View source for Social:Six degrees of separation

{{Short description|Concept of social inter-connectedness of all people}}

{{Confusion|Six degrees of freedom}}

[[File:Six degrees social network.png|thumb|upright=1.4|A map of several branches and degrees of a small social group: Ryan is six degrees of separation from Arnold]]
'''Six degrees of separation''' is the idea that all people are six or fewer social connections away from each other. As a result, a chain of "[[Social:Friend of a friend|friend of a friend]]" statements can be made to connect any two people in a maximum of six steps. It is also known as the '''six handshakes rule'''.<ref>{{Cite web |date=2020-06-10 |title=6 Handshake Rule - Are We Still 6 People Away From Each Other? |url=https://youth-time.eu/6-handshake-rule-are-we-still-6-people-away-from-each-other/ |access-date=2022-04-18 |website=Youth Time Magazine |language=en-US}}</ref>

The concept was originally set out in a 1929 short story by Frigyes Karinthy, in which a group of people play a game of trying to connect any person in the world to themselves by a chain of five others. It was popularized in John Guare's 1990 play ''Six Degrees of Separation''.

The idea is sometimes generalized to the average [[Path (graph theory)|social distance]] being [[Logarithm|logarithm]]ic in the size of the population.

== Early conceptions ==
=== Shrinking world ===
Theories on optimal design of cities, city traffic flows, neighborhoods, and demographics were in vogue after [[Social:World War I|World War I]]. These{{Citation needed|date=January 2010}}<!--What does statism have to do with this? Has some paranoic Libertarian been at work even here? ... Formally, I'm requesting a citation for the claim that the Karinthy story is connected to "statism" in city design.--> conjectures were expanded in 1929 by Hungarian author Frigyes Karinthy, who published a volume of short stories titled ''Everything Is Different.'' One of these pieces was titled "Chains" or "Chain-Links". The story investigated—in abstract, conceptual, and fictional terms—many of the problems that captivated future generations of mathematicians, sociologists, and physicists within the field of [[Network theory|network theory]].<ref name=newman>Newman, Mark, Albert-László Barabási, and Duncan J. Watts. 2006. ''The Structure and Dynamics of Networks.'' Princeton, NJ: Princeton University Press.</ref><ref name=bara/> 

Technological advances in communications and travel enabled friendship networks to grow larger and span greater distances. In particular, Karinthy believed that the modern world was "shrinking" from this ever-increasing connectedness of human beings. He posited that despite great physical distances between the globe's individuals, the growing density of human networks made the actual social distance far smaller.<ref>[https://djjr-courses.wdfiles.com/local--files/soc180%3Akarinthy-chain-links/Karinthy-Chain-Links_1929.pdf Karinthy, Frigyes. (1929) "Chain Links"]. Accessed 22 January 2023.</ref>

As a result of this hypothesis, Karinthy's characters believed that any two individuals could be connected through at most five acquaintances. In his story, the characters create a game out of this notion. He wrote:<blockquote>A fascinating game grew out of this discussion. One of us suggested performing the following experiment to prove that the population of the Earth is closer together now than they have ever been before. We should select any person from the 1.5 billion inhabitants of the Earth—anyone, anywhere at all. He bet us that, using no more than ''five'' individuals, one of whom is a personal acquaintance, he could contact the selected individual using nothing except the network of personal acquaintances.<ref name=karinthy>Karinthy, Frigyes. ''Chain-Links.'' Translated from Hungarian and annotated by Adam Makkai and Enikö Jankó.</ref></blockquote>

This idea influenced a great deal of early thought on [[Social:Social network|social network]]s, both directly and indirectly. Karinthy has been regarded as the originator of the notion of six degrees of separation.<ref name=bara>[http://www.nd.edu/~alb/ Barabási, Albert-László] {{webarchive|url=https://web.archive.org/web/20050304041427/http://www.nd.edu/~alb/ |date=2005-03-04 }}. 2003. ''[http://www.nd.edu/%7Enetworks/Linked/index.html Linked: How Everything is Connected to Everything Else and What It Means for Business, Science, and Everyday Life.] {{webarchive|url=https://web.archive.org/web/20070103151518/http://www.nd.edu/%7Enetworks/Linked/index.html |date=2007-01-03 }}'' New York: Plume.</ref>
A related theory deals with the quality of connections, rather than their existence. The theory of [[Social:Three degrees of influence|three degrees of influence]] was created by Nicholas A. Christakis and James H. Fowler.{{Citation needed|date = July 2016}}

