Suppose, instead, that there is a measurement at the slits
— Andrew M
Does this measurement physically affect a photon on its way to the far screen? — jgill
For single photons, the double-slit interference pattern can be made to disappear by using a marker.
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The which-path marker consists of two, mutually perpendicular, polarizing filters.
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When either the vertical or the horizontal filter covers both slits, the double-slit interference pattern is preserved, albeit at a reduced intensity compared to no filter. When the vertical filter covers one slit and the horizontal filter covers the other, the double-slit pattern disappears completely. Two superimposed single-slit patterns are all that remain. This new arrangement changes the setup into a which-path experiment in the sense that it is now (in principle) possible to know which slit the photon passed through; this destroys the quantum interference.
Introducing a third polarizing filter, the quantum eraser, between the marker and the detector thwarts the which-path experiment if it is oriented 45° with respect to the marker filters. Every photon reaching the detector is now polarized in the direction of the third polarizer and it is no longer possible to know which slit each photon passes through; as a result, the interference phenomenon is restored. — Young's double-slit experiment with single photons and quantum eraser - Rueckner, Peidle
The wave function in quantum mechanics evolves deterministically according to the Schrödinger equation as a linear superposition of different states. However, actual measurements always find the physical system in a definite state. Any future evolution of the wave function is based on the state the system was discovered to be in when the measurement was made, meaning that the measurement "did something" to the system that is not obviously a consequence of Schrödinger evolution
— ”Wiki: Measurement problem
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There are an infinite number of solutions depending upon that constant (measurement) - a superposition. Then the measurement takes place and a "collapse" occurs giving a particular solution. Did the measurement "do something" to the system, or does one simply experiment to find the appropriate value of the constant? Where is the magic? — jgill
https://mateusaraujo.info/2021/03/12/why-i-am-unhappy-about-all-derivations-of-the-born-rule-including-mine/
I don't have these same concerns, but I think it is important than many proponents of MWI do list similar concerns about other theories in quantum foundations. — Count Timothy von Icarus
If the physics in question is reversible, why do we posit a splitting universe instead of a merging one, aside from the fact that having it split in both directions (forwards and backwards in time) is incoherent?
Perhaps whenever we make a measurement we merge universes, such that we progress by such merges to one of many potential end points, final conditions, of the universe, assuming ad hoc that it has an end? This might work, but it blows up the rational-agent based derivations of the Born Rule. Rational agent models are not reversible, we don't say, "given what I observe now, what must have happened in the future, what endpoint must I be most likely to be converging on?" — Count Timothy von Icarus
I only skimmed this thread, but has the Born Rule problem really not come up?
To bring up the example before, it is like someone's spouse is either in spot A with probability 30% or spot B with probability 70%, except, get this, she is also in BOTH spots with probability 100%. Explaining that satisfactorily is going to be a doozy, and I don't think Dutch Book arguments really solve the problem. — Count Timothy von Icarus
In the end, a few premises are needed though, and I explicitly list that one (that humans are not special, and reality doesn’t supervene on my experience). I even attempt a logical demonstration of it, but I don’t think it constitutes a proof. — noAxioms
It is me that nobody seems to get that? I’m not saying that the alternative (that noumena supervenes on human phenomena or human language) is necessarily wrong, but that such a stance utterly destroys any hope of acquisition of knowledge — noAxioms
I think you meant the John Bell quote.
Thx, fixed that. One 4-letter B-word is the same as another, no? — noAxioms
I want to know more on the subject of what Aristotle meant by this. The eternal unchanging unmoved mover. — invicta
Hopefully someone with links will come along…I don’t know where to start with him. — invicta
My point was that this abductive construction isn’t in any way something unique to quantum theory. That’s not what make it different, and it certainly doesn’t indicate that physical processes require the presence of humans. Sure, the human knowledge of physics requires humans, but that knowledge isn’t necessary for trees to fall in the forest when nobody is around. — noAxioms
Please see the Bohr quote in Andrew M’s post a few back — noAxioms
Nonetheless the observer - or, even better, agent or person - closes the loop in the sense that it is human experience that grounds quantum theory and the quantities that can be measured.
— Andrew M
That also seems true of say Newtonian theory. — noAxioms
Is there some way in which human agency or observation makes a difference in (grounds) QT in a way that it doesn’t in NT? That would be a pretty incredible claim, that physics (and not just human theories/knowledge of physics) is different in the presence of humans than it is in a universe absent them. — noAxioms
The two TVs represent the two measurements. The reality is the soccer match. Obviously, the images on the two TVs have to correlate as they represent two views of a single reality. I think the point he is making is that there's a deeper reality than the physical world and therefore it's no surprise if two measurements correspond. — Art48
Isn't it the case that we know they do not have predefined values (unless we accept the pilot wave, Bohmian Mechanics interpretation)? — Art48
Suppose we have two spinning coins, separated by light years. Suppose if Alice causes her coin to stop spinning (analogous to doing a measurement) and it lands heads, that Bob causes his coin to stop spinning and it lands tails. Suppose Bob's coin always lands on the reverse side as Alice's coin. This is my metaphor for quantum entanglement as I understand it. Comments? — Art48
Even looking at the measurement dials has no impact on the collapse or not. Of course, the descriptions you quote give a special role to an observer (writing down the reading of the dial say), but 1, it doesn’t take a human (or actual ‘observation’) to do that, and 2, it being written down isn’t what causes collapse. If the dial says |here>, then the wave function is collapsed whether or not anything (or person) reads that dial since the dial is not inside Walmart. — noAxioms
Neville Mott worried way back in 1929 about cloud chambers. He said: “Look, an atom releases an ionizing particle at the center of a cloud chamber in an s-wave. And it makes a straight line track.
