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

[Chestermiller]

I’m relatively new to Physics Forums, so please go easy on me guys. I’m trying to get an understanding of the so-called Block Universe concept and its implications, but I need help. I’m going to start out by articulating my current understanding, and then try to apply this understanding to develop some interpretations (which may or may not be correct). I welcome your comments and criticisms.
My understanding is that, inherent in the Block Universe concept are the following three features:
1. the acceptance of time as a bona-fide spatial dimension, within the constraints of the Minkowski metric.
2. the requirement that all physical objects, both animate and inanimate, travel along their world lines at the speed of light.
3. The notion that all events occurring along an object’s world line exist simultaneously (in a 4D sense) and are equally real.
The only true axiom on this list is the first. The other two features seem to follow automatically from the predictions of the Lorentz Transformation.
Now for some interpretations:
In connection with feature 3, if all the events in a person’s life exist simultaneously in a 4D Block Universe and are all equally real, then it would seem to me that the only way this can happen is if there exists a continuous sequence of younger- and older versions of this same person strung out along his world line. For a person of a specific age, the younger versions must be situated behind him on his world line, and the older versions must be situated ahead of him. The actual distances between these versions can be calculated as the differences in age times the speed of light. But all the versions would exist simultaneously.
It would also seem to me that this very same type of interpretation can be applied not only to animate objects, but also to inanimate objects. Thus, in the case of the usual Train Example, if I am an observer in the S frame of reference on the ground and the train represents the S’ frame of reference, the middle of the train might be directly opposite me, and exhibiting a clock time of t’; but there would be another observer within my ground frame of reference further up the track that sees a clock in the caboose that exhibits a time reading greater than t’, and still another observer further down the track that sees a clock in the locomotive reading a time less than t’. Under this interpretation of the Block Universe concept, the clock in the caboose would be “older” than the one I see opposite me, and the clock in the locomotive would be “younger” than the one I see opposite me (assuming that all three clocks were fabricated at the same time in the S’ reference frame).
It would also seem that, in this Block Universe model, the rate at which each version of a person is aging is exactly one year for every light year of travel along his world line. As a result of this feature, from the perspective of a “stationary” observer viewing the Block Universe from outside, nothing within the Block Universe would appear to be changing. Younger versions would replace older versions at precisely the right rate so that the Block Universe would seem to be in a permanent condition of steady state equilibrium…frozen. The reality, however, would be much more dynamic than this. There would be a continuous flow of younger and older versions of each animate and inanimate object along each world line.
The flow of all the various versions of objects along each world line at the speed of light would also seem to translate into a continuous steady flow of mass along that world line. The sum total of all these continuous mass flow rates along all the world lines throughout hyperspace would represent an enormous continuous rate of mass flow. Where could all this continuous mass flow be coming from? The only logical answer, if we trace the flow back to its source, would seem to be the big bang. But, the big bang has always been viewed an instantaneous isolated mass injection event that took place ~14 billion years ago. The Block Universe interpretation of the big bang would appear to markedly differ from this. It would imply that, rather than representing an a single isolated injection event, the big bang could be viewed as an ongoing event representing a steady continuous point source of mass flow into 4D hyperspace… a sort of a black hole in reverse (in a 4D sense).
This completes what I wanted to discuss. Please give me feedback on whether my general understanding of the Block Universe concept is in any way correct, and if the interpretation I have presented makes any sense whatsoever. Thank you.

 

[bcrowell]

My understanding is that, inherent in the Block Universe concept are the following three features:
1. the acceptance of time as a bona-fide spatial dimension, within the constraints of the Minkowski metric.
2. the requirement that all physical objects, both animate and inanimate, travel along their world lines at the speed of light.
3. The notion that all events occurring along an object’s world line exist simultaneously (in a 4D sense) and are equally real.
The only true axiom on this list is the first. The other two features seem to follow automatically from the predictions of the Lorentz Transformation.

Most of this is not correct, most of it has nothing to do with the block universe, and most of it isn't physics.

"the acceptance of time as a bona-fide spatial dimension"
Time is a timelike dimension, not a spacelike one. Viewing time as a fourth dimension is not specific to the block universe picture. "Bona-fide" is meaningless here.

"the requirement that all physical objects, both animate and inanimate, travel along their world lines at the speed of light"
This sounds like Brian Greene's description, which is misleading and not a description widely used by physicists. In any case, it is something generic about relativity, not something specific to the block universe picture.

"The notion that all events occurring along an object’s world line exist simultaneously"
This is wrong. Relativity says that if event B lies inside event A's light cone, then they are not simultaneous in any frame.

"and are equally real."
This is meaningless, because "real" hasn't been defined.

"The only true axiom on this list is the first."
Huh? Why?

