I'm just giving a classical-world example of how a "branch" consisting of an event which did not occur in my "branch" (me blowing out the candle) could conceivably have a causal effect on the "branch" I inhabit going forward (me being more careful with candles).

We think about possible worlds that did not occur all the time, and those possible worlds which did not occur have causal effects. That is one way that we learn from mistakes. If there were no possible worlds to compare our actual world to, there would be no incentive to ever change behavior, for instance. It probably wouldn't occur to us to change behavior.

No, I am denying spooky action at a distance. Instead, I'm saying all detectors, anywhere in the universe, are constrained by transtemporal symmetry. In effect, this means that detectors are pre-syncronized. When you set the orientation of a spin detector, you change one and only one degree of freedom, but the multi-electron wave function has an uncountable number of degrees of freedom (as do all continuous forms). If the detector system has n electrons, the anti-symmetry condition imposes n!-n constraining equations (each of which spans all space-time) on the system wave function. (Note that n is typically in the order of Avagadro's number, ~10^23). This links the "separate" detectors, so they are anything but independent -- vitiating an essential premise of theorems like Bell's.

Yeah, sorry. I was a bit flippant.

The point is that in your example the interaction would give you some information of the other world(s). In MWI, you would observe superposition due to the interference of the branches (which would be very weird).

The fact we do not observe superposition is explained in MWI using decoherence, which suppresses the interference (well, technically, it renders it negligible...).

I think it's important too to differentiate between Everett's Interpretation and MWI, as first put forth by DeWitt. — i aM

My comments pretty much reflect the Everett interpretation, and not DeWitt's. Both are grouped under the same heading in the wiki list, but you point out some critical differences between the two.

I'm not sure why, in MWI, the separate branches are said to not be able to interact with one another.

Without interaction, there would be no interference. Seems a view that asserts lack of interaction can be falsified. I suppose they get around that by saying that superposition states are not different worlds interacting, but rather just one in that state, to be metaphysically separated at measurement time. There are experiments that demonstrate otherwise.

Please excuse my ignorance. I have done searches for "transtemporal symmetry" and didn't find anything, other than items written by you, in this thread.

In a Bell Inequality experiment, when one of the detectors (Alice's?) is "randomly" altered, after entangled "particles" have left the source, is the reading ultimately registered at the altered detector changed, or does it stay the same as if it hadn't been altered at all, because of this transtemporal symmetry? Or is it that the other detector (Bob's?) somehow recognizes that Alice's detector has been altered and for this reason registers a reading in correlation with Alice's reading.

I recognize that this question is in some fashion a reiteration of my previous question, but I didn't quite grasp your answer. Sorry.

idk, by my understanding decoherence would render interaction between specific separate branches highly improbable. But because there are SO MANY separate branches, it would happen regularly. Sorta like what happens with quantum tunneling.

The problem is that to say that the ordering is dependent on perspective means that there is no objective truth with respect to the order. — Metaphysician Undercover

Exactly so. That's why it is called the theory of relativity and not the theory of objectivity. It's only a problem if you add that additional premise as you are doing.

In the context of QM, consider that the wave-function is analogous to the potential of energy (capacity to work). It must remain constant, continuous, as time passes, according to conservation laws. Then there is a so-called collapse of the wave-function, and this is analogous to actual work being done, a potential being actualized. We cannot relate these two because "actual work being done" would remove potential and violate the conservation law. So we have a gap between the potential, which must always remain constant according to conservation laws, and the "actualizing of a potential", which would remove some of that potential placing it into a different category of "actual", thus violating the conservation law. — Metaphysician Undercover

I didn't really understand most of what you wrote, so I will just try to focus on this passage. What you seem to be ignoring is entropy; which is the continual dissipation of the capacity of energy to do any work, which in theory culminates in so-called 'heat death' the total absence of any potential for energy to do any work. Remember that matter and energy are equivalents, and the form of energy only obtains provided there are differentials in potential which allow energy to "flow'.

My argument has been based on the idea that potential energy consists in virtue of local differentials in potential, and that actual energy consists in the flows that occur. Energy is not lost insofar as new sets of different potentials are always coming into being, but the whole process, according to the second law of thermodynamics, consists in a gradual 'winding down' of differences of potential, and thus a diminishing of potential energy as well as a diminishing of actual energy flows, and consequently a diminishing of work done.

"Transtemporal symmetry" is my term, but it is based on the formulation of the exchange principle in Dirac's many-time formulation of relativistic quantum theory, which you can look up.

The control typically exercised over detectors in EPRB/Aspect type experiments is to change their orientation. If we change the orientation, then, of course the measured spin will be up or down the new orientation, not the old one.