Why should it make a straight line track? If I think about an s-wave, it is spherically symmetric. Why do they not get some spherically symmetric random distribution of sprinkles? Why should the track be a straight line? — Quantum Mechanics in Your Face - Sidney Coleman
Having imbibed a bit too much at the local pub he enters a state of superposition, thoroughly confused, an unknowing victim of a partial differential equation. — jgill
Now I will give an argument due to David Albert[21] with respect to Zurek’s question. Zurek asked: “Why do I always have the perception that I have observed a definite outcome?” To answer this question, no cheating: we can’t assume Zurek is some vitalistic spirit loaded with élan vital unobeying the laws of quantum mechanics. We have to say the observer—well I don’t want to make it Zurek, that would be using him without his permission, I’ll make it me, Sidney—has some Hilbert space of states, and some condition in Sidney’s consciousness corresponds to the perception that he has observed a definite outcome, so there is some projection operator on it, the definiteness operator. If you want, we could give it an operational definition: the state where the definiteness operator is +1 is one where a hypothetical polite interrogator asks Sidney: “Have you observed a definite outcome?”, and he says: “Yes”. In the orthogonal states he would say: “No, gee, I was looking someplace else when that sign flashed” or “I forgot” or “Don’t bother me, man, I’m stoned out of my mind” or, you know, any of those things. — Quantum Mechanics in Your Face - Sidney Coleman
The entire quantum subject would be better served if "observer" were eliminated everywhere and replaced by "measurement". — jgill
Here are some words which, however legitimate and necessary in application, have no place in a formulation with any pretension to physical precision: system, apparatus, environment, microscopic, macroscopic, reversible, irreversible, observable, information, measurement.
The concepts 'system', 'apparatus', 'environment', immediately imply an artificial division of the world, and an intention to neglect, or take only schematic account of, the interaction across the split. The notions of 'microscopic' and 'macroscopic' defy precise definition. So also do the notions of 'reversible' and 'irreversible'. Einstein said that it is theory which decides what is 'observable'. I think he was right - 'observation' is a complicated and theory-laden business. Then that notion should not appear in the formulation of fundamental theory. Information? Whose information? Information about what?
On this list of bad words from good books, the worst of all is 'measurement'. It must have a section to itself.
Against 'measurement'
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The first charge against 'measurement', in the fundamental axioms of quantum mechanics, is that it anchors there the shifty split of the world into 'system' and 'apparatus'. A second charge is that the word comes loaded with meaning from everyday life, meaning which is entirely inappropriate in the quantum context. When it is said that something is 'measured' it is difficult not to think of the result as referring to some pre-existing property of the object in question.
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In other contexts, physicists have been able to take words from everyday language and use them as technical terms with no great harm done. Take for example, the 'strangeness', 'charm', and 'beauty' of elementary particle physics.
No one is taken in by this 'baby talk', as Bruno Touschek called it. Would that it were so with 'measurement'. But in fact the word has had such a damaging effect on the discussion, that I think it should now be banned altogether in quantum mechanics.
The role of experiment
Even in a low-brow practical account, I think it would be good to replace the word 'measurement', in the formulation, by the word 'experiment'. For the latter word is altogether less misleading. However, the idea that quantum mechanics, our most fundamental physical theory, is exclusively even about the results of experiments would remain disappointing.
In the beginning natural philosophers tried to understand the world around them. Trying to do that they hit upon the great idea of contriving artificially simple situations in which the number of factors involved is reduced to a minimum. Divide and conquer. Experimental science was born. But experiment is a tool. The aim remains: to understand the world. To restrict quantum mechanics to be exclusively about piddling laboratory operations is to betray the great enterprise. A serious formulation will not exclude the big world outside the laboratory. — Against ‘measurement’ - John Bell, 1990
Then the casual physics dilettante could think, Yes, if I aim my flashlight at my keys on the table I don't disturb the keys, but if the keys were quantum size I might disturb them in the act of "observing" them. Just a comment. — jgill
The soccer game metaphor is presented from 5:00 to about 16:37. Imagine a soccer game as reality, as the thing in itself. The physical world is likened to seeing the game on TV, on two different TV channels using two different TV monitors. Each TV channel uses its own camera so the images on the two TV monitors correspond but are not identical. — Art48
Per QM, the system could either be weakly measured (giving some information without destroying the superposition) or strongly measured resulting in rapid decoherence. Alternatively, the system could be transformed such that the probabilities change (including to certainty).
