The Logic of Time Travel Can Get Pretty Trippy

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Time travel is a common theme in fiction—but writers, artists, and designers all have different ideas of what moving between different points in history would look like, and how these journeys would affect both the traveler and those they encounter. Minute Physics' video below explores the distinctions between time travel as presented in the book Ender's Game, movies like Planet of the Apes and Back to the Future, and the video game Braid, among others.

In Ender’s Game, for example, characters simply experience a slower passage of time while traveling, and the regular world progresses as normal. This means they can't change the past, or influence other characters to make time-altering decisions. This is a far cry from Back to the Future, in which teen Marty McFly nearly prevents his own birth by interfering in his parents' romance.

Get up to speed with the trippiness by watching the Minute Physics video below.

[h/t Futurism]

15 Facts about Isaac Asimov

M Stroud/Getty Images
M Stroud/Getty Images

Isaac Asimov is best known for writing science fiction novels like the Foundation and Robot series, but the amazingly prolific author also penned hundreds of mysteries, short stories, science guides, essays, and even a book of humor. And, of course, he consulted on Star Trek (though only after giving the show a second look). Check out these 15 facts about the famous Humanist.

1. Asimov's parents were immigrants who owned candy stores.

Born in Petrovichi (present-day Russia) in 1920 (-ish), Asimov was just 3 years old when he and his family emigrated to the U.S. After living in Brooklyn for a few years, Asimov's father, Judah, saved enough money from various odd jobs to buy a candy store. His parents worked around the clock to keep the store open 19 hours a day, and it was a success that kept them afloat through the Great Depression. Throughout the '30s, Judah Asimov purchased a series of confectionary shops in Brooklyn. During this time, the Asimov family lived in several apartments in the borough, including two above their stores. Isaac, his father, and his sister (a younger brother wasn't born yet, and his mother waited until 1938) became naturalized U.S. citizens in 1928.

2. He fell in love with science fiction at his first job.

When he was 9 years old, Asimov began working at the family candy stores. His father expected his son to work long hours, and Asimov consistently rose early and went to bed late to help run the shops. Even while employed at other part-time jobs—including one at a fabric company and as a typist for a college professor—he worked in the family business in some capacity, only leaving in his early twenties. In addition to candy, the stores sold magazines, and young Isaac devoured the science fiction stories he read in their pages and fell in love with the genre.

3. Asimov was rejected from nearly every school he applied to …

At 15 years old, Asimov applied to Columbia College but was rejected because "[the school's] quota for Jews for the coming year was already filled," he later wrote. Instead he attended Seth Low Junior College, which was affiliated with Columbia. That school closed soon after and he was transferred to Columbia, where he earned a Chemistry degree in 1939. Hoping to become a doctor, Asimov applied to five medical schools in New York, but was rejected by every one. For good measure, he applied again, and was turned down by each of them once more. He also applied to Columbia's graduate school for chemistry, but was denied entrance.

4. … but he eventually earned a doctorate.

After speaking to Columbia's faculty, Asimov managed to convince the school to accept him as a grad student for a year, on a probationary basis. His grades were up to snuff, and he earned his master's degree in chemistry in 1941. From 1942 to 1945, he worked at the Philadelphia Naval Air Experimental Station—he knew, following the Pearl Harbor attack five months earlier, that the draft was going to be coming, and he preferred to be of some service rather than try to hide behind being a Ph.D. candidate. He later wrote that he hoped that with this job "my labors might serve as directly useful for that war effort, and I knew I could do more as a reasonably capable chemist than as a panicky infantryman, and perhaps the government would think so too." When the war ended, he was drafted into a 9-month stint in the army; then he returned to Columbia, where he graduated with a Ph.D. in chemistry in 1948.

5. Asimov had a successful career in academia.

Isaac Asimov, circa 1950s.
Phillip Leonian, Wikimedia Commons // Public Domain

Asimov worked his way up the ladder of academia, moving from a postdoc position at Columbia—where he focused on how to combat malaria—to a job as a biochemistry instructor at Boston University's medical school. His lectures were popular, and within a few years he was promoted to associate professor. He also co-authored a biochemistry textbook called Biochemistry and Human Metabolism. In 1958, he stopped teaching and focused solely on writing science fiction. Years later, in 1979, Boston University awarded Asimov the title of full professor.