"The other two features seem to follow automatically from the predictions of the Lorentz Transformation."
In science, a "prediction" is something that can be tested against experiment. Neither 1 nor 3 can be tested against experiment, so neither is a prediction.

The block universe picture is philosophy, not physics.

Before we could meaningfully discuss your statements about what is "real" or "bona-fide," you would have to define what those terms meant to you.

 

[Chestermiller]

This is in response to the reply by bcrowell. Thank you for responding so quickly to my post, and thank you for identifying what you deemed to be wrong with my understanding of the Block Universe concept. I was hoping that in addition to pointing out what is wrong, responders would also articulate their own (correct) understanding of Block Universe to those of us who have puzzled long hours over this. I have seen many posts to PF on Block Universe asking about its basic features, but none of these seemed to make the concept very clear. I realize that there is substantial controversy over this subject, and, as an expert, you may not hold it in very high regard. As for myself, I haven't reached an opinion yet. But before I can, I need to have a better understanding of what it is saying. Do you think you would be capable of providing a balanced explanation in a few hundred words (or less) so that less experienced scientists like myself could get a clearer picture?
As for some of your other comments: I must admit that I am proud to be lumped in the same basket with Brian Greene, even if his description may not be mainstream. Also when I observed "that all events occurring along an object’s world line exist simultaneously", I didn't mean to use the s-word in its usual sense; I should have qualified it by saying that I was referring to simultaneity in a 4D Block Universe sense, in which an observer is viewing space-time from the outside. Finally, what I meant by "real" was, in the case of animate objects "living."
I'm really looking forward to reading your articulation of the Block Universe concept. Thanks so much.

 

[bcrowell]

It's not that I don't hold it in high regard, it's just that it's not physics, it's philosophy. If you want a clear explanation of it, you should ask a philosopher. PF does have a philosophy forum under general discussion.

 

[bobc2]

Here's a different view of the block universe: It is altogether physics. Don't look for help in the philosopher forum (I've tried it). They will get you way off into discussions of esoteric stuff that we physicists have no interest it. The block concept is of enormous significance to many physicists who are motivated to do theoretical physics because they feel it beckons one to pursue the understanding of external objective reality (see "The Road to Reality" by Roger Penrose). Fundamentally, that's the loftiest goal of physics.

However, physicists do not fully comprehend the block concept because at this point we are limited in our fundamental understanding of time and of consciousness.

Here is a space-time diagram sketch illustrating the motivation for the block universe concept. As you pointed out, it is based on the Lorentz transformations of special relativity.

 

[pervect]

"Block time" basically is a philosophical concept as Ben says. I'm not sure how much luck you'll have finding someone to talk about it, I regard philosophy as a sort of "necessary evil", so I'm not particularly good at it, or well read on it. You might or might not have better luck in the philosophy forums - you'll at least find people interested in philosophy there, but I'm not sure how many of them will be interested in this particular part of philosophy.

I do occasionally find myself having to discuss philosophy in order to get to the more interesting parts, which is the actual physics, but because philosophical discussions can drag on forever, I don't generally follow up much.

The current wiki article linked to "block time" seems to me to be relatively sane at the moment (this wasn't always true), see http://en.wikipedia.org/w/index.php?title=Eternalism_(philosophy_of_time)&oldid=480187569

I think you did get some of the elements of the phiilosophy right (from reading the article, at least).

From a physical point of view, though, all that's really necessary is to say that the set of events in space-time that observer "A" regards as being simultaneous is DIFFERENT from the set of points in space-time that observer "B" regards as being simultaneous, where A and B are observers at the same event in space-time who are moving at different veolcities.

In my view, "Block time" aka Eteranalism doesn't have some of the probelms that what Wiki calls "Presentism" has - if "only the present is real", but the present is different for observer A and observer B, then you have the problem of "reality" being different for A and B.

But realities are (in my view, at least) supposed to be the same for different observers. I"m pretty sure that not all philosphers will agree with this simple statement above, though (my opinion , for what it's worth, is that that's almost always a safe statement to say that philosphers will disagre about almost anytihng.). Thus it is better to say "observer dependent" and "observer independent" rather than "real" or "not real" - it's more precise - there is less extraneous "baggage".

So, being as precise as possible, we can say that the concept of "now" is observer-dependent in SR, where it was not observer dependent in classical physics.

The rest of "Block time" you can use if you like, or not use if you don't like, like most philosophies it doesn't matter to anything you can measure If it did matter to something you could measure, it wouldn't be a philosophical issue anymore, but one that could be decided by experiment - i.e. a scientific issue.

 

[atyy]

But, the big bang has always been viewed an instantaneous isolated mass injection event that took place ~14 billion years ago. The Block Universe interpretation of the big bang would appear to markedly differ from this.

