The idea of traveling between alternate realities is a common theme in speculative fiction. Multiverse stories are a logical extension of allohistory, and a close relative of that other grand old convention, time travel. The idea is often explained as inspired by the Many-Worlds Interpretation first formulated by Hugh Everett in 1957, but its use in literature and storytelling has been long with us. Jorge Luis Borges used the theme in his 1941 story "The Garden of Forking Paths". There are earlier examples in Margaret Cavendish's The Blazing World of 1666 (recently revisited by Alan Moore) and in one of the stories in the One Thousand and One Nights. Ancient multiverses can be found in the Hindu cosmology and the nine worlds of the Norse mythos were around long before Jack Kirby.

Right from the start, Banks' Transition has superficial similarities to Michael Moorcock, especially the Jerry Cornelius stories. Both books feature amoral agents with shifting loyalties, flitting between versions of Earth. They party down in exotic locales, averting or causing global calamity — like rock stars trashing an infinity of hotel suites. Victorian airships and super-assassins abound. The theory goes that all of Moorcock's fiction is one big multiverse, from the Sword and Sorcery worlds of Elric of Melniboné or Corum Jhaelen Irsei to the decadent Dancers at the End of Time. All the various characters in these works are aspects or avatars of a stock cast of meta-players often compared to the Commedia dell'Arte theater tradition with its tricksters, oafs, and backstabbers. Jerry Cornelius is a 20th Century face of the slightly mis-named Eternal Champion. He's an anarchist secret-agent, a super-slick antihero whirling in a blaze of intoxicants and ready fuck anything that fucking moves. David Bowie as Doctor Who, turned up to fuckin' twelve! While quite entertaining, it should be no surprise that these quintessential examples of SF's New Wave movement can be a wee bit disorienting. Product of the times.

For a speculative fiction ride of sex, drugs, and rock&roll that's less experimental (ahem, easier to read), I prefer Mick Farren, singer of the proto-punk band The Deviants, White Panther Party member, and Elvis scholar. Out of print, but well worth the hunt, are his multiverse romps in The DNA Cowboys Trilogy and Necrom, some truly weird fun shit. The dimension-tripping demon Yancey Slide from those adventures also turns up in the more recent Kindling and Conflagration He also wrote the Victor Renquist novels, a series of vampire novels that aren't totally lame. 2002's Underland has the CIA, vampires, and Nazis duking it out with flying saucers in the Hollow Earth beneath Antarctica. Yeah. Hell, just track down anything you can by Mick Farren.

Along with Moorcock, two other Monsters of Multiverse Literature ( or "Mul-Lit") are The Amber Chronicles by Roger Zelazny and the series that inspired that, World of Tiers by Philip José Farmer. They have much more of a fantasy feel than the above, especially because of an overuse of courtly language in the former and centaurs and other classic monsters in the latter. You'll also find plenty of complex machinations by powerful groups or families (Zelazny is notorious for Daddy Issues) and decadent, lusty adventure (more of Farmer's bag in trade, but evident in both). I enjoyed both of these series as a teen, but to be honest that was a long time ago and my impressions are murky at best. I recall the fiveTiers with more fondness, but that might be due to the risqué covers by Boris Vallejo. I can assert with some authority that the reader should stop after the first five Amber books, do not read the second series, do not collect the recent stuff written by John Gregory Betancourt. Sadly, Amber suffers from a terminal case of Herberts' Syndrome.

The quirky standalone Roadmarks by Zelazny could be considered a multiverse book. In it, the space-time continuum is an actual highway accessible to a few. The protagonist tools around the centuries in a dusty old pickup running guns to the Persians at Marathon. Occassionally he passes Hitler, his VW bug parked at the side of the road looking for the weed-choked off road to where he won WWII. I'm going to try and fit in some Amber andTiers, maybe revisit Riverworld too, just for old time's sake.

Now that I'm thoroughly soaked in nostalgia, allow me to wax rhetorical on multiverse comic books I always liked. Yes, they're old, I'm old; get used to it, and get off my urine-covered stoop.

The capes-and-tights set is plagued with multiverses, and they're always having Ultimate Critical Infinity Wars — boooring. A refreshing change from all that was the " Zenith" strip in2000 AD (1987-1992). This was young Grant Morrison and Steve Yeowell's contribution to the British superhero deconstruction attack of the 1980s. It had battles between multiple Earths, hippie/fascist versions of the same superheroes, the Lloigor from the Cthulhu Mythos, and a hero who was a real asshole. Yeowell's brushy B & W artwork was a sweet counterpoint to the usual 4-color superhero look, too.

For graphical goodies of a more science fictional bent, you cant go wrong with the ligne claire and spacey psychedlia of Jean Giraud better known as Moebius, co-creator of Métal Hurlant magazine. The Airtight Garage is a series of artificial pocket universes built into the asteroid Flower 51. They are the playgrounds/battlefields for the likes of Lady Malvina, Major Gubert, the crew of the spaceship Ciguri, and Jerry Cornelius. Hey, whaaa? Yep, Moorcock allowed other artists, writers, and musicians the use of the character in a sort of Open Source deal. For a while Marvel had a problem with that and the character was renamed Lewis Carnelian for a while. Weird. There are songs about Jerry by Blue Öyster Cult and Hawkwind, but I digress. Moebius returned to the Airtight Garage in '96 with Man from the Ciguri from Dark Horse. All lots of fun.

