Is Time Static Like Other Dimensions?

[dimensionless]

When I make plots and graphs, time is just another dimension. When I write an equation, it is just another variable. The present does not erase the past, and it does not preclude the future. Clearly our consciousness moves in the positive direction along the time axis, but time itself, does not appear to be moving anywhere. If you could travel back in time, my body would still be there. If you could travel forwards in time, my body would be there as well(or at least the mass and energy that used to be me). If you made a plot of me vs. time, I would exist everywhere along the time axis. Do you think that time is static in the same way that height, width, and depth are?

 

[ThomasT]

When I make plots and graphs, time is just another dimension. When I write an equation, it is just another variable. The present does not erase the past, and it does not preclude the future.

The universe appears to be evolving, changing from instant to instant. The past is our record of physical configurations that no longer exist. The future is our prediction, based on records of the past, of physical configurations that might evolve.

Clearly our consciousness moves in the positive direction along the time axis, but time itself, does not appear to be moving anywhere.

Time is motion, the recording of different physical configurations. The fact that each recorded configuration is unique, and that each unique configuration in our index is more like its close neighbors than its distant ones, suggests a preferred evolutionary direction -- ie., an arrow of time.

If you could travel back in time, my body would still be there.

You can't travel to something that doesn't physically exist any more -- except in your imagination of course.

If you could travel forwards in time, my body would be there as well(or at least the mass and energy that used to be me).

That's the point. The matter and energy of the universe are continually changing. 1000 years from now there won't be any you.

If you made a plot of me vs. time, I would exist everywhere along the time axis.

Yes, for as long as you actually exist. But even then, each instantaneous configuration of you would be unique. You, as all of us, are evolving to nonexistence.

Do you think that time is static in the same way that height, width, and depth are?

No.

 

[dimensionless]

The universe appears to be evolving, changing from instant to instant. The past is our record of physical configurations that no longer exist. The future is our prediction, based on records of the past, of physical configurations that might evolve.

I could also define past and future as volumes in space-time that merely have a value of "t" greater than or less than the present value.

Time is motion, the recording of different physical configurations. The fact that each recorded configuration is unique, and that each unique configuration in our index is more like its close neighbors than its distant ones, suggests a preferred evolutionary direction -- ie., an arrow of time.

This continuity exists in the other three dimensions as well, and I think we are in agreement that these are relatively static.

You can't travel to something that doesn't physically exist any more -- except in your imagination of course.

If space-time were defined as a function, say,

S(x,y,z,t),

it would exist. It would just be at a different location along the t-axis.

I once had a physics teacher that said "We don't see people getting younger, we see them getting older, therefore time goes forwards." I believe this logic is flawed, because even if time did go backwards we would be unable think. Our thoughts would be undone. Our acquired knowledge would be leak from our consciousness like video tape being rewound. My understanding of time is that it is stagnant and moves neither forwards nor backwards. In mathematical terms, I see now reason why

S(x,y,z,t_{present})

should exclude the existence of

S(x,y,z,t_{present}-\tau)

and

S(x,y,z,t_{present}+\tau)

 

[ThomasT]

Do you think that time is static in the same way that height, width, and depth are?

Yes, I see what you mean.

I was using the word time as a synonym for change or motion, and I see now that that's not correct.

Time is an index of recorded spatial configurations. Psychological time refers to our personal, subjective experience of the world wherein the index is made via our human biological data processing faculties following the direct detection of physical variables via our sensing faculties. Objectively, time refers to the generation of indexes via standardized protocols and time-keeping devices, and the physical data might be generated, accumulated, and processed via instruments used to amplify physical variables and augment our human biological capabilities.

Time is just an index, no more no less -- nothing mysterious there.

Spacetime refers to a coordinate backdrop onto which spatial configurations and time indexes are jointly mapped. Nothing mysterious there either.

The phrase 'time moves forward' refers to the observation that each spatial configuration in an index of real world spatial configurations is unique -- that is, no configuration is repeated.

There's an archetypal pattern regarding physical processes that's most clearly seen in the radiative 'arrow of time' (eg., the evolution of a wave produced by dropping a small round object into calm water).

So, while it's not quite correct to say that 'time moves forward', nevertheless all real world time indexes have a common feature. They're all asymmetric in the same way, in that as you look backward through the indexed configurations they appear increasingly different from the most recent.

I could also define past and future as volumes in space-time that merely have a value of "t" greater than or less than the present value.

Yes, but the convention is, t_past < t_present < t_future.

If space-time were defined as a function, say,

S(x,y,z,t),

it would exist. It would just be at a different location along the t-axis.

Records of past spatial configurations exist, but not the spatial configurations themselves.

My understanding of time is that it is stagnant and moves neither forwards nor backwards.

Insofar as the word, time, is used in ordinary language as a synonym for change or motion, then saying that it's static or stagnant without any elaboration can result in communication problems. But I now see what you're saying. Time is an index of motion (not motion itself) -- and the concept of an index is static in the same sense that the concepts of height, width and depth are static.

That is what you're saying, isn't it?

 

[xantox]

Do you think that time is static in the same way that height, width, and depth are?

This is a standard debate in philosophy of time. Cfr Eternalism and Presentism and there is no final word on it.

 

[dimensionless]

My understanding of time is that it is stagnant and moves neither forwards nor backwards.

Insofar as the word, time, is used in ordinary language as a synonym for change or motion, then saying that it's static or stagnant without any elaboration can result in communication problems. But I now see what you're saying. Time is an index of motion (not motion itself) -- and the concept of an index is static in the same sense that the concepts of height, width and depth are static.

That is what you're saying, isn't it?

I think that is more or less what i was trying to get at. There maybe other communication problems as well. I used words like "is," "would," and "are" and they can imply a specific point in time.

 

[ThomasT]

This is a standard debate in philosophy of time. Cfr Eternalism and Presentism and there is no final word on it.

Thanks xantox. I don't think that the eternalist or presentist philosophies of time have it right. And, the conventional model of time vis Wikipedia is a sort of layman's philosophical extension of the way that the word, time, is used in everyday discourse, but not equivalent to it.