Yes.

Lewis, Coordinate Confusion in Conformal Cosmology: "The choice of coordinates is down to personal preference, as both must give the same predictions. From all of this, it should be clear that it is futile to ask the question “is space really expanding?”; the standard-FLRW metric and its conformal representation are the same spacetime. No experiment can be formulated to differentiate one personal choice of coordinates from another."

Block universe just means the primary entity is spacetime not space + global time. There are many ways to split spacetime into space +global time, but none are "the best", so in the block time view spacetime is primary, and global time is not.

 

[bcrowell]

In my view, "Block time" aka Eteranalism doesn't have some of the probelms that what Wiki calls "Presentism" has - if "only the present is real", but the present is different for observer A and observer B, then you have the problem of "reality" being different for A and B.

This is going to depend completely on what one means by "real."

 

[pervect]

This is going to depend completely on what one means by "real."

Yes. That's why it's best to say "observer dependent" or "observer independent". Which I tried to mention later on.

It's my own personal philosophy (and not any generally agreed on statement) that says that observer independent quantities are 'real" and observer dependent quantities are not. I''d guess this is a common enough position to have a name in the philosophical literature, but I don't know what that name is, alas.

There are some other issues here as to how one might define observer dependent or observer independent. The individual components of tensor quantities vary between observers, for instance, but I'd regard the tensor as a whole as falling in the "observer independent" category.

 

[pervect]

Yes.

Lewis, Coordinate Confusion in Conformal Cosmology: "The choice of coordinates is down to personal preference, as both must give the same predictions. From all of this, it should be clear that it is futile to ask the question “is space really expanding?”; the standard-FLRW metric and its conformal representation are the same spacetime. No experiment can be formulated to differentiate one personal choice of coordinates from another."

Block universe just means the primary entity is spacetime not space + global time. There are many ways to split spacetime into space +global time, but none are "the best", so in the block time view spacetime is primary, and global time is not.

A bit off-topic, perhaps, but it seems my position has finally found a mirror in the literature that the whole expanding / not expanding thing is equivalent to arguing about coordinates.

Now they only need to note that relative velocity, as they've defined it, is ALSO down to a similar coordinate choice (along with distance). Specifically, you need to specify a surface of constant time to measure either - you don't need to specify the rest of the coordinates though.

In order to understand superluminal recession, we must first be very clear about how we are defining recession velocity in an expanding universe. A fundamental definition of distance in general relativity is the proper distance, defined as the spatial separation between two points along a hypersurface of constant time.

 

[bobc2]

Yes. That's why it's best to say "observer dependent" or "observer independent". Which I tried to mention later on.

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). In the purely physical sense each observes the other as an existing 3-dimensional physical body. In that same sense, each observes the Red observer to be a real 3-dimensional physical body.

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.

Putting a little more into the 4-dimensional reality picture, we have added in another observer to the previous space-time diagram: Another Red guy who is a companion to the first Red guy--he is at rest in the original Red's inertial frame of reference (moving at the same velocity as the original Red, with respect to the other observers). The event, R3, on the original Red world line is simultaneous with the new Red when the new Red meets with Brown and Blue at the intersection of all three world lines. Thus, the original Red is real and exists at event R3 as a 3-D body when the new Red guy meets up with Brown and Blue. The new red guy is viewing yet another 3-D cross-section view of the original 4-dimensional Red guy.

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 think Chestermiller was looking for help on understanding the implications of the block universe. But, I yield the floor after such extended verbage. Hopefully someone will help Chestermiller with some of those implications.

 

[Chestermiller]

The block universe picture is philosophy, not physics.

As a Senior Research Fellow at DuPont with 35 years of experience in mechanical engineering, chemical engineering, atmospheric science, and hydrology (when I retired in 2002), followed by 9 more years of successful independent consulting in these areas, I can confidently say that I have an extensive working knowledge of physics and math modeling. It doesn't matter how many times you say Block Universe is just philosophy. In my judgement, it is much more than that. I know how to recognize a math model when I see one, and that is exactly what Block Universe is. It is a math model of the fundamental geometric structure of space-time, together with kinematics and aging of objects moving through space-time. It is consistent with the Lorentz Transformation, and provides a framework for understanding the Lorentz Transformation predictions (which, after 107 years, in my judgment, no longer require experimental validation). The only question is whether the Block Universe model represents the physical reality of our space-time, or whether, when we attempt to extend its interpretation to more complex situations, it is no longer capable of matching experimental observations. This is the reason I introduced the extended interpretations of Block Universe in second part of my original posting (involving substantial mass flows along world lines, and an enormous mass flow summed over all the world lines, and originating from an ongoing big bang). I was hoping to receive feedback from PF respondents on whether these interpretations made any sense within the framework of the Block Universe model, and also whether any PF respondents were capable of devising experiments that could test these predictions. So far, total silence.

