In many time travel shows, the time machine is generally safe to operate, and the machinery itself is safe.
However, not all time machines are like that. Some could get downright dangerous to use, because trivial mistakes in any time of time machine operation could get time travelers dead. Worse, the world or more could get destroyed by the time machine itself. There can be many reasons on why the time machine itself is dangerous. What if the time machine overlaps matter on its arrival? What if what powers the time machine itself is dangerous, due to various reasons from radioactivity, instability, or just sheer amounts of power necessary? Or, what if some of the time machine's physics requirements are dangerous? Or what if the time traveler is likely to end up someplace unsafe, like anywhere but the surface of the earth?
Now, not all time-related dangers are related to time machines. There are also many forms of time dangers, such as those caused by difference in time's flow. For example if there was a bubble of space where time is running 20 times faster, and you stick your hand in it, your hand will get 1/20 as much blood and therefore will start to die! Not to mention all the blood that was in your hand at first quickly accumulating in your wrist. You could lose your hand in a short time.
- Played for Laughs in a 2013 commercial for British "pay day loan" company QuickQuid. It features a time machine that customers can use to bring back their money from the future. Their tester comes back from the future with a wad of bills, but as an old man, and the company decides to just offer easy loans instead.
- In Doraemon, Time Travel is achieved by going through a tunnel-like space on your Time Machine. Should one get knocked out of the machine and into the tunnel, one will be stranded in time. The problem is, Doraemon's time machine is basically just some futuristic devices bolted to a tatami, so the risk of being thrown overboard is always there. Dorami's is safe, because it's a flower-shaped capsule. Have we mentioned that some bad guys have their own time machine, so you can have a chase in time while you chase in time?
- In Marvel, a series of time travel disasters has caused a Time Crash that has snapped Rubber-Band History. This means any time traveller can permanently change history of the mainstream universe without worrying about causality. The Hulk is tasked with going through time to fix it since a normal man whose suit failed ended up with different parts of his body aged to different years ranging from 90 to 2 weeks old.
- In a strip from Calvin and Hobbes, the dangers of using a cardboard time machine are discussed.
Hobbes: Why do we have to wear goggles?
Calvin: Geez, do you think travelling years into the future is like driving down the street?! We've got to contend with vortexes and light speeds! Anything could go wrong! Of course we have to wear goggles!
Hobbes: Gosh, I think my goggles are in the bedroom. If I'm not back in a couple minutes, you can go without me.
- Child of the Storm has Doctor Strange's mastery of temporal manipulation, thanks to natural talent as a Time Master and a Seer being magnified by exposure to the Time Stone - which also made him The Ageless -, as the key part of what makes him so incredibly dangerous: it allows him to gather vast amounts of knowledge, which allows him to mastermind the grand-scale manipulation of the series' colossal Gambit Pile Up, manipulating characters from ordinary teenagers to the Endless themselves. It gets to the point where the combat related abilities, such as his ability to freeze the series' version of Bizarro in mid-air with minimal effort, are a courtesy detail. The fact that he is not infallible makes it even more worrying, as the events of the Forever Red arc in the sequel are precipitated by someone who's invisible to his precognitive senses, resulting in the world being turned upside down and the near-unleashing of the Dark Phoenix, an Eldritch Abomination that on its last rampage destroyed a galaxy. And this time, there'd be two of them.
- The sequel elaborates on this, showing the consequences of temporal warfare, and having Frigga state that if a civilisation even looks like trying to start using temporal warfare, other civilisations will band together to destroy them - and adds that Asgard mastered it, both before and after they became gods.
- Rosario Vampire: Brightest Darkness Act IV: In chapter 16, the angels take Luna and Falla to Heaven, stating their chrono magic is too dangerous and they've meddled with the timeline far too much. Rason is able to convince the Almighty to let them return to Earth, on the grounds that they never use their magic to Time Travel or alter the timeline again.
