Zero Escape: Zero Time Dilemma covers many paradoxes and elements of philosophy.

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Ethical and Reasoning Paradoxes

The Trolley Problem (Fire)

Problem

You are passing by the railway when you see a runaway trolley running down the tracks towards a group of 10 people. If it hits them, it will kill them, and there is no time to get them out of the way. You could, however, pull a switch which would divert the trolley onto another track, where only 1 person stands who will be killed instead. You have no particular responsibility for any of the other people or for the safety of the railway.

Which is it morally better to do: to allow 10 people to die who you could have saved, or to make a deliberate decision to kill 1 person?

Zero Time Dilemma

This problem occurs in the Fire decision point. Diana is forced to choose between certainly allowing Phi to die in an incinerator with no responsibility for her being there, or pulling the trigger and having a 50:50 chance of killing Sigma. The original problem gives no possibility of an outcome where everyone survives, which makes it significantly more sadistic than the version implemented in ZTD.

Delta's decision of killing of 6 billion people instead of having 8 billion killed by the terrorist can also be seen as a variation of this problem. In a similar situation, Diana chooses the opposite outcome - she refuses to actively kill Phi, whom she knows is carrying Radical-6, thereby causing the death of 6 billion people by proxy.

Newcomb's Paradox (Radical-6)

Problem

You are playing a game operated by an entity called The Predictor, which can predict people's behavior and has always been successful at predicting your behavior in the past. The game is as follows: you are offered two boxes, labeled A and B. You can choose to take either both boxes, or box B only. Box A contains $10. The Predictor then tells you that while setting up the game, he predicted your choice. If he predicted that you would choose only box B, then he has put $1000 in box B; if he predicted that you would choose both, or make your choice randomly, then he put nothing in box B. He will not tell you which of these actually happened.

Taking both boxes seems to be always the better choice, as you will get all the money available no matter what. However, if you decide to do that and The Predictor predicted you would, then there is only $10 available. If you pick box B only, you risk getting nothing, but if he predicted you would you will get $1000 instead. Is it rational to pick the worse choice in the presence of information about the prediction, and is it valid to say that by choosing your behavior you choose the result of the past prediction?

Zero Time Dilemma

After taking some syringes filled with Radical-6, team Q are told that they can inject themselves with it or not. Zero tells them that if he has predicted they will inject themselves, then he has previously injected them with FBR, a virus that is fatal on its own but counteracts radical-6 if both are present. If he has predicted they will not inject themselves with Radical-6, he has not injected them with FBR. Injecting themselves is a slightly safer choice as Radical-6 has only a 75% mortality rate, whereas FBR has a 100% rate.

This implementation does not fully implement Newcomb's paradox as the "safe choice" is still affected by prediction: if Zero's prediction is right the benefit to the team is the same no matter which they choose, whereas in the original problem if the Predictor is right the player is better not to take the safe option.

The Sleeping Beauty Problem (FCFS-Q Bad End)

Problem

A woman has volunteered for an experiment. On Sunday afternoon, she is given a full briefing so that she is aware of all the rules below, then she is put into cold sleep or suspended animation. On Sunday evening, while she is asleep, the experimenter flips a fair coin which will determine how the rest of the experiment will be scheduled:

If the coin flip is tails , she will be woken up from suspended animation on Monday and asked "What were the odds that the coin was heads?" She is not told what day it is. After giving her answer, she is given a drug that causes her to lose her memory of being woken and being asked that question, but will still remember she is part of the experiment and what the rules are. The same process will repeat on Tuesday.

, she will be woken up from suspended animation on Monday and asked "What were the odds that the coin was heads?" She is not told what day it is. After giving her answer, she is given a drug that causes her to lose her memory of being woken and being asked that question, but will still remember she is part of the experiment and what the rules are. The same process will repeat on Tuesday. If the coin flip is heads, the same occurs except she is only woken on Tuesday. She sleeps through Monday.

Regardless of the coin flip, on Wednesday the experiment is over and she is woken up and leaves.

Imagine that you are the sleeping woman and you are woken up and asked the odds of the coin. It seems that since the coin is fair the correct answer should be 50:50. However, this does not take account of what you may learn from the fact that you were woken up. If you were allowed to keep your memories and realized you were being woken for the second time, then you would know for certain that the coin was tails. But without that memory you are forced to estimate, and the fact that you are being woken up biases the answer towards tails because you are woken up more often if it is tails than if it is heads. Is it rational for you to state that the odds of the coin being heads are 1:3?

