Is Time a Series or a Theory: What Do Philosophers Think?

[GeorgeDishman]

After some thought, even if theories such as SR may suggest that there is a block universe, I think it is a mistake to go as far to say that there exists no change whatsoever in the world,

The block universe model doesn't say there is no change, change will still happen but, to some people in my present, those changes have already happened therefore must already have a fixed value. Viewed that way, it suggests that the future is not open to alteration by our decisions, it is predetermined and therefore the outcome of our decisions must also be predetermined. Thus it argues against free will.

However, that ignores Heisenberg Uncertainty which says that at the quantum level, outcomes are random and can only be constrained statistically. That reflects as true randomness in Brownian motion and thermal noise in electrical signals, both of which affect the connections between neurons in the brain. Hence I contend that sufficiently finely balanced decisions must have a random component and the future cannot be fully predetermined.

especially in the face of our own changing conscious experience. Personally, I see this experience in itself as being enough to support the A-series as I defined it, though some B-theorists may just accept it as an "illusion" to be explained. So even if I accept those theories, I believe that there has to be some way to reconcile this experience with reality, either by defining some "present moment" to the physical universe somehow, or maybe even going beyond that and distinguishing between the time of our experience and the time of the physical world.

Many would say that assigning a physical "present" to the universe conflicts with the observations that support relativity but that is still subject to some debate. Perceived time is another matter. The present is our "now" and after some thought, the only definition I can suggest for "now" is this:

Now is the moment that separates that part of my life which, in principle, I can remember from that which I can only anticipate.​

Looking back over your life, you never experienced anything that didn't happen "now" at the time when it happened and the same is true of future events, the time will be "now" when they happen too. It also means that your now and my now are independent, it does not require a universal now for all. Interaction is still constrained to be within our future and past light cones by causality of course.

It is tempting to think of "now" as a surface between a quantum entangled "many worlds" future versus the single-valued past described by history books, but that surface then identifies a form of presentism which again is questionable according to relativity. Instead, I think physics has symmetry in local time and Feynman's "sum over histories" suggests our past may also be entangled and multi-valued in some sense. The way my views are heading is that our preceived "now" is like a pinch-point in a quantum-entagled universe created by the past and future light cones which limit our experience and influence respectively.

 

[lmoh]

The block universe model doesn't say there is no change, change will still happen but, to some people in my present, those changes have already happened therefore must already have a fixed value.

Depends upon what you mean by "change". I was following my definition of change from the OP, which was referring to something like the flow of time (I apologize if I didn't make that explicit earlier). I agree that the block universe model in itself does not entail no change as I have defined it, as I said before, but that it is also compatible with the "Moving Spotlight" view of time which is part of the A-series.

Viewed that way, it suggests that the future is not open to alteration by our decisions, it is predetermined and therefore the outcome of our decisions must also be predetermined. Thus it argues against free will.

However, that ignores Heisenberg Uncertainty which says that at the quantum level, outcomes are random and can only be constrained statistically. That reflects as true randomness in Brownian motion and thermal noise in electrical signals, both of which affect the connections between neurons in the brain. Hence I contend that sufficiently finely balanced decisions must have a random component and the future cannot be fully predetermined.

The block universe model does not necessarily require determinism and it is compatible with indeterminism as far as I am concerned. There is no problem in imagining events on the block universe that have no strict connection to other events.

As for free will, for the most part, I am a pretty open compatibilist on the issue, so determinism (and even indeterminism) does not pose a problem for me. But that's a topic for another discussion.

Many would say that assigning a physical "present" to the universe conflicts with the observations that support relativity but that is still subject to some debate.

Yeah, I understand. That is why I am just holding out for either some hidden "present" that is compatible with relativity, or some way to define a "present moment" in later physics if that is possible. But if push comes to shove, there can be a block universe, but it would be like the Moving Spotlight view above.

As far as I am concerned, we experience the world in sequence, and that is enough to vindicate the A-series. Note that I am not talking about what we perceive, but how we perceive it. I am not going to say that the physical universe changes (indeed, it may be like a block universe), but at the very least, there is change when it comes to consciousness.

Perhaps this is related to the issue between mind and matter, at least this is how this paper I read years ago defines it: http://fqxi.org/data/essay-contest-files/Nikolic_FQXi_time.pdf. I highly recommend you read it, because some of it speaks to my own views on the matter, and probably describes it in a better way than mind.

 

[GeorgeDishman]

Depends upon what you mean by "change". I was following my definition of change from the OP, which was referring to something like the flow of time (I apologize if I didn't make that explicit earlier). I agree that the block universe model in itself does not entail no change as I have defined it, as I said before, but that it is also compatible with the "Moving Spotlight" view of time which is part of the A-series.

I was keeping it more general and simple meaning different states at different times without implying flow or any other model for time.

The block universe model does not necessarily require determinism and it is compatible with indeterminism as far as I am concerned. There is no problem in imagining events on the block universe that have no strict connection to other events.

Agreed but an indeterminate future together with a single-valued past implies a point between where the many possibilities become the one selected, perhaps like the Copenhagen Interpretation of QM. A surface joining those points looks like the present of a Moving Spotlight model (of which more later).

As for free will, for the most part, I am a pretty open compatibilist on the issue, so determinism (and even indeterminism) does not pose a problem for me. But that's a topic for another discussion.

As am I so it isn't a threat to my world view, but philosophically there is a fundamental difference which warrants consideration, perhaps even a dichotomy.

