There is also a parallel discussion in Physics Forums about this experiment: https://www.physicsforums.com/threads/a-realization-of-a-basic-wigners-friend-type-experiment.968181/

Yes, but how does that make a difference? Energy is the capacity to do work, therefore a potential. Kinetic energy is actually having that potential by virtue of being active, and potential energy is potentially having that potential. So potential energy is a double layer of potential. — Metaphysician Undercover

Energy is both the capacity to do work and the force that gets work done. The first is potential energy and the second is kinetic energy. I'm not sure if all forms of energy that get work done qualify, according to any conventional definition, as kinetic energy, but in any case we can generalize and call all forms of energy that get work done actual energy as opposed to potential energy.

Thanks for linking that. The comments from Demystifier and other members whose opinion I respect, align with my impression that this paper doesn't reveal anything new of significance. It effectively just affirms that if you insist on locality then you have to give up on CFD, which is in many ways the same thing as 'objective reality'. Bell told us that in the early sixties.

This emphasizes the fact that what's commonly thought of as objective is a psychic construction which happens to be mostly wrong.

Taking QM into account means we have to change which 3rd person statements we consider to be true. So the OP is really just a matter of semantics. — frank

:up:

Redefining "objective reality" so that contradiction is acceptable in an objective reality is not what I would consider as an acceptable solution. — Metaphysician Undercover

There isn't a contradiction. Do you accept the relativity of simultaneity in special relativity? If so, then you already accept that a correct account of events can be reference-frame dependent and not absolute.

As far as I understand "fields", they are always modeled as potentials, and this includes "the more fundamental fields" of QFT. If you understand them as a model of something actual, then I think you misunderstand the ontology of QFT. But perhaps I'm wrong, and you can show me how a field is modeled as something actual. — Metaphysician Undercover

Sean Carroll gave a lecture a few years ago entitled, Particles, Fields and The Future of Particle Physics. I recommend listening to his discussion of one of the slides (between 28:00 - 30:40) that includes the line, "Particles are what we see. Fields are what reality is made of." Do you disagree with Carroll's characterization of QFT?

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.

So Wigner's friend measured a definite value while Wigner measured a value in superposition? I am trying to decide if it is worthwhile to read this paper. — i aM

I don't think a superposition is measured as the measurement collapses the superposition. I think, from what I read, the paper reiterates Bell's inequality and that the test setup was rather impressive.

Has anyone linked to the Daily Nous 'response by physcists' post yet? (Did a quick scan, couldn't see anything) : http://dailynous.com/2019/03/21/philosophers-physics-experiment-suggests-theres-no-thing-objective-reality/

(EDIT: Ah, I see it was linked a couple of pages back. Still, it's a great read and worth mentioning again, I think!)

Some excerpts:

Karen Crowther: "In this ‘real life’ experiment, however, Wigner and his friend are not conscious observers, but pieces of machinery: they are measuring-and-recording devices. Proietti et al. (2019) argue that these devices can act as observers, defining an observer as any physical system that can extract information about another system (by means of an interaction) and can store that information in a physical memory. On this definition, computers and other devices can act as observers, just as humans can.

So, what is the philosophical interest in this particular experiment? The question is what this experiment demonstrates about QM that was not already known from the thought-experiment plus previous experimental results. Plausibly, what it shows is that a scenario analogous to the one imagined by Wigner is in fact physically possible, and in it the observers do record conflicting facts. Thus, the philosophical significance of the experiment is to make Wigner’s own interpretation of his thought-experiment look increasingly implausible: it is difficult to imagine that this experiment would not have been successful if the devices had conscious experiences.

But, on the other hand, the fact remains that these devices are not conscious, and so Wigner could stand resolute in his interpretation. If anything, he could point out that—in the same way that an observation of a non-black, non-raven provides a negligible sliver of confirmation for the claim that ‘all ravens are black’—the success of the experiment even provides inductive support in favour of his interpretation: the ‘observers’ in this experiment are able to record conflicting facts only because they do not experience these facts."

--

Sean Carroll: "There is a long tradition in science journalism—and one must admit that the scientists themselves are fully culpable in keeping the tradition alive—of reporting on experiments that (1) verify exactly the predictions of quantum mechanics as they have been understood for decades, and (2) are nevertheless used to claim that a wholesale reimagining of our view of reality is called for. This weird situation comes about because neither journalists nor professional physicists have been taught, nor have they thought deeply about, the foundations of quantum mechanics. We therefore get situations like the present one, where an intrinsically interesting and impressive example of experimental virtuosity is saddled with a woefully misleading sales pitch."

--

Tim Maudlin: "The way that this experiment is described—in terms of its significance—is complete nonsense. Physicists have become accustomed to spouting nonsense when quantum mechanics is the subject of discussion, which often takes the form of mind-blowing assertions about the loss of “classical reality” or even “classical logic”. The reason we know that all of this is nonsense right off the bat is that the experimental predictions of standard quantum mechanics can be accounted for—in several different ways—by theories that postulate an objective, unique physical reality governed by definite laws and using only classical logic and mathematics. So when the sorts of claims made in the title and abstract of the article are made, one knows immediately that they are unjustified hype."