- Practical Mythology, a Doctor Who fic, features a lot of fallout from the Last Great Time War, namely time distortions: bits of space where time flows at a different rate or backwards. They function as something akin to a particularly gruesome minefield (just imagine what happens if your leg is subjected to a faster timeflow than the rest).
- Timecop, as explained in the description, requires extremely high speed when they pass through the time travel field. There was one failure that just left two red spots on a heavy steel wall. That said, that's more No OSHA Compliance: After all, they could make the track twice as long to allow safe deceleration on failure... Or make the track a centrifuge, so it'd be trivial to make a second pass at higher acceleration... like one illegal time traveler did in one of the books.
- Timecop 2: The Berlin Decision: As opposed to the launch pad from the first film, here they use a different method of travel which can cause the time traveler to disintegrate upon departure, which is increasingly more probable if the same person goes through it repeatedly within a short period of time (from his/her point of view).
- In Back to the Future, the DeLorean has to be travelling at 88 miles per hour. Which means that unless you know what's going to be in front of you in the time period you're heading to, you're going to crash. By the third movie, Doc seems to be acknowledging this. Marty's a little less sure, but both times Doc assures him that the obstacle he's seeing in the present won't be there in the destination time. Or that something that isn't there in the present will be there in the future, (like the rest of the bridge.)
- In Primer excessive time travel causes strange physical problems: mysterious bleeding from their ears and deterioration of their handwriting. Word of God is that this is also a case of Clone Degeneration.
- In the 2002 film version of The Time Machine, the titular device creates a spherical bubble to protect the occupant. Reach outside, that protection no longer applies. The main character hurts his hand when he instinctively grabs at an item he dropped. A Morlock wrestling with him on the machine ends up hanging outside the bubble, aging into dust. Logically, any attempt to reach outside the bubble should have violently scattered their atoms across dozens of years of history, but the Rapid Aging looked cooler, presumably.
- The directors cut of The Butterfly Effect reveals that Evan suffers minor brain damage every time he majorly changes the past, resulting in severe migraines and nosebleeds as he gets the extra memories (often 20 years worth) burnt onto his existing ones. On the other hand, he's smart enough to realise that repeated time travel might ultimately kill him, causing him to intentionally think through what he wants to change before each trip.
- The film version of Lost in Space had Will's time machine slowly rip apart the planet due to the radiation it emitted.
- In Interstellar, the black hole Gargantua causes severe Time Dilation near its event horizon thanks to relativity. Racing against the clock to find a new home for humanity on Earth, the crew of the Endurance, including Cooper, a pilot anxious to get back to Earth in time to reconcile with his daughter, opts to travel to a planet close to the black hole's gravity well, where time has slowed to a crawl - seven years per hour. A trip lasting a few hours costs them 23 years on the outside, to the anguish of the crew. Later, with fuel dwindling, the ship must perform a risky flyby of the black hole's event horizon, in which fifty years pass in a matter of minutes. Cooper misses nearly the entirety of his daughter's adult life due to Time Dilation.
- In X-Men: Days of Future Past, Kitty Pryde's Mental Time Travel works by projecting one's consciousness into their past self long enough to alter the past. However, transferring a consciousness back too far into the past puts too much stress on the mind of the traveler, meaning that the only one capable of doing so is Wolverine, whose mind can heal as it is damaged. Furthermore, if the connection is broken at the wrong time, the changes that the traveler made in the past take effect, meaning that changing the wrong thing could potentially leave the surviving mutants worse off in the new timeline.
- In the 2006 film Déjà Vu, passing through a window into the past is possible, but exceedingly dangerous to living beings. Special Agent Carlin plans for this by teleporting himself into an ER with instructions to resuscitate him.
- In Doctor Strange, the titular sorcerer happens upon the Eye of Agamoto, which allows its wearer to manipulate time. When he is caught experimenting with the artifact, he's quickly chided by his mentors regarding its dangers, which include preventing one's own birth or getting stuck in a time loop. Strange weaponizes this by trapping Dormammu in one such time loop until he all but begs to be released from it.