=== Small world ===
{{Main|Social:Small-world experiment}}

Michael Gurevich conducted seminal work in his empirical study of the structure of social networks in his 1961 [[Organization:Massachusetts Institute of Technology|Massachusetts Institute of Technology]] PhD dissertation under [[Biography:Ithiel de Sola Pool|Ithiel de Sola Pool]].<ref>Gurevich, M (1961) The Social Structure of Acquaintanceship Networks, Cambridge, MA: MIT Press</ref> Mathematician Manfred Kochen, an Austrian who had been involved in urban design, extrapolated these empirical results in a mathematical manuscript, ''Contacts and Influences'',<ref>de Sola Pool, Ithiel, Kochen, Manfred (1978–1979)."Contacts and influence." ''Social Networks'' 1(1): 42</ref> concluding that in a U.S.-sized population without social structure, "it is practically certain that any two individuals can contact one another by means of at most two intermediaries. In a [socially] structured population it is less likely but still seems probable. And perhaps for the whole world's population, probably only one more bridging individual should be needed." They subsequently constructed [[Monte Carlo method|Monte Carlo]] simulations based on Gurevich's data, which recognized that both weak and strong acquaintance links are needed to model social structure. The simulations, carried out on the relatively limited computers of 1973, were nonetheless able to predict that a more realistic three degrees of separation existed across the U.S. population, foreshadowing the findings of American psychologist Stanley Milgram.{{Citation needed|date = July 2016}}

Milgram continued Gurevich's experiments in acquaintanceship networks at [[Organization:Harvard University|Harvard University]]. Kochen and de Sola Pool's manuscript, ''Contacts and Influences'',<ref>de Sola Pool, Ithiel, Kochen, Manfred (1978–1979)."Contacts and Influence." ''Social Networks'' 1(1): 5–51</ref> was conceived while both were working at the [[Organization:University of Paris|University of Paris]] in the early 1950s, during a time when Milgram visited and collaborated in their research. Their unpublished manuscript circulated among academics for over 20 years before publication in 1978. It formally articulated the mechanics of social networks, and explored the mathematical consequences of these (including the degree of connectedness). The manuscript left many significant questions about networks unresolved, and one of these was the number of degrees of separation in actual social networks. Milgram took up the challenge on his return from [[Place:Paris|Paris]], leading to the experiments reported in ''The Small World Problem'' <ref name="Stanley Milgram 1968">{{cite journal | last1 = Milgram | first1 = Stanley | year = 1967 | title = The Small World Problem | journal = Psychology Today | volume = 2 | pages = 60–67 }}</ref> in popular science journal ''Psychology Today'', with a more rigorous version of the paper appearing in ''[[Social:Social Psychology Quarterly|Sociometry]]'' two years later.<ref>Travers, Jeffrey, and Stanley Milgram, [http://www.cis.upenn.edu/~mkearns/teaching/NetworkedLife/travers_milgram.pdf "An Experimental Study of the Small World Problem"], ''Sociometry'' 32(4, December 1969): 425–443.</ref> 

Milgram's article made famous<ref name="Stanley Milgram 1968" /> his 1967 set of experiments to investigate de Sola Pool and Kochen's "small world problem." Mathematician [[Biography:Benoit Mandelbrot|Benoit Mandelbrot]], born in Warsaw, growing up in Poland then France, was aware of the Statist [[Rule of thumb|rule of thumb]], and was also a colleague of de Sola Pool, Kochen and Milgram at the University of Paris during the early 1950s. (Kochen brought Mandelbrot to work at the Institute for Advanced Study and later IBM in the U.S.) 

This circle of researchers was fascinated by the interconnectedness and "social capital" of human networks. Milgram's study results showed that people in the United States seemed to be connected by approximately three friendship links, on average, without speculating on global linkages; he never actually used the term "six degrees of separation". Since the ''Psychology Today'' article gave the experiments wide publicity, Milgram, Kochen, and Karinthy all had been incorrectly attributed as the origin of the notion of six degrees; the most likely popularizer of the term "six degrees of separation" was John Guare, who attributed the concept of six degrees to [[Biography:Guglielmo Marconi|Marconi]].<ref name=SDS-R-01>{{cite web |url=http://www.aaa.si.edu/exhibitions/peggy-bacon|title= The concept of Six degrees of separation stretches back to Italian inventor Guglielmo Marconi |date= 27 June 2012 |access-date=16 July 2012 }}</ref>

=== Continued research: Small World Project ===
In 2003, [[Organization:Columbia University|Columbia University]] conducted an analogous experiment on social connectedness amongst Internet email users. Their effort was named the Columbia Small World Project, and included 24,163 e-mail chains, aimed at 18 targets from 13 countries.<ref name="dodds">Dodds, Muhamad, Watts (2003)."Small World Project," Science Magazine. pp.827-829, 8 August 2003 https://www.science.org/doi/10.1126/science.1081058</ref> Almost 100,000 people registered, but only 384 (0.4%) reached the final target. Amongst the successful chains, while shorter lengths were more common, some reached their target after only 7, 8, 9, or 10 steps. Dodds et al. noted that participants (all volunteers) were strongly biased towards existing models of Internet users{{#tag:ref|"More than half of all participants resided in North America and were middle class, professional, college educated, and Christian, reflecting commonly held notions of the Internet-using population"<ref name="dodds"/>|group=Note}} and that connectedness based on professional ties was much stronger than those within families or friendships. The authors cite "lack of interest" as the predominating factor in the high attrition rate,{{#tag:ref|"suggesting lack of interest ... was the main reason" for the "extremely low completion rate"<ref name="dodds"/>|group=Note}} a finding consistent with earlier studies.<ref name="kleinfeld"/>