For those, like me, that are not averse to a Kantian-like sub-interpretation of CI, I suggest also this article by Cuffaro: http://philsci-archive.pitt.edu/14357/1/kant_bohr_hermann.pdf.
This paper also discusses the 'neo-Kantian' views of Grete Hermann (link to Wikipedia) who also much time earlier than Bell discovered that not all hidden variables theories are in conflict with the predictions of QM.

Another Kantian-like perspective as I said before is advocated by for instance Bitbol. For convenience I give again the link to Bitbol's paper: http://www.bourbaphy.fr/bitbol.pdf.

↪boundless Thanks for linking that. The comments from Demystifier and other members whose opinion I respect, align with my impression that this paper doesn't reveal anything new of significance. It effectively just affirms that if you insist on locality then you have to give up on CFD, which is in many ways the same thing as 'objective reality'. Bell told us that in the early sixties. — andrewk

Yes, I agree. This experiment does not 'reveal' anything new. This does not mean that it can be interpreted as an evidence that CFD is problematic, but we already knew that.

Energy is both the capacity to do work and the force that gets work done. The first is potential energy and the second is kinetic energy. I'm not sure if all forms of energy that get work done qualify, according to any conventional definition, as kinetic energy, but in any case we can generalize and call all forms of energy that get work done actual energy as opposed to potential energy. — Janus

You don't seem to understand. Energy is the potential to get work done. We make a judgement concerning a particular aspect of an active thing, its capacity to do work, and call that it's "energy".. You can say that this aspect of the thing is actual, in the sense of "real", just like the judgement that a thing is red is a judgement of something real, but that doesn't change the fact that in the case of "energy" what is being judged is a thing's potential. So all you are saying is that this potential which the active thing is judged to have (called "energy") is something real, actual. When we describe things in terms of "energy", we are describing potential, whether or not we believe that this potential is something real.

There isn't a contradiction. Do you accept the relativity of simultaneity in special relativity? If so, then you already accept that a correct account of events can be reference-frame dependent and not absolute. — Andrew M

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".

Sean Carroll gave a lecture a few years ago entitled, Particles, Fields and The Future of Particle Physics. I recommend listening to his discussion of one of the slides (between 28:00 - 30:40) that includes the line, "Particles are what we see. Fields are what reality is made of." Do you disagree with Carroll's characterization of QFT? — Andrew M

Whether or not I agree with Carroll that reality is made of fields is irrelevant to the issue here. The question is whether what is represented by "fields" is of the nature of potential or not. As I explained to Janus above, what is represented by the concept "energy" is potential. Many people believe that energy is what reality is made of, but that does not change the fact that what is represented by "energy" is potential. And if we represent reality as composed of potential, that's only half the picture, because it doesn't provide us with a representation of what is actual. You might say that the reality is that there is an endless number of possible worlds, but what makes one of those possible worlds into the one that we live in, the actual world? That's what's missing if you represent the totality of reality as potential, a principle by which there is an actual world. If you cannot give reality to this principle as well, then there is no actual world in your ontology.

We are starting to agree more and more, making these posts a bit shorter.

Sounds like what I have in mind as well. For me, unicorns don't exist. For the unicorn, I don't exist. You seem to indicate that what I've described is something else.
— noAxioms
[Also, IMHO unicorns here are not a good example. For me, they are simply impossible (but as you say, better not to be too dogmatic about this :wink: ).] — boundless

Well, I was presuming their possibility. It's just a horse-like thing with an evolutionary feature currently found on a narwhal and arguably a rhino (both mammals). It can happen, no? The being a sucker for human female virgins is implausible if there are no humans around, but I think its still a unicorn without that feature (or the blowing of rainbows out it's arse). Pick a different example if you find them impossible.

Thanks for the clarification but I still do not understand how you say that we can avoid some sort of 'selection' here.

To make it simpler, consider a radioactive decay experiment. There are two possibilities: Alice either observes the occurrence of the decay or not.

Radioactive decay is a wonderful example of a lot more than two possibilities since it could decay any time, thus infinite possibilities. Alice detecting it after one second is different than the Alice that measures it after two, but there is one Alice that doesn't measure it at all yet. This isn't to say that the one Alice is less probable. That depends on the half-life of the sample.
For the sake of your example, the device measures the decay destroys the 'when' part of it, so all Alice gets is a yes/no from the device when she makes her single query as to if it's happen already or not. Cat dead or alive so to speak, which as I recall was done in this manner.

Let's call these two possibilities, 'decay' and 'no decay' respectively. Let's also say that the probability of 'decay' is much less than the one of 'no decay'. Alice performs the measurement. And, say, she observes 'decay'.
If we do not accept the selection, we should accept that there is 'another Alice' that observes, instead, 'no decay'. And - besides the existence of 'another Alice' that observers 'no decay' - we have the different weights problem that occurs in MWI.