Time is just an index of a set of events or spatial configurations. Time indexes are generated by associating (correlating) configurations of some set or sets of spatial configurations with some other set or sets of spatial configurations. This interpretation is a generalization of SR's definition (or convention, regarding the procedure for generating time indexes) of the time of an event as the reading on a clock that is in the frame of reference of the object event or object configuration.

Time is a dimension in the sense that it is a set of measurements (correlations) that, collectively, organize (index) data accumulated via measurements of the spatial dimensions.

I think that that's all there is to it. Note that I'm not saying that time is like an index, but that it is an index (wrt both standard ordinary and technical scientific usage), no more, no less, no mystery, no problem. The word, time, as with any word, can be defined as something other than what it refers to in ordinary and technical scientific discourse. But what would be the point of that?

Can we revisit the spatial configurations catalogued in our recorded history, our time index, of the universe? This is the same as asking if we can rewind the evolution of the universe or any significant part of it? The evidence (salient features and emergent patterns revealed in the time indexes) suggests that we can't. The question of whether past universal configurations exist now is a nonsensical one.

Asking if we can take a shortcut through the natural evolution of the universe and sort of previsit temporally distant spatial configurations of some possible evolutionary path (wrt some possible future time index) that haven't happened yet, but might, is also a nonsensical question.

 

[ThomasT]

I think that is more or less what i was trying to get at. There maybe other communication problems as well. I used words like "is," "would," and "are" and they can imply a specific point in time.

I'm not sure what you mean. Can you provide some examples where using those words would present problems?

Maybe we should talk about this in the philosophy forum?

 

[dimensionless]

For example, I used the sentence

My understanding of time is that it is stagnant and moves neither forwards nor backwards.

This contained the phrase "is stagnant." Literally, this would mean that time is stagnant at the present time. It 'would' not, however, specify whether time 'would be' stagnant in the past or future.

It may have been better to put this in the philosophy forum, although some (more) mathematical arguments would be nice. Maybe the entire thread could be moved.

 

[xantox]

Can we revisit the spatial configurations catalogued in our recorded history, our time index, of the universe? This is the same as asking if we can rewind the evolution of the universe or any significant part of it? The evidence (salient features and emergent patterns revealed in the time indexes) suggests that we can't. The question of whether past universal configurations exist now is a nonsensical one.

Eternalists do not suggest that we can revisit the past, but rather that there is a time-less ontology which is defined globally, and that we just happen within a photogram of a global movie. It also implies that the present is observer-dependent. For presentists, only the present has a defined ontology. It also implies that the present is absolute.

 

[Dale]

Clearly our consciousness moves in the positive direction along the time axis, ... If you could travel back in time, my body would still be there. If you could travel forwards in time, my body would be there as well

Actually, if you are going to talk about consciousness and time then I would say that we travel backwards in time. If I walk "forwards" towards the north then I percieve objects to the north of me which I have not yet reached. On the other hand, if I walk "backwards" towards the north then I see objects to the south of me which I have already passed and have to guess about the position of objects I am approaching. Similarly with time, as I walk towards the future I remember only things in the past and I have to guess about things that I am approaching in my future. I think it is therefore pretty clear that as far as consciousness goes we travel backwards through time.

 

[ThomasT]

For example, I used the sentence, "My understanding of time is that it is stagnant and moves neither forwards nor backwards."

This contained the phrase "is stagnant." Literally, this would mean that time is stagnant at the present time. It 'would' not, however, specify whether time 'would be' stagnant in the past or future.

If we define time as an index (a certain sort of index, but an index nonetheless) of a set of physical states -- whether it's observed states in the near or distant past or extrapolated states which might include the future as well as the past -- then insofar as the index is a set of corrolations of 'stagnant' physical states (ie., each state is a 'snapshot' of the universe or some part of it that is associated with a 'snapshot' of a clock of some sort -- note that wrt time indexes the states aren't simply assigned a value according to some more or less arbitrary indexing scheme like, say, the Dewey Decimal System or whatever), then the states, or any subset thereof, specified in the index are all 'stagnant' whether they are past or present or future states.

Time indexes themselves, as records, aren't motion, and don't necessarily imply it. The word, motion, refers to the observation that at least some states in a time index are unique. An interesting feature of the time index of the universe is that all the states in that index are different, and they are different in a way that suggests that the universe is evolving away from previous states.

This feature of time indexes wrt any physical scale is what is commonly termed the 'arrow of time'.

I'm not sure if this adequately addressed your consideration, but it's the way I'm currently thinking about time. I used to equate time with motion or change, and I now think (as explained in my recent posts) that that's not quite correct.

I think we might be on the same page wrt this issue, but I'm not sure. The index that we call time is stagnant in the same sense that any index is stagnant. The general concept of an index is static in the same sense that the concepts of height, width, and depth are static.

The concept of time, just as the concept of motion, doesn't tell us anything about the physical world. These terms just refer to ways of organizing recorded data about the world and talking about it. And, as I mentioned, the evidence is that the world is indeed changing and will continue to change in ways revealed by our time indexes of it.

It may have been better to put this in the philosophy forum, although some (more) mathematical arguments would be nice. Maybe the entire thread could be moved.

Quantifiable mathematical shorthand representations are necessary to unambiguously communicate detailed statements about the world. But it's a good idea, I think, to have these sorts of semantic discussions in order to refine our ideas of what we're talking about and how it might be mathematically modeled.

For example, during the course of this discussion I discovered at least one error in the way I was thinking about the word, time.

If you think we're not on the same page wrt time, or if I've got it wrong in any of my ramblings, then your comments and criticisms are welcomed.

And, thanks for starting the thread.

 

[ThomasT]

Eternalists do not suggest that we can revisit the past, but rather that there is a time-less ontology which is defined globally, and that we just happen within a photogram of a global movie. It also implies that the present is observer-dependent. For presentists, only the present has a defined ontology. It also implies that the present is absolute.

Commonsensically we recognize that the word, time, refers to an index of sorts. But, without a detailed semantic analysis to more precisely ascertain what the word is referring to, we tend to reify it, and phrases like the flow of time or that we are moving in time emerge to confuse the issue. I view eternalism and presentism as byproducts of this confusion.

