Evidence record

What actually happens when we look?

Every sentence on the exploration belongs to at least one claim below. Each says what kind of statement it is, what it rests on, what the evidence does not establish, and how far it was checked. Nothing here is a score, and none of it is a verdict on a belief or a theory.

Last checked 24 September 2026.

Source checked: 61
Partly checked: 2
Presented as open: 3
A judgement, not a fact: 1

If something here is wrong, misquoted, out of date or unfair, write to support@unknownoceans.com and give the claim number, which does not change.

What the question takes for granted

A question about what a well-confirmed theory describes. The predictions are not in dispute; what the theory says is happening during a measurement is, and most proposed answers make the same predictions.

Something definite happens when a measurement is made
Contested
Many-worlds denies that one outcome occurs; QBism denies the quantum state describes what happens. The question’s “what actually happens” is itself one of the positions.
Quantum mechanics is empirically correct in the domain tested
Established
Every experiment so far agrees with it, including the tests designed to find a failure.
Experiment could in principle decide between the pictures
Open
Only for accounts that change the predictions, such as collapse models; the others are built to agree with the standard theory.

How the question is labelled

Claim: The measurement problem

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: Measurement

Kind: Framing. Signposting. It asserts nothing a source could check.

The question

Claim: Quantum mechanics predicts what our instruments record better than any theory before it, and leaves open what is going on.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

A compression of what two encyclopedia entries say: unmatched predictive success, and no agreement about what world the theory describes.

Supports
Collapse Theoriesopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: quantum mechanics is a theory which is excellent (in fact it has an unprecedented success in the history of science) in telling us everything about what we observe, but it meets with serious difficulties in telling us what there is.
Supports
Quantum Mechanicsopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: in that capacity, it is spectacularly successful: in terms of power and precision, head and shoulders above any theory we have ever had
Supports
Quantum Mechanicsopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: The question of what kind of a world it describes, however, is controversial; there is very little agreement, among physicists and among philosophers, about what the world is like according to quantum mechanics.

What this does not establish

“Better than any theory before it” is the entries’ judgement of power and precision, not a measured ranking.

Later work looked for

Crossref, 2016 on, "measurement problem interpretation experiment": no experiment reported that decides between the major approaches; SEP entries revised 2022 to 2026 say the same.

Corrected

24 September 2026. Previously: “Quantum mechanics predicts everything correctly and says nothing about what is going on.” "Predicts everything correctly" is a universal claim no source carries, and "says nothing" overstates: the theory’s formalism is well understood and its interpretation is disputed, not absent. Narrowed to what SEP "Collapse Theories" and "Quantum Mechanics" say.

Claim 3 · checked 24 September 2026 · AI-assisted audit

Claim: The most precisely tested theory in science comes with a set of mutually exclusive stories about what it describes,

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

The “stories” are the approaches to the measurement problem the page sets out in its last section.

Supports
Quantum Mechanicsopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: in that capacity, it is spectacularly successful: in terms of power and precision, head and shoulders above any theory we have ever had
Supports
Philosophical Issues in Quantum Theorysection 4.2
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: There are approaches that involve a denial that a quantum wave function (or any other way of representing a quantum state) yields a complete description of a physical system. ... There are approaches that involve modification of the dynamics to produce a collapse of the quantum state in appropriate circumstances.

Later work looked for

Crossref, 2016 on, "measurement problem interpretation experiment": no experiment reported that decides between the major approaches; SEP entries revised 2022 to 2026 say the same.

Claim 4 · checked 24 September 2026 · AI-assisted audit

Claim: and no experiment has yet decided between them.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: If one accepts that Everettians have a solution to the evidential problem, then, among the major lines of approach, none is favored in a straightforward way by the empirical evidence.
Qualifies
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: collapse theories have the intriguing feature of reproducing very close approximations to quantum probabilities for all experiments that have been performed so far but departing from the quantum probabilities for other conceivable experiments. This permits, in principle, an empirical discrimination between such theories and no-collapse theories.
Collapse theories can in principle be told apart from the others by experiment, and one version has been ruled out; none has been confirmed.

What this does not establish

The encyclopedia’s statement is conditional on Everettians solving their evidential problem. Experiments have ruled out one version of one collapse model (claim 74), which narrows the field without deciding it.

Later work looked for

Crossref, 2016 on, "measurement problem interpretation experiment": no experiment reported that decides between the major approaches; SEP entries revised 2022 to 2026 say the same.

Corrected

24 September 2026. Previously: “and no experiment has distinguished between them.” Experiments have distinguished one proposal from quantum mechanics: the parameter-free Diósi-Penrose model was ruled out (Donadi and others 2021). What no experiment has done is decide between the approaches.

Claim 5 · checked 24 September 2026 · AI-assisted audit

Claim: Quantum mechanics is the most accurate theory ever constructed.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum Mechanicsopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: in that capacity, it is spectacularly successful: in terms of power and precision, head and shoulders above any theory we have ever had
Supports
Collapse Theoriesopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: quantum mechanics is a theory which is excellent (in fact it has an unprecedented success in the history of science) in telling us everything about what we observe, but it meets with serious difficulties in telling us what there is.

What this does not establish

A judgement two reference works make about power and precision; there is no formal ranking of theories by accuracy.

Later work looked for

Crossref, 2016 on, "measurement problem interpretation experiment": no experiment reported that decides between the major approaches; SEP entries revised 2022 to 2026 say the same.

Claim 6 · checked 24 September 2026 · AI-assisted audit

Claim: Some of its predictions have been confirmed to twelve decimal places.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Measurement of the Electron Magnetic Momentabstract; main text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Measurement
The source reads: The most precisely determined property of an elementary particle tests the most precise prediction of the Standard Model (SM) to 1 part in 10 12.
Supports
Measurement of the Electron Magnetic Momentmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Measurement
The source reads: In the most precise confrontation of theory and measurement, the SM prediction agrees to 1 part in 1012.

What this does not establish

The prediction is the standard model’s, of which quantum electrodynamics is the main part; one part in 10¹² of a quantity close to 1 is agreement in about the twelfth decimal place.

Later work looked for

Crossref, 2023 on, "electron magnetic moment measurement" and "fine-structure constant measurement discrepancy": no newer electron measurement or resolution of the fine-structure disagreement found; nothing changes it.

Claim 7 · checked 24 September 2026 · AI-assisted audit

Claim: It also contains a step, right in the middle, where the mathematics stops describing a physical process and starts describing what happens when a measurement is made.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum Mechanicssection 3, Dynamics
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: has the effect of collapsing the system ... This is known as the Collapse Postulate. Which particular ... it collapses into is a matter of probability, and the probabilities are given by a rule known as Born’s Rule
Supports
Quantum Mechanicssection 3, Dynamics
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: The distinction between contexts of type 1 and 2 remains to be made out in quantum mechanical terms; nobody has managed to say in a completely satisfactory way, in the terms provided by the theory, which contexts are measurement contexts

What this does not establish

This is the theory as ordinarily formulated, with a collapse postulate. Whether any real process corresponds to that step is, in the entry’s words, an open interpretive question.

Other readings

Many-worlds and pilot-wave theory keep the smooth evolution throughout and treat collapse as apparent; collapse models make it a physical process.

Later work looked for

How a theory or interpretation is set out; not a finding later work revises.

Corrected

24 September 2026. Previously: “It also contains a step, right in the middle, where the mathematics stops describing a physical process and starts describing what happens when somebody looks.” The collapse postulate is stated for measurement contexts, not for a person looking; SEP "Philosophical Issues in Quantum Theory" 4.5 notes that none of the mainstream approaches gives conscious observers a special physical role.