 

[nitsuj]

As a Senior Research Fellow at DuPont with 35 years of experience in mechanical engineering, chemical engineering, atmospheric science, and hydrology (when I retired in 2002), followed by 9 more years of successful independent consulting in these areas, I can confidently say that I have an extensive working knowledge of physics and math modeling. It doesn't matter how many times you say Block Universe is just philosophy. In my judgement, it is much more than that. I know how to recognize a math model when I see one, and that is exactly what Block Universe is. It is a math model of the fundamental geometric structure of space-time, together with kinematics and aging of objects moving through space-time. It is consistent with the Lorentz Transformation, and provides a framework for understanding the Lorentz Transformation predictions (which, after 107 years, in my judgment, no longer require experimental validation). The only question is whether the Block Universe model represents the physical reality of our space-time, or whether, when we attempt to extend its interpretation to more complex situations, it is no longer capable of matching experimental observations. This is the reason I introduced the extended interpretations of Block Universe in second part of my original posting (involving substantial mass flows along world lines, and an enormous mass flow summed over all the world lines, and originating from an ongoing big bang). I was hoping to receive feedback from PF respondents on whether these interpretations made any sense within the framework of the Block Universe model, and also whether any PF respondents were capable of devising experiments that could test these predictions. So far, total silence.

You can measure the path of a photon as either time, length or the two at the same time. I can't see how this could be done in a block universe "reality". It's a continuum. Space is isotropic. Mass is measurable. All sorts of things...

I have almost 12 months of PF "experience" in the field of internet forum layman physics. (raising the point of your experience in the field is moot, unless you are a "leading expert" in the field there is no additional authority due to experience with regard to interpretation )

Lastly just from a conceptual perspective, I cannot envision 4 spatial dimensions, it makes no sense to me. 3 isotropic spatial dimensions with an, invariant limited speed does make sense to me and is more sensical in comparison to eternalism.

 

[bobc2]

...Neither 1 nor 3 can be tested against experiment, so neither is a prediction...

Here is an experiment to verify predictions of the block universe model. We have three observers, Brown, Blue and Light Brown. The experiment predicts observations associated with events indicated in the space-time diagram below. The events along with predictions of observations are planned in advance of the initiation of the events.

The space-time diagram presents the three world lines associated with the three observers along with the events. The green lines represent the world lines of signals transmitted between observers during the experiment (traveling at the speed of light in all inertial reference frames).

We wish to provide experimental verification of the existence of the light brown observer as a real physical 4-dimensional body (real body as defined in the earlier post #11). The experiment accomplishes this by providing experimental evidence that when the Blue observer and Brown observer meet, each establishes a separate 3-D existence for the Light Brown observer. That is the Light Brown observer exists at both event 11 and event 12 while Blue and Brown are together. The existence of the Light Brown observer is established at other points along Light Brown’s world line as well (events 8, 9, 10, and 13). Existence of separate 3-D bodies (observed simultaneously by two different observers--Blue and Brown in our experiment) require the existence of a 4-dimensional body, and different observers moving at different velocities relative to each other will observe different 3-D cross-sections of the 4-D body.

All three observers establish their existence as real bodies as they meet at event 1 before proceeding with trips into space-time. Each observer keeps data on each of the events indicated in the space-time diagram. Data is exchanged throughout the experiment with signal transmissions (including photographs of the observers as they perform their measurements, and time data along with computed distances, etc.). The Blue observer and Light Brown observer initially travel at high speed to event 8, where they both come to rest with respect to the Brown inertial frame of reference. The Blue observer then leaves the Light Brown observer, moving in the opposite direction, headed back for the encounter with the Brown observer at event 5.

The culmination of the experiment (not shown in the diagram) occurs with both Light Brown and Blue returning to join Brown. All three are together comparing their data to determine whether all observations and measurements are in agreement with the predictions made based on the Block Universe model. The predicted data include clock times and computed distances to be recorded by each observer at each of the events planned (as indicated in the space-time diagram)-- along with predictions of times and other content of transmitted information (transmissions indicated by green photon world lines). Particularly important is the prediction of content of information that is to be received at planned events.

At the final meeting of Brown, Light Brown and Blue, the observations and measurements are found to be in agreement with the predictions for the experiment (otherwise, special relativity would be invalidated).

 

[yuiop]

As far as I know Special Relativity does not take a position on whether the universe is deterministic or not. The block universe seems to adopt Special Relativity and take the deterministic position. Since there is no experiment that at least in principle could distinguish between a deterministic or non deterministic universe, any discussion of the block universe would have to be purely philosophical as it does not and cannot predict anything that is not already predicted by SR.