Yeah, I understand. That is why I am just holding out for either some hidden "present" that is compatible with relativity, or some way to define a "present moment" in later physics if that is possible. But if push comes to shove, there can be a block universe, but it would be like the Moving Spotlight view above.

A "present" is required by QM but incompatible with relativity, that's the problem with unified theories. I found a paper on this by Skow but haven't had time to read it yet:

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

As far as I am concerned, we experience the world in sequence, and that is enough to vindicate the A-series. Note that I am not talking about what we perceive, but how we perceive it. I am not going to say that the physical universe changes (indeed, it may be like a block universe), but at the very least, there is change when it comes to consciousness.

If you read my definition of "now", I think we are of like mind on this.

Perhaps this is related to the issue between mind and matter, at least this is how this paper I read years ago defines it: http://fqxi.org/data/essay-contest-files/Nikolic_FQXi_time.pdf. I highly recommend you read it, because some of it speaks to my own views on the matter, and probably describes it in a better way than mind.

OK, it's on a fairly long list though ;-)

 

[lmoh]

I was keeping it more general and simple meaning different states at different times without implying flow or any other model for time.

Yeah, that was the sort of definition I was expecting, and I don't think anybody would disagree with it. I should probably use a different word next time.

Agreed but an indeterminate future together with a single-valued past implies a point between where the many possibilities become the one selected, perhaps like the Copenhagen Interpretation of QM. A surface joining those points looks like the present of a Moving Spotlight model (of which more later).

Something doesn't sound right here, but I cannot pinpoint it exactly. If this conception has any relation to the Moving Spotlight model, then I am not sure what you are referring to by the terms "future" and "past" here.

Usually, I imagine an MS model would consist of two times, one of the Block universe, and one in which time lapses (this is what I would attribute to consciousness). The relation between these two times is pretty much as the name describes it: the latter time "moves" along the former time so to speak, shining upon each and every moment of it successively (like a moving spotlight). With that in mind, I cannot make out what you are saying here.

A "present" is required by QM but incompatible with relativity, that's the problem with unified theories. I found a paper on this by Skow but haven't had time to read it yet:

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

Even if I am holding out for some A-theory in physics, I am not so sure about that. I have heard that QM does not necessarily require a present moment, especially since we agree that indeterminism poses no threat here.

On another note, people have already combined QM and SR to form Quantum Field Theory, so they are not totally incompatible. It is QM and GR that are incompatible, according to my knowledge. Whether a combination of the two would open up a path for a "present moment" is still to be seen though.

As for the paper, I am not sure if I've read it before (I looked into the philosophy of time a while back, but barely have a recollection of it), but I will get back to it later if I can.

If you read my definition of "now", I think we are of like mind on this.

Yeah, I've read over it, but I felt as though the definition dealt more with the contents of experience rather than how we experience it, a distinction in which I referred to in my last post. But I am guessing if you were aware of this, then we would agree for the most part here.

OK, it's on a fairly long list though ;-)

No worries. Take your time . But if it takes some of the load off, the paper is fairly short.

 

[GeorgeDishman]

Yeah, that was the sort of definition I was expecting, and I don't think anybody would disagree with it. I should probably use a different word next time.

It's difficult to avoid implying a temporal model just because the concept is ingrained in our language.

Agreed but an indeterminate future together with a single-valued past implies a point between where the many possibilities become the one selected, perhaps like the Copenhagen Interpretation of QM. A surface joining those points looks like the present of a Moving Spotlight model (of which more later).

Something doesn't sound right here, but I cannot pinpoint it exactly. If this conception has any relation to the Moving Spotlight model, then I am not sure what you are referring to by the terms "future" and "past" here.

Usually, I imagine an MS model would consist of two times, one of the Block universe, and one in which time lapses (this is what I would attribute to consciousness). The relation between these two times is pretty much as the name describes it: the latter time "moves" along the former time so to speak, shining upon each and every moment of it successively (like a moving spotlight). With that in mind, I cannot make out what you are saying here.

That's how I view it too. You've probably seen sci-fi films where something is "scanned" by having a laser swept to form a plane of light which then moves across it. If the block universe is a glass paperweight with the big bang at one end and the heat death of the universe at the other, the "Moving Spotlight" is like that laser plane moving through it. Our present (the location of consciousness) is the point where the plane intersects our individual worldline and the time of cosmology is a measure of how far through the glass the plane has moved (13.7 billion years so far). In that model, the past is the section that has already been scanned and the future lies ahead of the spotlight plane.

Our perception of a "flow of time" in this model is like looking out of a train window and seeing the countryside flow past, but in fact the landscape ahead is already set in stone and the flow is an illusion. "Change" is the sequential variation of the intersection of the plane with the worms of our lifelines.

Yeah, I've read over it, but I felt as though the definition dealt more with the contents of experience rather than how we experience it, a distinction in which I referred to in my last post. But I am guessing if you were aware of this, then we would agree for the most part here.

Your distinction is rather subtle, I see our awareness of the passage of time as emergent, an interpretation of the accumulation of seemingly ordered memories. However, that gets us into the complexities of neuroscience and I'm far from up on that topic!

 

[lmoh]

Your distinction is rather subtle, I see our awareness of the passage of time as emergent, an interpretation of the accumulation of seemingly ordered memories. However, that gets us into the complexities of neuroscience and I'm far from up on that topic!