== Research ==
Several studies, such as [[Social:Small-world experiment|Milgram's small-world experiment]], have been conducted to measure this connectedness empirically. The phrase "six degrees of separation" is often used as a synonym for the idea of the "small world" phenomenon.<ref name=AFC-NA-21>[[Biography:Steven Strogatz|Steven Strogatz]], Duncan J. Watts and [[Biography:Albert-László Barabási|Albert-László Barabási]] {{cite web |title =  explaining synchronicity, network theory, adaption of complex systems, Six Degrees, Small world phenomenon in the BBC Documentary |work = BBC  |url=http://topdocumentaryfilms.com/six-degrees-of-separation/|access-date=11 June 2012}} "Unfolding the science behind the idea of six degrees of separation"</ref>

However, detractors argue that Milgram's experiment did not demonstrate such a link,<ref>[http://news.bbc.co.uk/1/hi/programmes/more_or_less/5176698.stm BBC News: More Or Less: Connecting With People In Six Steps] 13 July 2006, "Judith Kleinfeld ... told us, that 95% of the letters sent out had failed to reach the target."</ref> and the "six degrees" claim has been decried as an "academic urban myth".<ref name="kleinfeld">{{cite web|url=http://www.stat.cmu.edu/~fienberg/Stat36-835/Kleinfeld_SWP.pdf|title=The Small World Problem|publisher=Society (Springer), Social Science and Public Policy|author=Judith S. Kleinfeld, [[Organization:University of Alaska Fairbanks|University of Alaska Fairbanks]]|date=January–February 2002}}</ref><ref name="pt2002">{{cite magazine|url=http://www.psychologytoday.com/articles/200203/six-degrees-urban-myth|magazine=Psychology Today|date=March 1, 2002|title=Six Degrees: Urban Myth? Replicating the small world of Stanley Milgram. Can you reach anyone through a chain of six people.}}</ref>

=== Computer networks ===
In 2001, Duncan Watts, a professor at [[Organization:Columbia University|Columbia University]], attempted to recreate Milgram's experiment on the Internet, using an e-mail message as the "package" that needed to be delivered, with 48,000 senders and 19 targets (in 157 countries). Watts found that the average (though not maximum) number of intermediaries was around six.<ref>{{cite journal |author=Duncan J Watts, Steven H Strogatz |year=1998 |title=Collective dynamics of 'small-world' networks |journal=Nature |pages=440–442 |doi=10.1038/30918 |pmid=9623998 |volume=393 |issue=6684|bibcode=1998Natur.393..440W |s2cid=4429113 }}</ref>
A 2007 study by Jure Leskovec and [[Biography:Eric Horvitz|Eric Horvitz]] examined a data set of instant messages composed of 30 billion conversations among 240 million people. They found the average path length among Microsoft Messenger users to be 6.<ref>{{cite journal| arxiv=0803.0939| title=Planetary-Scale Views on an Instant-Messaging Network| author=Jure Leskovec and Eric Horvitz|date=June 2007| bibcode=2008arXiv0803.0939L}}</ref>

It has been suggested by some commentators<ref>{{cite web|url=http://www.masternewmedia.org/news/2006/03/20/the_power_of_open_participatory.htm|title=The Power Of Open Participatory Media And Why Mass Media Must Be Abandoned|author=Robin Good|work=Robin Good's Master New Media}}</ref> that interlocking networks of computer-mediated lateral communication could diffuse single messages to all interested users worldwide as per the six degrees of separation principle via information routing groups, which are networks specifically designed to exploit this principle and lateral diffusion.

===An optimal algorithm to calculate degrees of separation in social networks===
Bakhshandeh ''et al.''<ref>Reza Bakhshandeh, Mehdi Samadi, Zohreh Azimifar, Jonathan Schaeffer, "[http://www.aaai.org/ocs/index.php/SOCS/SOCS11/paper/view/4031 Degrees of Separation in Social Networks]", Fourth Annual Symposium on Combinatorial Search, 2011</ref> have addressed the search problem of identifying the degree of separation between two users in social networks such as Twitter. They have introduced new search techniques to provide optimal or near optimal solutions. The experiments are performed using Twitter, and they show an improvement of several orders of magnitude over greedy approaches. Their optimal algorithm finds an average degree of separation of 3.43 between 2 random Twitter users, requiring an average of only 67 requests for information over the Internet to Twitter. A near-optimal solution of length 3.88 can be found by making an average of 13.3 requests.

== Popularization ==
No longer limited strictly to academic or philosophical thinking, the notion of six degrees recently has become influential throughout [[Social:Popular culture|popular culture]]. Further advances in communication technology—and particularly the Internet—have drawn great attention to social networks and human interconnectedness. As a result, many popular media sources have addressed the term. The following provide a brief outline of the ways such ideas have shaped popular culture.

