The Block Universe - Refuting a Common Argument - Comments

[PAllen]

You are providing alternative to "solipsism". You are not free to redefine "real" as "subjective" in this context.

Observer dependent does not mean subjective. The latter implies it depends on state of mind (e.g. QM interpretations that attribute a key role to consciousness). Observer dependent simply means that the scope of what is fixed depends on the event of observation or measurement - emphasis on event, not state of mind.

Turning it around, suggesting that something unobservable and inherently unverifiable (BU and reality of simultaneity surface) must be considered real seems seems inherently subjective to me. If it is in principle not subject to verification, it is subjective.

 

[PeterDonis]

You are not free to redefine "real" as "subjective" in this context.

I'm not. I'm redefining it as "dependent on which event you pick." Events are objective; they are points in spacetime, and all observables at an event are invariants. There's no subjectivity.

 

[zonde]

I'm not. I'm redefining it as "dependent on which event you pick." Events are objective; they are points in spacetime, and all observables at an event are invariants. There's no subjectivity.

I don't know. I still think your argument is flawed. You take philosophical statement and provide an argument against it. There is generally recognized philosophical idea of "realism" that is alternative to "solipsism". If you want to provide valid argument in this context you have to stick to proper meanings of philosophical terms (in particular meaning of "real"). And for anybody reading the article there is no reason to expect that you would use "real" with some different meaning.

Maybe you can provide valid argument based on your idea but you have not done this in the article IMO.

 

[Ilja]

Ilja, does Presentism apply to non-local events?

Hm. Presentism means that what exists, exists now. The future does not yet exist, the past is past, and no longer exists, what exists, exists now. What exists is, of course, something global - the whole world. How this world is structured is an independent question.

 

[Ilja]

In what sense? Is the "present" just one event (whichever event I am at "now"), or is it more than that?

What is present is the whole world. A preferred space-like hypersurface of spacetime, the one which exists, while the other parts of the spacetime exist only in memories and hopes, but not actually in reality.

 

[Smattering]

There is generally recognized philosophical idea of "realism" that is alternative to "solipsism".

But this discussion is not about realism vs. solipsism, but rather about presentism vs. eternalism.

In particular, the growing block universe interpretation does not conflict with realism. The events just have to grow in a particular order such that the past light cone of every currently growing event has already grown before. But this does not imply that only my own past light cone is real. It's rather the other way around: My past light cone must exist or at least must have existed as a prerequisite for my own existence.

 

[PWiz]

Just curious - is there an argument which combines the Block Universe interpretation with the Many-Worlds interpretation? (I don't know if this should be in a separate thread or not. If any mentor feels it should be somewhere else, feel free to move it.)

 

[Smattering]

Just curious - is there an argument which combines the Block Universe interpretation with the Many-Worlds interpretation? (I don't know if this should be in a separate thread or not. If any mentor feels it should be somewhere else, feel free to move it.)

From my point of view, believing in the many worlds interpretation of QM would be an argument against the block universe - at least against a "classical" block universe that really resembles some kind of block. After all, an eternal many worlds universe would have a tree-like structure.

 

[rjbeery]

I have a general question for PeterDonis, but anyone else is welcome to give their opinion: do you think a "certain past" but an "uncertain future" implies time-asymmetry? It's difficult for me to accept the idea that the rules of Physics differ depending where in spacetime an observer is located.

 

[Smattering]

I have a general question for PeterDonis, but anyone else is welcome to give their opinion: do you think a "certain past" but an "uncertain future" implies time-asymmetry? It's difficult for me to accept the idea that the rules of Physics differ depending where in spacetime an observer is located.

Why do you think that a certain past and an uncertain future imply different physical laws for different observers?

 

[PAllen]

I have a general question for PeterDonis, but anyone else is welcome to give their opinion: do you think a "certain past" but an "uncertain future" implies time-asymmetry? It's difficult for me to accept the idea that the rules of Physics differ depending where in spacetime an observer is located.