— Andrew M
Can you elaborate these three, Andrew? What would be the act of a weak measurement? And, how could the probabilities involved with a specific system be changed to certainty without some form of measurement? To me, such a change would require a cause, and the cause would be a matter of "fixing" the system, like cheating if you're a gambler. But if "fixing" was possible then there would be no real mystery unless only the cheaters had figured it out. — Metaphysician Undercover
Allowing that causes of change which come from the inside are very real, and distinct from causes of change which come from the outside, forces the conclusion that systems theory does not provide an adequate representation. — Metaphysician Undercover
Until Walmart opened its otherwise impervious doors. Contrary to most of the posts you’re getting, it has nothing to do with anybody actually looking at anything, with good or bad eyes. — noAxioms
That’s just a different ordering, but any ordering can have a counting number assigned to each item in order. It’s still ordered. — noAxioms
A Heisenberg cut is a form of relational expression, that a system on one side of the cut is in some state (as represented by the wave function) relative to the system on the other side of the cut. Yes, the placement of the cut is arbitrary. The cut was first introduced as an epistemic cut (what one system knows about the other) but became a metaphysical one once the interpretation moved away from its epistemic roots. — noAxioms
The proper analogy would be that jgill observed interference effects until he and his wife met up and she pointed out that she had been standing there all the time.
— Andrew M
So we say that jgill has extremely bad eyes, and all he sees until he's about three metres from his wife is a strange interference pattern? Suppose he's 50 metres away. How would he interpret the interference pattern as probabilities for the actual location of his wife? Consider that if this is a true analogy, the closer that he gets, he ought to be able to observe changes to the interference pattern which would increase his certainty. — Metaphysician Undercover
Wrong, but interesting. :smile: — jgill
"(any enumeration, not just an ordered one)"
How can any enumeration not be ordered? — noAxioms
If collapse isn’t physical and isn’t epistemological, then what is it? — noAxioms
"The dividing line between the system to be observed and the measuring apparatus is immediately defined by the nature of the problem but it obviously signifies no discontinuity of the physical process. For this reason there must, within limits, exist complete freedom in choosing the position of the dividing line." — Heisenberg cut - Wikipedia
Very clever experiments but I did notice
"As to how the day-to-day reality of objects that we observe, such as furniture and fruit, emerges from such a different and exotic quantum world, that remains a mystery."
— Macro-Weirdness: Quantum Microphone Puts Naked-Eye Object in 2 Places at Once — Wayfarer
The problem is not the interpretation of quantum mechanics. That’s getting things just backwards. The problem is the interpretation of classical mechanics. — Quantum Mechanics in Your Face - Sidney Coleman (transcript and slides)
Now people say the reduction of the wave packet occurs because it looks like the reduction of the wave packet occurs, and that is indeed true. What I’m asking you in the second main part of this lecture is to consider seriously what it would look like if it were the other way around—if all that ever happened was causal evolution according to quantum mechanics. What I have tried to convince you is that what it looks like is ordinary everyday life. — Quantum Mechanics in Your Face - Sidney Coleman (transcript and slides)
While some might take this and claim Coleman as an Everettian, note that there’s zero mention anywhere of many-worlds. Likely he found that an empty idea that explains nothing, so not worth mentioning. — Peter Woit
Question: You said in passing that you were a follower of Everett.
Coleman: Yeah, but that's a tricky thing to say. That's like saying you're a Christian. I mean, Everett wrote this one truly wonderful paper and then everyone got on their horse and rode off in all directions. The position I'm advocating is a position that, at least in my case, was certainly largely inspired by Everett's paper. Whether it's really Everett's position or not I would prefer not to discuss. — Quantum Mechanics in Your Face - Sidney Coleman (video)
It's not a valid analogy, though. The strangeness of the observer problem in physics is that the act of observation itself is instrumental in determination of the outcome. The proper analogy would be that, prior to you seeing your wife, she didn't exist in any specific location at all, she's not simply in an unknown location. — Wayfarer
Show me a macroscopic entity existing in superposition. — Wayfarer
A piezoelectric "tuning fork" has been constructed, which can be placed into a superposition of vibrating and non-vibrating states. The resonator comprises about 10 trillion atoms. — Quantum superposition - Wikipedia
Researchers have demonstrated a device that can pick up single quanta of mechanical vibration similar to those that shake molecules during chemical reactions, and have shown that the device itself, which is the width of a hair, acts as if it exists in two places at once—a "quantum weirdness" feat that so far had only been observed at the scale of molecules.
