CINXE.COM

<!doctype html>     <html class="no-js" lang="en"> <head> <meta charset="utf-8"> <title>SFE: Black Holes</title> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <meta name="description" content="Welcome to the fourth edition of The Encyclopedia of Science Fiction." /> <meta name="keywords" content="" /> <meta name="viewport" content="width=device-width,initial-scale=1">  <script> window.ga=window.ga||function(){(ga.q=ga.q||[]).push(arguments)};ga.l=+new Date; ga("create", "UA-24275979-1", "auto"); ga("send", "pageview"); </script> <script async src="https://www.google-analytics.com/analytics.js"></script>  <link rel="icon" href="favicon.ico" type="image/x-icon"> <link rel="shortcut icon" href="favicon.ico" type="image/x-icon"> <link rel="apple-touch-icon" href="apple-touch-icon.png"> <link rel="stylesheet" href="/static/css/style.css?v=1"> <link rel="stylesheet" href="/static/css/media-queries.css"> <link rel="stylesheet" href="/css/cookie.css"> <script src="/static/js/libs/modernizr-2.0.6.min.js"></script> <style media="screen" type="text/css"> ::-moz-selection { background: navy !important; } html, body { margin:0; padding:0; height:100%; } #container { min-height:100%; position:relative; } #header { background:#ff0; padding:10px; } #body { padding-bottom:15px; /* Height of the footer */ } #footer { position:absolute; bottom:0; width:100%; height:15px; /* Height of the footer */ background:#6cf; } </style>  </head> <body style="overflow-x: hidden;"> <div id="container"> <div id="body"> <div id="minorNavWrapper"> <nav id="minornav" class="clearfix"> <ul class="clearfix" style="font-weight: bold;"> <li><a href="/">Home</a></li> <li><a href="/about-us">About us</a></li> <li><a href="/random.php">Random</a></li> <li><a href="/contact.php">Contact</a></li> <li><a href="/donate.php">Donate</a></li> </ul> </nav> </div> <div id="mainNavWrapper"> <nav id="mainnav"> <ul class="clearfix"> <li class="home"><a title="Home page" href="https://sf-encyclopedia.com/"><img id="sfeLogoSmall" src="/static/img/sfe.png" alt="SFE: The Encyclopedia of Science Fiction"><img id="sfeLogo" src="/static/img/logo.png" alt="SFE: The Encyclopedia of Science Fiction"></a><span class="logoArrow"></span></li> <li class="section-all"><a href="https://sf-encyclopedia.com/category/0">All entries</a></li> <li class="section-themes"><a href="https://sf-encyclopedia.com/category/theme">Themes</a></li> <li class="section-authors"><a href="https://sf-encyclopedia.com/category/everyone">People</a></li> <li class="section-media"><a href="https://sf-encyclopedia.com/category/media">Media</a></li> <li class="section-culture"><a href="https://sf-encyclopedia.com/category/culture">Culture</a></li> <li class="section-news"><a href="https://sf-encyclopedia.com/news/">News</a></li> </ul> </nav> </div> <div id="main"> <div class="colsWrapper clearfix"> <div class="column mainCol clearfix" style="background-color:white !important;"> <fieldset id="globalSearch"> <form name="srchenter" method="post" action="/search.php"> <select name="catfilter" class="searchFilter" style="width: 132px" title="Select entry category for headword or global search"> <option value="">Search all entries</option> <option value="chk">Checklist titles</option><option value="art">Art</option> <option value="author">Author</option> <option value="award">Award</option> <option value="character">Character</option> <option value="comics">Comics</option> <option value="community">Community</option> <option value="critic">Critic</option> <option value="editor">Editor</option> <option value="fan">Fan</option> <option value="film">Film</option> <option value="game">Game</option> <option value="house name">House Name</option> <option value="international">International</option> <option value="music">Music</option> <option value="people">People (media)</option> <option value="prelim">Prelim</option> <option value="publication">Publication</option> <option value="publisher">Publisher</option> <option value="radio">Radio</option> <option value="theatre">Theatre</option> <option