How does MWI handle probabilities in its branching of worlds? For instance if there are two possibilities (+ or -) and each has a probability of 50%, it makes sense to say that two separate branches result.

But what if the probability of + is 51% and the probability of - is 49%? In order to preserve probabilities we would need 100 worlds! (51 +, and 49 -).

It seems rather contrived to me that the number of branches would depend on probabilities like that. Or are some worlds considered to be more "probable" than others? (Which I understand to be a question that might not make sense, because all worlds are considered to be equally "real")

So, if the universal wave function is real, and continues evolving unitarily, probabilities would need to be somehow preserved. They would be reflected in the wave function itself. At least that's how I understand it.

I meant to tag you too in my question but couldn't find a way to do it. I'm still learning the idiosyncrasies of the site.

I meant boundless.

How does MWI handle probabilities in its branching of worlds? For instance
...
what if the probability of + is 51% and the probability of - is 49%? In order to preserve probabilities we would need 100 worlds! (51 +, and 49 -). — i aM

The worlds are not really separate under MWI. There is but the one wave function and the various solutions to the wave function. Excerpts from https://arxiv.org/pdf/quant-ph/9709032.pdf:

Everett does not postulate that at certain magic instances, the the world undergoes
some sort of metaphysical “split” into two branches that subsequently never interact.
...
According to the MWI, there is, was and always will be only one wavefunction, and only decoherence calculations, not postulates, can tell us when it is a good approximation to treat two terms as non-interacting. — Tegmark

So there are not separate worlds where one exists more than the other. It is all one thing in Hilbert space.

I think it's important too to differentiate between Everett's Interpretation and MWI, as first put forth by DeWitt. Everett's definition of "real" was anything that could affect the results of a future experiment. Everett was also pretty adamant that separate branches could affect one another; the separate branches, according to Everett's (relative State Formulation) https://plato.stanford.edu/entries/qm-everett/interpretation, can and do interact.

I'm not sure why, in MWI, the separate branches are said to not be able to interact with one another. Especially if, as you say, it is all one thing in Hilbert space.

Thanks for the very informative answer, again. I hope I'll can answer tomorrow (if not, I will on Saturday).

I am still confused about regarding 'observers' (as defined in RQM) as 'events' without duration but considering systems as abstractions denoting a stream of events is very interesting (note that I do not regard my confusion as an objection :smile: ...).

(sorry again for the edit... I misread a part of your answer)

Hi,

How does MWI handle probabilities in its branching of worlds? For instance if there are two possibilities (+ or -) and each has a probability of 50%, it makes sense to say that two separate branches result. — i aM

In MWI, you need an additional axiom AFAIK to include the Born Rule. I know that there have been some attempts to derive the Born Rule but I do not know if any of these attempts are regarded to be satisfactory. Note that some deny that such a derivation is necessary (I disagree, though - FWIW).

I'm not sure why, in MWI, the separate branches are said to not be able to interact with one another. Especially if, as you say, it is all one thing in Hilbert space. — i aM

In MWI, the branches can interact. But the likelihood of this interaction is negligible. (By the way, this is another really weird feature of MWI...)

"In MWI, the branches can interact. But the likelihood of this interaction is negligible. (By the way, this is another really weird feature of MWI...)"

I'm not sure how weird it is. As an analogy in the classical world suppose that I forget to blow out a candle before I go to sleep and the house burns down. I'll experience regret because there is some world out there where I did not forget to blow out the candle and the house did not burn down.

That alternative world will have a causal effect on my world in which the house DID burn down. I will be more careful in the future and make sure to blow out candles before I go to sleep (or not light them in the first place!). If no alternative world in which the house did not burn down existed, it would never occur to me to be more careful in the future.

I'm not sure how to put that analogy in direct terms of the wave function, but it allows me to see the possibility of different branches interacting. A possibility which didn't actually occur in my current branch could have a causal effect going forward.

Everett does not postulate that at certain magic instances, the the world undergoes
some sort of metaphysical “split” into two branches that subsequently never interact. — Tegmark

But it is implicit in the formulation. 'Many-worlds implies that all possible alternate histories and futures are real, each representing an actual "world" (or "universe"). In layman's terms, the hypothesis states there is a very large—perhaps infinite[2]—number of universes, and everything that could possibly have happened in our past, but did not, has occurred in the past of some other universe or universes. ...Before many-worlds, reality had always been viewed as a single unfolding history. Many-worlds, however, views historical reality as a many-branched tree, wherein every possible quantum outcome is realised.' (Wiki) Also the Scientific American article on Everett notes that Wheeler advised him to redact passages about 'splitting' from his thesis before it was submitted. The 'many' in 'many worlds' really means 'many'.