I just want to hammer in your last point here. Memories are necessary for a perceived change, are not necessarily required for changes in perception. I can be an animal with virtually no memory of my life, yet I can still experience t1, then t2, then t3, even if at t2, I have no perception that time has passed from t1 to t2 (because I barely have an ordered memory of it).You can say that neuroscience can deal with the former well, but as for the latter, it is a bit more complicated. In fact, if we are going to have a block universe scenario, then as I said before, the emergence of this kind of "passage of mind" may be entirely unrelated to the issue of matter. But with that said, it is possible to view our changing experiences as the byproduct of having brain states in different parts of the block universe, especially if you take in entropy as a description for why our experience moves from t1 to t2.

 

[mangaroosh]

Just a question about the A-theory of time, and presentism in particular: I thought the concept was fairly well understood, but in a discussion on this site, it appears that it might not be that well understood.

I'm just looking for a fairly concise explanation of presentism. I would say that it is the idea that there is a single, universal present moment, common to all observers. I would see this as being incompatible with the relativity of simultaneity, which I think leads to the B-theory of time, and the idea that there is no single, universal present moment, but that the present moment is relative to each individual (although it can be shared).

I was also under the impression that Lorentz Ether Theory incorporates presentism, I'm just wondering if anyone knows if this is true or not?

p.s. I don't want to get into a philosophical discussion about the accuracy, or otherwise of LET, I'm just wondering if it incorporates the concept of presentism [as I outlined above]

 

[GeorgeDishman]

Just a question about the A-theory of time, and presentism in particular: I thought the concept was fairly well understood, but in a discussion on this site, it appears that it might not be that well understood.

I'm just looking for a fairly concise explanation of presentism. I would say that it is the idea that there is a single, universal present moment, common to all observers.

Presentism is the belief that only the present moment exists. This is a basic article on it:

http://en.wikipedia.org/wiki/Presentism_(philosophy_of_time )

This is more comprehensive and introduces relativity too:

http://plato.stanford.edu/entries/temporal-parts/

I would see this as being incompatible with the relativity of simultaneity,

From the SEP page:

"If STR thereby rules out presentism, and if endurantism requires presentism in order to explain change (see section 3), then STR rules out endurantism: things have temporal parts. But not all endurantists agree that they must be presentists, and not all presentists agree that their view is undermined by STR."​

which I think leads to the B-theory of time, and the idea that there is no single, universal present moment, but that the present moment is relative to each individual (although it can be shared).

This article should give you a clearer idea of the A and B theories:

http://www.iep.utm.edu/time/#H1

This is a paper on B-theory by Pruss which might also give you some background:

http://www9.georgetown.edu/faculty/ap85/papers/BTheory.html

I was also under the impression that Lorentz Ether Theory incorporates presentism, I'm just wondering if anyone knows if this is true or not?

What I suggested in the other forum was that it is difficult to start from a presentist philosphical approach and not be driven to an aether-style theory but the converse need not be true. It is possible for example to assume clock effects caused by an aether within the philosophy of a block universe, but much of the motivation for the block view is then removed.

p.s. I don't want to get into a philosophical discussion about the accuracy, or otherwise of LET, I'm just wondering if it incorporates the concept of presentism [as I outlined above]

The accuracy or otherwise of theories is not a philosophical topic anyway and would probably be inappropriate here.

 

[lmoh]

I'm just looking for a fairly concise explanation of presentism.

Presentism is basically the idea that only the present exists. However, what is meant by "present" can vary. The present moment may consist of a single moment in time or consist of multiple moments or an "extended present" (Luigi Acerbi advocated this earlier in the thread) for example, and if you want, you can even extend presentism to include something like the moving spotlight view (which George Dishman mentioned in the other thread).

I would see this as being incompatible with the relativity of simultaneity, which I think leads to the B-theory of time, and the idea that there is no single, universal present moment, but that the present moment is relative to each individual (although it can be shared).

I would not necessarily say that the B-theory would follow, and there are some people would follow me on that point as George . As for myself, I would at best say that it may suggest a block time, but that does not necessarily vindicate the B-theory, and I would still hold on to an A-theory for my own reasons mentioned earlier.

I was also under the impression that Lorentz Ether Theory incorporates presentism, I'm just wondering if anyone knows if this is true or not?

I would not necessarily say that LET incorporates presentism, but is compatible with it, just as SR does not necessarily rule out presentism (assuming that you can assume an undetectable present that is not the same as an ether theory). Scientific theories are indfferent on philosophical issues such as this.

The only person that I can recall that uses LET to support presentism is William Lane Craig, who opts for a "neo-lorentzian" interpretation (and he is the only person to do so apparently according to a paper I've read a while ago). I am not a fan of his work though, but you can look him up if you want.

 

[mangaroosh]

Presentism is basically the idea that only the present exists. However, what is meant by "present" can vary. The present moment may consist of a single moment in time or consist of multiple moments or an "extended present" (Luigi Acerbi advocated this earlier in the thread) for example, and if you want, you can even extend presentism to include something like the moving spotlight view (which George Dishman mentioned in the other thread).

Thanks for the reply lmoh.

That would be my own general understanding also, but with the added qualification that there is only one present, common to all observers.

I would not necessarily say that the B-theory would follow, and there are some people would follow me on that point as George . As for myself, I would at best say that it may suggest a block time, but that does not necessarily vindicate the B-theory, and I would still hold on to an A-theory for my own reasons mentioned earlier.

I suppose it depends on what is meant by RoS; if it refers to the mutual simultaneity and non-simultaneity of events, then I think it would have to lead to a B-theory, because it would mean that there is no universal present.

I would not necessarily say that LET incorporates presentism, but is compatible with it, just as SR does not necessarily rule out presentism (assuming that you can assume an undetectable present that is not the same as an ether theory). Scientific theories are indfferent on philosophical issues such as this.