All fundamental classical physical laws have time symmetry (Standard Model does not, even at the fundamental level). However, emergent laws, e.g. thermodynamics are time asymmetric, leading to a common view (no idea of percentages) that the universe has an objective time arrow, and that evolution is viable interpretation (for geometric theories, it is treated under the umbrella of EBU - evolving block universe; George F.R. Ellis of "Hawking and Ellis" fame has written a series of papers and essays motivating this point of view.)

 

[rjbeery]

Why do you think that a certain past and an uncertain future imply different physical laws for different observers?

Because we can follow a causal string of events in both directions, right? "Unfrying an egg" is practically impossible but not unphysical; we could record an egg being cooked and reverse the video: there is no uncertainty as we unfry it, no physical laws are being broken, no stochastic processes are coming into play, and there are no options other than the resulting uncooked egg...so why do we believe that things must be different when they reside in our future light cones? Before QM came along there was no reason to question a clockwork universe, and I get the feeling that some people believe free will has been "saved" by the apparent statistical nature of QM.

Basically I'm trying to identify the resistance to a Block Universe.

 

[PAllen]

Because we can follow a causal string of events in both directions, right? "Unfrying an egg" is practically impossible but not unphysical; we could record an egg being cooked and reverse the video: there is no uncertainty as we unfry it, no physical laws are being broken, no stochastic processes are coming into play, and there are no options other than the resulting uncooked egg...so why do we believe that things must be different when they reside in our future light cones? Before QM came along there was no reason to question a clockwork universe, and I get the feeling that some people believe free will has been "saved" by the apparent statistical nature of QM.

Basically I'm trying to identify the resistance to a Block Universe.

I don't believe there is resistance. What I see here and elsewhere is that one side says BU is not a required interpretation, but a personal philosophic choice; while BU proponents argue that it is strongly preferred and engage in tendentious critiques of other possiblities.

[edit: note, that in classical physics, there was already the mystery of why all thermodynamic processes, everywhere/when seem to run in the same direction. This already suggested to many physicists an objective arrow of time, with an objective asymmetry for the universe as a whole]

 

[rjbeery]

I don't believe there is resistance. What I see here and elsewhere is that one side says BU is not a required interpretation, but a personal philosophic choice; while BU proponents argue that it is strongly preferred and engage in tendentious critiques of other possiblities.

Fair point. I'd like to point out that in this very thread there are some Presentists (which is basically incompatible with SR), so the only reason I might ever argue that BU is strongly preferred is because (in my experience) people have not fully grasped the consequences of Relativity.

 

[PAllen]

Fair point. I'd like to point out that in this very thread there are some Presentists (which is basically incompatible with SR), so the only reason I might ever argue that BU is strongly preferred is because (in my experience) people have not fully grasped the consequences of Relativity.

Presentism is not incompatible with SR. Preferred frame LET is an interpretation of SR that cannot be ruled out by any experiment or observation, and it trivially supports strict presentism. This is yet another example of insisting that personal choice is a requirement. Note that, aesthetically, I find preferred frame repugnant, but I would never argue that it is an invalid point of view.

 

[Smattering]

Because we can follow a causal string of events in both directions, right? "Unfrying an egg" is practically impossible but not unphysical;

I doubt that. Physics is all about observations. As the process if unfrying an egg has never been observed, and there is no theory that predicts how we could practically unfry an egg, I'd say that this is indeed unphysical.

we could record an egg being cooked and reverse the video:

But if you reverse the video, it does not represent anything that can be observed anymore.

there is no uncertainty as we unfry it, no physical laws are being broken,

No physical laws are being broken? Then please explain to me how to observe the process of unfrying an egg.

 

[RUTA]

No, it doesn't. It follows from relativity of simultaneity + no preferred frame + all events to the past of any observer's surface of simultaneity are fixed and certain. In the article, I used "relativity of simultaneity" to mean what you are calling "relativity of simultaneity + no preferred frame". But the article makes clear that that by itself is not sufficient; you also need the additional premise I just gave.

Your "additional premise" is subsumed by the other two, since you're not using solipsism. Simply look at the surfaces of simultaneity for observers in motion along your surface of simultaneity. No preferred frame then fixes your past (and future).