value="theme">Theme</option> <option value="tv">TV</option> </select> <input name="search" type="text" value="" style="margin: 0 0 5px 0; width: 155px !important;" onFocus="this.select()" onClick="this.select()" onHover="this.select()" class="searchText" id="defaultOpen">  <input type="submit" value="Headwords" class="button primary" style="margin: 5px 0 0 0;; padding-left: 8px; padding-right: 8px">  <input type="submit" name="glob" value="Global search" class="button primary" style="margin: 5px 0 0 0; padding-left: 8px; padding-right: 8px"> <input type="text" name="eofmode" value="" hidden> <div style="display:none;"> <p style="margin: 0px; float: left;"><input type="radio" name="tomeselect" value="sfe" checked> <i>Search SFE</i>   <input type="radio" name="tomeselect" value="eof"> <i>Search EoF</i></p> <p style="margin: 0px; float: right;"> <input type="checkbox" Name="noxref">  <i>Omit cross-reference entries</i>  </p> <script> document.srchenter.search.focus(); document.addEventListener("keydown", function(event) { if (event.code == "PageDown" || event.code == "ArrowDown" || ( !event.getModifierState("NumLock") && (event.code == "Numpad2" || event.code == "Numpad3"))) { document.srchenter.search.blur(); } }) </script> </div> </form> </fieldset> <article class="entryArticle content STeditorial"> <header class="entryHeader icon-theme"> <h1 class="entryTitle">Black Holes </h1> </header><p class='tagLine'>Entry updated 13 June 2022. Tagged: Theme.</p><div class="browsingBtns"> <span> <input class="button PNI previous" type="button" onclick="window.location.href='/next.php?id=p&entry=black_holes'" value="Prev" /> </span> <span> <input class="button PNI next" type="button" onclick="window.location.href='/next.php?&entry=black_holes'" value="Next" /> </span> <span> <input class="button PNI incoming" type="button" onclick="window.location.href='/incoming.php?entry=black_holes'" value="About This Entry" title="What links to the entry; contributor initials explained; how to cite; other information" /> </span> </div> <p>Item of sf <a href="/entry/terminology">Terminology</a> borrowed from <a href="/entry/cosmology">Cosmology</a>. The term was coined by the physicist John A Wheeler (1911-2008) in 1969 and adopted immediately and enthusiastically by sf writers. The concept of the black hole is quite complex, and is best approached by the layman through a reliable book of scientific popularization such as <i>A Brief History of Time: From the Big Bang to Black Holes</i> (<b>1988</b>) by Stephen W Hawking (1942-2018), one of the theoretical physicists to have done fundamental work on the concept. The scientific element of the present discussion has been much simplified.</p> <p>The possibility that a lump of matter might be compressible to the point at which its surface gravity would be so powerful that not even light could escape from it was first pointed out in the late eighteenth century by John Michell (1723-1793) and then by Pierre Simon, Marquis de Laplace (1749-1827). It was resuscitated in the twentieth century when the implications of General <a href="/entry/relativity">Relativity</a> became clear. It was not until the 1960s, however, that physicists began to speculate as to whether a collapsing star of sufficient mass, something over three times that of the Sun, might pass beyond even the <a href="/entry/neutron_stars">Neutron-Star</a> state of collapsed matter to become a black hole of this kind, centred on a singularity (a limiting point where the asymptotic approach to infinite gravity crushes matter and energy entirely out of existence) and bounded by an event horizon. The latter is defined by the distance from the singularity at which the escape velocity is that of light; the name "event horizon" derives from the fact that it is of course impossible to observe from outside any events occurring closer to the singularity than this.