"This is a milestone," says Wojciech Zurek, a theorist at the Los Alamos National Laboratory in New Mexico. "It confirms what many of us believe, but some continue to resist—that our universe is 'quantum to the core'." — Macro-Weirdness: 'Quantum Microphone' Puts Naked-Eye Object in 2 Places at Once
As I thought had been established, the interference pattern in the double-slit experiments is independent of time and space (shown by its rate independence), thus indicating an extraspatiotemporal cause. — Wayfarer
This new ontological picture requires that we expand our concept of ‘what is real’ to include an extraspatiotemporal domain of quantum possibility,” write Ruth Kastner, Stuart Kauffman and Michael Epperson.
Considering potential things to be real is not exactly a new idea, as it was a central aspect of the philosophy of Aristotle, 24 centuries ago. An acorn has the potential to become a tree; a tree has the potential to become a wooden table. — Quantum mysteries dissolve if possibilities are realities - Tom Siegfried
So whether they're discharged one electron at a time, or at a faster (or is that 'higher'?) rate, then you still get the same pattern.
The fact that the effect can't be replicated by a physical (water) wave is, I think, due to the interference pattern not actually being 'waves' as such, but something for which the interference patterns of waves is just an analogy.
The argument that started this was about whether this means that time (being 'rate') is not a factor; which also that means that space (i.e. proximity of particles) is not a factor (as proximity is an aspect of space-time.) So, what is causing the interference pattern is outside, or not a function of, space-time.
Cantor's proof (by contradiction) shows that the set of real numbers is uncountable and thus can't be enumerated. Since the set of real numbers can't be enumerated, the diagonalized number therefore can't be computed.
— Andrew M
But that number (from Cantor’s proof) is generated from a countable list of rationals, not an uncountable list of reals. So it can be computed. It doesn’t require the ordering of the reals. That was my point,. — noAxioms
Copenhagen-style interpretations also generally deny a physical collapse. So, in that sense, Copenhagen and Everett/MWI agree (and disagree with physical collapse theories such as GRW).
— Andrew M
I am not really clear on what a formal statement of metaphysical Copenhagen interpretation would say. I’m more familiar of its roots as an epistemological interpretation where collapse (of what is known) very much does occur, but it is just a change in what is known about a system, not a physical change. They’ve since created a not-particularly well defined metaphysical interpretation under the same name, and if it doesn’t suggest physical collapse, I’d accept that statement. — noAxioms
Just refresh my memory about what Ryle said was the correct view of the matter, if this is the incorrect view? — Wayfarer
This book offers what may with reservations be described as a theory of the mind. But it does not give new information about minds. We possess already a wealth of information about minds, information which is neither derived from, nor upset by, the arguments of philosophers. The philosophical arguments which constitute this book are intended not to increase what we know about minds, but to rectify the logical geography of the knowledge which we already possess. — The Concept of Mind - Gilbert Ryle
There have always existed in the breasts of philosophers, including our own breasts, two conflicting tempers. I nickname them the "Reductionist" and the "Duplicationist" tempers, or the "Deflationary" and the "Inflationary" tempers. The slogan of the first temper is "Nothing But ..."; that of the other "Something Else as Well ..." — Thinking and Saying - Gilbert Ryle
Descartes left as one of his main philosophical legacies a myth which continues to distort the continental geography of the subject.
A myth is, of course, not a fairy story. It is the presentation of facts belonging to one category in the idioms appropriate to another. To explode a myth is accordingly not to deny the facts but to re-allocate them. And this is what I am trying to do.
To determine the logical geography of concepts is to reveal the logic of the propositions in which they are wielded, that is to say, to show with what other propositions they are consistent and inconsistent, what propositions follow from them and from what propositions they follow. The logical type or category to which a concept belongs is the set of ways in which it is logically legitimate to operate with it. The key arguments employed in this book are therefore intended to show why certain sorts of operations with the concepts of mental powers and processes are breaches of logical rules. — The Concept of Mind - Gilbert Ryle
There are the ducks, and there is the row. When you have seen the ducks, you have seen the row. But there are not four things. Yet the row is no ghost. — unenlightened
That is, the university is something we can see by virtue of being creatures with minds.
— Andrew M
I think Ryle, (and certainly I,) would prefer to say that the university is something that we do together; if the building is lost, and the library burns, we can meet under a tree for a tutorial on whatever we can remember of the course. — unenlightened
Ryle points out that the foreigner's puzzle arose from his inability to understand how to use the concept of 'the University'
— Andrew M
But Ryle is creating a straw man because no one thinks like that. — Andrew4Handel
In the UK we have The Open University where you study from home.
