Does the Block Universe Theory Affect Our Understanding of Time and Reality?

[bobc2]

I don't think Einstein was talking about the "block universe" concept in that quote, at least not as "block universe" is being used in this thread. "Block universe" is an *interpretation* of what 4-d spacetime, as it's used in SR and GR, means. Einstein was just talking about the theoretical usefulness of 4-d spacetime, in particular how viewing it as a geometric object opened the door to letting that geometric object be dynamic instead of fixed, which led to GR. Einstein was not talking about any particular interpretation of what 4-d spacetime means.

In my response to Vandam's post I was trying to assure him that he is not alone in his feelings about the block universe. And there is some support for the view that Einstein embraced the concept. Here are excerpts from the other block universe link the you mentioned earlier. They go to the notion that Vandam should not feel alone in his views.

Paul Davies: The idea that events in time are laid out ‘all at once’ motivated Einstein to write the words… “The distinction between past, present and future is only an illusion, even if a stubborn one.”

Paul Davies: “…there is only one rational conclusion to draw from the relative nature of simultaneity: events in the past and future have to be every bit as real as events in the present.”

Paul Davies: “Einstein himself wasn’t too thrilled with the unified spacetime idea at first, dismissing Minkowski’s new four-dimensionality as ‘superflous’ pedantry, but he came around to the idea in due course.”

Paul Davies: ”Weyl once wrote: ‘The world does not happen, it simply is.’ If you believe Weyl, Einstein did; hence the quote penned in consolation to Besso’s widow following his death: ‘The distinction between past, present and future is only an illusion, even if a stubborn one.’

Paul Davies: “In their professional lives most physicists accept without question the concept of the block time, but away from work they act like everybody else, basing their thoughts and actions on the assumption of a moving present moment.”

Paul Davies: “I have already explained how the theory of relativity leads to the notion of block time, and the picture of time as the fourth dimension simply ‘laid out all at once.’ Since Einstein, physicists have generally rejected the notion that events ‘happen,’ as opposed to merely exist in the four-dimensional spacetime continuum.”

Paul Davies: “David Park is a physicist and philosopher at Williams College in Massachusetts with a lifelong interest in a time which he too thinks doesn’t pass. For Park, the passage of time is not so much an illusion as a myth, ‘because it involves no deception of the senses… One cannot perform any experiment to tell unambiguously whether time passes or not.’ “

“When it comes to the truly objective properties of the world, reference to the flow of time appears superfluous.”

Paul Davies: “Einstein scuttled the notion of a universal now, and pointed the way to ‘block time,’ in which all events—past, present and future—are equally real. To the physicist, human beings of the twenty-fifth century are ‘there’… They are there in the future.”

 

[nitsuj]

Vandam, you are actually in pretty good company, embracing the Block Universe concept: Physicists and mathematicians like Einstein, Hermann Weyl, Kurt Godel, and many others. Einstein commented that General Relativity would not have got any father than its long clothes without Minkowski's 4-dimensional continuum of special relativity.

I've read some wiki about "block universe"; it is seems to me to be a sort of "anti-continuum".

I am of the mind set the universe is a 4D continuum, and not a static block that plays tricks with the measurements/observations we make of time, noting a distinct (but not absolute) future-past continuum.

From the "perspective" of EM and whatever else maybe at that end of the time/length "spectrum" eternalism seems fine to me. I kinda like the PoV that "energy" "flows" at c, and from a causation perspective is an example of "eternalism". but isn't that,clearly, only one perspective of multiple measurable/observable dimensions?

imo bobc2, I think both physically & philosophically our minds have a better grasp of the 4D's, specifically time, than you give it credit for.

Paul Davies: The idea that events in time are laid out ‘all at once’ motivated Einstein to write the words… “The distinction between past, present and future is only an illusion, even if a stubborn one.”

RoS is plenty for all those "Einstein tidbits" in your #61 post, "Eternalism" is just some added poetry, added after the poor fellow cannot speak for himself. In addition I would guess Einstein was purposefully coy with that comment.

 

[Austin0]

But the point of the space-time diagram is that both events, R1 and R2, exist and are real, and the Red guy exists and is real at both R1 and R2 events. That is, when the brown guy and the blue guy meet, R1 exists in Blue's instaneous 3-D world while R2 exists in Brown's instantaneous simultaneous world.

