Since its original proposal, the view has evolved and attracted new followers in the physics community, but has been less warmly received by philosophers. Many, it seems, share the view of Hagar (2003) that “Fuchs’ ‘thin’ realism, and the entire ‘fog from the north’ which inspires it, are nothing but instrumentalism in disguise” (p.772).Footnote 1

Below is a philosophical reflection (not only for the Zotero team).We are still able to perform J.S. Bach music because music notation and instruments have not changed whithin 3 centuries. In computer science, every 6 months, software are upgraded, functionnalities and encoding very often change too. How can we work in such conditions? How can our human society survive in such a moving context ?

Put this in your address barchrome://flags/Then go to or copy paste in searchInsecure origins treated as secureThen enabled..

Dellu November 2, 2023 edited November 2, 2023 Zotero-file can be downloaded from this fork: https://github.com/DesBw/zotero-file

Dellu November 2, 2023 This fork has up to version 0.2.1: https://github.com/lychichem/zotero-file/tags

tim820 October 30, 2023 @knutatle you just use the standard Zotero routine: Tools\Manage Attachments\Convert Linked Files to Stored Files.

An integrated PDF reader, by contrast, was by far the most frequent reason people gave for not using Zotero, and there's been an overwhelmingly positive response to the new features in Zotero 6. If it's not for you, it's not for you, but your experience of using Zotero is not universal.

I don't need a fancy pdf reader like that in Mendeley, so the deep coupling of the new note editor under the hook cannot be justified by the introducing of that reader.

You could use the excuse that not many feedbacks about table were provided. But you cannot eliminate the possibility that most heavy users may have no interest in your years-long beta development at all, like me.

ou can use Markdown syntax

very few beta testers mentioned tables during that time. We'll consider supporting them in the new editor if there's enough demand.

I tried to reinstall Zotero 5, but the database was changed and locked for Zotero 6.

For me, it is a catastroph !

I'm surprised if it doesn't use HTML at all, since the annotation templates (which control exporting PDF annotations into notes, right?) take HTML. I wonder if it might be possible to simply allow the user to reactivate TinyMCE via preferences, since the two editors are probably interchangeable in the code?

which could be changed easily in HTML mode

The new editor isn't HTML, so no HTML view, sorry.

But it's not currently possible to parse Markdown on import, no

Bell must explain theproblem with von Neumann’s then widely accepted result. He does this rather informally,condensing von Neumann’s four assumptions into “Any real linear combination of anytwo Hermitian operators represents an observable, and the same linear combination ofexpectation values is the expectation value of the combination.

Von Neumann’s proof is quite straightforward. Three decades later Andrew Gleasonproved what is now known as Gleason’s Theorem: that the density matrix form (4) followsfrom premises essentially equivalent to Assumptions A′, I, and II. Gleason does not useassumption B′ for physical quantities that are not jointly measurable. His argument isnotoriously intricate (and requires that the Hilbert space have three or more dimensions).

the resultingsubensembles would be free of dispersion:Expφ,λ(R2) = (Expφ,λ(R))2 (5)for all physical quantities R

Von Neumann addresses the question of hidden variables on p. 323.15 He asks whetherthe dispersion of any ensemble characterized by a wave function φ could result from thefact that such pure states are not the fundamental states, but only statistical mixtures ofseveral more basic states. To specify such “actual states” one would need additional data— “hidden parameters”, which we denote here collectively by λ

The Exp function characterizing a pure quantum state φ is indeed of the form (4)with the density matrix U given by |φ〉〈φ|

n modern language there must be a density matrixU , such that the Exp function for the ensemble is the trace of the product of that densitymatrix with the Hermitian operator that corresponds to that physical quantity.14

Indeed, von Neumann immediately remarks that B′ characterizes such a linear combination“only in an implicit way”, since there is “no way to construct from the measurement[instructions] for R, S, . . . such [instructions] for R + S + · · · .”8

Extending the scope of AssumptionB′ to quantities R, S, . . . that are not jointly measurable is problematic,

it is one of the most important features of quantum mechanics that not allphysical quantities can be simultaneously measured.7

f several different physical quantities R, S, . . . can be simultaneously measured

Assumption B′: (p. 311) If R, S, . . . are arbitrary physical quantities, not necessarilysimultaneously measurable, and a, b, . . . are real numbers then the expectation functionExp is linear:Exp(aR + bS + · · ·) = a Exp(R) + b Exp(S) + · · · . (1)

we are reading von Neumann just as she does.

The relation is, however, not self-evidentfor quantum mechanical quantities between which uncertainty relations hold, and in factfor the reason that the sum of two such quantities is not immediately defined at all: sincea sharp measurement of one of them excludes that of the other, so that the two quan-tities cannot simultaneously assume sharp values, the usual definition of the sum of twoquantities is not applicable.

This crucial assumption is equivalent to von Neumann’s B′.

