Sirva de señal de esta evolución el hecho de que aún noha recibido un premio Nobel ninguna persona nacida después de 1950

e deducen algunas tendenciaspreocupantes, como el envejecimiento progresivo de los científicos que los han recibido.

De nuevo, frente al Progreso Indefinido,tenemos una infinita sucesión de altibajos

Auguste Comte (1798-1857) insiste sobre las etapassucesivas de Condorcet, que reorganiza en tres: la teológico-militar, la metafísico-jurídica y lacientífico-industrial. Naturalmente, ninguna de las etapas tiene vuelta atrás. Nuestra llegada a la eracientífica es definitiva

La Utopía siempre está a la vuelta de la esquina

ue invierte la idea medieval deun pasado mejor y sostiene que el futuro es siempre superior al presente

La cultura es acumulativa.

En la literatura y las artes no hay progreso.

e aquí el poco interés de los pensadores deaquella época por la originalidad

Durante la Edad Media y el Renacimientodominó la teoría de que los grandes maestros de la Antigüedad eran insuperables

Experimentos recientes realizados con tomografía de emisión de positrones han demostrado que en elcerebro humano no existen zonas infrautilizadas

El título de silencioso hizo pensar equivocadamente aalgunos no expertos (entre los que se contaba Einstein) que esa parte del cerebro estaba desocupada

voces

se dedujo una tendenciahacia la disminución y se predijo

wishfulthinking

Todas ellas quedan fuera del métodocientífico

Col viso ritornai per tutte guantele sette spere, e vidi questo globotal, ch'io sorrisi del suo vil sembiante.

Cicerón, en su Somnius Scipionis, hace emprender a Escipión un viaje por las esferas celestes.Al mirar hacia la Tierra desde las alturas y verla tan pequeña (ver el mito anterior), Escipión seasombra por la importancia que se da en aquella mota a cosas tan ridículas como el Imperio Romano(que ni siquiera es visible desde donde él está)

Claudio Ptolomeo (100-170) escribió en su He Mathematik Syntaxis (más conocido por su nombreárabe, Almagesto): La Tierra, en relación con la distancia de las estrellas fijas, no tiene tamañoapreciab1e y debe considerarse como un punto matemático (Libro I, Capítulo 5).

existen mitos en la Ciencia, pero elhombre tiene una capacidad inagotable para crearlos y aferrarse a ellos

Los cálculos de Arquímedes eran conocimiento común de todos los eruditos de la antigüedad.

Dos siglos antes de Cristo, Arquímedes (287-212 a.C.) escribió un libro, El Arenario, en el quedescribe su intento de calcular cuestiones tan modernas como el número de partículas del universo y ladistancia de las estrellas (en su tiempo se creía que todas las estrellas fijas estaban situadas a la mismadistancia de nosotros). Para trabajar con números tan grandes, se vio obligado a idear su propio sistemade numeración, detallado en ese libro. Transformado a las medidas que hoy utilizamos, su resultado esasombrosamente exacto: las estrellas estarían a una distancia aproximada de un año-luz

Al llegar allí, Dante introduce un sorprendenteefecto de ciencia-ficción: Para pasar al otro hemisferio, Dante y Virgilio deben descender agarrándosea los pelos de Satanás, que está hundido en el hielo en el mismísimo centro de la Tierra. Pero en elmomento de pasar por él, tienen que darse la vuelta, porque la dirección

Sólo la gente ignorante creía, durante la Edad Media, la leyenda de que la Tierra es plana y losbarcos que llegaran a su extremo se caerían

l cálculo de Eratóstenes fue la causa de que losgeógrafos portugueses rechazaran los planes de Colón

durante el solsticio de verano en dos localidades de Egipto (Siena y Alejandría)

Él siempre creyó haber demostrado sus teorías

staba fuera del alcance de la náutica de la época

Pero, al revés que los geógrafos portugueses, que estimaban su circunferencia enunos 40.000 km, él creía que sólo media unos 25.000.

Como todas las personas educadas de la Edad Media y de la Antigüedad

El mito del Progreso Indefinido afirma que, una vez que hemos entrado en la era de la Ciencia,el desarrollo científico no puede volver atrás. Los inventos y los descubrimientos se irán sucediendo aun ritmo siempre acelerado, por lo que la curva del desarrollo científico se aproximaría a unaexponencial

La Ciencia, con mayúscula, siempre se ha dirigido (al menos en teoría) al descubrimiento de laverdad

Aquí utilizo el término en su sentido clásico: como sinónimo de "leyenda", "fábula","ficción", no en el más reciente, que lo deja reducido a un sinónimo innecesario de "famoso".

With respect to the last question: "Is quantum theory only an incidental historical construction instead of the closest approximation of the truth?" The relation between physical theories and "truth" is not that simple

On some level, even Feynmann knows these arguments are circular. You can tell by the uncharacteristic frustration in his voice around 39:30 when he says "i don't know how much I can emphasize this...it IS particles in every way..."

It's circular because he uses the clicks in the photomultiplier as proof that light is corpuscular, but to explain how the photomultiplier words, he relies on the "fact" that light is made of photons.