I knew where you were going with this. It seems solved by MWI by exactly what you quoted from Tegmark: There isn't actually any metaphysical split. There is but the one wave function with different solutions, and thus one Alice in two unequally weighted states. There are not two separate worlds, one metaphysically weighted more than the other. But the weight never changes from the '1' that it always was.
This argument is a great one against the whole metaphysical split interpretation of MWI.

In fact, this scenario is not very different from MWI. The only difference is that here we do not have a 'universal wave-function'.

On the other hand, if a selection is accepted, there is only one outcome.

I thought we were discussing MWI there. Looking back at the exchange, maybe you mean RQM here. Under RQM, the Alice that measured no-decay does not exist in relation to the one that measured decay, so there is no weight problem. There is no selection since there is but the one world in relation to any particular state. The Alice that had measured the decay is not the same event as the pre-measurement Alice, so no selecting took place for either of them. That's at least how I've been wording it.

BTW, the table on the Wiki article on the interpretations of QM, says that RQM is 'agnostic' about determinism. So, maybe RQM is simply silent about the selection.

I noticed that. It seems not to matter. In relation to me (or to anything else), what has happened is what has happened (fixed, in the past), and what will happen is meaningless since none of it can happen to me. Multiple future possibilities will be able to claim me as prior state, but that fact doesn't change if the list of those future possibilities is determined or not. Hence agnostic: it works either way.

"Physicists have long suspected that quantum mechanics allows two observers to observe different, conflicting realities. Now they’ve performed the first experiment that proves it by experimental realisation of what was previously a thought-experiment called ‘Wigner’s Friend’."

in my opinion this is equavalent to in medieval times when people didn't understand something they just said it was magic. I recently watched a video and read some articles on quantum mechanics and one of the recurring things they say is that they don't completely understand the situation. There are 100s of known particles smaller than an electron. How those particles interact with each is a mystery in many ways at this point in history. One of the key things said in these videos is alot of the results can only be predicted using probability and statistics. Probability and Statitistics does not rule out a root cause for something that happens but it just means the future is much harder to predict then a statement where someone says if A occurs then B will happen following that.

Well, I was presuming their possibility. It's just a horse-like thing with an evolutionary feature currently found on a narwhal and arguably a rhino (both mammals). It can happen, no? The being a sucker for human female virgins is implausible if there are no humans around, but I think its still a unicorn without that feature (or the blowing of rainbows out it's arse). Pick a different example if you find them impossible. — noAxioms

Well, yeah in that case it might be a possibility. Who knows :smile:

BTW, regardless unicorns, I believe that the ontological status of possible yet unactualized 'things' it is a very interesting topic. Suppose that X is possible but it is never actualized in the past, the present or the future. Is that possible? Well, yeah, I believe. As I said before I am a free will believer. So, there are choices that I could have made in the past but I chose not to make them. Indeed, they were 'possible'.

Maybe those choices are simply 'unreal'. Yet, they are not 'unreal' in the same sense that dragons are (assuming that they cannot exist). Or in the same sense that the academic career of a dragon is. What makes something possible? What it means for X to be possible?
Using a MWI-like reasoning, one might say that whatever is possible is, in fact, actualized 'somewhere'. But for people like me who do not accept that kind of reasoning, it is an interesting conundrum.

Radioactive decay is a wonderful example of a lot more than two possibilities since it could decay any time, thus infinite possibilities. Alice detecting it after one second is different than the Alice that measures it after two, but there is one Alice that doesn't measure it at all yet. This isn't to say that the one Alice is less probable. That depends on the half-life of the sample.
For the sake of your example, the device measures the decay destroys the 'when' part of it, so all Alice gets is a yes/no from the device when she makes her single query as to if it's happen already or not. Cat dead or alive so to speak, which as I recall was done in this manner. — noAxioms

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.

Or maybe it becomes a binary event if the measurement tells only if the decay happened during a certain time interval (I am not sure if you were saying this in the second paragraph).

I knew where you were going with this. It seems solved by MWI by exactly what you quoted from Tegmark: There isn't actually any metaphysical split. There is but the one wave function with different solutions, and thus one Alice in two unequally weighted states. There are not two separate worlds, one metaphysically weighted more than the other. But the weight never changes from the '1' that it always was.
This argument is a great one against the whole metaphysical split interpretation of MWI. — noAxioms

I partly disagree. In Tegmark's view, there is no metaphysical split at the level of the universal wave-function. So, in that case there are indeed different 'Alice-s' there. It is not a 'real split' because what is truly real is the universal wave-function.

I thought we were discussing MWI there. Looking back at the exchange, maybe you mean RQM here. — noAxioms

Yeah, I was referring to RQM. Pardon the lack of clarity.

Under RQM, the Alice that measured no-decay does not exist in relation to the one that measured decay, so there is no weight problem. There is no selection since there is but the one world in relation to any particular state. The Alice that had measured the decay is not the same event as the pre-measurement Alice, so no selecting took place for either of them. That's at least how I've been wording it. — noAxioms

Ok, I think I see what you mean. Nice work!