Don't overcomplicate the problem by asking what you mean by real. I think we all know what we are talking about. We simply use a protype example of real. When Blue and Brown meet, Brown observes that Blue is a real observer and Blue observes that Brown is a real observer. If you and I are standing in a room talking, I identify you as a real body and you identify me as a real body--that's our prototype example of real--unless you are a Solipsist--but Einstein was quite emphatic about prohibiting solipsism in relativity).

Now, it is not a question of whether Brown or Blue correctly identifies the Red observer as being real. Both Brown and Blue are correct in observing that a real Red body exists in their respective 3-D worlds at the event of Brown's and Blue's world lines intersecting (Brown and Blue meet).

That's the whole point of the block concept: the Red body must be a 4-dimensional body for both Brown and Blue to each have Red existing as a 3-D body in their respective instantaneous 3-D worlds. Brown and Blue each observe a different 3-D cross-section of Red's 4-dimensional body.


Again, by extension, we could keep adding more and more observers with different Lorentz boosts until the original Red world line is seen to be a continuous 4-dimensional body, i.e., a real physical body extending continuously along Red's world line. We could then develop the concept for every other observer and every other object in the universe until we recognize the entire universe is 4-dimensional populated by 4-dimensional objects. That's the block universe concept.

I thought you got the concept in that other thread that simultaneity was not transitive in SR So R1 being simultaneous to R according to Blue's clocks and R2 being simultaneous to R by Browns clocks does NOT mean that R1 and R2 are simultaneous.
Any such statement is totally in contradiction of fundamental SR which says that any evaluation of distant events regarding temporal relationship is purely conventional and without any real temporal meaning.
In this case Both Red and Brown would disagree with Blue that R1 and R were simultaneous.
Both Red and Blue would disagree with Brown that R2and R were simultaneous.

So you have just selectively chosen two arbitrary frame evaluations of a set of events,applied an interpretation of actual simultaneity to the clocks in both Blue and Brown systems which is against the principles of SR and then concluded that this is proof that SR necessarily implies a Block Universe.
To me this appears self evidently circular. Applying the block time interpretation and expectations to SR to prove block time,ignoring the fact that this contradicts fundamental SR principles in the process.

 

[bobc2]

I've read some wiki about "block universe"; it is seems to me to be a sort of "anti-continuum".

I am of the mind set the universe is a 4D continuum, and not a static block that plays tricks with the measurements/observations we make of time (past-future).

Hi, nitsuj. It's always good reading your posts. Actually, the block universe concept is definitely based on the continuum concept. Einstein never would relenquish his continuum, and insisted it must be that way. I recall a specific reference, but will have to look it up to make sure I'm presenting it correctly.

From the "perspective" of EM and whatever else maybe at that end of the time/length "spectrum" eternalism seems fine to me, but isn't that,clearly, only one perspective of multiple measurable/observable dimensions?

imo bobc2, I think both physically & philosophically our minds have a better grasp of the 4D's, specifically time, than you give it credit for.

You may have a good point there. I have trouble working through the concept of time as the 4th dimension and various observers having different cross-section views of space-time, with different "mixtures" of space and time.

I can easily handle the process of watching a woven waste basket sitting statically over in the corner of my room while time is passing. But, it's much easier for me to handle conceptually by thinking of the basket extended into the 4th dimension as a 4-dimensional structure (the spaghetti-like picture represented by the world line extending 10^13 miles along the 4th dimension).

In that picture the 4-dimensions are all spatial and the 4-D basket just sits in 4-D space while time passes. But, evidently, that is not the picture that Einstein and all physicists subscribe to. So, in that sense, I'm presenting a speculative concept, which I really don't wish to do on this forum. Einstein definitely refers to space-time with time as the 4th dimension (I know of a reference for this comment, but again it would take a little while to dig it up).

 

[nitsuj]

I had typed up a somewhat lengthy post explaining my interpretation and how it's not compatible with "eternalism".

But luckily had re-read Dalespams post a realized I was merely being opinionated in a physics thread.

bobc2 I do find the Block Universe interpretation fascinating, but philosophically (and from a physics perspective) I don't subscribe.

I am sure you can appreciate the difficulty in conveying such a complex interpretation as "eternalism" in particular via typing it out. You seem to have a deep grasp of the Block Universe Concept and feel strongly about it. Who am I to try and "knock" that, I have no authority on the subject.

So this is all that is left of that "lengthy" post.