6. He used the pen name Paul French.

In the '50s, Asimov wrote a series of six science fiction novels for children using the pseudonym Paul French. The books, collectively called the Lucky Starr series, follow David "Lucky" Starr and his adventures around the solar system. Because the publisher, Doubleday, was hoping to turn the series into a TV show, Asimov used a pen name just in case the television adaptation was terrible—he didn't want to be attached to something cringeworthy, but he also hated that people began to think he was using the pseudonym in order to protect his reputation in the science community. In the end, the TV show didn't happen, and some of the books are now credited to both French and Asimov.

7. Asimov wrote a movie musical for Paul McCartney.

Look in the Boston University archives, and you might find a story outline called "Five and Five and One." Asimov penned it for Paul McCartney, a long-time science fiction fan who had asked him to write a screenplay for a sci-fi musical. The former Beatles' idea centered on a band that realized it was being impersonated by aliens, and he thought Asimov would be the perfect writer for the job. Sadly, McCartney didn't like Asimov's treatment, and the movie was never made.

8. He was an on-again, off-again member of Mensa.

Asimov wasn't shy about joining clubs. Some of the groups he belonged to were the Baker Street Irregulars (an exclusive organization for Sherlock Holmes fans), the Gilbert and Sullivan Society, the Wodehouse Society, and Mensa. After joining the oldest high-IQ society in the world, Asimov participated in events and was an Honorary Vice President. But he drifted in and out of active membership due to some unpleasant members who were "brain-proud and aggressive about their IQs," as he described them. "They were, as I had been in my youth, forcing their intelligence on unwilling victims. In general, too, they felt underappreciated and undersuccessful. As a result, they had soured on the Universe and tended to be disagreeable."

9. After an initial tiff, Asimov collaborated with the creator of Star Trek.

In 1966, Asimov wrote a critique for TV Guide arguing that the then-current crop of sci-fi shows—including Star Trek—were inaccurate in their depiction of science fiction. Gene Roddenberry, the show's creator, wrote a letter to Asimov defending himself. After admitting that he was a big fan of the author's work, Roddenberry explained that the show hired multiple scientific consultants to ensure accuracy and struggled to produce a new show every week. Roddenberry ended his letter by stating his belief that Star Trek would turn new people—who would purchase Asimov's books—into science fiction fans.

The two men then became friends, and Asimov became a fan of the show. He served as a consultant for Star Trek, giving Roddenberry a few plot and characterization suggestions. For his part, Roddenberry attempted to make a movie based on Asimov's I, Robot, but it never happened under him (both Roddenberry and Asimov had died a decade before the 2004 Will Smith film was in the works).

10. He coined the word robotics.

Karel Čapek, a Czech writer, gave us robot when he used the word in a play in 1921. Derived from a Slavic term for a slave, the word described man-like machines that worked on a factory assembly line. But in 1941, in his own short story called "Liar!," Asimov became the first person to use the word robotics, referring to the technology that robots possess. The next year, he wrote another short story, called "Runaround," in which he introduced his three Laws of Robotics. These laws explain that a robot cannot hurt a human, must obey humans, and must protect themselves, so long as it doesn't conflict with the first two laws.

11. He had extreme acrophobia and aviophobia.

Asimov was a staunch man of reason, but he could never reason his way out of his two biggest fears: heights and flying. In his early twenties, two terrifying experiences on roller coasters made him realize he was an acrophobe—and unfortunately, both experiences happened on dates. "From what I had seen of it in movies, it seemed to me that my date would scream and would cling to me, something which, I thought, would be delightful," Asimov wrote in his memoir of taking his girlfriend on a roller coaster at the 1939 World's Fair in New York. Instead, the ride had the opposite effect. "I screamed in terror and I hung on desperately to my date, who sat there stolid and unmoved."

A second similar coaster ride at Coney Island confirmed his fear, and after two early trips on planes, he never set foot on an airplane again. To travel, he took cars and trains around the U.S., and he took cruise ships on his trips to Europe, Africa, and the Caribbean. Quite ironic for the man whose Foundation series has now flown out to deep space, thanks to SpaceX.

12. He met his second wife at an autograph signing.

Asimov married his first wife, Gertrude—she of the second roller coaster adventure—in 1942 after a six-month courtship, and they had two children together. As he described it, their marriage slowly began to deteriorate: "It's just that annoyances multiply, frictions come slowly to seem irreconcilable, forgiveness comes more reluctantly and with worse grace." Worse grace was right—later on, he partially blamed his wife's smoking habit and rheumatoid arthritis on their split, though he insisted on staying together until their children were older.

