Will this prediction of doom affect the way you go about your life? — Bitter Crank

Probably not. I already know about it, so the prediction changes nothing.

Suppose the problem went away. Suppose some trivial solution existed and the climate would remain reasonably unchanged despite what we're doing. Would that change the outlook for humanity in say the next century? If not, perhaps there are bigger fish to fry.

But physicists DO differ about what HE concludes about HER current age DURING his trip. — Mike Fontenot

This seems to conflict with this subsequent statement:

Special relativity says that, for two perpetually-inertial observers (meaning that they have never accelerated, and never will accelerate), they EACH will conclude that the other is ageing more slowly. — Mike Fontenot

OK, maybe not, since both are wrong.

Physicists do not differ about this, although they might word it differently. At any point during the exercise, there is no ambiguity of the age of one person relative to the other in the frame of either person (or more exactly, in the frame in which the person is currently stationary). Without the frame specification, statements about simultaneity are ambiguous
.
It has nothing to do with being perpetually inertial. An inertial frame is defined by a reference to an object at a specific moment, so if that object is accelerating, its current inertial frame is changing.

"For the traveler traveling away or the observer staying behind their is no difference in their relative speed so they age at the same rate." — Mike Fontenot

That was an example of a statement without a frame specification, and thus wrong. In either frame in which one person is stationary, the other ages more slowly.

If two people have equally good evidence for contradictory positions, it does not follow that they are both correct. — Bartricks

There are no contradictory positions in this scenario. Both parties agree on all facts at all times. Confusion only arises when the frame references are omitted.

Sophisticat seems to be the first poster with a sensible reply.

You are not inertial, you are accelerating towards the centre of the Earth. — A Seagull

Gravity is not part of special relativity. That said, under GR, on Earth you are accelerating upward, not downward, else the water in your cup would stay in only if inverted. The force on me from my chair pushes me up, not down.

Number theory are rules about numbers, which are language expressions.
...
The physical universe cannot be a model of number theory, because it is not a structure that consists exclusively of language expressions. — alcontali

Tegmark is not suggesting the universe is a structure of language expressions. You're confusing mathematics with the methods used to convey mathematical concepts. Tegmark's mathematical universe is an ontological proposition, not an epistemological one.

At some point, you will run out of physical miles, because the universe is deemed finite.

Is it now? You have some evidence of this?

From there on, you will run into facts that are true in the natural numbers but not true in the physical universe.

Nobody said the universe was the set of natural numbers. I can think of plenty of finite sized mathematical structures.

I am personally not particularly interested in the grand unification attempt in physics. I do not believe that Tegmark is either. — alcontali

Well surprise, because Tegmark is a physicist by profession where empirical results count. His dabbling on the side into metaphysics produces no falsification tests and thus is metaphysics, which in turn is philosophy. Not to discredit what he says, since it is mostly those metaphysical positions which interest me.
Many philosophers only have a weak background (if any) in physics, and thus often produce philosophies that directly contradict physics. I appreciate Tegmark because he's not among these.

If a sentence is provable in the ToE, it is guaranteed to appear as a true fact in the physical universe. This is not the case for any other mathematical theory.

Going to have to give me some examples so I can figure out what you mean by this.

It will not work for number theory, set theory, or another partial theory in mathematics, which are merely Platonic abstractions, divorced from the real, physical world.

Tegmarks statement, as quoted by whoever authored that quote you posted, says quite the opposite: "all structures that exist mathematically exist also physically". Platonic abstractions are mathematical structures, and thus are posited to exist physically by Tegmark. I will not go so far, for the reasons I posted before. I personally don't give meaning to something 'existing physically' or 'being real'. That means I'm not a realist I guess. Tegmark definitely is one. But I like the rest of what he says.

The sentence "2+2=4" is true in the abstract, Platonic world of the natural numbers

It's true in many more worlds that just that one; e.g. it's true in the world of real numbers, and it's true in our world. But that was not my point. My point was about the truth of it not being contingent on instantiation. The world of natural numbers can be real or just abstract, and it is still true for that world in both cases.

We cannot seek to abolish the distinction between mathematics and science.

Was proposing no such thing since I am suggesting nothing scientific here. It is a straight philosophical proposition, still entirely distinct from science.

Max Tegmark has made an interesting attempt at modeling the "Ultimate Ensemble theory of everything" (ToE):

... whose only postulate is that "all structures that exist mathematically exist also physically". This simple theory, with no free parameters at all, suggests that in those structures complex enough to contain self-aware substructures (SASs), these SASs will subjectively perceive themselves as existing in a physically "real" world."... — alcontali

First of all, Tegmarks premise there is not what is usually referred to as the theory of everything. The latter is what you're talking about here:

Prominent contributors were Gunnar Nordström, Hermann Weyl, Arthur Eddington, David Hilbert,[19] Theodor Kaluza, Oskar Klein (see Kaluza–Klein theory), and most notably, Albert Einstein and his collaborators. Einstein intensely searched for, but ultimately failed to find, a unifying theory.[20]:ch 17 (But see:Einstein–Maxwell–Dirac equations.) More than a half a century later, Einstein's dream of discovering a unified theory has become the Holy Grail of modern physics. — alcontali

That 'holy grail' is a unified theory, and Tegmarks comment paves no way towards unifying gravity with quantum field theory. It's just a philosophical postulate about the question of why existence exists.

