Time travel is the concept of moving objects forward or backward in time. It has been used as a plot device in fiction since at least the 19th century. Some notable examples include Charles Dickens' A Christmas Carol, H.G. Wells' The Time Machine, The Terminator, and Back to the Future. In reality, current human understanding of physics does not permit traveling backwards in time, but using Albert Einstein's special and general theories of relativity, it is theoretically possible to travel forward in time by means of time dilation.
The method by which characters are usually shown to have moved through time in fiction, is by way of a special device that carries an individual to the distant past or future; for example, the DeLorean in Back to the Future or the TARDIS in Doctor Who. In Somewhere in Time, A Christmas Carol, and The Time Traveler's Wife, the displacement of time is by supernatural means. In other stories, a character's perception of the past or future is seen as a means to communicate with those moments in time in order to bring light to the present.
As time is generally seen as the fourth dimension, a related concept is that of moving to a parallel universe by means of a portal, wormhole or supernatural means. The end result being that the individual has traveled to a location or dream state unreachable from our own universe by physical means. Examples include The Wizard of Oz, Alice in Wonderland, and South Park's Imaginationland.
Physical time displacement
- In The Muppet Show episode 519, Chris Langham uses a device that moves him backwards in time while the outside viewer perceives time as moving forward.
- One of Muppet Labs' first attempts at building a time machine was depicted in the 1981 book Kermit & Cleopigtra. Stored in a broom closet, Kermit and Beauregard stumble upon the device and find themselves transported back to ancient Egypt where they meet Cleopigtra. Back in the present, Robin and Scooter are able to observe their friends in the past by way of the history books and ultimately succeed in bringing the travelers home.
- On Sesame Street, Kermit the Frog often reported from famous points in history such as the Boston tea party, the site of George Washington's cherry trees, the maiden voyage of Christopher Columbus, and various others.
- In Elmo Saves Christmas, Elmo visits the future with Lightning the reindeer to see how Christmas every day has affected the residents of Sesame Street after some time has passed.
- In The Street We Live On, Elmo is feeling nostalgic about Sesame Street, so Grover takes him on a trip through time in his taxi cab to see what life on Sesame Street was like before he was born. He witnesses a Hooper's Store under the care of Mr. Hooper, Maria and Luis's wedding, Gabi's birth, and the adoption of Miles.
- For a number of years, the Jim Henson Company planned a movie titled Muppet Time Travel in which Animal travels back in time via Dr. Bunsen Honeydew's time machine and becomes one of evolution's missing links.
- The Muppet Experiment was an online and Disneyland game held in 2008 in which the Muppets became trapped in the year 1937 thanks to a device called the Time Rewinder. Using Muppet Labs' Dial-a-Time Phone, Dr. Honeydew was able to communicate with Kermit, who provided clues to players in the present as to how to find his friends.
- The Muppet Babies episode "Back to the Nursery" features the babies traveling back to Nanny's past in order to retake a picture from her youth that they'd ruined. Their mode of travel is a DeLorean, inspired by the events in Back to the Future.
- Unable to stand the wait for a playset to arrive at the nursery in "Six-to-Eight Weeks", Baby Gonzo runs around in circles fast enough to create a blue hole (black holes are too scary for kids) transporting himself and Baby Piggy into the future.
- After discovering what a typewriter is used for, Baby Gonzo creates a character inspired by Sam Spade for his novel in the Muppet Babies episode "Romancing the Weirdo". Realizing that he needs to bring his lead characters together for the ending, his character uses a time machine to travel back to where he left her in chapter four.
- In "Muppet Babies: The Next Generation," a phone booth inspired by Bill & Ted's Excellent Adventure carries Baby Rowlf to his grandson Woof on the starship Boobyprise where he learns a valuable lesson about taking care of the future in the present.
- In Muppets Tonight episode 101, Bunsen Honeydew (as a contestant on a dating game) tells Michelle Pfeiffer that their date might consist of examining the skin cells from their "bippies" in his lab. He later adds that they could also manipulate time with their bippies.
- In Muppets Tonight episode 108, Bunsen mistakes Hercule Poirot for Superman (skipping over everyone else's confusion that he is Hercules) and asks if he will fly around the Earth backwards to go back in time, as Superman did in Superman: The Movie. Breaking character, Jason Alexander states that it's not possible to travel back in time by flying backwards around the Earth.
- In Jim Henson's Muppets for GameBoy, Kermit and Animal have to rescue their friends, who are transferred back in time by Bunsen's time machine. Among the eras they visit include one million B.C., ancient Egypt, the Roman Empire, Mayan civilization, the Dark Ages and America's western frontier.