Von Neumann assumes thatExp(R + S) = Exp(R) + Exp(S). (6)In words: the expectation value of a sum of physical quantities is equal to the sum of theexpectation values of the two quantities [her italics]: von Neumann’s proof stands or fallswith this assumption. [our italics]”

8 We conjecture that she may have found von Neumann’s blatant oversight so surprisingthat she tried, unsuccessfully, to guess what else he may have had in mind

7 Perhaps in 1935 the distinctions von Neumann relied on had not yet been absorbedinto a terminology that obscured important distinctions.10

In 1935, three years after the publication of von Neumann’s book and three decadesbefore John Bell’s criticism of that book, Grete Hermann wrote about it.26

thank Ulrich Mohrhoff for bringing Dieks, 2017, to our attention

Hermann calls von Neumann“Neumann”

when Bell mentionsthat “a measurement of a sum of noncommuting observables cannot be made by combiningtrivially the results of separate observations on the two terms” because “it requires a quitedistinct experiment,”

24 Bell often fails to distinguish between “noncommuting operators” and “not jointlymeasurable physical quantities”

3 Bell does make the distinction in an earlier introductory section, but unlike von Neu-mann he does not repeatedly insist on it. His use of “observable” to mean “physicalquantity” is unfortunate, since by 1966 most physicists used the term for both physicalquantities and Hermitian operators

emphasizes von Neumann’s distinction be-tween physical quantities and Hermitian operators.23

Bub and Dieks both take this to mean that von Neumann uses assumption B′ todefine linear combinations of physical quantities that are not simultaneously measurable.This is the entire basis for their criticisms of Bell and Hermann. If B′ is just a definition,it cannot also be an invalid assumption, as Hermann and Bell maintain. But as we shallsee below, the full set of von Neumann’s four assumptions contains another way to definelinear combinations of physical quantities that are not simultaneously measurable. Withthat alternative definition, Assumption B′ can indeed impose a nontrivial constraint onthe values an Exp function can have for such linear combinations. There is no reason toinsist that Assumption B′ must be taken as a definition

Recently posted at https://arxiv.org/abs/1802.10119; threeminor errata have been repaired, some footnotes of commentary have been added, and thepresent manuscript is announced as forthcoming

e, however, agree with Hermann’s and Bell’s reading ofvon Neumann, and believe that Bub and Dieks fail to make sense of the surprising gap invon Neumann’s argument that Hermann and Bell correctly identified.

recently Dennis Dieks, 2017, expanded on Bub, adding similar criticismof the earlier work of Hermann

Recently Jeffrey Bub, 2010, claimed that Bell had misunderstood von Neumann’s ar-gument

Unknown to Bell, Grete Hermann, 1935, had published the same criticism three decadesearlier.

ohn Bell, 1966

Bub, 2011, adds Mermin, 1993, to his list of those who read von Neumann wrong

We disagree with recent papers claiming that Hermann andBell failed to understand what von Neumann was actually doing

I thank Michael Cifone for insightful discussions on Bohm’s theory

His dynamical theory plays a similar role, in showing howEuclidean geometry can be preserved, as Bohm’s dynamical theory of measurement inexplaining how the quantum statistics can be generated in a classical or Boolean theoryof probability

Lorentzaimed to maintain Euclidean geometry and Newtonian kinematics and explain theanomalous behavior of light in terms of a dynamical theory about how rods contract asthey move through the ether

thequantum statistics defined by the trace rule for quantum observables is an artefact ofa dynamical process that is not in fact a measurement of any physical quantity of thesystem

Bohm comments [3, pp. 386–387]:This means that the measurement of an ‘observable’ is not really ameasurement of any physical property belonging to the observed systemalone. Instead, the value of an ‘observable’ measures only an incom-pletely predictable and controllable potentiality belonging just as muchto the measuring apparatus as to the observed system itself. . . . We con-clude then that this measurement of the momentum ‘observable’ leads tothe same result as is predicted in the usual interpretation. However, theactual particle momentum existing before the measurement took place isquite different from the numerical value obtained for the momentum ‘ob-servable,’ which, in the usual interpretation, is called the ’momentum.’

variables—particle positions—has reached equilibrium

For example, the momentum of a Bohmian particle is the rate of change of posi-tion, but the expectation value of momentum in a quantum ensemble is not derived byaveraging over the particle momenta. Rather, the expectation value is derived via atheory of measurement, which yields the trace formula involving the momentum op-erator if we assume, as a contingent fact, that the probability distribution of hidden6

This is pre-cisely what Bohm does in his hidden variable theory [3], on the basis of a disturbancetheory of measurement that generates the quantum statistics

In [1, p. 448], Bell constructed a toy hidden variable theory for spin-1/2 systems,i.e., for quantum systems represented on a 2-dimensional Hilbert space, in which eigen-values are assigned to the spins in all directions, given a quantum pure state |ψ〉 and avalue of the hidden variable. On the face of it, this would seem to be a counterexampleto von Neumann’s theorem

As we saw, von Neumann regarded a sum of physical quantities thatcannot be measured simultaneously as implicitly defined by the statistics, and he drewthe conclusion that such an implicitly defined physical quantity cannot be representedby the operator sum in a hidden variable theory

According to Bell, von Neumann proved only the impossibility of hidden determin-istic states that assign values to a sum of physical quantities, R+S, that are the sums ofthe values assigned to the quantities R and S, even when R and S cannot be measuredsimultaneously

sum of noncommuting operators is equal to the sum of the eigenvalues of the summedoperators. For a spin-1/2 particle, for example, the eigenvalues of σx and σy are both±1, while the eigenvalues of σx + σy are ±√2, so the relation cannot hold

As Bell pointed outin [1], for dispersion free states the expectation value of a physical quantity is equal tothe eigenvalue in the dispersion free state, and it is clearly false that the eigenvalue of a

As is well-known, Gleason’s theorem [4] later established the same result on thebasis of weaker assumptions for Hilbert spaces of more than two dimensions: in effect,II is required to hold only for simultaneously measurable quantities.