Secondly, if Tegmark says that all such structures exist physically, then the SAS will exist in a physically real wold, and not just perceive themselves to. Not sure who wrote your quote, but it obviously wasn't Tegmark. The comment isn't entirely self consistent.

I am a big fan of Tegmark, and he has deeply influenced my beliefs. This postulate of his is a sticking point with me though since it makes pretty much everything physically real, making it not distinct from something that isn't physically real. But it points out that there is no distinction between mathematics that exists and mathematics that does not. 2+2=4 is true whether or not something physical performs the sum or not.

This has led me to a a different approach where being 'real' is not a property of something (like a rock say) but rather a relation. The rock is real to the water it diverts. But such a view is very different now than what Tegmark is proposing.

I don't see how that's not basically just making up arbitrary SciFi-like crap. — Terrapin Station

How wonderfully well (and typically) argued... You're free to disagree, but if you cannot point out an inconsistency in it without dragging in some strawman assumption of your own, then it is not crap at all.

None of the above.
— noAxioms
Can you describe this in words? — TheMadFool

C is not at rest relative to either A or B.

II was thinking about. Motion doesn't mean simply a change in distance rather a change in position too qualifies as motion. When you twirl the triangle the distance stays the same, yes, but there is a change in position no? Is that not motion?

Of course it is, yet your OP suggested otherwise, stating that the distance AB must be changing if the position of the points is changing, and thus motion cannot happen if length AB stays the same.

Now take any other object C in the universe.

C must be either be at rest relative to:

1. both A and B
2. A
3. B — TheMadFool

Whatever happened to 4: None of the above.

The vast majority (like all) objects C are at rest relative to neither A nor B.
Some of it depends on your coordinate system. My fork and knife appear to be at rest relative to each other, but only because I'm using a rotating and accelerating reference frame.

Imagine A, B and C are points on a triangle. We know that A and B are in relative motion. So the distance AB is always changing.

I can take a triangle and twirl it about and yes, there is motion but that doesn't imply that the length AB is changing. The Earth moves quickly around the sun, but its distance from it (length AB) stay more or less the same. It would stay exactly the same for an object with a perfectly circular orbit.

So I assume you're talking about a dynamic triangle formed by moving objects, in which case all 3 of the lengths are possibly constantly changing.

C is the other vertex of this triangle. If AC is constant and BC is constant but that means AB also has to be constant

Imagine a salad tong, with C at the hinge and A/B the two grasping ends. As you squeeze the tong, AC and BC lengths remain constant but AB is getting smaller. This counterexample demonstrates that AB does not have to be constant.

Thus, ALL objects in the universe are in motion relative to something else. All is motion.
Is there anything wrong with this argument?

It draws conclusions that don't follow from the arguments. Even if all objects are indeed in relative motion, you've not shown it by your logic.

Still, if another celestial body with big enough gravity aproaches Earth, wouldn't then be possible to actually fall upward, even if for just a couple of moments before the humanity extinction — Childish Daydream

Sure. The moon is already trying to do this, and the tides are the result of the water trying to fall up as you say. Pass a mass close enough and it will pull you away, and everything around you as well. Get it close enough and it will pull the nails off your fingers.

As for there being other universes, the term is left completely undefined.
For instance, the region of space centered 100 billion light years away is 'another universe'. It is as detached from us as the parallel world where the dinosaurs still live today.

Does that distant universe exist? Does it have a defined state? I say no, it doesn't, because to say it has such a state is a couterfactual statement. I personally have rejected the principle of counterfactual definiteness and thus pretty much would not say that such places (like the universe separated from us only by distance) exist in any meaningful way.

Neither time nor distance is infinitely divisible; the Plank time and the Plank size are shortest and the smallest. — PoeticUniverse

This assertion is of course nonsense since there is no evidence whatsoever that neither time nor distance cannot be divided after some point. It's just below the ability to measure after a point.

So the argument nevertheless ties into the wording of the OP: There is very much a finite time interval (well above the Planck time) below which no 'experience' can take place, therefore shorter durations are not experienced. You have a finite number of 'experiences' in your life, and when they've run out, you're done.

Mr x (1976 to 2019). x has to first reach 1997 and before that he has to reach 1986 and before that 1981and before that 1971 each time interval can halved indefinitely. The math says so. Is the problem with math or a subset of math infinity? — TheMadFool

The math also says that you can cut the cheese as many times as you like and it doesn't give you more cheese. You f***ed up when you drew a different conclusion from the mathematics.

I also don't think Mr X ever needed to reach 1971, but that's just a nit.