In MWI, the 'Alice that observed decay' would know that, indeed, 'Alice that observed no-decay' exists. In RQM, however, the answer is, you say, negative. Why? The meaning of 'existence' is different in RQM: it is relational. So, we cannot treat the 'pre-measurement Alice' as the 'Alice that observed decay'. So, a negative answer is perfectly fine.
I know that it is problematic within a relational framework, but it appears that there is no reason to believe that the other event did not occur. It seems a bit 'solipsistic' for 'Alice that observed decay' to declare that 'her' counterpart that observed no-decay is simply real, in this case.

Furthermore, as I said before, I find RQM somewhat vague in the definition of 'perspectives'. According to RQM, every physical system is an 'observer'. Fine, but if we consider, for instance a pen, it can be argued that its parts can be considered a 'physical system'.
So, it seems that there is actually a very, very huge number of 'physical systems' (and, consequently, 'perspectives'). I believe that this is a legitimate criticism to RQM (as legitimate as the criticism to MWI to have too many 'branches').

And if we unite these two aspects we end up with an even more huge number of perspectives!

I noticed that. It seems not to matter. In relation to me (or to anything else), what has happened is what has happened (fixed, in the past), and what will happen is meaningless since none of it can happen to me. Multiple future possibilities will be able to claim me as prior state, but that fact doesn't change if the list of those future possibilities is determined or not. Hence agnostic: it works either way. — noAxioms

Ok, it seems so from a RQM point.

We are starting to agree more and more, making these posts a bit shorter. — noAxioms

Well, I believe that we are certainly understanding each other more and more. Not sure about the agreement :wink: Anyway, thank you very much for the very clarifying explanations. Now I feel that I understand RQM much better!

To summarize, I believe that RQM has two serious problems.

1) I believe - as I said previously - that there are indeed too much 'perspectives'. If every physical system defines a 'perspective'/'reference frame' (i.e. is an 'observer' according to Rovelli), then there is an incredibly huge number of perspectives.

2) If after a 'measurement' the measuring physical system becomes something else, we are, indeed, implying that after every physical interaction (for Rovelli, measurements are physical interactions) 'creates' new perspectives.

IMO, these two are very problematic features of RQM. YMMV!

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

For all those Alices (Alici? :confused:) to exist, you need to change the definition of 'exist' from the RQM one to the MWI one. The change of definition is what distinguishes the two, not that there's all these Alices.

Or maybe it becomes a binary event if the measurement tells only if the decay happened during a certain time interval (I am not sure if you were saying this in the second paragraph).

Yes, I was forcing a (still imbalanced) binary event from a non-binary situation.

I partly disagree. In Tegmark's view, there is no metaphysical split at the level of the universal wave-function. So, in that case there are indeed different 'Alice-s' there. It is not a 'real split' because what is truly real is the universal wave-function.

Sounds pretty similar to me. There is one universal wave function, some solutions including an Alice in one state or another.

In MWI, the 'Alice that observed decay' would know that, indeed, 'Alice that observed no-decay' exists. In RQM, however, the answer is, you say, negative. Why? The meaning of 'existence' is different in RQM: it is relational.

Yes, the other Alices don't exist, per definition. We can still, just like the MWI person does, say that the decay measurement doesn't exist relative to the no-decay Alice. She was a real (and even more probable) outcome of the quite real pre-measurement Alice. The unicorn is more difficult due to the vast improbability of one from a 100 million year ago wave function of Earth. Of course humans are near equally as (if not more) unlikely per that same wave function.
Pop quiz: At what distance in the past does the wave function of Earth have the highest probability of there ever being a unicorn today?

So, we cannot treat the 'pre-measurement Alice' as the 'Alice that observed decay'. So, a negative answer is perfectly fine.

Note that above I did treat the pre-measurement Alice as being real to either post-measurement Alice. Both have memory of that state and thus have taken a measurement.

I know that it is problematic within a relational framework, but it appears that there is no reason to believe that the other event did not occur.

It is not valid to state "the other event did occur" in a relational framework. The statement is an objective one, and has no meaning in a relational framework. It seems to constitute a counterfactual statement just like "The decay occurred". It didn't. It occurred relative to me, but it didn't just 'occur'. Thus just say that the other event occurred to the measurer of the other outcome. I tried to do what with the no-decay Alice above. I carefully avoided a wording like 'she exists' or 'the decay was not measured'. I tried to be careful to always include the relations.

It seems a bit 'solipsistic' for 'Alice that observed decay' to declare that 'her' counterpart that observed no-decay is simply real, in this case.

Non-mind idealism of a sort, but not solipsism. If existence hinges on an interactive relation with a subject, then that subject defines its own existence, which is interaction-idealism. But there is symmetry. Everything does it, so it isn't solipsism. The table lamp does it, so it isn't mind-idealism.
A table lamp might measure a different version of me and thus I cease to exist in relation to it, but I always exist relative to myself, so I'm here. Under solipsism, I would not exist because only the table lamp (or whatever the one privileged thing is) counts.