The ontological status of time is that it's a certain sort of index.

 

[xantox]

Commonsensically we recognize that the word, time, refers to an index of sorts. But, without a detailed semantic analysis to more precisely ascertain what the word is referring to, we tend to reify it, and phrases like the flow of time or that we are moving in time emerge to confuse the issue. I view eternalism and presentism as byproducts of this confusion.

It's not about the reification of time. Eternalists and presentists talk about events. Eternalists consider that all events share the same ontology. Presentists consider that only present events have an ontology.

 

[ThomasT]

Actually, if you are going to talk about consciousness and time then I would say that we travel backwards in time. If I walk "forwards" towards the north then I percieve objects to the north of me which I have not yet reached. On the other hand, if I walk "backwards" towards the north then I see objects to the south of me which I have already passed and have to guess about the position of objects I am approaching. Similarly with time, as I walk towards the future I remember only things in the past and I have to guess about things that I am approaching in my future. I think it is therefore pretty clear that as far as consciousness goes we travel backwards through time.

When Koko the signing gorilla was asked to point to the future she would point behind her. She could see the past, so it was in front of her. Or something like that

Anyway, what you wrote is compatible with the definition of time as an index of our experience.

 

[ThomasT]

It's not about the reification of time. Eternalists and presentists talk about events. Eternalists consider that all events share the same ontology. Presentists consider that only present events have an ontology.

Define an event as an indexed set of snapshots (subjective, ie., biologically sensed and recorded; or objective, ie., instrumentally recorded or via agreement of two or more subjective reports) of the world.

Subjective events and objective events share the same ontological status.

What we call the present, either wrt a subjective or an objective time index of the world, is the most recent past.

What we call the future is a projection or prediction regarding possible, but not yet recorded, events. A past might also be a backward extrapolated time index of possible, but not recorded, events.

Events (subjective and objective) and possible events don't share the same ontological status.

The word, time, doesn't refer to the object events of a time index or to any motion or change that might be revealed by the index. It refers to the index itself. An operational definition specifies a procedure for generating such an index. That's the ontological status of time.

 

[xantox]

What we call the future is a projection or prediction regarding possible, but not yet recorded, events. A past might also be a backward extrapolated time index of possible, but not recorded, events. All events don't share the same ontological status. Some are recorded and some aren't.

Recorded by who? Eternalists consider that all events no matter their time coordinate are recorded by some observer, so they all exist in some local present. They are just like events happening in a different space, say a different city : they all exist for someone who lives there. This means that the ontology of an event is independent from its space and time location, and that all events are recorded in Nature, which is like a giant Babel's library of all events.

For a presentist this is not true: only present events are real, and an event which happened in year 1020 only exists in present memories of it (which are in fact, other events), but the "original" event itself does not exist in Nature, which has a single memoryless state.

 

[ThomasT]

Originally Posted by ThomasT
What we call the future is a projection or prediction regarding possible, but not yet recorded, events. A past might also be a backward extrapolated time index of possible, but not recorded, events. All events don't share the same ontological status. Some are recorded and some aren't.

Recorded by who?

By us or instruments that we construct.

Eternalists consider that all events no matter their time coordinate are recorded by some observer, so they all exist in some local present. They are just like events happening in a different space, say a different city : they all exist for someone who lives there.

Our time indexed records, our objective histories, seem to indicate that this isn't the case. The conjectured occurance of certain events doesn't establish their existence in any sense other than as constituents of the projected or extrapolated time index in which they occur.

Of course, not having an objective record of some possible event or other doesn't necessarily mean that it can't or didn't happen. And the universe of our records is itself a record of sorts that preserves at least some aspects of its more distant history.

However, the idea that recorded past events exist in some physical sense other than as records would involve a reification of the time index, and there's no reason to do that. The time index, like any index, is just an index, a data organizing tool.

This means that the ontology of an event is independent from its space and time location ...

The ontological status of an event is a function of our apprehension of it in time indexes of spatial configurations.

... and that all events are recorded in Nature, which is like a giant Babel's library of all events.

As I mentioned, remnants of more distant past events might be found in more recent events, but there's no reason to suppose that (say) the Chicago of 1920 exists in any physical way other than the remaining remnants of it and as part of our historical records of it.

I think it's reasonable to reject eternalism.

For a presentist this is not true: only present events are real, and an event which happened in year 1020 only exists in present memories of it (which are in fact, other events), but the "original" event itself does not exist in Nature, which has a single memoryless state.

This makes more sense. However, as I've mentioned, what we call the present is actually a subset of the past.

Nevertheless, we can reasonably assume that there is single, memoryless spatial configuration that is the object of the most recent snapshot in our time index of an event.

 

[xantox]

I think it's reasonable to reject eternalism

However, only a physical theory, not reason alone, can be invoked to falsify whatever interpretation of reality (provided it is logically consistent). Special and general relativity falsify vanilla presentism, and are compatible with eternalism, so eternalism is the mainstream view amongst physicists. Since there is no full theory of quantum gravity, there is still a possibility that eternalism, or both eternalism and presentism, are wrong. According to some current incomplete theories of quantum gravity, some also falsify presentism and a very few others are compatible with both.

 

[ThomasT]

However, only a physical theory, not reason alone, can be invoked to falsify whatever interpretation of reality (provided it is logically consistent).

Physical theories are the result of reason applied to observations of the world.

Special and general relativity falsify vanilla presentism ...

I don't think so. It's just that since we get all of our info about the world via em, and since the rate of em propagation is finite, then we need a standard set of definitions, conventions, and procedures for generating time indexes in order to unambiguously communicate the information that those time indexes contain.

The idea that there is a single spatial configuration of the universe corresponding to each spatial configuration in a time index of an event isn't at odds with either SR or GR.

... and are compatible with eternalism ...

Yes, SR and GR can't be used to decide between presentism and eternalism.

... so eternalism is the mainstream view amongst physicists.

I don't think that's true. I don't think you'll find many physicists who think that the phrase "Plato exists" has any physical meaning other than wrt our historical records of him.