You're not imprisoned on Earth. Earth is your species' natural home. — Unseen

If we're propagating to the stars, then the galaxy is my species' natural home. My species' natural home is somewhere in Africa, and I have been kept away from there mostly from choices made by others.

And no third party decided you or I were going to spend our meager existences on Earth.

I'm of dutch decent and some third party (my parents) decided I was going to spend my meager existence on another continent. The kids will do fine on the ship, better than the volunteers that miss Earth they once knew. They'll be told stories of places they'll never see just like I'm told. I hope the people on the ship are kept busy. It would be pretty unethical for them to just be passengers the whole way. That's the zoo I was worried about.

Except for those who are there at the end of the journey and, one hopes, find suitable digs, the generations of crews are born for one purpose only: to get that last bunch to the new Earth-like home.

And the one purpose of that last bunch is the bunch that comes after them. It's my purpose here as well right now, so what's changed?

Their lives are being used, ;pure and simple. In order to keep the peace, they may not even be told that they are basically slaves. They may never be told about the home planet they left or even that their ship is on a mission.

You want this mission to not fail, but you're not going to tell the people why they're on the ship? Not a great way to go about it.

The obvious solution is to let the trip take 100,000 years and the population rides as test tube embryos to be grown and raised by machines after they've terraformed the destination. That reduces the human component to not being in charge, probably ever. Servitude maybe, or maybe just zoo specimen.

This is not a discussion of whether interstellar travel is possible. Why not do something constructive like accepting the premise as a hypothetical? — Unseen

OK, skip the practical solutions then. How is all these people spending their lives on a ship less ethical than imprisoning them on a planet? It's the environment they're born in, one good enough to live out a life. What's wrong with that? I don't see myself being issued a world cruise as apparently is my right, and certainly not a spaceship ride.

The Turing test is used to check whether an AI (artificial intelligence) is at human-level intelligence or not. — TheMadFool

I don't buy this. By this logic, If there is a test to communicate with a squirrel and convince the squirrel that the entity at the other end of the test is a fellow squirrel, then humans have not yet achieved the intelligence of a squirrel.
I think AI will have long since surpassed humans in intelligence and consciousness before one is capable of imitating a human to this degree.

Does that necessarily preclude what I stated in my post: that when you raise it to a higher level than the quantum level, things still start looking pretty deterministic? Take the laws of physics. If I throw a ball, the odds are pretty darned good that it's going to leave my hand and fly through the air. What are the odds that it won't leave my hand? 1 in a trillion? quadrillion? quintillion? Even if things are probabilistic and not certain at the quantum level, it seems that when you raise it up high enough, things still start to look pretty deterministic. — MattS

Not in any long run, no. Small differences are amplified, not lost in the averages. Get familiar with chaos theory, or what is popularly known as the butterfly effect.

How can we actually have control of our thoughts/actions when these thoughts/actions are driven by chemical reactions at a level that we can't possibly control?

How do you not have control of your thoughts and actions if the parts are functioning correctly? If you had conscious control over that function, such abilities would be lost, not gained. The free-will proponents sometimes talk about initiating cause rather than propagating it. I cannot see how that would be a benefit in a situation, for example one trying to cross a street at a time of ones own free choosing.

I can't trigger a chemical reaction by my will alone

Why would one want to do that? There are those that claim to have this ability (pyrokinesis say), and it isn't evidence of free will if they can actually do it any more than me using a match to achieve the same ends.

So in the end, how did I myself affect the chemical reaction that caused the electrical impulse in my brain that led to a thought/action? Help me understand.

I think you're confusing will with the means by which your will is implemented. I'm a monist, so I consider my will to be free. If a 'soul' were to suddenly possess my mind and make this body do different (more moral say) things, that would be a great example of my will suddenly being overridden by this possessing influence. It would no longer be free. I'd be just a vehicle (an avatar) then and responsibility for my actions falls on my 'driver', not on me, and my suppressed will would be epiphenomenal at best. "There is no Dana, there is only Zuul".

I don't see determinism as changing any of that.

Determinism has almost nothing to do with it. Lack of determinism doesn't mean ones will is not a function of physics.

I watched it enough to see that it was the same thing as the sites that come up with the same search.

What they are calling dimensions is not the geometric definitions. They describe Hilbert space, which isn't additional dimensions with length and ordering and such like you get with the first 4. You can't draw a curve through them. The whole OP was about curved lines being straight in a higher dimension, but the 'higher dimensions' are not dimensions at all, so no curves can be defined.

What they call dimensions 5 through 8 are all the same thing, corresponding to Tegmark's level-3 multiverse. Dimension 9 is the level-2, and 10 is level-4. None of these are linear dimension that have a concept of length or orthogonality or ordering of points. They are therefore not dimensions.

Finally, I see an attempt to associate this idea with superstring theory, which actually does have many more dimensions, but which are real dimensions and have nothing to do with what the list-of-10 is all about.