Bryan Talbot's The Adventures of Luther Arkwright is also often compared to Moorcock, and in many ways improves upon him. Frankly, when you want to read about sexy psychic spies fighting transdimensional evil, it's hard to top the Arkwright stories. I love Talbot's vision of alternate Britains, like the one where Cromwell's Revolution still rages on and the Puritans terrorize the skies from massive airships. The complex plot jumps around jarringly in the original series, before finally coalescing, as you begin to see the multiverse as Luther does. There is also an audio version with the voices of David Tennant and Paul Darrow, I've never heard it — but wow, fangasm. The later 1999 sequel, Heart of Empire from Dark Horse again, follows the story of Luther's daughter in a much more linear fashion, with absolutely gorgeous art and much of that retro-Victorian futurism the kids like.

I have a particular fondness for the idiosyncratic doodles of doom by of Matt Howarth. His anarchic city-world of Bugtown is the home of indestructible assassins, rockstars, giant sharks, and nuclear goddesses; all of whom flit through the most surreal and impossible alternate universes imaginable. The series Those Annoying Post Brothers and Savage Henry are just packed full of crazy. Many experimental underground musicians make regular appearances in Howarth's work. There are adventures featuring Conrad Schnitzler, The Residents, and Micheal Moorcock collaborators, Hawkwind. Geez, that guy gets his beard into everything. Howarth also draws great aliens that look really alien, like cacti crossed with really uncomfortable furniture. Look for the very funny SF Konny & Czu strips.

"So Grey", I hear you say, " how about something less reminiscent of your college-dorm lava-lamp days? Something more, y'know [describes a circle in the air] for the kids?"

Well, the most well known Young Adult books with multiverse themes would probably be Philip Pullman's His Dark Materials. Chris Roberson should be getting a lot more attention for his time-space tripping adventures of the Bonaventure-Carmody family in novels likeHere, There & Everywhere, Paragea, and End of the Century. Oh and big surprise, Roberson has worked with Michael Moorcock often.

For something different, try Changing Planes by Ursula K. LeGuin. This is a collection of bright and witty capriccios about a woman who discovers how to shift to alternate worlds by being bored and dyspeptic in airport waiting rooms. As usual, LeGuin makes many wry observations about society and class. There's one story about a civilization of flightless avian people and their transcontinentaln migrations...the ending is beautiful. I could mention Dark Tower series by Stephen King or Charles Stross' The Merchant Princes but I'm just not into them, so I won't. Philip K. Dick's doesn't make the cut either: that's really only a duoverse.

I really loved Neal Stephenson's Anathem and it's all about the multiverse, but does it really belong with these other stories? Well of course it does! If for no other reason than it's completely different from the Michael Moorcock imitators. Yes, all the action takes place in one cosmos — going to another world is a one-way trip and requires a big honkin' generation starship. There is the mystery of Fraa Jaad, who appears to be able to move at will between the slightest possibilities. I noticed something odd, even though Stephenson beats us about the head and neck with tons of higher mathematics and metaphysics, he's awfully vague about the actual mechanism for traveling from one reality to another. This is probably the smartest move. Some writers do a lot of handwaving about Quantum and dress it up in blinky lights and an Einstein-Rosen bridge. But usually, it just boils down to closing your eyes and clicking your heels three times. How very apt for a thought experiment.

Multiverse stories are becoming more prevalent on TV these days. That kid from Stand by Me fought Nazi cavemen from Dimension X or whatever in Sliders. The color coded Charlie Jade looked interesting, but I haven't watched it yet. Lost has used the Many Worlds Interpretation, but they will try just about anything these days.

I see Leonard Nimoy is going back and forth in alternate worlds a lot these days (in Fringe and the Star Trek movie.) Glad to see that sort of thing again.

Somebody asked me recently if multiverses were the Next Big Thing in Speculative Fiction? I like the multiverse concept and would like to see different takes on it, that aren't all about decadent ubermensch and their interdimensional power struggles.

And honestly, we don't need Next Big Things. Trendy conventions in writing are a symptom of a lack of originality. Speculative fiction itself should be a glorious sprawling multiverse exploring all manner of settings and styles. Right now, too many of the worlds in the new book section are getting too recognizable, I'm looking at you Contemporary Urban Fantasy! And you with the top hat and goggles, we've talked before about this, you need to seek help.

So yeah, this trip down multiverse lane has been fun — but I think it points out a flaw in sub-genre stories. Why do they all start running together? Why so many Shadowy Conspirancies, Power Hungry Libertarian Scensters and Moral Relatavisim in a majority of these alternate reality adventures. The Multiverse must have more possibilities than that.