- In Spy Kids: All the Time in the World, the Big Bad creates a time machine to save his father. Each time he goes back in time it starts to mess up time in the present, until time in the present is going ridiculously fast.
- See You Yesterday: Claudette and Sebastian take into account they have only 10 minutes to fix the past due to the time machines getting unstable afterwards.
- In one of Larry Niven's Gil "The ARM" stories, the time compressor invention was used to hide a murder. First, a witness was murdered in an impossible way - his head burnt to ash by a flashlight from inside time compression sphere. The light come out hundreds of times stronger and literally burned the victim alive. Then another witness lost her arm poking the compressor, as she stuck her arm into an area where time moved faster - and deprived it of blood for several minutes. In the final arrest, the murderer was stuck inside the bubble and the cop was outside holding on to him by his legs. Unfortunately, the compression of time affected the killer in such a way that he died by thirst. Yes, the cop literally held the killer until he died of thirst. The effects of double time compression (One inside another) were discussed, and one of effects is that light speed inside the time compression sphere would be just a few feet per second. It means if a punch was thrown, the arm would get shorter!
- In The Time Ships, the time traveling jeep was blown to pieces by intersection with a reverse growing tree while they were traveling backwards with expiring fuel. Lucky, the time travelers survived.
- One of Michael Moorcock's Dancers at the End of Time short stories has a time traveller trying to warn her era about the future, only to find that time itself won't let her. The harder she tries the more her time machine overheats, but she refuses to give up and dies in agony.
- In the novel Timeline, travel is accomplished by copying the information required to rebuild a perfect copy (at the atomic level) of the traveler and beaming this information into the past. Errors in copying are possible (in fact, inevitable if the machine isn't properly shielded) leading to Clone Degeneration. The beginning of the film version, the dead scientist's body scan revealed that part of his body appear to be slightly shifted from their normal place.
- In the short-short story "The Man from When" by Danny Plachta a time-traveller arrives from the future and states that his departure caused such an expenditure of energy that it completely wiped out the Earth of his time. He then reveals that he has travelled back all of eighteen minutes.
- In Kevin O'Donnell's story "Gift of Prometheus" a malfunctioning time bracelet freezes its wearer outside of time and space with a bullet in his gut, unable to do anything but suffer and wonder if it will last forever.
- The Diving Universe: Stealth tech creates bubbles of altered time, which are usually fatal to anyone unfortunate enough to stumble into them.
- In the Magic: The Gathering novel Time Streams, a lab explosion results in areas where the passage of time is slowed down or sped up; blindly stumbling into these areas from the outside is usually a cheap ticket to a messy death. Several students are caught in an area of extreme slow time, where decades later they're still living out the initial seconds after the explosion. Passage into and out of these desynchronized areas is eventually developed, allowing research to skip ahead at a prodigious pace.
- In Strange Attractors by William Sleator, the creation of a Crapsack World Alternate Universe is almost the only outcome that could come of sending anything (much less a person) into the past.
- In the Hostile Takeover (Swann) series, going the wrong way through a wormhole takes you back in time. The entrances of wormholes are heavily guarded, though, and anyone coming through is shot. Also, because of the butterfly effect, you're in a new timeline, which will never become the exact future you came from.
- This becomes the whole point from the second book of the saga written by the Spaniard writer JJ Benitez' El Caballo de Troya: Due to an unseen side effect due to time travel, both characters will invariably die, since they will start to age more quickly than usual as their genes were affected due to time travel.
- The Dresden Files:
- The sixth of the seven laws of magic is "Thou Shalt Not Swim Against the Currents of Time", meaning no Time Travel and it places heavy restrictions on divination. The reasoning is that the risk of a Temporal Paradox is too heavy, and frankly nobody knows what would happen if one did.