=== Popularization of offline practice ===
==== John Guare's ''Six Degrees of Separation'' ====

American playwright John Guare wrote a play in 1990 and released a 1993 film that popularized it; it is Guare's most widely known work. {{Citation needed|date = July 2016}} The play ruminates upon the idea that any two individuals are connected by at most five others. As one of the characters states:

<blockquote>
I read somewhere that everybody on this planet is separated by only six other people. Six degrees of separation between us and everyone else on this planet. The President of the United States, a gondolier in Venice, just fill in the names. I find it A) extremely comforting that we're so close, and B) like Chinese water torture that we're so close because you have to find the right six people to make the right connection... I am bound to everyone on this planet by a trail of six people.<ref name=imdb>Memorable quotes from ''Six Degrees of Separation.'' Accessed Nov. 11, 2006 from [https://www.imdb.com/title/tt0108149/quotes IMDB.com].</ref>
</blockquote>

Guare, in interviews, attributed his awareness of the "six degrees" to Marconi.{{Citation needed|date = July 2016}} Although this idea had been circulating in various forms for decades, it is Guare's piece that is most responsible for popularizing the phrase "six degrees of separation."{{Citation needed|date = July 2016}} Following Guare's lead, many future television and film sources later incorporated the notion into their stories.{{Citation needed|date = July 2016}}

J. J. Abrams, the executive producer of television series ''Six Degrees'' and ''Lost'', played the role of Doug in the film adaptation of this play.<ref>{{cite web |url=https://www.imdb.com/title/tt0108149/fullcredits?ref_=tt_cl_sm#cast |title=Six Degrees of Separation (1993) - Full Cast & Crew |website=IMDb |access-date=2021-06-15 }}</ref>

==== Kevin Bacon game ====
The game "Six Degrees of Kevin Bacon"<ref name=SDS-T-02>{{cite news|url=https://www.telegraph.co.uk/technology/facebook/8704891/Six-degrees-of-separation-theory-tested-on-Facebook.html |archive-url=https://ghostarchive.org/archive/20220112/https://www.telegraph.co.uk/technology/facebook/8704891/Six-degrees-of-separation-theory-tested-on-Facebook.html |archive-date=2022-01-12 |url-access=subscription |url-status=live|title=Six degrees of separation' theory tested on Facebook|work=Telegraph|access-date=7 May 2012|date=17 August 2011}}{{cbignore}}</ref> was invented as a play on the concept: the goal is to link any actor to Kevin Bacon through no more than six connections, whereby two actors are connected if they have appeared in a movie or commercial together. It was created by three students at [[Organization:Albright College|Albright College]] in Pennsylvania,<ref name=SDS-T-03>{{cite news|url=https://www.telegraph.co.uk/news/celebritynews/8560483/Actors-Hollywood-career-spawned-Six-Degrees-of-Kevin-Bacon.html |archive-url=https://ghostarchive.org/archive/20220112/https://www.telegraph.co.uk/news/celebritynews/8560483/Actors-Hollywood-career-spawned-Six-Degrees-of-Kevin-Bacon.html |archive-date=2022-01-12 |url-access=subscription |url-status=live|title=Actor's Hollywood career spawned 'Six Degrees of Kevin Bacon'|work=Telegraph|access-date=7 May 2012|date=6 June 2011}}{{cbignore}}</ref> who came up with the concept while watching ''Footloose''. On September 13, 2012, Google made it possible to search for any given actor's "Bacon Number" through its search engine.<ref>{{Cite web|url=https://www.cnbc.com/2012/09/13/whats-your-bacon-number-just-ask-google.html|title = What's Your 'Bacon Number?' Just Ask Google|website = {{wipe|CNBC}}|date = 13 September 2012}}</ref>

Upon the arrival of the 4G mobile network in the United Kingdom, Kevin Bacon appears in several commercials for the EE Network in which he links himself to several well known celebrities and TV shows in the UK.

==== John L. Sullivan ====
An early version involved former world heavyweight boxing champion John L. Sullivan, in which people asked others to "shake the hand that shook the hand that shook the hand that shook the hand of 'the great John L.'"<ref>{{cite news |url=http://www.thesweetscience.com/component/content/article/41-articles-of-2005/1514-the-great-john-l-sullivan |title=The Great John L. Sullivan |first=Robert |last=Ecksel |date=1 January 2005 |access-date=5 October 2019 |work=The Sweet Science |publisher=IBofP}}</ref>

=== Websites and software ===
==== Internet ====
In 2013, Hungarian physicist [[Biography:Albert-László Barabási|Albert-László Barabási]] discovered that, on average, there are 19 degrees of separation between any 2 web pages.<ref>[https://www.pcworld.com/article/2028714/any-two-web-pages-are-separated-by-just-19-clicks-study-finds.html /any two web pages are separated by just 19 clicks study finds]</ref>

==== Six Degrees of Wikipedia ====
Several "degrees of Wikipedia" web services have been created, which automatically provide the shortest paths between two Wikipedia articles.<ref>{{cite news |title=Play Six Degrees of Wikipedia |url=https://lifehacker.com/play-six-degrees-of-wikipedia-1823392997 |access-date=4 March 2021 |work=Lifehacker |date=28 February 2018 |language=en-us}}</ref>