Still, changing the orientation does not exert control over the details of the detector's electron wave function. The details will be controlled, in part, by the exchange principle and resulting constraints.

Alice's observations can inform her of conditions at Bob's location. If she performs her obseervation, she is informed, but if she does not, she is not informed.

How could an experiment at Alice's location inform us of conditions at Bob's location? Before I try to answer this, it is important to note that it does. Once Alice has measured spin up, she knows that conditions at Bob's location are such that he will measure spin down. Further, it does not matter if she learns of the conditions at Bob's space-time location in a reference frame where she learns of it before Bob does his measurement, or after. All that is important is that an observation at Alice's space-time location can inform us of conditions at Bob's.

I am suggesting that the reason Alice's observation informs her of conditions at Bob's location is symmetry. If we lived in a model world in which Bob's observations must mirror Alice's, then Alice would be able to predict Bob's results from hers without a hint of non-locality. The actual case is more complex, but the principle is the same.

Exactly so. That's why it is called the theory of relativity and not the theory of objectivity. It's only a problem if you add that additional premise as you are doing. — noAxioms

Adding the premise doesn't make it into a problem, it's the thought that there ought to be an objective reality which makes it into a problem. If you don't mind an ontology with no objective reality, then there's no problem.

I didn't really understand most of what you wrote, so I will just try to focus on this passage. What you seem to be ignoring is entropy; which is the continual dissipation of the capacity of energy to do any work, which in theory culminates in so-called 'heat death' the total absence of any potential for energy to do any work. Remember that matter and energy are equivalents, and the form of energy only obtains provided there are differentials in potential which allow energy to "flow'. — Janus

No, entropy is something completely different. Energy is defined as the capacity to do work. Entropy cannot rob energy of this unless it left energy as something other than energy. And entropy does not violate conservation laws.

So, in the purportedly inevitable heat death of the universe there will still be energy with the potential to do work? Can you explain how that will work?

This may help you understand what I am saying:

There is yet another way of expressing the second law of thermodynamics. This version relates to a concept called entropy. By examining it, we shall see that the directions associated with the second law—heat transfer from hot to cold, for example—are related to the tendency in nature for systems to become disordered and for less energy to be available for use as work. The entropy of a system can in fact be shown to be a measure of its disorder and of the unavailability of energy to do work.

From here: https://opentextbc.ca/physicstestbook2/chapter/entropy-and-the-second-law-of-thermodynamics-disorder-and-the-unavailability-of-energy/

That certain energy is not available to a human being with the desire to use energy, does not mean that this energy is no longer the capacity to do work. That would be contradiction.

I've no idea how or why you think what you respond with here has any relevance to what you were responding to. Can you explain your thought process?

You are mixing together, the definition of energy (the capacity to do work), with the relative condition of "available". Whether or not the energy is available to us has no impact on whether or not it is the capacity to do work. Energy on the other side of the world is not available to me, yet it is still the capacity to do work. Here's a quote from you referenced article:

"Recall that the simple definition of energy is the ability to do work. Entropy is a measure of how much energy is not available to do work. Although all forms of energy are interconvertible, and all can be used to do work, it is not always possible, even in principle, to convert the entire available energy into work. That unavailable energy is of interest in thermodynamics, because the field of thermodynamics arose from efforts to convert heat to work."

Entropy has no affect on energy's capacity to do work. The condition "available" just reflects the limits of the system used to harness the energy. Various different ways of harnessing energy (converting it from one form to another in a controlled manner), have differing degrees of efficiency. There is no such thing as one hundred per cent efficiency or else we'd have perpetual motion. The fact that some of the energy is lost into unharnessed forms does not mean that it is not energy. When a system has 85 per cent efficiency, the remaining 15 per cent is still the capacity to do work (energy), despite the fact that it is unavailable, it has just slipped into unharnessed areas because of the limitations of the system..

idk, by my understanding decoherence would render interaction between specific separate branches highly improbable. But because there are SO MANY separate branches, it would happen regularly. Sorta like what happens with quantum tunneling. — i aM

:up:

Well, that's another good argument IMO against the view that decoherence is enough to solve the measurement problem (even in MWI).

Sure, absolutely. I'm not querying whether fields are real or the effectiveness of field theory. The point I was taking issue with was 'Particles are what we see. Fields are what reality is made of.' — Wayfarer

So what Carroll means is that fields are fundamental and particles (and everyday things generally) emerge from the interaction of those underlying fields.