I have done no such thing. Saying that events to the past of a given observer's surface of simultaneity, but not in that observer's past light cone, are not fixed and certain, is not at all the same as "denying simultaneity". Unless, of course, when you say "simultaneity" you are implicitly smuggling in the additional premise I referred to above. But that additional premise is there, whether you want to admit it or not.

BW follows deductively from the two premises I listed, so you're either denying the first or the second and clearly it's not the second.

None, as far as I'm concerned. But you posted 5 articles about "blockworld", which would seem to indicate that it does make a difference to you.

It certainly does. See for example: “Modified Regge Calculus as an Explanation of Dark Energy,” W.M. Stuckey, Timothy McDevitt & Michael Silberstein,Classical & Quantum Gravity 29 055015 (2012). http://arxiv.org/abs/1110.3973.

 

[rjbeery]

Presentism is not incompatible with SR. Preferred frame LET is an interpretation of SR that cannot be ruled out by any experiment or observation, and it trivially supports strict presentism. This is yet another example of insisting that personal choice is a requirement. Note that, aesthetically, I find preferred frame repugnant, but I would never argue that it is an invalid point of view.

Ahh, of course you're right! I think of Presentism as being ambiguous by design but there's nothing preventing someone from simply claiming a preferred frame. Not very...elegant...but not technically wrong.

 

[rjbeery]

I doubt that. Physics is all about observations. As the process if unfrying an egg has never been observed, and there is no theory that predicts how we could practically unfry an egg, I'd say that this is indeed unphysical.
But if you reverse the video, it does not represent anything that can be observed anymore.
No physical laws are being broken? Then please explain to me how to observe the process of unfrying an egg.

Unfrying an egg is not unphysical. No physicist would say otherwise.

If the molecules in the walls and ceiling surrounding the stove emit energy (in the form of heat and sound waves) in just the right way, directed toward the fried egg sitting in the pan, then that energy can break the egg white proteins which have bound together, freeing the individual proteins to reattach to themselves rather than their neighbors. The result is an uncooked egg. While we're discussing this "conspiracy of molecules" we could also go into how the stove top is coordinating its heat energy, directing what will eventually be electrical energy back into the city grid.

"Observing" such a phenomenon is unlikely to say the least but it is not unphysical in any way.

 

[PeterDonis]

You take philosophical statement and provide an argument against it.

No, I'm not. I'm taking a particular argument for a "philosophical" statement and showing that it's not valid. That's not an "argument against" the statement; I'm not proving that the statement is wrong. I'm just proving that a particular argument that claims to prove the statement is true, is not valid. That's all I'm doing. Nothing else. No more than that.

(I feel the need to keep repeating that because people continue to say I claimed something in the article that I didn't claim, that the article said I didn't claim, and that I've already said several times in this thread I didn't claim.)

 

[PAllen]

Your "additional premise" is subsumed by the other two, since you're not using solipsism. Simply look at the surfaces of simultaneity for observers in motion along your surface of simultaneity. No preferred frame then fixes your past (and future).

How is the alternative presented in the article solipsism - that instead of "all events to the past of any observer's surface of simultaneity are fixed and certain" you adopt "all events in the past light cone of any observer are fixed and certain"?

 

[PeterDonis]

do you think a "certain past" but an "uncertain future" implies time-asymmetry?

Distinguishing "past" and "future" in itself already implies time asymmetry. We do it because that's what we observe: the two "directions" of time don't work the same. We can remember the past but we can't remember the future; entropy increases towards the future but not the past; etc.

It's difficult for me to accept the idea that the rules of Physics differ depending where in spacetime an observer is located.

Time asymmetry doesn't mean the laws are different at different events. It just means the laws, which are the same at every event, are time asymmetric; the "future" direction works differently from the "past" direction.

However, it's not necessarily true that time asymmetry in our observations is due to time asymmetry in the laws; it could also be due to time asymmetry in the initial conditions. See below.

