No interpretation is a cop out, but MWI cannot have those observers in different world branches since they communicate. Alice knows the polarity and tells Bob that she does. Bob knows that the particle is still in superposition and tells Alice so. That cannot happen if the two are in different branches.
— noAxioms
In the experiment, Alice can communicate to Bob that she has measured a definite polarity (without the polarity itself being revealed) while the lab she is in remains isolated (and Bob does not communicate back, which would presumably constitute a measurement entangling him with Alice). So there are actually three MWI branches here. One where Alice measures a horizontal polarization, one where she measures a vertical polarization, and one that is the superposition of those two branches where Bob detects interference (and knows that Alice has made a measurement). — Andrew M

I have to disagree about the restrictions to communication you convey above. Alice knows the result of a measurement, and that makes for 2 Alice's now, one for each result. Those two version of Alice, being in different worlds, cannot communicate or otherwise be aware of each other. But they behave exactly identically because they're keeping that knowledge a secret. To Bob, Alice is in superposition of knowing those two states, and Bob can thus communicate two-way with both Alice's since they, by acting identically, are completely coherent. They can make out if they want. In reality, humans are incapable of this coherence, which is why they never use humans to play the role of Alice or Bob.

Anyway, point is, Alice learning of the measurement results splits Alice, but does not split the universe, as is commonly assumed. Bob, being able to speak to both versions of Alice, is still in a common world. So yes to the three worlds if you count them that way: One for each Alice, and one for Bob. But there is obviously communication between the Bob world and both Alice worlds, but Bob cannot pass a message from one Alice to the other. With the communication, Bob's world is clearly not isolated from Alice's world, and hence doesn't really count as a separate world.

BTW, I believe that other than the very problematic concept of 'many worlds', MWI has a serious problem, check: https://arxiv.org/abs/1210.8447 . The usual claim that the 'preferred basis problem' is solved by decoherence. But it is not correct. Decoherence solves the 'preferred basis problem' (in fact, 'for all practical purposes' in my feeble understanding) only if you already assume that there is a well-defined factorization in the Hilbert space (which is the only 'reality' in MWI, AFAIK). Without well defined subsystems, the factorization is completely arbitrary (also, it should be added that, in fact, one has no, a priori, reasons to do a factorization in the first place).
I do not know how MWI-supporters handles this in a non-circular way. — boundless

I actually don't know the terminology that well, in particular 'factorization'.

So perhaps I don't understand the problem here.

I also add that MWI and RQM are close. The difference being that RQM does not accept the reality of the 'universal wavefunction' because, in RQM, wave-functions are well-defined in relation to a specific physical system (the 'observer' in this interpretation).

I'm an RQM guy myself, and yes, nothing is just 'real', things are only real in relation to something else, so how can the universal wave be real when there is nothing to which it is real in relation? The view would be self inconsistent if it were to be otherwise.

I agree that QBism, Copenaghen interpretation (CI), RQM in their own ways reject 'realism'. But how about MWI. In MWI, the only 'truly real thing' is the universal wave-function (UW). The UW never collapses in MWI. It rejects counterfactual definiteness. But the UW is still objective. — boundless

Agree. MWI says there is an objective reality, but it is entirely in superposition, and measurement just entangles the measurer with the measured thing. It does not collapse any wave function. Hence there is no defined state of anything (like dead cat), and hence no counterfactual (or even factual) definiteness.

If most interpretations reject objective reality, then how is the article referred to in the op saying anything new? — Metaphysician Undercover

They're not. They're spinning it as something new. But if they've actually disproven the principle of counterfactual definiteness like the wording of the article implies (but does not actually state), then I'd like to hear from the side of those that assert it, like a Bohmian guy interpreting the results. I don't know enough about the interpretation to know how they interpret a superposition state.

If you reject "objective reality", is there any interpretation other than Many Worlds which is acceptable? — Metaphysician Undercover

Most interpretations reject it. You take away Bohmian mechanics and Stochastic and Transactional interpretations, the latter two being interpretations with which I am not familiar. But all the ones you hear about (Copenhagen, MWI, Consistent histories, objective collapse, Wigner, QBism and Relational) all reject an objective reality. I have a personal preference for Relational, but I don't assert the other ones must be wrong.