Special thanks to Alan Beatts and Chris Braak for their helpful ideas.
Top image from Heart of Empire by Bryan Talbot, 1999.

Commenter Grey_Area is known on many worlds as Chris Hsiang. He brachiates through the endlessly forking branches of possibility frightening all the turtledoves.

The film follows Penikett's character, Matt Ellman, after his death when he wakes up in a new world along with everyone else who died — including September 11th victims and Mark Twain. He's determined to find his girlfriend, (Laura Vandervoort) who also died with him. But lots and lots of insanity gets in the way including one very blue Alan Cumming.

Here's the official synopsis:

When American war zone journalist Matt Ellman (Tahmoh Penikett, Battlestar Galactica) and his fiancée, Jessie Machalan (Laura Vandervoort, Smallville), are killed in an explosion, Matt awakens, separated from Jessie, on the banks of a river snaking endlessly across a mysterious new plane of existence. On Riverworld, everyone who has ever lived on Earth, ever soul throughout time, has been reborn along the banks of a seemingly endless river. Determined to locate Jessie, Matt aligns with Tomoe (Jeananne Goossen, Falcon Beach) , a 13th century female warrior, Allegra (Romina D'Ugo, Hairspray), a 15th century courtesan of shifting alliances, and American novelist and Riverboat captain Samuel Clemens (Mark Deklin, Justice), better known as Mark Twain. With a full crew of adventurers, they embark upriver to understand where they are, why they are here, and to what unknowable end the river winds.

Under the guidance of the peculiar Caretaker (Alan Cumming, Tin Man), their quest takes them below to a torturous Cavern of Souls and the Underworld prison, above in a Zeppelin piloted by a brilliant German engineer, and forward to cross paths with renowned explorer Sir Richard Francis Burton (Peter Wingdfield, 24) who has joined forces with Francisco Pizzaro to conquer and destroy Riverworld. For Matt, each unfathomable day, each nefarious encounter, only deepens the conundrum of Riverworld and raises more questions…What happened to Earth and when? What is the purpose of the burning Orb? What powers are contained in the infamous Dark Tower? And why is their every move being followed by the watchful eye of an alien being? The answers are waiting beyond the endless swells of Riverworld.

Charting a territory somewhere between Gulliver's Travels and The Lord of the Rings" (Time), Philip Jose Farmer's Nebula Award-winning saga becomes a spectacular miniseries event-a feast for the eyes, the mind, and the heart of everyone who longs to explore the meaning of life, the mysteries of death, and everything that lies between.

Riverworld will be on Syfy in early 2010.

Orbit is seeking suggestions for a title and blurbs, to come up with the worst book cover of all time, and I bet we can help:

Over the next few weeks we'll be asking for your help coming up with the most ridiculously bad high-concept SFF book cover in the universe – think Wyvern II: The Wyverning, or Martian Under the Doormat. (We know you can do better) Once we've settled on the titles we'll work out the reading line, the blurbs, and cover elements. And then, with your help, our fearless Orbit US Creative Director Lauren is going to design a cover for it that will present it in all its mad glory.

I have great faith in the ability of the internet to spawn some truly awful science fiction book ideas. But just in case someone is lacking for inspiration, here are some truly hideous covers to make your eye-sockets bleed:

Heraclitus said you can't step into the same river twice, but that's what Syfy, having adapted Riverworld into a standalone feature in 2003, is trying with next year's more ambitious, four-hour miniseries based on Philip José Farmer's beloved novels. Judging by this Q&A at SciFiWire, however, scribe Robert Hewitt Wolfe (Star Trek: Deep Space Nine, The 4400) seems undaunted by the prospect of alienating Farmer's loyal readers with an adaptation that ditches the original's storylines and relegates its protagonists to supporting character (or antagonist) status.

The basic premise is the same: deceased humans from across time find themselves living in a watery limbo, a planet-traversing river, where famous historical personages and obscure folk unite to unravel the mystery of their situation. Like the 2003 movie, however, the Wolfe miniseries will push aside the first book's protagonist (real-life Victorian explorer Sir Richard Francis Burton) in favor of a contemporary American protagonist (to be played by Dollhouse's Tahmoh Penikett) with a simple motive: to find his missing love (Smallville's Laura Vandervoort), who died with him in a suicide bombing.

Wolfe (whose strong résumé includes multiple episodes of Andromeda, Star Trek: Deep Space Nine, and The 4400) suggests that he wants to leave the saga's spiritual and philosophical underpinnings intact, but downgrading the swashbuckling, complex, real-life protagonist to a supporting role because American TV viewers might find him too obscure and unlikable doesn't speak well for the project's literacy and thoughtfulness. In fact, Wolfe hints that Burton may be more of an antagonist than a protagonist. Mark Twain, the hero of the second book, will turn up early on, having managed to build himself a riverboat.

