitrarily. So -how- do you define the "universal spacelike present", since there is not a single one?

One universal spatial configuration can correspond to many different local clock readings. But for any single clock reading on any local clock there's only one corresponding universal spatial configuration, only one "universal spacelike present".

Our conceptual frame of reference is the universe. But to resolve the argument, our frame of reference can be your computer screen. Or my computer screen. Or whatever.

Lets use your computer screen. Assuming your computer clock is working normally, how many configurations of your computer screen correspond to a readout of, say, 5:02:32 PM, Friday, January 2, 2009, on your computer screen? One, right?

SR calls this clock readout the proper time of the screen configuration that it's correlated with, and restores absolute time and space by translating this from your computer screen frame of reference to my computer screen frame of reference. There's one PRESENT screen configuration on your computer corresponding to the above time readout on your computer -- and that fact is the same for any and every observer, even though the screen configuration on your computer corresponding to the above time readout on your computer might correspond to a different time readout on everyone else's computer. SR and GR allow us to unambiguously translate from one frame of reference to another. They don't say that there isn't a PRESENT spatial configuration of the universe that corresponds to the above time readout on your computer.

You're using as argument the very conclusion which you're supposed to derive from it. In all the post you're formulating different arguments which are clearly variants on a single deduction where you're -postulating- this idea that "there is a universal present space configuration". This idea is for you an axiom without needs of justification whatsoever since it looks fine with everyday perceptions, no matter which arguments relativity can offer to show that it is a wrong assumption.

Relativity doesn't say that there's no set of spatial configurations which define the present. What are the times, the spatial configurations, of your computer clock as you're reading this? Are there spatial configurations of the room you're in that correspond to your reading this? The building you're in? The city? The planet you're on?

Just as you can take a 'snapshot' of your computer screen or your house, etc., NOW and call it the PRESENT (this is what your eyes, brain, etc. are doing), we can imagine a 'snapshot' of the PRESENT state of the universe. (We can actually take pictures of a volume with a radius of about 14 billion light years. For the purposes of our discussion, this horizon can be the boundary of the universe.)

The time of an event is the reading on a clock in the same frame of reference as the event. Our (conceptual) frame of reference is the universe.

It isn't many universal configurations corresponding to one local clock reading, it's many local clock readings corresponding to one universal configuration.

The good way of arguing against eternalism would be to start where relativity leaves us, and going ahead to possibly show how a sudden turn could restore presentism, or make both wrong, but not side-stepping relativity entirely and using perceptual axioms of the same category as "earth is flat".

We're not side stepping relativity. As we've seen, relativity doesn't require us to "abandon the idea of an absolute present". It does require us to use the same definitions, conventions, and translational formulas if we want to unambiguously communicate our experience of it.

Either we postulate, "200BC does not exist" - so that we don't need any other justification for this belief. Or we use scientific models of physical reality to support this at least in part, and in this case, relativity invites us to abandon the idea of an absolute present.

No, we simply determine what spatial configurations in the physical world 200 BC refers to. And we find that it refers to records and remnants of a time interval, an ordered set of spatial configurations, that no longer exists.

Those who maintain that 200 BC does exist, in any sense other than as historical records or remnants or unwarranted interpretations of theoretical constructs, are obliged to supply physical evidence of its existence.

The fact that an equivalence class of observers agrees on the observation of a Plato system is here an operational -definition- of Plato existence, nothing non-significant here. It's not even linked in itself to a physical theory, it's more or less the same way of forming the concept of existence as when as childs we play with boxes or hear stories about Santa.

I agree. Believing in eternalism is like believing in Santa Claus or the tooth fairy.

All this would be far clearer if we would move in our everyday life at speeds of 0.99c.

Wrt what?

You said that originally you liked presentism, but came to favor eternalism. I'm curious about your experience regarding this conversion. Can you present your learning/thinking process chronologically?

 

[Charlie G]

You have a good point, time's arrow really is a very hard thing to come up with an explanation for.

 

[xantox]

One universal spatial configuration can correspond to many different local clock readings. But for any single clock reading on any local clock there's only one corresponding universal spatial configuration, only one "universal spacelike present".

There is no such a thing as an "absolute universal spacelike present" in GR. Each event has a "local" present and each observer has its own worldline along which it is possible to define a proper time, but there is no "absolute universal present", since it is possible to define infinite different space+time slicings of spacetime all compatible with the same dynamics, and there is no "universal proper time", since proper time is only defined on the world line of each specific observer.

Lets use your computer screen. Assuming your computer clock is working normally, how many configurations of your computer screen correspond to a readout of, say, 5:02:32 PM, Friday, January 2, 2009, on your computer screen? One, right?

A physical screen configuration defines a timelike, not spacelike, surface – since we need to wait that information propagates on the screen circuits, which could imply a significant delay if the screen measures say 10 light years, or if the circuits are very slow. But to make things worse, imagine to place half of this big screen, including the clock readout (the clock circuits being supposed local to the readout), inside an even larger black hole. If we live on a planet located say on the utmost portion of the screen outside the black hole, we will find that the image gets permanently stuck, no new clock signals arriving anymore. So how you now define the "global" screen "present" configuration?