==== Facebook ====
{{Bar chart
| title = Facebook friend distances as reported in Feb 2016 <ref name="facebook2016" /><ref>{{cite news|title=Facebook says there are only 3.57 degrees of separation|newspaper=The Telegraph|date=4 February 2016|url=https://www.telegraph.co.uk/technology/2016/02/04/facebook-says-there-are-actually-357-degrees-of-separation/ |archive-url=https://ghostarchive.org/archive/20220112/https://www.telegraph.co.uk/technology/2016/02/04/facebook-says-there-are-actually-357-degrees-of-separation/ |archive-date=2022-01-12 |url-access=subscription |url-status=live|access-date=4 February 2016|last1=Titcomb|first1=James}}{{cbignore}}</ref>
| label_type = Year
| data_type = Distance
| float = right

| label1 = 2008
| data1 = 5.28
| label2 = 2011
| data2 = 4.74
| label3 = 2016
| data3 = 4.57
}}
A Facebook platform application named "Six Degrees" was developed by Karl Bunyan, which calculates the degrees of separation between people. It had over 5.8 million users, as seen from the group's page. The average separation for all users of the application is 5.73 degrees, whereas the maximum degree of separation is 12. The application has a "Search for Connections" window to input any name of a [[Company:Facebook|Facebook]] user, to which it then shows the chain of connections. In June 2009, Bunyan shut down the application, presumably for issues with Facebook's caching policy; specifically, the policy prohibited the storing of friend lists for more than 24 hours; following this policy would have made the application inaccurate.<ref>{{cite web|url=http://blog.karlbunyan.com/2009/06/24/six-degrees-come-in-your-time-is-up/|title=Six Degrees: come in, your time is up|work=K! - the blog of Karl Bunyan|date=24 June 2009}}</ref> A new version of the application became available at Six Degrees after Karl Bunyan gave permission to a group of developers led by Todd Chaffee to re-develop the application based on Facebook's revised policy on caching data.<ref>{{cite web|url=http://apps.facebook.com/sixdegreesearch|title=Six Degrees on Facebook - Facebook|work=facebook.com}}</ref><ref>{{cite web|url=http://www.insidefacebook.com/2010/04/21/facebook-removing-24-hour-caching-policy-on-user-data-for-developers/|title=Facebook Removing 24 Hour Caching Policy on User Data for Developers|work=insidefacebook.com}}</ref>

The initial version of the application was built at a Facebook Developers Garage London hackathon with Mark Zuckerberg in attendance.<ref>{{cite web |url=http://blog.mikamai.co.uk/2010/06/mikamai-participates-with-zuck-in-london-facebook-hackathon/ |title=MIKAMAI participates with Zuck in London Facebook Hackathon &#124; Unconventional Everything - MIKAMAI UK |access-date=2010-09-11 |url-status=dead |archive-url=https://archive.today/20120707013246/http://blog.mikamai.co.uk/2010/06/mikamai-participates-with-zuck-in-london-facebook-hackathon/ |archive-date=2012-07-07 }}</ref>

Yahoo! Research Small World Experiment has been conducting an experiment and everyone with a Facebook account can take part in it. According to the research page, this research has the potential of resolving the still unresolved theory of six degrees of separation.<ref name=SDS-T-02/><ref>{{cite web |url=http://smallworld.sandbox.yahoo.com/ |title=Yahoo! Research Small World Experiment |access-date=2011-09-27 |url-status=dead |archive-url=https://web.archive.org/web/20110926141619/http://smallworld.sandbox.yahoo.com/ |archive-date=2011-09-26 }}</ref>

Facebook's data team released two papers in November 2011 which document that amongst all Facebook users at the time of research (721 million users with 69 billion friendship links) there is an average distance of 4.74.<ref name=SDS-T-01>{{cite news|url=https://www.telegraph.co.uk/technology/facebook/8906693/Facebook-cuts-six-degrees-of-separation-to-four.html |archive-url=https://ghostarchive.org/archive/20220112/https://www.telegraph.co.uk/technology/facebook/8906693/Facebook-cuts-six-degrees-of-separation-to-four.html |archive-date=2022-01-12 |url-access=subscription |url-status=live|title=Facebook cuts six degrees of separation to four|work=Telegraph|access-date=7 May 2012|first=Emma|last=Barnett|date=22 November 2011}}{{cbignore}}</ref><ref name="facebook2016" /> Probabilistic algorithms were applied on statistical metadata to verify the accuracy of the measurements.<ref>{{cite arXiv|eprint=1111.4570|title=Four Degrees of Separation|last=Backstrom|first=Lars |author2=Boldi, Paolo |author3=Rosa, Marco |author4=Ugander, Johan |author5=Vigna, Sebastiano|date=2011-11-19|class=cs.SI}}</ref> It was also found that 99.91% of Facebook users were interconnected, forming a large connected component.<ref>{{cite arXiv|eprint=1111.4503|title=The Anatomy of the Facebook Social Graph|last=Ugander|first=Johan|author2=Karrer, Brian |author3=Backstrom, Lars |author4= Marlow, Cameron |class=cs.SI|year=2011}}</ref>

Facebook reported that the distance had decreased to 4.57 in February 2016, when it had 1.6 billion users (about 22% of the world population).<ref name="facebook2016">{{cite web|title=Three and a half degrees of separation – Facebook Research|date=4 February 2016|url=https://research.fb.com/three-and-a-half-degrees-of-separation/|access-date=9 July 2017}}</ref>

==== LinkedIn ====
The [[Company:LinkedIn|LinkedIn]] professional networking site operates the degree of separation one is away from a person with which he or she wishes to communicate. On [[Company:LinkedIn|LinkedIn]], one's network is made up of 1st-degree, 2nd-degree, and 3rd-degree connections and fellow members of LinkedIn Groups. In addition, LinkedIn notifies users how many connections they and any other user have in common.