Claim 8 · checked 24 September 2026 · AI-assisted audit

Claim: A century later, there is no agreement about what that step means.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum Mechanicsopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: The question of what kind of a world it describes, however, is controversial; there is very little agreement, among physicists and among philosophers, about what the world is like according to quantum mechanics.
Context
Quantum-Bayesian and Pragmatist Views of Quantum Theorysection 1.3
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Some have followed Dirac (1930) and von Neumann (1932) in assuming that a measurement is a physical process in which a quantum state almost never evolves linearly but rather changes discontinuously and stochastically
Dates the measurement step to Dirac (1930) and von Neumann (1932), a little under a century ago.

What this does not establish

“A century” is approximate: the collapse postulate was set out by Dirac in 1930 and von Neumann in 1932.

Claim 9 · checked 24 September 2026 · AI-assisted audit

What the experiments have settled

Claim: What the experiments have settled

Kind: Framing. Signposting. It asserts nothing a source could check.

The predictions work, without exception

Claim: The predictions work, without exception

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: collapse theories have the intriguing feature of reproducing very close approximations to quantum probabilities for all experiments that have been performed so far but departing from the quantum probabilities for other conceivable experiments. This permits, in principle, an empirical discrimination between such theories and no-collapse theories.
Supports
Philosophical Issues in Quantum Theorysection 2.3
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Standard quantum mechanics works very well.

What this does not establish

Without exception so far: the encyclopedia’s claim is about the experiments that have been performed.

Later work looked for

Crossref, 2016 on, "test of quantum mechanics", "wave function collapse models bounds" and "matter-wave interference": the 2026 sodium-cluster interference reports no breakdown and collapse tests continue to bound, not detect, deviations; nothing changes it.

Claim 11 · checked 24 September 2026 · AI-assisted audit

Claim: Every experiment performed so far has agreed with its predictions, including those designed to catch it failing.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

The tests designed to catch it failing are the collapse-model searches and large-mass interference described further down the page.

Supports
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: collapse theories have the intriguing feature of reproducing very close approximations to quantum probabilities for all experiments that have been performed so far but departing from the quantum probabilities for other conceivable experiments. This permits, in principle, an empirical discrimination between such theories and no-collapse theories.
Supports
Collapse Theoriessection 7
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: specific bounds have already been obtained for the parameters characterizing the theories under investigation
Supports
Probing quantum mechanics with nanoparticle matter-wave interferometryDiscussion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Observing matter-wave interference of the most massive objects to date reveals no breakdown of the quantum superposition principle related to mass or size alone.

Later work looked for

Corrected

24 September 2026. Previously: “Every experimental test of quantum mechanics has agreed with it.” Reworded to match what SEP says ("for all experiments that have been performed so far"), and to name the tests that probe for a failure.

Claim 12 · checked 24 September 2026 · AI-assisted audit

Claim: No result has yet required a change to the formalism.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: All of the above-mentioned approaches are consistent with observation.
Supports
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: collapse theories have the intriguing feature of reproducing very close approximations to quantum probabilities for all experiments that have been performed so far but departing from the quantum probabilities for other conceivable experiments. This permits, in principle, an empirical discrimination between such theories and no-collapse theories.

Later work looked for

Claim 14 · checked 24 September 2026 · AI-assisted audit

Claim: The electron’s magnetic moment is the sharpest case.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Measurement of the Electron Magnetic Momentabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Measurement
The source reads: The most precisely determined property of an elementary particle tests the most precise prediction of the Standard Model (SM) to 1 part in 10 12.
Supports
Measurement of the Electron Magnetic Momentmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Measurement
The source reads: The most precise SM prediction is the electron magnetic moment in Bohr magnetons

Later work looked for

Claim 15 · checked 24 September 2026 · AI-assisted audit

Claim: It has been measured to 0.13 parts per trillion, and it tests the most precise prediction the standard model makes to one part in a trillion.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Measurement of the Electron Magnetic Momentabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Measurement
The source reads: 1.001 159 652 180 59 (13) [0.13 ppt], is determined 2.2 times more accurately than the value that stood for 14 years.
Supports
Measurement of the Electron Magnetic Momentabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Measurement
The source reads: The most precisely determined property of an elementary particle tests the most precise prediction of the Standard Model (SM) to 1 part in 10¹².
Notation restored: The superscript restored from the glyph positions in the arXiv PDF (arXiv:2209.13084, read with pdftotext -bbox), 2026-09-24. The text as extracted reads: The most precisely determined property of an elementary particle tests the most precise prediction of the Standard Model (SM) to 1 part in 10 12.

What this does not establish

One group’s measurement, in a single-electron trap; it agrees with the group’s own 2008 value.

Later work looked for

Corrected

24 September 2026. Previously: “It has been measured to thirteen digits, and it tests the most precise prediction the standard model makes to one part in a trillion.” "Thirteen digits" does not match the paper, which gives a value to fifteen significant figures with an uncertainty of 0.13 parts per trillion. The paper’s own figure is used.

Claim 16 · checked 24 September 2026 · AI-assisted audit

Claim: What limits that test now is not the measurement but disagreeing values of the fine-structure constant, which the prediction needs.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Measurement of the Electron Magnetic Momentabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Measurement
The source reads: The test would improve an order of magnitude if the uncertainty from discrepant measurements of the fine structure constant α is eliminated since the SM prediction is a function of α.

Later work looked for

Corrected

24 September 2026. Previously: “” Added: the paper says the comparison would improve tenfold if the disagreement between measurements of the fine-structure constant were resolved, which a reader needs in order to read "one part in a trillion" correctly.

Claim 17 · checked 24 September 2026 · AI-assisted audit

The world is not locally realistic

Claim: The world is not locally realistic

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresmain text, conclusion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Our observation of a loophole-free Bell inequality violation thus rules out all local realist ... theories that accept that the number generators timely produce a free random bit and that the outputs are final once recorded in the electronics.
Supports
The Nobel Prize in Physics 2022prize summary
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026
The source reads: The Nobel Prize in Physics 2022 was awarded jointly to Alain Aspect, John F. Clauser and Anton Zeilinger "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science"

What this does not establish

Conditional, as every Bell test is: the result excludes local realist theories that accept the setting choices were free and the recorded outcomes final. The page’s own passage says so.

Later work looked for

Crossref, 2016 on, "loophole-free Bell inequality violation": later loophole-free tests and reviews confirm the violation; none removes the setting-independence assumption; nothing changes it.

Claim 18 · checked 24 September 2026 · AI-assisted audit

Claim: John Bell showed in 1964 that any theory in which particles have definite pre-existing properties and no influence travels faster than light must obey certain statistical limits.

Kind: A proved result. A mathematical theorem, as its proof or a reference work states it. What it says about the world depends on how well the mathematics fits.
Review: Source checked. The cited passage was read, and it says this.

The “statistical limits” are Bell’s inequality on the correlations between distant measurements.

Supports
On the Einstein Podolsky Rosen paradoxsection I, Introduction
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Primary text
The source reads: In this note that idea will be formulated mathematically and shown to be incompatible with the statistical predictions of quantum mechanics.
Supports
On the Einstein Podolsky Rosen paradoxsection I, Introduction
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Primary text
The source reads: It is the requirement of locality, or more precisely that the result of a measurement on one system be unaffected by operations on a distant system with which it has interacted in the past, that creates the essential difficulty.
Supports
On the Einstein Podolsky Rosen paradoxsection I, Introduction
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Primary text
The source reads: should be supplemented by additional variables. These additional variables were to restore to the theory causality and locality
Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresopening
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Bell showed that in any local realist theory the correlations between distant measurements satisfy an inequality and, moreover, that this inequality can be violated according to quantum theory.