It is hard to deny Einstein since his work is what popularized time being a 4th dimension instead of the alternative flowing 3D model that still stands for the majority that don't give the subject matter any particular thought. If you're pushing this video, it presents time as a dimension, which you cannot do if you reject the spacetime geometry of Einstein's relativity theory.

So I stand behind my initial two assessments of the OP, one of which is that there seems to be no example of a curved line that is straight in a higher dimensional space. The video gave no such example.

I don't usually watch youtubes. If there is a concept from it you'd like to convey, post the gist of it.

I don't agree with everything Albert Einstein concluded about special relativity and general relativity (perhaps its the way some modern scientists explain it). These are very important concepts for being a rational thinker in the day and age we live in. — christian2017

Having a hard time parsing this statement. The only way that makes sense is if you're saying that such concepts are important for a rational thinker, but not important to you.

That said, I cannot think of an example of a curved path that is straight in a higher dimension. In a lower dimension, sure. An airplane takes a curved path through 3D space but a straight path on the lower dimension 2D surface of the earth.

Buy it for 2 cents, and one of the wishes is to produce a buyer at a penny.

This exercise seems chock full of loopholes.

Another way is to set up a Hilbert's Hotel sort of arrangement where each new buyer pays but a cent which is passed up the list to prior sellers, thus each time raising the price at which it was bought by a penny. You pay in installments of one cent every time the bottle changes hands. Problem solved.

I would agree that lot's of people build philosophies with an (generally completely unfounded) belief SR, GR, QM and/or QFT* supports their ideas. I find it philosophically relevant to refute such arguments (at least the part connecting to modern science). — boethius

Your choice of QM interpretation most definitely go with certain philosophical stances and not others. It seems important to be compatible. But I agree that I don't see this with relativity.

However, I don't see how SR, or GR and QM for that matter, displacing Newtonian physics had a big impact on presentism and eternalism, the debate pre-existed both and continues.

I think relativity moved a lot of people (those who thought about such things and understood it) to the less intuitive camp of eternalism. It certainly did for me, even if I continue to defend the opposite stance as not being in contradiction.

I have though of my own 'proof' of presentism being wrong, but I think it is invalid like the attempts others have made. If time on Earth is dilated (running slow) due to its motion and gravity well, how much faster does time actually flow? If my Earth clock says a million seconds went by, how many seconds actually went by as measured by a clock measuring absolute time, stationary and at zero gravitational potential? Gravitational potential is negative, so zero is 'in no gravity well', as high as one can possibly be.

The complete lack of an answer to this in the absolutist web sites (like conspiracyoflight.com for example) seems to be my evidence against their position. They avoid it, like it's embarrassing or something.

Light moves at c relative to any frame. This has been experimentally confirmed.
— noAxioms

I don't argue with this statement above. This fact of reality does not have any impact on what I am claiming is wrong with the interpretation of Special Relativity. What physicists say is that all the laws of physics look the same to you regardless of how fast you are traveling. I interpret that to mean as I have been told by others that you cannot tell that your clock is slowing and you cannot notice that your length in the direction of motion is shrinking and that your increase in mass is also not noticeable — MrCypress

You make it sound like speed is a property of an object. It isn't. I am not moving at some speed. I can only have speed relative to an arbitrary reference. So for instance, relative to a muon in the upper atmosphere, I am moving at .995c which is the only reason I can get to and measure that stationary muon before it decays in a couple microseconds. At that speed, the distance between myself and that stationary muon is decreased by a factor of about 10, as is my height, and yet I don't notice anything weird about that compression except that I get to the muon before it decays, something that I would no be able to do if I had to travel a 10x longer distance.
This experiment has been done countless times, and makes for a nice empirical test with a significant dilation factor.

So I agree with what you say above, despite the nonexistence of the implied property of speed.

It is my belief that as one gradually accelerates and approaches the speed of light a person on board that space ship they will be flattened and pressed back into their chair. The ship length will be compressed and it will require more and more thrust to continue to accelerate to the speed of light. Eventually the human brain will not be able to function because the electrons in their brain will no longer be able to move forward in the direction of motion that the ship is traveling.

So this is completely wrong. Again, it uses the concept of a property of speed. There is no such thing. In the frame of the ship, the occupant will notice nothing and his brain works just fine. There is no contraction at all since the occupant is stationary in this frame. He is not going fast at all, but the stuff outside the window certainly is, which accounts for its red and blue shifts.

What are the philosophical implications of relativity? — boethius

The primary one is the philosophical interpretations of time: presentism and eternalism. The former was always the default until relativity gave equal if not better footing for the latter, but scientifically (empirically), the two are not distinct. SR does not assert a block universe even if the assumption of one makes the calculations simpler. Hence the difference is philosophical.

Now what if they don't have any window and they only observe things from within the spacecraft? I believe that they would still be able to notice gravitational effects that wouldn't be present if they weren't moving in that way relative to the galaxies, considering there is an asymmetry in the way they are moving relative to the matter around the spacecraft. — leo

SR says that local experiments would not be able to detect the speed, meaning no differences. Looking out of the window constitutes a non-.local test, but there is no way to tell if you're moving or the galaxies you see are moving fast.
Anyway, there would be no local gravity differences. There is no asymmetry. In the frame of the 'ship', the ship is stationary and the galaxies are moving incredibly fast and their clocks are the ones running slow.

