Albert Einstein and Charlie Chaplain attending the 1931 Los Angeles premiere of \u201cCity Lights\u201d \u00a0\u00a0(Wikimedia Commons)<\/figcaption><\/figure>\n\u00a0<\/p>\n
I\u2019m making some notes for myself here, in order to ensure that (as far as it\u2019s possible and to the limits of my capacity) I accurately understand some concepts in physics that, someday, I intend to discuss briefly in something that I\u2019m writing.<\/p>\n
\u00a0<\/p>\n
The topic today is \u201cquantum entanglement.\u201d \u00a0If anything in the utterly unoriginal and very preliminary notes below is incorrect or misleadingly formulated \u2014 I am, to put it mildly, not operating in my familiar element with this subject \u2014 I would appreciate it if somebody who is better versed in quantum theory would correct me.<\/p>\n
\u00a0<\/p>\n
Quantum entanglement is a phenomenon in particle physics. \u00a0It concerns pairs of particles or even groups of particles for which the state of one particle \u2014 for example, its momentum, spin, position, or polarization \u2014 cannot be described without reference to the state of the other paired particle or to the state of the other particles in the group. \u00a0The states of the relevant particles are said to be \u201ccorrelated,\u201d either because of the way they\u2019ve been generated or the way in which they interact, or because they\u2019re spatially proximate to each other.<\/span><\/p>\n\u00a0<\/p>\n
For instance, if the total \u201cspin\u201d of a pair of particles is known to be zero, and if one particle is found to have a clockwise spin on a particular axis, then the spin of the partner particle, if it\u2019s measured on that same axis, will invariably be counterclockwise.<\/span><\/p>\n\u00a0<\/p>\n
But this fact leads to some very puzzling implications. \u00a0For example, if a property of a particle is measured, that measurement will inescapably cause a quantum collapse for that particle. \u00a0However, if the particle is \u201centangled\u201d with another particle or particles, the effect of that collapse will extend to the totality of the entangled system. \u00a0Somehow, the other particle or particles seem to \u201cknow\u201d that a measurement has been performed on the other particle \u2014 even if they\u2019re physically very far apart \u2014 and to \u201cknow\u201d what the outcome of that measurement was, even at sometimes perfectly enormous distances (conceivably at opposite sides of the cosmos).<\/span><\/p>\n\u00a0<\/p>\n
The classical papers on the subject are, evidently,<\/span><\/p>\n\u00a0<\/p>\n
Einstein A., Podolsky B., and Rosen N.,\u00a0\u201cCan Quantum-Mechanical Description of Physical Reality Be Considered Complete?\u201d\u00a0Phys. Rev<\/i>. 47 (1935) 10:777\u2013780.<\/span><\/p>\nSchr\u00f6dinger E. (1935), \u201cDiscussion of probability relations between separated systems,\u201d\u00a0Mathematical Proceedings of the Cambridge Philosophical Society<\/i>\u00a031 (1935) 4:555\u2013563.<\/span><\/p>\nSchr\u00f6dinger E. (1936), \u201cProbability relations between separated systems,\u201d\u00a0Mathematical Proceedings of the Cambridge Philosophical Society<\/i>\u00a032 (1936) 3:446\u2013452.<\/span><\/p>\n\u00a0<\/p>\n
Einstein, for one, very much disliked the whole idea, which he famously dismissed as\u00a0spukhafte Fernwirkung<\/em>, which has come into English as \u201cspooky action at a distance.\u201d \u00a0He considered it impossible and said that, if quantum theory predicted it, so much the worse for quantum theory; it must be mistaken or incomplete.<\/span><\/p>\n\u00a0<\/p>\n
However, the phenomenon has been verified experimentally since that time \u2014\u00a0with\u00a0photons,<\/sup>\u00a0neutrinos,\u00a0electrons,\u00a0relatively large\u00a0molecules,<\/sup>\u00a0and even small diamonds. \u00a0Still, for a while it was thought that the result of the test on one particle, or at least something about the nature or character of the test, might somehow have been transmitted to the other particle, thereby causing the result.<\/span><\/p>\n\u00a0<\/p>\n
In more recent research, though, \u201cloophole-free\u201d tests have been conducted on particles located so far apart that communications between them at the speed of light \u2014 the fastest speed that current physics (under the special theory of relativity) permits \u2014 would have taken longer (and, in one case, as much as 10,000 times<\/em> longer) than would be permitted by the interval between measurements of the two particles. \u00a0In other words, \u201ccommunication\u201d between the two particles appears to be impossible under current doctrines of physics.<\/span><\/p>\n\u00a0<\/p>\n
\u00a0<\/p>\n<\/body><\/html>\n","protected":false},"excerpt":{"rendered":"
\u00a0 \u00a0 I\u2019m making some notes for myself here, in order to ensure that (as far as it\u2019s possible and to the limits of my capacity) I accurately understand some concepts in physics that, someday, I intend to discuss briefly in something that I\u2019m writing. \u00a0 The topic today is \u201cquantum entanglement.\u201d \u00a0If anything in […]<\/p>\n","protected":false},"author":1019,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-68139","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"yoast_head":"\n
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![\"Einstein](\"https:\/\/wp-media.patheos.com\/blogs\/sites\/186\/2016\/05\/530px-Albert_Einstein_and_Charlie_Chaplin_-_1931.jpg\")
<\/a>