I think it is a nice notion that scientific theories are indifferent on philosophical issues, but insofar as they are based on certain assumptions, they tacitly assume a philosophical position on certain specific issues.

LET appears to be founded on Newtonian assumptions about space and time, which was inherently presentism-friendly; while Einsteinian relativity doesn't appear to be presentism-friendly.

I don't mean to be facetious, but saying that SR doesn't necessarily rule out presentism, assuming that you can assume an undetectable present that is not the same as an ether theory, sounds a bit like saying, it doesn't rule out presentism as long as you can find an undetectable present that is compatible with SR.

If the above description of RoS is accurate, and SR incorporates it, then it is incompatible with the definition of presentism above.

The only person that I can recall that uses LET to support presentism is William Lane Craig, who opts for a "neo-lorentzian" interpretation (and he is the only person to do so apparently according to a paper I've read a while ago). I am not a fan of his work though, but you can look him up if you want.

I discovered as much, myself, after learning about LET on here, when trying to find out more about it. It is an unfortunate fact that it's WLC who happens to be trying to resurrect it, given his expressed motivation for doing so, but it might provide for healthy debate of the issue, to a certain extent that is.

 

[GeorgeDishman]

I would not necessarily say that the B-theory would follow, and there are some people would follow me on that point as George . As for myself, I would at best say that it may suggest a block time, but that does not necessarily vindicate the B-theory, and I would still hold on to an A-theory for my own reasons mentioned earlier.

I suppose it depends on what is meant by RoS; if it refers to the mutual simultaneity and non-simultaneity of events, then I think it would have to lead to a B-theory, because it would mean that there is no universal present.

As has been said many, many times, the term "relativity of simultaneity" comes from SR and in SR it refers to the consequences of clock synchronisation. Since clocks in reality behave in one particular fashion RoS must apply to any theory that accurately describes that behaviour regardless of any philosophy.

However, SR also has a geometric interpretation (often attributed to Minkowski rather than Einstein) which is also carried forward to GR. That interpretation describes a 4-dimensional hypervolume we call spacetime. Within that, there is nothing intrinsic which uniquely distinguishes the basis vector of time. Since a surface of uniform time (isotemporal?) would be perpendicular the time vector, it too cannot be physically meaningful, thus the geometric interpretation of SR which is fundamental to GR supports the B-theory (and 4-dimensionalism in particular).

The effect known as "relativity of simultaneity" is irrelevant from the philosophical perspective.

 

[petm1]

Since a surface of uniform time (isotemporal?) would be perpendicular the time vector,it too cannot be physically meaningful,

Isn't the surface of matter a surface of uniform time, with every point of its surface perpendicular to its center of mass? If the act of being re/emitted only happens in the present then it only happens at what I see as the surface of matter, when coupled with the sun as the spotlight looks more like A=series.

 

[GeorgeDishman]

Isn't the surface of matter a surface of uniform time,

No, I wasn't talking about matter at all. Are you perhaps thinking of the geoid defining the surface of the Earth being a surface of uniform gravitational potential?

with every point of its surface perpendicular to its center of mass?

The rotation of the planet makes it slightly oblate so, other than at the poles and equator, a perpendicular to the surface doesn't pass through the centre.

If the act of being re/emitted only happens in the present then it only happens at what I see as the surface of matter, when coupled with the sun as the spotlight looks more like A=series.

I have no idea what that is supposed to mean, sorry.

None of your comment appears to relate to foliation of spacetime.

 

[mangaroosh]

Are the A- and B-theories of time linked to any scientific theories?

The impression that I get is that B-theory is linked to Einsteinian relativity, or that it is compatible with it, while A-theory is not compatible with Einsteinian relativity.

 

[mangaroosh]

EDIT: I don't want to derail this thread into a discussion about RoS, so I will just reply to this one post and leave it at that.

As has been said many, many times, the term "relativity of simultaneity" comes from SR and in SR it refers to the consequences of clock synchronisation. Since clocks in reality behave in one particular fashion RoS must apply to any theory that accurately describes that behaviour regardless of any philosophy.

One of the consequences of that clock synchronisation appears to be that events that are simultaneous in one reference frame can be non-simultaneous in another; at least that is the definition that was supplied by some of the other posters on here. If that is the case, then it is incompatible with presentism, or the idea that there is a universal present, common to all observers, and therefore incompatible with the A-theory.

However, SR also has a geometric interpretation (often attributed to Minkowski rather than Einstein) which is also carried forward to GR. That interpretation describes a 4-dimensional hypervolume we call spacetime. Within that, there is nothing intrinsic which uniquely distinguishes the basis vector of time. Since a surface of uniform time (isotemporal?) would be perpendicular the time vector, it too cannot be physically meaningful, thus the geometric interpretation of SR which is fundamental to GR supports the B-theory (and 4-dimensionalism in particular).

The effect known as "relativity of simultaneity" is irrelevant from the philosophical perspective.

Again, if one of the consequences of the effect known as RoS is that events which are simultaneous in one reference frame are non-simultaneous in another - as mentioned by DaleSpam and Harrylin - then it preculedes the philosophical perspective of A-theory and favours B-theory.

 

[harrylin]

[..] One of the consequences of that clock synchronisation appears to be that [..] it is incompatible with presentism, or the idea that there is a universal present, common to all observers, and therefore incompatible with the A-theory.[..]

Quite to the contrary - the cited reference of the OP explains as one variant of the A-model:
"it can be plausibly argued that the theory [of relativity ] [..] has no bearing on whether there is such a phenomenon as absolute simultaneity."