Here is where the the incorrect interpretations start to breakdown. We have both just agreed that you can tell you are moving at 99% the speed of light by using Doppler effect. — MrCypress

Speed is relative to something, so this is correct. The galaxy and I have a .99c difference, but in the frame of either, it is the other that is moving.

That frame of reference is moving so slow relative to the speed of light that it is essentially stationary.

This is totally wrong. Frames don't move relative to light. Light moves at c relative to any frame. This has been experimentally confirmed.

So in reality if you are moving at the speed of light relative to the earth you are essentially moving at the speed of light relative to everything else in the Universe.

Again, not true. Earth moves at the same speed as only a few relatively local things. If you are going that fast relative to Earth, you're stationary relative to some other galaxy that happens to move at about that velocity. The expansion of space assures that there is a galaxy that is stationary relative to you. Hence you're not moving fast at all. You're just far away from the stuff which is also stationary.

The only differences will be slight because of their relative motions relative to you and the stationary back ground of space. The Doppler measurement is the first anomaly that gives the person in the spacecraft a clear indication they are moving at 99% the speed of light.

If you were at that stationary galaxy going the same speed, the background would be isotropic: no doppler difference in any direction.

Wayfarer is right: This thread belongs in a physics forum. It has philosophical implications, but none of them were brought up by anybody.

I am not sure I am following you. In fact, I just am saying that the cause precedes the effect in all reference frames without FTL. Isn't it right? :smile: — boundless

Yes. With locality, which is essentially saying no FTL.

Ok, I see. Interesting, thanks! I wonder if this can be used to reconcile SR with pilot-wave theory... :smile:

Pilot wave is a form of Bohmian mechanics: Pro counterfactual definiteness (objective state) and denial of locality. So I wonder how they interpret spooky action at a distance using pilot waves. I don't know the official line on that. They certainly cannot reproduce spooky action using a classic pilot wave setup like they use for double slit.

Can you "discover" something that is non-physical? — Pattern-chaser

Obviously yes, your topic being a prime example.

Mathematics is not part of the scientific space-time universe, except trivially.

I choose to interpret it otherwise.

How could you "discover" maths when there's nothing to come upon, and say "Oo look, that seems handy!"

Yet that is exactly how mathematical progress was always made. Nobody found it under a rock or through a telescope. Not even talking about mathematical models of the universe here. I'm just talking about pure mathematics like Calculus, imaginary numbers, 14 dimensional space, and octonions and such. These are not 'come upon', yet are discovered.

As for pi, as soon as you invent numbers, and all the stuff that goes with them, you notice pi as soon as you start considering circles. Bearing in mind that circles - not just things that are roughly circular - occur rarely if at all in the real world....

Exactly. We notice pi despite the complete absence of any actual circles in nature to measure. Figuring out pi to a lot of precision doesn't involve hunting down an ever closer physical approximation to a circle.

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

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

Maybe it's embarrassed. :yikes:
— Wayfarer

Well, possibly! :razz: — boundless

This is why I resist describing RQM under presentist terms. If time is external to the structure that is the universe, then such selection is an objective act relative to this realm under which time exists, and it isn't really RQM anymore if such an objective action takes place.

With time being part of the structure, no event/state (something to which a relation can be made) 'flows' to a different event, necessitating such a selection. Thus there is no selection postulate.
This isn't an embarrassment, just an implication of a relative interpretation.

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

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

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

The Andromeda Paradox is about the ambiguity of what time it is elsewhere, not about the state being definite. The former is a frame dependent thing and the latter is a statement of superposition of something unmeasured. I think you meant the former but your wording suggested the latter.

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

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

I didn't say that. I said the set of events in a given light cone is frame independent. The ordering of those events is still quite frame dependent.

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

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

I have done an advocatus diaboli thread defending the compatibility of relativity and presentism, so I maintain that they're not incompatible. SR says that the preferred frame cannot be determined given the special case after which it is named. But inability to detect such a frame does not mean that there isn't a special one. Presentism doesn't even require it to be a inertial frame, and no presentist that knows their physics seems to assert that it corresponds to such a frame. The foliation is always bent, which has the interesting paradoxical implication that no two stationary observers are simultaneous in each other's inertial frames. I find that hilarious, but not paradoxical.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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.

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.

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.

I actually am not sure. — boundless

Well good. Being sure is being closed minded. I try not to be sure about anything, but I do it anyway.

I would not call what a table lamp does 'epistemic', so again, I do not personal hold view described there.
— noAxioms

Ok, I agree. Bad choice of terms on my part. For the sake of generality, let's just say 'not ontic' instead of 'epistemic' and drop using the word 'knowledge' in favor of 'addition of new 'information'' (for the lack of a better term).