It is assumed that each physical quantity of a quantum me-chanical system is represented by a (hypermaximal)3 Hermitian operator in a Hilbertspace

he observes that we measure the energy by the measuring the frequency of thespectral lines in the radiation emitted by the electron, not by measuring the electron’sposition and momentum, computing the values of P2/2m and V (Q), and adding theresult

the question is whether the quantumprobabilities, for physical quantities construed as beables, can be derived by averagingover the distribution of dispersion free states associated with a given quantum state

in the context of the hidden variable ques-tion, he has in mind something like Bell’s notion of ‘beable,’ rather than ‘observable,’the standard terminology of quantum mechanics

Von Neumann alternates between the term ‘measurable quantity’ and ‘physicalquantity.’

2Bell [2, p.174]: “The beables of the theory are those elements which might correspond to elements ofreality, to things which exist. Their existence does not depend on ‘observation.’ Indeed observation andobservers must be made out of beables.

the notion of a physical system as characterized by a set of ‘measurablequantities’ and their functional relations

What von Neumann provedwas the impossibility of recovering the quantum probabilities from a hidden variabletheory of dispersion free (deterministic) states in which the quantum observables arerepresented as the ‘beables’ of the theory, to use Bell’s suggestive term.2

Bell rejected von Neumann’sargument as fatally flawed. In an interview for the magazine Omni (May, 1988, p. 88),he went so far as to state:1Yet the von Neumann proof, if you actually come to grips with it, fallsapart in your hands! There is nothing to it. It’s not just flawed, its silly!. . . When you translate [his assumptions] into terms of physical disposi-tion, they’re nonsense. You may quote me on that: The proof of von Neu-mann is not merely false but foolish!

Thatis, the quantum probabilities could not reflect the distribution of pre-measurementvalues of beables, but would have to be derived in some other way, e.g., as inBohm’s theory, where the probabilities are an artefact of a dynamical process thatis not in fact a measurement of any beable of the system

What von Neumannproved was the impossibility of recovering the quantum probabilities from a hid-den variable theory of dispersion free (deterministic) states in which the quantumobservables are represented as the ‘beables’ of the theory, to use Bell’s term

ll raised the question whether it could be shown that anyhidden variable theory would have to be nonlocal, and in this sense ‘like Bohm’stheory.’ His seminal result provides a positive answer to the question

Joel came up with the idea for the song when he turned 40. A chance meeting with Sean Lennon, son of John Lennon and Yoko Ono, made him realize how each subsequent generation feels things are getting worse and worse while ignoring the troubles of the past.

death metal, populated by artists such as Ozzy Osbourne and Judas Priest

The Process of creativityIn chapter 17 of Gell-Mann’s The Quark and the Jaguar, the physicist Gell-Mann explains theprocess of creativity:Stages leading to creative idea (stages expressed by Hermann von Helmholtz)- Saturation: filling our minds with everything about the problem- Incubation: letting it churn subconsciously- Illumination: idea comes at some random time or circumstanceIncubation can be aided by brainstorming, and applying random thoughts or random learningto the idea.Characteristics of those who are creative and escape to deeper basins of thought: "Thosecharacteristics include a dedication to the task, an awareness of being trapped in an unsuitablebasin, a degree of comfort with teetering on the edge between basins, and a capacity forformulating as well as solving problems."From M. Gell-Mann. The Quark and the Jaguar. Little, Brown and Co., 1994.

Imagine if, instead of atoms, there were two distant boxes, each with a ball in it. The ball might be removed and sent to you from either box. At some median location, you receive a ball in the post. Immediately, the boxes become correlated — one is empty, and the other is not — because you don’t know which box the ball came from

Upon his arrival in New York, him and Elsa were met at quarentine by Edgar Bamberger and Herbert Maass (trustees of the IAS) who handed Einstein a letter from Flexner which read, in part:“There is no doubt whatsoever that there are organized bands of irresponsible Nazis in this country. I have conferred with the local authorities […] and the national government in Washington, and they have all given me the advice […] that your safety in America depends upon silence and refraining from attendance at public functions […] You and your wife will be thoroughly welcome at Princeton, but in the long run your safety will depend on your discretion”

Figure 1. The three types of bistable images. On the left is The vase-face illusion (in figure-ground reversals). In the center is being shown the Necker cube (in perspective reversal). On the right is My girlfriend or my mother-in-law (in meaning-content

El neurocientífico y fisiólogo británico David Marr afirmaba que "la percepción es la construcción de una descripción" y este dibujo serviría para probar su teoría.

Salvador Dalí estaba fascinado por las imágenes engañosas y llegó a crear una propia con su “extraña mujer”

La obra en cuestión fue asignada en su momento al caricaturista inglés W. E. Hill, quien la publicó en 1915. Pero el hombre en cuestión no habría más que adaptado a la ilustración de un concepto original que ya circulaba alrededor del mundo en formato de tarjetas coleccionables e intercambiables.Su registro más antiguo tomó la forma de una postal de origen alemán, fechada en 1888. Un ejemplar de 1890 la tituló "Mi esposa y mi suegra", haciendo clara alusión a la diferencia generacional y de aspecto entre ambas mujeres.La misma fue luego adaptada y alterada por otros, entre los que se destacaron los psicólogos R. W. Leeper y E. G. Boring que la popularizaron entre sus pares hacia la década del treinta.