The grounds for rejecting eternalism and Plato's continued existence is in the information revealed in our time indexes of the world.

Since there is no full theory of quantum gravity, there is still a possibility that eternalism, or both eternalism and presentism, are wrong. According to some current incomplete theories of quantum gravity, some also falsify presentism and a very few others are compatible with both.

Our experience of the world is the final arbiter of statements about it, and our experience seems to indicate that time is an index -- no more, no less. Presentism is a reasonable extension of that. Eternalism isn't.

Both presentism and eternalism are nonsensical in that our experience can never (and hence no physical theory can ever unequivicably) establish the truth or falsity of either.

But, eternalism is the more nonsensical.

 

[xantox]

Physical theories are the result of reason applied to observations of the world.

Yes, which means indeed not reason alone.

The idea that there is a single spatial configuration of the universe corresponding to each spatial configuration in a time index of an event isn't at odds with either SR or GR.

If which is time for one observer is space for another and the opposite, how you consider it's not at odds? Perhaps you could elaborate this point.

I don't think you'll find many physicists who think that the phrase "Plato exists" has any physical meaning other than wrt our historical records of him.

It's even worse for quantum physicists, many of them considering that even "Plato may exist" has a physical meaning.

The grounds for rejecting eternalism and Plato's continued existence is in the information revealed in our time indexes of the world.

You seem to consider that "our time indexes of the world" have a preferred status vs those of an infinite number of other observers located elsewhere in spacetime.

Our experience of the world is the final arbiter of statements about it, and our experience seems to indicate that time is an index -- no more, no less. Presentism is a reasonable extension of that. Eternalism isn't.

The fact that time is an index says nothing about the ontology of events. Both presentists and eternalists will agree that time is what is indicated by a clock. The different ontologies of the two viewpoints concern the reality status of non-present events. Our understanding of the world is relativistic, and if simultaneity is relative there is a prima facie problem with presentism which is not trivial to solve.

 

[bassplayer142]

The way I see it, time as a fourth dimension is needed for the mathmatical model. The term "forward" when talking about time is just too abstract.

 

[ThomasT]

Originally Posted by ThomasT
Physical theories are the result of reason applied to observations of the world.

Yes, which means indeed not reason alone.

Right, what I was getting at was that we can use observation and reason to decide whether eternalism or presentism is closer to reality -- that we don't necessarily need a physical theory per se.
------------

Originally Posted by ThomasT
The idea that there is a single spatial configuration of the universe corresponding to each spatial configuration in a time index of an event isn't at odds with either SR or GR.

If what is time for one observer is space for another and the opposite, how do you consider it's not at odds? Perhaps you could elaborate this point.

The time of an event is, itself, an event. The time of a spatial configuration (or set thereof) is, itself, a spatial configuration (or set thereof).

Time is an index of events. Of course, acceleration (which includes gravity) affects time indexes -- and, SR and GR provide tools for transforming, and unambiguously communicating, time indexes from one frame of reference to another.
--------------

Originally Posted by ThomasT
I don't think you'll find many physicists who think that the phrase "Plato exists" has any physical meaning other than wrt our historical records of him.

It's even worse for quantum physicists, many of them considering that even "Plato may exist" has a physical meaning.

Ok. However, there's no particularly compelling reason to believe that all possible events in imaginary spaces (phase, Hilbert, spacetime, etc.) are in one to one correspondence with the real world. Physicists routinely discard solutions (allowed by models) that contradict observations.

One of the open questions in physics has to do with the problem of identifying a fundamental physical dynamic that makes events like broken teacups spontaneously reassembling themselves or Plato suddenly popping into existence (which, while so improbable that they'll never happen, are, nevertheless, possible wrt at least one model that's used extensively in physics) that have never been observed, and which would be contrary to the observed arrows of time, not just highly improbable but impossible in our universe.

An important thing to realize, imho, is that many (maybe most) of the various mathematical models of modern physics (especially wrt the quantum theory) aren't, and weren't developed as, descriptions of reality in any sense other than that they provide a framework or a scheme for predicting the outcomes of experiments.
-------------

Originally Posted by ThomasT
The grounds for rejecting eternalism and Plato's continued existence is in the information revealed in our time indexes of the world.

You seem to consider that "our time indexes of the world" have a preferred status vs those of an infinite number of other observers located elsewhere in spacetime.

Sure, I think our recorded observations of real spatial configurations (and extrapolations thereof) have a preferred status vs possible events in imaginary spaces (and extrapolations thereof). Don't you?
--------------

Originally Posted by ThomasT
Our experience of the world is the final arbiter of statements about it, and our experience seems to indicate that time is an index -- no more, no less. Presentism is a reasonable extension of that. Eternalism isn't.

The fact that time is an index says nothing about the ontology of events.

Ok -- but the indexes themselves do. I think that presentism is a reasonable extension of our experience and that eternalism isn't. Our experience is our time indexes of the physical world -- the world of our sensory experience.

(Of course, experimental results suggest that reality is deeper than that -- that there are spatial configurations in media that aren't amenable to our senses. It's reasonable to assume that there are wave structures, particulate media, and possibly non-particulate media that underly the behavior of the world of our senses. It's also reasonable to assume that, say, the wave mechanics of a deeper reality is not essentially different from the wave mechanics of the world of our sensory apprehension. But the eternalist assumption that the once extant now of the presentist still exists, somewhere in time, requires time to be something more than or other than just our indexes of our experience -- and, as I've mentioned, I don't think that the word, time, refers to anything more than or other than that.)
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Both presentists and eternalists will agree that time is what is indicated by a clock.

Yes, sort of like Copenhageners and MWIers agree that qm is a set of rules for calculating the probabilities of certain experimental preparations.

However, MWIers and eternalists attribute more, or a different, physical significance to their objects of consideration -- qm wavefunctions and time indexes, respectively -- than is necessary to understand their physical meaning.

The way that we resolve arguments about the world is by looking at the world. Our experience is the final arbiter of physical meaning. One problem that MWIers and eternalists have is that arguments concerning the truth or falsity of the physical states that they advocate are unresolvable.
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The different ontologies of the two viewpoints concern the reality status of non-present events.