The table lamp does acquire information (physics definition), so I can go with that.

Disturbingly close, yes, to the point where no arbitrarily close inspection will yield a difference. This is not true of the paper map of Paris.
— noAxioms

Again, you are right! I should have said, instead: 'non-representational' means that the wave-function simply does not have any ontological meaning.

It may or it may not. Wasn't this the thing we said we're not sure about? It seems quite interpretation dependent, even to the point of interpreting the meaning of 'ontological'. Tegmark's mathematical universe says that the wave function is what the universe is. It doesn't just describe it, but it actually is it. That's one kind of ontological statement: mathematics is fundamental, not just descriptive. Another kind would be two different interpretations of this mathematical universe where the mathematical structure has the property of existing (MWI variant) as opposed to RQM, where 'exists' is a relation, not a property. That's a different sort of ontological statement. RQM doesn't say that the universe doesn't exist (isn't nihilistic). It just gives no meaning to the phrase.

And no, neither MWI nor RQM needs to accept this mathematical foundation. I just used the mathematical universe example to illustrate two different kinds of ontology.

I am not sure if what you are describing here can be applied to the 'version' of RQM that I have in mind where after the observation, for the observer, the other branches do not exist.

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.

BTW, I am sympathetic to some kind of realism for mathematics. I do not believe that mathematics is entirely a product of our minds but, at the same time, the usual version of mathematical Platonism does not convince me. So, maybe mathematical relations are 'real' (but not 'physical'). Interesting view

Or maybe they're physical but not real.

Apologies for slow reply time.

I believe that if you say that something 'not real' describes 'a real thing' you're just re-asserting a realist/representational view. The 'unreal'/'non-representational' view of the wave-function advocated by Rovelli, Bitbol etc is that the wave-function does not describe anything. It is just a tool. — boundless

A tool (a map of Paris say) may be just a tool and not be the thing it describes, but it very much still describes Paris. Thus I object to the statement that the tool doesn't describe anything.
I guess I'm not much in that camp since I personally suspect the wave function isn't just a tool.

This is very compatible with the view that collapse is due to an increase of knowledge (i.e. an 'epistemic', not 'ontic' view).

I would not call what a table lamp does 'epistemic', so again, I do not personal hold view described there.

In other words, 'real' and 'representational' should be taken as synonyms (or very close to that) - the point is that there is a biunivocal correspondence between mathematical formalism and reality.

Disturbingly close, yes, to the point where no arbitrarily close inspection will yield a difference. This is not true of the paper map of Paris.

The point in bringing this distinction between two different 'sub-interpretations' of dBB was simply to explain better what I mean by 'real'. If you think that the wave-function has some ontological meaning, then the wave-function is real/representational. If not, it is just a tool of some sorts.

I don't think there is just the two choices. It is certainly not representational in my opinion, but the wave function has meaning only in relations, not objectively, so it isn't ontological as in 'is real' but more like 'does relate to'. 5 really is less than 7 and that is not just a representational property of the tool that is the integers, and yet the integers don't need to have Platonic realism (ontological meaning) for that relation to be true.

The issue here is how to interpret the wave-function. If you interpret it as 'real' (or 'representational'), then you are right, there is no selection and the 'other branches' are still 'real' after the measurement.

If, instead, the wave-function is not treated as real/representational (as I think Rovelli does), it does not give a description of reality. — boundless

I have a rough time with this distinction. Something not real can still be used to describe a real thing. It just isn't the actual thing. I think more on the lines of what is more fundamental. So I exist, but I'm made of more fundamental matter. Matter exists, but the mathematics underneath seem more fundamental. Below that is what, law of form? None of this stuff 'is real' under RQM, but one part really does relate to others.

There is a single outcome given by a probabilistic law.

That doesn't follow from either interpretation of the wave function. It seems to require an additional postulate. A unreal wave function can still describe a multi-state system, and in fact must in order to describe superposition.

Everett was forced to reign in his views in order to gain acceptance. — noAxioms

Reign... Brain fart. :yikes:

I see. [Everett's] proposal was certainly revolutionary (regardless whether one agrees with him or not).

He was shunned by the physics community after his PHD and went into the defense industry instead, but was asked to present his work 5 years after the paper was published. Somewhere around that time DeWitt coined the MWI term from Everett's original "relative state formulation" which sounds an awful lot like RQM.

I say it isn't selected at all.
— noAxioms

If one sees the wave-function as real then there is no selection, I agree. Otherwise, there is a 'selection'.

That works given a postulate of such selection going on. My statement was an opinion, not an assertion.

But this is IMO the position of RQM. On the other hand, I do not believe that there is only one 'version' of RQM. In fact, I believe that there are different relational approaches to QM. So, maybe some versions accept that all outcomes occur. — boundless

There is certainly no one version of probably any of the interpretations, but there are probably some fundamental features that characterize each. Take that away and it isn't really a different version of something (like RQM), but rather a whole different interpretation. So sure, all outcomes occur, but they don't all occur to a given X (or anything else). They very much occur (are real) to things Y that interact with (measure) them.