Furthermore, as I said before, I find RQM somewhat vague in the definition of 'perspectives'. According to RQM, every physical system is an 'observer'. Fine, but if we consider, for instance a pen, it can be argued that its parts can be considered a 'physical system'.

If you get right down to the details, an observer is an event, and a system is not. No pen is in a consistent state with itself since at any given moment, parts of it are separated by about a nanosecond of speed-of-light space, and thus the ball of the pen is in superposition relative to the clicker at the other end. So in that sense, I do not exist as a system with a state. Right now I am completely undefined since no point of me has had time to measure any other part. In hindsight (say a microsecond later), that state is mostly defined and immutable. I mean, suppose that my retina has just measured the decay result from the first photon from the device giving answer to my query. OK, several other parts of the front of me also measured that, but not yet the innards (brain in particular), which are still in superposition of decay happened or not. Relative to different parts of me, the measurement was taken or not. It isn't entirely correct to say that the measurement has been taken relative to me since 'me' is not an event.

So, it seems that there is actually a very, very huge number of 'physical systems' (and, consequently, 'perspectives'). I believe that this is a legitimate criticism to RQM (as legitimate as the criticism to MWI to have too many 'branches').

As legitimate, yes, but I find neither argument to have any teeth. Yes, it is an obscenely large number. Physics is full of those. One measurement such as a decay has seemingly infinite possibilities (not a discreet list), so even a trivial system already has infinite worlds. If one is to worry about how such a list can be instantiated (where do we find room to put them all?), then you're applying classic wording to a Hilbert-space problem. It is a good argument against the universe as computer simulation hypothesis since the implementation really would need to find room to put it all.

I noticed that. It seems not to matter. In relation to me (or to anything else), what has happened is what has happened (fixed, in the past), and what will happen is meaningless since none of it can happen to me. Multiple future possibilities will be able to claim me as prior state, but that fact doesn't change if the list of those future possibilities is determined or not. Hence agnostic: it works either way.
— noAxioms

Ok, it seems so from a RQM point.

Still, the wave function is a pure function just like it is in MWI. Without interference from outside tweaking the terms, how can it not be deterministic? Sure, RQM doesn't care either way, but the same reasoning that MWI uses also works with RQM.
I'm now arguing against what I said above. I also do not know the meaning of the 'agnostic' designation on the wiki list for RQM.

For all those Alices (Alici? :confused:) to exist, you need to change the definition of 'exist' from the RQM one to the MWI one. The change of definition is what distinguishes the two, not that there's all these Alices. — noAxioms

Agreed! Until yesterday I did not fully understand RQM, I believe. My confusion was about the treatment of the ontological status of Alice: for me the 'Alice' that does the observation was the same as the 'Alice' observed by 'Bob'. Which is not true in RQM.

Or maybe it becomes a binary event if the measurement tells only if the decay happened during a certain time interval (I am not sure if you were saying this in the second paragraph). — boundless

Yes, I was forcing a (still imbalanced) binary event from a non-binary situation. — noAxioms

Ok!

I partly disagree. In Tegmark's view, there is no metaphysical split at the level of the universal wave-function. So, in that case there are indeed different 'Alice-s' there. It is not a 'real split' because what is truly real is the universal wave-function. — boundless

Sounds pretty similar to me. There is one universal wave function, some solutions including an Alice in one state or another. — noAxioms

I am not sure that I understand you here but I think we agree :wink:

In MWI, the 'Alice that observed decay' would know that, indeed, 'Alice that observed no-decay' exists. In RQM, however, the answer is, you say, negative. Why? The meaning of 'existence' is different in RQM: it is relational. — boundless

Yes, the other Alices don't exist, per definition. We can still, just like the MWI person does, say that the decay measurement doesn't exist relative to the no-decay Alice. She was a real (and even more probable) outcome of the quite real pre-measurement Alice. The unicorn is more difficult due to the vast improbability of one from a 100 million year ago wave function of Earth. Of course humans are near equally as (if not more) unlikely per that same wave function. — noAxioms

Ok!

Pop quiz: At what distance in the past does the wave function of Earth have the highest probability of there ever being a unicorn today? — noAxioms

I would say at the beginning of the history of the Universe (unless one believes to ancient mythologies that actual unicorns wandered on the Earth).

So, we cannot treat the 'pre-measurement Alice' as the 'Alice that observed decay'. So, a negative answer is perfectly fine. — boundless

Note that above I did treat the pre-measurement Alice as being real to either post-measurement Alice. Both have memory of that state and thus have taken a measurement. — noAxioms

Ok.

To summarize, in RQM, according to the pre-measurement 'Alice' both 'Alice-s' (or 'Alici' :wink: ) will exist. But both post-measurement 'Alice-s' regard the other one as 'non-existent' and the 'pre-measurement' as having existed in the past. There is no contradiction here because the states are perspective dependent.