That is what the MIT abstract says that it does:

Wigner can...perform an experiment to determine whether this superposition [in respect of a particular particle] exists or not. This is a kind of interference experiment showing that the photon and the measurement are indeed in a superposition. — Wayfarer

That the photon's state is in superposition. The other measurement is not in superposition with the photon. I suppose you can word it that the result of that known measurement is in superposition.
Anyway, yes, they can take the photon and do an experiment on it where it interferes with itself, without measuring the state. If they have learned of the result of the measurement taken by the other, this superposition is not observed.

From Wigner’s point of view, this is a fact— the superposition exists. And this fact suggests that a measurement cannot have taken place.

Yes, the superposition exists. The suggestion that a measurement cannot have taken place is false. The article does suggest this, but QM rules do not under any interpretation. From the beginning, Schrodinger's cat is in superposition despite the measurement obviously having taken place.

But this is in stark contrast to the point of view of the friend, who has indeed measured the photon’s polarization and recorded it. The friend can even call Wigner and say the measurement has been done (provided the outcome is not revealed).

So the two realities are at odds with each other. “This calls into question the objective status of the facts established by the two observers,” say Proietti and co.

Are they at odds? Schrodinger's reality is not at odds with that of the cat, and never has been. You can put a human in the box watching the cat if your interpretation insists that humans are special, but I assure you that none of the measurements mentioned by that article were made by humans. Humans learn of the results (of probably thousands of runs) only well after the fact.

Many Worlds has those observers in different world branches,
— Andrew M

I don’t regard that as an explanation so much as a cop-out.

No interpretation is a cop out, but MWI cannot have those observers in different world branches since they communicate. Alice knows the polarity and tells Bob that she does. Bob knows that the particle is still in superposition and tells Alice so. That cannot happen if the two are in different branches.

The wording of the paper seems to be a argument against counterfactual definiteness (an objective reality). I'm all for that since I don't think there is such a thing, and Bell's theorem demonstrated long ago that you can't have both that and locality.
Anyway, Bohmian mechanics seems to be the interpretation that asserts counterfactual definiteness. There are other interpretations that do, but not very mainstream ones. It would be interesting to describe the experiment from that perspective.

Wigner knows that his friend knows which way the spin goes, but Wigner doesn't know which way. So Wigner models the lab as a superposition while the friend does not.
— andrewk

As I said to W., if it were that simple then it wouldn’t rate a comment.

I think to resort to Schodinger’s famous simile, it’s as if Bob observes a live cat, and Alice a dead one - and they’re both right. — Wayfarer

It isn't a live and dead cat, a blatant contradiction which cannot arise. Bob observes the cat and knows if it is dead or alive. Alice measures the cat still in superposition. That's very different than Alice measuring a dead cat and Bob a live one.

It is more complicated than what AndrewK says, one knowing the answer and the other not. The real conflict is that Bob knows the one answer, and Alice knows there are still two answers.
This sort of thing has been going on long ago. I can entangle a pair of particles. Bob measures one and Alice (far away) measures the 2nd one to still be in superposition. The difference here is they seem to be doing to the same object, instead of leveraging entanglement.

All four of them are invalid, but the 2nd one might just be poorly worded.
I would have concluded that one cannot be a valuable asset to both your school and your team.

It seems that few posters know their theory very well.

Einstein reasoned that if he were to travel at the speed of light then clocks would appear to stop moving (since the light from the clocks would never reach him). Einstein concluded that time slows down the faster to the speed of light you travel. — philosophy

Einstein did not reason thus, nor did he conclude that time slows for any observer. Anybody will observe their own clock (one in their presence) to run at the normal rate, regardless of speed relative to other objects.

In other words, time is not the same as a measuring device (e.g. a clock).

On the contrary. Time, to Einstein at least, is exactly what clocks measure. If one twin is younger than another, it is because it has been less time since birth for that twin than the other. But if those twins are moving relative to each other, then each twin ages slower than the other one in his own frame, which means the twin that stayed home ages at a reduced pace both in the inertial frame of the departing twin and in the inertial frame of the returning twin.

Oh, well that's a good question! I guess the answer would be yes, because computing a game is the same result. — Marchesk

I was going to ask you about games played on alien planets that don't necessarily exist in our observable universe, but the AI question is a good start to that.