What this does not establish

Bell’s locality condition is that a measurement result is unaffected by operations on a distant system; “no influence travels faster than light” is the usual gloss.

Claim 19 · checked 24 September 2026 · AI-assisted audit

Claim: Quantum mechanics predicts violations of those limits.

Kind: A proved result. A mathematical theorem, as its proof or a reference work states it. What it says about the world depends on how well the mathematics fits.
Review: Source checked. The cited passage was read, and it says this.

Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresopening
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Bell showed that in any local realist theory the correlations between distant measurements satisfy an inequality and, moreover, that this inequality can be violated according to quantum theory.
Supports
On the Einstein Podolsky Rosen paradoxsection I, Introduction
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Primary text
The source reads: In this note that idea will be formulated mathematically and shown to be incompatible with the statistical predictions of quantum mechanics.

Claim 20 · checked 24 September 2026 · AI-assisted audit

Claim: Those violations have been measured.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresabstract; main text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: We perform 245 trials testing the CHSH-Bell inequality
Supports
The Nobel Prize in Physics 2022prize summary
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026
The source reads: The Nobel Prize in Physics 2022 was awarded jointly to Alain Aspect, John F. Clauser and Anton Zeilinger "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science"
Context
Experimental Test of Bell’s Inequalities Using Time-Varying Analyzersabstract
Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Physical systems · Experiment
The source reads: The results are in good agreement with quantum mechanical predictions but violate Bell's inequalities by 5 standard deviations.

Later work looked for

Crossref, 2016 on, "loophole-free Bell inequality violation": later loophole-free tests and reviews confirm the violation; none removes the setting-independence assumption; nothing changes it.

Claim 21 · checked 24 September 2026 · AI-assisted audit

Claim: Each round of experiments closed another way the result could have been an artefact rather than a fact about the world, until in 2015 a test was reported that needed none of the extra assumptions earlier ones had.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: because of experimental limitations, all experiments to date required additional assumptions to obtain a contradiction with local realism, resulting in loopholes
Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Here we report on a Bell experiment that is free of any such additional assumption
Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Our experiment realizes the first Bell test that simultaneously addresses both the detection loophole and the locality loophole.

What this does not establish

245 trials, with a p-value of 0.039 in the authors’ analysis. Two other loophole-free tests were reported the same year and are not cited here.

Later work looked for

Crossref, 2016 on, "loophole-free Bell inequality violation": later loophole-free tests and reviews confirm the violation; none removes the setting-independence assumption; nothing changes it.

Corrected

24 September 2026. Previously: “until in 2015 a test was reported that needed no extra assumption about the apparatus at all.” Hensen and others remove the fair-sampling, locality and memory assumptions, but their conclusion still assumes the random setting choices were free and the outputs final; "no extra assumption at all" overstated it.

Claim 22 · checked 24 September 2026 · AI-assisted audit

Claim: Its authors add that no Bell test can exclude every conceivable local theory.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresmain text, conclusion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Strictly speaking, no Bell experiment can exclude the infinite number of conceivable local realist theories, because it is fundamentally impossible to prove when and where free random input bits and output values came into existence

Corrected

24 September 2026. Previously: “” Added from the paper’s own conclusion, so the result is not read as more than its authors claim.

Claim 23 · checked 24 September 2026 · AI-assisted audit

Claim: Unless the choice of settings was itself somehow fixed in advance, the world is not a collection of objects with definite independent properties interacting only locally.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresmain text, conclusion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Our observation of a loophole-free Bell inequality violation thus rules out all local realist ... theories that accept that the number generators timely produce a free random bit and that the outputs are final once recorded in the electronics.

What this does not establish

The paper’s condition has a second part, that outputs are final once recorded. Which of locality or realism fails is not settled by the experiment.

Other readings

Pilot-wave theory keeps definite positions and gives up locality; many-worlds is argued by its defenders to keep locality by giving up single outcomes; superdeterministic views deny the free choice of settings.

Later work looked for

Crossref, 2016 on, "loophole-free Bell inequality violation": later loophole-free tests and reviews confirm the violation; none removes the setting-independence assumption; nothing changes it.

Corrected

24 September 2026. Previously: “Whatever the world is, it is not a collection of objects with definite independent properties interacting only locally.” Hensen and others rule out local realist theories only on the assumption that the setting choices were free; the conclusion now carries that condition.

Claim 24 · checked 24 September 2026 · AI-assisted audit

Claim: From theorem to measurement to prize

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: 1964

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Source checked. The cited passage was read, and it says this.

Supports
On the Einstein Podolsky Rosen paradoxCrossref record
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026
The source reads: issued 1964-11-01

Claim 26 · checked 24 September 2026 · AI-assisted audit

Claim: Bell states the statistical limits any locally realistic theory must obey.

Kind: A proved result. A mathematical theorem, as its proof or a reference work states it. What it says about the world depends on how well the mathematics fits.
Review: Source checked. The cited passage was read, and it says this.

Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresopening
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Bell showed that in any local realist theory the correlations between distant measurements satisfy an inequality and, moreover, that this inequality can be violated according to quantum theory.
Supports
On the Einstein Podolsky Rosen paradoxsection I, Introduction
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Primary text
The source reads: In this note that idea will be formulated mathematically and shown to be incompatible with the statistical predictions of quantum mechanics.

Claim 27 · checked 24 September 2026 · AI-assisted audit

Claim: 1982

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Partly checked. Only part of the source could be read. What was not read is listed.

Supports
Experimental Test of Bell’s Inequalities Using Time-Varying Analyzersrecord
Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026
The source reads: Physical Review Letters 49, 1804 (1982)

What this does not establish

Read as abstract and record only.

Claim 28 · checked 24 September 2026 · AI-assisted audit

Claim: Aspect measures violations of them, with loopholes a determined sceptic can still use.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Partly checked. Only part of the source could be read. What was not read is listed.

Supports
Experimental Test of Bell’s Inequalities Using Time-Varying Analyzersabstract
Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Physical systems · Experiment
The source reads: The results are in good agreement with quantum mechanical predictions but violate Bell's inequalities by 5 standard deviations.
Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: because of experimental limitations, all experiments to date required additional assumptions to obtain a contradiction with local realism, resulting in loopholes

What this does not establish

The 1982 paper was read only as its abstract; that earlier tests left loopholes is Hensen and others’ statement. Aspect worked with Dalibard and Roger, and earlier experiments, by Clauser among others, had already measured violations.

Later work looked for

Crossref, 2016 on, "loophole-free Bell inequality violation": later loophole-free tests and reviews confirm the violation; none removes the setting-independence assumption; nothing changes it.

Claim 29 · checked 24 September 2026 · AI-assisted audit

Claim: 2015

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Source checked. The cited passage was read, and it says this.

Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Here we report on a Bell experiment that is free of any such additional assumption
Nature 526, 682 to 686, published 2015.

Claim 30 · checked 24 September 2026 · AI-assisted audit

Claim: A loophole-free test closes the detection and locality loopholes together.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresmain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Our experiment realizes the first Bell test that simultaneously addresses both the detection loophole and the locality loophole.