In 1956, Asimov was signing autographs at a convention when he met Janet Jeppson, a psychiatrist and fan of his writing. A few years later, they met again at a writers' banquet. They began a friendship and correspondence over the next decade, and when, in 1970, Asimov and Gertrude separated, Jeppson helped him find an apartment in New York just a few blocks from her own. They started dating soon after, and when his divorce was finalized in 1973, Asimov married Janet two weeks later.

13. Asimov and Jeppson collaborated on numerous writing projects.

Cover of Asimov on his science fiction magazine
CHRISTO DRUMMKOPF, Flickr // CC BY 2.0

Asimov collaborated with Jeppson on several sci-fi novels, including the Norby series. While she did most of the writing, he polished her manuscripts and let publishers add his name to the book covers so more copies would sell. In the '70s, Jeppson began writing science fiction novels for children, using the name J.O. Jeppson, and she took over her husband's pop-science column after his death. She also compiled and edited a few of Asimov's memoirs, collecting entries from his journals and excerpts from his letters.

14. Asimov was infected with HIV during a blood transfusion …

In 1977, Asimov had a heart attack. Six years later, in December 1983, he had a triple bypass surgery, during which he received a blood transfusion. Unfortunately, unbeknownst to doctors, the blood they gave him was infected with HIV. Asimov contracted the virus, and it developed fully into AIDS. He died of heart and kidney failure, caused by AIDS, on April 6, 1992.

15 … but his true cause of death wasn't revealed until 2002.

Although the family considered telling the world Asimov had AIDS, his doctors dissuaded him—the general public was still fearful of HIV and very little was understood about it. His HIV status remained a secret until 2002, a decade after his death, when Janet disclosed it in It's Been A Good Life, a posthumous collection of letters and other writings that she edited. "I argued with the doctors privately about this secrecy, but they prevailed, even after Isaac died," Janet further explained in a letter to Locus Magazine (a science fiction and fantasy publication). "The doctors are dead now, and … Isaac's daughter and I agreed to go public [about] the HIV."

15 People Who Could Have Played The Doctor on Doctor Who

James Pardon, BBC America
James Pardon, BBC America

British sci-fi TV series Doctor Who has had a long and storied history since it first premiered in 1963 (and its 2005 revival). Although its iconic protagonist, the Time Lord known only as “The Doctor,” never seems to truly age, he has gone through quite a few changes in appearance and demeanor over his past 13 regenerations—most notably last year, when Jodie Whittaker, the Thirteenth and current Doctor, became the first woman to take on the lead role.

While each Doctor has brought his or her own unique flair to the role—it’s hard to imagine anyone else in Fourth Doctor Tom Baker’s striped scarf or Tenth Doctor David Tennant’s classic Chuck Taylors—casting decisions could have gone much differently. Here are 15 other actors who were considered for the role.

1. Hugh David

The first would-be Doctor, Hugh David, was also the first actor to be turned down for the role. David had the distinct honor of receiving an offer from Rex Tucker to originate the role. Tucker was a personal friend of David's who happened to be a member of the production team preparing for the series’ launch. But when the show named Verity Lambert as its producer, she made the executive call that David, who was 38 years old at the time, was too youthful to play the wise and relatively wizened Doctor she envisioned.

David was passed over in favor of William Hartnell, an actor two decades his senior, though the smooth-faced Matt Smith would later be cast as the Eleventh Doctor at the tender age of 26. David did get a chance to leave his mark on the Whoniverse though; he directed two Doctor Who serials—season four's "The Highlanders" and season five's "Fury From the Deep"—both of which are part of the series' infamous missing episodes.

2. Geoffrey Bayldon

9th October 1970: English actor Geoffrey Bayldon, playing Catweazle, the starring role in the children's television series 'Catweazle Returns'. In one episode his tonic becomes mixed up with a fertilizer, resulting in a pair of ever-growing marrows
Paul Fievez, BIPs/Getty Images

Theater-trained thespian Geoffrey Bayldon was lined up as a potential First Doctor after Verity Lambert said no to Hugh David’s youthful visage, but he wasn’t thrilled by the lengthy commitment the role would have required of him. He was also concerned about being pigeonholed into “old” roles. Instead, he took on another starring role on British television: Catweazle (pictured above), a befuddled wizard from the 11th century accidentally thrust into the 1960s, in stark contrast to the more experienced time-traveling Doctor. After Catweazle took off, Bayldon was devoted to the career-defining role and refused a second offer to become the Second Doctor.