Plus, Wolfe envisions future installments of this possible ongoing series, where he uses Farmer's platform as an opportunity to dig up various historical figures and watch them fight. "I'd love to do a story where the real Macbeth finds out about this play that has been written about him and is freaking pissed off because it makes him look like a dick!" Heh heh. Watch your back, Shakespeare!

Farmer, who died in February at 91, was reportedly upbeat about the prospect of this miniseries. These days, however, he's probably on a steamboat somewhere with Twain and Shakespeare, plotting vengeance.

1. Samuel R. Delany (1942- )
His 1975 novel Dhalgren is a hugely complex, at times incomprehensible tome reminiscent of the works of Thomas Pynchon. It also showcases every imaginable form of human sexuality, including a long-term polyamorous relationship between the protagonist, his lover Lanya Colson, and a gang member called Denny.

2. Philip José Farmer (1918-2009)
It would be a stretch to say Farmer invented sexual science fiction (especially considering some of the people on this very list predate him), but he did shatter the mainstream notion that sex had no place in science fiction. His 1953 short story "The Lovers" was an overnight sensation for its sophisticated, intelligent depiction of love between a human and an alien, which he followed up with five more stories in a similar vein in his 1960 anthology Strange Relations. He explored unconventional relationships both allegorically within science fiction and literally in his 1962 novel Fire and the Night, which looked at an interracial relationship before they had gained widespread social acceptance.

3. Robert Heinlein (1907-1988)
Nothing if not an iconoclast, Heinlein was a militarist who also passionately believed in free love, at least if his writings are to be believed. It's actually not that hard to reconcile when seen in terms of his ironclad libertarianism, which led him to foresee a future where homosexuality was fully accepted, public nudity was commonplace, and couples were far from the only acceptable number of people for romantic relationships. A noted advocate for polyamory, his works consistently shattered taboos, ranging from relatively mundane topics for the 1970s such as open homosexuality to a full-fledged incestuous romance between immortal time traveler Lazarus Long and his own mother - and all of that was in just one book, 1973's Time Enough for Love. But perhaps his crowning achievement for mixing sex and science fiction was his wonderfully twisted 1959 short story "All You Zombies", in which time travel and a sex change operation allows the story's protagonist to become both his own mother and father, not to mention just about everyone else who appears in the story.

4. Ursula K. Le Guin (1929- )
Le Guin has extensively studied alternative conceptions of gender, both as a critical theorist (in such essays as 1976's "Is Gender Necessary?") and in books like The Left Hand of Darkness. Her novel, published in 1969, considered the Gethenians, a humanoid alien race with no inherent gender. Instead, Gethenians experience the activation of either male or female sexual organs in roughly monthly cycles. To humans, this means they constantly switch genders, although this is a rather quaint notion to the Gethenians themselves.

5. William Moulton Marston (1893-1947)
Marston, the creator of Wonder Woman, may not have the literary credentials of the other people on this list – although he did invent the lie detector test, for what that's worth – but his creation of the first female superhero might have the most pop culture impact. His personal idiosyncrasies, which included living with his wife and girlfriend in a polyamorous relationship, influenced the character's subtext, often leading to Wonder Woman being tied up by other Amazons in situations that evoked bondage imagery (there are entire sites devoted to tracking this very phenomenon). In an era when even recognized comic book geniuses like Will Eisner were content to rip off Superman, it took an uncompromisingly unique individual like Marston to create the first and still the best superheroine, and the medium is infinitely better for it.

6. Joanna Russ (1937- )
One of the first and most important lesbian science fiction writers, Russ confronted sexism head-on in the 1970s with a number of works, both fiction and non-fiction. Her most notable science fiction was probably 1975's The Female Man, which considered four women living on four different parallel universes who then travel between each other's worlds. The different universes include a universe where the Great Depression is still going strong, one that is essentially the same as the real world, another that is a utopian society without any men at all, and a universe where the two genders are literally at war. Russ uses this multiversal backdrop to compare how the various characters' situations influence their conceptions of gender politics and sexuality.

7. Alice Bradley Sheldon (1915-1987)
Better known by her male pseudonym, James Tiptree Jr., Sheldon spent her science fiction career methodically deconstructing supposed boundary lines of sex and gender (she herself was bisexual). She looked at the nature of sex, at times characterizing it as a playful expression of human free will, but otherwise seeing it more as an animalistic force in such stories as "Love Is the Plan the Plan Is Death" and "The Screwfly Solution." Her 1975 novella "Houston, Houston, Do You Read?" dealt with three male astronauts thrown through an anomaly in space to an Earth inhabited solely by women, which Sheldon characterizes as a peaceful but stagnant society. "The Women Men Don't See", on the other hand, depicted two women who used an alien abduction as an opportunity to escape the limitations of their lives on Earth. She depicted sex with a frankness and clarity that was exceptional for science fiction authors of the day, male or female.

8. Olaf Stapledon (1886-1950)
His 1935 novel Odd John is one of the earliest to explore sexual themes in science fiction. Following John Wainwright, a British mutant with extraordinary mental abilities, the novel in part addresses the sorts of relations a superhuman such as John could have with regular people. Although Stapledon never quite comes out and says it explicitly, Odd John almost certainly suggests that Wainwright has sex with both his own mother and a young boy. Ultimately, he concludes that all relations with normal humans are morally wrong on the grounds that his advanced intellect makes any such act essentially bestiality.