</p> <p>Many early sf stories dealing with the theme seized upon the extreme relativistic time-dilation effect associated with objects falling towards the event horizons of such holes; examples include Poul <a href="/entry/anderson_poul">Anderson</a>'s "Kyrie" (in <i>The Farthest Reaches</i>, anth <b>1968</b>, ed Joseph <a href="/entry/elder_joseph">Elder</a>), Brian W <a href="/entry/aldiss_brian_w">Aldiss</a>'s "The Dark Soul of the Night" (in <i>The Ides of Tomorrow</i>, anth <b>1976</b>, ed Terry <a href="/entry/carr_terry">Carr</a>) and Frederik <a href="/entry/pohl_frederik">Pohl</a>'s <i>Gateway</i> (<b>1977</b>). These stories make interesting metaphorical connections between physics and psychology, perhaps helping to cast some light on the intriguing question of why the black-hole concept became one of the most charismatic ideas in late twentieth-century physics. Few other notions have had such an immediate imaginative impact, or spawned so many exercises in lyrical quasi-scientific philosophizing. John <a href="/entry/taylor_john">Taylor</a>'s <i>Black Holes: The End of the Universe?</i> (<b>1973</b>), one of several books which helped to popularize the notion in the 1970s, is a rather eccentric ideative rhapsody built on the debatable supposition that "the black hole requires a complete rethinking of our attitudes to life".</p> <p>Further tense psychological melodramas using black holes to develop analogies between extraordinary physics and mental processes include Robert <a href="/entry/silverberg_robert">Silverberg</a>'s "To the Dark Star" (in <i>The Farthest Reaches</i>, anth <b>1968</b>, ed Joseph <a href="/entry/elder_joseph">Elder</a>), Barry N <a href="/entry/malzberg_barry_n">Malzberg</a>'s <i>Galaxies</i> (<b>1975</b>) and John <a href="/entry/varley_john">Varley</a>'s "Lollipop and the Tar Baby" (in <i>Orbit 19</i>, anth <b>1977</b>, ed Damon <a href="/entry/knight_damon">Knight</a>) – which features an intelligent black hole – but stories of this kind soon petered out. Familiarity bred contentment if not contempt, and the black hole was soon domesticated by sf writers into a standard image of no great moment. The idea proved, however, to be surprisingly adaptable. At first it seemed that anything falling into a black hole was destined for certain destruction, but this narrative inconvenience was frequently sidestepped. It was independently and for different reasons hypothesized by cosmologists and sf writers alike that – supposing one <i>could</i> travel through a black hole – the point of emergence might be far removed from the point of entry. Because this property of black holes offered an apparent means of dodging the relativistic limitations on getting around the Universe at <a href="/entry/faster_than_light">Faster-than-Light</a> speeds, they quickly began to crop up as "star gates" – rapid transit systems – as in Joan D <a href="/entry/vinge_joan_d">Vinge</a>'s <i>The Snow Queen</i> (<b>1980</b>). Early examples of stories in which they perform this function tend, in order to obscure the fundamental problem, to use fudge-names for them: George R R <a href="/entry/martin_george_r_r">Martin</a>'s "The Second Kind of Loneliness" (December 1972 <a href="/entry/analog">Analog</a>) speaks of a "nullspace vortex" while Joe <a href="/entry/haldeman_joe">Haldeman</a>'s <i>The Forever War</i> (June 1972-January 1975 <a href="/entry/analog">Analog</a>; fixup <b>1974</b>) refers to "collapsars". Obliging physicists soon began to speculate about the possibility of avoiding destruction within a black hole. According to some theoretical physicists, some solutions of the equations of General <a href="/entry/relativity">Relativity</a> as they apply to rotating (rather than static) black holes offer the slim possibility that a spacecraft that entered such a hole might be able to avoid the naked singularity and so, rather than being crushed out of existence, might instantaneously re-emerge elsewhere in the Universe (travelling via a hypothetical bridge or tunnel known as a <a href="/entry/wormholes">Wormhole</a>) – the word "elsewhere" referring to some other place, some other time (which would create havoc with the principle of causality), or both. Some physicists went further, proposing that the