 

[harrylin]

Vandam, you are actually in pretty good company, embracing the Block Universe concept: Physicists and mathematicians like Einstein, Hermann Weyl, Kurt Godel, and many others. Einstein commented that General Relativity would not have got any father than its long clothes without Minkowski's 4-dimensional continuum of special relativity.

Hi Bob, if you refer to his early comments about GR then that's certainly a misinterpretation of what he meant as he did not want to suggest anything philosophical - quite the contrary as Peterdonis suggested:

"Space is a three-dimensional continuum. [..] the world of physical phenomena which was briefly called "world" by Minkowski is naturally four dimensional in the space-time sense. For it is composed of individual events, each of which is described by four numbers".
See: http://www.bartleby.com/173/17.html

And for a discussion of Paul Davies we have your other thread.

 

[Dale]

Vandam, you are actually in pretty good company, embracing the Block Universe concept: Physicists and mathematicians like Einstein, Hermann Weyl, Kurt Godel, and many others. Einstein commented that General Relativity would not have got any father than its long clothes without Minkowski's 4-dimensional continuum of special relativity.

So what? You can take any position on any topic and compile a similar list of "good company". Particularly if you are willing to take quotes out of context.

 

[Dale]

In that picture the 4-dimensions are all spatial and the 4-D basket just sits in 4-D space while time passes.

That picture is wrong. The signature is -+++, not ++++, so the dimensions are not all spatial.

 

[bobc2]

I had typed up a somewhat lengthy post explaining my interpretation and how it's not compatible with "eternalism".

But luckily had re-read Dalespams post a realized I was merely being opinionated in a physics thread.

bobc2 I do find the Block Universe interpretation fascinating, but philosophically (and from a physics perspective) I don't subscribe.

I am sure you can appreciate the difficulty in conveying such a complex interpretation as "eternalism" in particular via typing it out. You seem to have a deep grasp of the Block Universe Concept and feel strongly about it. Who am I to try and "knock" that, I have no authority on the subject.

So this is all that is left of that "lengthy" post.

Nitsuj, I certainly have no more authority on the subject than you and would be embarrassed to think anyone would think I considered myself to have more access to truth than anyone else here.

Besides, there are experienced physicists around here, whereas I spent only a year or so as a college physics instructor (undergraduate courses only) and since have had a career limited to applied classical physics with no work at all related to special relativity or QM. You've probably been exposed to more relativity topics from your years on the forum than I have (probably less than a year on the forum for me).

In any case these discussions have nothing to do with me, and my personal views are not relevant. I've tried mainly to present concepts expressed by real physicists to help new visitors to the site find a wider range of views that are out there in the physics community. DaleSpam, harrylin and PeterDonis have fairly called me out on the speculative comments, and I need to be more careful there.

 

[Vandam]

4D spacetime consists of events. Events are the buiding blocks, permanantly available to be part of a 'now'world. A 'now' world is your world at a specific point in time.
How one's worldline runs through spacetime determines which events out of total spacetime you will select as being 'simultaneous'. Our 3D world is a construction (made by ourselves) of a limited collection of in spacetime permanently available events. This collection is your world during a split second in your life. In spacetime there are no 'simultaneous' events as such, because 'simultaneity' is something we stick onto the events that we consider happening the same time. Other people will put the simultaneity sticker to oher events.
Whether a world at a specific point in time (= per definition made of simultaneous events) is 'physical' or 'real' is not that important (this gets philosophical), BUT if you consider one world 'real', then all other now worlds of all other 'moving' systems are also to accepted as 'real'. Therefore: all events of spacetime are 'real', or none is 'real'.
Every day I find it mindboggling that this is so difficult to understand by people juggling with Einstein's formulas. Relativity of simultaneous events is so easy, but apparently for many a too great mental step to take...?
I have not read every post of bobc2, but I think bob took that step.

 

[bobc2]

4D spacetime consists of events. Events are the buiding blocks, permanantly available to be part of a 'now'world. A 'now' world is your world at a specific point in time.
How one's worldline runs through spacetime determines which events out of total spacetime you will select as being 'simultaneous'. Our 3D world is a construction (made by ourselves) of a limited collection of in spacetime permanently available events. This collection is your world during a split second in your life. In spacetime there are no 'simultaneous' events as such, because 'simultaneity' is something we stick onto the events that we consider happening the same time. Other people will put the simultaneity sticker to oher events.
Whether a world at a specific point in time (= per definition made of simultaneous events) is 'physical' or 'real' is not that important (this gets philosophical), BUT if you consider one world 'real', then all other now worlds of all other 'moving' systems are also to accepted as 'real'. Therefore: all events of spacetime are 'real', or none is 'real'.
Every day I find it mindboggling that this is so difficult to understand by people juggling with Einstein's formulas. Relativity of simultaneous events is so easy, but apparently for many a too great mental step to take...?
I have not read every post of bobc2, but I think bob took that step.