9. Theodore Sturgeon (1918-1985)
The same year as Philip José Farmer's "The Lovers" broke new ground with love between species, Theodore Sturgeon shattered the taboo against depictions of homosexuality in science fiction with his short story "The World Well Lost." The story follows a pair of seemingly male and female alien lovers who visit Earth and become celebrities until their home planet demands their extradition. When the aliens reveal to one of the astronauts tasked with bring them home that they are both male and that their crime is love, he sets them free, in part because he nurses a secret love for his copilot. The story was so controversial that it barely got published; the first editor Sturgeon showed it to actively called other editors, demanding they not publish it. Thankfully, Universe magazine saw it differently, and science fiction is infinitely better for it.

10. John Varley (1947- )
His "Eight Worlds" stories depict how technology manages to make homophobia obsolete (well, more obsolete). In a future culture where people can change their gender instantly, there is little room for views that see homosexual relationships as different from heterosexual ones, as a person could wake up one day in one relationship and go to sleep in the other.

Top image from Clyde Caldwell's cover illustration for Farmer's Strange Relations.

Sherlock Holmes wasn't the first master detective (that honor probably goes to Edgar Allan Poe's Auguste Dupin, who in his first case worked out the murderer was a knife-wielding orangutan), but his exploits pretty much perfected the genre. Arthur Conan Doyle created a character whose impossibly rational mind and superhuman powers of observation and deduction made him transcend the sixty original stories in which he appeared to become one of the most famous people of his era, real or fictional. Conan Doyle's stories may have remained mostly rooted in reality (although a man partially turned into a monkey, mention of the giant rat of Sumatra, and Holmes's almost superhuman physical prowess pushed the boundaries at times), but later writers have found that Sherlock Holmes and Dr. Watson fit in just as well in far more fantastic settings. Here now are but a few of those stories.

Sherlock Holmes in the 22nd Century does pretty much exactly what it promises to do, transplanting a recently unfrozen Sherlock Holmes to the year 2104, where he teams up with a robotic Dr. Watson and a descendant of his Scotland Yard contact Inspector Lestrade to take on a clone of his arch-nemesis, Professor James Moriarty. This animated series set out to do reasonably faithful adaptations of the original Conan Doyle stories, except with more flying cars and a much prettier Lestrade (which really were the two main flaws of the originals, to be fair). Although the opening titles seemed to go to exorbitant lengths to prove that, yes, this really is Sherlock Holmes and he really is in the 22nd century.

Of course, the Filmation series BraveStarr actually does one better with its two-part episode, "Sherlock Holmes in the 23rd Century." Here, Holmes falls through a time warp to the year 2249 during his climactic battle with Moriarty, who then freezes himself cryogenically so he can continue his battle with Holmes in the future. Galactic Marshall Bravestarr from the planet New Texas enlists Holmes's help in tracking down a kidnapped boy. Not to give anything away, but anyone want to guess which recently unfrozen Victorian supervillain might be behind the kidnapping?

Lest you think that this sort of thing was limited to animation, the 1987 CBS TV movie The Return of Sherlock Holmes involved private detective Jane Watson, a descendant of the good Doctor, discovering Holmes having cryogenically frozen himself to avoid dying from a dart tipped with bubonic plague. The movie tried to tackle some important questions, such as what would happen if Sherlock Holmes went into a pornographic bookshop? (Answer: Hilarity would ensue.) The concept never became a series, although a different bunch tried pretty much exactly the same idea with almost exactly the same title six years later with Sherlock Holmes Returns.

At this point, I'm sure you're wondering, "This Sherlock Holmes stuff is all well and good, but what about John Cleese?" Well, The Strange Case of the End of Civilization as We Know It involves the Monty Python legend as the detective's grandson, Arthur Sherlock Holmes, as he investigates the murder of a thinly disguised Henry Kissinger with the rather counterproductive help of a bionic Doctor Watson. The word "bionic" is pretty much the only reason I'm including this. Well, that and John Cleese.

David Dvorkin's Time for Sherlock Holmes also places the detective in the far future, although this time Holmes gets there via immortality, which he notes with some regret has made him rather more rigid in his thinking than he used to be. Conan Doyle isn't the only author from whom Dvorkin freely borrows; Moriarty manages to catch up to the eternal detective using H.G. Wells's time machine. And that's not the only Wells/Conan Doyle crossover out there - Manly Wade Wellman's Sherlock Holmes's War of the Worlds follows Holmes, Watson, and another Conan Doyle creation, Professor George Edward Challenger, as they take on the Martian invaders. Unlike the Wells book, which finds humanity utterly defenseless against the alien menace, Holmes and company spend pretty much the entire book kicking Martian ass. If only Steven Spielberg had used this version of War of the Worlds...