The interpretations of quantum mechanics are full of the type of circular reasoning which Bob identifies. The most glaring examples come from identifying photons as particles. Even Feynmann is guilty of this, as you can see in this video clip: https://www.youtube.com/watch?v=eLQ2atfqk2c

@Bob Yes, so it goes. A nice example: experiments with ββ\beta decay seemed to show that the energy conservation principle is violated. Then, Pauli proposed a particle that he named "neutron". Chadwick found a particle more massive, the neutron, which wasn't satisfactory. So, the research had to continue. In 1956 Cowan, Reines, Harrison, Kruse, and McGuire published confirmed that they had detected the neutrino. But the neutrino had or didn't have rest-mass? So, more research. And so on, and so on. \endgroup – Sofia Dec 23, 2014 at 18:58

@Bob: You have a very restricted model of "common sense" . "Common sense" before Galileo was Aristotle's four elements theory of why gases rise to the heavens and earth can be found closer to the center of the universe. It was also Ptolemy's common sense that everything in the heavens rotates around the Earth. And isn't that obvious when you look up there? \endgroup – CuriousOne Dec 23, 2014 at 15:47

His second question is "how the information is exchanged between them". To this, indeed, we have no answer at all. \endgroup – Sofia Dec 13, 2014 at 9:06

There is no precise answer to the cause of entanglement is known (I did not come across any such answer). The superposition principle and the tensor product structure of Hilbert space of combined system leads to the possibility of entangled state. It is well understood in the case of pure state, but for the mixed state case it is quite involved.

our comment is too much sophisticated (I apologize for saying this - no intention to upset you - but I was a teacher for many years). The question is clear, the fellow asks what we do to the particles for entangling them. And the answer is also simple, we destroy one or more of the state-products. People that begin studying QM ask typical questions. \endgroup – Sofia Dec 13, 2014 at 1:12

You are asking an unscientific question. Physics does not give causes, it merely describes observations. The structure of the theory of quantum mechanics was chosen to reflect the observed data (which was mostly spectra, scattering, spins and chemical reactions). As it turns out, that structure was chosen so well, that it happens to describe entanglement correctly, even though at the time of the development of QM the phenomenology of entanglement was not known, yet. One could, falsely, say that the structure of QM causes entanglement, but it's really the other way around. \endgroup – CuriousOne Dec 13, 2014 at 0:54

This question already has answers here: What is quantum entanglement? [closed] (3 answers) Closed 7 years ago. What is the cause of quantum entanglement?

The nucleus is small so the chance of the electron being in the nucleus is small, but there is no reason it can't be in the nucleus. \endgroup – George Herold Jan 12, 2015 at 0:43

But the biggest probability is that the electron be outside the nucleus. The radius of the electron cloud is 10−810−810^{-8}cm, and the radius of the nucleus is cca. 10−1210−1210^{-12}cm.

As you can see from the left side column in the picture, in the state n=1n=1n=1, i.e. on the inner electron shell, the electron has a non-zero and non-negligible probability to be found at the nucleus position - see the innermost bright region. Moreover, the phenomenon of electron-capture by a nucleus is known, see here.

It can be. This is why "beta capture" or "inverse beta decay" happens: transmuting some radioisotopes to nucleusses with the next lowest atomic number. \endgroup – Selene Routley Jan 12, 2015 at 0:58

What for, density matrices? Why complicate the things? Would it explain the collapse? I remember that von Neumann had some proof about partitions of an ensemble, but the proof was criticized. Why get into all this? \endgroup – Sofia Dec 10, 2014 at 0:31

Take a photon, put it in a superposition of left and right polarized light (this is no problem) and then send it through a right-polarizor. What you observe is: Either the photon goes through or it doesn't. You prepared it in a state that is neither left polarized nor right polarized but after the polarizer, it is polarized. That's the collapse. How to explain it? How does the photon choose whether it is right- or left polarized and subsequently passes the polarizer or doesn't? And how does it become one of the two options, if it is previously something different? As I said, we don't know.

The mathematician and physicist that dealt with this question was John von Neumann. But, to go straight to the conclusion, he wasn't able to give an answer. He introduced the phrase "wave-packet reduction", or in short, "collapse". It's just a name, because we don't know how the things work in fact

@ACuriousMind: you realize that this is the Feynman diagram equivalent of the "shut up and calculate interpretation" of quantum mechanics. Telling people they're not supposed to think is always a bad idea. \endgroup – Peter Shor May 18, 2015 at 2:35

"There is no "action at a distance" in nature." - That is a bold assertion. Also, what would be the difference between action at a distance and an action mediated by something undetectable (i.e. virtual particles)? \endgroup – ACuriousMind ♦ Nov 16, 2014 at 17:13

There is no "action at a distance" in nature

Bohm's interpretation didn't get into the internal dynamics of elementary particles. Look also what says D. Durr, in his book "Bohmian Mechanics": "Spin is indeed a truly quantum mechanical attribute." \endgroup – Sofia Jan 24, 2015 at 20:31

This answers also your last question, why "the spin of a particle is always measured with its full magnitude along the plane of measurement?" Because this is what the wave-functions gives us: for a spin 1/2 fermion it gives us two possible beams, or, if the spin is polarized in the direction of the field, one beam

I also saw your question 2) "if a bohmian particle only has position, how does it interact with other bohmian particles to transfer momentum? Surely the bohmian particle itself has momentum as well as position, right? Which would mean that properties of the particle are at least mass, position, and velocity." NO!!! It's not the Bohmian particle that interacts with another Bohmian particle. The wave-guides interact, exactly as requires the Schrodinger equation. We get a two-body wave-function - wave-guide - that guides the two-particles. And the two Bohmian particles have, each one, at any time, position and Bohmian velocity.

FINALLY to your question 3) "Answers to my question here seem to say that the imaginary position of the bohmian particle actually has nothing to do with "where" the detector detects the particle." That's exactly opposite. Exactly for this purpose was built the BI. It was proposed as a tentative to get rid of the collapse, i.e. that part of the wave-function that comprises the Bohmian particle, that part makes the detector to do a recording. See my explanations above. The detector is supposed to produce a recording iff the Bohmian particle passes through the detector, and at the time when it passes.

About I do not participate to this site any longer. I do not accept a situation in which, a scientific answer not understood by some users, is downvoted repeatedly instead of asking clarifications from the poster of the answer. And such a situation is considered normal, instead of being avoided. And when the poster of the answer protests, he/she is considered not O.K. Given this situation, I don't see any reason why offering my knowledge at all.