re-emergence might be into a <i>different</i> universe. Sf writers gladly accepted the imaginative warrant provided by these ideas, which were popularized by such bold works of "speculative nonfiction" as Adrian <a href="/entry/berry_adrian">Berry</a>'s <i>The Iron Sun: Crossing the Universe through Black Holes</i> (<b>1977</b>). Stories in which <a href="/entry/starship">Starships</a> simply dived into black holes and passed through <a href="/entry/wormholes">Wormholes</a> to distant parts of the Universe or to other universes began to appear in some profusion. The popularity of the theme was further boosted by the film <i>The</i> <a href="/entry/black_hole_the">Black Hole</a> (<i>1979</i>), and quickly became so routine that recent writers have had to work hard to sustain the melodramatic potential of the notion. A notable example of conscientious work of this kind is Paul J <a href="/entry/mcauley_paul_j">McAuley</a>'s <i>Eternal Light</i> (<b>1991</b>), while a more casual approach is manifest in Roger MacBride <a href="/entry/allen_roger_macbride">Allen</a>'s <i>The Ring of Charon</i> (<b>1991</b>), in which the Earth is kidnapped through a wormhole. The idea of a return journey from a black hole is more ingeniously deployed in Ian <a href="/entry/wallace_ian">Wallace</a>'s <i>Heller's Leap</i> (<b>1979</b>).</p> <p>Although black holes formed through stellar collapse would have to be at least three times the mass of the Sun, the concept of miniature black holes emerged in the early 1970s, first in technical papers and then in sf. They were featured in "The Hole Man" (January 1974 <a href="/entry/analog">Analog</a>) by Larry <a href="/entry/niven_larry">Niven</a> and adapted for use in a <a href="/entry/spaceships">Spaceship</a> drive in Arthur C <a href="/entry/clarke_arthur_c">Clarke</a>'s <i>Imperial Earth</i> (<b>1975</b>), but they really came into their own when theorists attempting to figure out the mechanics of the Big Bang decided that vast numbers of tiny black holes might have been created at that time (along with even more peculiar black hole-like entities called cosmic strings). However, it was soon theorized mathematically – Hawking described some of this work in a seminar in 1973 – that mini black holes would be unstable, slowly decaying as a result of "quantum leakage" of radiation. (Such leakage would affect all black holes, of course, but only in the case of mini black holes would it be significant.) Any primordial black hole whose initial mass was less than about a billion tons would already have disappeared, although more massive (but still mini) primordial black holes might still exist. The never firmly identified "Agent" whose impact or passage destroys our <a href="/entry/moon">Moon</a> in Neal <a href="/entry/stephenson_neal">Stephenson</a>'s <i>Seveneves</i> (<b>2015</b>) may, as is speculated in the novel, be one such. Meanwhile, sf writers have had little difficulty in imagining accessory stabilizing methods for unfeasibly small black holes, such as the one featured in Gregory <a href="/entry/benford_gregory">Benford</a>'s thriller <i>Artifact</i> (<b>1985</b>). David <a href="/entry/brin_david">Brin</a>'s <i>Earth</i> (<b>1990</b>) simply ties neat knots in cosmic strings in order to make them available for mind-boggling high jinks of various kinds; the knotting of cosmic strings had earlier been examined less reverently by Rudy <a href="/entry/rucker_rudy">Rucker</a> in "The Man Who Was a Cosmic String" (in <i>Universe</i>, anth <b>1987</b>, ed Byron <a href="/entry/preiss_byron">Preiss</a>).