Consistent with that (and despite the fact that I don't believe in a literal "flow of time"), I will now vote A.
A very hasty reading gives me the impression that I largely agree with Taggert, as I define time as being a measure of progress of physical processes - which implies change.

PS however, I now see that Taggert claimed that A is wrong, despite the fact that he largely agreed with my thinking; and like him I also hold that time doesn't really exist. And I definitely disagree with B. Thus perhaps I should change my vote to "other"?

 

[harrylin]

I now see that it's impossible to correct a vote; thus it's not a very good poll, regretfully. While I certainly disagree with B, I'm not sure that I fully agree with A.

 

[lmoh]

Consistent with that (and despite the fact that I don't believe in a literal "flow of time"), I will now vote A.

A very hasty reading gives me the impression that I largely agree with Taggert, as I define time as being a measure of progress of physical processes - which implies change.

If by "literal flow of time" you are referring to some substance called time that flows from past to future, then I essentially agree with what you are saying. For me, what you are saying sounds more like the issue of whether or not time or change is fundamental (you can refer to Section 2 of my orignal link for more info). Many (including myself) would argue the same that time cannot exist without change, that it is simply a measure of change, but I don't see how that matches up with McTaggert's thinking.

I now see that it's impossible to correct a vote; thus it's not a very good poll, regretfully. While I certainly disagree with B, I'm not sure that I fully agree with A.

Same here. I actually felt like changing my position to "A" from "I don't know" after some recent thought, but apparently I can't change my vote either.

 

[harrylin]

[..] Same here. I actually felt like changing my position to "A" from "I don't know" after some recent thought, but apparently I can't change my vote either.

Did you not create this poll? I guess that it depends on how the poll is set up...
Still it gives a very rough indication about how participants think about time; it appears that there is no clear majority view!

 

[GeorgeDishman]

Many (including myself) would argue the same that time cannot exist without change, that it is simply a measure of change, but I don't see how that matches up with McTaggert's thinking.

Do you think there is an aether which interacts with physical systems moving through it so that clocks (including radioactive decay) tick more slowly rather than the geometric explanation given by SR? If not, I may be able to give an example that sheds some light on the question.

It might be tomorrow, I have to go out soon.

 

[lmoh]

Do you think there is an aether which interacts with physical systems moving through it so that clocks (including radioactive decay) tick more slowly rather than the geometric explanation given by SR? If not, I may be able to give an example that sheds some light on the question.

It might be tomorrow, I have to go out soon.

I am not sure what you are referring to, but in regards to your question, I am going to say no. Let's see where this goes.

 

[GeorgeDishman]

I am not sure what you are referring to, but in regards to your question, I am going to say no. Let's see where this goes.

Just checking, I've got a lot to type and I'd be wasting my time if you said yes so leave that aside now.

I want to approach this through a slightly different pair of philosophies, enduratism versus perdurantism, then return to presentism at the end.

Endurantism says that an object is wholely present at one instant of time, i.e. objects are 3-dimensional and change as objects or in relation to other objects as a function of time while perdurantism says that objects as 4-dimensional entities so what we see at any moment is a mere snapshot or a slice intersecting their worldline.

Consider the classic twins scenario. Bob and Alice have their joint 20th birthday party on a space station near Earth in the year 2020 after which Alice is to fly 4 light years to a space station near Alpha Centauri. They agree to meet up for another joint party on the station on her return.

She travels at 0.8c so it takes her 5 years of Earth time and by Pythagoras 3 years of ship (proper) time. Hence she celebrates her 23rd birthday near Alpha Centauri in the year 2025. She then flies back to Earth at the same speed arriving on Earth just in time to have her 26th birthday party on the space station in 2030. Four years later, she will celebrate her 30th birthday on the same station in the year 2034.

For a moment, suppose the endurantist view of existence applies to people but not inanimate objects. Alice exists only at one instant; on a spacetime diagram you can think of a bright point moving along her worldline. The line has no reality, it is merely a representation of the history of her life, she exists only at one point on the line. If there is no aether-like slowing of her metabolic processes, her 30th birthday happens 10 years after her 20th, and she celebrates with a party in the station in the year 2034. Bob also celebrates his 30th in the space station, but since he has been on Earth all the time, he does so in the year 2030. Now since each of them only exists at one instant, they may be in the same place but they are in different years, they cannot meet! (In fact in the endurantist view, the problem would also apply to the space station which could only be present in one of the years.)

The predurantist view doesn't suffer this problem. For example if you think of a person like a "worm" stretching through time, the perdurantist says that all parts of their life have an equal claim to existence. Thus the 26 year old Alice meets up with 30 year old Bob and they can have a joint party in 2030. You could also add other siblings who make similar trips at different speeds and the general result is that the whole of Alice's life must exist equally, not just two moments.

OK, let's relate that back to presentism. Imagine a crowd of people all standing still in a hall. Their worldlines are parallel and in the endurantist there's a bright spot moving along each (this is the moving spotlight idea of course) which identifies their 3D existence at any instant. We can draw a plane through all the dots and that must be "the present" since nobody exists at any other time. You can then construct a vector normal to the plane and that identifies a unique axis for time.

In the perdurantist view however, there are no bright spots on the worldlines of people or objects, all parts of ones lifetime have an equal claim on existence, so you cannot construct a unique plane, all planes are equal, and therefore there is no such thing as a uniquely identifiable physical "present". Equivalently it is impossible to identify a preferred direction for time as a normal to that plane.