 

[bobc2]

...any discussion of the block universe would have to be purely philosophical as it does not and cannot predict anything that is not already predicted by SR.

But, I just presented an experiment that would predict outcomes based on the Block Universe Model.

Please indicate where in my example you fee that it fails to demonstrate a positive result.

 

[Last_Exile]

In reply to post #16

Referring to Space and Time in Specal Relativity by Mermin p41

Our findings apply only to clocks which are moving uniformly. But if we wish to bring the two clocks back to the same place , at least one of them has to be turned around, and while it is being turned around, that clock is not moving with constant velocity (or, more technically, it is not in an inertial frame). Therefore we must be careful in reaching any conclusions.

 

[bobc2]

In reply to post #16

Referring to Space and Time in Specal Relativity by Mermin p41

Yes. One should be very careful. I was very careful to assure the constant velocity travel paths were very very long compared to the turn-around paths for traveling observers. On the scale of my space-time sketch you would have to zoom in at great magnification to detect the curvature of that short turn-around path. We can assure a negligible effect on the final data from the turn-around.

I'm sure folks on this forum do not discount the results of the twin paradox thought experiment on the basis of the turn-around for the traveling twin.

 

[Dale]

Here is an experiment to verify predictions of the block universe model.

There is no possible way to make an experimental test that would distinguish between a block universe and a deterministic non-block universe.

 

[bobc2]

There is no possible way to make an experimental test that would distinguish between a block universe and a deterministic non-block universe.

Why? Please explain. I provided an explanation via the thought experiment. Point out where the experiment produces a negative result.

And please explain what you mean by a "deterministic non-block universe."

 

[yuiop]

But, I just presented an experiment that would predict outcomes based on the Block Universe Model.

Please indicate where in my example you fee that it fails to demonstrate a positive result.

You have stated several times that the block universe is consistent with SR. I would consider a positive result to be one that is not consistent with the predictions of SR, otherwise it is just SR with a different philosophical interpretation.

 

[yuiop]

Yes. One should be very careful. I was very careful to assure the constant velocity travel paths were very very long compared to the turn-around paths for traveling observers. On the scale of my space-time sketch you would have to zoom in at great magnification to detect the curvature of that short turn-around path. We can assure a negligible effect on the final data from the turn-around.

I'm sure folks on this forum do not discount the results of the twin paradox thought experiment on the basis of the turn-around for the traveling twin.

These are valid comments and SR can handle acceleration or non inertial motion as in the twins paradox. Last_Exile was just pointing out we need to take care in these situations and for example we should not expect symmetrical results when non inertial motion is analysed.

 

[Dale]

Why? Please explain. I provided an explanation via the thought experiment. Point out where the experiment produces a negative result"

The problem isn't that the experiment produces a negative result, the problem is that any alternative Lorentz-compatible model will also predict a positive result. For instance, LET would also predict a positive result.

In order for an experiment to qualify as evidence for theory A over theory B then not only does it need to be in accordance with theory A but it must also be in contradiction to theory B. That is what yuiop was mentioning:

You have stated several times that the block universe is consistent with SR. I would consider a positive result to be one that is not consistent with the predictions of SR, otherwise it is just SR with a different philosophical interpretation.

 

[bobc2]

The problem isn't that the experiment produces a negative result, the problem is that any alternative Lorentz-compatible model will also predict a positive result. For instance, LET would also predict a positive result.

In order for an experiment to qualify as evidence for theory A over theory B then not only does it need to be in accordance with theory A but it must also be in contradiction to theory B. That is what yuiop was mentioning:

It is refreshing to see that forum members recognize that the Block Universe concept is actually a feature of special relativity (follows directly from special relativity) and no new theory is required to affirm the reality of the 4-dimensional bodies required by the Block Universe (or by special relativity). I've never described the Block Universe as a theory different from special relativity.

The "Block" terminology may have originated with Kurt Godel after working through his closed curve solutions to Einstein's General Relativity theory. Hermann Weyl's observations (predating Godel) were consistent with the "Block" concept. A number of contemporary physicists have recognized the concept as a feature of special relativity. None of them (to my knowedge) have proposed this concept as a new theory, but rather an obvious result of special relativity.

When the twin paradox is presented it is never presented as a new theory, nor should the Block Universe.

I had been under the impression that people on this forum had been objecting to the Block Universe based on their rejection of the concept of a 4-dimensional universe populated by real physical 4-dimensional objects.

 

[Dale]

Personally, the block universe concept is one that I like and use a lot. My objections to your comments here and elsewhere are just objections to some of the specific things that you say about it, not the block universe concept itself. Many of your comments about the block universe are (IMO) either incorrect or inappropriate, which bothers me since the block universe is (IMO) a very elegant concept.