</p> <p>Brin's <i>Earth</i> mentions an idea encountered elsewhere: that even tiny black holes might qualify as entire universes in their own right (thus, perhaps, re-opening some potential for the kind of microcosmic romance that Ray <a href="/entry/cummings_ray">Cummings</a> used to write; see <a href="/entry/great_and_small">Great and Small</a>). Pohl, having introduced black holes into <i>Gateway</i>, continued to explore their potential in subsequent volumes of his <b>Heechee</b> series; the mysterious Heechee turn out to be hiding inside one in <i>Beyond the Blue Event Horizon</i> (<b>1980</b>) and venture forth again in <i>Heechee Rendezvous</i> (<b>1984</b>). Pohl's fascination with the notion is further extended in <i>The Singers of Time</i> (<b>1991</b>), with Jack <a href="/entry/williamson_jack">Williamson</a>, which involves interuniversal travel via <a href="/entry/wormholes">Wormholes</a> and includes a series of rhapsodic <a href="/entry/infodump">Infodump</a> chapters celebrating the wonders of modern theoretical physics.</p> <p>Yet another variant on the black-hole theme is based on the concept that a low-density black hole of enormous mass – perhaps 100,000 times greater than that of the Sun – might commonly occur at the centre of galaxies, our own included; there is considerable astronomical evidence that this is indeed the case. The physics constraining the properties of such low-density black holes seems to admit the possibility that whole stars and planets could go on existing inside them. Even more massive black holes, of perhaps 100,000,000 times solar mass, might exist at the heart of those incredibly distant, highly energetic galaxies known to astronomers as Seyfert galaxies and quasars. (The term quasar derives from their earlier description as "quasi-stellar radio sources".) The immense black hole at the galactic core has become almost a <a href="/entry/cliches">Cliché</a> of contemporary <a href="/entry/space_opera">Space Opera</a>, from the above-cited <i>Beyond the Blue Event Horizon</i> to Greg <a href="/entry/egan_greg">Egan</a>'s highly intellectual <i>Incandescence</i> (<b>2008</b>).</p> <p>Further uses of black holes continued to be found. They become ultimate weapons in David <a href="/entry/langford_david">Langford</a>'s <i>The Space Eater</i> (<b>1982</b>) and others, and Gregory <a href="/entry/benford_gregory">Benford</a>, in <i>Beyond the Fall of Night</i> (<b>1990</b>), his sequel to Arthur C <a href="/entry/clarke_arthur_c">Clarke</a>'s classic <i>Against the Fall of Night</i> (November 1948 <a href="/entry/startling_stories">Startling</a>; <b>1953</b>), uses one as a <a href="/entry/prisons">Prison</a> for the Mad Mind referred to the earlier novel, where Clarke describes it only as the "strange artificial star called the Black Sun." Another black-hole prison is used to confine an invulnerable immortal in the <a href="/entry/superman_character">Superman</a> tale "For the Man Who Has Everything" (1985 <i>Superman Annual #11</i>) by Alan <a href="/entry/moore_alan">Moore</a> and Dave <a href="/entry/gibbons_dave">Gibbons</a>. Intelligent black holes of a sort return in Charles <a href="/entry/sheffield_charles">Sheffield</a>'s <i>Proteus Unbound</i> (<b>1989</b>) – where signals from miniature black-hole "kernels" imply gateways to alien civilization in other <a href="/entry/dimensions">Dimensions</a> – and more plausibly in Gregory <a href="/entry/benford_gregory">Benford</a>'s <i>Eater</i> (<b>2000</b>), whose eponymous intelligence is sustained by complex electromagnetic fields associated with the dirigible black hole's accretion disc. More modestly – though the risk factor would seem highly intimidating – internally-positioned miniature black holes provide inhabitants of <a href="/entry/asteroids">Asteroids</a> and <a href="/entry/space_habitats">Space Habitats</a> with the comforts of gravity in Charles <a href="/entry/sheffield_charles">Sheffield</a>'s <i>Proteus Unbound</i> (already cited), Alastair <a href="/entry/reynolds_alastair">Reynolds</a>'s <i>House of Suns</i> (<b>2008</b>) and Iain M <b>Banks</b>'s <i>Surface Detail</i> (<b>2010</b>). Still more bizarrely, the titular construction material of Wil <a href="/entry/mccarthy_wil">McCarthy</a>'s <i>The Collapsium</i> (<b>2000</b>) is made from tiny black holes "held rigidly into stable lattices". It remains to be seen whether the changes have now been comprehensively rung, or whether there is further narrative colour yet to be discovered in the notion.