R I V I S T A D E L NUOVO CIMENTO VOL. 4, N. 2 1981Quantum Mechanics Reality and Separability.F. SELLERII s t i t u t o d i E i s i e a dell' Universitd - B a r iI s t i t u t o lqazionale di F i s i e a _Nueleare - Sezione d i B a r iO. T~mozzi(')I s t i t u t o d i F i l o s o / i a dell' Universitd - P e r u g i a(rieevuto il 19 Iqovembre 1980)

A) Unlike Bell's theorem, the GHZ argument is based on unverifiedassumptions concerning the physical reality of a particular state vector andmeasurability of certain Hermitian operators pertaining to a system of threecorrelated spin-(l/2) particles.B) Unlike Bell's theorem, the GHZ formulation is limited to determinis-tic local theories.C) A direct experimental test of the GHZ argument is probably imposs-ible.

It is interesting to recall here the commentmade by Gell-Mann[132]: ((Niels Bohr brainwashed a whole generation ofphysicists into believing that the problem had been solved fifty years agog>

It is this notion which Bohm refers to as unbroken wholeness that isassociated with a system of two correlated quantum particles. This may seemsimilar to Bohr's idea of individed wholeness but there is an important differ-ence. Bohm's approach implies that the ((whole~>is analysable in thought (e.g.,through the concept of nonclassical but causal trajectory of a particle acted onby the quantum potential); in constrast, Bohr maintained that the entireexperimentally relevant situation was inherently an unalysable whole aboutwhich nothing could be said at all

Here itmay be noted parenthetically that Einstein was not sympathetic to thequantum-potential point of view, primarily because he insisted on a descriptionof physical reality in space-time with only local interactions.

Thenonlocal connection is manifested only in the correlations (revealed througha comparison of the experimental data independently gathered at each of thetwo particles) and not at the level of statistical properties of the particles ateach end of the connection

But in theclassical domain it is always possible to assign a priori well-defined values to allobservable quantities. This result of Garg and Mermin is disturbing for thecoherence and rationality of the existing quantum theory, which seems toextend its (~magic,) predictions also to the macroscopic domain where classicalphysics had successfully banished all <(magicab) approaches

Other interesting consequences of local realism were found by Garg andMermin[61] who were able to deduce Bell-type inequalities for two spin-jparticles (with arbitrary j). They could show that the singlet state for twoparticles with spin j leads to violations of local realism for arbitrarily largevalues of j right up and above the threshold of the classical world

We disagree with the contention by Mermin [46] that the GHZ formulation(ds an altogether more powerful refutation of the existence of elements ofreality than the one provided by Bell's theorem~. The reasons are, first of allthat one can talk of refutation only after an unambiguous experimental verdict,and moreover

-Pn (formerly known as -P0 and -PN) instructs Nmap to skip the host discovery phase, and instead assume that all hosts are up.

there's either nothing there, or there's a firewall configured to drop all traffic directed to it.

The nmap result "filtered" implies that (if you know there is a host with that IP address) access to the port has been blocked by a firewall or similar, which is dropping the traffic.

It's possible that the host's firewall has rules that are denying access to the IP from which you're running the scan

Netcat Nc o Netcat se utiliza para una gran variedad de objetivos relacionados con redes y sus diferentes protocolos. Puede hacer cosas desde abrir conexiones TCP/UDP, enviar paquetes, escuchar en puertos de nuestra elección, realizar un escaneo de puertos… Permite escribir la salida a un fichero local, con lo que perfectamente vale para traspasar ficheros y de hecho se utiliza en ciencia forense informática para exfiltrar archivos de sistemas cuando es preciso un análisis en vivo (con el sistema funcionando) sin provocar modificaciones que invaliden la investigación. Escaneo de un puerto con Netcat nc -zv 127.0.0.1 80 Analizar varios puertos con Netcat nc -zv 127.0.0.1 22 80 443 Analizar un rango de puertos con Netcat nc -zv 127.0.0.1 20-30 nc -w2 127.0.0.1 22 </dev/null Nota: el valor w hace referencia al «wait» time, valor que quizá nos interese controlar si vamos a examinar muchos puertos o si queremos incluir el comando en un script.

Nmap Nmap o Network Mapper es una herramienta open source válida para auditoría de redes y también auditoría de seguridad, pudiendo lanzar incluso scripts contra servicios vulnerables. La información que puede ofrecer es inmensa y valiosa, por lo que sigue siendo sin duda the way to go siempre que esté disponible. Para el caso que nos ocupa, podemos usar alguna de estas variantes: Escanear uno/varios puertos. Separaremos con un guión el primero y el último: nmap -p 80-995 192.168.1.43 Escanear todos los puertos de un host nmap -p- 192.168.1.43 Más comandos y pautas para utilizar Nmap.

The version of OpenSSH included in 16.04 disables ssh-dss. There's a neat page with legacy information that includes this issue: http://www.openssh.com/legacy.html In a nutshell, you should add the option -oHostKeyAlgorithms=+ssh-dss to the SSH command: ssh -oHostKeyAlgorithms=+ssh-dss root@192.168.8.109

However, if the test file is in fact 0 bytes, then your shell is behaving, but it is possible that you just have a very old version of rsync. You can tell the client end (assuming it is the newer end) to not advertise such a high version that the old rysnc server version doesn't recognize it. You can do this using the --protocol= option. In my case, using --protocol=30 did the trick. If you are still having trouble, try ssh in as the user rsysnc is connecting with and try running rsync --version to see if the shell can find rsync. If you get something that says command not found, then rsync might not be installed on the machine you are connecting to or it might not be in the path. Rsync does have options for specifying the path of the remote end, read the man page(s). ShareShare a link to this answer Copy linkCC BY-SA 3.0 Improve this answer Follow Follow this answer to receive notifications answered Jul 16, 2014 at 20:28 AzendaleAzendale 1,50522 gold badges1111 silver badges1414 bronze badges 2 +1 for the hint about --protocol which solved my problem with a 2.5.6 server (protocol version 26) and a 3.1.0 client (protocol version 31) – MattBianco