Relativity doesn't say that there's no set of spatial configurations which define the present.

I think I repeated it clearly several times, the problem is not that in GR it is not possible to define a "present configuration" (it can be defined as a 3-geometry in the hamiltonian formulation of GR), the problem is that GR shows that there are -infinite- possible slicings of spacetime into space + time defining entirely different "present configurations" – and that nothing in the theory allows to single out one of them instead of another.

You said that originally you liked presentism, but came to favor eternalism. I'm curious about your experience regarding this conversion. Can you present your learning/thinking process chronologically?

Roughly:

1. everyday perception suggesting an absolute present, and
2. finding a consistent mapping onto Newtonian physics and classical computation paradigm, however later
3. finding this absolute present mapping is broken in GR, and moreover
4. finding it is even more broken in QM, and
5. not finding other specific needs for an absolute present given the consistency with observation already offered by GR and QM, so
6. abandoning the idea of an absolute present, however since
7. local realism is at odds with QM, and finer-grained definitions of existence are possible, and since
8. more fundamental dynamics could be defined, then
9. digging on how 7. and 8. could switch things back or render the presentism/eternalism dichotomy obsolete.

 

[Sorry!]

i read a book called i believe fabric of the cosmos by brian greene goes into quite a bit of depth about the 'arrow' of time... and i believe he explains it and why we perceive it as so very well.


++ this book is a book about physics (if u cudnt tell by the name lol) not really the 'philosophy' of time or anything but i wrote a paper for my philosophy course on a similar topic this book helped loads.

 

[ThomasT]

As exemplified wrt SR's twins (when they're reunited they both agree on the elapsed time of the traveling twin's journey wrt the Earth-Sun frame of reference even though their personal clocks record different times for the same journey), there's a hierarchy of reference frames. A room. A house. The Earth. The solar system. The Milky Way. And so on, to the universe. Of course, we have to use our imaginations a bit when it comes to what the spatial configurations of some of these things correlated with our NOWS might be -- because the universe is in a continual state of flux and the speed of light is finite -- but that doesn't imply that there isn't a universal configuration that corresponds to our local and personal NOWS. Remember the trees and forests, etc. Not knowing the current state of the forest doesn't imply that there isn't a current state of the forest.

We define the current or present spatial configuration of the observable universe based on observations and what we know about the behavior of light. Of course, some of the assumptions and inferences involved might be wrong, but, again, that doesn't mean that there isn't a current spatial configuration of the universe.

The well founded idea that the universe is an evolving spatial configuration, which we are a part of and not just traveling through, and wrt which (due to the fundamental dynamic of isotropic expansion) no instantaneous configuration can be repeated, is clearly at odds with eternalism.

I don't think we should interpret the mathematical constructs of GR (and QM as well) literally, because there's no definitive reason to think of them as qualitative descriptions of deep physical reality, and there are reasons to think that they're not very accurate as qualitative descriptions of deep physical reality. They're a means of calculating quantifiable instrumental behavior, and they should be taken as descriptions only wrt the instrumental level.

Apparently we do select some slicings as present (and probable future) configurations rather than others, else GR wouldn't be of much use.

I agree that, observationally, there's no absolute present. But, as noted above, this doesn't mean that there's no set of spatial configurations in higher order frames of reference corresponding to the set of spatial configurations in my personal experience of the world that I refer to as the present. I might not know what these are (eg., I don't know if any trees fell in the forest last night), but that doesn't mean that there isn't a present configuration of the forest, or any other frame of reference, as well as a present configuration of the room I'm in.

If TIME is an index, an ordered record, of discretized, unique, and transitory spatial configurations of an expanding evolving universe, then none of the spatial configurations that collectively define TIME exist in any form other than as historical records of one sort or another.

So, what do the words NOW and the PRESENT mean? Obviously, they have some physical meaning. We all use these words, and their use elicits predictable responses.

Eternity, on the other hand, is a rather more sticky wicket.

 

[xantox]

We define the current or present spatial configuration of the observable universe based on observations and what we know about the behavior of light. Of course, some of the assumptions and inferences involved might be wrong, but, again, that doesn't mean that there isn't a current spatial configuration of the universe. [..]
I don't think we should interpret the mathematical constructs of GR (and QM as well) literally, because there's no definitive reason to think of them as qualitative descriptions of deep physical reality, and there are reasons to think that they're not very accurate as qualitative descriptions of deep physical reality.

In GR there is fundamentally no time and no space, but just pure dynamics. It's true that this could be wrong, but GR (or even Newtonian theory) offers a more fundamental and correct view on nature than common sense does.