What this does not establish

The freedom of the setting choices remains an assumption; no experiment removes it.

Later work looked for

Crossref, 2016 on, "loophole-free Bell inequality violation": later loophole-free tests and reviews confirm the violation; none removes the setting-independence assumption; nothing changes it.

Corrected

24 September 2026. Previously: “Loophole-free tests close the last of them.” "The last of them" overstated: the authors say no Bell test can exclude every conceivable local theory, and their result assumes free setting choices. They claim the first test addressing both main loopholes at once.

Claim 31 · checked 24 September 2026 · AI-assisted audit

Claim: 2022

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Source checked. The cited passage was read, and it says this.

Supports
The Nobel Prize in Physics 2022prize summary
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026
The source reads: The Nobel Prize in Physics 2022 was awarded jointly to Alain Aspect, John F. Clauser and Anton Zeilinger "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science"

Claim 32 · checked 24 September 2026 · AI-assisted audit

Claim: Aspect, Clauser and Zeilinger share the Nobel Prize in Physics for the experiments.

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Source checked. The cited passage was read, and it says this.

Supports
The Nobel Prize in Physics 2022prize summary
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026
The source reads: The Nobel Prize in Physics 2022 was awarded jointly to Alain Aspect, John F. Clauser and Anton Zeilinger "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science"

Corrected

24 September 2026. Previously: “The Nobel Prize in Physics is awarded for the work.” "For the work" read as though the 2015 test were honoured; the prize went to Aspect, Clauser and Zeilinger for experiments with entangled photons.

Claim 33 · checked 24 September 2026 · AI-assisted audit

Decoherence explains why we never see superpositions

Claim: Decoherence explains why we never see superpositions

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
The Role of Decoherence in Quantum Mechanicssection 2.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: while decoherence does explain why we do not observe superpositions of measurement results, it does not explain why we do observe measurement results in the first place.

What this does not establish

Superpositions of measurement results, specifically, and in practice: interference has been shown with large objects in controlled conditions (claims 44 and 45).

Later work looked for

Crossref, 2015 on, "decoherence experiment matter wave interferometry": nothing that changes the account; the SEP entry was revised in January 2025.

Claim 34 · checked 24 September 2026 · AI-assisted audit

Claim: Interaction with an environment rapidly destroys the interference between components of a superposition, making them effectively independent.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Philosophical Issues in Quantum Theorysection 4.4
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: As a result, the reduced state of such a system quickly becomes a mixture of quasi-classical states, a phenomenon known as decoherence.
Supports
Philosophical Issues in Quantum Theorysection 4.4
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: then this completely destroys the interference fringes: the particles interact with the screen as if they determinately went through one slit or the other

Later work looked for

Crossref, 2015 on, "decoherence experiment matter wave interferometry": nothing that changes the account; the SEP entry was revised in January 2025.

Claim 35 · checked 24 September 2026 · AI-assisted audit

Claim: This is well understood, experimentally confirmed, and it is crucial to why large objects behave classically.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Decoherence, the measurement problem, and interpretations of quantum mechanicssection I
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: since decoherence effects have been studied extensively in both theoretical models and experiments ... their existence can be taken as a well-confirmed fact.
Supports
The Role of Decoherence in Quantum Mechanicssection 4.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: What seems very clear is that decoherence is crucial for the emergence of much of the macroscopic world around us
Qualifies
The Role of Decoherence in Quantum Mechanicssection 4.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: The detailed picture of the world that emerges from decoherence, however, is full of subtleties.

What this does not establish

The encyclopedia calls decoherence crucial to the emergence of much of the macroscopic world and warns that the detailed picture is full of subtleties.

Later work looked for

Crossref, 2015 on, "decoherence experiment matter wave interferometry": nothing that changes the account; the SEP entry was revised in January 2025.

Claim 36 · checked 24 September 2026 · AI-assisted audit

Claim: It does not explain why a measurement has a result in the first place.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
The Role of Decoherence in Quantum Mechanicssection 2.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: while decoherence does explain why we do not observe superpositions of measurement results, it does not explain why we do observe measurement results in the first place.
Context
Decoherence, the measurement problem, and interpretations of quantum mechanicssection I
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field
The source reads: By itself, decoherence is therefore neither an interpretation nor a modification of quantum mechanics.

Later work looked for

Crossref, 2015 on, "decoherence experiment matter wave interferometry": nothing that changes the account; the SEP entry was revised in January 2025.

Corrected

24 September 2026. Previously: “It does not explain why one outcome occurs rather than another.” The encyclopedia’s point is sharper than the page’s: decoherence does not explain why there are measurement results at all. Reworded to its claim.

Claim 37 · checked 24 September 2026 · AI-assisted audit

What the wavefunction is

Claim: What the wavefunction is

Kind: Framing. Signposting. It asserts nothing a source could check.

What the wavefunction is

Claim: What the wavefunction is

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: Is it a physical thing, a description of our information, or a bookkeeping device with no referent?

Kind: Open question. Something the page says is not known.
Review: Presented as open. The page says this is unresolved, and the review found that it is.

Supports
Philosophical Issues in Quantum Theorysection 4.2
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: We include in the first category approaches that deny that a quantum state should be thought of as representing anything in reality at all.
Supports
Philosophical Issues in Quantum Theorysection 5.2
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: The major realist approaches to the measurement problem are all, in some sense, realist about quantum states.

Claim 40 · checked 24 September 2026 · AI-assisted audit

Claim: Each answer has serious defenders and each leads to a different picture of reality.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Philosophical Issues in Quantum Theorysection 4.2
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: We include in the first category approaches that deny that a quantum state should be thought of as representing anything in reality at all.
Supports
Philosophical Issues in Quantum Theorysection 4.2.2
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: quantum mechanics is a tool for coordinating our experience and for forming expectations about the outcomes of experiments.
Supports
Philosophical Issues in Quantum Theorysection 5.2
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: The major realist approaches to the measurement problem are all, in some sense, realist about quantum states.

Claim 41 · checked 24 September 2026 · AI-assisted audit

Claim: A theorem of Pusey, Barrett and Rudolph narrows the field, but only for anyone who grants its framework and its assumption that two systems can be prepared independently of each other.

Kind: A proved result. A mathematical theorem, as its proof or a reference work states it. What it says about the world depends on how well the mathematics fits.
Review: Source checked. The cited passage was read, and it says this.

It narrows the field by ruling out, under its assumptions, models on which the quantum state is only information about an underlying physical state.

Supports
Philosophical Issues in Quantum Theorysection 5.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: any ontological model that reproduces quantum predictions and satisfies this Preparation Independence assumption must be a
Supports
Philosophical Issues in Quantum Theorysection 5.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: the assumption that it is possible to prepare a pair of systems in such a way that the probabilities for ontic states of the two systems are effectively independent
Supports
Philosophical Issues in Quantum Theorysection 5.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: an anti-realist about quantum states could reject the Preparation Independence assumption, or reject the framework within which the theorem is set

Corrected

24 September 2026. Previously: “but only for anyone who grants its assumption that two systems can be prepared independently of each other.” The encyclopedia names two ways out for an anti-realist, rejecting the independence assumption or rejecting the framework; the page named one.