I never used the word 'universe' in what you quoted since it means such different things to different people.
— noAxioms

Yeah, but when MWI-supporters deny that there is a 'splitting', they actually do not usually deny that there is a splitting that others have in mind IMO (of course, there are exceptions).

Tegmark is kind of funny this way. An MWI person might refer to 'universe' as the one universal wave function and all these resulting worlds, but Tegmark often uses 'multiverse' splitting into universes so that it falls under his type-3 multiverse. But other times he speaks of worlds and one universe.
Tegmark also argues effectively that the 'split' is never a full separation into separate disjoint worlds, and others (e.g. Wayfarer) often do, which I feel misrepresents the view. To quote Tegmark again (same link):
"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."
So worlds don't actually split off, but different terms simply become sufficiently decoherent for their interaction to become negligible.

Everything in that paper seems to apply to RQM since it seems to separate out the needless metaphysical assertions piled on top of the one postulate. Section III-C seems to offer a choice between effectively MWI and RQM, making RQM a valid offshoot of MWI physics.

Yes, there is a splitting in this sense. What I meant is that for each reference, there is no splitting. In your example of the polarization, if 'I' observe a horizontal polarization the observation of a vertical polarization does not occur in RQM (for 'me'). In MWI, it does.

Sounds good.

OK, I see better now what CH proposes that is unique. You'd think they'd put that in plain language in the introduction somewhere. How is what Hawking and Weinberg push different from the CH view then? Why add a 2nd postulate when the first one perfectly predicts the experience we have?
— noAxioms

IMO, the difference is that in the MWI 'version' of Hawking and Weinberg the axiom is not stated (in fact, my 'proposed interpretation' consisted to add this axiom).

It isn't stated in MWI because it doesn't need it. All worlds are real, so none of them is in need of selection over the other. It's only when you have a metaphysical selecting (dice throwing as Einstein disdained) that such a postulate is introduced.

Agreed! I believe that there is some controversy on Everett's own views.

Everett was forced to reign in his views in order to gain acceptance. It was dumbed-down to a reasonably finite number of worlds, not this full blown Hilbert space thing. That has since been put back, but I wonder what else never was. It's not like Everett really ever contributed much after being driven from the physics community like he was. He needed more of the PR engine that was behind Einstein. His thinking was too out-of-box for the time.

some persistence over time seems required.

I think information preservation principle gives the persistence needed. If I measure the photon and then the big boot hits me from the sky (Python-style) before I can pass on the findings, was the measurement done? Information preservation says yes, the boot doesn't erase that.

Regarding empty space, I am not sure if it can be an 'observer' in RQM.

Agree. Nothing to collapse a wave function.

What about QFT? In QFT, the 'vacuum state' is not really 'void'. So, maybe quantum fields can be used as 'events'? (hope this makes sense)

Maybe so. Not up on QFT enough to comment with anything but the ignorance PoV.

Anyway, I do not believe that this affect my point. I would say that the point where the screen is hit is 'selected randomly'.

I say it isn't selected at all.

Just a curiosity: has anyone ever suggested an interpretation where the 'universal wavefunction' is real (like in MWI) and a single branch is 'selected' by a probabilistic rule (as in Consistent Histories as I understand it)? — boundless

Such an interpretation would seem to propose counterfactual definiteness. Somewhere off to the side, some measurement is taken by not-me and causes some state to be real and the other results not.

From the Rovelli bit you quoted in the post above:

Even beyond its foundational role in relativistic field theories, locality constitutes, therefore, the base of the relational methodology: an observer cannot, and must not, account for events involving systems located out of its causal neighborhood (or light-cone).10 — Rovelli

An interpretation that such selecting of reality is going on outside of some privileged light cone is doing exactly this: accounting for events involving systems located out of its light cone. As such, the interpretation bears little resemblance to local interpretations like MWI or CH as I understand it.
Per you post above, it seemed that Hawking and Weinberg posited something along these lines, so I wonder what they'd say to my point here.

I agree with what you said here. But I am not sure that it solves the 'measurement problem' completely. It explains why we do not observe superposition. — boundless

I think we observe it every day, but you take it as an ordinary observation. A rainbow is quite impossible to see without superposition. The lens of my eye would not work without it. Most directly, Bob in the OP is able to directly measure superposition even after Alice has taken a measurement.

BUT you need an additional assumption in order to explain why only one outcome actually occurs.

If your interpretation says that a single outcome occurs.

Not sure why you think you are disagreeing with me. If by 'universe' in MWI you mean the 'universal wavefunction' then I agree with you and Tegmark.

I never used the word 'universe' in what you quoted since it means such different things to different people.

But this is not normally what one means by 'world' or even 'universe', so, in fact, I think that one can definitely say that there is splitting. And this is for me a reason to not accept MWI.