If testfile is NOT 0 bytes, then the trouble is that your shell is outputting something. Check /etc/profile, .profile, .bashrc, .cshrc, etc. If it is, you can change it to check if your terminal is interactive and only output text by using the following code in a bashrc. Something equivalent exists for other shells as well: if shopt -q login_shell; then [any code that outputs text here] fi or alternatively, like this, since the special parameter - contains i when the shell is interactive: if echo "$-" | grep i > /dev/null; then [any code that outputs text here] fi

you saved my day!!!!! ...but not the last night..:/.. – Nikita

Hominin timeline

Noah 12 January 2013 / 1:30 pm There seems to be a lot of confusion in the comments. #5 (Peter): there is no recombination in mt DNA, it is transmitted from mother to child unchanged and simply undergoes periodical mutation at a relative constant rate (admittedly depending on the environment, but as is any DNA). So that doesn’t explain the difference at all. This difference needn’t explaining though, there is no reason why mt Eve and Y Adam should be contemporary. #6 (Eve) and #9 (Tommy): this article is old and the theory of a faster clock rate has been dismissed long ago.

extendería

se lo denomina ACMR-Y (en inglés Y-MRCA), siglas del «ancestro común más reciente según el cromosoma Y».

el Adán cromosómico o Adán cromosómico-Y habría sido un hombre africano (homólogo de la Eva mitocondrial) que en la evolución humana correspondería al ancestro común más reciente humano masculino que poseía el cromosoma Y del cual descienden todos los «cromosomas Y» de la población humana actual

DF27: vasco-ibérico

R1b Y-full tree Haplogroup YTree v8.10.00 2012-2021 YFull™

The values ±μB do thus not correspond to the continuum of values −μ·B Einsteinand Ehrenfest had conjectured. The energy term V = −μ·B is a macroscopic quantity. It is a statistical average overa large ensemble of fermions distributed over the two microscopic energy states ±μB, and as such not valid for in-dividual fermions.

the fermions precess around the magnetic-field just likeEinstein and Ehrenfest had conjectured.

he exact theory of the Stern-Gerlach experiment andwhy it does not imply that a fermion can only have itsspin up or downGerrit Coddens

Medidas Stern-Gerlach sucesivas sobre electrones (imagen del libro «La realidad cuántica», de RBA ediciones, colección «Un paseo por el cosmos», número 32).

Según el Principio de superposición, aplicado al espín de un electrón, en ausencia de determinación de su proyección sobre una dirección cualquiera, marcada como OZ, en la correspondiente función de onda se superponen todas las orientaciones con origen en O y sobre la superficie de dos conos enfrentados por su vértice común en O (únicas compatibles con el hecho de que, bajo medida de la componente , el resultado sea bien ( ,»hacia arriba»), bien ( ,»hacia abajo»).

Así que, si lo ha leído alguna vez, olvídelo: el espín no tiene nada que ver con un momento angular de rotación de una partícula

Tal y como cuenta Gerlach en sus memorias la plata estaba reaccionando con los vapores de mercurio que provenían de su respiración y de los cigarrillos que fumaba habitualmente»

cuantizaciones para el momento angular orbital y su tercera componente según y

En los modelos pre-cuánticos de la época del experimento, ese solitario electrón era supuesto en órbita en torno al núcleo del átomo y el conjunto de capas electrónicas internas llenas, siendo él solo el responsable del momento magnético, al aportar los restantes electrones una contribución neta nula al momento angular

Obsérvese que el momento magnético dipolar tiene igual dirección que el momento angular orbital, y sentido opuesto

Consequently, when thisbeam enters the next Stern-Gerlach device with the field oriented in the z direction, all theatoms will emerge in the S z = − 12 ! beam. This is in agreement with the probabilities thatfollow from Eq. (6.28) with θi = π, i.e.P(S z = 12 !|S z = − 12 !) = cos2 ( 12 π) = 0P(S z = − 12 !|S x = 12 !) = sin 2 ( 12 π) = 1 (6.32)

“En esta tesis doctoral describimos por primera vez la evolución en el tiempo de los experimentos de Stern-Gerlach consecutivos

En este caso, la emisión del fotón ocurre sin que el electrón cambie su órbita en torno al núcleo atómico, lo único que cambia es el sentido de su orientación. Este fenómeno de hecho ocurre y ha sido observado. El ejemplo más importante, históricamente hablando, ocurrió en los años treinta del siglo XX cuando se descubrió un “silbido” de radiofrecuencia que variaba en un ciclo diario y que parecía ser de origen extraterrestre. Tras sugerencias iniciales de que este “silbido” pudiera ser ocasionado por el Sol, se observó que las ondas de radio parecían venir del centro de la galaxia. Estos descubrimientos fueron publicados en 1940, y fue Hendrik van der Hulst quien en 1944 descubrió que el hidrógeno neutral podía producir una radiación con una frecuencia de 1420.4058 MHz a causa de dos niveles de energía cercanamente espaciados correspondientes al estado basal (fundamental) del hidrógeno. De este modo, la línea de 21 centímetros (1420.4 MHz) fue detectada por vez primera en 1951,

dándosele arbitrariamente al momento magnético intrínseco del electrón el valor de un magnetón de Bohr

Antes de llevarse a cabo un experimento Stern-Gerlach, se supone que los átomos de plata antes de entrar en el campo magnético están orientados al azar. Si el 47avo electrón en el átomo de plata se comportase como una partícula clásica, esperaríamos ver reflejados todos los valores posibles del momento magnético entre |μ| y |-μ| al llevarse a cabo las alineaciones con el campo magnético. Pero al llevarse a cabo el experimento, sólo se ven dos valores. De este modo, los dos valores posibles de la componente-z del spin S que llamaremos Sz+ y Sz- resultan ser múltiplos de alguna unidad fundamental del momento angular, la cual resulta ser precisamente ħ.