La obra fue asignada en su momento al caricaturista inglés W. E. Hill, quien la publicó en 1915

In 1930, Walther Bothe and Herbert Becker performed an experiment, which was further improved by Irène and Frédéric Joliot-Curie. These authors, however, misinterpreted their results and believed to have observed γ-rays while they had seen neutrons. After additional experimental verifications, James Chadwick gave the correct interpretation of these experiments in 1932. Immediately, the new particle, the neutron, became an essential actor of nuclear and elementary particle physics, and completely changed the whole research landscape.

A quantum algorithm succeeds not because the superposition principle allows 'the computation of all values of a function at once' via 'quantum parallelism,' but rather because the structure of a quantum state space allows new sorts of correlations associated with entanglement, with new possibilities for information-processing transformations between correlations, that are not possible in a classical state space

Article PDF first page preview

A revised version of arXiv: 1711.01604, following referees' comments

the statement (attributed to Bohr by Aage Petersen) that "there is no quantum world,"

Today I found that Microsoft PDF Printer behaviour changed

Who cares if Microsoft fixes this

Disappointed, but not surprised...

Solution 1: install Google Chrome, open web page, Print, and select destination as "Save to PDF".

Exactly the same here! How disappointing... I printed a web page from Edge and wanted to highlight some text and send to someone. It can't be done. I couldn't find any settings in the Microsoft PDF Printer to change this

It looks like the new Edge broke Microsoft Print to PDF printer driver function

. This started happening in June of this year

Elements making up usual matter. Left (a): Periodic table arranged by Theodor Benfey* showing progress in complexity in the building up of atoms.

You can also try to reduce the number of if statements: remember that: IF a>b RETURN TRUE Is the same of: RETURN a>b

For teachers and parents and people who hate cursing: here’s a clean, Rated G version.

This year, I'm on leave to work at OpenAI on theoretical foundations of AI safety.

It’s like how young college graduates need experience to get a job but can’t get a job without experience

but it does not explain the special stability which occurs when nuclei have special "magic numbers" of protons or neutrons

Then the picture of a nucleus as a drop of incompressible liquid roughly accounts for the observed variation of binding energy of the nucleus:

Early models of the nucleus viewed the nucleus as a rotating liquid drop

Liquid drop model

Neutron stars[edit] In neutron stars, neutron heavy nuclei are found as relativistic electrons penetrate the nuclei and produce inverse beta decay, wherein the electron combines with a proton in the nucleus to make a neutron and an electron-neutrino: p  +  e−  →  n  +  νe As more and more neutrons are created in nuclei the energy levels for neutrons get filled up to an energy level equal to the rest mass of a neutron. At this point any electron penetrating a nucleus will create a neutron, which will "drip" out of the nucleus. At this point we have:[citation needed] E F n = m n c 2 {\displaystyle E_{\text{F}}^{n}=m_{n}c^{2}\,} And from this point onwards the equation E F n = ( p F n ) 2 c 2 + m n 2 c 4 {\displaystyle E_{\text{F}}^{n}={\sqrt {\left(p_{\text{F}}^{n}\right)^{2}c^{2}+m_{n}^{2}c^{4}}}\,} applies, where pFn is the Fermi momentum of the neutron. As we go deeper into the neutron star the free neutron density increases, and as the Fermi momentum increases with increasing density, the Fermi energy increases, so that energy levels lower than the top level reach neutron drip and more and more neutrons drip out of nuclei so that we get nuclei in a neutron fluid. Eventually all the neutrons drip out of nuclei and we have reached the neutron fluid interior of the neutron star.

I recently put up my first paper on the arXiv and have been dealing with the torrent of e-mails asking for citations. This is normal and part of the publication process,

Para terminar, quisiera recordar que hace cincuenta años, en 1972, se estrenó una película llamada Soylent Green, una distopía malthusiana que tiene lugar en el entonces lejano 2022, donde Charlton Heston interpreta a un policía que debe investigar la extraña procedencia del único alimento al alcance de unas masas al borde de la revuelta. La frase promocional de la película decía: «Año 2022, nada marcha bien, nada funciona, pero la gente sigue siendo la misma y hará lo que sea para conseguir lo que necesite». La película recibió en castellano el título de Cuando el destino nos alcance.

In this paper we discuss the so called "quantum omelette" created by Bohr and Heisenberg through the mix of (ontic) objective accounts and (epistemic) subjective ones within the analysis of Quantum Mechanics (QM). We will begin by addressing the difficult relation between ontology and epistemology within the history of both physics and philosophy. We will then argue that the present "quantum omelette" is being presently cooked in two opposite directions: the first scrambling ontological problems with epistemological solutions and the second scrambling epistemic approaches with ontological questions. A good example of the former is a new type of argumentation strategy attempting to justify the use of decoherence, namely, the "For All Practical Purposes" (shortly known as FAPP) type of justification

In this paper we address a deeply interesting debate that took place at the end of the last millennia between David Mermin, Adan Cabello and Michiel Seevinck, regarding the meaning of relationalism within quantum theory. In a series of papers, Mermin proposed an interpretation in which quantum correlations were considered as elements of physical reality. Unfortunately, the very young relational proposal by Mermin was too soon tackled by specially suited no-go theorems designed by Cabello and Seevinck

A Franson-type test of Bell inequalities by photons 10.9 km apart is presented. Energy-time entangled photon pairs are measured using two-channel analyzers, leading to a violation of the inequalities by 16 standard deviations without subtracting accidental coincidences. Subtracting them, a two-photon interference visibility of 95.5% is observed, demonstrating that distances up to 10 km have no significant effect on entanglement. This sets quantum cryptography with photon pairs as a practical competitor to the schemes based on weak pulses.