"Unfrying an egg" is practically impossible but not unphysical; we could record an egg being cooked and reverse the video: there is no uncertainty as we unfry it, no physical laws are being broken, no stochastic processes are coming into play, and there are no options other than the resulting uncooked egg...so why do we believe that things must be different when they reside in our future light cones?

Because of the initial conditions--or more precisely the conditions at the instant of time where the egg has just been fried, which aren't really "initial", but we're assuming we can "back-predict" as well as "forward predict" here so that doesn't matter. The conditions at the instant of time where the egg has just been fried are asymmetric: the microscopic motions of all the particles in the egg back-predict that it was unfried in the past, but they do not forward-predict that it will unfry itself in the future; they forward-predict that it will stay fried, at least until it gets digested.

So the asymmetry here isn't in the laws; it's in the particular solution of the laws that is being realized. The time symmetry of the laws (assuming for the moment that we know the laws are in fact time-symmetric, which isn't actually true in all cases--weak interactions, at least, aren't) shows up in the complete set of solutions, not in any particular solution. If there is a solution with the egg unfried in the past and fried in the future, there is also a solution that is the exact time reverse of that one, with the egg fried in the past and unfried in the future. Observation just tells us which particular solution we happen to be living in.

 

[PeterDonis]

Simply look at the surfaces of simultaneity for observers in motion along your surface of simultaneity. No preferred frame then fixes your past (and future).

You are assuming that "past" and "future" are the only two categories. Did you read my article? It discusses this exact error. There is a third category, which I called "elsewhere" in the article. You can't just help yourself to the assumption that all events to the past of any surface of simultaneity are fixed; that's precisely the additional premise that is not logically required by SR.

In other words, your statement quoted above is just another way of stating the additional premise; it doesn't help establish it at all.

BW follows deductively from the two premises I listed

No, it doesn't. See above.

 

[Smattering]

"Observing" such a phenomenon is unlikely to say the least but it is not unphysical in any way.

O.k., but given the fact, that frying is many magnitudes more likely than unfrying, how can you seriously consider this an example for symmetry?

 

[rjbeery]

O.k., but given the fact, that frying is many magnitudes more likely than unfrying, how can you seriously consider this an example for symmetry?

Because on the microscopic level the physical laws are being applied in a time-symmetric manner. The actual difference between past and future is purely epistemological (meaning what we know, as opposed to what actually is). This is a consequence of an entropy gradient in spacetime. This gradient gives us an asymmetry in information available but that does not mean that physical laws are time-asymmetric.

 

[PeterDonis]

given the fact, that frying is many magnitudes more likely than unfrying, how can you seriously consider this an example for symmetry?

To put rjbeery's response in somewhat different words, as I said in a previous post, the asymmetry is in the initial conditions, not the laws--i.e., it's in the particular solution of the laws that is realized in the universe we live in. The symmetry of the laws shows up in the complete set of all possible solutions; it does not have to show up in a particular solution taken by itself.

 

[RUTA]

How is the alternative presented in the article solipsism - that instead of "all events to the past of any observer's surface of simultaneity are fixed and certain" you adopt "all events in the past light cone of any observer are fixed and certain"?

You can avoid the BW conclusion of RoS + no preferred frame by getting rid of either premise. If you don't assume the reality of all points on a surface of simultaneity, but only the point where you exist, then you've gotten rid of the notion of a surface of simultaneity and dispensed with the first premise.

 

[Smattering]

Because on the microscopic level the physical laws are being applied in a time-symmetric manner.

Then why is frying observed so often, but unfrying almost never?

Edit: PeterDonis has already answered this.

but that does not mean that physical laws are time-asymmetric.

I never claimed that physical laws are time-asymmetric.

 

[RUTA]

You are assuming that "past" and "future" are the only two categories. Did you read my article? It discusses this exact error. There is a third category, which I called "elsewhere" in the article. You can't just help yourself to the assumption that all events to the past of any surface of simultaneity are fixed; that's precisely the additional premise that is not logically required by SR.

In other words, your statement quoted above is just another way of stating the additional premise; it doesn't help establish it at all.