El spin del electrón S, siendo el símil (aunque intrínseco) del vector momento angular L, apunta en dirección opuesta a la dirección del vector momento magnético μ por la misma razón señalada arriba, la signo negativo de la carga del electrón

Obsérvese que se asigna (vectorialmente) al momento magnético μ una dirección opuesta a la dirección vectorial del momento angular L, en virtud de la carga eléctrica negativa del electrón (para una partícula con carga positiva μ y L apuntan en la misma dirección).

en el experimento Stern-Gerlach no se hace saltar al electrón de una capa energética discreta a otra. Estamos entonces ante otro tipo de fenómeno que no involucra “saltos” de energía y en el cual el número cuántico n del nivel de energía en que se encuentra cada átomo permanece igual antes y después de pasar por un aparato Stern-Gerlach, lo cual nos obliga a ir pensando ya en la adjudicación de un nuevo número cuántico al átomo que es independiente del número cuántico que caracteriza a la energía del átomo. Fue precisamente el físico teórico Wolfgang Pauli el que sugirió la adopción de un nuevo número cuántico, un cuarto número cuántico a ser agregado a los otros tres números cuánticos que ya se conocían, simbolizado como s. Y aunque éste nuevo número cuántico resulta ser una propiedad que depende en forma intrínseca del electrón

Lo que sucede en el experimento Stern-Gerlach es de naturaleza eminentemente magnética. Al igual que como ocurre con la aguja magnetizada de un compás que tiende a alinearse en el sentido Norte-Sur, algo en el átomo debe estar actuando también como un pequeño imán que lo hace alinearse con el campo magnético que le es aplicado. Expresamos esto formalmente diciendo que los campos magnéticos ejercen fuerzas sobre objetos y partículas que tienen momentos magnéticos. Estas fuerzas son bien comprendidas, y las mismas reglas parecen aplicar para objetos macroscópicos que para objetos sub-microscópicos

A largo plazo, con ordenadores de más de 10.000 qubits podríamos violar la seguridad de la inmensa mayoría de las transacciones electrónicas.

Esa “explicación” está plagada de problemas. Por ejemplo, nada que esté sucediendo en Alfa Centauri puede afectarnos hasta dentro de 4,63 años.

el problema es empeñarse en explicar los fenómenos cuánticos usando conceptos inadecuados

Los observadores no juegan ningún papel esencial.

Mes: agosto 2012

Mes: diciembre 2013

Mes: septiembre 2014

Mes: diciembre 2014

-P: Pero cuando hablas de preguntas, te refieres a mediciones, ¿no?. -R: Sí, mediciones. Tenemos un determinado observable físico, anotamos el resultado, a continuación sobre ese mismo sistema, otro. Además son observables sencillos, solo tienen dos posibles valores, + 1 o -1. A continuación medimos un segundo, anotamos, y a continuación medimos un tercer observable físico. Hay seis situaciones distintas, y éstas involucran nueve medidas diferentes. Son seis situaciones medidas de tres observables, uno tras otro. Hay una desigualdad que se tiene que cumplir en cualquier teoría de las llamadas de variables ocultas no-contextuales que dice que tiene que ser como mucho 4. La mecánica cuántica, en un caso ideal, si no tuviésemos ningún tipo de imperfecciones, tendría que salir 6. En el experimento, que tiene ciertas imperfecciones inevitables, no llega a salir 6, pero sale 5,5. Sobre conjuntos mínimos de contextos cuánticos: A. Cabello, «El teorema Kochen-Specker llega al laboratorio«, Investigación y Ciencia 461 (2015) 8-9.

Pruebas experimentales de la contextualidad

Mes: agosto 2015

Bibliografía [GAL-89] A. Galindo y P. Pascual, Mecánica Cuántica I, Eudema, Madrid, 1989. A. Einstein, B. Podolsky and N. Rosen, Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?, Physical Review 47 (1935) 777-780. G. García Alcaine, Enredo cuántico (también en Enredo cuántico). E. Schrödinger, Discussion of probability relations between separated systems, Proceedings of the Cambridge Philosophical Society 31 (1935) 555-562. Density Matrix Formalism: http://www.cithep.caltech.edu/~fcp/physics/quantumMechanics/densityMatrix/densityMatrix.pdf http://www.pa.msu.edu/~mmoore/Lect34_DensityOperator.pdf http://pages.uoregon.edu/soper/QuantumMechanics/density.pdf http://ocw.mit.edu/courses/chemistry/5-74-introductory-quantum-mechanics-ii-spring-2009/lecture-notes/MIT5_74s09_lec12.pdf K.T. McDonald: Density-Matrix Description of the EPR «Paradox«

Advertencia: correlaciones cuánticas sin entrelazamiento: Correlaciones cuánticas clásicamente inalcanzables en sistemas sin entrelazamiento: Una demostración experimental de la violación de las desigualdades de Kochen y Specker para un único sistema cuántico, un fotón que puede viajar a lo largo de tres caminos posibles donde se realizan diferentes medidas cuyos resultados deben ser compatibles entre sí: R. Lapkiewicz et al, «Experimental non-classicality of an indivisible quantum system», Nature 474 (2011) 490-493. En análisis de A. Cabello: A. Cabello, «»Correlations without parts», Nature 474 (2011) 456-458: Kochen and Specker noticed that quantum mechanics is in conflict with classical physics even for non-composite systems. This conflict can be converted into experimentally testable violations of classical correlation inequalities and into experiments showing that quantum correlations occur for any quantum state, not necessarily just for entangled ones. (Lapkiewicz and colleagues´) findings are therefore of fundamental importance, because they confirm that quantum correlations also occur in system in which entanglement, which is supposed to be the most emblematic feature of quantum mechanics, cannot be defined. It seems that Bell experiments, composite systems and entangled states are not enough to provide a complete understanding of the physical principles behind quantum mechanics: quantum correlations exist without them.