Claim 42 · checked 24 September 2026 · AI-assisted audit

Where the classical world begins

Claim: Where the classical world begins

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: Interference has been demonstrated with increasingly large objects, most recently, in 2026, with sodium clusters of more than seven thousand atoms.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Probing quantum mechanics with nanoparticle matter-wave interferometryabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: an experimental platform that extends matter-wave interference to large metal clusters ... We specifically demonstrate quantum interference of sodium nanoparticles, which can each contain more than 7,000 atoms at masses greater than 170,000 Da.
Supports
Probing quantum mechanics with nanoparticle matter-wave interferometryabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Over the years, this has been explored with a series of objects of increasing mass and complexity
Context
Quantum superposition of molecules beyond 25 kDaabstract
Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Physical systems · Experiment
The source reads: we report interference of a molecular library of functionalized oligoporphyrins ... with masses beyond 25,000 Da and consisting of up to 2,000 atoms, by far the heaviest objects shown to exhibit matter-wave interference to date
The previous record the page cited.

What this does not establish

One group’s experiment; the clusters are more than 170,000 atomic mass units and were delocalized by more than ten times their own diameter.

Later work looked for

Crossref, 2019 on, "matter-wave interference record" and the coordinator’s pointer: Pedalino and others 2026 supersede the 2019 molecules as the heaviest interfered objects; page updated.

Corrected

24 September 2026. Previously: “Interference has been demonstrated with increasingly large molecules, most recently with objects of two thousand atoms.” Out of date: Pedalino and others (Nature, 2026) interfered sodium clusters of more than 7,000 atoms, beyond the 2019 molecules of up to 2,000.

Claim 44 · checked 24 September 2026 · AI-assisted audit

Claim: In 2023 the vibration of a sixteen-microgram crystal was put in superposition over a far shorter distance, about two billionths of a nanometre.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Schrödinger cat states of a 16-microgram mechanical oscillatorabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Here we demonstrate the preparation of a mechanical resonator with an effective mass of 16.2 micrograms in
Supports
Schrödinger cat states of a 16-microgram mechanical oscillatormain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: delocalized over a distance of 2.1 · 10⁻¹⁸ m
Notation restored: The superscript restored from the glyph positions in the arXiv PDF (arXiv:2211.00449v1, read with pdftotext -bbox), 2026-09-24. The text as extracted reads: delocalized over a distance of 2.1 · 10−18 m
Supports
Schrödinger cat states of a 16-microgram mechanical oscillatorfigure 1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: The inset shows the superposition of two opposite-phase oscillations of atoms in the crystal lattice.

What this does not establish

The sixteen micrograms is an effective mass of one vibration mode, and depends on a choice the authors describe; the superposition is of the crystal’s oscillation phase, not of its position as a whole.

Later work looked for

Crossref, 2019 on, "matter-wave interference record" and the coordinator’s pointer: Pedalino and others 2026 supersede the 2019 molecules as the heaviest interfered objects; page updated.

Corrected

24 September 2026. Previously: “” Added so the record is stated for both senses of size, mass and separation, as on the page about how big a quantum object can be.

Claim 45 · checked 24 September 2026 · AI-assisted audit

Claim: No boundary has been found,

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Probing quantum mechanics with nanoparticle matter-wave interferometryDiscussion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: Observing matter-wave interference of the most massive objects to date reveals no breakdown of the quantum superposition principle related to mass or size alone.

Later work looked for

Crossref, 2019 on, "matter-wave interference record" and the coordinator’s pointer: Pedalino and others 2026 supersede the 2019 molecules as the heaviest interfered objects; page updated.

Claim 46 · checked 24 September 2026 · AI-assisted audit

Claim: and there is no agreed criterion for when a system counts as macroscopic.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
The Role of Decoherence in Quantum Mechanicssection 4.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: there is no clear-cut criterion for when a system should count as macroscopic.
Context
Schrödinger cat states of a 16-microgram mechanical oscillatorabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: it is still unclear why we do not observe macroscopic objects to be in superpositions of states that can be distinguished by some classical property.

Later work looked for

Crossref, 2015 on, "decoherence experiment matter wave interferometry": nothing that changes the account; the SEP entry was revised in January 2025.

Corrected

24 September 2026. Previously: “and there is no agreed criterion for where to look for one.” Reworded to what the encyclopedia actually says: there is no clear-cut criterion for when a system counts as macroscopic.

Claim 47 · checked 24 September 2026 · AI-assisted audit

Claim: Whether a boundary exists (and whether gravity enforces it) is an open experimental question that several groups are actively pursuing.

Kind: Open question. Something the page says is not known.
Review: Presented as open. The page says this is unresolved, and the review found that it is.

The interference groups, the mechanical-oscillator groups and the underground radiation searches are the several groups; the gravity proposal is the Diósi-Penrose model.

Supports
Probing quantum mechanics with nanoparticle matter-wave interferometryMain
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: They assume that the wave function collapses to a localized state, spontaneously ... or induced by gravity
Supports
Collapse Theoriessection 7
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: due to fast technological improvements, experiments in which one might test the deviations from Standard Quantum Theory implied by Collapse Models, seems to have become more and more feasible.
Supports
Underground test of gravity-related wave function collapseabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: the results of a dedicated experiment at the Gran Sasso underground laboratory to measure this radiation emission rate.

Corrected

24 September 2026. Previously: “Whether it exists (and whether gravity enforces it)” Antecedent made explicit after the preceding sentence changed.

Claim 48 · checked 24 September 2026 · AI-assisted audit

The measurement problem

Claim: The measurement problem

Kind: Framing. Signposting. It asserts nothing a source could check.

Why a single outcome happens

Claim: Why a single outcome happens

Kind: Open question. Something the page says is not known.
Review: Presented as open. The page says this is unresolved, and the review found that it is.

Supports
Philosophical Issues in Quantum Theorysection 4.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: linear evolution of quantum states, when applied to macroscopic objects, will routinely lead to superpositions of macroscopically distinct states. Among the circumstances in which this will happen are experimental set-ups

Other readings

On many-worlds no single outcome happens; every outcome does, in a different branch.

Claim 50 · checked 24 September 2026 · AI-assisted audit

Claim: The theory gives probabilities.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum Mechanicssection 3, Dynamics
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: has the effect of collapsing the system ... This is known as the Collapse Postulate. Which particular ... it collapses into is a matter of probability, and the probabilities are given by a rule known as Born’s Rule

What this does not establish

Born’s rule gives the probabilities of measurement outcomes; the smooth evolution between measurements is deterministic.

Later work looked for

How a theory or interpretation is set out; not a finding later work revises.

Claim 51 · checked 24 September 2026 · AI-assisted audit

Claim: An experiment shows one result.

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Bayesian and Pragmatist Views of Quantum Theorysection 1.3
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: would almost always leave these in a state that describes the measurement as having no outcome, contrary to the direct experience of countless experimentalists

Other readings

SEP "Philosophical Issues in Quantum Theory" 4.2 calls it misleading to say we never observe superpositions, since it is unclear what observing one would be like.

Later work looked for

How experience is described; not a finding later work revises.

Corrected

24 September 2026. Previously: “Reality delivers one result.” "Reality delivers one result" takes a side the page later presents as open: on many-worlds every result occurs. What is not in dispute is that an experimenter sees one.

Claim 52 · checked 24 September 2026 · AI-assisted audit

Claim: Nothing in the standard formalism says what process takes the one to the other, or exactly when,

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Philosophical Issues in Quantum Theorysection 2.3
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: None of the standard formulations are precise about when the collapse postulate is to be applied; there is some lee-way as to what is to count as an experiment
Supports
Quantum Mechanicssection 3, Dynamics
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: The distinction between contexts of type 1 and 2 remains to be made out in quantum mechanical terms; nobody has managed to say in a completely satisfactory way, in the terms provided by the theory, which contexts are measurement contexts

Later work looked for

Crossref, 2016 on, "measurement problem interpretation experiment": no experiment reported that decides between the major approaches; SEP entries revised 2022 to 2026 say the same.