If you discount them, then existence is anthropocentric, which seems distasteful. So I'm glad you include them.

However, I'm open to questioning whether an AI actually plays chess against itself, as opposed to manipulating matrices or neural network weights.

Isn't that essentially what humans do? How might the human ones count then if that's all the AI is doing?

The rules allow it to happen, but a player can claim a draw if it does happen... see the threefold repetition rule. — Kippo

According to the OP, we're talking about possible chess games (some huge number), not actually played ones (as per Marchesk's constructivist definition). Both ways, the list seems finite.
The number of possible games is infinite if the 50 move rule is allowed to be bypassed (not noticed). The repeated-position stipulation can be ignored, allowing positions to be repeated up to 50 times.\

But my definition was incomplete. Revised defintion of a complete game of chess...including draws of two types and resignations

Your definition seems to be the constructivist one then: Played games where there are players involved. In that case, the list is very definitely finite since only so many games are played in all history. Far less than 10^120. In possible games, any game can be aborted by resignation or something at any point, so it is really a count of valid chess states since it is legal to do so in any state.

In it, [Shannon] made a quick calculation to determine how many different games of chess were possible, and came up with the number 10^120. This is a very, very large number — the number of atoms in the observable universe, by comparison, is only estimated to be around 10^80. — CuriosityStaff

Off topic: Shannon miscalculates. The average sensible game might last 80 moves, but the average legal game averages about 5000 moves, so the number is more like 10^400.
The number of atoms in the visible universe is far different from the number of atoms in the universe, and the huge chess number is less than the latter. I hate such comparisons to that or 'grains of sand' and such.

On topic:The game of tic-tac-toe seems to have human countably many games, and this doesn't change the subject being discussed. The size of the number is irrelevant.

@kill jepetto:
The moves are possibilities yes, but not random. They're totally determined and the number of legal chess games or positions is quite defined and some exact finite number. Kippo points this out.

There are a finite number of them if you disallow repeat configurations. — Kippo

The rules do not allow repeat configurations (beyond 2), so such games would not be legal games. There is also a max length game, so the count is finite in that direction as well.

- - -

So do these games 'exist'? I suppose that depends on how one defines what it means to exist, and what things qualify as existing by that definition. I'm a relativist, so thing 1 exists to thing 2. Thus I might say that all of them exist as abstractions to humans (I can distinguish two different games from each other, or tell if two games are the same one), but they don't exist as abstractions to a rock since rocks seem not to make those abstract distinctions. That answer is consistent with my definitions, but there seems to be no correct definitions.

My original point was that I cannot make sense of the notion of unchanging phenomena, so "phenomena changes" is a tautology that says nothing. One might as well have said "phenomena is phenomena" or "change is change".

So to my mind, there isn't room for two concepts, namely that of phenomena and that of temporal change. — sime

The two words are different. Phenomenon implies an experienced thing, whereas change does not imply experience. So two concepts, since it makes sense to speak of non-phenomenal change.

'Temporal change' is not necessarily the same as change. Perhaps Terrapin thinks otherwise, since my example of a non-temporal change was dismissed. But equating change to only temporal change seems begging the equality of change and time, not evidence of two being the same thing.

I think change is simply a difference in one variable as a different variable is altered. So one can plot the brightness of my house paint over time, but not necessarily over time, and it presumes a sort of identity of the thing labeled as 'the brightness of my house paint' that can be evaluated at different points in the variable being altered.
Then also, if my house doesn't fade, then the brightness is not a function of time, and it is meaningless to speak of the time at which the brightness of it was value X.

Again, comparative difference is not the same thing as change. I pointed that out with the atmospheric density example. — Terrapin Station

Ah, a different definition of change. Perhaps that is the fault in my example.

Got to go for now.
If time was distinguishable in the million-decay example, then you could distinguish the events running forwards (with half of the decays happening before the first half life) from the scenario in reverse, with most of the state changes happening near the end.

How did your example show that? I certainly didn't agree that it showed that. — Terrapin Station

You can measure change: A count of the particles that have decayed. You have not proposed a way to measure time from that.