For Everett "real" meant "something that could affect the results of an experiment"; and, Everett was pretty clear that these different branches do interact.

All you need to do is google "energy" to see that "energy" is the capacity to do work, not "work getting done". I described very clearly the difference between potential energy and kinetic energy in my last post. — Metaphysician Undercover

I googled and got this first:
"William Rankine (1820–1872) Scotland: first mention of "potential energy" as distinguished from "actual energy". Since kinetic energy was the first form identified, he attached a modifier to the form of energy he discovered. Thus the unfortunate notion that kinetic energy is actual energy and potential energy is energy that has the potential to be actual energy. Energy is energy. No form of energy is any more or less "actual" than any other. The unfortunate terminology is due to Aristotle who applied the dichotomous terms potentiality and actuality to several disciplines — motion (Physics, Physica, Τα Φυσικη), causality (Metaphysics, Metaphysica, Τα Μετά Τα Φυσικά), ethics (Nicomachean Ethics, Ethica Nicomachea, Ηθικά Νικομάχεια), and physiology (On the Soul, De Anima, Περὶ Ψυχῆς)."

From here: https://physics.info/energy/

After reading the above I think we may be talking about different senses of 'actual". I agree with what is expressed in the above passage: that all energy, both energy in potential, as in the example of a nuclear weapon that has not done any work yet, and the actual energy which is released when the weapon is activated are equally real, that is equally actual in that sense. I was using 'actual' in the sense of acting or actualizing.

My point is simply that if you want to say that energy has an actual potential to get things done, then there must be an activation or actualization of that energy when it gets things done. It is the distinction between 'energy at rest' and energy at work.

If I am mistaken in this view I am open to being corrected, but it will need to be something better than

I've read a heck of a lot about it already, and submitted an extensively researched paper in university on the development of the concept of energy. — Metaphysician Undercover

From Sabine Hossenfelder

(I still go with Copenhagen.)

Are 'different versions of yourself' objectively real? I suggest that as soon as you say 'that depends', then the argument is lost. — Wayfarer

If you are objectively real in your world, then why not the alternative versions of you in their worlds? I am still not seeing what the objection is.

If you are objectively real in your world, then why not the alternative versions of you in their worlds? — Janus

Do you believe it is objectively the case that there are other worlds? You see, I would have thought that if it were objectively the case, then there would be no room for disagreement. But plenty of people disagree with Everett's meta-theory. Therefore, it's a matter of interpretation, and if it's a matter of interpretation, then it's not objective.

Do you believe it is objectively the case that there are other worlds? You see, I would have thought that if it were objectively the case, then there would be no room for disagreement. But plenty of people disagree with Everett's meta-theory. Therefore, it's a matter of interpretation, and if it's a matter of interpretation, then it's not objective. — Wayfarer

I believe that it is objectively the case that either there are other worlds or there are not. No interpretation is involved in what is objectively the case, so I still can't understand your objection. Of course some people will argue that it is not even objectively the case that there is this world. I don't see any difference in principle between the two cases, although there is the epistemological difference that this world is experienced by us. But if there are other versions of us in other worlds, then for them our world would be an "other world".

I believe that it is objectively the case that either there are other worlds or there are not. — Janus

Then why doesn't everyone agree with the many-worlds hypothesis? According to you, there's no scope for disagreement.

I still don't understand why you say that. I didn't say it was objectively the case that there are other worlds; I said that it is objectively the case that either there are other worlds or there are not. The fact that people may have different opinions about it doesn't seem to come into it as far as I can see.

Before many-worlds, reality had always been viewed as a single unfolding history. Many-worlds, however, views historical reality as a many-branched tree — Wayfarer

It is usually thought of like that, but it doesn't have to be. Another version is that there is no splitting, but just an infinite number of parallel worlds and for each world W and time t there are infinitely many that are identical to W up to time t, but that differ in some respect after t, which could be because of an observation at that time having a different outcome.

Under that perspective, the 'splitting' is epistemic rather than ontological. We were always in the world in which the measured spin on a particle at midday on 20/4/19 was going to be Up and not the one in which it would be Down, but we didn't know which one we were in until 20/4/19.

Since the differences between this setup and the branching one are by definition unobservable, it is moot which one we believe (if we believe either - I don't agree with the suggestion somewhere above that one has to believe some form of many-worlds).