As I understand it, the eternalist is saying that the real physical spatial configurations that correspond to the past, present, and future of the physical universe all exist simultaneously and eternally.

The presentist, on the other hand, is saying that existence is fleeting, and that the real physical spatial configuration of the universe that corresponded 5:00 pm on my clock doesn't exist by the time I percieve 5:00 pm on my clock.
---------------

Our understanding of the world is relativistic, and if simultaneity is relative there is a prima facie problem with presentism which is not trivial to solve.

Astronomers (who use SR and GR) are being presentists when they tell us that light that travelled, say, 10 light years is a record of a star or a galaxy as it existed 10 years ago.

Cosmologists (who also use SR and GR) routinely model the universe from a god's eye point of view. If the whole universe is the frame of reference, then there's no problem talking about one universal configuration corresponding to one configuration (say 5:00 pm) of some local clock.

The prima facie problem is with the eternalist who says that existence is eternal, because our experience tells us that it isn't.

 

[xantox]

Sure, I think our recorded observations of real spatial configurations (and extrapolations thereof) have a preferred status vs possible events in imaginary spaces (and extrapolations thereof). Don't you?

Your home exists as much as my one, though I never observed your living room. Thus both have the same ontological status independently from a spatial coordinate. Relativity implies in addition that, since the spatial slicing of spacetime is arbitrary and observer-dependent, the ontological status of events must also be independent from a time coordinate.

I think that presentism is a reasonable extension of our experience and that eternalism isn't. Our experience is our time indexes of the physical world -- the world of our sensory experience.

It is indeed more compatible with everyday experience. But are quarks compatible with everyday experience? Are particle physics observations less reliable than sensory experiences of cups of tea?

If the whole universe is the frame of reference, then there's no problem talking about one universal configuration corresponding to one configuration (say 5:00 pm) of some local clock.

The point of general relativity is precisely to say that there is no absolute "frame of the whole universe" like there was one in the Newtonian universe.

 

[IMP]

If anything anywhere changes in any way, time has lapsed. These changes only increase disorder so time only moves in one direction.

 

[ThomasT]

---Quote (Originally by ThomasT)---
Sure, I think our recorded observations of real spatial configurations (and extrapolations thereof) have a preferred status vs possible events in imaginary spaces (and extrapolations thereof). Don't you?

Your home exists as much as my one, though I never observed your living room. Thus both have the same ontological status independently from a spatial coordinate.

But not independently from our experience -- and our experience is coordinate dependent.

The location in real 3D space of some extant object can't be independent of the spatial coordinates that define the location.

We make the reasonable assumption that we exist at the same time at different coordinate locations in a 3 dimensional volume bounded by our sensory experience.
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Relativity implies in addition that, since the spatial slicing of spacetime is arbitrary and observer-dependent, the ontological status of events must also be independent from a time coordinate.

Spacetime is an imaginary space.
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---Quote (Originally by ThomasT
I think that presentism is a reasonable extension of our experience and that eternalism isn't. Our experience is our time indexes of the physical world -- the world of our sensory experience.

It is indeed more compatible with everyday experience. But are quarks compatible with everyday experience?

Not with my everyday experience. But they're certainly part of the everyday experience of physicists who use QCD in their work. Don't confuse some imagined, deep reality mode of existence of quarks with their actual mode of existence which is as mathematical constructs which relate various material and instrumental manipulations and behaviors. Independent of these sorts of events in someone's sensory experience of our world quarks don't exist.
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Are particle physics observations less reliable than sensory experiences of cups of tea?

Particle physics observations and teacup observations are both time indexes of spatial configurations of our 3D world, and my guess is that particle physics observations are less ambiguously communicated than teacup observations.
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---Quote (Originally by ThomasT)---
If the whole universe is the frame of reference, then there's no problem talking about one universal configuration corresponding to one configuration (say 5:00 pm) of some local clock.

The point of general relativity is precisely to say that there is no such "frame of the whole universe" like there was one in the Newtonian universe.

Nevertheless, the universe can be modeled as a bounded, expanding and evolving 3D volume whose internal spatial configurations are also continually changing. If you were to look at one frame of a movie of the universe, then it would show one unique spatial configuration and no others. In any specific 'now' of the universe there are no other 'nows'. If time is an idex of unique 'nows', and our collective experience seems to indicate that it is, then it would be incorrect to say that the universe, or any physical process for that matter, is 'moving through time' as the eternalist does.

Which do you like better, eternalism or presentism?

 

[xantox]

The location in real 3D space of some extant object can't be independent of the spatial coordinates that define the location.

OK for the location, but let's just talk about its existence, since that's where eternalism and presentism differ. If we consider that some object at the north pole keeps existing despite we're are in another continent, the relativity of simultaneity (which is an experimental fact) indicates that it must also keep existing despite we're in another time.

Don't confuse some imagined, deep reality mode of existence of quarks with their actual mode of existence which is as mathematical constructs which relate various material and instrumental manipulations and behaviors.

I suggested that the same applies to teacups. Teacups are theoretical constructs we form in our minds to relate various manipulations with the world - whose ontology is however not in our minds (no solipsism).

Nevertheless, the universe can be modeled as a bounded, expanding and evolving 3D volume whose internal spatial configurations are also continually changing. If you were to look at one frame of a movie of the universe, then it would show one unique spatial configuration and no others.

But again, nothing allows to choose a preferred 3D slicing instead of another, leading to the definition of a preferred time variable. The "state of the universe at a time T" is perfectly meaningless in general relativity.

Which do you like better, eternalism or presentism?

I used to dislike eternalism on the same basis one can dislike MWI at first, but afterwards found nothing wrong with it while noticing that literal presentism has a much weaker basis. However, eternalism has also various issues. This whole dichotomy will probably disappear by deepening the monolithic notion of "existence" into a much more fine-grained set of concepts.

 

[ThomasT]

OK for the loation, but let's just talk about its existence, since that's where eternalism and presentism differ. If we consider that some object at the north pole keeps existing despite we're are in another continent, the relativity of simultaneity (which is an experimental fact) indicates that it must also keep existing despite we're in another time.