I brought up effects and differences and distinctions and such. It is my counterexample.
My example showed something where change was quite measurable but time was not, and if the two were ontologically the same, then if you could measure one, you should be able to measure the other.

My proposal has absolutely nothing to do with effects on anything or distinctions between systems. — Terrapin Station

OK, I was finding inconsistency with "I'm saying that what time is ontologically is change or motion". Your 'proposal' is perhaps something else. I was finding a counterexample to the quoted statement there.

Without an argument, it just seems like arbitrary ideas that have a non sequitur connection with what I'm claiming. — Terrapin Station

I'm not proposing anything. I'm finding inconsistency in your proposal.

This is what I wrote: "I don't really understand what you're asking there. Because I don't understand how you're using "meaning" really. If you're literally talking about semantics, meaning is subjective. It's a mental act of association. So are you asking if someone (who?) performs associative acts in that situation? " — Terrapin Station

OK, I think I described how I'm using the word in my prior post.

And then you responded with something about "simulation" for some reason.

Heh... I read you wrong. You said 'situation', not 'simulation'. So much for the eyes.

So are you asking if someone (who?) performs associative acts in that situation? — Terrapin Station

There is nobody performing acts in my scenario. There were only the million particles.

If you want to make an argument to the effect of "time can only be change if that (that=maybe time, change--whatever you'd need) has an effect on something" or "time can only be change if there is a distinction between a system with x and a system without x" or whatever you'd want to claim, then I'd check out the argument, but you'd have to make the argument.

I didn't really define time. I just brought up points that seem to find flaw in equating time with change.

If anything, time seems to be meaningless without change, but change is not necessarily meaningless without time, so change is arguably more fundamental. Meta might think otherwise since he asserts meaning to time without change, but I find that scenario to be indistinguishable from the same lack of change without the time.

You're ignoring the issues I brought up re "meaningful." — Terrapin Station

What post again? My take on something being meaningful is that X is meaningful if there is a distinction between a system with X and a system without X. A distinction other than the presence of X.

So I can assert that all hairs on my head have a virtual serial number, and sure, that is distinct from a universe without that because the hairs there don't have a virtual serial number, but there is no distinction to me. I cannot test for which universe I'm in. The serial numbers have no effect on anything. Thus they are not meaningful, in the way I mean that word.

You were positing something decaying at different speeds where there's only that particle decaying? That wasn't clear from your earlier comment. — Terrapin Station

I had one particle at first, but immediately moved on to the example of a million such particles.

"At different speeds" would be nonsensical in that situation. "At different speeds" has to be relative to another change.

Agree. My example illustrates that: change without meaningful time. Time is not equivalent to change.

It's always based on some set of changes. — Terrapin Station

Yes. The changes are the particles that have already decayed, and the ones that have not. There is nothing else to go on.

You posited a change in the universe. So it would be whatever you assign to that change.

The change is the decay of one of the particles. Not sure what you're thinking I'm assigning to that change other than the order in which it occurs. It is meaningless to say they decay at a fast rate at first, and tapering off. That case is not in any way distinct from them decaying slowly at first, and quickly at the end.

I thought of an example of change without meaningful time: I have a universe with an unstable particle. It eventually decays. The time it takes to do that is meaningless.
— noAxioms

Talking about time in the sense of measurement there, if that's all you have in your universe, "the time it takes to decay" is simply whatever unit you apply to the change in question. — Terrapin Station

There can be no units. There is nothing on which said units could possibly be based.

So are you asking if someone (who?) performs associative acts in that situation?

There is no simulation. It is a universe with ordered events.

If you were using the wheel that goes around twice as fast as the change for time measurement, then it would mean twice as much time. — Terrapin Station

Then you're relating processes anywhere to that wheel, and not to time.

Okay. That makes sense but you're just pointing out that time is relative (in a different sense than the special relativity sense) to whatever we're using as the change for measurement. In other words, "In the same time"=you have to be referring to some set of changes that you're using for the relative measurement. For example, the changes in a clock. — Terrapin Station

Don't understand what you're saying. It doesn't need to be any particular amount of time for the one wheel to change twice as fast as the other. I chose rotation because rotation is absolute, not relative to anything. Sure, there are two wheels and thus there is a relation to them, but I didn't need to specify the relation with time (the RPM of either) to make my point.