I think most people understand that a University is more than just a collection of buildings and that it is not just one building but a learning institution with a wide reach. — Andrew4Handel
It is not synonymous with the problem of squaring mental states with brain states and physicality with non physicality. — Andrew4Handel
There is a doctrine about the nature and place of minds which is so prevalent among theorists and even among laymen that it deserves to be described as the official theory. — The Concept of Mind - Gilbert Ryle
Such in outline is the official theory. I shall often speak of it, with deliberate abusiveness, as ‘the dogma of the Ghost in the Machine’. I hope to prove that it is entirely false, and false not in detail but in principle. It is not merely an assemblage of particular mistakes. It is one big mistake and a mistake of a special kind. It is, namely, a category-mistake. — The Concept of Mind - Gilbert Ryle
It is likely that many on the forum have read Ryle's work, so to what extent does his critique throw important light on the mind and body connection? — Jack Cummins
This book offers what may with reservations be described as a theory of the mind. But it does not give new information about minds. We possess already a wealth of information about minds, information which is neither derived from, nor upset by, the arguments of philosophers. The philosophical arguments which constitute this book are intended not to increase what we know about minds, but to rectify the logical geography of the knowledge which we already possess. — The Concept of Mind - Gilbert Ryle
A foreigner visiting Oxford or Cambridge for the first time is shown a number of colleges, libraries, playing fields, museums, scientific departments and administrative offices. He then asks ‘But where is the University? I have seen where the members of the Colleges live, where the Registrar works, where the scientists experiment and the rest. But I have not yet seen the University in which reside and work the members of your University.’ It has then to be explained to him that the University is not another collateral institution, some ulterior counterpart to the colleges, laboratories and offices which he has seen. The University is just the way in which all that he has already seen is organized. When they are seen and when their co-ordination is understood, the University has been seen. His mistake lay in his innocent assumption that it was correct to speak of Christ Church, the Bodleian Library, the Ashmolean Museum and the University, to speak, that is, as if ‘the University’ stood for an extra member of the class of which these other units are members. He was mistakenly allocating the University to the same category as that to which the other institutions belong. — The Concept of Mind - Gilbert Ryle
What do you think this means, to assume numbers which cannot be counted nor computed? — Metaphysician Undercover
Since axioms are produced by mathematicians who practise pure mathematics, and those people who apply mathematics have a choice as to which axioms are used, it would appear like we ought not use axioms like these, which necessitate that aspects of reality will be unintelligible to us. Instead, we ought to look for axioms which would render all of reality as intelligible. — Metaphysician Undercover
The computable numbers include the specific real numbers which appear in practice, including all real algebraic numbers, as well as e, π, and many other transcendental numbers. Though the computable reals exhaust those reals we can calculate or approximate, the assumption that all reals are computable leads to substantially different conclusions about the real numbers. The question naturally arises of whether it is possible to dispose of the full set of reals and use computable numbers for all of mathematics. This idea is appealing from a constructivist point of view, and has been pursued by what Errett Bishop and Fred Richman call the Russian school of constructive mathematics. — Computable numbers - Use in place of the reals - Wikipedia
I was seduced by infinity at an early age. Georg Cantor’s diagonality proof that some infinities are bigger than others mesmerized me, and his infinite hierarchy of infinities blew my mind. The assumption that something truly infinite exists in nature underlies every physics course I’ve ever taught at MIT — and, indeed, all of modern physics. But it’s an untested assumption, which begs the question: Is it actually true?
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Yet real numbers, with their infinitely many decimals, have infested almost every nook and cranny of physics, from the strengths of electromagnetic fields to the wave functions of quantum mechanics. We describe even a single bit of quantum information (qubit) using two real numbers involving infinitely many decimals.
Not only do we lack evidence for the infinite but we don’t need the infinite to do physics. Our best computer simulations, accurately describing everything from the formation of galaxies to tomorrow’s weather to the masses of elementary particles, use only finite computer resources by treating everything as finite. So if we can do without infinity to figure out what happens next, surely nature can, too — in a way that’s more deep and elegant than the hacks we use for our computer simulations.
Our challenge as physicists is to discover this elegant way and the infinity-free equations describing it—the true laws of physics. To start this search in earnest, we need to question infinity. I’m betting that we also need to let go of it. — Infinity Is a Beautiful Concept – And It’s Ruining Physics - Max Tegmark
I pondered over this for several days trying to understand the arguments. I still hold to what I said. The section you mention nicely shows that the x generated from the list of computable numbers is not itself a computable number, but I was speaking of the x generated from Cantor’s original proof of some real not being a rational number. That x is computable, but not rational, and thus cannot be used as evidence that there are some real numbers not computable.
The page you linked does show other ways to demonstrate exactly this, but the diagonalization method is not one of them. — noAxioms
Collapse seems to be a choice of classical description of a quantum state, in other words, an interpretation-dependent thing. In interpretations with ‘jumping’, yes, it happens all the time, everywhere. In interpretations without it (such as Everett’s relative state formulation, pre DeWitt’s MWI), it’s just a classical effect, not anything physical that happens. — noAxioms
"Presumably [the AI in the box] wouldn't. But an AI (unlike a human) could be run on a quantum computer as part of a carefully controlled experiment, thus testing physical collapse theories that differ from standard quantum theory."