==== SixDegrees.com ====
SixDegrees.com was an early social-networking website that existed from 1997 to 2000. It allowed users to list friends, family members and acquaintances, send messages and post bulletin board items to people in their first, second, and third degrees, and see their connection to any other user on the site. At its height, it had 3,500,000 fully registered members.<ref>{{cite book |last1=Kirkpatrick |first1=David |title=The Facebook Effect: The Inside Story of the Company That Is Connecting the World | publisher = Simon & Schuster
 | year = 2010 | isbn = 978-1439102121 |title-link=The Facebook Effect }}</ref> However, it was closed in 2000.
<ref>{{cite journal|last1=boyd|first1=d. m|last2=Ellison|first2=N. B|title=Social network sites: Definition, history, and scholarship.|journal=Journal of Computer-Mediated Communication|volume=13 | issue = 1 |pages=210–230|doi=10.1111/j.1083-6101.2007.00393.x|year=2007|doi-access=free}}</ref>

==== Twitter ====
Users on Twitter can follow other users creating a network. According to a 2010 study of 5.2 billion such relationships by social media monitoring firm [[Company:Sysomos|Sysomos]], the average distance on Twitter is 4.67. On average, about 50% of people on Twitter are only four steps away from each other, while nearly everyone is five steps or less away.<ref>Apr 30, 2010, [https://web.archive.org/web/20100502005723/http://sysomos.com/insidetwitter/sixdegrees/ Six Degrees of Separation, Twitter Style], from [[Company:Sysomos|Sysomos]].</ref>

In another work, researchers have shown that the average distance of 1,500 random users in Twitter is 3.435. They calculated the distance between each pair of users using all the active users in Twitter.<ref name=bakhsh>Reza Bakhshandeh, Mehdi Samadi, Zohreh Azimifar, Jonathan Schaeffer ''[http://www.aaai.org/ocs/index.php/SOCS/SOCS11/paper/view/4031 Degrees of Separation in Social Networks.]'' Fourth Annual Symposium on Combinatorial Search, 2011</ref>

== Mathematics ==
Mathematicians use an analogous notion of ''collaboration distance'':<ref>{{cite web|url=http://www.ams.org/mathscinet/collaborationDistance.html|title=MR: Collaboration Distance|work=ams.org}}</ref> two persons are linked if they are coauthors of an article. The collaboration distance with mathematician [[Biography:Paul Erdős|Paul Erdős]] is called the [[Erdős number]]. Erdős-Bacon numbers and Erdős-Bacon-Sabbath (EBS) numbers<ref>{{cite web|url=http://erdosbaconsabbath.com/|title=EBS Project|work=erdosbaconsabbath.com|url-status=dead|archive-url=https://web.archive.org/web/20170724075829/http://erdosbaconsabbath.com/|archive-date=2017-07-24}}</ref> are further extensions of the same thinking.

Watts and Strogatz showed that the average path length (APL) between two nodes in a random network is equal to {{math|ln ''N'' / ln ''K''}}, where {{math|''N''}} = total nodes and {{math|''K''}} = acquaintances per node. Thus if
{{math|''N''}} = 300,000,000 (90% of the US population) and {{math|''K''}} = 30 then ''Degrees of Separation'' = APL = 19.5 / 3.4 = 5.7 and if {{math|''N''}} = 6,000,000,000 (90% of the World population) and {{math|''K''}} = 30 then ''Degrees of Separation'' = APL = 22.5 / 3.4 = 6.6.
(Assume 10% of population is too young to participate.)

== Psychology ==
A 2007 article published in ''The Industrial-Organizational Psychologist'',<ref>[http://www.siop.org/tip/Oct07/Sheridan%20PDFs/452_029to035.pdf (Michel, 2007)]</ref> by Jesse S. Michel from Michigan State University, applied Stanley Milgram's small world phenomenon (i.e., "small world problem") to the field of [[Social:Industrial and organizational psychology|I-O psychology]] through co-author publication linkages. Following six criteria, Scott Highhouse (Bowling Green State University professor and fellow of the Society of Industrial and Organizational Psychology) was chosen as the target. Co-author publication linkages were determined for (1) top authors within the I-O community, (2) quasi-random faculty members of highly productive I-O programs in North America, and (3) publication trends of the target. Results suggest that the small world phenomenon is alive and well with mean linkages of 3.00 to top authors, mean linkages of 2.50 to quasi-random faculty members, and a relatively broad and non-repetitive set of co-author linkages for the target. The author then provided a series of implications and suggestions for future research.