In the endurantist model, if you extend the plane of the present to include Alice during her trip or project her clock onto the time axis, you can see that the ship's clock ticks off 3 years while one back on Earth the crowd measures 5 years, hence one or more must be affected in some way by some currently unknown physical process (which seems to imply a Lorentzian approach). For the perdurantist view however, proper time is measured along a worldline no matter how it curves so Alice's clock is keeping accurate time even though it registers fewer years between her departure and return than Bob's because the ticks have the same spacing (invariant interval).

In relativity, the model of the 4-dimensional manifold matches that of the perdurantist view in that there is no unique plane we can call the present and perfect clocks in motion maintain the invariant spacetime sepparation of ticks hence relativity seems to require the perdurantist model if the problem outlined at the start is to be avoided, with Alice being in the year 2034 while Bob has only reached 2030.

IMHO, what all that says is that relativity is incompatible with presentism hence I adopt the perdurantist view and, if I understand the link to A versus B correctly, I have voted 'B' accordingly.

 

[lmoh]

Well, that was quite a bit to digest, but your argument was suprisingly clear and easy to read through, even to me, a layperson with little background to SR. The argument does create problems for presentism, but I am already aware of these problems SR creates (so again, I am still confused as to what relevance this has to my #48).

I may have to look over it again, but the only point in which I feel needs addressing is to ask whether or not you are also arguing against the moving spotlight theory of time or just presentism in general. Although you seem to view the moving spotlight view and the growing block view as being equivalent to presentism, I personally prefer to distinguish them (which was why I set them apart in my poll) because they each have some unique differences, differences which may poke a hole in your argument if you are also arguing against something like the moving spotlight view.

On another note, I may have to revise my previous answer (I only answered no because I wanted to see what was on your mind!). As I said, though I am currently committed to the A-series, that is as far as I will go on the issue. I am pretty open when it comes to which A-theory to adopt, which also means I am open to the idea of a hidden present within physics that is compatible with relativity. Now whether or not this hidden present entails an aether theory I don't know (Hopefully you can give some of your input here), but I also want to add that I don't even know whether or not I object completely to the possibility of an aether (though I will follow the mainstream view and just say it does not exist).

 

[GeorgeDishman]

Sorry I didn't have time to reply before we went away for the weekend.

Well, that was quite a bit to digest, but your argument was suprisingly clear and easy to read through, even to me, a layperson with little background to SR. The argument does create problems for presentism, but I am already aware of these problems SR creates (so again, I am still confused as to what relevance this has to my #48).

You said

Many (including myself) would argue the same that time cannot exist without change, that it is simply a measure of change, but I don't see how that matches up with McTaggert's thinking.

I was trying to show how the manner in which change is measured (by clocks) seems to support eternalism and be against presentism which the poll then equates to B theory rather than A.

I may have to look over it again, but the only point in which I feel needs addressing is to ask whether or not you are also arguing against the moving spotlight theory of time or just presentism in general. Although you seem to view the moving spotlight view and the growing block view as being equivalent to presentism, I personally prefer to distinguish them (which was why I set them apart in my poll) because they each have some unique differences, differences which may poke a hole in your argument if you are also arguing against something like the moving spotlight view.

I'm a newbie at philosophy so I may not have grasped the subtleties in the terms but my understanding is that the Moving Spotlight, Growing Block and Endurantism are all different varieties of presentism (and there are probably more).

On another note, I may have to revise my previous answer (I only answered no because I wanted to see what was on your mind!). As I said, though I am currently committed to the A-series, that is as far as I will go on the issue. I am pretty open when it comes to which A-theory to adopt, which also means I am open to the idea of a hidden present within physics that is compatible with relativity. Now whether or not this hidden present entails an aether theory I don't know (Hopefully you can give some of your input here), ..

Lorentz's aether theory (LET) assumed there was absolute time and that motion through the aether resulted in phenomena including length contraction and clock slowing. The result of those is that the "preferred frame" could not be determined thus hiding the existence of a "present". If you consider a hidden present exists, I believe you are forced to revert to something indistinguishable from LET and abandon relativity.

but I also want to add that I don't even know whether or not I object completely to the possibility of an aether (though I will follow the mainstream view and just say it does not exist).

I consider GR to be a valid description of gravity, but I also think that the fact that Hulse and Taylor's evidence strongly supports the existence of gravitational waves. If such ripples in the geometry of spacetime can transport energy and momentum across regions of pure vacuum, it seems to me that spacetime must have some physical existence. That philosophy is called substantivalism in general but you will often see it said that the Hole Argument falsifies that. In fact there are two versions and while the Hole Argument can be used against Manifold Substantivalism, it doesn't cause a problem for Metric Substantivalism which says the gravitational field has a physical existence. Manifold Substantivalism is essentially Newton's "absolute space" so the Hole Argument is a problem for Lorentz's aether.

The Stanford article gives a good description of the argument but doesn't differentiate between the forms, essentially only discussing the manifold variant:

http://plato.stanford.edu/entries/spacetime-holearg/

 

[lmoh]

Sorry I didn't have time to reply before we went away for the weekend.

Don't worry about it.

I was trying to show how the manner in which change is measured (by clocks) seems to support eternalism and be against presentism which the poll then equates to B theory rather than A.

I was more referring to Harrylin's remark about time and change, and how it relates to Mctaggart's arguments. By that, I mean the question of whether time requires change, or change requires time (a "literal flow of time"). As far as I can tell, there isn't much of a connection between both. Your response appears to be going a little beyond what I was saying here, but I won't argue the point further.