I think the assertion that fields are what ‘reailty Is made of’ indicates deep confusion. We don’t even know what fields are - all we see is effects in respect of those particular phenomena in which field effects are visible. But what if there are non-physical fields, like Rupert Sheldrake’s morphic fields, or other forms of fields, like mental fields? There’s nothing to say there can’t be. Oh, I know - ‘scientists don’t think so.’ But that’s because their entire approach is based on studying matter, particles, radiation, and the other phenomena that can be studied using physical instruments. What’s that great analogy? 1. Metal detectors have had far greater success in finding coins and other metallic objects in more places than any other method. 2. Therefore what metal detectors reveal to us (coins and other metallic objects) is all that is real. — Wayfarer

QFT provides a physical mechanism (mathematically specified) for what is observed that is predictive and testable. It's been extremely successful and many physicists, including Feynman, have won nobel prizes for their work on it.

Regarding non-physical hypotheses, it's not that scientists don't think so. It's that without a physical mechanism, there's nothing to test. One person's speculation is as valid as anyone else's. So a physical mechanism provides a constraint on speculation.

I think that the relativity of simultaneity allows for the same type of contradiction. It allows that it is true that two events are simultaneous, and also true that two events are not simultaneous. That is contradiction, plain and simple. The relativity of simultaneity undermines the objectivity of the law of non-contradiction in a very fundamental way. This law states that the same predication cannot be both true and false at the same time. The relativity of simultaneity allows discretion, choice, in the judgement of "at the same time". — Metaphysician Undercover

Per the LNC, there is also "and in the same sense". In this case, the reference frames differ. Do you reject special relativity?

Whether or not I agree with Carroll that reality is made of fields is irrelevant to the issue here. — Metaphysician Undercover

The issue was whether fields are real in the ontology of QFT which Carroll's comments confirm.

Ok, well as you say they are all indeed different cases. But suppose that as per above, not everything that is possible actualizes. Hence also in this case, only one 'event' happens. Of course, I am assuming that not everything happens. But note that if you, instead, accept the 'existence' of all those Alice-s, how RQM is really different from MWI (except for the universal wave-function)? I believe that Tegmark pointed this out to Rovelli. — boundless

My reading of RQM (and Rovelli) is that RQM doesn't accept the existence of more than one Alice (or, at least, need not). Per RQM, all that is known to Wigner is that Wigner's friend has made a measurement and that the value is (physically) indefinite for Wigner until it is localized in his reference frame.

It's (QFT) been extremely successful and many physicists, including Feynman, have won nobel prizes for their work on it. — Andrew M

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.'

SR is also quite consistent for the same reason: different orderings of events are not contradictory if they're from different perspectives. Meta for instance commits this fallacy by deliberately omitting the perspective references: — noAxioms

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. Therefore the two propositions "A is prior to B", and "A is not prior to B" may be both true, and this is contradiction That you blame this contradiction on "different perspectives" does not make the contradiction disappear, it's just a sort of rationalization. You're just saying that this contradiction is acceptable, kind of like if I said that the best dinner is beef steak and you said that the best dinner is pork chop, we'd accept this contradiction because it's a matter of perspective. But it doesn't make the contradiction go away

My point is simply that if you want to say that energy has an actual potential to get things done, then there must be an activation or actualization of that energy when it gets things done. It is the distinction between 'energy at rest' and energy at work. — Janus

It's very simple, energy is the capacity to do work. As a capacity it is a potential. We look at things and attribute "energy" to these things, and energy is a potential which the things have. If you want to say that this potential is "actual", in the sense of being real, that's fine, but it's really just conceptual, it's a value we assign to the thing.

Now, according to the law of conservation of energy, it is not correct to say that the energy ever gets actualized. When the energy "gets things done", it is just transformed from one form to another, remaining as energy, and therefore remaining as potential. Energy is always potential, and never gets actualized because that potential (the capacity to do work) is always conserved in the temporal continuity of existence. That's why some people get hooked on the idea of perpetual motion. This is just the way that we've come to describe motion, we assign it a value, energy, it has proven to be a very useful way.

[

Per the LNC, there is also "and in the same sense". In this case, the reference frames differ. Do you reject special relativity? — Andrew M

"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.

The issue was whether fields are real in the ontology of QFT which Carroll's comments confirm. — Andrew M

No, the issue was whether or not the thing modeled as "a field" has the nature of potential or not. As I explained to Janus, energy is modeled as potential, but this does not mean that energy is not real. That fields are modeled as potential does not mean that they are not real. However, just like in the example of "energy", potential is the property of something which is actual. 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.