Star Trek: The Next Generation famously placed Data in the Holmes role as he tangled with a holodeck Professor Moriarty in "Elementary, Dear Data" and "Ship in a Bottle." Sure, the real Holmes and Watson never showed up, but Data and Geordi La Forge made for two very reasonable stand-ins. For that matter, Data didn't even need the holodeck to get his Sherlock on – just a ludicrously out-of-place pipe, some painfully stilted dialogue, and a highly amused Will Riker.

Oh, and Spock quotes one of Holmes's most famous lines in Star Trek VI: The Undiscovered Country when he says, "An ancestor of mine maintained that if you eliminate the impossible, whatever remains – however improbable – must be the truth", which totally implies Holmes is his great-great-great-great-great-great-grandfather or something. You know, come to think of it, I can sort of see the resemblance.

Speaking of "Elementary, Dear Data", apparently there was some rule in the late eighties/early nineties stipulating that every show that includes the great detective had to use this same formula for its title. Thus we have The Real Ghostbusters and "Elementary, My Dear Winston" as well as Teenage Mutant Ninja Turtles and "Elementary, My Dear Turtle." I suppose now is as good a time as any to point out that Sherlock Holmes never actually, you know, said those exact words in any of the original Conan Doyle stories. Still, when we're talking about mutated, super-intelligent turtles falling through a time slip and helping Sherlock Holmes recover an atomic clock from Moriarty before he can somehow use it to change history and declare himself the emperor of the world, a slight misquote should probably be the least of my logical issues.

Moving to Doctor Who, although the Doctor has never shared the screen with Sherlock Holmes, that doesn't mean they haven't had an adventure or two together. The biggest was the seventh Doctor novel All-Consuming Fire, in which the two team up to take on the chaos god Azathoth. At the time, there was even some thought of making Holmes and Watson the Doctor's new companions, which I guess they decided was just too nutty, even by the standards of nineties Doctor Who novels (not that that's necessarily a bad thing). And, although there aren't any explicit mentions made to the great detective, the Doctor's costume in the The Talons of Weng-Chiang, complete with deerstalker cap, is clearly inspired by Holmes.

There are plenty of anthologies of Sherlock Holmes stories with science fiction elements, so I won't attempt anything more than a general sampling of what's out there. For instance, in Sherlock Holmes in Orbit, edited by Mike Resnick and Martin H. Greenburg, you can find Dean Wesley Smith's "Two Roads, No Choices", which involves time-travelers from the 21st century asking Holmes to investigate why the Titanic never sank, which I'm going to assume ends with a certain master detective introducing a certain unsinkable ship to a certain iceberg. There's also Josepha Sherman's story "The Case of the Purloined L'isitek", which features super-intelligent horses called Shrr'loks that live on the planet Kholmes under the rule of a pony that acts an awful lot like Sherlock Holmes himself – none of which technically involves the man himself, but it deserves mentioning if only for the sheer insanity of the premise.

Isaac Asimov edited the anthology Sherlock Holmes Through Time and Space, which among others featured two stories by the late Philip José Farmer set in his Wold Newton universe: "The Problem of the Sore Bridge - Among Others" and "A Scarletin Study". Holmes's ancestors were among those affected by the radioactive meteorite that hit Wold Newton, Yorkshire in 1795, along with pretty much every other character in the history of literature. The first story deals with that most impossible of ideas - three cases Sherlock Holmes failed to solve - while the second story finds the detective finally meeting his match in the form of a German Shepard with a 200 IQ.

Sadly, Asimov never really tackled the character himself, despite being a proud member of the Baker Street Irregulars, the preeminent Holmes appreciation society. Still, he did write a short story, "The Ultimate Crime", involving his puzzle-solving Black Widowers characters wherein a Holmes enthusiast asks them to work out the precise topic of Professor Moriarty's famed physics The Dynamics of an Asteroid. Since the hypothetical solution involves blowing up the Earth, I'm counting it as just sneaking over into science fiction territory.

Holmes has also made his fair share of appearances in comics. Perhaps his biggest role was in Warren Ellis's Planetary, in which he agrees to mentor series protagonist Elijah Snow in the secret history of the world that he had helped shape. The fiftieth anniversary issue of Detective Comics finds Batman along with some of the DC Universe's other great sleuths taking on a bunch of Moriarty's descendants. After they wrap up the case, Sherlock Holmes himself shows up to congratulate them and acknowledge the Dark Knight as his true successor. I've got to say, he's looking pretty good for 135, but something is definitely a bit off with Batman's mask.

There was also this past week's Sherlock Holmes/Kolchak: The Night Stalker, which was reasonably diverting if beset with a couple unfortunate Americanisms (you'll never get me to accept Holmes would say "pants" instead of "trousers"). He only appeared in one scene of the Victorian public domain character orgy that is The League of Extraordinary Gentlemen (which has since expanded to include pretty much every fictional character ever created), as writer Alan Moore acknowledged that Holmes was, along with Dracula, just too big a character to place in the midst of an ensemble, since he'd simply take over the whole story. Still, his presence looms large over that entire enterprise as well, with both Moriarty and his brother Mycroft Holmes playing major roles.