- In From the Balcony episode 27, Superman reverses the rotation of the Earth so that he can return a video tape rental on time without being charged late fees.
- Shalom Sesame's "Chanukah" episode features Yoav and Jeremy Miller visiting the city of Modi'in during the time of Judah Maccabee and singing a rendition of "The People in Your Neighborhood."
- A Movie Mania short spoofing The Terminator features Kermit the Frog as a cybernetic entity from the future, sent back through time to save humanity. His efforts are halted when Miss Piggy mistakes him for her Kermit, and suspects him of having an affair with Sarah Connor.
- When Mokey, Wembley, and Boober re-enact an ancient ceremony in the Sacred Cave in "Mokey, Then and Now," they're mysteriously transported back to the past, to an era of bald Fraggles who never laugh.
- In issue #7 of the Muppet Babies comic book, Baby Bunsen crafts a beanie for Baby Fozzie that enables him to go back and meet some of his ancestors. His travels include a visit in 1850, 19th century France, ancient Rome, the legendary Camelot and prehistoric times.
- Various Muppet versions of A Christmas Carol retell the story of Ebenezer Scrooge being taken on a journey through time to experience points of his life from a different perspective. The most prominent examples of time travel include Charles Dickens (Gonzo) and Rizzo the Rat hitching a ride through time in The Muppet Christmas Carol, and A Sesame Street Christmas Carol in which Oscar the Grouch relives Sesame Street Christmas specials of the past and gets to see what Christmases in the future will look like with the help of a robot specter.
- In the Dog City episode "Future Schlock," Rottweiler commissions a doggie door time portal machine though which Rosie and Dot take a trip to a futuristic amusement park.
- In The Muppet Show Comic Book preview, Dr. Honeydew's time machine gets Beaker stuck in a 30-second time loop.
- When Jason Segel announces that Florence and the Machine are the musical guests on the episode of Saturday Night Live that he's hosting, Statler jokes that he hopes Florence brought a time machine so he and Waldorf can go back to before they heard Segel's song with the Muppets.
- An early script for The Muppets features a Temporal Displacement Machine invented by Bunsen that slows down time so that Beaker may redirect the trajectory of the bowling ball in Gonzo's act. Later, Tex Richman pulls a gun on Piggy and Kermit. Bunsen uses the machine to induce Bullet-Point-of-View, which slows down normal time once again. While Kermit reminds Fozzie that they're supposed to be acting in slow-motion, Gonzo's bowlling ball flies off his hand and deflects the bullet.
- In The Muppets episode "Going, Going, Gonzo", Lips says Scooter would need a time machine to take Dr. Teeth's advice of leaving home at the age of 14. Floyd offers his friend Eddie's time machine which Zoot says he uses on weekends, "I climb in there on Friday, when I get out, it's Saturday. The whole thing takes about a day."
- In The Muppet Show episode 216, Fozzie Bear uses phrenology to look into the future of Kermit the Frog.
- Reading his life line in The Muppet Show episode 511, and looking into his future, a gypsy tells Paul Simon to sing fast (implying he doesn't have much time left).
- The Farscape episode "Back and Back and Back to the Future" includes a plot in which John Crichton receives an electric shock that enables him to see the future.
- A concept for Johnny Carson and the Muppet Machine would have seen Johnny Carson enter the land of the Kazeeziks by way of a living machine.
- Alice in Wonderland tells the story of a girl who travels to a realm of practical impossibilities after she follows a white rabbit through a rabbit hole. The suggestion is made that the events take place in Alice's dreams, but leave it up to the viewer as to whether or not she has actually traveled there. Versions of the story that retain the excursion to Wonderland include Abby in Wonderland, Dreamchild, and the 1999 Creature Shop-effects TV movie Alice in Wonderland.
- The Wizard of Oz is another example of displacement in an otherwise inaccessible land that may or may not only have taken place in the protagonist's head. The Muppets' Wizard of Oz takes a more literal tone as Dorothy Gale is shown to have been transported back to the real world without an indication that it was just a dream.
- Labyrinth plays on similar "did-she-or-didn't-she" themes presented in Alice in Wonderland and The Wizard of Oz, but with far more evidence for displacement. For example, Jareth appears in the real world and the Goblins are shown to monitor Sarah's actions from the other side.
- In It's a Very Merry Muppet Christmas Movie, Kermit is granted the privilege of seeing what the world would look like had he never been born. Thanks to his guardian angel Daniel, Kermit visits an alternate reality before realizing that things could be a lot worse for his friends and returns to his proper place in time.
- In Muppet Robin Hood issue #4, when the Muppets try to find where the narration is coming from, Robin the Frog suggests that maybe it's from a wormhole in an alternate universe where they are pirates or lost boys and Robin Hood can fly.