So, if our positions are not going to converge further we shall acknowledge that one difference on our views is that while we both agree that both common sense and GR or QM have no last word to say on ontological issues such as the presentism vs eternalism debate, I consider that GR or QM have more, not less, to say than common sense, and that they can't be sidestepped. While their concepts may seem more abstract, they are in fact less abstract, as apart from modeling known phenomena they can predict new subtler ones which are confirmed by observation, and that modeling, prediction and observation feedback is exactly the same process that we (or anything having knowledge, say birds) use, to validate their own common sense models of reality too. So while the mathematical concepts of GR and QM are certainly not exact, and should not be taken too literally, the common sense models should be taken even less literally.

I agree that, observationally, there's no absolute present. But, as noted above, this doesn't mean that there's no set of spatial configurations in higher order frames of reference corresponding to the set of spatial configurations in my personal experience of the world that I refer to as the present.

If we use higher order representations, then different names have to be used too for them. Space and time is something quite precisely defined and a higher order present is not what we should call a present. And it would not lead to presentism, but to higher order presentism – already a first step away from the vanilla dichotomy we started with. In hamiltonian general relativity this higher order present could be some point in superspace, though there is still no mean to select a preferred foliation within the theory.

Here is where the best theories leave us today. A step forward, though we already enter speculation, is to consider causality as a more fundamental basis than spacetime. Or suppose some underlining process similar to a cellular automata. However quantum mechanics is at odds with such a view and causality itself. However a further step forward is possible by considering causal sets or quantum computation graphs. And another step forward is possible by considering superpositions of them. And these tortuous paths continue. So while no solution and no final word is offered by following them, it seems to me that this help at least to understand the non-trivial nature of these questions and the incredible deepness of nature.

 

[ThomasT]

In GR there is fundamentally no time and no space, but just pure dynamics. It's true that this could be wrong, but GR (or even Newtonian theory) offers a more fundamental and correct view on nature than common sense does.

So, if our positions are not going to converge further we shall acknowledge that one difference on our views is that while we both agree that both common sense and GR or QM have no last word to say on ontological issues such as the presentism vs eternalism debate, I consider that GR or QM have more, not less, to say than common sense, and that they can't be sidestepped.

While their concepts may seem more abstract, they are in fact less abstract, as apart from modeling known phenomena they can predict new subtler ones which are confirmed by observation, and that modeling, prediction and observation feedback is exactly the same process that we (or anything having knowledge, say birds) use, to validate their own common sense models of reality too. So while the mathematical concepts of GR and QM are certainly not exact, and should not be taken too literally, the common sense models should be taken even less literally.

Well put, and I agree. However, the idea that the universe is a spatial configuration in continual transition isn't a common sense idea -- and the eternalism suggested by a literal translation of GR constructs is at odds with this. Taking the observations and what I consider to be the most reasonable interpretations of the formal constructs of GR, QM, and Newtonian physics into account, I think that the observational and inferential evidence supports the transitory view, and hence, some version of presentism.

If we use higher order representations, then different names have to be used too for them. Space and time is something quite precisely defined and a higher order present is not what we should call a present. And it would not lead to presentism, but to higher order presentism – already a first step away from the vanilla dichotomy we started with. In hamiltonian general relativity this higher order present could be some point in superspace, though there is still no mean to select a preferred foliation within the theory.

I meant higher order in terms of scale, not dimension. Speaking of the present state of the 3D universe is conceptually the same as speaking of the present state of the room I'm in, or the present state of the forest in the park that's about a mile from my house.

Here is where the best theories leave us today. A step forward, though we already enter speculation, is to consider causality as a more fundamental basis than spacetime. Or suppose some underlining process similar to a cellular automata.

Or perhaps a fundamental wave mechanical dynamic(s).

However quantum mechanics is at odds with such a view and causality itself.

I don't think that QM is at odds with a wave mechanical view of things. Isn't quantization a function of harmonic ordering?

QM isn't at odds with causation, it just isn't a causal (ie., realistic) theory, but rather a correlational, probabilistic one.

However a further step forward is possible by considering causal sets or quantum computation graphs. And another step forward is possible by considering superpositions of them. And these tortuous paths continue.

Yes, tortuous, and, imho, essentially incorrect if what is being sought is a unifying conceptual basis for all physical theories.

So while no solution and no final word is offered by following them, it seems to me that this helps at least to understand the non-trivial nature of these questions and the incredible deepness of nature.

I agree that Nature is deeper than common sense -- that there's more to reality than meets the eye, so to speak. But, at the same time, we and what we sense are part of Nature -- and I see no reason to assume that the dynamics of processes in media that are invisible to us are essentially different than the dynamics which govern the world of our senses.

Quantum experimental phenomena seem to me to suggest that deep reality is as transitory as our (common) sensory reality seems to be -- at least, they don't provide any evidence that it isn't.

 

[ThomasT]

xantox, since writing the above I've learned a few more things and, I agree, the possible paths (steps) toward a deeper understanding of Nature that you mention (including info theory) will all come into play and have something to contribute.

This discussion has been very helpful for me, even if I don't fully understand all the issues, and ways of talking about them, that are involved (especially the ways that professional philosopher deal with it).