Tangles with superheroes are no longer limited to the pages of comic books, however, as last Friday's Batman: The Brave and the Bold ably demonstrates. Everyone's (well, Graeme's) favorite lighthearted Caped Crusader finds himself summoned by Holmes to Victorian London to help clear the name of the lovably demonic Jason Blood. Since the show isn't called Sherlock: The Brave and the Bold, Batman does outwit him once or twice, but Holmes holds his own in a fight with the week's villain (who, refreshingly, is not Moriarty), and at the end Batman declares Holmes "the world's greatest detective." You said it, Bats.

I read the Riverworld series as a teen and it still sticks with me - I was thinking about it the other day. It represents 1970s science fiction at its trippiest and most random. Everyone who has ever lived on Earth wakes up together on a huge planet with an endless, winding river. They're all naked and bald, and they discover at length that they cannot die - at least not at first. His second series, World Of Tiers, follows a group of humans traveling through a series of stacked artificial parallel universes.

Farmer is also known for his first published short story, 1952's "The Lovers," which broke the taboo on explicit sexuality in science fiction and won a Hugo for Most Promising New Writer. According to Christopher Paul Carey:

[T]ravel back in time to the early 1950s. A young new writer, struggling to support his family by working overtime in a steel mill, submits his first piece of science fiction to Astounding. John W. Campbell doesn't want it. The writer sends the story to H.L. Gold at Galaxy, but the manuscript is again returned. The story is just too mature for a genre marketed toward adolescent males: 'there is no sex in science fiction'. Disgruntled, the writer resigns to try one last time and submits the story to Sam Mines at Startling Stories. This time comes a different response. Mines, sensing he has a winner, albeit a controversial one; buys the story and publishes it in his August 1952 issue. The story is The Lovers and the unknown author bears the strangely exotic sounding name of Philip José Farmer. The response from readers is electric. "Letters poured into Startling Stories praising the story," says Michael Croteau, web-master of The Official Philip José Farmer Home Page, who has extensively researched the history of Farmer's groundbreaking novella. "Several commented on how good the story was for a first time author," Croteau continues, "while others speculated that the story must have been written by an established pro who used a pseudonym because of the story's subject matter."

The Lovers tells the tale of Hal Yarrow, an Earthman sent on assignment to the planet Ozagen, who finds himself daring to rebel against his own planet's religious fundamentalism by engaging in intimate contact with an alien female. The story is tame by today's standards, but the mix of Farmer's raw talent, his ingenious description of photo-kinetic reproduction, and subject matter that was risqué for its day led to an ecstatic reaction among science fiction readers, who suddenly found their misbegotten genre gaining some maturity. "So many letters came in [to Startling Stories] over the next several months," says Croteau, "that six months or so after the story appeared, people started writing letters about the letters." In fact, letters about Farmer's story continued to be printed consistently in the magazine for the next two years. Many came from readers who had missed the August issue in which the novella appeared and desperately wanted to get their hands on a copy so they could join in the excitement. It was not surprising that in the year following the publication of The Lovers, Farmer won the Hugo award for 'most promising new talent'. "Science fiction never had any sexual relationships in it," says the now 88-year-old Farmer. "I felt that that was a part of life and so should be a part of SF." History has proved Farmer unquestionably right.

And then there's Farmer's bizarre pseudonymous novel, Venus On The Half Shell, written under the pseudonym Kilgore Trout - who's the itinerant struggling science fiction author in Kurt Vonnegut's writing. VonnegutWeb quotes Edgar L. Chapman, explaining how this came to happen:

A strong admirer of Vonnegut, Farmer has also confessed to a deep identification with Trout (who was actually suggested by Theodore Sturgeon). The identification was strengthened by many things: Farmer's own years as a struggling science fiction author in the early and middle stages of his career; Farmer's experience as a misunderstood social critic; and Farmer's identification with pornography as an Essex House author, a fate that plagued Trout. Finally, not long after Farmer had returned to Peoria, he was accused in 1970 of having written a letter signed ''Trout'' in the Peoria Journal Star criticizing President Nixon's Vietnam policy-another ironic identification of Farmer and Trout. (The letter is believed to have actually been penned by a college student.)