Bibliografía [BOH-79] Bohm, D., Quantum Theory, Dover, 1979. [ESP-95] Espagnat, B.d’; Veiled Reality. An analysis of Present-day Quantum Mechanical Concepts, Addison-Wesley, 1995. [FER-96] Ferrero, M., Fernández-Rañada, A., Sáchez-Gómez, J.L. y Santos, E.; Fundamentos de Física Cuántica. Curso de verano de El Escorial, Complutense, Madrid, 1996. [JAM-74] Jammer, M.; The philosophy of Quantum Mechanics,Wiley, 1974. [SEL-88] Selleri, F., ed.; Quantum Mechanics Versus Local Realism. The Einstein-Podolsky-Rosen Paradox, Plenum, New York, 1988. A. Cabello: Tesis doctoral: Pruebas algebraicas de imposibilidad de variables ocultas en mecánica cuántica. C. Saulder: Contextuality and the Kochen-Specker Theorem.

 Como ilustración adicional, puede consultarse la excelente divulgación sobre el tema: Cassinello; Rev. Esp. Fís., dic. 1997, p. 52. A. Cassinello and A. Gallego, The quantum mechanical picture of the world, American Journal of Physics 73, 3 (2005); pp. 273-281.

Es interesante recalcar que, aunque en un sentido matemático la violación del realismo local pueda considerarse una consecuencia especial de la contextualidad cuántica (correspondiente al caso en que las medidas se realizan en regiones separadas), la violación de un teorema tipo Bell es considerada por algunos autores más fundamental que la violación de la no-contextualidad: al invocarse contextos espaciales separados, pareciera que la causalidad relativista debiera desterrar la contextualidad… ¡pero no lo hace!

El teorema de Bell-Kochen-Specker (1966-1967) divulgó y generalizó la aceptación de la contextualidad cuántica (en realidad establecida ya en el teorema de Gleason de 1957), una propiedad cuántica más general que la no-localidad (¡entendida ésta a la Bell!, véase el apartado terminología en la entrada sobre el teorema EPR), y existen ya experimentos realizados que han probado la contextualidad cuántica.

Las matemáticas de la cuántica: índice

Interferómetro de Franson

Bibliografía y referencias

Divisores de haz e interferómetros

La realidad cuántica, por María C. Boscá: Un libro que introduce y divulga la mecánica cuántica. En la colección Un paseo por el cosmos, de RBA ediciones:

Bibliografía [BEL-90] Bell, J.S.; Lo decible y lo indecible en mecánica cuántica, Alianza Univ., 1990. [ESP-76] Espagnat, B.d’; Conceptual Foundations of Quantum Mechanics, Benjamin, 1976. [GAL-89] Galindo, A. y Pascual, P.; Mecánica Cuántica, Eudema, Madrid, 1989. [ICA-91] Icaza, J.J.; La construcción de la Mecánica Cuántica, Univ. del País Vasco, Bilbao, 1991. [JAM-74] Jammer, M.; The philosophy of Quantum Mechanics,Wiley, 1974. [NEU-91] Neumann, J. von; Fundamentos matemáticos de la Mecánica Cuántica, Consejo Superior de Investigaciones Científicas, Madrid, 1991. [SEL-88] Selleri, F., ed.; Quantum Mechanics Versus Local Realism. The Einstein-Podolsky-Rosen Paradox, Plenum, New York, 1988. [WHE-83] Wheeler, J.A. y Zurek,W.H., eds.; Quantum Theory and measurement, Princenton Univ., Princenton, 1983.

1. Cuando en 1952 Bohm publicó su teoría de V.O., fue completamente ignorada, a pesar de que su mera existencia como teoría de V.O. determinista (no local) capaz de reproducir los resultados de la M.C. (no relativista) debiera haber suscitado la atención, al menos sobre cómo era posible su misma existencia. 2. Bell ha narrado como, atraído fuertemente por el argumento EPR y la posibilidad relacionada de elaborar una descripción teórica más completa que la de la M.C., en cuanto tuvo conocimiento de que von Neumann había demostrado su imposibilidad abandonó el tema. Posteriormente, sin embargo, «al ver lo imposible realizado», decidió analizar cómo era posible, es decir, si es que el teorema de von Neumann era erróneo: J.S. Bell, «On the impossible pilot wave», Foundations of Physics, 12 (1982) 989-999; trad. en [BEL-90], pp. 221-233.

famosa prueba de imposibilidad de V.O. que realizó von Neumann en 1932, el tema quedó “dormido”, hasta que D. Bohm, en 1952, conseguiría revitalizarlo

Born como Heisenberg, en sus artículos básicos “demoledores” del indeterminismo, sobre la interpretación probabilística de ψ y las relaciones de indeterminación

Algunos enlaces: Sven Aerts, Paul Kwiat, Jan-Ake Larsson and Marek Zukowski; Two-photon Franson-type experiments and local realism. https://qutools.com/qued/qued-sample-experiments/sample-experiments-franson-interference/ https://www.researchgate.net/publication/348741037_The_Franson_experiment_revisited Two-photon Franson-type experiments and local realism

Cuando se consigue la indistinguibilidad entre los dos procesos LL y SS, se está en las condiciones de aplicación de la suma de amplitudes a la Feynman, de modo que las correspondientes amplitudes de probabilidad se suman según , proporcionando la probabilidad de coincidencia en los detectores

hermosa demostración de la imposibilidad teórica del realismo local.

que:

3)  El fotón sigue el camino corto y el otro, , el largo: 4) El fotón sigue el camino largo y el otro, , el corto:

1) Ambos fotones 1 y 2 (o idler y signal) siguen el camino largo: 2) Ambos fotones siguen el camino corto S en su interferómetro:

3) El fotón signal sigue el camino largo y el idler el corto. 4) El fotón signal sigue el camino corto y el idler el largo.

Como siempre, si este desfase óptico   se hace mucho mayor que el tiempo de coherencia del fotón, no se observarán interferencias.

