# "Spooky action achieved at record distance" Hidden variables dead? **URL:** \ **Category:** Factual Questions\ **Created:** [June 24, 2017, 1:50am UTC](https://boards.straightdope.com/t/spooky-action-achieved-at-record-distance-hidden-variables-dead/789718 "2017-06-24T01:50:42Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [June 24, 2017, 1:50am UTC](https://boards.straightdope.com/t/spooky-action-achieved-at-record-distance-hidden-variables-dead/789718/1 "2017-06-24T01:50:42Z")
[The brief version](http://science.sciencemag.org/content/356/6343/1140): > [@](#): > > … Here we demonstrate satellite-based distribution of entangled photon pairs to two locations separated by 1203 kilometers on Earth, through two satellite-to-ground downlinks with a summed length varying from 1600 to 2400 kilometers. We observed a survival of two-photon entanglement and a violation of Bell inequality by 2.37 ± 0.09 under strict Einstein locality conditions … The full articles about it beyond the paywall are mostly focused on the potential application for secure communication by use of a quantum key, but do I understand correctly that violating Bell’s inequality in this manner effectively also lays to rest any “hidden variable” interpretation of QM? ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [June 24, 2017, 1:59am UTC](https://boards.straightdope.com/t/spooky-action-achieved-at-record-distance-hidden-variables-dead/789718/2 "2017-06-24T01:59:25Z")
Only local hidden variable theories, which is an expected result. Non-local hidden variable theories such as De Broglie–Bohm pilot wave theory remain intact, provided we can accept the consequences of nonlocality (i.e. the local causality assumption in general relativity does not hold for interactions at the level of quantum mechanics). Stranger ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [June 24, 2017, 10:24am UTC](https://boards.straightdope.com/t/spooky-action-achieved-at-record-distance-hidden-variables-dead/789718/3 "2017-06-24T10:24:15Z")
Additionally to what **Stranger** said above, I’d say it’s unlikely that this constitutes a definitive Bell test (although I haven’t read the full paper yet)—there are other issues, such as the fair-sampling (or data rejection or detection efficiency) loophole, which basically points out that if you can’t guarantee to detect a large enough subset of all events that you could have detected, you can’t guarantee that the detected subset obeys the same statistics as the full set of events. Thus, inefficient detectors may lead to ‘spurious’ violations of Bell inequality even in local realistic theories. There are further loopholes, but I’d say that guaranteeing both strict Einstein locality conditions and high enough detection efficiency are still the main hurdles to definitive Bell tests, which were in fact only jointly overcome for the first time in 2015—so credit for dismissing the possibility of local hidden variables should really go to the experiments discussed [in this article](https://physics.aps.org/articles/v8/123). ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [June 25, 2017, 1:06pm UTC](https://boards.straightdope.com/t/spooky-action-achieved-at-record-distance-hidden-variables-dead/789718/4 "2017-06-25T13:06:03Z")
I think I read somewhere (on this board?) about entangled photons split by a gravity lens galaxy…a distance on the order of _lightyears._ ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [June 25, 2017, 5:35pm UTC](https://boards.straightdope.com/t/spooky-action-achieved-at-record-distance-hidden-variables-dead/789718/5 "2017-06-25T17:35:07Z")
It was [this thread](http://boards.straightdope.com/sdmb/showthread.php?t=829310), but it was about quantum superposition, not entanglement. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [June 25, 2017, 6:09pm UTC](https://boards.straightdope.com/t/spooky-action-achieved-at-record-distance-hidden-variables-dead/789718/6 "2017-06-25T18:09:12Z")
…and it’s a _thought_ experiment.