We might define existence in terms of the similarities between, or degree of congruence of two spatial configurations.

Consider a freeze-frame of a movie of the spatial configurations bounded by our behavior, the various movements of you and I. In that one configuration, the readings on local clocks that you and I refer to will be different if you and I have different acceleration histories - - even if you and I started out from the same location with identical clocks with identical settings.

Nevertheless, we exist at the same time wrt a view which encompasses both of our locations -- ie., wrt a single spatial configuration that contains both of us.

Suppose we get back together and don't reset our clocks so that they show the same time, and the Earth explodes and we're blasted to smithereens. According to our local clocks, this explosion (that ended our existence) happened at different times. But to an observer on, say, the moon, you and I became smithereens at the same time.

The point is that it's reasonable to think of the universe (or any arbitrary grouping of objects therein) as a singular entity, and the evolution of the universe (or whatever) in terms of successive singular spatial configurations. If an object (a specific subset, including a proper subset, of a spatial configuration) isn't in a particular spatial configuration, and if the spatial configuration is the physical universe, then we say that the object doesn't exist.

Wrt the eternalist view, it's simply illogical to say that two different (incongruent) spatial configurations of the universe exist at the same time, if the time of the universe is it's spatial configuration (if 'a' time of the universe is a 'unique' spatial configuration), and if there is only one 'our universe'.

For the eternalist view to be coherent then, it's necessary that there be not just a larger but an infinite 'space' containing all the coexisting 'our universes'. And so time is rendered as a meaningless term. But the word, time, isn't meaningless. We use it, and it refers to something -- the question is, what?
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I used to dislike eternalism on the same basis one can dislike MWI at first, but afterwards found nothing wrong with it while noticing that literal presentism has a much weaker basis.

This stuff is new to me, and I thank you for intruducing me to it. My notion of time has changed during the course of this thread.

Presentism seems to be based on the idea of time as an index. Which is what I think time is -- no more, no less, and nothing other than.

The eternalist view of time has it as some sort of 'thing' that we're traveling through.
What's the basis for this view? I suggest that it, like presentism, comes from the notion of time as an index -- it's just that the eternalist's notion of that is less clear and this lack of clarity has led to thinking of time as something more, or other than, what it is. (We do, in a sense, 'travel through' our time indexes of the world in that they are our sensory experience, and our sensory experience is the world. The meaning of 'time passing' is equally understandable.)

It would seem that both presentism and eternalism are compatible with the idea of time as an index -- just as the Copenhagen and MW interpretations of qm are both compatible with the idea of qm as a probability calculus. But in their desire to have time and qm be more that what we can unambiguously say they are, the eternalists and MWIers have succeeded only in creating unresolvable problems and clouding the issue(s).

So, in defining time as an index, we have, I think, clearly abstracted its essence.
------------------------

This whole dichotomy will probably disappear by deepening the monolithic notion of "existence" into a much more fine-grained set of concepts.

I think a discussion along those lines might obfuscate the issue irreparably, if it isn't already.
--------------------------

---Quote (Originally by ThomasT)---
Don't confuse some imagined, deep reality mode of existence of quarks with their actual mode of existence which is as mathematical constructs which relate various material and instrumental manipulations and behaviors.

I suggested that the same applies to teacups. Teacups are theoretical constructs we form in our minds to relate various manipulations with the world - whose ontology is however not in our minds (no solipsism).

Yes, some particular teacup (eg., the one I'm now drinking tea out of) has a different mode of existence from the concept or abstraction, 'teacup'.

The difference between teacups and, say, photons (I don't know much at all about quarks) is that the unambiguous symbolic representation, 'this' teacup, refers to a single object of the world of our sensory experience that I can pick up or point at. The unambiguous symbolic representation, 'this' photon, however, refers to a set of mathematical symbols which in turn refer to many objects of the world of our sensory experience requiring various manipulations to (maybe) produce a set of instrumental behaviors which one could then point at as, collectively, corresponding to 'this' photon.
-------------------------
---Quote (Originally by ThomasT)---
Nevertheless, the universe can be modeled as a bounded, expanding and evolving 3D volume whose internal spatial configurations are also continually changing. If you were to look at one frame of a movie of the universe, then it would show one unique spatial configuration and no others.

But again, nothing allows to choose a preferred 3D slicing instead of another, leading to the definition of a preferred time variable.

There's no compelling reason to think that the universe isn't a bounded, expanding and evolving 3D volume whose internal spatial configuration is continually changing. So, any instantaneous 'snapshot' of its evolution should show a unique spatial configuration, just as any frame of some video you might shoot of the real world will be a unique picture.

The time (index) variables are the frames per second at which you are recording the video and the view that each snapshot encompasses (the reference frame). Elaborating how these variables affect our psychological or subjective time indexes should be an interesting exercise.
----------------------

The "state of the universe at a time T" is perfectly meaningless in general relativity.

What does 'time' mean in general relativity?

 

[xantox]

The point is that it's reasonable to think of the universe (or any arbitrary grouping of objects therein) as a singular entity, and the evolution of the universe (or whatever) in terms of successive singular spatial configurations.

Again, there is no way to define a preferred spatial configuration of the universe - just like for bread, which can be sliced in various ways, at various angles, etc so there cannot be a universal "present" slicing all observers can agree with.

What's the basis for this view? I suggest that it, like presentism, comes from the notion of time as an index

More or less yes - but in one case only present events are stored in nature's books, in the other all eternal events are written there once and for all.

So, in defining time as an index, we have, I think, clearly abstracted its essence.

Physical time has an operational definition - it is the reading of clocks. However it is not necessarily something fundamental, just like snow has been found not to be a fundamental substance. The only way to know more about that, is to build physical theories and obtain experimental confirmation.

The difference between teacups and, say, photons [..]

Yes, there is a little longer chain, but it looks like there is no essential difference between manipulating of photons with photon detectors and teacups with hands and eyes (well, photons look of course different than teacups because of their non-classical behavior, but that's another story).

What does 'time' mean in general relativity?