A very nice and efficient summary of the situation, Vandam.

 

[Dale]

Every day I find it mindboggling that this is so difficult to understand by people juggling with Einstein's formulas. Relativity of simultaneous events is so easy, but apparently for many a too great mental step to take...?

Translation: "I have an untestable philosophical position that I have good reasons for liking. Therefore everyone who doesn't like it as strongly as I do must be mentally deficient."

 

[Vandam]

Translation: "I have an untestable philosophical position that I have good reasons for liking. Therefore everyone who doesn't like it as strongly as I do must be mentally deficient."

Wow, Dale, that's definitely not my way of seeing it.

May I ask you following question:
If you only consider your world of simultaneous events as real, but not the world of simultaneous events of somebody moving relative to you, do you accept that that other person will say to you: "Mr Dale, my world of simultaneous events is real, but not your world of simultaneous events" ?
What do you answer him? Do you think he will not consider his world of simultaneous events as real? Why not? He's using exactly the same procedure (lightspeed information into his eyes) as you do to make up his world of simultaneous events. And both worlds are different. So what's the problem, or where's the problem?

 

[PeterDonis]

4D spacetime consists of events. Events are the buiding blocks, permanantly available to be part of a 'now'world. A 'now' world is your world at a specific point in time.

But this "world" is a construction, as you yourself say just a bit later on:

Our 3D world is a construction (made by ourselves) of a limited collection of in spacetime permanently available events.

But the "permanently available events" you use to make this construction are outside your past light cone, so you have no direct information about them. In order to construct your model of those events, you must extrapolate from the information that is in your past light cone, and that information is not sufficient to determine what happens at those spacelike separated events. So your model of those events may be wrong.

Therefore, as I've pointed out to bobc2 before, by asserting that those events are "real" or "permanently available" or whatever phrase you want to use, you are putting yourself in the position of asserting the reality of events that may not actually happen. This seems like a very odd position to take. I've commented along these lines in this thread before, but there was also another thread (I think the one that was linked to a few posts back) where this was hashed out.

 

[PeterDonis]

He's using exactly the same procedure (lightspeed information into his eyes) as you do to make up his world of simultaneous events.

This procedure doesn't tell you, or him, what is in either of your simultaneous spaces. It only tells you what's in your past light cone. You have to extrapolate from that information to construct your simultaneous spaces, and that extrapolation is not determinate--the information in your past light cone is not sufficient to nail down exactly what happens in your simultaneous space.

So I would say that both of your simultaneous spaces--and in fact both of your models of any events that are spacelike separated--are tentative constructions; they're in your heads, not in reality. You won't know what's in reality until you get direct information from those events.

 

[Dale]

Wow, Dale, that's definitely not my way of seeing it.?

If that was not your intention then you should avoid comments like

"this is so difficult to understand" and "for many a too great mental step to take"

Which appear to presume that your philosophical position is undeniably correct and that the only possible reason for disagreement is a lack of understanding or some other mental deficiency.

May I ask you following question:
If you only consider your world of simultaneous events as real, but not the world of simultaneous events of somebody moving relative to you, do you accept that that other person will say to you: "Mr Dale, my world of simultaneous events is real, but not your world of simultaneous events" ?
What do you answer him?

I give him the same answer I give anyone who asks a question about what is "real". I ask him to provide an experiment which could be performed to determine whether or not a given event is "real" according to his concept of "real". If he provides an experiment then I use standard physics to predict the outcome and reply accordingly. If he does not provide an experiment then I tell him that his idea of "real" is unscientific and so I couldn't care less which events he chooses to label "real" and which he chooses not to.

I myself would never assert that my world of simultaneous events is "real" for exactly this reason.

 

[harrylin]

[..]Therefore: all events of spacetime are 'real', or none is 'real'.
Every day I find it mindboggling that this is so difficult to understand by people juggling with Einstein's formulas. [..]