Or, as Wikipedia puts it, "QFT treats particles as excited states (also called quanta) of their underlying fields, which are—in a sense—more fundamental than the basic particles."

"In the same sense" means using the words in the same way. It has nothing to do with reference frames unless "temporal order" has a different meaning from one reference frame to the next. — Metaphysician Undercover

The truth of a statement depends on its reference in the world. For example, when it is noon in London, the statement "It is noon" will be true for London observers while false for Sydney observers.

Now consider the train-and-platform scenario (including the two traincar pictures). Per special relativity, the statement "The light reached the front and back of the traincar simultaneously" is true for an observer on the moving traincar while false for an observer on the train platform.

As with the noon example, there is no contradiction when the statement is indexed to an observer (or, equivalentally here, a reference frame).

So a field would be the property of something because there needs to be something actual which has that potential For example an electromagnetic field is a property of an object. — Metaphysician Undercover

And that's not the way it's modeled in QFT. In QFT, objects (including particles) emerge from the interactions of more fundamental fields. That is, the existence of the object is dependent on the existence of the fields.

Well, more or less I always understood RQM in that way! :smile: ... After my dialogue with noAxioms, I am not sure about it. In fact, the 'relativization' of existence makes perfect sense in RQM. For each 'Alice' (each 'Wigner's friend') the other(s) cannot be said to 'exist'. — boundless

I agree. But that interpretation of RQM would only be a semantic difference from MWI, not a substantial one. My understanding is that RQM is a more abstract interpretation that captures what Rovelli considers to be the key elements of QM and nothing more. For example in his RQM paper he says, "From the point of view discussed here, Bohr’s interpretation, consistent histories interpretations, as well as the many worlds interpretation, are all correct." That is, they all share those key elements (albeit they commit to further things as well that differentiates them from each other, such as many worlds versus a single world).

But unless one adds a selection postulate, I believe that before the measurement 'Alice'/'Wigner's friend' can safely say that all 'Alice-s'/'Wigner's friends' will remember 'her'/'him'. What do you think? — boundless

I'm not sure I see the issue you're raising here. But I would agree that post-measurement, Wigner's friend (or friends on a MWI-style reading) would have a memory of themselves prior to measurement.

Regarding a selection postulate for RQM, I think it's just unknown and RQM doesn't commit to anything specific.

So what Carroll means is that fields are fundamental and particles (and everyday things generally) emerge from the interaction of those underlying fields.

Or, as Wikipedia puts it, "QFT treats particles as excited states (also called quanta) of their underlying fields, which are—in a sense—more fundamental than the basic particles." — Andrew M

‘in a sense’ ;-)

When it comes to this matter, that phrase carries a lot of weight.

Now consider the train-and-platform scenario (including the two traincar pictures). Per special relativity, the statement "The light reached the front and back of the traincar simultaneously" is true for an observer on the moving traincar while false for an observer on the train platform. — Andrew M

Right, we are talking about the temporal ordering of two events, when the light reaches the front of the traincar, and when the light reaches the back. Special relativity allows for contradiction in the ordering of these events. The "noon" example is just a name given to one event, so it's not a proper analogy. What I call "noon" you might call "midnight", and it's just a matter of translation, we are still talking about the same time under different names. Calling the same thing by different names is a matter of identity, not contradiction But in the case of special relativity it is a matter of predication. One event is predicated as prior in relation to the other, and to allow the opposite as well, is contradiction. Noon in Sydney is prior to noon of the same day in London, no matter what your reference is, and.there is no contradiction

And that's not the way it's modeled in QFT. In QFT, objects (including particles) emerge from the interactions of more fundamental fields. That is, the existence of the object is dependent on the existence of the fields. — Andrew M

Right, that's why I'm pointing this out as a problem with QFT. The way that fields are modeled, they cannot have reality unless the field is the property of an object. Remove the electromagnetic field from the object which it is a property of, and it's just a piece of theory. If QFT does not model its fields as properties of some object, or objects, they are theories without reality. Physics does not have the principles required to model free standing fields, from which particular existence arises, the fields are dependent on the prior existence of objects. That dependence needs to be included in the models.

Matter exists, but the mathematics underneath seem more fundamental. — noAxioms

Nit-pick: you think that maths, a human invention, is more fundamental than the stuff of which the universe is built? I don't think so.

I agree. But that interpretation of RQM would only be a semantic difference from MWI, not a substantial one. My understanding is that RQM is a more abstract interpretation that captures what Rovelli considers to be the key elements of QM and nothing more. For example in his RQM paper he says, "From the point of view discussed here, Bohr’s interpretation, consistent histories interpretations, as well as the many worlds interpretation, are all correct." That is, they all share those key elements (albeit they commit to further things as well that differentiates them from each other, such as many worlds versus a single world). — Andrew M

:up: I completely agree!