For example, your claims that all four dimensions are spatial or that you can have experimental proof about it. I believe that neither of those claims are correct. Or for example, the consciousness aspects that you seem inclined to drag into these discussions. I don't have a stance on the correctness of those claims, just their appropriateness for the forum.

Although I cannot speak for others, I suspect that many of their objections are similar.

 

[bobc2]

Personally, the block universe concept is one that I like and use a lot. My objections to your comments here and elsewhere are just objections to some of the specific things that you say about it, not the block universe concept itself. Many of your comments about the block universe are (IMO) either incorrect or inappropriate, which bothers me since the block universe is (IMO) a very elegant concept.

Those are not unreasonable comments, DaleSpam. Hopefully, visitors to the forum will appreciate seeing the different views concerning special relativity.

For example, your claims that all four dimensions are spatial or that you can have experimental proof about it. I believe that neither of those claims are correct.

I tried to avoid any reference to a spatial 4th dimension in my current posts since our forum monitor locked up the last thread involving that subject, indicating that my last posts there "...had zero physics."

My current posts above, particularly the thought experiment, focused on establishing objects (bodies) as real physical 4-dimensional objects.

Or for example, the consciousness aspects that you seem inclined to drag into these discussions. I don't have a stance on the correctness of those claims, just their appropriateness for the forum.

In my posts I have primarily attempted to inform those intereseted in special relativity here of the implications of a Block Universe that have been recognized by a few of the prominent physicists--from the early days of relativity (Hermann Weyl) to those close to Einstein in his later years (Kurt Godel) and some of the contemporary physicists. Hermann Weyl seems to be the earliest to talk of consciousness moving along the world line of the 4-dimensional body. The implication of consciousness coupling to the 4-dimensional body was not lost on Godel and Einstein.

Contemporary physicists like Brian Greene (the 4-D loaf of bread guy), Paul Davies, Roger Penrose, and others have noticed special relativitiy's implications of the block universe. Of course philosophers like Hilary Putnam have picked up on the implications of special relativity and written much about it.

I don't think anyone here has yet pointed to a flaw in the logic of my thought experiment presented above that directly implies the existence of real 4-dimensional objects. That argument (not original with me, and with aspects of Penrose's Andromeda Galaxy paradox) has had a strong influence on my understanding of special relativity.

However, again, it must be said that physics has a limited understanding of time at the fundamental level--and perhaps much less understanding of consciousness. But, that should not detract from the importance of the above thought experiment as a subject of real physics--not philosophy. Philosophers will try to make it part of their turf, but we physicists should not trust them with it.

Although I cannot speak for others, I suspect that many of their objections are similar.

I have no doubt about that.

 

[Dale]

My current posts above, particularly the thought experiment, focused on establishing objects (bodies) as real physical 4-dimensional objects.

That is precisely what it does not accomplish. It does not accomplish that because the experimental outcomes are the same for the block-universe and any other interpretation of the Lorentz transforms. Not only does your experiment not accomplish that, but no other possible experiment does.

Please, use the block universe concept. Teach and explain it to others. Advocate for it and promote it. Continue making and posting your drawings. But please stop thinking that the block universe concept can be proven experimentally or that it makes time into a spatial dimension.

 

[bobc2]

That is precisely what it does not accomplish. It does not accomplish that because the experimental outcomes are the same for the block-universe and any other interpretation of the Lorentz transforms. Not only does your experiment not accomplish that, but no other possible experiment does.

Please show some specific demonstration that indicates that a different interpretation of Lorentz transforms would yield the same observations and measurements as the block universe thought experiment.

Please, use the block universe concept. Teach and explain it to others. Advocate for it and promote it. Continue making and posting your drawings.

Thanks.

But please stop thinking that the block universe concept can be proven experimentally or that it makes time into a spatial dimension.

The results of the block universe experiment presented earlier manifestly requires the existence of 4-dimensional objects. If that is not the case, someone should show specifically where the thought experiment fails in that regard.

I have said nothing in my present posts about whether time or spatial is the appropriate representation for the 4th dimension (I yield to the forum monitor's judgement on the appropropriateness of that topic). I'm also refraining from comments about consciousness, except where you bring it up.

 

[Dale]

Please show some specific demonstration that indicates that a different interpretation of Lorentz transforms would yield the same observations and measurements as the block universe thought experiment.

OK, calculate any specific measurement that the block universe interpretation predicts and I will calculate using the LET interpretation.

 

[PeterDonis]

I don't think anyone here has yet pointed to a flaw in the logic of my thought experiment presented above that directly implies the existence of real 4-dimensional objects.