It is well known since the work of J.S. Bell, that one cannot have locally preexistent values for all physical quantities, whether they are deterministic or stochastic

A quantum state represents neither properties of a physical system nor anyone's knowledge of its properties

adamsmith April 18, 2023 This works -- make sure it says "CERN Document Server" when you hover over the save icon. If it doesn't, your translator just hasn't updated -- should happen within 24hs or you can force it from the Advanced Tab of the Zotero preference and the connector preferences. Xuefeng Ding April 18, 2023 Looks good. Now it works on CDS! Thanks.

roberto.franceschini September 17, 2021 I think I disagree on Inspires not having unique IDs. As a matter of fact I have python scripts (for BibDesk) that import from Inspires and CDS.Here is the doc https://github.com/inspirehep/rest-api-docand one example of document retrieval in JSONhttps://inspirehep.net/api/literature/451647CDS as well has an APIhttps://cds.cern.ch/help/hacking/search-engine-apiand one example of XML outputhttps://cds.cern.ch/record/2743741/export/xm?ln=en

adomasven January 18, 2017 Oh, I was not aware of this, but certainly needs to be looked into. I've created an issue to track progress. adomasven July 20, 2017 This is now supported in the connectors. Find the config editor under [ext_url]/preferences/config.html. You can generally obtain the [ext_url] by navigating to the connector preferences.

adamsmith January 11, 2017 so (from memory, but I think this is right) the connectors load up the translators into memory from Standalone, but they don't store the info for preference values anywhere. They then don't interact with Standalone while they execute the scraping code and only send the whole "package" (data and attachments) to Standalone, which is why the value for the preferences (which are in Standalone) come back as undefined. Or in other words, the translator.getHiddenPref function doesn't work in the connectors currently. There have been significant improvements for the next version of connectors made by Adomas, who I ping above, so I was hoping he'd know whether they handle this better.

None of the 'Z.getHiddenPref("ACS.highResPDF")' actually return a value, rather 'Undefined' even though these properties are clearly present in about:config of Zotero Standalone.

Nowhere it is assumed that the noncontextual factorizabilityused in Eq. 18 should be accepted. A formula like Eq. 18 can certainly be obtained forsome noncontextual hidden-variables models but these models cannot agree with quantummechanics

The claim of Lochak-Fine re-used, repeatedly by many authors (e.g., [14, 23] and referencestherein), is thus that Bell’s reasoning implicitly takes for granted that such non-contextualand non-physical joint probabilities like P (A1, A2, B1, B2) exist. As written in [10] ‘the ex-istence of deterministic [Local] hidden variables violates the quantum mechanical conditionthat joint probability distributions are well defined only for commuting observables

The claim is that assuming Bell’s factorizability for probabilitygenerally implies the existence of joint probabilities

Thebeauty and logic of the EPR deduction/theorem is often underappreciated and the fact thatcounterfactuality and determinism are actually derived and not inferred by EPR are stillnowadays misunderstood

(i) was favored by Einstein, (ii) by Bohm, and (iii) by Bohr and followers3

PR leads to three alternatives:(i)QM-L & QM-IC(ii)QM-NL & QM-IC(iii)QM-NL & QM-C (4)6

EPR founda clean way to go around Heisenberg’s principle limitations

his is becausefor a single particle one could invoke Heisenberg’s principle to impose a strong form of com-plementarity and contextuality: It is impossible to record in one single experiment the spinprojection for the x and z direction because σx and σz don’t commute. Therefore, one mustchoose between one experiment or the other and if one is doing sequential experiments it isknown that dispersion will occur in agreement with Heisenberg’s principle

Of course EPR understood perfectly well that counterfactual reasoning is in general forbid-den for a single particle using the usual approach to quantum mechanics

Asa direct consequence we can make a counterfactual reasoning: If Bob records along thex−direction and obtain for example +1 and Alice obtained for example the result −1 alongthe z−direction then we know for sure that Alice should have obtained the result −1 alongthe x−direction and Bob the result +1 along the z−direction even thougth these experimentshave not actually be done. Crucially the legitimacy of the counterfactual reasoning of EPRis mandated by Einstein-locality and is not an independent hypothesis. This justifies thefamous introduction of ‘elements of reality’ by EPR:If, without in any way disturbing a system, we can predict with certainty (i.e.,with probability equal to unity) the value of a physical quantity, then there exists5

The main idea is that a local operation made by Alice on particle 1 at space-time point x1should not influence what is happening to the second particle recorded by Bob at space-time point x2 if the two events are space-like separated (so that no-signal could propagatebetween the two points). As Einstein wrote in 1949 :But on one supposition we should, in my opinion, absolutely hold fast: the realfactual situation of the system S2 is independent of what is done with the systemS1 which is spatially separated from the former.[8], p. 85

Rigorously we should also include Φj (Xj ) the non-overlapping spatial parts of the wave function associatedwith the two remote particles.

suggesting that some effects or correlations having an empirical nature are not predicted orexplained by the theory. Of course, since quantum mechanics is supposed to describe every-thing this is apriori impossible.