== In popular culture ==
=== Films ===
* The Oscar-winning film ''Babel'' is based on the concept of six degrees of separation. The lives of all of the characters were intimately intertwined, although they did not know each other and lived thousands of miles from each other.
* ''Six Degrees of Separation'' is a 1993 drama film featuring Will Smith, Donald Sutherland, and Stockard Channing.

=== Games ===
* One of the achievements in the video game ''[[Software:Brütal Legend|Brütal Legend]]'' is called "Six Degrees of Schafer", after the concept and Tim Schafer, who was presumably in the handful of players to have the achievement as of the game's release. A player can only obtain this achievement by playing online with someone who already has it, further paralleling it to the concept.

=== Literature ===
*''Joined-Up Thinking'' and ''Connectoscope'' by Stevyn Colgan are trivia books based upon the idea of "Six Degrees" of information; that everything is connected.

=== Music ===
* The No Doubt song "Full Circle" has a central theme dealing with six degrees of separation.
* The Weird Al song "Lame Claim to Fame" has the lines: "I know a guy who knows a guy who knows a guy/Who knows a guy who knows a guy who knows Kevin Bacon"
* "Six Degrees of Separation" is the 10th track on the second disc ''The Heart'' of the 2016 double album ''The Weight of These Wings'' by American country artist Miranda Lambert. It is the 22nd track overall. 
* "Six Degrees of Separation" is the 2nd track on The Script's third album, ''#3''.
* "Six Degrees" is the sixth track on Scouting for Girls' album, ''The Light Between Us''.
* ''Six Degrees of Inner Turbulence'' is a 2002 album by progressive metal band Dream Theater.
* English progressive rock band Arena released an album titled ''The Seventh Degree of Separation'' in 2011.
* "Nessun grado di separazione" is a 2016 song by Italian singer Francesca Michielin. A bilingual English and Italian version of the song called "No Degree of Separation" represented Italy in the Eurovision Song Contest 2016 held in [[Place:Stockholm|Stockholm]], Sweden.

=== Television ===
* ''Six Degrees'' is a 2006 television series on ABC in the US. The show details the experiences of six {{wipe|New York City}} who go about their lives without realizing they are affecting each other, and gradually meet one another.<ref>{{cite web|url=http://abc.go.com/primetime/sixdegrees/index.html|title=ABC TV Shows, Specials & Movies - ABC.com|work=ABC}}</ref>
* ''Lonely Planet Six Degrees'' is a TV travel show that uses the "six degrees of separation" concept: The hosts, Asha Gill and Toby Amies, explore various cities through its people, by following certain personalities of the city around and being introduced by them to other personalities.
* The Woestijnvis production ''Man Bijt Hond'', broadcast on Flemish TV, features a weekly section ''Dossier Costers'', in which a worldwide event from the past week is linked to Gustaaf Costers, an ordinary Flemish citizen, in six steps.<ref>Het Nieuwsblad, 25 September 2009 {{cite web |url=http://www.nieuwsblad.be/article/detail.aspx?articleid=GDC2FNI8B |title=Het Nieuwsblad - Alle wegen leiden naar Gustaaf |access-date=2010-02-25 |url-status=dead |archive-url=https://web.archive.org/web/20110501073520/http://www.nieuwsblad.be/article/detail.aspx?articleid=GDC2FNI8B |archive-date=2011-05-01 }}{{cite web |url=http://www.nieuwsblad.be/article/detail.aspx?articleid=GDC2FNI8J |title=Het Nieuwsblad - Man bijt hond: 'We spelen niet vals' |access-date=2010-02-25 |url-status=dead |archive-url=https://web.archive.org/web/20110501073602/http://www.nieuwsblad.be/article/detail.aspx?articleid=GDC2FNI8J |archive-date=2011-05-01 }} ([[Social:Dutch language|Dutch]])</ref>
* ''Six Degrees of Martina McBride'' is a [[Engineering:Television pilot|television pilot]] wherein six aspiring country singers from America's smallest towns tried to connect themselves to Martina McBride in under six points of human connection. Those who made it from "Nowhere to Nashville to New York," got both a shot at a studio session with McBride and a record deal with SONY BMG. It was not picked up as a series.
* "Six Degrees of Separation" is an episode of the reimagined ''Battlestar Galactica'' series.
* ''Six Degrees of Everything'' is a comedy series starring Benny Fine and Rafi Fine, in which they illustrate that everything in the world is connected by a six-degree separation.<ref name="Futon Critic 07-13-15">{{cite web|last1=staff|title=SIX DEGREES OF EVERYTHING (TRUTV) Premieres Tuesday, August 18|url=http://www.thefutoncritic.com/devwatch/six-degrees-of-everything/|access-date=August 12, 2015|website=Futon Critic|date=July 13, 2015}}</ref>
* ''Jorden runt på 6 steg'' is a three-episode infotainment series produced by Nexiko Media which aired in Swedish Kanal 5 in 2015. For each episode, hosts Filip Hammar and Fredrik Wikingsson selected one random person (in Bolivia, Nepal and Senegal) and traced their relationships to three respective celebrities, Leif G. W. Persson, Gordon Ramsay, and [[Biography:Buzz Aldrin|Buzz Aldrin]] within a week of travelling. They reached Persson within seven steps, and Ramsay and Aldrin within six steps. The second season features Michael Bolton, Jeremy Clarkson, Pamela Anderson, and Charlie Sheen.