I know that it is problematic within a relational framework, but it appears that there is no reason to believe that the other event did not occur. — boundless

It is not valid to state "the other event did occur" in a relational framework. The statement is an objective one, and has no meaning in a relational framework. It seems to constitute a counterfactual statement just like "The decay occurred". It didn't. It occurred relative to me, but it didn't just 'occur'. Thus just say that the other event occurred to the measurer of the other outcome. I tried to do what with the no-decay Alice above. I carefully avoided a wording like 'she exists' or 'the decay was not measured'. I tried to be careful to always include the relations. — noAxioms

Yeah, sorry! You are correct :smile:

It seems a bit 'solipsistic' for 'Alice that observed decay' to declare that 'her' counterpart that observed no-decay is simply real, in this case. — boundless

Non-mind idealism of a sort, but not solipsism. If existence hinges on an interactive relation with a subject, then that subject defines its own existence, which is interaction-idealism. But there is symmetry. Everything does it, so it isn't solipsism. The table lamp does it, so it isn't mind-idealism. — noAxioms

Ok, I see what you mean. But since yesterday, I am doubting that RQM is really consistent. But maybe the situation is the same as in the case of SR if one does not accept the 'block universe' (well, to be honest, I am not completely sure that even SR without the 'block universe' is really consistent...).

[But if one accepts some sort of panpsychism it is a mind-idealism :lol: Well, I believe that RQM and Process Philosophy can fit nicely together.]

A table lamp might measure a different version of me and thus I cease to exist in relation to it, but I always exist relative to myself, so I'm here. Under solipsism, I would not exist because only the table lamp (or whatever the one privileged thing is) counts. — noAxioms

Yeah in RQM, 'you' according to yourself and 'you' according to the table lamp are different. The table lamp according to itself is different from the table lamp according to you.

Furthermore, as I said before, I find RQM somewhat vague in the definition of 'perspectives'. According to RQM, every physical system is an 'observer'. Fine, but if we consider, for instance a pen, it can be argued that its parts can be considered a 'physical system'. — boundless

If you get right down to the details, an observer is an event, and a system is not. No pen is in a consistent state with itself since at any given moment, parts of it are separated by about a nanosecond of speed-of-light space, and thus the ball of the pen is in superposition relative to the clicker at the other end. So in that sense, I do not exist as a system with a state. Right now I am completely undefined since no point of me has had time to measure any other part. In hindsight (say a microsecond later), that state is mostly defined and immutable. I mean, suppose that my retina has just measured the decay result from the first photon from the device giving answer to my query. OK, several other parts of the front of me also measured that, but not yet the innards (brain in particular), which are still in superposition of decay happened or not. Relative to different parts of me, the measurement was taken or not. It isn't entirely correct to say that the measurement has been taken relative to me since 'me' is not an event. — noAxioms

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.

So, it seems that there is actually a very, very huge number of 'physical systems' (and, consequently, 'perspectives'). I believe that this is a legitimate criticism to RQM (as legitimate as the criticism to MWI to have too many 'branches'). — boundless

As legitimate, yes, but I find neither argument to have any teeth. Yes, it is an obscenely large number. Physics is full of those. One measurement such as a decay has seemingly infinite possibilities (not a discreet list), so even a trivial system already has infinite worlds. If one is to worry about how such a list can be instantiated (where do we find room to put them all?), then you're applying classic wording to a Hilbert-space problem. It is a good argument against the universe as computer simulation hypothesis since the implementation really would need to find room to put it all. — noAxioms

This is not true, however, for CI. In CI, only a specific class of entities can be considered an observer (which kind of 'entity' is subject to interpretation). At the same time, however, Relativity seems to imply something analogous.

I noticed that. It seems not to matter. In relation to me (or to anything else), what has happened is what has happened (fixed, in the past), and what will happen is meaningless since none of it can happen to me. Multiple future possibilities will be able to claim me as prior state, but that fact doesn't change if the list of those future possibilities is determined or not. Hence agnostic: it works either way.
— noAxioms

Ok, it seems so from a RQM point. — boundless

Still, the wave function is a pure function just like it is in MWI. Without interference from outside tweaking the terms, how can it not be deterministic? Sure, RQM doesn't care either way, but the same reasoning that MWI uses also works with RQM.
I'm now arguing against what I said above. I also do not know the meaning of the 'agnostic' designation on the wiki list for RQM. — noAxioms

From the perspective of the 'pre-measurement observer' if no 'selection' is made, then I'd agree it is deterministic. But if you consider the perspective of each 'post-measurement observer', the situation changes. For the 'Alice that observed decay' attributing the status of either 'existence' or 'non-existence' to the 'Alice that observed no decay' is meaningless (and vice versa). So, in this sense maybe we should understand the term 'agnostic'.

(sorry for the late edit!)