By a complete physicaltheory they meant that: ‘every element of the physical reality must have a counterpartin the physical theory

ohr convinced Einstein that quantum mechanics is mathematically and physicallyself-consistent, and that it is illusory to try defeating Heisenberg’s principle directly

Retrospectively, one can say that perhaps what was the most astonishing for Einstein was the existenceof Heisenberg’s shift cut or split allowing to describe any measuring apparatus as quantum or classical inorder to remove paradoxes involving the uncertainty principle. Heisenberg also applied this approach inhis unpublished response to EPR.

Once more, Bohr showedto Einstein that it is not allowed to beat quantum mechanics with this kind of approachsince quantum mechanics must be used for describing every parts of the whole indivisiblesystem in agreement with the complementarity principle.

ohr recollection of these discussions shows thatEinstein at that time underestimated the coherence of quantum mechanics and didn’t realizethat the entanglement between particles and macroscopic systems in Einstein’s ‘which-path’experiment only makes sense if the macroscopic apparatus are also analyzed within quantummechanics1

Moreover, for Einstein realismwas a central prerequisite (more central even than determinism). In 1953 in a festschriftbook to honor de Broglie achievements Einstein wrote: I am not blushing to put the conceptof ‘real state of a system’ at the center of my meditation ([9], p. 7)

For Einstein the fact that quan-tum mechanics is a statistical theory should be explained by a deeper dynamical approach(probably deterministic) able to complete the statistical predictions by a classical-like me-chanical and realistic explanation.

Everything starts with Einstein who disliked very much the way quantum mechanics isbuilt and axiomatized as a complete undeterministic theory

Most confusions concerning EPR, Bell’s theorem and nonlocality arise from wavyand vague arguments associated with the definitions of Einstein locality and realism

The major-ity view considers that Bell’s theorem concerns what is known as ‘local realism’ i.e., thatit forces us to either abandon realism or locality

The previous summary is the view advocated by some physicists and philosophers, in-cluding Sheldon Goldstein [12], Tim Maudlin [18], Jean Bricmont [5], Travis Norsen [19, 20],David Albert [1] and of course John Bell [3], but this is not the majority view

In 1964 John Bell,based on EPR work, discovered his famous theorem ([3], chap. 2) firmly establishing thatquantum mechanics (irrespectively of being complete or incomplete) must be nonlocal

Bohm in his 1952 work showed that his own hidden-variables theory able to com-plete quantum mechanics is explicitely non-local.

More precisely EPR shows that either quantum mechanicsis incomplete or quantum mechanics is nonlocal i.e., it violates Einstein’s locality principle

the goal of theEPR article [7] was to show that if we assume the principle of Einstein locality quantummechanics must be incomplete

was actually a rediscovery of the old pilot-wave theory presented by Louis deBroglie in 1927 at the fifth Solvay conference

desde el punto de vista cuántico no hay ninguna diferencia entre una partícula y una cuasipartícula, pues lo fundamental (lo que realmente existe) son los campos, y no hay diferencia en física cuántica entre un campo efectivo y uno fundamental (de hecho mucha gente cree que los campos del modelo estándar son campos efectivos de una teoría fundamental unificada).

Mucha gente tiene en mente que un partícula es un «puntito» del espaciotiempo con ciertas propiedades (números cuánticos), pero esta visión clásica hay que desterrarla pues no tiene nada que ver con la realidad (aunque se use en la teoría de los campos clásicos antes de su cuantización y mucha gente se olvide de lo que significa realmente cuantizar un campo).

emulenews en 19 abril 2012 a las 11:06 dijo: Hector04, ¿qué es una partícula? Una fluctuación localizada de un campo que cumple ciertas propiedades. Un electrón es un fluctuación del «campo electrón» (que tiene 4 componentes divididas en dos parejas) localizada en cierta región del espacio (del tamaño de su longitud de Compton que depende de la energía de la fluctuación) y cuya energía (E) y momento (p) según el tensor energía-momento del campo cumple la famosa ecuación de Einstein E^2=(p c)^2+(m c^2)^2; qué es un electrón virtual, lo mismo pero sin cumplir dicha ecuación. El concepto «clásico» de partícula puntual con una función de onda asociada solo es aplicable para fluctuaciones del «campo electrón» con p=0. El vacío corresponde a las soluciones con E=0 y p=0.

git, y se puede obtener gratuitamente. El primer encontronazo puede ser un poco impactante si no estás acostumbrado a las aplicaciones de consola. El uso de interfaces gráficas puede ayudar bastante durante las primeras etapas. En particular, yo utilicé una llamada SourceTree

We present this account of history by relying on Peter Coles’s paper,so readers will notice that perhaps what is displayed at “Einstein andEddington” movie, which was publicly released on several TV channels,was not historically correct at least, or may be just plainly redacted.

COMPUTATIONAL SCIENCE AND ENGINEERINGHow Physicists Can Be Usefulby Martin Plumer, Centre de Recherche en Physique du Solide et Département de Physique, Université de Sherbrooke,Sherbrooke, Québec, Canada J1K 2R1ABSTRACTAs traditional employment opportunities in academic as well as in industry and government-funded basic research environmentscontinue to diminish, an increasing number of physics (and other science) graduates have found jobs developing and solving"numerical models" of a wide variety of physical (and other) phenomena

Having searched for truthvia both the physical andthe social sciences, I thenwent into politics wheretruth is completely irrelevant

"Así es como he intentado siempre que la física cobrase vida para mis estudiantes. Creo que es mucho más importante que recuerden la belleza de los descubrimientos que centrarse en las complicadas matemáticas; a fin de cuentas, la mayoría no acabarán dedicándose a la física." Walter Lewin

"Estamos aquí para desaprender las enseñanzas de la iglesia, el estado y nuestro sistema educativo. Estamos aquí para tomar cerveza. Estamos aquí para matar la guerra. Estamos aquí para reírnos del destino y vivir tan bien nuestra vida que la muerte tiemble al recibirnos."C. Bukowski.