- Then again Merlin used time travel to visit a place at five different times in its history, wove magic overlapping from those different point in history to weave a higher-dimensional construct. This was all for creating the prison under the isle of Demonreach, which is practically inescapable to the deity-level horrors trapped within.
- Word of God states that Harry will eventually have to break all the laws of magic as he works to protect the world. There has been a subtle hint in Changes that he may have the rule against time travel "already".
- The next planned book has the working title of Mirror, Mirror, which involves an alternate version of Harry, and likely involves time travel to get there. The alternate Harry differs fundamentally from one key decision and everything flowing from that.
- The Peace War:
- The bubbles of stopped time turn out to be dangerous in various ways, such as a war ship that manages to stop time while it is exploding, so when it exits the bubble it explodes. It could happen to any bubble, as they did not know which bubble contained what.
- In Marooned in Realtime, one person is trapped outside the bubble, so she ages to death while waiting for them to return after making a sign at where the camera is pointing. (The bubble pops and appears in a millisecond each year for them to see what is going on.)
- Seven Days: There are so many things wrong with the Sphere. First of all, while it's very accurate in time travel, landing it where you want to be requires precise piloting. Second, Our Time Travel Is really painful. Third, well, go to the page and check out the list of Phlebotinum Breakdowns the machine suffered. That's probably not even the full list!
- Doctor Who has this crop up fairly often since the main character is a time traveller from a species that not only mastered Time Travel, but actually invented it, who're pretty much defined by it, what with being called "Time Lords". Ergo, they weaponised it. Examples include the De-Mat Gun, which quite literally erases its target from space and time, never having existed. And then there was the Time War.
- Looking at the Time Vortex is a bad idea. 8 year old Time Lords look into the Untempered Schism, seeing the Vortex, and either get inspired, go insane (like the Master) or run away (like the Doctor). This is a relatively mild effect, because this is a species that's evolved for billions of years to adapt to time travel. Others, like Margaret the Slitheen, aren't so lucky. She got deaged and transformed into an egg.
- Also, absorbing the power of the Time Vortex is a bad idea for you and anyone in your way. It'll turn you into an all-powerful god with total mastery over space and time, capable of vaporising a Dalek Empire with the wave of a hand and permanently resurrect someone with a thought, but it will also burn you alive.
- Dalek Caan ended up taking an unprotected jaunt through the Time Vortex and turned into a madly giggling insane oracle. Or so it seemed. In fact, he saw what the Daleks really were and decided to destroy them, and became much more concise and lucid once his deception was revealed.
- The Outer Limits (1995):
- In "A Stitch In Time", the result of Ripple Effect-Proof Memory is that an entirely new lifetime's worth of memories gets added onto the existing one, which could result in brain damage.
- The episode "Breaking Point" had a time traveller end up a few days in the future to see his wife dying from a gunshot wound. He goes back and tries to prevent it. However, the side effect of the trip is physical and mental degradation. By the end, his wife has had enough and decides to leave him. In a deranged state, he ends up shooting her. Seems to be a case of You Already Changed the Past, doesn't it? Then the episode does a 180 on this idea and has the guy go back to the night he first met his wife and shoot his younger self, himself turning to dust. Of course, the worst part is that she was planning on killing herself that day.
- Sanctuary: A time bubble allows people to enter, but violently destroys anything attempting to leave. Time inside the bubble runs six years to each day outside, resulting in three-year periods of no sunlight. Naturally, this is not good for a self-contained ecosystem. Furthermore, if the bubble had expanded too far, the time differential between the different parts of the Earth would have destroyed the planet. Will and Magnus manage to reverse it, but at the cost of ret-goning everyone born inside the bubble.
- Sapphire and Steel: Time is outside the (metaphorical) safe corridor in which human life and history exist, and it is constantly trying to exploit weak spots in the corridor walls and break in. This, when it happens, is not a good thing. Time is the enemy.