But unless one adds a selection postulate, I believe that before the measurement 'Alice'/'Wigner's friend' can safely say that all 'Alice-s'/'Wigner's friends' will remember 'her'/'him'. What do you think? — boundless

I'm not sure I see the issue you're raising here. But I would agree that post-measurement, Wigner's friend (or friends on a MWI-style reading) would have a memory of themselves prior to measurement.

Regarding a selection postulate for RQM, I think it's just unknown and RQM doesn't commit to anything specific. — Andrew M

Well, I worded it badly. I simply meant that without the selection postulate, it seems that RQM implies the splitting.

Anyway, I agree with you. RQM seems simply silent on this point.

I see what you mean, but 'pre-measurement Alice' can predict that 'she' will be 'remembered' by both 'post-measurement Alici'. — boundless

I thought about that and it seems that post-measurement Alice has the same relationship to pre-measurement Alice as the relationship to post-measurement Bob, which is a superpostition of multiple unmeasured states. The perspectives are quite different but the relationships are essentially identical.
Therefore the future does exist to Alice, just not a specific state. The cat exists to Bob, even when in superposition of dead and alive.

Ok, I agree. But my point was another. If you say that 'your' present exist (the 't=0' 3D hypersurface), then the Andromeda Paradox is unavoidable.

This hypersurface exists. So does this different hypersurface. That's just two different things, not a paradox.

The answer to this objection is to not regard what is outside the light cone in the same way of what is inside from an ontological point of view.

Totally agree. Two observers at the same place but different frames might disagree about what is going on at Andromeda, but they'll agree entirely about what has been measured. The light cone from that location is a frame independent thing.

On the other hand, it seems intuitive to accept the 'existence' of the present (e.g. I will observe the present state of the Sun at t=8 minutes).

Interesting corollary for a presentist, who by definition cannot observe any existing thing. In 8 minutes, the thing I observe will not be the present state of the sun. It will be an observation of something nonexistent.

There is nothing physical that connects my current state to that past state as opposed to any other random arrangement of matter. Identity is abstract, not real. There are plenty of philosophical arguments that demonstrate this.
— noAxioms

I sort of agree with this (but the reasons are not exactly the same...as I said I have a different view about mind) - it seems that there is some kind continuity without, however, a persisting identity (but we are digressing maybe...). This is not IMO however a complete denial of the existence of 'individuality' (and 'identity' in some sense).

Agree that what I said depends on my personal choice for philosophy of mind. Some interpretations do give identities to things. Mine just happens not to.
Not sure how you combine your mind interpretation with your QM one. Does the pre-Alice ontologically become one of the post-measurement Alici to the exclusion of the others because the mind-identity can only follow one of them? That's a very different QM interpretation.

Nit-pick: you think that maths, a human invention, is more fundamental than the stuff of which the universe is built? — Pattern-chaser

I consider it something discovered, not invented. If invented, pi would not be the same value in another world. OK, odds are the aliens don't express the value in base 10. That base is definitely a human invention.

So, are you saying that in the heat death scenario, when thermal equilibrium or the state of maximum entropy is reached, there is still potential energy ("potential energy" in the sense which you earlier defined as "the capacity to do work")?

Nit-pick: you think that maths, a human invention, is more fundamental than the stuff of which the universe is built?
— Pattern-chaser
I consider it something discovered, not invented. If invented, pi would not be the same value in another world. — noAxioms

:up:

I simply meant that without the selection postulate, it seems that RQM implies the splitting.

Anyway, I agree with you. RQM seems simply silent on this point. — boundless

Maybe it's embarrassed. :yikes:

I see what you mean, but 'pre-measurement Alice' can predict that 'she' will be 'remembered' by both 'post-measurement Alici'. — boundless

Therefore the future does exist to Alice, just not a specific state. The cat exists to Bob, even when in superposition of dead and alive. — noAxioms

Ok! Agreed! :smile:

Ok, I agree. But my point was another. If you say that 'your' present exist (the 't=0' 3D hypersurface), then the Andromeda Paradox is unavoidable. — boundless

This hypersurface exists. So does this different hypersurface. That's just two different things, not a paradox. — noAxioms

Well, I think I see where you are getting at but I am not sure you can really avoid the paradox if you say that all events in the hyper surface are in a definite state. I am not saying you are wrong, I just do not know.