"Aunque lo que decís es correcto, exponer este material a los no científicos es el equivalente intelectual de dejar que los niños jueguen con pistolas cargadas". Objeción de un físico a los autores del libro.

como se dice en el libro, en la universidad te sueltan los postulados de la mecánica cuantica y te ponen a resover ecuaciones diferenciales, sin que nunca sepas en profundidad lo que estás haciendo aunque apruebes el examen con nota.

Leer este tipo de libros hace que cada vez este más a favor del "calcula y calla" en las clases de Cuántica.

En mi opinión es lo peor y precisamente lo que le quita todo el rigor. Sin matemáticas no hay Cuántica. Desengañate la divulgación jamas te enseñara Cuántica. Si quieres saber Cuántica empieza estudiando los Espacios de Hilbert y si quieres saber Relatividad aprende Geometría diferencial, el resto son atajos para perder el tiempo y no enfrentarse a la realidad.

He sido un lector compulsivo de divulgación científica hasta que me di cuenta de que si la divulgación es buena te deja a medias y si es mala no hace más que liarte.

If you find any part of these notes illegible

So the problem is rooted in the notion of individuality, which is seen as inherent to classical mechanics. Therefore, so the argument goes, the problem is resolved by quantum mechanics, which treats indistinguishable particles in the right way. This argument raises a number of questions concerning the nature of individuality in classical and quantum mechanics, the way of counting states in both the Boltzmann and the Gibbs approach, and the relation of SM to thermodynamics

The standard textbook resolution of the paradox is that classical SM gets the entropy wrong because it counts states that differ only by a permutation of two indistinguishable particles as distinct, which is a mistake (Huang 1963).

If we then calculate the entropy of the initial and the final state of the two gases, we find that the entropy of the mixture is greater than the entropy of the gases in their initial compartments. This is the result that we expect.

An alternative is to interpret SM probabilities as propensities, but many regard this as problematic because propensities would ultimately seem to be incompatible with a deterministic underlying micro theory (Clark 2001).

However, long-run time averages are not a good indicator for how a system behaves because, as we have seen, they are constant and so do not indicate how a system behaves out of equilibrium.

the probabilities are interpreted epistemically as in Jaynes’ account (§6.6). But, as we have seen, a subjective interpretation seems to clash with the realist intuition that SM is a physical theory that tells us how things are independently of what we happen to know about them. This requires probabilities to be objective.

doloroso. Un caso especialmente sangrante es el del catedrático Ruiz de Elvira, que tiene una columna en el diario El Mundo, y que ya se está ganando el puesto de ser el divulgador que más absurdeces dice de todo el país

Albert8 de septiembre de 2015, 0:34Hoy he visto publicado otro post sobre este tema. Lo enlazo como información complementaria, saludos:http://www.cienciakanija.com/2015/09/07/mas-pruebas-para-apoyar-la-accion-fantasmal-a-distancia/

después de conceder una entrevista como "experto en energía nuclear", cosa que no es.

doloroso. Un caso especialmente sangrante es el del catedrático Ruiz de Elvira, que tiene una columna en el diario El Mundo, y que ya se está ganando el puesto de ser el divulgador que más absurdeces dice de todo el país

Albert17 de julio de 2014, 7:05Las tonterías que habitualmente suelta el tal Ruiz de Elvira son proverbiales. Un ejemplo:http://naukas.com/2013/12/19/fisica-de-particulas-conspiraciones-y-el-poder-de-los-medios/

Por supuesto, puedes hacer colisionar electrones y positrones a altas energías, pero ese es otro tema

En la desintegración electrón-positrón a velocidades bajas ambas partículas (permitidme que use el término "partícula" también para el positrón, aunque sea una antipartícula) suelen formar un estado ligado, llamado positronio, y luego emitan dos fotones. Estos fotones salen siempre en la misma dirección, pero con sentidos opuestos, para que se conserve así el momento lineal y tienen cada uno una energía de 0.511 MeV. ¿Qué obtenemos si multiplicamos la masa del electrón por la velocidad de la luz al cuadrado? Sorpresa, sorpresa, 0.511 MeV. Es decir, que pasamos de tener un electrón y un positrón con una masa de 0.511 MeV/c2 a tener dos fotones de una energía de 0.511 MeV.

El autor es Antonio Ruiz de Elvira, catedrático en física por la Universidad de Alcalá de Henares, del campo de la Física del Clima. Por desgracia, la Relatividad Especial no es su fuerte

la mejor estrategia para sacar buenas notas es saber que suele preguntar el profesor en cuestión, y qué tipo de respuestas está esperando encontrar en un examen

Una de mis frustraciones cuando estaba en la universidad es que sabía que el profesor estaba buscando una respuesta específica

en una reciente entrevista el responsable de Recursos Humanos de Google afirmó que el expediente académico no sirve para nada

Cuando estudiaba física pensaba que el método de evaluación era totalmente inadecuado. Largos exámenes en los que había que vomitar la información sin necesidad de entenderla. Resolución de problemas con una matemática muy complicada, pero sin ningún trasfondo físico. Siempre tuve la sensación de que la evaluación era innecesariamente difícil y que aún así la preparación que recibíamos tampoco era especialmente buena

Los modelos de colapso de la función de onda se basan en un simple principio, que la ecuación de Schrödinger es sólo aproximada, y que a partir de una cierta masa, combinada con un cierto tamaño de interferencia, ya no se puede usar. Está claro que estos modelos de colapso proponen una modificación a la teoría y no simplemente una interpretación. Por ese motivo, hay propuestas experimentales para testar los distintos modelos en combinación con la decoherencia. (Ver la referencia [1] para una extensa discusión).