"Mindboggling" you say? What I find "mindboggling" is that it is so difficult to realize that the above conclusion is wrong after this has been explained already in this thread and the other thread. For example Bell (who taught SR and QM) argued for the QM interpretation that the events of a single space-time are "real", only we cannot know which one. But his interpretation must be impossible (erroneous) if your understanding is correct; thus, according to you he did not understand Einstein's formula's and must have made a logical mistake. Which one?

 

[bobc2]

But this "world" is a construction, as you yourself say just a bit later on:



But the "permanently available events" you use to make this construction are outside your past light cone, so you have no direct information about them. In order to construct your model of those events, you must extrapolate from the information that is in your past light cone, and that information is not sufficient to determine what happens at those spacelike separated events. So your model of those events may be wrong.

Therefore, as I've pointed out to bobc2 before, by asserting that those events are "real" or "permanently available" or whatever phrase you want to use, you are putting yourself in the position of asserting the reality of events that may not actually happen. This seems like a very odd position to take. I've commented along these lines in this thread before, but there was also another thread (I think the one that was linked to a few posts back) where this was hashed out.

Hi, PeteDonis, it's always good to exchange views with you. On this point, as I've pointed out in other threads, Einstein would be revulsed. He often cautioned against being led into solipsism, as your logic would lead us.

The thing about it is that you may argue that logically you cannot present a proof that solipsism is not the correct reality--and that's the problem. But there seems to come a point in pursuing a concept of physical reality that you simply reject concepts that seem absurd on the face of it.

Nevertheless, there are those who would cling to solipsism and defy you to prove them wrong.

Vandam has manifestly presented better logic than any solipsist could offer.

 

[Vandam]

But this "world" is a construction, as you yourself say just a bit later on:

If its a construction, all the worlds are a construction, also yours! Why should your world NOT be a construction?

But the "permanently available events" you use to make this construction are outside your past light cone, so you have no direct information about them. In order to construct your model of those events, you must extrapolate from the information that is in your past light cone, and that information is not sufficient to determine what happens at those spacelike separated events. So your model of those events may be wrong.

Therefore, as I've pointed out to bobc2 before, by asserting that those events are "real" or "permanently available" or whatever phrase you want to use, you are putting yourself in the position of asserting the reality of events that may not actually happen. This seems like a very odd position to take. I've commented along these lines in this thread before, but there was also another thread (I think the one that was linked to a few posts back) where this was hashed out.

whatever, inside or outside lightcone, als you like, but so do the events that you use to make up your now world... Don't you realize this? Think about it.
So why should your world be real and not the other?

 

[Dale]

He often cautioned against being led into solipsism, as your logic would lead us.

How so? I don't see how his comments lead to solipsism.

 

[PeterDonis]

On this point, as I've pointed out in other threads, Einstein would be revulsed. He often cautioned against being led into solipsism, as your logic would lead us.

I don't see this at all. Where have I said that I am the only thing that exists? I am simply trying to draw a distinction, which you repeatedly refuse to see, between what is known and what is only extrapolated. I really don't see why the distinction is so hard to grasp.

 

[PeterDonis]

If its a construction, all the worlds are a construction, also yours! Why should your world NOT be a construction?

You are missing the point. I'm not saying that your world is constructed and mine is not. I agree that "all the worlds are a construction" (assuming that by "worlds" you mean "simultaneous spaces").

Pick an event E where two observers in relative motion, A and B, meet. The past light cone of event E is invariant, so A and B both agree on which events are in that past light cone. Those events are known to A and B at event E.

A and B can each *construct* their simultaneous spaces at event E; these will be different spacelike surfaces, SA and SB, that each contain event E. But of *all* the events in either SA or SB, the *only* one, strictly speaking, that is known to A or B at event E is event E itself. *Every* other event in SA *and* SB is constructed; all those events are spacelike separated from E, so they are outside E's past light cone, so they are not known to A or B at event E. So both "worlds", yours and mine (A's and B's) are constructed.

But there's more to it than that. First, *nothing* that happens at any event in SA or SB, other than E, can have any effect on what A and B observe at event E. So whether you call the events in SA and SB, other than E, "real" or not, the actual observations of A and B at event E are the same. (You'll notice that I didn't use the word "real" at all in what I said above.)