Bayldon appeared in a supporting role as Organon in Doctor Who's 17th season, but by the new millennium, he finally consented to take on the mantle of the Doctor—albeit only as a voice actor in the alternate-universe Doctor Who Unbound audio plays. He was 80 years old when the second of his two episodes aired, making him the oldest actor to ever play the Doctor and rendering his earlier objections highly ironic. Bayldon passed away on May 10, 2017 at the age of 93.

3. Richard Griffiths

Richard Griffiths attends the royal film performance of Martin Scorsese's 'Hugo in 3D' at the Odeon Leicester Square on November 28, 2011 in London, England
Ian Gavan, Getty Images

Venerated stage and screen actor Richard Griffiths, renowned in England as Uncle Monty of Withnail and I and Harry Potter’s nasty Uncle Vernon, was twice considered a possible Doctor. He was on the shortlist to succeed Tom Baker, but was passed over in favor of Peter Davison. Producers kept him in mind, and again considered casting him as a replacement for Seventh Doctor Sylvester McCoy, but the show was canceled before Griffiths could step foot inside the TARDIS.

4. Catherine Zeta-Jones

Actress Catherine Zeta-Jones attends the Broadway opening after party for 'A Little Night Music' at the Tavern On The Green on December 13, 2009 in New York City
Neilson Barnard, Getty Images

Though Jodie Whittaker made history in 2017 when it was announced that she would be the first woman to take over the TARDIS, the notion of a “Time Lady” isn’t new to the 21st century. Russell T. Davies, the writer/producer responsible for the series’s 2005 revival, was intrigued by the prospect of a female Doctor. He was particularly excited about the idea of Catherine Zeta-Jones as David Tennant’s potential successor—certainly a more glamorous choice than had ever been considered, but one with a long history of diverse dramatic roles to her name. However, Davies had no real pull with the casting decision, as he turned the show over to Steven Moffat in 2010, who in turn ushered in the reign of Matt Smith and his bow ties.

5. and 6. Joanna Lumley and Dawn French

Joanna Lumley, British actress, wearing a floral print dress while posing in a garden at Pinewood Studios during filming of 'The New Avengers', in Iver Heath, Buckinghamshire, England, Great Britain, 12 July 1976
Fox Photos/Hulton Archive/Getty Images

The idea of a female Doctor was also floated in the 1980s, when the series was experiencing a ratings slump so severe that it was put on temporary hiatus from airing. Sydney Newman, the show’s original creator, suggested reviving audiences' interest with a female lead. He was called in to advise BBC One on how to bolster the show’s reputation. His plan consisted of temporarily bringing back Patrick Troughton as the Second Doctor before regenerating the Seventh Doctor in female form, though not “a flashy, Hollywood Wonder Woman because this kind of heroine with no flaws is a bore.” Candidates for this game-changing new Doctor included future Absolutely Fabulous star Joanna Lumley (pictured above) and The Vicar of Dibley's Dawn French—both well-respected, established actresses felt to be equal to the historic role. The BBC nixed Newman’s radical proposal, choosing to keep the Time Lord a lord, not a lady, and the show’s waning popularity led to its 1989 cancellation.

7. Frances de la Tour

At the same time Lumley and French were being considered to take over the role of The Doctor, Frances de la Tour—the Tony and Olivier Award-winning actress who played Mrs. Lintott in The History Boys in both London and on Broadway—was also in the running. But her name made headlines yet again in 2017 when, after announcing his departure from the show, Twelfth Doctor Peter Capaldi said that de la Tour was his personal pick to replace him. "I would like Frances de la Tour to be first female doctor," Capaldi told The Mirror.

8. Liam Cunningham

 Liam Cunningham attends the Night For Love Charity Ball in aid of The Samuel L Jackson Foundation and Irish Autism Action on February 13, 2010 in Dublin, Ireland
Phillip Massey, Getty Images for Samuel L Jackson Foundation

The crowded field of aspiring Doctors vying for the part after Sylvester McCoy stepped down attests to the show executives’ confusion about who could best rekindle Doctor Who’s former glory. Irish actor Liam Cunningham put in a bid to become the Eighth Doctor, using both his natural Dublin accent as well as a put-upon “neutral American” one. Though neither voice netted him the job, he appeared as Captain Zhukov in the revived series. He found even greater fame on the small screen as Davos Seaworth in Game of Thrones.