"This confirms what I said earlier about the non-independence of detectors in Aspect-type experiments. The detector wave functions are related and constrained by a transtemporal symmetry extending through all space-time. So, entanglement does not involve action at a distance, but transtemporal symmetry."

... and if the settings on one of the detectors is changed randomly, before a particle has reached it, but not soon enough for any subluminal signal to have reached the other detector...what? The "randomness" used to change the setting on the detector wasn't really "random", but part of the "transtemporal symmetry"?

Now, according to the law of conservation of energy, it is not correct to say that the energy ever gets actualized. When the energy "gets things done", it is just transformed from one form to another, remaining as energy, and therefore remaining as potential. — Metaphysician Undercover

I understand that energy is conserved, and that it does always "remain as energy" But, why would it not be correct to say that potential energy is actualized? If, as in your example of water held in a dam that is not doing any work, the water is released and does the work of turning the turbine, should be not speak of the energy potential being actualized? You acknowledge that energy may be 'transformed from one form to another". The example of the nuclear weapon, or even better, the fusion reactor makes this even clearer. Matter contains enormous potential energy which can only be actualized via certain technologies.

And to repeat my earlier point; it would seem to make little sense to say that energy is the potential to do work, and yet energy is not capable of doing any actual work. Yet you seem to want to say this, and have as yet, given no argument or explanation for why you want to say it.

if the settings on one of the detectors is changed randomly, before a particle has reached it, but not soon enough for any subluminal signal to have reached the other detector...what? — i aM

When we change the macroscopic setting of a detector, the microscopic details of its multi-electron wave function (our ignorance of which we call "randomness") remain constrained by transtemporal symmetry -- and that wavefunction interacts with the incident quanta to produce the detection event.

But, why would it not be correct to say that potential energy is actualized? If, as in your example of water held in a dam that is not doing any work, the water is released and does the work of turning the turbine, should be not speak of the energy potential being actualized? — Janus

That's just the way it's been conceptualized, energy is a property of something moving, just like momentum, and motion does not just disappear, or become something other than motion, as described by Newton's laws. So modern physics does not employ the ancient concept of potential being actualized in the case of the concept energy. There is potential (energy), and this potential remains constant as it takes many different forms.

"Potential" in the sense of "potential being actualized", really has only a philosophical meaning, because its ontology is considered as dubious. Here, "potential" means a possibility rather than a capacity (or power), as in energy. When there are numerous possibilities, and one is actualized, we might say that this specific potential is actualized. But to bring those possibilities into reality, rather than just logical possibilities requires a denial of causal determinism. This is why we need to keep the "potential of energy, as capacity or power, separate from the "potential" of "actualizing a potential", because physics does not have the ontological principles to relate these two. Notice that the former refers to "potential" in a general or universal sense, and the latter requires a particular "potential", so category mistake could occur.

And to repeat my earlier point; it would seem to make little sense to say that energy is the potential to do work, and yet energy is not capable of doing any actual work. Yet you seem to want to say this, and have as yet, given no argument or explanation for why you want to say it. — Janus

This is that ontological gap which we have no principles to form a bridge. To do "actual work" is just a matter of perspective. When is the work actually done, when the water turns the turbine, when the electricity is transmitted through the wires, when it runs the compressor on my fridge, when the cold keeps my food fresh? So, we keep the potential of energy (the capacity to do work) as completely separate from any work actually being done, in order that the conservation principles are maintained. It is important to understand that the concept of "energy" was produced as a conservation principle to compete with Newton's conservation of momentum. The reason why the thing which is conserved, as time passes, has the nature of "potential", goes back to Aristotle's concept of matter, as the thing which does not change as time passes, and matter is designated as potential. So the conceptual structure was already there, by which potential remains constant as time passes.

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.

Are you saying that by randomly changing the detector settings of one detector the other detector's multi-electron wave function is likewise changed through transtemporal symmetry?

My reading of RQM (and Rovelli) is that RQM doesn't accept the existence of more than one Alice (or, at least, need not). Per RQM, all that is known to Wigner is that Wigner's friend has made a measurement and that the value is (physically) indefinite for Wigner until it is localized in his reference frame. — Andrew M

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'. 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?