Your thought experiment basically boils down to this: two observers who are spatially separated receive light signals "at the same time" from different events on a third observer's worldline. This implies that different events on the third observer's worldline, which occur at different proper times according to that observer, must "both exist at the same time", hence the third observer (and by extension *any* observer) must be a real 4-dimensional object.

The phrase I quoted, "at the same time", is key to your argument. (I don't say that you've explicitly stated it that way, but when I boil your argument down to its essentials, that's what I come up with.) That phrase, of course, won't work as it stands, because simultaneity is relative; but you could substitute "at spacelike separated events" for "at the same time" and the logic would basically be the same.

I actually have no quarrel with the argument as I have stated it above (one could quibble about using the word "exist", but I think that could be satisfactorily unpacked if necessary). However, you should be careful in specifying exactly what this argument proves. It proves that any event on the third observer's worldline that has sent a light signal which has been received by some other observer, must "exist" (because it's been observed). It does *not* prove that the *entire* worldline of the third observer, including its extrapolation to "future" events that have not yet sent light signals to anyone, must "exist". But many of the claims you have made about the "block universe" strongly suggest, at the very least, that you are making the latter claim, which is not justified by your argument. That's why you have gotten pushback from several people here, including me.

 

[bobc2]

OK, calculate any specific measurement that the block universe interpretation predicts and I will calculate using the LET interpretation.

If the thought experiment outcome does not contradict LET, that just means that LET also requires 4-dimensional objects. That in no way detracts from the 4-dimensional objects required of special relativity.

 

[bobc2]

...However, you should be careful in specifying exactly what this argument proves. It proves that any event on the third observer's worldline that has sent a light signal which has been received by some other observer, must "exist" (because it's been observed)...

Wait a minute--you've just left out the most important part: Brown and Blue share the same simultaneous 3-D space at an event where each one occupies a different 3-D cross-section of the 4-D universe. Further, Brown's simultaneous space includes one 3-D cross-section of the 4-dimensional Light Brown body, and Blue's simultaneous space includes a different 3-D cross-section of the 4-dimensional Light Brown.

...It does *not* prove that the *entire* worldline of the third observer, including its extrapolation to "future" events that have not yet sent light signals to anyone, must "exist".

I take it from the way you stated this that you at least acknowledge that we have established that Light Brown, as a minimum, has been shown to exist at two events along his world line, one being simultaneous with Brown and the other being simultaneous with Blue while Brown and Blue share their intersection event.

In the interest of brevity I just indicated that by extending the experiment we could establish the same Light Brown existence for any arbitrary point along his world line--or with sufficient tedium (perhaps with the use of mathematical induction) we could establish the existence of Light Brown at a continuum of points along the world line, i.e., a 4-dimensional object.

...But many of the claims you have made about the "block universe" strongly suggest, at the very least, that you are making the latter claim, which is not justified by your argument. That's why you have gotten pushback from several people here, including me.

Of course that is the claim I have made. A push-back is not unexpected.

And of course a stronger argument could be made, providing more explicit data, adding more and more observers with different Lorentz boosts, all intersecting in a way that shares one point from their respective inertial frames of reference.

The experiment can be further embellished by establishing an array of objects, spaced at specified distances from the Brown observer and all at rest in Brown's frame of reference (each accompanied by a clock, computer based controls system with appropriate algorithms for sending transmissions of various kinds of on-board information--two-way distance, computations, time marked videos, etc.).

Yet another array of objects can be sent out at the same velocities, programmed to travel to selected rest frame objects, then return to the Brown observer (all the while computing, storing and transmitting data).

Finally an array of objects travel at different velocities and finally all intersect at a specified event along with the Brown observer (similar to the above experiment).

Experiments could be conducted over and over again over a period of many years (although the distances and velocities do not have to be extreme--after all, experimenters have carried clocks on airplanes to verify time dilation).

If you give it some thought, you can probably come up with a better battery of experiments than I have proposed. I think you can see intuitively, without putting in specific numbers, that the outcome of these kinds of experiments would provide very strong evidence of 4-dimensional objects.

 

[bobc2]

By the way, it's obvious that we are susceptible to problems with semantics when we try to talk about time in the context of Block Universe. I've tried to avoid saying that Light Brown exists simultaneously at two different events on his world line. That language is self-contradictory in terms of normal usage of "simultaneous" in special relativity.

I noticed that Chestermiller, in his original post used a qualifier something like "in the 4D sense." I knew immediately what he meant but noticed some push-back from some here.