Interferómetro de Franson

Figura del montaje experimental del doble cristal de Zou-Wang-Mandel; fuente: http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.67.318.

Like most experiments, this one can be confusingif you think about it the wrong way (e.g.,semiclassically), but is simple & unambiguous if you remember the Feynman rules.

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This symmetry shows that Alice and Bob cannot, in fact, use their EPRpair to communicate faster than the speed of light, and thus resolves the apparent paradox.

the actual experimental valuesare invariant under change of observer. The experimental results can be explained equallywell by Bob’s measuring first and causing a change in the state of Alice’s particle, as theother way around.

as Einstein, Podolsky and Rosen recog-nized, in deep inconsistencies when combined with relativity theory

The second standard description is in terms of cause and effect. For example, we saidearlier that a measurement performed by Alice affects a measurement performed by Bob.However, this view is incorrect also,

However, the result of actual experiments performing these measurements show that Bell’sinequality is violated. Thus quantum mechanics cannot be explained by any local hiddenvariable theory. See [Greenstein and Zajonc 1997] for a highly readable account of Bell’stheorem and related experiments

However, this point of view cannot explain the results of measurementswith respect to a different basis

Einstein, Podolsky and Rosen proposed that each particle has some internal state thatcompletely determines what the result of any given measurement will be. This state is,for the moment, hidden from us, and therefore the best we can currently do is to giveprobabilistic predictions. Such a theory is known as a local hidden variable theory. Thesimplest hidden variable theory for an EPR pair is that the particles are either both instate |0〉 or both in state |1〉, we just don’t happen to know which. In such a theory nocommunication between possibly distant particles is necessary to explain the correlatedmeasurements

There are two standard ways that people use to describe entangled states and their mea-surement. Both have their positive aspects, but both are incorrect and can lead to misun-derstandings.

Further analysis, as we shall see, showsthat even though there is a coupling between the two particles, there is no way for Alice orBob to use this mechanism to communicate

he others are reflected

Those that are reflected by the filter all have polarization |↑〉.

Thephotons which, after being measured by the filter, match the filter’s polarization

hus, unless the original state happened to be one of the basis vectors,measurement will change that state, and it is not possible to determine what the originalstate was.

Measurement of a state transforms the state into one of themeasuring device’s associated basis vectors

The measurement postulate of quantum mechanics states that any device measuring a 2-dimensional system has an associated orthonormal basis with respect to which the quantummeasurement takes place.

Next, when filter C is inserted the intensity of the output drops to zero. None of thehorizontally polarized photons can pass through the vertical filter. A sieve model couldexplain this behavior

The function of filter A cannot be explained as a “sieve” that only lets those photons passthat happen to be already horizontally polarized. If that were the case, few of the randomlypolarized incoming electrons would be horizontally polarized, so we would expect a muchlarger attenuation of the light as it passes through the filter.

Finally, after filter B is inserted between A and C, a small amount of light will be visibleon the screen, exactly one eighth of the original amount of light

Mark GarrettBig fan of the physics model we now enjoy. · Author has 886 answers and 791.9K answer views · 5y · RelatedWhy does metallic surface reflect light without polarizing it, whereas nonmetallic does?Basically because there is refraction in the second case and not in the first. For light hitting a conducting surface (metal), no wave can exist inside the material, so all of the energy is reflected intact. Or, in terms of the differential equation, at the boundary, you have the condition that the E field must be zero, so the reflected wave is the “solution” that when added to the incident wave, results in satisfying the boundary condition correctly. In an insulator, the boundary value problem is different. Note, water is an insulator here. The fact that water with dissolved ions conducts electricity doesn’t really come into play with light, because the light wave interacts with the water surface only at the boundary. So … now the boundary value problem allows a non-zero E-field, and you have the fact that the velocity of light is different in the water than in the air. The solution works out to have the incident wave, refracted wave and the reflected wave all add up to satisfy the properties at the boundary. The details of the math give you a solution where the polarization matters, and only one polarization can be reflected. The rest of the energy goes into the refracted wave.

The component that is parallel to the analyzer axis and is allowed to pass through is Ecostheta. The component that is perpendicular to the axis is completely absorbed.

Mark BartonPhD physicist with University of Glasgow · Author has 15K answers and 18.1M answer views · Updated 7y · It depends on the type. The sort used in polarized sunglasses transmits one polarization and absorbs the other. A polarizer based on the Brewster's angle effect transmits one and reflects the other at an angle. (These are commonly used in laser optics.)

John Bell at CERN around 1982. Bell seems to be contemplating Alain Aspect’sexperimental scheme with variable polarizers5 for testing the inequalities now bearingBell’s name. The left-hand-side part of the inequality on the blackboard (describing thecorrelations between different measurement outcomes in the experiment sketchedbelow) is ≤2 in a local realism view of the world a la Einstein (top) and equal to2 2 inquantum mechanics (bottom). Image courtesy of CERN

Any forumthat invites contributions on the topic ofquantum mechanics is likely to receive anumber of submissions from enthusiastswith little to no expertise in studyingfoundational questions

Imagining that human observersthemselves can be in superpositions clarifieswhat a complete theory of wavefunctioncollapse would imply6

owever, JohnStewart Bell proved4 that such an approachcannot explain the quantum mechanicaloutcomes

Thischange is instantaneous and so seems toviolate the physical law that no informationcan travel faster than the speed of light

the outcome of measuring one particledetermines the state of the other.

By the rulesof quantum mechanics, a measurementof which state the system is in producesa probabilistic outcome.