</p> <p>The existence of black holes had long seemed inevitable in the light of our understanding of the ways in which matter/energy behaves, but such theorizing was no substitute for proof. Since black holes of any significant size are by definition black, only indirect observations are possible; but eventually the circumstantial evidence became compelling. It is agreed by astronomers that the X-rays from certain intense periodic X-ray sources in our galaxy (the first discovered being Cygnus X-1, in 1971) are being emitted from particles falling towards a black hole which is in orbital partnership with a supergiant star; such systems are known as X-ray binaries. Something close to direct observation is also possible through gravitational lensing, with the location of a black hole inferrable by its distorting effect on light from farther-off stars and galaxies. Convincing evidence of supermassive black holes at the centres of many galaxies – including our own Milky Way – has been gathered. Such a black hole at the core of the elliptical galaxy Messier 87 was observed by the Event Horizon Telescope array in 2017 and a direct image released in 2019. Lists of known black holes are now routinely published and updated. The intense bursts of gravity waves caused by merging black holes have also been detected, and a number of such apocalyptic mergers identified. In this growing area of established observational science, there is little remaining conceptual leeway for the twentieth century's wilder sf fantasies about the properties of black holes. [BS/PN/DRL]</p> <p><b>see also:</b> <a href="/entry/white_holes">White Holes</a>.</p> <p><b>further reading</b></p> <ul class="x"> <li>Jerry <a href="/entry/pournelle_jerry">Pournelle</a> and John F <a href="/entry/carr_john_f">Carr</a> [anonymous], editors. <em>Black Holes and Other Marvels</em> (London: Futura, <b>1978</b>) [anth: pb/Tony <a href="/entry/roberts_tony">Roberts</a>]</li> </ul> <p><b>previous versions of this entry</b></p> <ul><li><a href='https://web.archive.org/web/*/http://www.sf-encyclopedia.com/entry/black_holes' target='_blank'>Internet Archive</a></li></ul><br /><br /></article></div> <div class="sideBarsWrapper"> <div class="sideBarsColsWrapper clearfix"> <div class="column sideBar12 clearfix"> <div class="columnForm"><aside id="blogFeed" class="widget"> <div class="content STeditorial clearfix"> <h2>Recently visited entries<span style="background:url(/images/thingSFE2.png) !important"></span></h2><ul style='width: 50%; float: left;'> </ul> <p align=center style="float:right; padding-top:20px; padding-bottom:20px;">ISSN 3049-7612<br /> <a href="/facts.php?id=logo"> <img src="/images/VitMan.gif" width=150 height=150 title="Click for larger version of this SFE logo"></a><br /> <b><a href="/donate.php"><img src="/images/Paypal-Donate.gif" WIDTH="92" HEIGHT="26" BORDER="0" /></a><br /><a href="/">Home/Welcome page</a></b></p><div style="margin-bottom:10px;"></div></div> </aside><aside id="blogFeed" class="widget"> <div class="content STeditorial clearfix"> <h2><i>SFE</i> Special Features<span></span></h2><p style="margin-top: 10px;"><input type="button" value="What’s New" style="width: 150px !important;" class="button primary" onclick="window.location.href='/whatsnew.php'">  Latest entries; <a href="/updated.php">latest updates</a></p> <p style="line-height:1.6em;"><input type="button" value="In Memoriam" style="width: 150px !important;" class="button primary" onclick="window.location.href='/timeline.php?rip'">  Recent deaths</p> <p style="line-height:1.6em;"><input type="button" value="On This Day" style="width: 150px !important;" class="button primary" onclick="window.location.href='/today.php'">  Anniversaries; also <a href="/timeline.php">Timeline</a></p> <p style="line-height:1.6em;"><input type="button" value="Gallery" style="width: 150px !important;" class="button primary" onclick="window.location.href='/gallery.php'">  <i>SFE</i> Picture Gallery; <a href="/gallery.php?list&new">What’s New</a></p> <p style="line-height:1.6em;"><input type="button" value="Shopping" style="width: 150px !important;" class="button