- Star Trek: The Next Generation: In "Timescape", Picard is injured when he sticks his hand across the edge of a "time bubble", which causes his fingernails to age faster than his arm. Later, he experiences symptoms of "temporal narcosis" due to a malfunction of the equipment protecting him from being frozen in time. Ironically, its mentioned that taking the "armband" off would merely freeze someone in that timeframe with no ill-effects from the rapid transition from one to the other. Time is funny like that. Or because that particular time bubble was an extreme slowdown while the one encountered earlier that harmed Picard's hand was an extreme speed up. It would make sense that taking off the armband would move you into that time reference. Meaning if you took off your arm band in an extreme speed up it would age you into dust, while taking it off inside a slow down would well... slow you down .
- Star Trek: Voyager:
Annorax: When I tell that Time has moods, a disposition to be intuited, I'm not speaking metaphorically.
- In "Blink of an Eye", an astronaut from a planet were time operates in a faster rate than the regular universe, ends up dying during the transition to the timeframe on Voyager, while the other one barely survives.
- In "Year of Hell", Mad Scientist Annorax invents a temporal weapon to restore his race to supremacy, only to inadvertently wipe his wife from existence. He's spent hundreds of years trying to master the art of time manipulation to correct his mistake.
Chakotay: What do you mean?
Annorax: Anger is one of it's moods. Anger and the desire for retribution, vengeance. Time itself has tried to punish me for my arrogance. It has kept me from my wife, denied me my future.
- In "Shattered", Chakotay ends up in a temporal anomaly that results in various parts of his body having different ages. The Doctor manages to stabilize him. Apparently, they covered this at the Starfleet Medical Academy.
- Timecop: In "The Future, Jack, the Future", the protagonist and his temporary partner (played by Bruce Campbell) find a mothballed time travel lab in the past. They find an early version of the pod still using rocket boosters instead of the so-called "timecop propulsion". When Bruce Campbell asks what happened if the speed wasn't high enough, the protagonist pointed him towards the blackened wall at the end of the track.
- Achron: You can Chronoport your units back in time. It's like teleporting, but for time instead of space. You just need to make sure the arrival point isn't occupied by anything. Like, say, your unit's past self.
- Final Fantasy XIII-2: Resolving paradoxes and fixing the timeline forces the seeress (Yeul) to see all of the changes caused, up and down the timeline. This happens to shorten her lifespan a little every time, the symptoms progressing from collapsing, to falling unconscious to (ultimately) dying. Serah happens to have the same powers. It makes for a depressing ending.
- In EarthBound, the Phase Distorter 3 destroys living things when it travels, requiring the party to have their minds uploaded into robotic bodies before they can use it.
- It also turns out that the original Phase Distorter prototype wasn't exactly safe, either, as MOTHER 3 shows that Porky Minch was eventually given Age Without Youth from abusing it.
- Life Is Strange: The game goes to great lengths to stress the dangers of having time-manipulation powers:
- Max's powers are immediately shown to be very taxing to use. If one tries to rewind too far, she complains that she feels sick and the screen disintegrates in the style of celluloid burning until you stop.
- Max starts getting nosebleeds and migraines in Episode 2.
- Near the end of Episode 2, Max also manages to freeze time entirely, but the fallout from this incident leaves her unable to use her powers for several hours, and she expresses fear of becoming stuck in time in the following episode.
- After creating a timeline where she is a member of the Vortex Club, William Price is alive and Chloe is in a terminal condition from a spinal injury, Max decides that her ability to alter history using photographs is far too dangerous because the Butterfly Effect is in full force.
- In Episode 5, Max suffers several nosebleeds from altering history from within history itself, which at one point leaves her 'between realities'.
- Episode 5 also implies that the storm threatening to destroy the town is the universe trying to clean up all of the ripple effects of Max using her powers, and the only way Max can stop it is by going back one last time and creating a timeline in which she doesn't use her powers to change anything...including Chloe's death.