Nothing - it does not exist. It is not part of the fundamental theory.

 

[ThomasT]

---Quote (Originally by ThomasT)---
The point is that it's reasonable to think of the universe (or any arbitrary grouping of objects therein) as a singular entity, and the evolution of the universe (or whatever) in terms of successive singular spatial configurations.

Again, there is no way to define a preferred spatial configuration of the universe - just like for bread, which can be sliced in various ways, at various angles, etc so there cannot be a universal "present" slicing all observers can agree with.

I see the problem. I'm just talking about this for illustrative purposes, to sort out the logical implications. The fact that we can't actually take a picture of the whole universe is irrelevant.
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---Quote (Originally by ThomasT)---
What's the basis for this view? I suggest that it, like presentism, comes from the notion of time as an index

More or less yes - but in one case only present events are stored in nature's books, in the other all eternal events are written there once and for all.

Doesn't it seem sort of obvious that the latter (eternalism) is an unnecessary and unwarranted (not to mention physically meaningless) 'interpretation' -- given that they're both talking about the same thing?
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---Quote (Originally by ThomasT)---
So, in defining time as an index, we have, I think, clearly abstracted its essence.

Physical time has an operational definition - it is the reading of clocks.

Yes, we're discussing the physical meaning of the word, time. We have a general definition, an abstraction of the physical referents of time. They're indexes. The reading of 'clocks' is part of the process of generating those indexes.
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However it is not necessarily something fundamental, just like snow has been found not to be a fundamental substance.

I agree. Time isn't fundamental. Indexes aren't fundamental.

It could be argued that the expansion of the universe is fundamental. What do you think?
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The only way to know more about that, is to build physical theories and obtain experimental confirmation.

To know more about what is fundamental? Yes, I agree. There are reasons to believe that what science generally regards as fundamental might not be fundamental. But modern science is in its infancy. And advances in theory and hardware, and more and better data, will possibly lead to discoveries and realizations that are only just hinted at, or maybe not even imagined, now.
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---Quote (Originally by ThomasT)---
The difference between teacups and, say, photons [..]

Yes, there is a little longer chain, but nothing fundamentally different seems to separate the manipulating of photons with photon detectors and of teacups with hands ...

The point is that we have no direct apprehension of an underlying quantum 'reality' that quantum experimental phenomena suggest exists. Anything about such a reality, even its existence, has to be inferred from our sensory experience. So, the physical meaning of 'photon' isn't some entity or other that 'exists' in some 'reality' that we can't directly apprehend. The physical meaning of 'photon' is the experimental preparations that produce events called photon detections and the mathematical schemes which relate those preparations and events.
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---Quote (Originally by ThomasT)---
What does 'time' mean in general relativity?

Nothing - it does not exist. It is not part of the fundamental theory.

I don't think that's true. Isn't the physical meaning of 'proper' time the same in GR as in SR -- clock readings?

 

[xantox]

It could be argued that the expansion of the universe is fundamental. What do you think?

Do you mean, using the expansion as a clock?

There are reasons to believe that what science generally regards as fundamental might not be fundamental. But modern science is in its infancy. And advances in theory and hardware, and more and better data, will possibly lead to discoveries and realizations that are only just hinted at, or maybe not even imagined, now.

I certainly agree.

Doesn't it seem sort of obvious that the latter (eternalism) is an unnecessary and unwarranted (not to mention physically meaningless) 'interpretation' -- given that they're both talking about the same thing?

It is an argument about ontologies.. the difference is, roughly, that more events "exist" for an eternalist than for a presentist.

The physical meaning of 'photon' is the experimental preparations that produce events called photon detections and the mathematical schemes which relate those preparations and events.

This would become a separate discussion, but I still consider knowledge about photons qualitatively similar to knowledge about teacups - there are also teacup preparations producing teacup experiences, and some theory is encoded in our psychological schemas relating them.

I don't think that's true. Isn't the physical meaning of 'proper' time the same in GR as in SR -- clock readings?

I mean, there is no time at the fundamental level of the theory, where one is supposed to describe a "state of the universe" (which could then be the basis of what a presentist considers "existing"). Since the GR field equations are invariant under changes of spacetime coordinates, the theory do not describe evolution in time.

 

[baywax]

For example, I used the sentence

This contained the phrase "is stagnant." Literally, this would mean that time is stagnant at the present time. It 'would' not, however, specify whether time 'would be' stagnant in the past or future.

It may have been better to put this in the philosophy forum, although some (more) mathematical arguments would be nice. Maybe the entire thread could be moved.

Change is not stagnant. We use the "dimension" of time to "measure" change.

 

[ThomasT]

Originally Posted by ThomasT
It could be argued that the expansion of the universe is fundamental. What do you think?

Do you mean, using the expansion as a clock?

Yes as a clock, maybe 'the' universal clock, and as a (or the?) fundamental physical force.
-----------------

Originally Posted by ThomasT
Doesn't it seem sort of obvious that the latter (eternalism) is an unnecessary and unwarranted (not to mention physically meaningless) 'interpretation' -- given that they're both talking about the same thing?

It is an argument about ontologies.. the difference is, roughly, that more events "exist" for an eternalist than for a presentist.

Eternalism seems to be attributing a meaning to the word, time, that available or obtainable physical evidence doesn't and can't support.

Just as we've, I think, demonstrated that the word, time, has a clear conceptual physical meaning, it seems also that the physical meaning of the word, exist, should be amenable to the same sort of analysis.

I think that when we've done this analysis, then we'll see that the physical meaning of the word, exist, doesn't imply any sort of eternalistic interpretation of the word, time, just as the physical meaning of the word, time, doesn't imply any sort of eternalistic interpretation of the word, exist.
------------------

Originally Posted by ThomasT
The physical meaning of 'photon' is the experimental preparations that produce events called photon detections and the mathematical schemes which relate those preparations and events.

This would become a separate discussion, but I still consider knowledge about photons qualitatively similar to knowledge about teacups - there are also teacup preparations producing teacup experiences, and some theory is encoded in our psychological schemas relating them.