primary" onclick="window.location.href='/sfeshop.php'">  Affiliate settings</p> <p style="line-height:1.6em;"><input type="button" value="Random" style="width: 150px !important;" class="button primary" onclick="window.location.href='/random.php'">  Show a random <i>SFE</i> entry</p> <p style="line-height:1.6em;"><input type="button" value="SFE Facts" style="width: 150px !important;" class="button primary" onclick="window.location.href='/facts.php'">  Bar charts, awards and more</p> <p style="line-height:1.6em;"><input type="button" value="Entry Data" style="width: 150px !important;" class="button primary" onclick="window.location.href='https://sf-encyclopedia.com/incoming.php?entry=black_holes'">  Incoming links, who wrote it, etc</p> <p style="margin-bottom:15px;"><a href="/searching">Search help</a> | <a href="/rss.php" target="_blank">RSS feed</a> <img src="/static/img/external.gif"> | <a href="/fe/"><i>Encyclopedia of Fantasy</i></a> <img src="/static/img/external.gif"></p><div style="margin-bottom:10px;"></div></div> </aside><aside id="connect" class="widget"> <div class="content STeditorial clearfix"> <h2>Connect with <i>SFE</i> <span></span></h2> <ul> <li> <h3 style="text-align: left !important;"><a href="/donate.php">Donate towards <i>SFE</i> expenses</a></h3> </li> <li> <h3 style="text-align: left !important;"><a href="/contact.php">Send email feedback to the <i>SFE</i> editors</a></h3> </li> <li style=" display:none;"> <h3 style="text-align: left !important;"><a href="https://twitter.com/john_clute" target="_blank">John Clute on Twitter [X]</a></h3> <a href="https://twitter.com/john_clute" class="twitter-follow-button">Follow @john_clute</a> <script src="https://platform.twitter.com/widgets.js" type="text/javascript"></script> </li> <li style=" display:none;"> <h3 style="text-align: left !important;"><a href="https://twitter.com/sfencyclopedia" target="_blank"><i>SFE</i> on Twitter [X]</a></h3> <a href="https://twitter.com/sfencyclopedia" class="twitter-follow-button">Follow @sfencyclopedia</a> <script src="https://platform.twitter.com/widgets.js" type="text/javascript"></script> </li> <li> <h3 style="text-align: left !important;"><a href="https://www.facebook.com/pages/Sf-Encyclopedia/138995776178949" target="_blank"><i>SFE</i> on Facebook</a></h3> </li> <li> <h3 style="text-align: left !important;"><a href="https://www.facebook.com/john.clute.5" target="_blank">John Clute on Facebook</a></h3> </li> <li> <h3 style="text-align: left !important;"><a href="https://bsky.app/profile/sfencyclopedia.bsky.social" target="_blank"><i>SFE</i> on BlueSky</a></h3> </li> <li> <h3 style="text-align: left !important;"><a href="https://mastodon.social/@SF_Encyclopedia" target="_blank"><i>SFE</i> on Mastodon</a></h3> </li> </ul> </div> </aside> </div></div> </div> </div> </div> </div> </div> <div id="cookieConsent"> <div id="closeCookieConsent" onclick="hidepopup()">x</div> This website uses cookies.  <a href="/cookies" target="_blank">More information here</a>. <a class="cookieConsentOK" onclick="setcookie()">Accept Cookies</a> </div> <script type="text/javascript"> function hidepopup() { document.cookie = "hidecookiepopup=yes; path=/"; // session only document.getElementById("cookieConsent").style.display = "none"; } function setcookie() { document.cookie = "cookiesOK=yes; max-age=31536000; path=/"; // 1 year document.getElementById("cookieConsent").style.display = "none"; } var cookiestring = document.cookie; // document.getElementById("connect").innerHTML = cookiestring; // TEST only if ( cookiestring.indexOf("cookiesOK=yes") == -1 ) { if ( cookiestring.indexOf("hidecookiepopup=yes") == -1 ) { document.getElementById("cookieConsent").style.display = "block"; } } </script> <div id="footer" style="background:#fff; padding: 5px;"> <footer id="globalFooter" class="clearfix"> <div id="credit">Website design by Ansible Editions </div> <div id="credit" style="float: left !important; padding-left:20px;">Site and <i>SFE</i> content © 2011-2025 John Clute & David Langford</div> </footer> </div> </div> </body></html>