Corrected

24 September 2026. Previously: “Nothing in the formalism describes the transition,” The standard formalism does state the transition, as the collapse postulate; what it lacks, per SEP, is an account of the process and a precise rule for when it applies.

Claim 53 · checked 24 September 2026 · AI-assisted audit

Claim: and no account that leaves the predictions alone has produced a way to tell itself apart from the others.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: If one accepts that Everettians have a solution to the evidential problem, then, among the major lines of approach, none is favored in a straightforward way by the empirical evidence.
Supports
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: collapse theories have the intriguing feature of reproducing very close approximations to quantum probabilities for all experiments that have been performed so far but departing from the quantum probabilities for other conceivable experiments. This permits, in principle, an empirical discrimination between such theories and no-collapse theories.

What this does not establish

Collapse theories are excluded from this by design: they change the predictions, which is how they can be tested.

Later work looked for

Crossref, 2016 on, "measurement problem interpretation experiment": no experiment reported that decides between the major approaches; SEP entries revised 2022 to 2026 say the same.

Claim 54 · checked 24 September 2026 · AI-assisted audit

What “measurement” means

Claim: What “measurement” means

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: The theory as ordinarily taught treats measurement as primitive, without saying what physically constitutes one.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum Mechanicssection 3, Dynamics
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: The distinction between contexts of type 1 and 2 remains to be made out in quantum mechanical terms; nobody has managed to say in a completely satisfactory way, in the terms provided by the theory, which contexts are measurement contexts
Supports
Philosophical Issues in Quantum Theorysection 2.3
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: None of the standard formulations are precise about when the collapse postulate is to be applied; there is some lee-way as to what is to count as an experiment

Later work looked for

Crossref, 2016 on, "measurement problem interpretation experiment": no experiment reported that decides between the major approaches; SEP entries revised 2022 to 2026 say the same.

Claim 56 · checked 24 September 2026 · AI-assisted audit

Claim: A detector is made of atoms that obey the same equations.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Philosophical Issues in Quantum Theorysection 4.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: If quantum theory is meant to be (in principle) a universal theory, it should be applicable, in principle, to all physical systems, including systems as large and complicated as our experimental apparatus.

What this does not establish

On the assumption that quantum theory is universal, which is how the encyclopedia states it.

Later work looked for

How a theory or interpretation is set out; not a finding later work revises.

Claim 57 · checked 24 September 2026 · AI-assisted audit

Claim: That tension is the measurement problem, stated plainly.

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

Follows from claims 56 and 57: a theory that treats measurement as special, applied to apparatus built of what it describes.

Supports
Philosophical Issues in Quantum Theorysection 4.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: For this reason, the interpretational issues have come to be referred to as the measurement problem.
Supports
Philosophical Issues in Quantum Theorysection 4.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: linear evolution of quantum states, when applied to macroscopic objects, will routinely lead to superpositions of macroscopically distinct states. Among the circumstances in which this will happen are experimental set-ups

Corrected

24 September 2026. Previously: “This circularity is the measurement problem, stated plainly.” The problem as the encyclopedia states it is a conflict between universal smooth evolution and definite outcomes, not a circular definition.

Claim 58 · checked 24 September 2026 · AI-assisted audit

Four incompatible pictures

Claim: Four incompatible pictures

Kind: Framing. Signposting. It asserts nothing a source could check.

Everything happens

Claim: Everything happens

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Many-Worlds Interpretation of Quantum Mechanicssection 1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: every time a quantum experiment with different possible outcomes is performed, all outcomes are obtained, each in a different, newly created world

What this does not establish

A summary of what the interpretation holds, not evidence that it is true.

Later work looked for

SEP entry read at its current revision (see sources); how the approach is stated, not a finding later work revises.

Claim 60 · checked 24 September 2026 · AI-assisted audit

Claim: The many-worlds interpretation removes the collapse step entirely: the wavefunction always evolves smoothly, and every outcome occurs in a branch of a continually splitting universal state.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Many-Worlds Interpretation of Quantum Mechanicssection 1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: every time a quantum experiment with different possible outcomes is performed, all outcomes are obtained, each in a different, newly created world
Supports
Many-Worlds Interpretation of Quantum Mechanicssection 1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: the ontology of the Universe is a quantum state evolving according to the Schrödinger equation or its relativistic generalization.
Supports
Philosophical Issues in Quantum Theorysection 4.2
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: hold that quantum states undergo unitary evolution at all times and that a quantum state-description is, in principle, complete.

What this does not establish

What the interpretation says; no experiment has confirmed it over the others (claim 5).

Later work looked for

SEP entry read at its current revision (see sources); how the approach is stated, not a finding later work revises.

Claim 61 · checked 24 September 2026 · AI-assisted audit

Claim: Its defenders call it the most economical theory available, because it keeps the laws of standard quantum theory and drops the collapse postulate.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Many-Worlds Interpretation of Quantum Mechanicssection 7.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: From this perspective, the MWI emerges as the most economical theory. It retains all the laws of standard quantum theory but eliminates the collapse postulate, which is the most problematic of those laws.
Supports
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Everettians take, as a virtue of the approach, the fact that it does not involve an extension or modification of the quantum formalism.

What this does not establish

Its probability rule is a postulate that its defender says adds nothing to the mathematics; critics dispute that the laws alone explain experience.

Corrected

24 September 2026. Previously: “because it drops a law and adds none.” The entry’s own words; "adds none" is contested, since the entry concedes a probability postulate is added to the part connecting the theory with experience.

Claim 62 · checked 24 September 2026 · AI-assisted audit

Claim: Its critics call the worlds an extravagance.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Many-Worlds Interpretation of Quantum Mechanicssection 7.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Critics argue this constitutes an extreme violation of Ockham’s principle
Context
Many-Worlds Interpretation of Quantum Mechanicssection 7.1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Hemmo and Shenker (2022) agree that the postulates of the MWI are economical and therefore advantageous from the point of view of Ockham’s Razor, but they argue that this advantage is irrelevant

Claim 63 · checked 24 September 2026 · AI-assisted audit

Claim: A difficulty its critics press, and one of its defenders calls arguably the most serious, is saying where the probabilities come from when every outcome happens.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

The defender is the author of the many-worlds entry, which argues for the interpretation.

Supports
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: A criticism that has been raised against Everettian theories is that it is not clear whether they can even make sense of statistical testing of this kind
Supports
Many-Worlds Interpretation of Quantum Mechanicssection 7.4; section 8, Why the MWI?; author line
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: The issue, termed the “incoherence” probability problem by Wallace (2003), is arguably the most serious difficulty. How can probability exist if all possible outcomes occur? ... The MWI resolves most, if not all, paradoxes of quantum mechanics ... Lev Vaidman

Corrected

24 September 2026. Previously: “Both sides agree that its hardest problem is saying where the probabilities come from when every outcome happens.” No source says both sides agree; the entry calls it "arguably the most serious difficulty" and reports defenders who argue it is no disadvantage.

Claim 64 · checked 24 September 2026 · AI-assisted audit

Particles have definite positions all along

Claim: Particles have definite positions all along

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Bohmian Mechanicsopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: In Bohmian mechanics a system of particles is described in part by its wave function, evolving, as usual, according to Schrödinger’s equation. However, the wave function provides only a partial description of the system. This description is completed by the specification of the actual positions of the particles.