Insofar as our qualitative apprehension of either (or of anything for that matter) is based on sensory data, they're similar. But the vague heuristic, 'photon', is imho different from the physical abstraction, 'teacup'. I'm not sure how to articulate this to see if my intuition about it makes any sense, so a separate discussion in another thread here in the philosophy forum would be cool. Some aspects of that discussion might be related to our discussion of the difference between eternalism and presentism. I don't know -- so I'll start a new thread.
-----------------------

Originally Posted by ThomasT
I don't think that's true. Isn't the physical meaning of 'proper' time the same in GR as in SR -- clock readings?

I mean, there is no time at the fundamental level of the theory, where one is supposed to describe a "state of the universe" (which could then be the basis of what a presentist considers "existing"). Since the GR field equations are invariant under changes of spacetime coordinates, the theory does not describe evolution in time.

I know very little GR, so I don't really have any opinion about the correctness of your interpretation(s) of its relationship to our time indexed records of sensory experience. What I do know of it suggests to me that it can't be used as a basis for evaluating the ontological status of the objects of those records.

I still don't know what the eternalist means when he says "Plato exists". I do however know what the presentist means when he says that the Plato of antiquity no longer exists in any physical sense other than as an object of our historical records, and as an object of thoughts and communications regarding those records.

It seems that there's no way to establish, absolutely, the correctness of either eternalism or presentism -- but presentism makes a lot more sense to me. That is, presentism seems to be an acceptable logical extension of our experience of the world, whereas eternalism doesn't.

We've agreed that the physical meaning of time is that the word, time, refers to indexes or ordered records of our experience. In what sense do we travel through time other than simply perusing those records -- whether they be data streams from physics experiments, or photo albums, or written rememberances, or configurations of internal components of our brains and bodies, or etc.?

 

[xantox]

[..]It could be argued that the expansion of the universe is fundamental [..] as a clock, maybe 'the' universal clock, and as a (or the?) fundamental physical force.

It is possible to choose the scale factor of the universe (its "radius") as a temporal parameter, but it is only valid under special conditions, as for example if the universe recollapses, then it is no longer a well-defined clock. Also, it remains one, completely arbitrary, choice between infinite possible others.

I think that when we've done this analysis, then we'll see that the physical meaning of the word, exist, doesn't imply any sort of eternalistic interpretation of the word, time.

I don't see any obvious demonstration like that so I can't comment, perhaps try to sketch it.

I know very little GR, so I don't really have any opinion about the correctness of your interpretation(s) of its relationship to our time indexed records of sensory experience. What I do know of it suggests to me that it can't be used as a basis for evaluating the ontological status of the objects of those records.

GR provides a far superior knowledge about spacetime than our everyday understanding based on our sensory experiences. Either our everyday knowledge cannot be used too as a basis for that ontological questioning (meaning this questioning has no meaning at all), either the theory encoding more knowledge about the same objects shall also pretend to better enlighten us on their ontology.

I still don't know what the eternalist means when he says "Plato exists".

He means about the same as we means when we say "Rio de Janeiro exists", or "Andromeda exists", eg he considers the ontology of events in distant times equal to that of events in distant spaces.

It seems that there's no way to establish, absolutely, the correctness of either eternalism or presentism -- but presentism makes a lot more sense to me. That is, presentism seems to be an acceptable logical extension of our experience of the world, whereas eternalism doesn't.

There is probably no way to establish the absolute correctness of any physical theory either. However, eternalism makes a lot more sense within general relativity, and, general relativity is the most acceptable logical extension of our experience of spacetime that we have – this is the stronger chain. On the other side, measuring ontological questions directly within the shorter-sighted horizon of our everyday experience is the weaker chain.

We've agreed that the physical meaning of time is that the word, time, refers to indexes or ordered records of our experience. In what sense do we travel through time other than simply perusing those records -- whether they be data streams from physics experiments, or photo albums, or written rememberances, or configurations of internal components of our brains and bodies, or etc.?

Again, ontological questions are separate from the way a particular observer can or cannot access/travel the world, as they are supposed to be the objective foundations of what can be accessed by at least some others (local) observers. Trees in the forest fall even when we're not there to see them.

 

[ThomasT]

It is possible to choose the scale factor of the universe (its "radius") as a temporal parameter, but it is only valid under special conditions, as for example if the universe recollapses, then it is no longer a well-defined clock.

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

Also, it remains one, completely arbitrary, choice between infinite possible others.

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.

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.

I don't see any obvious demonstration like that so I can't comment, perhaps try to sketch it.

Physical meaning is synonymous with sensory data. The physical meaning of a statement about physical reality is disambiguated via operational definition of the object or event or process in question.

GR provides a far superior knowledge about spacetime than our everyday understanding based on our sensory experiences.

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.

Either our everyday knowledge cannot be used too as a basis for that ontological questioning (meaning this questioning has no meaning at all), or the theory encoding more knowledge about the same objects shall also pretend to better enlighten us on their ontology.

"Pretend" is the key word. But, I'll agree that some metaphysical concepts make more sense than others. I think that, eg., the notion of 'spacetime curvature' is a gross oversimplification. There are better candidates, such as complex wave interaction, for the deep nature of gravitational kinematics.

He (the eternalist) means about the same as we mean when we say "Rio de Janeiro exists", or "Andromeda exists", eg he considers the ontology of events in distant times equal to that of events in distant spaces.

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.

There is probably no way to establish the absolute correctness of any physical theory either. However, eternalism makes a lot more sense within general relativity, and, general relativity is the most acceptable logical extension of our experience of spacetime that we have – this is the stronger chain.

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

On the other side, measuring ontological questions directly within the shorter-sighted horizon of our everyday experience is the weaker chain.

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. They're physical theories in that they're schemes for calculating experimental results. That's all. Also, there's observational evidence that tells us that eternalism (as well as MWI) is just bad metaphysics.

Again, ontological questions are separate from the way a particular observer can or cannot access/travel the world, as they are supposed to be the objective foundations of what can be accessed by at least some others (local) observers.

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.

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.

Trees in the forest fall even when we're not there to see them.

OK ... what's this supposed to be analogous to in the context of our discussion?

 

[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.