At any rate, Farmer, when afflicted with a temporary writer's block, conceived the idea of writing one of Trout's nonexistent novels and publishing it under Trout's name. He obtained Vonnegut's permission and went to work. When Venus on the Half-Shell was published by Dell, with Farmer wearing a false beard and a Confederate hat as a disguise on the back cover, the book was a ninety-day wonder, until Farmer's authorship, which Farmer made little effort to conceal, became known. Although the novel brought Farmer some unaccustomed notoriety (and made Vonnegut regret giving his permission to the project), the revelation of Farmer's authorship created a tendency to dismiss the work as simply an amusing parody and literary hoax. An additional irony in this episode has been Vonnegut's claim in a recent interview with Charles Platt (recorded in a book published in 1980) that Farmer failed to avow his authorship of Venus for a long period, presumably in the hope that sales would be increased by association with Vonnegut's reputation. This allegation, however, is not borne out by fact: Farmer told numerous friends, colleagues, and fans of his authorship; in fact, he informed the present writer of it when Venus was appearing as a serial in Fantasy and Science Fiction. Vonnegut's reaction is perhaps not surprising, since Trout is his invention. But when Vonnegut professes to feel anxiety that Farmer's book may somehow have harmed his literary reputation, it is hard to take him seriously. Such concern might have been better devoted to the effect of Vonnegut's self-indulgent seventies novels, Breakfast of Champions and Slapstick.

The sprawling saga that loses the thread is a more common problem in fantasy books than in science fiction — think the Robert Jordan's Wheel Of Time, or Marion Zimmer Bradley's Darkover books. But science fiction still has its own never-ending stories that really ought to end. Here are the biggest problems:

Changing the rules: When I first read To Your Scattered Bodies Go by Philip Jose Farmer, I was incredibly excited by its story of an artificial planet where everybody who's ever lived comes back to life. Until I got to the end of the book and realized it was actually Book One in a long series, and none of my nagging questions about the resurrection planet, Riverworld, would be answered for another three or four books. I was even more annoyed when a friend of mine told me that Farmer changes the rules of Riverworld after the first book, to make it easier to keep spinning out tales. I think there my have been some book-throwing involved.

The heir apparent. As I mentioned, a reviewer coined the term "Herbert's Syndrome" in 1984, when Frank Herbert was still alive and had yet to publish his sixth Dune novel, Chapterhouse: Dune. The reviewer defined it as when "a large advance induces a good writer to extend a successful series beyond its natural span." You may have your own opinions about whether six Dune books were too many — but since Herbert's death, his son Frank and his collaborator Kevin J. Anderson have already written seven Dune books, with more on the way. Say it with me: "The cash must flow."

The neat trilogy that becomes a messy tetralogy, and more. The first two Hitchhiker's Guide To The Galaxy books by Douglas Adams seemed pretty well-rounded, encompassing more or less the same arc as the original radio series and TV series. So I was a little nervous about the third book, Life, The Universe And Everything, but it was still a fun ride and seemed to move things forward. I was less thrilled by the fourth volume in what Adams called "the increasingly inaccurately named Hitchhiker's trilogy." So Long And Thanks For All The Fish, felt sort of anemic, as if Adams really didn't have any more ideas for the series, but he needed the Ningis. And then I think I read the fifth volume, but I have no memory of it whatsoever.

The need to explain the meaning of everything. Feminist science fiction blogger Liz Henry says this is where many series break down:

People write a series, and then they feel the need to finish it off and Explain it and they go all mystical and metaphysical. [They] try to solve every giant Burning Issue of Existence and good and evil, and why does the universe exist at all, and [the meaning of] utopia. So often, you get the underlying Manifesto or attempt to come up with a coherent philsopy of the author, but all too often, you sure wish they hadn't. By the time Herbert hits God Emperor of Dune, he has gone compeltely mad, trying to explain Everything, and there is no plot any more.

The random left turn. Isaac Asimov gave into fans' pressure, after a thirty-year gap, and started writing more Foundation novels again. And few would argue that Foundation's Edge or Foundation And Earth are in the same league as the original trilogy. One major problem: a slew of new characters, including one who's introduced right at the end of Foundation And Earth, who might have played a bigger role in a final Foundation book, had Asimov written one. But in the end, it just feels as though Asimov is floundering a bit, in the unnecessary sequels.

The miraculous save. In Suzette Haden Elgin's Native Tongue series, there's a clan of women and children who become language experts, and learn a ton of alien languages so they can serve as translators. But over time, they create their own secret language that the men don't understand. Which is great, but then in the third book, suddenly the women discover that they can eat sounds. They can survive by ingesting noises — sort of like a plant's photosynthesis, except noisier.

The shrinking protagonist. Harry Harrison's Stainless Steel Rat books become less and less fun, as his roguish protagonist, Slippery Jim DiGriz, becomes more and more of a pussycat. But worse yet is when we get a new protagonist whose story cheapens our original hero, like Bean in Orson Scott Card's Ender's Shadow.

To be fair, why shouldn't novels go on and on and on? It's what movies do, with their endless sequels. And TV series — who really thinks Smallville deserves an eighth season? On the other hand, the thing that makes novels superior to other media is the fact that they have a single author, who puts his/her stamp on them. When that one person runs out of ideas, the novels themselves start to deflate.

With TV, movies, comics and other media, as long as the corporate copyright-holder can find another Akiva Goldsman or Roberto Orci to spin out a new idea, you can have endless installments. In theory, no TV series ever needs to go stale, as long as the writers have the grace to leave when they run out of ideas. (Which almost never happens.) It's a bit harder with books though — and I like picking up a novel and discovering a new universe for the first time.