What this does not establish

What pilot-wave theory holds, not evidence that it is true.

Later work looked for

SEP entry read at its current revision (see sources); how the approach is stated, not a finding later work revises.

Claim 65 · checked 24 September 2026 · AI-assisted audit

Claim: Pilot-wave theory restores definite trajectories guided by a real wave.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Philosophical Issues in Quantum Theorysection 4.2.2
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: According to this theory, there are particles with definite trajectories, that are guided by the quantum wave function.
Supports
Bohmian Mechanicsopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: In Bohmian mechanics a system of particles is described in part by its wave function, evolving, as usual, according to Schrödinger’s equation. However, the wave function provides only a partial description of the system. This description is completed by the specification of the actual positions of the particles.

What this does not establish

“Real” is the theory’s own commitment; what kind of thing the guiding wave is remains debated (SEP "Philosophical Issues" 5.2).

Later work looked for

SEP entry read at its current revision (see sources); how the approach is stated, not a finding later work revises.

Claim 66 · checked 24 September 2026 · AI-assisted audit

Claim: It accounts for everything non-relativistic quantum mechanics accounts for,

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Bohmian Mechanicsopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: It accounts for all of the phenomena governed by nonrelativistic quantum mechanics, from spectral lines and scattering theory to superconductivity, the quantum Hall effect and quantum computing.

What this does not establish

Its predictions match those of the non-relativistic theory; that does not make its trajectories observable, and matching is not evidence for it over the alternatives.

Later work looked for

SEP entry read at its current revision (see sources); how the approach is stated, not a finding later work revises.

Claim 67 · checked 24 September 2026 · AI-assisted audit

Claim: and it makes explicit a non-locality that its proponents say no theory reproducing quantum mechanics can avoid.

Kind: Disputed. A contested point, where the page reports a side or the disagreement.
Review: Source checked. The cited passage was read, and it says this.

Supports
Bohmian Mechanicsopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Bohmian mechanics inherits and makes explicit the nonlocality implicit in the notion, common to just about all formulations and interpretations of quantum theory, of a wave function on the configuration space of a many-particle system. It accounts for all of the phenomena governed by nonrelativistic quantum mechanics
Supports
Bohmian Mechanicssection 14
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Since quantum theory itself, by virtue merely of the character of its predictions concerning EPR-Bohm correlations, is irreducibly nonlocal
Cuts against
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Several authors have approached this issue in somewhat different ways, with a common conclusion that Everettian quantum mechanics is, indeed, local.

Other readings

Several authors conclude that Everettian quantum mechanics is local, which denies that the non-locality is unavoidable.

Claim 68 · checked 24 September 2026 · AI-assisted audit

Claim: It is not Lorentz invariant, and cannot easily be made so.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Bohmian Mechanicssection 14
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Bohmian mechanics is not Lorentz invariant. Nor can it easily be modified to accommodate Lorentz invariance.
Supports
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Broglie-Bohm theory requires a distinguished relation of distant simultaneity for its formulation

What this does not establish

Single-particle Lorentz invariant versions exist; the difficulty is for many particles.

Later work looked for

SEP entry read at its current revision (see sources); how the approach is stated, not a finding later work revises.

Claim 69 · checked 24 September 2026 · AI-assisted audit

Collapse is a real physical process

Claim: Collapse is a real physical process

Kind: Hypothesis. A proposed explanation, not an established one.
Review: Source checked. The cited passage was read, and it says this.

Supports
Collapse Theoriesopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: this approach consists in accepting that the dynamical equation of the standard theory should be modified by the addition of stochastic and nonlinear terms.

What this does not establish

Proposed, not established: no collapse has been detected, and the experiments so far only bound the models.

Claim 70 · checked 24 September 2026 · AI-assisted audit

Claim: Objective collapse models add a genuine, spontaneous collapse mechanism to the dynamics.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Collapse Theoriesopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: this approach consists in accepting that the dynamical equation of the standard theory should be modified by the addition of stochastic and nonlinear terms.
Supports
Philosophical Issues in Quantum Theorysection 4.2.3
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: There are approaches that involve a denial that a quantum wave function (or any other way of representing a quantum state) yields a complete description of a physical system. ... There are approaches that involve modification of the dynamics to produce a collapse of the quantum state in appropriate circumstances.

What this does not establish

A modification of the theory, proposed and not established; no collapse of this kind has been detected.

Later work looked for

SEP entry read at its current revision (see sources); how the approach is stated, not a finding later work revises.

Claim 71 · checked 24 September 2026 · AI-assisted audit

Claim: Unlike most interpretations these make predictions that differ slightly from standard quantum mechanics,

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Philosophical Issues in Quantum Theorysection 4.5
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: collapse theories have the intriguing feature of reproducing very close approximations to quantum probabilities for all experiments that have been performed so far but departing from the quantum probabilities for other conceivable experiments. This permits, in principle, an empirical discrimination between such theories and no-collapse theories.
Supports
Collapse Theoriesopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Collapse Theories qualify themselves as rival theories of quantum mechanics and one can easily identify some of their physical implications which, in principle, would allow crucial tests discriminating between the two.

What this does not establish

The departures are predicted, not observed: for every experiment performed so far the models reproduce quantum probabilities closely.

Later work looked for

SEP entry read at its current revision (see sources); how the approach is stated, not a finding later work revises.

Claim 72 · checked 24 September 2026 · AI-assisted audit

Claim: and experiments are actively narrowing the space they can occupy.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Collapse Theoriesopening
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Physical systems · Reference work
The source reads: specific bounds have already been obtained for the parameters characterizing the theories under investigation
Supports
Collapse Theoriessection 7
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Physical systems · Reference work
The source reads: due to fast technological improvements, experiments in which one might test the deviations from Standard Quantum Theory implied by Collapse Models, seems to have become more and more feasible.

Later work looked for

Crossref, 2021 on, "Diósi-Penrose model test" and "gravity-related collapse radiation": later work extends the model and proposes tests; nothing reverses the result. SEP "Collapse Theories" (revised September 2025) reports it the same way.

Claim 73 · checked 24 September 2026 · AI-assisted audit

Claim: The parameter-free form of the Diósi-Penrose model was ruled out that way, by a search under a mountain for the faint radiation such a collapse should emit.

Kind: Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review: Source checked. The cited passage was read, and it says this.

Supports
Underground test of gravity-related wave function collapseabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: resulting, if charged, in the emission of radiation. Here, we compute the radiation emission rate, which is faint but detectable.
Supports
Underground test of gravity-related wave function collapseabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: rules out the natural parameter-free version of the
Supports
Underground test of gravity-related wave function collapsemain text
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Physical systems · Experiment
The source reads: characterized by a rock overburden
Supports
Collapse Theoriessection 7
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Moreover, the so-called Diosi-Penrose model has been falsified experimentally (Donadi et al. 2021), at least in its simpler formulation.

What this does not establish

One experiment; versions with an adjustable size parameter survive, and the predicted radiation depends on the model’s form.

Later work looked for

Claim 74 · checked 24 September 2026 · AI-assisted audit

The theory is about information, not the world

Claim: The theory is about information, not the world

Kind: Hypothesis. A proposed explanation, not an established one.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Bayesian and Pragmatist Views of Quantum Theoryopening; section 1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: QBists argue that from this point of view quantum theory faces no conceptual problems associated with measurement or non-locality.