I'm a newbie at philosophy so I may not have grasped the subtleties in the terms but my understanding is that the Moving Spotlight, Growing Block and Endurantism are all different varieties of presentism (and there are probably more).

They all sound more like varieties of the A-theory, then of presentism. I actually think the differences are quite clear, though. Presentism only says that the present exists, but not the past and the future. The growing block says that the past and present exist, while the moving spotlight view states that there exists a block universe in which all physical times exist, but that there is also a second dynamic time in which moves along this block-time. If you want some more information, you can probably do a search, but I don't have any specific links in mind.

They can all probably be a part of presentism if you essentially define it as a belief in the existence of a present in which time flows (which is what I think you are doing). It doesn't matter what the present is (whether physical or not), just so long as it exists. In that way, then, all A-theories are equivalent to presentism, but I personally don't like this definition, because it is misleading.

Also, as for endurantism being equivalent to presentism, I don't really focus much on the issue to really say whether or not that is correct. But it seems as though you disagree with your earlier quoted phrase,

From the SEP page:

"If STR thereby rules out presentism, and if endurantism requires presentism in order to explain change (see section 3), then STR rules out endurantism: things have temporal parts. But not all endurantists agree that they must be presentists, and not all presentists agree that their view is undermined by STR."

Lorentz's aether theory (LET) assumed there was absolute time and that motion through the aether resulted in phenomena including length contraction and clock slowing. The result of those is that the "preferred frame" could not be determined thus hiding the existence of a "present". If you consider a hidden present exists, I believe you are forced to revert to something indistinguishable from LET and abandon relativity.

Ok. I often hear people say that a hidden present is compatible with relativity, but I never got what they meant specifically. I only assumed that this "hidden present" was referring to something more broad.

I consider GR to be a valid description of gravity, but I also think that the fact that Hulse and Taylor's evidence strongly supports the existence of gravitational waves. If such ripples in the geometry of spacetime can transport energy and momentum across regions of pure vacuum, it seems to me that spacetime must have some physical existence. That philosophy is called substantivalism in general but you will often see it said that the Hole Argument falsifies that. In fact there are two versions and while the Hole Argument can be used against Manifold Substantivalism, it doesn't cause a problem for Metric Substantivalism which says the gravitational field has a physical existence. Manifold Substantivalism is essentially Newton's "absolute space" so the Hole Argument is a problem for Lorentz's aether.

The Stanford article gives a good description of the argument but doesn't differentiate between the forms, essentially only discussing the manifold variant:

http://plato.stanford.edu/entries/spacetime-holearg/

Fair enough. As I said, I have little knowledge of physics so I probably won't be able to do your argument justice, so the best I can do right now is just take your word for it. I will take some time in order to read it over though when I can.

 

[harrylin]

[..] [..] I often hear people say that a hidden present is compatible with relativity, but I never got what they meant specifically. I only assumed that this "hidden present" was referring to something more broad. [..]

It certainly is more broad than just compatibility with interpretation of a certain theory. Concerning relativity, this is already mentioned in the OP's reference as I cited before:
"it can be plausibly argued that the theory [of relativity ] [..] has no bearing on whether there is such a phenomenon as absolute simultaneity."

In other words: a "hidden present", if I correctly understand what you mean with it, is compatible with a Lorentz ether interpretation of relativity but not with a block universe interpretation of the same. The block universe interpretation is now under discussion here: https://www.physicsforums.com/showthread.php?t=595021

 

[GeorgeDishman]

I mean the question of whether time requires change, or change requires time (a "literal flow of time"). As far as I can tell, there isn't much of a connection between both.

Well if you take a snapshot, you get a static picture so it can be argued that change requires time (which is what the SEP page mentions) but equally "time" can be considered as emergent based on change. However, it isn't as easy to argue that time requires change to exist but it is plausible to say that, even if it exists indepenently of change, something must change if we are to measure it.

I actually think the differences are quite clear, though. Presentism only says that the present exists, but not the past and the future. The growing block says that the past and present exist, while the moving spotlight view states that there exists a block universe in which all physical times exist, but that there is also a second dynamic time in which moves along this block-time.

I completely agree with that, what they have in common is a hypersurface (the present, the 'new' boundary of the growing block or the spolight plane) which uniquely identifies a physical simultaneity. That doesn't exist in the block universe model.

They can all probably be a part of presentism if you essentially define it as a belief in the existence of a present in which time flows (which is what I think you are doing).

Almost, I would say presentism is a belief that a unique "present" moment physically identifies a subset of events in a representational block model and that that subset is subject to change, so if you like it could be "belief in a present in which our perception of a flow of time is emergent from the experience of change whether or not time exists in physical sense". I think that's sufficiently general to cover all the above.

It doesn't matter what the present is (whether physical or not), just so long as it exists. In that way, then, all A-theories are equivalent to presentism, but I personally don't like this definition, because it is misleading.

I'm not suggesting they are all equivalent, rather seeing them as different but sharing a common reliance on a meaningful "present".

Personally, I don't think a present can exist if GR is correct, my view is that we each have our own "now" which separates what we remember from the rest ('future part') of our lives, and then communication with others creates the false illusion that it is a shared moment. Every moment of your life is "now" when you are experiencing it so no individual "now" is physically identifiable.

Also, as for endurantism being equivalent to presentism, I don't really focus much on the issue to really say whether or not that is correct. But it seems as though you disagree with your earlier quoted phrase,

From the SEP page:

"If STR thereby rules out presentism, and if endurantism requires presentism in order to explain change (see section 3), then STR rules out endurantism: things have temporal parts. But not all endurantists agree that they must be presentists, and not all presentists agree that their view is undermined by STR."