Your "additional premise" is only required if you first get rid of the reality (co-existence) of the events on your surface of simultaneity (SoS), i.e., you abandon the first premise because you get rid of the notion of a SoS. You can certainly disassemble M4 into individual perspectives. You just don't have anything to say about what's happening Now anywhere other than your location on your worldline at any given instant. That's essentially solipsism.

 

[PAllen]

You can avoid the BW conclusion of RoS + no preferred frame by getting rid of either premise. If you don't assume the reality of all points on a surface of simultaneity, but only the point where you exist, then you've gotten rid of the notion of a surface of simultaneity and dispensed with the first premise.

You are bundling things that need not be bundled. Relativity of simultaneity, to me, means NOTHING more than if two observers in relative motion synchronize clocks using the same procedure, each will think the other's clocks to be out of synch. It has nothing to do with a surface of simultaneity, nor with the FURTHER assumption that such surface has anything to do with what is fixed and certain. Further, you keep stating that believing 'past light cone is fixed' means only current event is real. I completely disagree with this coupling as well.

 

[PeterDonis]

Your "additional premise" is only required if you first get rid of the reality (co-existence) of the events on your surface of simultaneity (SoS),

I'm not "getting rid of" it; you're assuming it. It's not logically required by the laws of SR, so it's an additional premise you have to assume, not something I have to "get rid of".

you abandon the first premise because you get rid of the notion of a SoS

No, I just say that events on the SoS are not "fixed and certain" with respect to an observer, at a particular event, whose SoS it is. Your argument implicitly assumes that events on the SoS are "fixed and certain"; but that is not logically required by the laws of SR. It is just as consistent with the laws of SR to say that only events in the past light cone of a given event are "fixed and certain" with respect to an observer at that event.

If you don't assume the reality of all points on a surface of simultaneity, but only the point where you exist

The past light cone is not the same as a single event.

Please, take the time to read what I'm actually saying. You have not responded at all to what I actually said in the article.

 

[PAllen]

Your "additional premise" is only required if you first get rid of the reality (co-existence) of the events on your surface of simultaneity (SoS), i.e., you abandon the first premise because you get rid of the notion of a SoS. You can certainly disassemble M4 into individual perspectives. You just don't have anything to say about what's happening Now anywhere other than your location on your worldline at any given instant. That's essentially solipsism.

That's your personal, extreme, and IMO false definition of solopsism.

[edit: More: It is patently false that 'past light cone certain' means you can't say anything about what is happening beyond the past light cone elsewhere. It simply means that such a statement is prediction, based on information in the past light cone; and such statement may have exceedingly high probability of being verified. Finally, you wouldn't be inclined to make such a prediction and expect it to be born out if you thought there was no 'reality' outside the past light cone. I continue to be amazed at how you bundle logically separate concepts in the ONE WAY YOU PREFER that you define as THE ONE WAY POSSIBLE.]

 

[zonde]

No, I'm not. I'm taking a particular argument for a "philosophical" statement and showing that it's not valid. That's not an "argument against" the statement; I'm not proving that the statement is wrong. I'm just proving that a particular argument that claims to prove the statement is true, is not valid. That's all I'm doing. Nothing else. No more than that.

It's hard to decipher your post but I wrote the argument as I understand it.
So there are three statements:
1. Events to the past of any observer’s “3D world” at a given event are fixed and certain.
2. Solipsism (only my present event is real).
3. Events in any observer’s past light cone at a given event are fixed and certain.
You are arguing against an argument that one has to choose between statements 1. and 2. as we can choose statement 3. instead (I tried to write it similar to 1.)
Seems fine that way.

 

[Dale]

@RUTA nowhere have I ever seen Peter Donis advocate for solipsism. Nor have I ever seen anyone else on PF do so during any block universe discussion.

 

[PeterDonis]

You are arguing against an argument that one has to choose between statements 1. and 2. as we can choose statement 3. instead (I tried to write it similar to 1.)

Yes, this is one way of summarizing what I was saying in the article, taken as a whole.