But more important than that, when A and B construct their simultaneous spaces, SA and SB, the only information they can use for the construction is the information contained in the past light cone of E. They have to extrapolate from that information to construct SA and SB, and their extrapolations could be wrong, because the information in E's past light cone is not sufficient to determine what actually happens at the events in SA and SB other than E (or indeed at *any* that's event spacelike separated from E). So if you insist on calling all the events in SA and SB "real", you are claiming that there are "real" happenings that might not actually happen. (bobc2 and I went through this in detail in the other thread.)

 

[Dale]

So why should your world be real and not the other?

Why should either be "real"? I notice that you have not proffered an experiment by which we can experimentally determine the "real"-ness of any event.

 

[bobc2]

How so? I don't see how his comments lead to solipsism.

In the sketch below you see a representation of space-time with observers A, B, C, D, and E moving through time. You can ask whether there is an external objective real world for observer A. For the solipsist relying on ideas from special relativity, he has no external world for his present instant. He is forever moving forward in time at the apex of his past light cone. No information from his otherwise "simultaneous space" is available to him, so he is obliged to affirm that he is the only thing that exists, whether it be at his instant t1 or t2, t3, t4, t5, t6, etc.

Einstein rejected solipsism and would affirm the existence of reality in the external simultaneous space, "...Physics is an attempt conceptually to grasp reality as it is thought independently of its being observed. In this sense one speaks of 'physical reality' ."

 

[Vandam]

You are missing the point. I'm not saying that your world is constructed and mine is not. I agree that "all the worlds are a construction" (assuming that by "worlds" you mean "simultaneous spaces").

Pick an event E where two observers in relative motion, A and B, meet. The past light cone of event E is invariant, so A and B both agree on which events are in that past light cone. Those events are known to A and B at event E.

A and B can each *construct* their simultaneous spaces at event E; these will be different spacelike surfaces, SA and SB, that each contain event E. But of *all* the events in either SA or SB, the *only* one, strictly speaking, that is known to A or B at event E is event E itself. *Every* other event in SA *and* SB is constructed; all those events are spacelike separated from E, so they are outside E's past light cone, so they are not known to A or B at event E. So both "worlds", yours and mine (A's and B's) are constructed.

But there's more to it than that. First, *nothing* that happens at any event in SA or SB, other than E, can have any effect on what A and B observe at event E. So whether you call the events in SA and SB, other than E, "real" or not, the actual observations of A and B at event E are the same. (You'll notice that I didn't use the word "real" at all in what I said above.)

But more important than that, when A and B construct their simultaneous spaces, SA and SB, the only information they can use for the construction is the information contained in the past light cone of E. They have to extrapolate from that information to construct SA and SB, and their extrapolations could be wrong, because the information in E's past light cone is not sufficient to determine what actually happens at the events in SA and SB other than E (or indeed at *any* that's event spacelike separated from E). So if you insist on calling all the events in SA and SB "real", you are claiming that there are "real" happenings that might not actually happen. (bobc2 and I went through this in detail in the other thread.)

Why should either be "real"? I notice that you have not proffered an experiment by which we can experimentally determine the "real"-ness of any event.

I'm happy you agree that all worlds are constructed, but I never said that at one specific event (your event E, where A en B meet) somebody knows what the world (sim events) is at that moment. But that doesn't mean there was no world!
One receives information over a certain time, and based on length, time measurements, speed of light, he concludes what his world was at (f.ex.) event E.
If the two observers do this exercise, they will not agree on their world (sim events).

The real/unreal discussion is indeed philosophical, bus IF you call one world real, THEN all worlds are real.

If for you the world is nothing real, but only a subjective/conscious dream, then all worlds are dreams. But SR tells you there's also total spacetime of dreamevents. And A's dreamworld is a section trough dreamspacetime. And B's world is a section through dreamspacetime. That's logic.

Maybe you don't accept that there exists a 'somebody else with consciousness' to 'construct' his own (dream)world. Then you are really a hard solipsist ;) Are you?

 

[nitsuj]

If for you the world is nothing real, but only a subjective/conscious dream, then all worlds are dreams. But SR tells you there's also total spacetime of dreamevents. And A's dreamworld is a section trough dreamspacetime. And B's world is a section through dreamspacetime. That's logic.

And that commentary greatly degrades the "quality" of this topic.