I'm not saying they are equivalent, there are other forms of presentism but AIUI the SEP is saying endurantism could not explain change if neither the past nor the future exists and the present is a static snapshot.

Ok. I often hear people say that a hidden present is compatible with relativity, but I never got what they meant specifically. I only assumed that this "hidden present" was referring to something more broad.

Personally, I don't agree with that but that's another matter. It is of course compatible with the Lorentz Transforms but I think the combination forces an aether-like philisophy rather than non-Euclidean geometry and hence rules out GR.

Fair enough. As I said, I have little knowledge of physics so I probably won't be able to do your argument justice, so the best I can do right now is just take your word for it. I will take some time in order to read it over though when I can.

Please don't take my word for it, just see it as an argument I have advanced, I'm very much a beginner in this discipline too and may well be wrong.

 

[lmoh]

I'm osrry if this response sounds a little off, since I am just trying to catch up with our earlier discussion. It seems as though you are responding on a weekly basis (which kind of throws me off), even though you come on every other day.

I'm not suggesting they are all equivalent, rather seeing them as different but sharing a common reliance on a meaningful "present".

Understood. But applying this definition of "present" to the following:

Personally, I don't think a present can exist if GR is correct, my view is that we each have our own "now" which separates what we remember from the rest ('future part') of our lives, and then communication with others creates the false illusion that it is a shared moment. Every moment of your life is "now" when you are experiencing it so no individual "now" is physically identifiable.

I don't completely agree here. As I suggested before, arguments from SR or GR cannot affect something like the moving spotlight model, so it is not the knockdown argument that you seem to be suggesting it is. IMHO these arguments have more to say about the physical block time then about the time in which the spotlight/s move (of course, what the "present" refers to in this model would probably be completely distinct from that suggested by presentism and the growing block model).

Your argument would make more sense here if you are arguing that there is no physical present (as in absolute simulataneity of events within the block universe). If you are arguing against presentism as I defined it, then I would be more inclined to agree.

Please don't take my word for it, just see it as an argument I have advanced, I'm very much a beginner in this discipline too and may well be wrong.

Well, I don't always agree with you, but when it comes to physics, I am not really confident in what I know. Until I take my own time to consider these issues myself, I am willing to concede to what you are saying here. At least you have a physics PhD unlike me .

 

[GeorgeDishman]

I'm osrry if this response sounds a little off, since I am just trying to catch up with our earlier discussion. It seems as though you are responding on a weekly basis (which kind of throws me off), even though you come on every other day.

Sorry, that wasn't intended. I have limited time available and I don't like to rush off a glib reply to topics where some deeper thought is called for. This is an area where I am feeling my way rather than repeating something I've already gone into in detail.

I'm not suggesting they are all equivalent, rather seeing them as different but sharing a common reliance on a meaningful "present".

Understood. But applying this definition of "present" to the following:

Personally, I don't think a present can exist if GR is correct, my view is that we each have our own "now" which separates what we remember from the rest ('future part') of our lives, and then communication with others creates the false illusion that it is a shared moment. Every moment of your life is "now" when you are experiencing it so no individual "now" is physically identifiable.

I don't completely agree here. As I suggested before, arguments from SR or GR cannot affect something like the moving spotlight model, so it is not the knockdown argument that you seem to be suggesting it is. IMHO these arguments have more to say about the physical block time then about the time in which the spotlight/s move (of course, what the "present" refers to in this model would probably be completely distinct from that suggested by presentism and the growing block model).

Your argument would make more sense here if you are arguing that there is no physical present (as in absolute simulataneity of events within the block universe). If you are arguing against presentism as I defined it, then I would be more inclined to agree.

I've had a look down the page and I saw you defined time as a measure of change. That may be reasonable but doesn't in itself lead to a definition of the present. Sorry if you've done it before but can you repeat that definition, just give me a post number if I've missed it.

At least you have a physics PhD unlike me .

No, I got a BSc with Hons in 1974 and then went into the electronics industry, I'm here to learn as much as to pass on what I know. :-)

 

[lmoh]

Sorry, that wasn't intended. I have limited time available and I don't like to rush off a glib reply to topics where some deeper thought is called for. This is an area where I am feeling my way rather than repeating something I've already gone into in detail.

No problem. Its best to take a slow and steady approach. That is not to say that I am willing to take a break (I usually don't ), but I often find that taking some time off from certain issues allows me to get a better understanding of the issue, when I am committed to it. We will just see how this discussion goes.

I've had a look down the page and I saw you defined time as a measure of change. That may be reasonable but doesn't in itself lead to a definition of the present. Sorry if you've done it before but can you repeat that definition, just give me a post number if I've missed it.

I have tried to read this over, but I am not sure what you are trying to say. I don't think I have said that time being a measure of change would lead to a definition of the present, but I think I have given some ideas of what the present can mean back in #55, where I have defined the present of the A-theory as being the moment in which time flows (this is a crude definition, though). But what that moment is however, can vary among the different theories (presentism, to me, would incorporate a physical present, while the moving-spotlight view would have it placed within a time separate from the block-universe). AFAIK, this does not necessarily say anything about reductionism or platonism with respect to time.

(I never really got what you meant when you responded to my initial remark about time and change a couple of weeks back, I don't know if that was what you are referring to.)

No, I got a BSc with Hons in 1974 and then went into the electronics industry, I'm here to learn as much as to pass on what I know. :-)

Oh, I thought that degree you referred to was a doctorate. But at least it is still better than having no background at all .