Yo no soy de los científicos prepotentes que opinan que la filosofía es una idiotez, pero hay que intentar diferenciar la ciencia de lo que no es ciencia.

la epistemológica, que afirma que la función de onda es simplemente una herramienta matemática que nos da información sobre un sistema. Según esta segunda tendencia, no tiene sentido hablar del colapso de la función de onda en sí, porque lo que ocurre al medir es, simplemente, que actualizamos nuestra información.

so es algo que nunca había leído, hasta el artículo en Naukas, donde se afirma: "Es tan erróneo preguntarse qué significa el colapso de la función de onda como preguntarse si existe un dios." Es cierto que en este tema la filosofía juega un papel muy importante, pero de nuevo la afirmación anterior es bastante rara.

Sinceramente, no puedo entender como científicos con formación pueden hacer afirmaciones categóricas sobre este tema sin revisar antes la bibliografía. Mucho menos puedo entender que descalifiquen a gente que quiere investigar en esta dirección. Como he explicado hay una pregunta abierta, y hasta que no se cierre es perfectamente lícito indagar en ella. Es válido y es científico, no filosófico como dicen algunos. Hablamos de teorías y experimentos que pueden refutar esas teorías

Aunque yo creo profundamente que la naturaleza es probabilística

No olvidemos que el consenso no demuestra que algo sea de una determinada manera

Daniel Manzano5 de noviembre de 2012, 5:39Hola Emilio. Lo siento, pero no puedo acceder a esa revista. Ninguna de mis dos universidades está suscrita a ella. Si me puedes mandar el paper te lo agradecería. Podéis incluso subirlo a arXiv, donde estará accesible a todo el mundo. Por otro lado no te discuto hasta leer tu paper, pero hay bastante consenso sobre el tema. Te dejo unos apuntes de un profesor mío, que son muy ilustrativos. Ahí se plantea un experimento mental, el de San Jorge y el Dragón. En ese experimento, si supones que hay un sólido rígido, la lanza de San Jorge, que por lo tanto puede transmitir información de manera instantánea o supralumínica, te da una paradoja bastante clara. http://www.ugr.es/~jillana/SR/trans5.pdfResponderEliminarRespuestasEmilio López5 de noviembre de 2012, 14:12Hola Daniel, En el comentario anterior te pongo el enlace a la publicación original en inglés y la versión española. Lo cierto es que el enlace en español se ve mal, corto y pego de nuevo: http://www.dominguez-montes.com/images/docs/RelatividadEspecialSinRetrocausalidad-Espanol-16-10-10.pdfNo está formateado como aparece en la publicación, pero es la traducción directa.Sigo sin ver una publicación en la que se muestre el supuesto viaje al pasado al superar la velocidad de la luz. Todo el mundo lo da por hecho, pero nadie acaba por demostrarlo. EliminarRespuestasResponderDaniel Manzano6 de noviembre de 2012, 5:13Gracias, Emilio. Ya lo tengo impreso. En una primera ojeada me ha llamado la atención una cosa. Trabajáis con "ciclos cerrados", es decir que el los dos eventos se dan en la misma posición en un determinado sistema de referencia. ¿No es así? Lo que no termino de ver es si el observador también sigue un ciclo cerrado, como una trayectoria circular o algo así. Lo miraré con más detalle cuando tenga más tiempo. Saludos.

Emilio López5 de noviembre de 2012, 3:38Estimado Daniel, hace tiempo colaboré en un artículo publicado en Physics Essays acerca de la no retrocausalidad al superar la velocidad de la luz. Puedes consultarlo aquí: http://physicsessays.org/doi/abs/10.4006/1.3461009?prevSearch=dominguez+montes&searchHistoryKey=&La versión en español está aquí: http://www.dominguez-montes.com/images/docs/RelatividadEspecialSinRetrocausalidad-Espanol-16-10-10.pdfSe insiste en el asunto del "viaje al pasado" de manera habitual cuando se habla de velocidades superlumínicas, pero la cuestión no es tal. No hemos encontrado ninguna referencia del propio Einstein donde lo afirmara y, tal y como se indica en muchos medios de comunicación. Las velocidades superlumínicas serán o no posibles, pero su inexistencia no se debería a la violación de la retrocausalidad.

No es lo mismo entonces? Evidentemente no, si lo fuera no estaríamos tantos estudiando el tema del entrelazamiento

La medición afecta al estado, pero no es la que hace que tengamos incertidumbre

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sin embargo la comprensión completa de la asignatura y sobre todo de cada tema ,debido a la importancia que algunos o cada uno de ellos tienen para la formación del alumno, requieren de más tiempo,

el recuperatorio, en el que estaba Luke Skywalker (que para la información de los ayudantes, no viaja a velocidades cercanas a la velocidad de la luz) fue para tomerle el pelo a los aterrados alumnos