I should reword. Yes, the odds are almost a certainty from the beginning that the unicorn will occur in some world, but I meant given a single measurement giving one random collapse. You only get one try. From the beginning of the universe, there's not even a planet on which a single measurement might hope to collapse a unicorn. I would presume an existing Earth with life already on it would raise the odds of a unicorn considerably from the odds from a blank slate. — noAxioms

Ok, I agree!

To summarize, in RQM, according to the pre-measurement 'Alice' both 'Alice-s' (or 'Alici' :wink: ) will exist. — boundless

Such statements are why I balk at A-series wordings like that. Under RQM, both post-measurement Alici (the plural is so stupid I am compelled to use it) consider the pre-measurement Alice to be part of their history. To pre-measurement Alice, the other two do not exist. The future is unmeasurable and thus doesn't exist to that instance of Alice. So there's no 'will-exist' except to indicate that certain future events (post-measurement Alici) consider certain past events to exist and others (like the one where Alice didn't measure it at all) to not exist. — noAxioms

I see what you mean, but 'pre-measurement Alice' can predict that 'she' will be 'remembered' by both 'post-measurement Alici'. This is not too very different from what MWI says. According to this view, MWI and RQM would be similar (not the same, but similar...).

I agree about the lack of contradiction. I know what you're saying and agree with it, but I don't like the A-series wording of it. 'Will exist' makes it sound like existence is something objective that occurs, and not the relation to something. The future Alici cannot exist ever to the pre-measurement one because there is no 'ever' to that version. She's an event, and events don't move into the future. — noAxioms

OK! That's fine. Note however that if one accepts presentism the past and the future do not 'exist'. Only the present does. It is true that the past can be said to 'exist' in the sense that there are data, in the present, about it. At the same time, it is also true that it is possible to make predictions about the future.

So, it seems to me that the relation between the future Alici and the past Alice is more or less the same of the reverse. So, before the experiment, Alice can predict the 'appearance' of the future Alici. So, for her, it seems legitimate to say that a 'split' happens.

SR is also quite consistent for the same reason: different orderings of events are not contradictory if they're from different perspectives. — noAxioms

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. 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. 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). If you follow your intuition, you end up with the Andromeda Paradox. I am not absolutely certain that the intuition is wrong, though (if not, dBB supporters would be very happy).

Well, 'I', from an RQM standpoint, am an event, despite my whole me being an abstract worldline. So in that event sense, I don't exist to myself, I only have memory of some past consistent state. From a pure event perspective, any two events (the table lamp and I at two specific moments) cannot exist in relation to each other. Neither exists to the other if the two events are space-like separated, and only one might exist to the other if not. It isn't paradoxical since no such mutual existence relation is ever posited. — noAxioms

Well, this seems also the implication of presentism plus SR/GR.

All different events, so not comparing the same thing. There is no 'the lamp' any more than there is a 'me' making that decision. We're both a series of events, any of which can relate to other events. The fact that a certain event in the past is considered 'also me, yesterday' is an abstract designation I make. 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).

(But I am not sure about this :smile: we are probably digressing here)

I think I see what you are getting at*. But I do not believe that this really solves the problem that I have in mind. Unless you specify a duration for the events. — boundless

I'm sorry, but what was the problem? I thought the lack of duration was exactly what solved the problem. — noAxioms

Yeah, it seems so.

Not even familiar with the term Process Philosophy, but perhaps I am discussing it anyway. I'm a poet and don't even know it. — noAxioms

Well, I do not know very much about it. It is a kind of presentist ontology. 'Objects' are not regarded as substantial entities but rather as patterns in succession of events. On the other hand, existence is not defined in a relational way.

I think that works as well, yes. I seem to have a pretty weak grasp on the panpsychism idea. It doesn't seem to have a consistent interpretation from one person to the next. — noAxioms

Yeah, there are a lot of different versions of it. The parallelist variety, for instance, holds that everything has both a physical and a 'mental' aspect. The more complex an entity is, the more complex are both its physical and mental sides. In other words, mind and matter are like two sides of the same coin. But this is off-topic :sad:

I'm not sure how weird it is. As an analogy in the classical world suppose that I forget to blow out a candle before I go to sleep and the house burns down. I'll experience regret because there is some world out there where I did not forget to blow out the candle and the house did not burn down. — i aM

...

If no alternative world in which the house did not burn down existed, it would never occur to me to be more careful in the future. — i aM

But you can explain regret in that way only if you accept the concept of parallel universes, i.e. if you accept the idea that whatever is possible, happens which is precisely what says MWI.

Honestly, I do not find any compelling reason to accept the idea of parallel universes/branches etc.