I thought of an example of change without meaningful time: I have a universe with an unstable particle. It eventually decays. The time it takes to do that is meaningless.

I have a million such particles, and at some point, x% of them have decayed. Is there any meaning to a half-life of them? Is there meaning to the concept of half-life at all, as distinguishable from just a list of the order in which the million particles decay? The latter is just a numbered list. I don't see how 'time' has any effect on that where it is meaningful to assert that a lot of particles decay at first, but the last ones take much longer between decay events. Maybe the curve is the other way around and the final ones take place 'close together'. There would be no way to distinguish that model from another.

Two equal size wheels spinning, and one goes around twice as fast as the other. That seems to be twice the motion (change) in the same time. The one changes by 2 degrees while the other changes by 1 degree, and if change were equivalent to time, the one must take twice the time of the other to do that.

OK, but twice as much motion is not twice as much time.
It's like saying that momentum is kinetic energy. An object can't have one without the other, but it doesn't follow that they're ontologically the same thing.
'Change' is better than 'motion', the latter being just a subset of change. The paint on my house fades over time. That's change, but not motion. I can also have change without time: The air gets thinner with altitude: change over altitude vs change over time. Change seems not to be ontologically equivalent to time.

More consecutive funniness.

Time may require change to be meaningful, but change is not what it is.
— noAxioms

That's pretty close to what I've been trying to tell Terrapin, change requires time, but change is not what time is. — Metaphysician Undercover

I'm contrasting this with what Terrapin quotes immediately after:

I've already explained to you how time can pass or proceed without any change or motion. — Meta

So you loosely agree that time without change is not meaningful, but here you say time can pass without any change.

T-S, You seem to defend a definition of time as change, but complain about common language use, which I was not trying to do. I haven't read all your posts, but perhaps you could point to a post where you explain that if that's what you claim.

I said you cannot assert that a change has not taken place just because it cannot be measured. But you are asserting exactly that.
— noAxioms

I was not asserting that. — Metaphysician Undercover

Fair enough. You said physicists have determined that, and they don't claim that.

I've been saying that time is not change

With that I agree. "I changed my political viewpoint after the last election" "How much?" "By just over 2 hours"
Indeed, that makes no sense. Time may require change to be meaningful, but change is not what it is.

I think that you cannot truthfully state that a change has taken place unless that change has been measured. — Metaphysician Undercover

Another fallacious mistake. I said you cannot assert that a change has not taken place just because it cannot be measured. But you are asserting exactly that.

Imagine a very short period of time, Planck length or shorter. Physicists have determined that no physical change can occur in a shorter period of time. — Metaphysician Undercover

Sorry to jump in on this discussion, but you contradict yourself. Physicists have determined no such thing, especially since this would violate conservation laws.

Wikipedia:
"The Planck time is by many physicists considered to be the shortest possible measurable time interval; however, this is still a matter of debate." — Metaphysician Undercover

You quote the definition, which is about measurable interval, and yet above you claim that no change takes place in that interval. It simply does not follow that something doesn't exist (small change) just because it cannot be measured.

You are conflating "passage of time" (which is measured by clocks) with the wikipedia expression "objective flow of time" (which doesn't exist). — Inis

I have to agree with Luke on this one. 'Passage of time' implies flow to the average person, and I don't think the typical eternalist would ever use that term. I wouldn't. Clocks measure duration (length in the temporal dimension), and you seem to equate 'passage' with that, but I don't, and neither does most of the literature, as Luke has been pointing out.

How about we say that things interact with each other, but interacting things do not necessarily measure each other. — Metaphysician Undercover

Interaction implies two way relationship, so perhaps a 1-way interaction.

The moon is a poor example since we're in the gravitational field of the moon at all times and it is impossible for it not to be there, even if hidden behind a curtain. A specific state can be collapsed to us only after at least a second, but the moon in general cannot cease existence just by no longer looking at it, so to speak.

Measuring is a special activity of comparison which human beings with minds do.

You're describing a different dictionary definition of the word. A QM measurement is nothing of the sort, unless you ascribe to the Wigner interpretation I guess. I'd rather not limit myself to such a solipsistic interpretation of QM. Even Wigner himself bailed on support of his own interpretation for that reason.