From the Daily Nous analyses

What about “objective reality” and “Wigner’s friend” and what-not? Well, the non-local theories that we have—pilot wave theories such as Bohm’s theory, objective collapse theories such as the Ghirardi-Rimini-Weber theory, and the Many Worlds theory of Hugh Everett—all postulate a single objective reality. — Tim Maudlin

Qualified with the following caveat:

although in the Many Worlds theory observers have experimental access only to a small part of the objective reality

Likewise Sean Carroll:

My own preferred version of quantum mechanics is the Everett, or Many-Worlds formulation. It is a thoroughly realist theory, and is completely compatible with the experimental results obtained here. Thus, we have a proof by construction that this result cannot possibly imply that there is no objective reality.

Which again begs the question of ‘what is objective’? How does a 'many worlds interpretation' posit a 'single objective reality'? Because if there are indeed infinite numbers of 'other worlds' or parallel dimensions, or if the universe 'splits' into different universes as is implicit in this 'meta-theory', then each of these universes are inaccessible from any other one. So how could they be considered ‘objective' when they can't even be known?

How does a 'many worlds interpretation' posit a 'single objective reality'? Because if there are indeed infinite numbers of 'other worlds' or parallel dimensions, or if the universe 'splits' into different universes as is implicit in this 'meta-theory', then each of these universes are inaccessible from any other one. So how could they be considered ‘objective' when they can't even be known? — Wayfarer

Each is known by the observers in that world, and not by the observers in any other world.

In a sense, the many-worlds hypothesis is a reductio ad absurdum of the notion of objective reality, because everything possible happens in at least one world, so there is no objective fact of the matter about whether any given event happens. What is objective is the god's eye view of all the worlds. But only gods can have that view.

Each is known by the observers in that world, and not by the observers in any other world. — andrewk

What I said. And the casual way in which this is accepted as an explanation or rationalisation of the 'observer problem' strikes me as either disingenuous or naive. In any case, in no way does it resolve the basic issue of ultimate objectivity.

In a sense, the many-worlds hypothesis is a reductio ad absurdum of the notion of objective reality, because everything possible happens in at least one world, so there is no objective fact of the matter about whether any given event happens. What is objective is the god's eye view of all the worlds. But only gods can have that view. — andrewk

So it's an objective fact that everything possible is actually happening, at every moment of time, in the many-worlds hypothesis?

Energy is the potential to get work done. — Metaphysician Undercover

Potential energy is the potential to get work done, actual energy is the getting of work done; in any actual doing of work some of the energy is "wasted" and discharged as heat (heat energy which of course itself does other "work").

Think of a nuclear bomb; when it is just sitting there the energy which it "contains" may be activated via a chain reaction of fission is potential, and if the chain reaction is initiated then it will be released as actual energy which will bring about changes in the environment.

You're looking at only half of the picture, and thus failing to see the distinction between potential and actual. If this doesn't clear up your misunderstanding I don't know what else I could add.

In any case, in no way does it resolve the basic issue of ultimate objectivity. — Wayfarer

Why would you say that?

Potential energy is the potential to get work done, actual energy is the getting of work done; in any actual doing of work some of the energy is "wasted" and discharged as heat (heat energy which of course itself does other "work"). — Janus

That's incorrect, energy is the capacity to do work, it is not "the getting of work done". Flowing water for example has a certain amount of kinetic energy, as the capacity to turn a turbine etc. (do work). The energy is there whether or not the turbine is. If we build a dam, the water is held up from flowing, and that held up water has potential energy. Release the water through the flood gate and the potential energy turns to kinetic energy, the capacity to do work. Run it through the turbine and the kinetic energy of the flowing water is transformed into electrical energy (the capacity to do work). Energy is not the getting done of work.

Surely you can see it's problematic to reconcile what we understand as 'objectivity' with the notion that reality comprises an endless series of parallel (but ever so slightly different) universes, only one of which we can ever be aware of. I'm sure I'm not the only person who this strikes as preposterous.

(I've often referred to the Peter Byrne article, The Many Worlds of Hugh Everett, which is an abstract of his book of that name.

Everett’s scientific journey began one night in 1954, he recounted two decades later, “after a slosh or two of sherry.” He and his Princeton classmate Charles Misner and a visitor named Aage Petersen (then an assistant to Niels Bohr) were thinking up “ridiculous things about the implications of quantum mechanics.” ...

...He described the macroscopic world quantum mechanically and thought of large objects as existing in quantum superpositions as well. Breaking with Bohr and Heisenberg, he dispensed with the need for the discontinuity of a wave-function collapse. ...

...Everett saw that under those assumptions, the wave function of an observer would, in effect, bifurcate [i.e. 'split'] at each interaction of the observer with a superposed object. The universal wave function would contain branches for every alternative making up the object’s superposition. Each branch has its own copy of the observer, a copy that perceived one of those alternatives as the outcome. According to a fundamental mathematical property of the Schrödinger equation, once formed, the branches do not influence one another. Thus, each branch embarks on a different future, independently of the others.

Everett did eventually meet with Bohr:

They met several times during a six-week period but to little effect: Bohr did not shift his position, and Everett did not reenter quantum physics research.