"total spacetime of dreamevents" what on Earth is that?? (Rhetorical)

 

[Vandam]

In the sketch below you see a representation of space-time with observers A, B, C, D, and E moving through time. You can ask whether there is an external objective real world for observer A. For the solipsist relying on ideas from special relativity, he has no external world for his present instant. He is forever moving forward in time at the apex of his past light cone. No information from his otherwise "simultaneous space" is available to him, so he is obliged to affirm that he is the only thing that exists, whether it be at his instant t1 or t2, t3, t4, t5, t6, etc.

Einstein rejected solipsism and would affirm the existence of reality in the external simultaneous space, "...Physics is an attempt conceptually to grasp reality as it is thought independently of its being observed. In this sense one speaks of 'physical reality' ."

As I answered to Peter it is feasible to make out what your world WAS at a previous event.
And what will the real solipsist then say? Everything of the past is not part of my now, so I don't know wheter it existed or not. Gotcha ;)
Solipsist only believe in ther own now event.

 

[Vandam]

And that commentary greatly degrades the "quality" of this topic.

"total spacetime of dreamevents" what on Earth is that?? (Rhetorical)

Please read al the posts of this tread. Then you will understand why I wrote this.

 

[bobc2]

As I answered to Peter it is feasible to make out what your world WAS at a previous event.
And what will the real solipsist then say? Everything of the past is not part of my now, so I don't know wheter it existed or not. Gotcha ;)
Solipsist only believe in ther own now event.

Solipsists only believe in ther own NOW event You've got it for sure, Vandam. And Einstein did not like solipsism and warned against being led into that trap.

 

[PeterDonis]

I'm happy you agree that all worlds are constructed, but I never said that at one specific event (your event E, where A en B meet) somebody knows what the world (sim events) is at that moment. But that doesn't mean there was no world!

And I have never said "there was no world". Nor have I said there was a world. I don't think either statement has meaning, for the reasons DaleSpam has already given--there's no experiment you can do to tell whether "the world" as you define it is "real" or not.

One receives information over a certain time, and based on length, time measurements, speed of light, he concludes what his world was at (f.ex.) event E.

If you mean the "world" is constructed after the fact--after the observer has already received light signals from all the events in his "world" at some instant--then that's something different than what we've been discussing up to now, because the observer will have to wait for some time *after* a given event before he can construct his "world" at that event. (In fact, if he wants to construct his *entire* "world" at a given event, he might have to wait an infinite amount of time--to the best of our knowledge, the universe is spatially infinite.)

On this view there is no reason to claim that the "world" is "real" at event E; you're only claiming events are "real" after you've received light signals from them, so you know what happens in them. In other words, you are limiting your claims to what's actually known--what's in your past light cone.

If the two observers do this exercise, they will not agree on their world (sim events).

Only if they insist on identifying their "world" with their simultaneous space at a given event. But since no events spacelike separated from a given event can affect what any observer observes at that event, their different choices of simultaneous space have no observable consequences, as DaleSpam has pointed out. So there's nothing that *requires* them to disagree. They could both just say that the entire set of spacelike separated events is "elsewhere" (Roger Penrose's term), and defer making any claims about them until they receive more information (as discussed above).

Or, if either one wants to extrapolate from what's known, what's in their past light cone, to *predict* what might be happening at some event that's spacelike separated from them, why would either one need to restrict his predictions to just his own simultaneous space at a given event? Why couldn't observer A make a prediction about what might be happening at an event that is simultaneous with observer B at event E? Why must each one restrict their predictions to their own "world"? Or even to the other's "world"? Why couldn't either of them make a prediction about *any* event that's spacelike separated from them? There's nothing stopping them; they have the same amount of information (in the past light cone) to extrapolate to *any* spacelike separated event. So there's nothing that even picks out either one's "world" as being any different from any other set of spacelike separated events.

The real/unreal discussion is indeed philosophical, bus IF you call one world real, THEN all worlds are real.

I haven't called any of the worlds "real", so this doesn't apply to me.

If for you the world is nothing real, but only a subjective/conscious dream, then all worlds are dreams.

I have never said the world is only a dream. How are you getting that out of what I said? Are you actually reading what I post? You seem to be making a lot of assumptions about what I am saying that are invalid.

Maybe you don't accept that there exists a 'somebody else with consciousness' to 'construct' his own (dream)world. Then you are really a hard solipsist ;) Are you?

Of course not. If you had actually read what I posted, it would be obvious; I talked explicitly about multiple observers and what each one observes, constructs, etc. I never said that any observer, including me, was "privileged" in any way; they are all on an equal footing.