Things which interact with each other are not necessarily gather information into one point. Do you know what it means to gather information? Or are you just making up a nonsense definition of that, to go along with your nonsense definition of measurement?

I don't think I used the term 'gather information' so far.

So the rock compares it's own state prior to its interaction with the photon to its own state posterior to its interaction with the photon? That requires a memory. The day you find a rock capable of doing that comparison, let me know.

You make comparison sound like a decision. I'm just saying that the rock is in a different state with the photon than it would be without (or with a different) photon. It doesn't make a comparison between those two states. Nothing can since any system has access to only one of the two states.
Rocks have great memory. Ask the geologists. But that is on a classic scale. From a QM standpoint, all matter has perfect memory, hence physics' conservation of information principle. There, now I've used the term 'information', but the physics definition, not the one you're using.

Anyway, I think we cannot communicate on this subject. You insist on the everyday language meaning of my words and not the physics ones.

Under presentism, there has to be a present hypersurface, and there has to be only one of them. Unless you pull the trick of denying objective reality etc. — Inis

Agree, but a hypersurface is 3D surface in a 4D space, and under presentism, there is no 4D space, only the 3D 'all of reality'. It isn't a hypersurface anymore if it is all of reality, no? That was my point, and perhaps it is just semantic.

It seems like you do not know what measurement is. — Metaphysician Undercover

Then choose another word to refer to what I'm describing, else we cannot communicate.

Measurement, by definition requires a comparison. The measurement devices in QM are calibrated to perform comparisons.

So when I open the box to check if the cat is dead or alive, what carefully calibrated device to I need to do this? It can be done in the total darkness if that helps.

The rock is doing a comparison of photon detected vs photon not detected. The state of the rock is different depending on this comparison.

This would be like saying that light hitting a rock is an act of measurement. — Metaphysician Undercover

I had mentioned the rock above. Yes, it very much is a measurement. Thing X (source of photon) has now caused an effect on said rock, and X now exists to the rock. That's how QM measurements work. It causes the state of X and the state of the rock to become entangled. The special equipment in labs is only special because it records the measurement precisely for the purpose of the knowledge of the lab guys, but measurement itself is trivial.

You can assert otherwise, but then we're just talking about different things. You asked me what it means for an extended object (not all in one point in space) to not be in a defined state at the present, and this is what I mean by that.

Of course measurement requires processing, it is a process. You cannot measure something without actually measuring it. — Metaphysician Undercover

We have different definitions of measurement. I'm speaking of measurement in the QM wave-function collapse sort of way. That interaction is 'actually measuring it'.

Measuring creates a knowing. If there is no knowing, then there has been no measuring.

Yes, I figured that was the definition under which you were working. I'm not talking about knowing.

Wouldn't you agree that the movements of my arms and legs ought to be understood as occurring in a different frame of reference from the movements occurring within the neurology of my brain, and my nervous system?

I don't see how any of that doesn't occur in all frames of reference. Maybe I don't understand how you're using the term. I'm interpreting it as 'inertial frame of reference' but maybe you mean POV or something, except no POV is specified then.

Why would this event, which measures all the defined states as one state, need to be in the future of those states? Can't the different defined states just be compared as occurring in different frames of reference? — Metaphysician Undercover

It takes time to gather all information about the spread-out state into one point (said future event) which can be anywhere, not necessarily an event that is part of me.

Choosing different frames of reference just defines a different set of events to be 'my state'. Under presentism, there is only the preferred frame, and other frames don't represent my actual state.

The light hitting your eyes is processed, and the image is created. — Metaphysician Undercover

Measurement doesn't require processing. The light hits me somewhere (eyes, toenail, whatever) and I've measured the moon. It exists to me now. The processing is only necessary for me to know it exists, but knowing doesn't define existence except under idealism where the photon never hit me at all.

What do you think it means for an entity not to exist all at one place? Could one part of that entity be in one frame of reference, and another part be in another? — Metaphysician Undercover

All (reasonably local, like not outside the Hubble Sphere) parts exist in all frames.
Being not all in one place means I am not in a defined state except to an event which has measured that entire state, which can only be in the future of the state being defined.