== See also ==
{{div col}}
* {{annotated link|Composition of relations}}
* {{annotated link|History:Connections (British documentary)|''Connections''}}, a TV documentary that follows a similar concept but involving history and science
* {{annotated link|Erdős number}}
* {{annotated link|Social:Jewish geography}}
* {{annotated link|Social:Professional network service}}
* {{annotated link|Organization:SixDegrees.org}}
* {{annotated link|Social:Small-world experiment}}
* {{annotated link|Social:Social network}}
* {{annotated link|Philosophy:The Game (mind game)}}
* {{annotated link|Three-click rule}}
{{div col end}}

== Notes ==
{{reflist|group=Note}}

== References ==
{{Reflist|30em}}

== External links ==
*[https://www.naraview.com/#/ naraview] – A game which you need to find a connection between two articles in Wikipedia.
*[http://apps.facebook.com/sixdegreesearch Six Degrees] – The new version of the Facebook application originally built by Karl Bunyan.
*[http://www.insidefacebook.com/2010/04/21/facebook-removing-24-hour-caching-policy-on-user-data-for-developers/ Facebook revised policy on caching data] – Facebook's revised policy removing the 24-hour limit on caching of user data.
*[https://archive.today/20120707013246/http://blog.mikamai.co.uk/2010/06/mikamai-participates-with-zuck-in-london-facebook-hackathon/ Facebook Developers Garage London hackathon] – The June 2010 Facebook Developers Garage London hackathon at which the new version of the Six Degrees Facebook application was built.
*[http://findthebacon.com/ Find The Bacon] – is a site built for finding the connections between actors and the movies they have played in.
*[http://whocanfindme.blogspot.com/ whocanfindme – the quest] – Off- and online contest based on the six degrees of separation principle
*[http://www.sixdegrees.org.au Six Degrees Campaign], a [[Earth:Climate justice|climate justice]] campaign initiated by Friends of the Earth Brisbane based on the principles of small world theory
*"[http://www.sciam.com/article.cfm?articleID=0001297C-C5F8-1F32-9AD380A84189F2D7 E-mail Study Corroborates Six Degrees of Separation]", a 2003 ''Scientific American'' article about a study conducted at [[Organization:Columbia University|Columbia University]].
*[http://www.judithkleinfeld.com/ar_bigworld.html Could it be a big world?] – 2001, Judith Kleinfeld, University of Alaska Fairbanks
*[https://web.archive.org/web/20070528053016/http://www.pumpthemusic.com/oracle/ Pumpthemusic Oracle] – The 6 degrees theory applied to the musical universe
*[http://oracleofbacon.org/ The Oracle of Bacon] – The 6 degrees theory applied to movies and TV
*{{cite web|url= http://www.dau.mil/pubscats/pubscats/atl/2005_03_04/war-ma05.pdf |title=Knock, Knock, Knocking on Newton's Door }}&nbsp;{{small|(223&nbsp;[[Kibibyte|KiB]])}}, by Dan Ward – Journal article published by Defense Acquisition University, applies principles from Duncan Watts's book [https://web.archive.org/web/20070328231936/http://www2.wwnorton.com/catalog/fall03/032542.htm Six Degrees] to technology innovation and scientific research.
*http://www.steve-jackson.net/six_degrees/index.html
*[http://expertvoices.nsdl.org/cornell-info204/2008/05/01/measuring-degrees-of-separation Measuring Degrees of Separation] – Demonstrates how a small sample size can be used to accurately measure the degrees of separation
*[http://www.facebook.com/group.php?gid=135906196456742&v=app_2344061033&ref=ts#!/group.php?gid=135906196456742 Using The Six Degrees Of Separation concept along with Social Networking to find my birthparents] – An adoptee conducts an experiment based on the 6 degrees of separation and the power of social networking, his goal: to get the word out about his birth to as many people as possible until he finds people with answers to his questions.
*[http://djjr-courses.wdfiles.com/local--files/soc180:karinthy-chain-links/Karinthy-Chain-Links_1929.pdf "Chains," or "Chain-Links."]
*[http://www.cinemadoku.com/ Cinemadoku] – A web game that combines the six degrees of movies and actors concept with the grid logic of Sudoku.
*[http://sixdegreesofkanyewest.com Six Degrees of Kanye West]
*[http://www.6degreesofvincegill.com/ 6 Degrees of Music With Vince Gill] – The 6 degrees theory applied to music with Vince Gill at the Center
{{Social networking}}
{{Psychology}}

[[Category:Social networks]]
[[Category:Sociological theories]]

{{Sourceattribution|Six degrees of separation}}