I have serious doubts about that. It is a suggestion that there is an empirical difference between the interpretations, and yet I see not explicit prediction from any pair of interpretations that differ. — noAxioms
The fundamental idea is that the unitary evolution of the wave function describing the state of a quantum system is approximate. It works well for microscopic systems, but progressively loses its validity when the mass / complexity of the system increases.
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Such deviations can potentially be detected in dedicated experiments, and efforts are increasing worldwide towards testing them. — Objective-collapse theory - Wikipedia
This Article is intriguing. At first I thought they had found a way to reverse time in the quantum world, but rather they rejuvenated a photon, taking it back to a previous state.
The mathematics involved is probably linear (much is in the quantum world), since most non-linear systems are not reversible. — jgill
"Let’s begin with a thought-experiment: Imagine that all life has vanished from the universe, but everything else is undisturbed. Matter is scattered about in space in the same way as it is now, there is sunlight, there are stars, planets and galaxies—but all of it is unseen. There is no human or animal eye to cast a glance at objects, hence nothing is discerned, recognized or even noticed."
— Charles Pinter, Mind and the Cosmic Order — Wayfarer
"Objects in the unobserved universe have no shape, color or individual appearance, because shape and appearance are created by minds. Nor do they have features, because features correspond to categories of animal sensation. This is the way the early universe was before the emergence of life—and the way the present universe is outside the view of any observer."
— Charles Pinter, Mind and the Cosmic Order — Wayfarer
"The computable numbers are countable since they be put in a one-to-one correspondence with the natural numbers."
— Andrew M
Not to disagree, but an assertion like that requires a demonstration that they’re countable. — noAxioms
The computable numbers are an infinite set. We have provided an injective function g that maps every computable number to a single natural number: a Godel number. Any set with such a function is countable, and therefore computable numbers are countable. — Alan Turing and the Countability of Computable Numbers - Adam A. Smith
"However the real numbers are not countable per Cantor's diagonalization proof. Thus there are some real numbers that are not computable."
— Andrew M
Interestingly, the real number generated by Cantor's diagonalization proof is a computable number, so I’m not sure if this counts as evidence that there are some real numbers not computable. Once again, not disagreeing with the conclusion, only with how it was reached. — noAxioms
OK, they managed to test something whose outcome (the CHSH inequality violation) was already predicted by quantum theory. It’s a new test, but not one that changed the theory or any of its interpretations in any way. — noAxioms
Thanks for the larger context Bell statement. I agree with it fully. What is ‘jumping’ in that quote? “Do we not have jumping then all the time?”. — noAxioms
Meanwhile, I still don’t see what the AI in the box will do. Bell’s statement is pretty clear that a real human in there wouldn’t serve any special role or purpose, so why would an AI be any different? — noAxioms
That sounds mostly reasonable, but the branching part based on something making observations still bothers me a bit. What is the branching mechanism? Perhaps I should have started with that question instead. — Marchesk
To see an interference pattern, you'd have to perform a joint measurement on the two qubits together. But what if the second qubit was a stray photon, which happened to pass through your experiment on its way to the Andromeda galaxy? Indeed, when you consider all the junk that might be entangling itself with your delicate experiment -- air molecules, cosmic rays, geothermal radiation ... well, whatever, I'm not an experimentalist -- it's as if the entire rest of the universe is constantly trying to "measure" your quantum state, and thereby force it to become classical! Sure, even if your quantum state does collapse (i.e. become entangled with the rest of the world), in principle you can still get the state back -- by gathering together all the particles in the universe that your state has become entangled with, and then reversing everything that's happened since the moment of collapse. That would be sort of like Pamela Anderson trying to regain her privacy, by tracking down every computer on Earth that might contain photos of her! — Decoherence and Hidden Variables - Scott Aaronson
I don’t agree that Nagel’s diagnosis is erroneous. I think he pinpoints something real and insidious. — Wayfarer
And Bell's Theorem did nothing to validate Einstein's realist objections to 'spooky action at a distance'. — Wayfarer
You’ve said that before, and even though I obviously agree, I don’t think it’s as obvious, nor as insignificant, as you make it seem. As you might know, one of Thomas Nagel’s books is called ‘The View from Nowhere’. His point is to critique the widespread understanding that science provides a ‘view from nowhere’, meaning a view that is uncontaminated by anything we deem ‘subjective’, the aim being to arrive at a view which is at once universal and objective. — Wayfarer
The fact that observation has an unavoidably subjective dimension is the very thing that Einstein strenuously objected to - ‘does the moon continue to exist when nobody’s looking at it?’, he asked. He strongly believed that there was a reality that existed just so, independently of any act of observation, and it was science’s job to discern that. Insofar as it had to make concessions to ‘the method of observation’, then quantum mechanics was, to him, obviously incomplete. Wasn’t that the gist of the Einstein-Bohr debates? — Wayfarer
Both qualify as a computable number. The diagonalization method used... — noAxioms
"So, if one accepts the authors' definitions for an observer and measurement, then one of the assumptions of free choice, locality, and observer-independent facts must be false."
