Anything in existence will continue to exist until a sufficient force acts against it.
Ontological Inertia acts as a buffer against changes to the cosmic status quo: You cannot (well, not completely) undo something that already exists.
Writer Fritz Leiber
agreed with this trope in his Change War
series of stories involving time travel, and devised the "Law of Reality Conservation" as a way to show how things couldn't just un-happen
. In that context, it states that you can
change the past (in fact he named one of the stories in the series, "Try and Change the Past"), but Fate will force a coincidental event to ensure that history proceeds down its intended path without paradox; every time you try to prevent one historical trend or event, a similar one will take its place in history.
On the other hand, what can happen instead is if you do change something in history that is significant, the time line "fractures", a whole new universe is created at that point, and you and the new event are in a completely different reality with the change you caused. So either you go back to your universe where the change never happened, or you end up going forward to the equivalent time in the new universe with the change that you made propagating from that point. If you don't like the result, you can try to go back and change time again, in which case, guess what, time "fractures" again to compensate for that new incident, and the cycle starts all over again.
Simon Hawke's Time Wars
has a similar Law of Historical Inertia, and any change you make will be like a stone dropped in the river of time: History will simply flow round it and, for the most part, end up exactly where it was before (so if you wanted to actually change it, you'd essentially need a really big
"stone" to divert the river, the consequences of which could be disaster).
A particular case of You Can't Fight Fate
. See also In Spite of a Nail
. Contrast with (but not the exact opposite of) No Ontological Inertia
. May explain Hitler's Time Travel Exemption Act
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Anime & Manga
- Used in Higurashi no Naku Koro ni.
- And in the Kai finale, averted entirely.
- A defining trope of Shakugan no Shana. When a person's existence is eaten by a Rinne, they are gone but replaced by a "Torch", who acts as a shock absorber; they look the same, and even have the original's memories. As their flame burns out over time, their presence and impact on the world lessens - they become apathetic and do little, people overlook them - until they disappear completely. When this happens, no one remembers them, and it is as though they never had existed, ever. This happens all the time.
- A key point in Vampire Princess Miyu is that Miyu fights against and defeats monsters but - as a curse she obtained by refusing to become a monster herself - is always unable to reverse any of the evil they have done. For example, when she defeats a ghost who has been luring women travelling on underground trains to an abandoned station where they are transformed into statues, she can seal the station, but can do nothing about the statues already created who remain imprisoned, petrified and weeping forever.
- Explored in the 2002 version of The Time Machine, with the time traveler's fiancée Emma acting as fate bait.
- It's a singularly interesting example. If she doesn't die, he doesn't invest the time and effort into creating the time machine. Her death CANNOT be changed, or he CANNOT go back to change. Down to the particular time limit (read: that very night, no matter what he tries). It's not like going back in time and stepping on a mosquito, the flow of time CANNOT continue if she does not die. Paradox, anyone?
- In the first three Terminator movies, good terminator androids, bad terminator androids, and one human are sent back in time to either prevent the upcomming apocalypse or kill off the future leader of the human rebellion. As each successive movie shows, attempts to change the future by either side will inevitably fail as long as there exists a demand for more Terminator movies.
Live Action TV
- LOST plays with this in Season 5. For example, when handling a nuke, Daniel assures them that it can't explode because the island still exists in the future they came from.
- The Legendary Adventures Of Hercules had an episode where they were worried about how their time travel might affect the present, but Hercules assured them that Time would correct itself, so nothing would change.
- In the final episode of Kamen Rider Decade, when Big Bad Apollo Geist is defeated, his forcible merger and destruction of the multiverse continues unabated. In fact, if anything it actually speeds up. This leads to Decade receiving a What the Hell, Hero? speech from his predecessors.
- FlashForward (2009) had elements of this. It was possible to change your future but very, very hard. In one case a character kills himself to prevent a future where he causes the death of a woman. In the altered timeline the person who replaces him on the team ends up causing the death instead.
- In the Twilight Zone episode "Of Late I Think of Cliffordville," when the protagonist realizes that he is still 70 years old (but looks like 30) and no one believes his ideas of "inventions" that he know will be coming, he asks Miss Devlin to return him to where he started. She says she can but that is will be a time set in motion by events as they are now and there is a fee. He sells the only thing he has of worth to a the guy who was sweeping the streets, and returns to his "present." Only thing is, now that guy, who has been the janitor in his building now owns the company, and he is the janitor!
- Also, in "Back There", Russell Johnson finds himself in Washington DC before Lincoln's assassination. He tells a cop, but can't stop the act when he is drugged by John Wilkes Booth. When Johnson's character returns to his present, the man who was butler at his club is now one of the wealthiest members. His great grandfather was the copy and afterwards became famous and rich because he tried to stop the assassination as well.
- The Dragonlance Saga even uses the stone in a time-stream example. The world as created by the gods does not allow past events to be changed. Unfortunately, several races have come into existence that were not intended at the time of the world's birth. They more or less are fine in the present, but all the "you can't change anything" rules of time travel don't apply to kender, Dwarves, and Draconians.
- Strangely used in Code Lyoko. Although there's a Reset Button that the heroes can use to travel into the immediate past and undo most of the damage the Big Bad causes, if anyone dies before they use it, they'll stay dead, even after the past is changed; their death still possesses ontological inertia in the new time-line. Presumably they'd just drop dead from no apparent cause, but since the heroes never allowed anyone to die in the course of their adventures, the viewer never really saw how it'd work.
- Additionally, the heroes, (and only the heroes, even if someone else were brought into the fold of this whole "XANA" shenanigan for this particular problem of the week) would remember the events of the erased day, presumably so someone would know the world had been saved to begin with.
- One of the flashback episodes demonstrates that you retain your memory if you've been scanned into the supercomputer.
- The Reset Button even becomes a plot point because they learn Xana grows more powerful each time they reset showing just who can ignore it.