Instead Everett became part of the team whose task it was to figure out the optimal re-entry trajectories for ICBMs. (A difficult and emotionally withdrawn figure, he died young, leaving instructions for his ashes to be put out with the trash.)

Interestingly, the very last line in that essay is a quote from the unedited version of his dissertation:

“Once we have granted that any physical theory is essentially only a model for the world of experience, we must renounce all hope of finding anything like the correct theory ... simply because the totality of experience is never accessible to us.”

Which is rather a pregnant phrase, I think.)

in no way does it resolve the basic issue of ultimate objectivity. — Wayfarer

I suppose that depends on what one believes that issue to be. It's not an issue I am familiar with - at least not by that name.

So it's an objective fact that everything possible is actually happening, at every moment of time, in the many-worlds hypothesis? — Metaphysician Undercover

Personally, I wouldn't say that, because I think the useful everyday word 'objective' loses its meaning when it is deployed in a philosophical context. But it seems to me that the statement is at least as reasonable as most other statements in which I can recall people using 'objective' in a philosophical context.

The turning of the turbine is working getting done. The powering of lights and appliances is work getting done. You still don't seem to understand the distinction between potential and actual. How could there be "capacity to get work done" if there were no work getting done in which the potential energy is actualized? Maybe try reading up on it.

I still don't understand why you think the "endless series of parallel universes" should not be considered objectively real even if it would be different versions of ourselves who have access to them.

I still don't understand why you think the "endless series of parallel universes" should not be considered objectively real even if it would be different versions of ourselves who have access to them. — Janus

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

Surely you can see it's problematic to reconcile what we understand as 'objectivity' with the notion that reality comprises an endless series of parallel (but ever so slightly different) universes, only one of which we can ever be aware of. I'm sure I'm not the only person who this strikes as preposterous. — Wayfarer

The problem here I think is that there is no real principle whereby we can say that there is "only one which we can ever be aware of". That's what destroys objectivity in many-worlds, that we are aware of only "one world" is an illusion.

Maybe try reading up on it. — Janus

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. 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. I conclude that you're hopelessly lost, and helplessly refusing to acknowledge you misunderstanding.

Pop quiz: At what distance in the past does the wave function of Earth have the highest probability of there ever being a unicorn today?
— noAxioms

I would say at the beginning of the history of the Universe (unless one believes to ancient mythologies that actual unicorns wandered on the Earth). — boundless

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.

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

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.

But both post-measurement 'Alice-s' regard the other one as 'non-existent' and the 'pre-measurement' as having existed in the past. There is no contradiction here because the states are perspective dependent.

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.

I've been on the RQM wagon for a while and I've learned to be careful about how things are worded.

It seems a bit 'solipsistic' for 'Alice that observed decay' to declare that 'her' counterpart that observed no-decay is simply real, in this case.
— boundless

Non-mind idealism of a sort, but not solipsism. If existence hinges on an interactive relation with a subject, then that subject defines its own existence, which is interaction-idealism. But there is symmetry. Everything does it, so it isn't solipsism. The table lamp does it, so it isn't mind-idealism.
— noAxioms

Ok, I see what you mean. But since yesterday, I am doubting that RQM is really consistent. But maybe the situation is the same as in the case of SR if one does not accept the 'block universe'.

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:

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. — Metaphysician Undercover

The law of non-contradiction says there is only a contradiction if the thing is both true and false in the same way, but it is not the same way here. That part always gets omitted. Nowhere does SR say that that two events are simultaneous, and also not simultaneous. There is in fact no assessment of simultaneity at all between two space-like separated events without a frame reference.

(well, to be honest, I am not completely sure that even SR without the 'block universe' is really consistent...)

One need not accept a block model of the universe (spacetime) for SR to work. It is more complicated, but it works fine in a space-with-flowing-time model. We digress.

[But if one accepts some sort of panpsychism it is a mind-idealism :lol: Well, I believe that RQM and Process Philosophy can be good together.]

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.

A table lamp might measure a different version of me and thus I cease to exist in relation to it, but I always exist relative to myself, so I'm here. Under solipsism, I would not exist because only the table lamp (or whatever the one privileged thing is) counts.
— noAxioms

Here we see one paradoxical side of RQM. 'You' according to yourself and 'you' according to the table lamp are different. The table lamp according to itself is different from the table lamp according to you.

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.

At a certain point you decide to turn on the table lamp. Now, the turned on table lamp according to you is different from the turned on table lamp according to itself.

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.

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.

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

[Interestingly, this sounds again very similar to Process Philosophy - I know you are not a panpsychist of sorts but I find it interesting...]

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.

From the perspective of the 'pre-measurement observer' if no 'selection' is made, then I'd agree it is deterministic. But if you consider the perspective of each 'post-measurement observer', the situation changes. For the 'Alice that observed decay' attributing the status of either 'existence' or 'non-existence' to the 'Alice that observed no decay' is meaningless (and vice versa). So, in this sense maybe we should understand the term 'agnostic'.

OK, I can buy that.