That just sounds like Bell’s theorem (old news). What in 2019 was added to that? — noAxioms
Sorry, but I don’t see what the AI adds that any simple device (like the circuit on the camera) doesn’t. — noAxioms
I like Carroll’s definition of observer, appropriate for something like MWI.
'As John Bell inquired, "Was the wave function waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer for some highly qualified measurer—with a PhD?"'
— Andrew M
This does not seem to reference that definition, but more of the dictionary definition of observer. — noAxioms
It would seem that the theory [quantum mechanics] is exclusively concerned about "results of measurement", and has nothing to say about anything else. What exactly qualifies some physical systems to play the role of "measurer"? Was the wavefunction of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system ... with a Ph.D.? If the theory is to apply to anything but highly idealized laboratory operations, are we not obliged to admit that more or less "measurement-like" processes are going on more or less all the time, more or less everywhere. Do we not have jumping then all the time?
The first charge against "measurement", in the fundamental axioms of quantum mechanics, is that it anchors the shifty split of the world into "system" and "apparatus". A second charge is that the word comes loaded with meaning from everyday life, meaning which is entirely inappropriate in the quantum context. When it is said that something is "measured" it is difficult not to think of the result as referring to some preexisting property of the object in question. This is to disregard Bohr's insistence that in quantum phenomena the apparatus as well as the system is essentially involved. If it were not so, how could we understand, for example, that "measurement" of a component of "angular momentum" ... in an arbitrarily chosen direction ... yields one of a discrete set of values? When one forgets the role of the apparatus, as the word "measurement" makes all too likely, one despairs of ordinary logic ... hence "quantum logic". When one remembers the role of the apparatus, ordinary logic is just fine.
In other contexts, physicists have been able to take words from ordinary language and use them as technical terms with no great harm done. Take for example the "strangeness", "charm", and "beauty" of elementary particle physics. No one is taken in by this "baby talk". ... Would that it were so with "measurement". But in fact the word has had such a damaging effect on the discussion, that I think it should now be banned altogether in quantum mechanics. — John Bell, Against 'Measurement'
Ever seen the Andrei Linde interview on Closer To Truth? He talks explicitly about the role of the observer. — Wayfarer
When one remembers the role of the apparatus, ordinary logic is just fine. — John Bell, Against 'Measurement'
It has nothing to do with consciousness or intelligence (of course). An “observation” in quantum mechanics happens whenever any out-of-equilibrium macroscopic system becomes entangled with the quantum system being measured
— Squelching Boltzmann Brains (And Maybe Eternal Inflation) - Sean Carroll
That is an a priori assertion, but which really could only ever be validated by observation. — Wayfarer
It's still weird to me that the observer is a necessary component of making sense of MWI, since decohered branches are still in universal superposition, which is what infinite De sitter space will become, except without the decohered observers. — Marchesk
... It has nothing to do with consciousness or intelligence (of course). An “observation” in quantum mechanics happens whenever any out-of-equilibrium macroscopic system becomes entangled with the quantum system being measured. It will then decohere (become entangled with the wider environment), which causes a splitting of the wave function into separate branches.
It’s key that the macroscopic device in question starts out far from equilibrium. Otherwise it would already be entangled with everything, and the measurement/splitting process couldn’t occur.
...
The informal notion of an “observer” requires a macroscopic system that is out of equilibrium. In de Sitter space, everything is in equilibrium. — Squelching Boltzmann Brains (And Maybe Eternal Inflation) - Sean Carroll
The standard story says that the inflaton field undergoes quantum fluctuations, which then get imprinted as fluctuations in density. What we’re saying is that the inflaton doesn’t actually “fluctuate,” it’s just in some calculable quantum state. But there’s nothing “observing” it, causing decoherence and branching of the wave function. At least, not while inflation is going on. But when inflation ends, the universe reheats into a hot plasma of matter and radiation. That actually does lead to decoherence and branching — the microscopic states of the plasma provide an environment that becomes entangled with the large-scale fluctuations of the inflaton, effectively measuring it and collapsing the wave function. So in our picture, all of the textbook predictions for inflation perturbations remain unchanged. — Squelching Boltzmann Brains (And Maybe Eternal Inflation) - Sean Carroll
I can still express the length √2 with two characters, a very finite state. Humans deal only with such representable numbers, and they’re countable.— noAxioms
Yes, computable numbers.
— Andrew M
OK, maybe, but it’s a very different definition. Is there an example of something that isn’t in this set? — noAxioms
"That question seems relevant to the physical Church-Turing thesis (Church-Turing-Deutsch principle) which says that any bounded physical system can be simulated by a Turing machine to any desired precision."