9. Billy Connolly

Comedian Billy Connelly attends the 'War Horse' world premiere at Avery Fisher Hall at Lincoln Center for the Performing Arts on December 4, 2011 in New York City
Neilson Barnard, Getty Images

Better known as a comedian and folk singer, Billy Connolly was another contender for the Doctor’s eighth regeneration. Though he was shortlisted for the part, it seems the decision was never his to make. "It was brought up in a meeting, apparently, but nobody told me until after they decided against it," Connolly told The Scotsman in 2010. "If I had done it, he would have been angrier, a much angrier Doctor Who. I would have loved it. I'd have taken it."

10. Mark McGann

Liverpudlian Mark McGann auditioned for the role of the Eighth Doctor at the same time as his older brother Paul. In a double blow to Mark, he didn't get the part—but his brother did. Talk about sibling envy.

11. Hugh Grant

Hugh Grant attends the UK premiere of 'The Pirates! In An Adventure With Scientists' at The Mayfair Hotel on March 21, 2012 in London, England
Ben Pruchnie, Getty Images

Rom-com star Hugh Grant may seem like an unlikely choice for a sci-fi hero, but he was one of the first actors approached when casting a Ninth Doctor for the 2005 series revival. Grant said no, due to skepticism about the show’s potential to succeed, but he later got a second chance of sorts when playing one of the Doctor’s regenerations in a 1999 spoof production for charity (which also featured fellow would-be Doctor Joanna Lumley). With trademark self-deprecation, the actor notes that while he regrets his choice, it might have done the show some good, as he’d “probably make a mess of it” anyway. 

12. Bill Nighy

British actor Bill Nighy arrives for the premiere of `The Boat That Rocked' at the Dendy Opera Quays on March 31, 2009 in Sydney, Australia
Lisa Maree Williams, Getty Images

Bill Nighy also said no to playing the Doctor, but unlike his Love Actually castmate Grant, his refusal was due to a premonition that the show would take off and garner him an excess of unwanted media scrutiny. It was a character, he claimed, that came with “too much baggage.” He did, however, make an uncredited but significant appearance in 2010 as Musée d’Orsay curator and Vincent van Gogh enthusiast Dr. Black.

Although Nighy was forthcoming about his reasons for passing on the role when he came clean in 2012, he didn’t indicate at what point he turned down the opportunity. Out of respect to “whoever did” take the role, he has refused to say which Doctor he might have been. Despite speculation that he might have been the Ninth Doctor instead of Christopher Eccleston, Nighy’s career has spanned most of the show’s 55-year run, so there’s really no telling.

13. Eddie Izzard

 Actor Eddie Izzard arrives at the National Movie Awards at the Royal Festival Hall on September 8, 2008 in London, England
Dan Kitwood, Getty Images

Comedian Eddie Izzard was once rumored to have been cast as the Tenth Doctor, with word coming straight from the mouth of the Fourth Doctor himself. In 2003, former Doctor Who star Tom Baker claimed on BBC Radio Five Live that Izzard had landed the role, touting Izzard as “mysterious and strange and seem[ing] like he has a lot of secrets”—all qualities befitting the inscrutable Doctor. The BBC itself discounted his comments as mere "speculation," and a spokesman said simply that no decision had yet been made.

14. Benedict Cumberbatch

ctor Benedict Cumberbatch attends The Academy Of Television Arts & Sciences Performer Nominees' 64th Primetime Emmy Awards Reception at Spectra by Wolfgang Puck at the Pacific Design Center on September 21, 2012
Imeh Akpanudosen, Getty Images

When David Tennant departed Doctor Who after three seasons as The Doctor, he took a special interest in who his successor might be. He thought Benedict Cumberbatch had the chops for the role, but the Sherlock star didn't think it would be a good fit. "David [Tennant] and I talked about it but I thought it would have to be radically different," Cumberbatch said. "And anyway, I didn’t really like the whole package—being on school lunch boxes."

15. Michael Jackson

Michael Jackson performs on stage during is 'HIStory' world tour concert at Ericsson Stadium November 10, 1996 in Auckland, New Zealand
Phil Walter, Getty Images

The King of Pop could have been the man from Gallifrey. In the late 1980s, at the height of Jackson’s on-screen success with Moonwalker, Paramount Pictures proposed a full-length Doctor Who film starring the chart-topping singer. It’s not clear that he was offered the role of the Doctor himself, though the information lends itself to that interpretation.

An earlier version of this story ran in 2013.

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