When referring to the block universe, Brian Greene uses language something like, "It is just all there at once." Right away he has given some physicists something to fuss about. Other physicists use similar language. I think it was Hermann Weyl who said something like, "...things don't happen--they just are." Maybe that is a little better than Greene. Einstein simply remarked something like, "...We physicists make no distinction between the past, present and future." And he remarked to Rudolf Carnap that he was "...very troubled by NOW." He indicated that NOW has no place in physics, and yet it is such a strong and compelling part of our experience. Paraphrasing Einstein somewhat: "Time is a stubborn persistent illusion." Reading Stephen Hawking's book by that title I anxiously anticipated Hawking's discussion of "Block Time" only to discover I could not find one reference to Einstein's comment anywhere in the book (what a bait and switch!).

Perhaps someone here can suggest some terminology we could adapt so that we all know what we are talking about. One physicist has published a paper about why so many physicists don't accept the block universe concept. He claims it is because there are two different kinds of time being used. So he recommends the time of physics be called "pime" and the other time just "time." I don't like his idea at all. And I don't accept his premise.

I think the real problem is that physics does not yet understand time at the most fundamental level. The logical positivists and operationalists offer the solution that you only talk about time measurements using clocks, etc. But that seems to fall short when attempting an understanding of the block universe.

 

[PeterDonis]

Wait a minute--you've just left out the most important part: Brown and Blue share the same simultaneous 3-D space at an event where each one occupies a different 3-D cross-section of the 4-D universe.

As it stands, this is nonsense. If Brown and Blue are in relative motion (which as I understand it, they are), they can't possibly "share the same simultaneous 3-D space" at any event. Each one, as you say, "occupies a different 3-D cross section of the 4-D universe"--the "3-D cross section" *is* the "simultaneous 3-D space". So you are contradicting yourself here, unless you mean these standard terms in some other way (in which case you should define how you're using them).

Further, Brown's simultaneous space includes one 3-D cross-section of the 4-dimensional Light Brown body, and Blue's simultaneous space includes a different 3-D cross-section of the 4-dimensional Light Brown.

Yes. But this doesn't mean what you think it means. See below.

I take it from the way you stated this that you at least acknowledge that we have established that Light Brown, as a minimum, has been shown to exist at two events along his world line, one being simultaneous with Brown and the other being simultaneous with Blue while Brown and Blue share their intersection event.

No. Read my post again, carefully. I said that Brown and Blue can each vouch for the "existence" of events on Light Brown's worldline *from which they have received light signals*. Those events are *not* events in their "simultaneous spaces"; they are events in their *past light cones*.

The "simultaneous spaces" are not "real" (at least, not "yet"--see below). They are *constructed* from the data that is known, the data in Brown and Blue's past light cones. But, because Brown and Blue do not have complete information about *all* of the initial conditions (only those in their past light cones), each of their *constructions* of what is in their "simultaneous spaces" at a given moment of their time are not *guaranteed to be right*. The constructions are only verified (if indeed they turn out to be right) *later*, when light signals from those events reach Brown and Blue at later points on their worldlines--but then, of course, there are *new* "simultaneous spaces" that have to be constructed, and whose constructions are not guaranteed to be right.

This is the basic flaw in your claim that *all* of the 4-D "block universe" has to "exist" all at once: *we don't have the necessary data* to establish it. We only have data from our past light cone. The rest of the "block universe" is *constructed* from that, but because we have incomplete knowledge, that construction may be wrong. In a thought experiment scenario, we can ignore this because we are making up the scenario: we can simply *stipulate*, by fiat, what the events are. In the real world, we can't do that. And no matter how many experiments we run, we will still only have incomplete data; we will *never* be able to *know* for sure what is happening in regions of spacetime that are spacelike-separated from us. Your strong claim about the "block universe" would require us to be sure, and we aren't.

 

[PeterDonis]

When referring to the block universe, Brian Greene uses language something like, "It is just all there at once." Other physicists use similar language. Perhaps someone here can suggest some terminology we could adapt so that we all know what we are talking about.

This language is fine when referring to the block universe as a *model*. Where it goes wrong is in trying to claim that the block universe must describe "reality", when our actual knowledge in the real world (as opposed to the model world of a thought experiment) is limited.

I think the real problem is that physics does not yet understand time at the most fundamental level. The logical positivists and operationalists offer the solution that you only talk about time measurements using clocks, etc. But that seems to fall short when attempting an understanding of the block universe.

It may well be true that we don't have a good fundamental physical understanding of time. But that's irrelevant to the "block universe" as a model. The block universe model is very simple: "time" is one of the four dimensions, and it's distinguished from the spatial dimensions (roughly speaking) by having an opposite sign in the metric. Once again, there's nothing wrong with this conceptually, as a *model*; but to claim that it must describe "reality" requires one to believe that we can somehow have complete knowledge of initial conditions, which we don't. Including our lack of knowledge in our model of reality complicates the model; it is no longer the simple "block universe" we have been talking about, but something more complex. (And including quantum mechanics adds further complications, as does including gravity.)