— Andrew M
Does the statement above apply to non-classical physical systems? Can it simulate say a quantum computer to arbitrary precision? — noAxioms
Another interesting note about the above statement is that a Turing machine cannot simulate itself, which is not a violation of the statement. — noAxioms
OK, I said I’d get back on this one. I admittedly get lost in the complex examples, but I did at least want to comment on some of the assumptions the paper is making, assumptions which are very interpretation dependent. The topic here is about how MWI would handle it. — noAxioms
An observer is apparently a clerk, reacting to a measurement and putting into some non-volatile state. A digital camera for instance has a CCD (the measurement device) and an SD card (the persistent state) and a bit of circuitry (the observer) to move the data from the CCD to the SD card. — noAxioms
This is nothing particularly special, but they give it a very special role in the paper:
The observer’s role as final arbiter of universal facts [1] was imperilled by the advent of 20th century science.
…
in quantum theory, all physical processes are continuous and deterministic, except for observations, which are proclaimed to be instantaneous and probabilistic.
— PPGBKBRF
It seems that they’ve given this clerical role some special metaphysical status, that of arbiter of what is fact or not, and also the only physical process which is probabilistic instead of deterministic. I’m not sure if they’re asserting these things and strawman arguments to knock down or they’re actually pushing this. — noAxioms
for the no-go theorem we tested here [4] it is sufficient that [the observers] perform a measurement and record the outcome. — Experimental test of local observer-independence - Proietti, et al., 2019
Modulo the potential loopholes and accepting the photons’ status as observers, the violation of inequality (2) implies that at least one of the three assumptions of free choice, locality, and observer-independent facts must fail." — Experimental test of local observer-independence - Proietti, et al., 2019
Wigner can now perform an interference experiment in an entangled basis containing the states of Eq. (1) to verify that the photon and his friend’s record are indeed in a superposition—a “fact” from his point of view
— PPGBKBRF
Rightly so. There are no facts, just points of view. The friend is measured to be in superposition of having recorded one fact and of having recorded a different fact, pretty much demonstrating a lack of universal facts. Establishment of those universal facts were the only apparent role of these observers, so with that neatly shot down, the observer plays no role at all.
This pretty much answers the topic title here, at least from that article’s description. Facts are relative to a system state, which makes it ‘observer dependent’ if you want to apply the label of ‘observer’ to a specific system state, but I see no point in the special label. — noAxioms
I can still express the length √2 with two characters, a very finite state. Humans deal only with such representable numbers, and they’re countable. — noAxioms
Actual numbers in nature (such as the ratio of the half lives of two specific isotopes) are not in this countable set. I have a hard time with a model of the universe that requires only the former sort of number, such as one would get in a simulation. Actual numbers are more analog, like ‘so big’ with your hands held apart. — noAxioms
Going to get back to you on this one. Interesting read, but the introduction is already full of interpretation dependent assumptions, such as counterfactual statements. I will look at it from my relational perspective which doesn’t make those assumptions, but thus far I’ve not read enough to really comment on it. — noAxioms
Another option is to give up observer independence completely by considering facts only relative to observers [24], or by adopting an interpretation such as QBism, where quantum mechanics is just a tool that captures an agent’s subjective prediction of future measurement outcomes [25]. — Experimental test of local observer-independence - Proietti, et al., 2019
Ouch. It would really such if nature allowed such approximations. I’d always envisioned pure mathematics behind the physics, not digital mathematics where all numbers are representable with finite states. — noAxioms
Geometrically, the square root of 2 is the length of a diagonal across a square with sides of one unit of length; this follows from the Pythagorean theorem. — Square root of 2
The discussion was about observer effect (the observer causing effects), not observed effects (effects merely noticed by the observer), Relativity effects seem to fall under the latter category, prompting my foul call. — noAxioms
"A related test has been carried out at a microscopic level (using photons instead of AI's) where it was shown that physical collapse does not occur." - Andrew M
Not sure what this is. Got a link for this one? — noAxioms
In a state-of-the-art 6-photon experiment, we realise this extended Wigner’s friend scenario, experimentally violating the associated Bell-type inequality by 5 standard deviations. If one holds fast to the assumptions of locality and free-choice, this result implies that quantum theory should be interpreted in an observer-dependent way. — Experimental test of local observer-independence - Proietti, et al., 2019
What if the ratio isn’t rational? — noAxioms
For any wave function with irrational squared-amplitudes there exist arbitrarily similar wave functions with rational squared-amplitudes (as the rationals are a dense subset of the reals). — Self-Locating Uncertainty and the Origin of Probability in Everettian Quantum Mechanics - Sebens and Carroll, 2015
"While the laws of physics are the same for all observers, they may describe things differently from their respective reference frames." - Andrew M
That’s quite different than the interaction (measurement) actually changing the system being measured, which is what this topic is about. — noAxioms
In a state-of-the-art 6-photon experiment, we realise this extended Wigner’s friend scenario, experimentally violating the associated Bell-type inequality by 5 standard deviations. If one holds fast to the assumptions of locality and free-choice, this result implies that quantum theory should be interpreted in an observer-dependent way. — Experimental test of local observer-independence - Proietti, et al., 2019
So I'll give you the gist in a more straight forward way. — Metaphysician Undercover