There is splitting of a sort in RQM also. To me, the photon is polarized vertical. Relative to another me, the photon is horizontal. Relative to a 3rd reference, there's not even a me or a photon. Sounds like those are separate worlds, some connected more than others.

Well, I know that some supporters of MWI consider only one branch as 'real' and other branches as 'unreal' ( e.g. apparently Hawking and Weinberg are supporters of this 'flavor' of MWI, see the Wikipedia article on MWI).

That very much goes against the Everett postulate. It is a different interpretation and should have a different name.

But unfortunately, MWI cannot IMO justify that without an additional axiom (as in Consistent Histories, where there is the axiom that a 'history' is selected probabilistically. In dBB one 'branch' is occupied by particles).

OK, I see better now what CH proposes that is unique. You'd think they'd put that in plain language in the introduction somewhere. How is what Hawking and Weinberg push different from the CH view then? Why add a 2nd postulate when the first one perfectly predicts the experience we have?
That's why I like RQM which is the main Everett postulate: "All isolated systems evolve according to the
Schrodinger equation" without MWI's secondary metaphysical postulate that said equation is real. The latter postulate makes no change to the evolution of the equation and thus 'what happens', and thus isn't needed to explain what the experience would be.

My point is that this version of MWI simply does not explain why the 'other branches' are 'unreal'.

So the inhabitants of those 'other branches' don't continue to post in their forums philosophical discussions about how their world being more real than ours? The Schrodinger equation says they very much do, and none of these additional postulates make any modifications to that.

On the other hand, Deutch, DeWitt etc consider all branches as physical, 'real'. So it is not just me that understands MWI in that way.

I'm not sure that Everett did. It was a physics interpretation of QM, not necessarily making any metaphysical assertion. MWI as we know it might have been built on Everett's work, but I don't believe he called it 'MWI'.

and RQM doesn't really have selections that happen. A measurement isn't really done by any observer who is but an event with only a history, but not the ability to 'select'. I cannot measure the photon, but I can have already measured it, so no 'selection' is ever done. At least that's how I interpret RQM.
— noAxioms

I do not understand this.

I figured. That one is hard to explain. RQM says such and such is real to a second thing, say 'me', but 'me' needs definition. A worldline doesn't work because it isn't defined after a certain point. So that point (one event) is 'me', and that event cannot take a measurement. It may or may not have an abstract worldline leading up to it, but none has a worldline leading from it. Hence an event (me) can have already taken a measurement, but it cannot take a new one. Such new measurement are taken by future events, and the future does not exist to 'me', thus 'I' cannot take a new measurement, only something else which will happen to include 'me' as part of its past worldline. So 'I' do not select anything and thus what is real never changes for me. One of my future events (say one that measures a vertical polarity) can have already measured that polarity and that event considers that state of affairs to be real to it, but it never becomes real to (is selected by) any particular 'me' event, which, being an event, cannot flow through the selection process to its future, however much it might intuitively anticipate doing so.
That was a very eternalist way of describing things, but I cannot think of a way to do it in presentist terms. I consider 'observers' (that to which a reality relates) to be events in RQM, and consequently almost anything can be such an event. Humans are not special at all. Not sure if empty space is a valid event since there is nothing there to take a measurement of anything. It has to be something capable of being affected by state.

Take the double-slit experiment. When you observe that an electron passes through slit A then you either explain this observation of a single outcome via a selection or you accept that the 'other history' is equally true as in MWI. So, I believe that both CI and RQM leave it unexplained.

I never observe an electron passing through a slit. If I do, it goes through one and doesn't interfere with itself. So I don't get this scenario. What I have observed is where the electron hit the screen, or the pattern from many such electrons. At no point does any local interpretation of QM interpret the electron taking one path to get there. I think pilot wave theory might assert it, but they've really shot that one to hell when they put a partition between the two slits

I agree again. My point however is that there is no explanation why there is a probability of finding a Moon, an electron or whatever in the first place. If one accepts hidden-variables this is of course explained.

Take a point exactly 50 billion LY north. There is a nearly pure wavefunction describing what exists there, and one set of solutions to that wave function is finding a moon like ours nearby, or just an electron, or whatever. If there was a way for 'me' to just suddenly teleport and take a measure of that point, under MWI, I (a whole multitude of 'I', however many it takes) would measure every one of these possibilities. Under RQM, each of these possibilities would be real to the 'me' that appears there. Same story, but different wording. Both views also say that to an observer on that moon or at any of the other possible states there, I'd probably not suddenly appear in front of them. My appearance there is as unlikely as is theirs to me.

Right, you find the Moon again because you already measured it. As you say it is not that remarkable. It is more remarkable that you find an electron probabilistically when you perform a measurement without hidden variables.

How does one go about 'finding' an electron? What sort of measurement are we talking about here? With the moon, sure, you look up on a clear day and see if there's one there, but for an electron, it seems more difficult to not find one since they're everywhere. OK, 50 BLY away I might not find one in a sample radius since odds are I encounter fairly empty space, but I'm not sure if that's what you mean.