Conflict between the Block Universe and Bell Tests?

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PeterDonis
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I don't think it is necessary true.
More precisely: the Block Universe as an interpretation of classical, non-quantum special relativity is deterministic, because classical, non-quantum special relativity is itself deterministic. (So is classical, non-quantum general relativity, for that matter, so you could apply a Block Universe interpretation to any curved spacetime solution in GR.)

Imagine, for instance, that the world is a random set of points (events) on the spacetime manifold.
We're not allowed to just "imagine" anything we like in this discussion. We are only allowed to imagine things that are consistent with whatever laws of physics we are using. If we are using the laws of classical, non-quantum relativity, then we are only allowed to imagine scenarios that are deterministic--initial data on any spacelike hypersurface determines the entire spacetime.
 
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More precisely: the Block Universe as an interpretation of classical, non-quantum special relativity is deterministic, because classical, non-quantum special relativity is itself deterministic. (So is classical, non-quantum general relativity, for that matter, so you could apply a Block Universe interpretation to any curved spacetime solution in GR.)
Let me just note that I applied block universe to black hole information paradox
http://de.arxiv.org/abs/0905.0538
which involves GR and QFT.
 
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Lynch101
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I don't think it is necessary true. Imagine, for instance, that the world is a random set of points (events) on the spacetime manifold. Since it is random, I would not call it deterministic. But if I interpret spacetime manifold itself as a block spacetime, without a fundamental difference between future and past and without a notion of the flow of time, then I still have a block universe.
It would still allow for only one possible outcome for Bell tests, however. This would presumably mean that it isn't compatible with indeterministic QM, no?
 
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It would still allow for only one possible outcome for Bell tests, however. This would presumably mean that it isn't compatible with indeterministic QM, no?
I would say no. Or more precisely, it depends on what do you mean by "possible" and "indeterministic". Here is an example. Suppose that coin flipping is a random process and suppose that the outcome of this process turned out to be heads. Is there only one possible outcome in this case? Is the outcome "heads" indeterministic?
 
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I would say no. Or more precisely, it depends on what do you mean by "possible" and "indeterministic". Here is an example. Suppose that coin flipping is a random process and suppose that the outcome of this process turned out to be heads. Is there only one possible outcome in this case? Is the outcome "heads" indeterministic?
It is possibly my misunderstanding of your previous post, coupled with how I understand the Block Universe but my understanding of the Block Universe is that the Universe would comprise all events on an objects world line. If these events are just random points in Block Spacetime, perhaps this would negate the determinism of the Block Universe but it wouldn't negate the fact that the event labelled "outcome of the Bell test" is "eternally etched in the Block". The outcome is already "out there" so to speak.

Does that make sense?
 
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If these events are just random points in Block Spacetime, perhaps this would negate the determinism of the Block Universe but it wouldn't negate the fact that the event labelled "outcome of the Bell test" is "eternally etched in the Block". The outcome is already "out there" so to speak.

Does that make sense?
Yes it does.
 
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While the outcomes of any particular measurement in QM are indeterministic, their distribution in the classical context of 4D spacetime is totally deterministic. When you have so many such quantum exchanges, say of photons, that you might expect the contribution to the stress-energy tensor will bear on the metric per GR, you simply use the corresponding classical field (per the Faraday tensor in the case of photons) in the action for Einstein's equations. Whether or not you consider 4D spacetime to be "real" is irrelevant. The deterministic QM distribution is 4D meaning we're necessarily talking about averages of events distributed over space and time. See these Insights for example: Bell States and Conservation of Spin Angular Momentum and Answering Mermin's Challenge with Wilczek's Challenge.
 
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Of course there is conflict between the Block Universe and Bell Tests.
The Block Universe is a classical concept for a classical Universe.
The real Universe is not classical, so classical physics fundamentally doesn't apply to the actual real Universe.
(but classical physics is still very useful and a very good within its domain of validity)
 
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The Block Universe is an interpretation of SR, and SR is a deterministic theory
Wouldn't we say SR is not deterministic because my past light cone at any time is larger than it was at an "earlier time." So, according to SR, I have no way to know if I will be bombarded with X-rays in the next instant.

Maybe I'm using the wrong definition of deterministic? At least SR makes it impossible for any observer to predict the future, right?
 
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Wouldn't we say SR is not deterministic because my past light cone at any time is larger than it was at an "earlier time." So, according to SR, I have no way to know if I will be bombarded with X-rays in the next instant.
Your not knowing what you will observe in the next instant has nothing to do with whether what you will observe in the next instant is fully determined by initial conditions.

SR makes it impossible for any observer to predict the future, right?
Only because, to predict the future in a deterministic spacetime, you need initial data on an entire spacelike 3-surface, and the only data any observer can actually have is in their past light cone, which will never cover an entire spacelike 3-surface.
 