The answer to this objection is to not regard what is outside the light cone in the same way of what is inside from an ontological point of view. — boundless

Totally agree. Two observers at the same place but different frames might disagree about what is going on at Andromeda, but they'll agree entirely about what has been measured. The light cone from that location is a frame independent thing. — noAxioms

Yes! In Relativity the ordering of events in every light cone is an invariant (unless one accepts tachyons or any FTL influence).

On the other hand, it seems intuitive to accept the 'existence' of the present (e.g. I will observe the present state of the Sun at t=8 minutes). — boundless

Interesting corollary for a presentist, who by definition cannot observe any existing thing. In 8 minutes, the thing I observe will not be the present state of the sun. It will be an observation of something nonexistent. — noAxioms

Yep! Presentism is somewhat problematic in Relativity. I would say that 'global presentism' is simply incompatible with relativity of simultaneity. Maybe a form of 'local presentism' can be saved but it is surely counter-intuitive (I personally lean towards some form of presentism and I admit that I am troubled by this).

There is nothing physical that connects my current state to that past state as opposed to any other random arrangement of matter. Identity is abstract, not real. There are plenty of philosophical arguments that demonstrate this. — noAxioms

I sort of agree with this (but the reasons are not exactly the same...as I said I have a different view about mind) - it seems that there is some kind continuity without, however, a persisting identity (but we are digressing maybe...). This is not IMO however a complete denial of the existence of 'individuality' (and 'identity' in some sense). — boundless

Agree that what I said depends on my personal choice for philosophy of mind. Some interpretations do give identities to things. Mine just happens not to. — noAxioms

I see!

Not sure how you combine your mind interpretation with your QM one. Does the pre-Alice ontologically become one of the post-measurement Alici to the exclusion of the others because the mind-identity can only follow one of them? That's a very different QM interpretation. — noAxioms

Well, note that I do not currently accept RQM as 'my interpretation'. But it is one of my favorites.

Anyway, I do not believe that the mind is something immutable. So, for me, it is more like a 'stream of consciousnesses'. When I said that, in some sense, 'individuality' is preserved I meant that these 'streams' or 'continuums' are distinguishable. Yet, I do not believe that there is 'something' that 'persists' in the process (a 'substance') - in other words, I do not believe in a substantial identity.

Personally, I do not like the idea of the 'branching'/'splitting' - that's why I am insisting with the 'selection' postulate. On the other hand, I think that this kind of position about the mind is logically consistent with the 'branching' idea. Furthermore, I do not believe that the 'splitting' is a necessary feature of RQM. Before this discussion, I believed that there was a selection postulate in RQM. I now think that the theory is simply silent on it.

Nit-pick: you think that maths, a human invention, is more fundamental than the stuff of which the universe is built?
— Pattern-chaser
I consider it something discovered, not invented. If invented, pi would not be the same value in another world.
— noAxioms

:up: — Wayfarer

+ 1 :wink:

(More precisely, I believe that there is something in maths that is discovered. It cannot be totally invented)

I simply meant that without the selection postulate, it seems that RQM implies the splitting.

Anyway, I agree with you. RQM seems simply silent on this point.
— boundless

Maybe it's embarrassed. :yikes: — Wayfarer

Well, possibly! :razz:

I can't answer that, I don't know the heat death scenario

So what Carroll means is that fields are fundamental and particles (and everyday things generally) emerge from the interaction of those underlying fields.

Or, as Wikipedia puts it, "QFT treats particles as excited states (also called quanta) of their underlying fields, which are—in a sense—more fundamental than the basic particles."
— Andrew M

‘in a sense’ ;-)

When it comes to this matter, that phrase carries a lot of weight. — Wayfarer

I would have thought that one sense was enough. How many senses are you requiring? ;-)

Right, we are talking about the temporal ordering of two events, when the light reaches the front of the traincar, and when the light reaches the back. Special relativity allows for contradiction in the ordering of these events. — Metaphysician Undercover

No, the relative ordering of events necessarily follows from the invariant speed of light in different reference frames. Since the traincar is moving away from the train platform then the light emitted from the middle of the traincar, travelling at velocity c in the train-platform observer's reference frame, will take longer to reach the front of the traincar that is moving away from it than the back of the traincar that is moving toward it.

I simply meant that without the selection postulate, it seems that RQM implies the splitting.

Anyway, I agree with you. RQM seems simply silent on this point. — boundless

I think splitting might be implied only because Copenhagen and Consistent Histories don't specify any physical mechanism, whereas MWI does. But since some other unknown physical mechanism can't be ruled out at this point, then being silent seems a reasonable option (and treating interference as unactualized potential).