But, as with searches beyondthe standard model in particle physics,there is no guarantee that experiments willfind anything new in the near term

the dynamics of awavefunction collapse has never beenobserved

Quantumsystems can be in a superposition of statesbut when measured by a classical observerthese are apparently collapsed to a classicaloutcome

we learn theaxioms of quantum mechanics and how toapply these rule

One can even set up quite ridiculouscases. A catis penned up in a steel chamber,along with the fol-lowing diabolical device (which must be securedagainst directinterferenceby the cat): in a Geigercounterthereis a tinybit of radioactivesubstance,sosmall,that perhaps in the course of one hour one ofthe atoms decays, but also, with equal probability,perhaps none; if it happens, the countertube dis-chargesand througha relayreleasesa hammerwhichshattersa small flask of hydrocyanicacid. If onehas leftthis entiresystemto itselffor an hour, onewould say thatthe cat stilllives ifmeanwhileno atomhas decayed. The firstatomic decay would havepoisoned it. The q+-functionof the entire systemwould expressthis by havingin it the livingand thedead cat (pardon the expression) mixed or smearedout in equal parts.It is typicalof these cases that an indeterminacyoriginallyrestrictedto the atomic domain becomestransformedinto macroscopicindeterminacy,whichcan then be resolved by direct observation. Thatprevents us from so naively accepting as valid a"blurred model" for representingreality. In itselfit would not embodyanythingunclear or contradic-tory. There is a differencebetweena shakyor out-of-focusphotographand a snapshotof clouds and fogbanks

I consider it acceptable to express thisreasoningsequenceas follows:Theorem 1: If different+-functionsare underdis-cussionthesystemis in differentstates.If one speaksonlyof systemsforwhicha +-functionis in general available,then the inverseof this the-oremruns:Theorem2: For the same +-functionthe systemisin thesamestate

Let us pause for a moment. This result in itsabstractnessactuallysays it all: Best possibleknowl-edge of a whole does not necessarilyincludethe samefor its parts. Let us translatethis into terms ofSect. 9: The whole is in a definitestate, the partstakenindividuallyare not."How so? Surely a systemmust be in some sortof state." "No. State is +-function,is maximalsumof knowledge. I didn't necessarilyprovide myselfwiththis,I may have been lazy. Then the systemisin no state.""Fine, but then too the agnostic prohibitionofquestionsis not yet in forceand in our case I cantell myself:the subsystemis alreadyin some state,Ijust don'tknowwhich.""Wait. Unfortunatelyno. There is no 'I justdon't know'. For as to the total system,maximalknowledgeis at hand . . "The insufficiencyof the /-functionas model re-placementrests solely on the fact that one doesn'talwayshave it. If one does have it,thenby all meanslet it serve as descriptionof the state. But some-timesone does not have it, in cases whereone mightreasonablyexpectto. And in thatcase, one dare notpostulatethat it "is actually a particularone, onejust doesn't know it"; the above-chosenstandpointforbidsthis. "It" is namelya sum of knowledge;and knowledge,that no one knows,is none

There's no doubt about it. Every measurementisfor its systemthe first. Measurementson separatedsystems cannot directlyinfluenceeach other-thatwould be magic. Neithercan it be by chance,if froma thousandexperimentsit is establishedthatvirginalmeasurementsagre

Quantum pre-dictionsare indeed not subject to test as to theirfullcontent,ever, in a single experimen

But one canrepeatthe experimentab ovo a thousandtimes; eachtimeset up thesame entanglement;accordingto whimcheckone or theotherof the equations

So one cannotcheckboth equationsin a single experimen

A singlemeasurementof q or p or Q or P resolvesthe entanglementand makes both systemsmaximallyknown. A second measurementon the same systemmodifiesonly the statementsabout it, but teachesnothingmore about the othe

The con-ceptual joining of two or more systems into oneencountersgreat difficultyas soon as one attemptsto introducethe principleof special relativityintoQ.M.

he electromagneticfield. Its laws are "relativitytheorypersonified,"a non-relativistictreatmentbeingin generalimpossible. Yet it was this field,whichintermsof theclassicalmodelof heat radiationprovidedthe firsthurdleforquantumtheory,thatwas the firstsystemto be "quantized."

t consists,tomentionthis briefly,at firstsimplyof the productof the two individualfunctions;which,since the onefunctiondependson quite differentvariablesfromtheother,is a functionof all these variables,or "acts ina space of much higherdimensionnumber"than theindividualfunction

When two systemsinteract,their+-functions,as wehave seen,do notcomeintointeractionbut rathertheyimmediatelycease to exist and a single one, for thecombinedsystem,takes their place

7A. Einstein,B. Podolsky,and N. Rosen,Phys. Rev. 47:777 (1935). The appearanceof this work motivatedthepresent-shallI say lectureor generalconfession

11. Resolutionof the"Entanglement."ResultDependenton theExperimenter'sIntentiontWe returnto the general case of "entanglement,"withouthaving specificiallyin view the special case,just considered,of a measurementprocess. Supposethe expectation-catalogsof two bodies A and B havebecomeentangledthroughtransientinteraction.Nowlet the bodies be again separated. Then I can takeone of them,say B, and by successivemeasurementsbringmyknowledgeof it, whichhad becomeless thanmaximal,back up to maximal. I maintain:just assoon as I succeed in this,and not before,then first,the entanglementis immediatelyresolvedand, second,I will also have acquired maximal knowledgeof Athroughthe measurementson B, makinguse of theconditionalrelationsthatwerein effect

And what if we don't look? Let's say it wasphotographicallyrecorded and by bad luck lightreachesthe filmbeforeit is developed. Or we inad-vertentlyput in black paper instead of film. Thenindeed have we not only not learned anythingnewfromthe miscarriedmeasurement,but we have suf-feredloss of knowledg

f the two bodies have again separated,it is not again split into a logical sum of knowledgesabout the individualbodies.

The combined expectation-catalogconsistsinitiallyof a logical sum of the individualcatalogs

then there occurs regularlythat which I have justcalled entanglementof our knowledgeof the twobodies

Any "entanglementof predictions"that takes placecan obviouslyonly go back to the fact that the twobodies at some earlier time formedin a true senseone system,that is were interacting,and have leftbehindtraceson each other

A measurementon one cannotpossiblyfurnishany grasp of what is to be expected of the othe