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Your not knowing what you will observe in the next instant has nothing to do with whether what you will observe in the next instant is fully determined by initial conditions.
OK, I was thinking that may be the definition of deterministic. However, if we reject the block universe, aren't we saying that there aren't real, fixed initial conditions? Not sure, still thinking...
 
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if we reject the block universe, aren't we saying that there aren't real, fixed initial conditions?
No. We're just pointing out that no observer can ever know a complete set of initial conditions for the entire universe. But any observer can know a complete set of initial conditions for what happens at his current present event, since the only set of initial conditions required for that event is what happens in its past light cone. He just doesn't know, at that event, a sufficient set of initial conditions to predict what happens in his future, since those conditions will include events that are outside his current past light cone.
 
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No. We're just ...
It seems to me that accepting a fixed, real time slice is accepting BU. Surely there's not one special time slice that's fixed and real, but others are not. Right?
 
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It seems to me that accepting a fixed, real time slice is accepting BU.
What is a "fixed, real time slice" and where did I talk about "accepting" one?
 
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There seems to be some confusion over the term “block universe.” Let me try to clarify what that means.

We all experience Now as unique from past experiences or experiences that are yet to happen (I won’t qualify all such statements with “I assume”). We tend to believe that we only exist (are only “real”) Now, i.e., my past self no longer exists and my future self has yet to exist. I assume there are other things that coexist with me at each Now, e.g., my twin brother who lives 600 miles away has a Now of his own and his Now coexists with my Now. When we turned 50 our 49 year-old selves no longer existed and our 51 year-old selves were yet to exist. We use this reasoning out of necessity nearly every day. If I want to call my brother I first ask myself, “What is my brother doing Now?“ because I don’t want to call if I believe he is sleeping or at work, for example. Not only is it perfectly reasonable to assume the validity of a shared set of Nows with other people, but it is absolutely necessary in dealing with objects at large distances. If I work for NASA and I’m in charge of a probe circling Jupiter 40 light-min away, I need to know where it is at any given Now, so I know where it will be 40 min from that Now when it receives my next orbital command. When I talk to engineers in Australia who will take over command of that spacecraft in 12 hours, we all share the same notion of our set of overlapping Nows, albeit with different time stamps for our different time zones. Of course, it could be that our probe has been struck by a meteor and it doesn’t exist where I think it does at some Now — I won’t know it has been struck for at least 40 min. But, that’s simply a result of the finite speed of light that carries information to me from the probe. That is, it’s a fact about my knowledge of the probe at some Now, not about whether or not the probe actually coexists with me (is “equally real”) at any Now. The probe doesn’t experience Now, but it’s meaningful to think about it as only existing (as only being “real”) at each Now. If everyone agrees on a shared collection of Nows, that would constitute a global “Now slice“ of spacetime. That is Presentism and that accords nicely with our everyday experience.

Unfortunately, that intuitive notion cannot hold if everyone measures the same speed of light regardless of their motion relative to the source, which is an empirical fact. That empirical fact is itself very counterintuitive. If we are at rest with respect to each other and I throw a ball away from me and towards you at 5 m/s relative to me, then you measure the speed of the ball to be 5 m/s relative to you. If I’m in a car moving at 30 m/s towards you and I throw a ball away from me and towards you at 5 m/s relative to me (and the car), then you measure the speed of the ball to be 35 m/s relative to you. That’s intuitive. But, if I do the same with a flashlight, you always measure the speed of the light from my flashlight to moving towards you at c. Even if I’m moving towards you at 0.5c, in which case intuition tells us you should measure the light from my flashlight to be moving towards you at 1.5c, you will still measure its speed to be c.

As a consequence of that fact, observers moving relative to each other will no longer agree on what events are simultaneous (are “equally real”), i.e., on what events occupy a “Now slice.” Thus, if everyone continues to attribute “existence” only to those events in spacetime that share their Now slice at any given moment of time in their existence, e.g., my attributing existence to the version of my twin brother that is the exact same age as me, then there is some frame of reference in which my Now coexists with a younger (or older) version of my brother. Thus, that special feeling of Now that I experience along my worldline in spacetime exists equally everywhere along my worldline as far as other observers are concerned. Here is 9-min video showing the relativity of Now slices (aka the relativity of simultaneity) that results from the light postulate. That is the block universe and it violates our everyday experience.

Of course, that doesn’t entail that our dynamical experience of time is ”an illusion” as the video implies. You can rather believe that the block universe is simply a tool for coordinating, explaining, and predicting our experiences. See Section 5 of this paper by Mermin, for example. That’s an “interpretative” aspect of block universe.
 

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