Other readings

Realist approaches take the quantum state, or something it guides, to describe physical reality; QBists deny it describes the system at all.

Claim 75 · checked 24 September 2026 · AI-assisted audit

Claim: Some approaches treat the quantum state as a description of an agent’s expectations rather than of physical reality.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Bayesian and Pragmatist Views of Quantum Theorysection 1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: The quantum state assigned by an agent then provides a convenient representation of an important part of his or her own overall state of belief.
Supports
Quantum-Bayesian and Pragmatist Views of Quantum Theorysection 1.3
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: QBists avoid this problem by denying that a quantum state (even incompletely) describes the system to which it assigned.

Claim 76 · checked 24 September 2026 · AI-assisted audit

Claim: On this view, its holders argue, the measurement problem does not arise, because there is no physical state to collapse.

Kind: An argument. An argument a named thinker makes. That it is made is checked; whether it succeeds is argued.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Bayesian and Pragmatist Views of Quantum Theorysection 1
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: QBists argue that from this point of view quantum theory faces no conceptual problems associated with measurement or non-locality.
Supports
Quantum-Bayesian and Pragmatist Views of Quantum Theorysection 1.3
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: QBists avoid this problem by denying that a quantum state (even incompletely) describes the system to which it assigned.

Corrected

24 September 2026. Previously: “The measurement problem does not arise, because on this view there is no physical state to collapse.” Attributed to QBists, who argue it; the page stated it in its own voice.

Claim 77 · checked 24 September 2026 · AI-assisted audit

Claim: Critics, among them the philosopher Christopher Timpson, answer that such a theory cannot explain why things are as they are: why sodium conducts, rather than why an agent should expect it to.

Kind: An argument. An argument a named thinker makes. That it is made is checked; whether it succeeds is argued.
Review: Source checked. The cited passage was read, and it says this.

Supports
Quantum-Bayesian and Pragmatist Views of Quantum Theorysection 2.3
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Timpson (followed by Brown 2019) objects that QBists cannot account for its explanatory success.
Supports
Quantum-Bayesian and Pragmatist Views of Quantum Theorysection 2.3
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Ultimately we are not interested in agents’ expectation that matter structured like sodium would conduct; we are interested in why it in fact does so. (Timpson 2008: 600)
Qualifies
Quantum-Bayesian and Pragmatist Views of Quantum Theorysection 2.3
Cited · Link answered, 19 October 2026 · The cited passage was read, 24 September 2026 · Reference work
The source reads: Fuchs & Schack (2015) reply that explanations offered by quantum theory have a similar character to explanations offered by probability theory and give examples.

Other readings

Fuchs and Schack reply that quantum explanations resemble those of probability theory.

Corrected

24 September 2026. Previously: “Critics answer that a theory describing nobody’s world has given up on explaining why the world is as it is.” "Describing nobody’s world" is not the objection in the literature and misstates QBism, which does not deny a world. The objection the encyclopedia reports is Timpson’s, about explanation, and it is now attributed and stated.

Claim 78 · checked 24 September 2026 · AI-assisted audit

What was read

On the Einstein Podolsky Rosen paradoxPhysics Physique Fizika · Scanned reprint, pages 403 to 408, footer "Originally published in Physics, 1, 195-200 (1964)", at drchinese.com; the introduction read from its page image; Crossref record for the dateThe cited passage was read, 24 September 2026 · Copyright; quoted brieflyExcerpts transcribed from the page image.
Experimental Test of Bell’s Inequalities Using Time-Varying AnalyzersPhysical Review Letters · Abstract as served by INSPIRE-HEP from APS; journals.aps.org refuses this environmentAbstract only, 24 September 2026 · Copyright; quoted briefly
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometresNature · arXiv:1508.05949v1 (24 August 2015), the submitted manuscript of Nature 526, 682 to 686Read in full, 24 September 2026 · Copyright; quoted briefly
The Nobel Prize in Physics 2022The Nobel Foundation · nobelprize.org summary pageRead in full, 24 September 2026 · Copyright; quoted briefly
Measurement of the Electron Magnetic MomentFan, Myers, Sukra and Gabrielse, Physical Review Letters · arXiv:2209.13084 (dated 8 December 2022), the manuscript of Physical Review Letters 130, 071801Read in full, 24 September 2026 · Copyright; quoted brieflyPDF text extraction renders 10^12 as "10 12" and "1012"; excerpts keep it as served.
Quantum superposition of molecules beyond 25 kDaFein and colleagues, Nature Physics · Nature Physics 15, 1242 to 1245; abstract from the article page; full text paywalledAbstract only, 24 September 2026 · Copyright; quoted briefly
Probing quantum mechanics with nanoparticle matter-wave interferometryPedalino, Ramírez-Galindo, Ferstl, Hornberger, Arndt and Gerlich, Nature 649, pages 866 to 870 · Nature 649, 866 to 870, open-access article page; read abstract, main text and DiscussionRead in full, 24 September 2026 · CC BY 4.0
Schrödinger cat states of a 16-microgram mechanical oscillatorBild, Fadel, Yang, von Lüpke, Martin, Bruno and Chu, Science 380, pages 274 to 278 · arXiv:2211.00449v1 (1 November 2022); read abstract and main textRead in full, 24 September 2026 · Copyright; quoted brieflyPDF text extraction renders exponents inline ("10−18"); the excerpt keeps it as served.
Decoherence, the measurement problem, and interpretations of quantum mechanicsMaximilian Schlosshauer, Reviews of Modern Physics 76, pages 1267 to 1305 · arXiv:quant-ph/0312059v4 (28 June 2005); read the abstract and section IRead in full, 24 September 2026 · Copyright; quoted briefly
Underground test of gravity-related wave function collapseDonadi and colleagues, Nature Physics · arXiv:2111.13490v1 (26 November 2021); read abstract and main textRead in full, 24 September 2026 · Copyright; quoted briefly
Quantum MechanicsStanford Encyclopedia of Philosophy · SEP, substantive revision 18 January 2025; read the opening and section 3The cited passage was read, 24 September 2026 · Copyright; quoted briefly
Philosophical Issues in Quantum TheoryStanford Encyclopedia of Philosophy · SEP, substantive revision 23 March 2022; read sections 2.3, 4 and 5.1 to 5.2The cited passage was read, 24 September 2026 · Copyright; quoted briefly
Bohmian MechanicsStanford Encyclopedia of Philosophy · SEP, substantive revision 20 September 2025; read the opening and sections 13 and 14The cited passage was read, 24 September 2026 · Copyright; quoted briefly
Collapse TheoriesStanford Encyclopedia of Philosophy · SEP, substantive revision 30 September 2025; read the opening and section 7The cited passage was read, 24 September 2026 · Copyright; quoted briefly
Quantum-Bayesian and Pragmatist Views of Quantum TheoryStanford Encyclopedia of Philosophy · SEP, substantive revision 8 September 2026; read the opening and sections 1 to 1.3 and 2.3The cited passage was read, 24 September 2026 · Copyright; quoted briefly
Many-Worlds Interpretation of Quantum MechanicsStanford Encyclopedia of Philosophy · SEP, substantive revision 17 June 2026; read sections 1, 4 and 7The cited passage was read, 24 September 2026 · Copyright; quoted briefly
The Role of Decoherence in Quantum MechanicsStanford Encyclopedia of Philosophy · SEP, substantive revision 23 January 2025; read the opening, sections 2 and 2.1, 3.3 and 4.1The cited passage was read, 24 September 2026 · Copyright; quoted briefly