- In Quantum Break, chronon particles are very useful for creating time manipulation including a Stable Time Loop Time Machine, but are also the cause of Chronon Syndrome through repeated or intensive exposure to the radiation they generate. The syndrome's symptoms include Sanity Slippage, physical pain and the end result is the afflicted individual being subjected to an And I Must Scream fate before becoming a shifter. The shifters can only act in frozen time and, if they ''can act in normal time like Martin Hatch, are in constant agony in that situation.
- The Command & Conquer: Red Alert series has several takes on this trope, all consequences of deploying Chronosphere technology. This is further complicated by the Chronosphere acting as a time machine in cutscenes, but being used as a unit teleporter in-game instead. For starters, the chrono field is lethal to insufficiently protected humans, so trying to chrono-shift infantry results in a bunch of dead infantry. Some games let you circumvent this by loading your infantry into APCs and then shifting the vehicles without incident; others transport the vehicles but empty them of their occupants during the journey. Another, far more serious consequence of using Chronosphere tech, however, are the frequently devastating changes to the timeline that occur every time someone tries to make history go their way. As the series grew Denser and Wackier with every installment, these historical changes escalated alongside it until the original game's mostly sane Alternate History of WW II and the Cold War had turned into something utterly removed from real-world history.
- A Mindmistress story explores some dangers of time flow differences. Among other dangers, it's very unwise to hit anything hard while sped up. Being trapped in high speed was not too healthy for someone, as she died by age in short real time.
- Real Life Comics: One strip touches this subject with a discussion after a time bubble was used to rapidly age mead 6 months.
- In Homestuck, any time-travel that doesn't end in a Stable Time Loop results in the swift death of the time-traveler, as the universe actively destroys all timelines that branch off from the main one.
- Girl Genius is a world ruled by Mad Scientists (badly). Some of their experiments have dabbled with time manipulation - and end up terrifying even them. If for no other reason that they get the attention of things beyond our world. Hints are occasionally dropped that something time-related is the Greater-Scope Villain in the setting.
Castle Heterodyne: Master Robur thought they were angels. [...] He believed heaven itself was coming to punish him- though he WAS rather fuzzy on what sin in particular had crossed the line. He experienced a genuine crisis of faith. He didn't like it. So he smashed his device, which banished the... well, banished whatever they were... and then he had pie. Crisis over. In many ways, he was a refreshingly simple man.
- In the Batman: The Animated Series episode "Time Out of Joint", Clock King uses a time-altering device to trap Batman and Robin in a "bubble" of slowed time, where seconds for them pass as hours on the outside. Batman points out that objects "outside" the bubble are moving relatively at tens of thousands of miles an hour while they are comparatively "standing still". Meaning there will be an enormous (think asteroid impact or nuclear weapon) explosion if anything collides with them in their "frozen" state. Fortunately Batman defuses the trap before it can happen. Fridge Logic suggests that everybody outside the bubble just saw the Batmobile parked in the middle of the highway for a full day (or however long they were trapped), with the dynamic duo sitting nearly motionless inside. It's a good thing nobody tried to knock on the window to see if they were ok.
- The final episode of Futurama deals with the Professor inventing a literal Reset Button that rewinds time by ten seconds, affecting anyone who isn't in the button's radius or in the Professor's special shelter. When someone or something leaves the shelter and the button is used immediately afterwards, the something or someone is disintegrated. This happens to both a ten dollar bill the Professor scams Zoidberg out of using the button, and the Professor himself, though he manages to undisintegrate himself later on. And when Fry accidentally breaks the button by stepping in it, it freezes time for everyone and everything except him and Leela, who were both in the button's radius at the time.
- In the Justice League episode "The Once and Future Thing: Weird Western Tales", Chronos breaks into a storage locker on the Watchtower by locally speeding up time so that a section of the door ages and disintegrates in a few seconds.