The Anthropic Principle (Anthropic Principle)

Problem

"Some things are the way they are because if they were not, we would not be here to ask that."

The Anthropic Principle is the principle that some things in the Universe can only be explained by chance. Humans and all sentient life on Earth owe their existence to the random variables that lead to the creation of the earth, the sun, the solar system, and the universe itself in the manner in which it did. There is no particular scientific reason why the universe should be this way; we observe it as such only because, if the Universe were any other way, we would not exist to study it.

Zero Time Dilemma

The Anthropic Principle is invoked in Zero Time Dilemma in a "game" where the players must roll three 1's on three six-sided dice or die. Since passing this fairly would require several hundred replays, the game does not play this fairly: the dice will always roll three 1's on the third replay of the scene from the player's point of view. After the players win the game and survive, Junpei and Carlos are stunned at the remote chance of this happening; but Akane suggests that this is not the first time they have rolled the dice, and the only reason they do not remember and do not perceive the previous rolls is because they were killed after they happened.

The Teletransportation Paradox (Transporter)

Problem

A machine exists which scans your atomic structure, produces an exact copy of it at another place, and then destroys the original. If you use this machine to teleport, what is your experience? Do you experience getting into the machine and then leaving at the other end, or do you get into the machine and then die by being destroyed, while a clone of you exits at the other end? How could anyone, other than you, tell the difference between this clone and the version of you who is now dead?

If the machine is then altered to not destroy the original, but to make a copy, then after you step in the machine, which copy's experiences do you go on to have? And who, or what consciousness, experiences the other copy?

Zero Time Dilemma

This paradox appears in two places in Zero Time Dilemma.

In the Door Of Truth scenario, Sigma and Diana are able to use the alien transportation machine to send themselves to an alternate history. However, rather than destroying them, the machine copies them. The original Sigma and Diana will still wake up trapped in the shelter. Which consciousness do they experience?

scenario, Sigma and Diana are able to use the alien transportation machine to send themselves to an alternate history. However, rather than destroying them, the machine copies them. The original Sigma and Diana will still wake up trapped in the shelter. Which consciousness do they experience? In the Reality ending, Q is told by Zero that his simulated mind can be uploaded into a utopian virtual reality, but another copy of his mind will continue to exist in the real world with Zero too. Uploading will be of no benefit to the existing Q if his consciousness is not the one that will end up in the virtual reality.

In both cases, the decision is resolved by the player using the fragment selection system, essentially avoiding the paradox while calling into doubt the nature of the consciousness of the game characters.

The Binary Number System (Poison)

The binary number system is a system in which each column can contain only the digits 1 or 0. To count higher than 1, new columns are used in the same way they are normally: so the count goes 0, 1, 10, 11, 100, 101, and so on. Note however than 10 binary is two, not ten; it is just written in a different way. 2 + 2 = 4 in binary is written as 10 + 10 = 100 but it is still two plus two equals four; there is no system in which ten plus ten equals one hundred.

The binary number system is important because it allows numbers to be represented by a series of yes/no choices or questions. It is famously used in computers to represent numbers by the presence or absence of electrical charge on a memory cell.

Zero Time Dilemma

The binary number system is used by Akane in the Infirmary in the Poison setting. The group are offered 8 possible antidotes, only one of which is real, and a small sample of each. Touching the sample of the real antidote with their tongue will produce numbness after 3 minutes. However, the group only have 5 minutes before the poison will kill them if they do not find and take the real antidote, so they only have time for one sample. However, there are 3 people in the group.

Akane does not fully explain her solution in the game, but it is based on assigning a binary number to each of the antidotes: 000, 001, 010, 011, 100, 101, 110, 111. She then assigns a member of the team to each column: each person tastes the antidotes for which their column is 1. For example, Akane herself takes the first column and tastes the last four antidotes because their binary numbers begin with 1. In this way, the combination of people who experience tongue numbness will uniquely identify the binary number of the real antidote. If Akane feels tongue numbness then she knows that the first binary digit of the correct antidote is 1. If she does not it is 0. Based on Junpei and Carlos' experiences she can identify the other two digits and thus pick the correct antidote. For example, if Akane and Carlos feel numbness but Junpei does not, that indicates the number 101, or antidote E. Nobody licks antidote A because it is 000, so if nobody feels tongue numbness it must be the correct one.

The game plays this fairly and randomizes the correct antidote each time.

This solution can also be understood in terms of combinations. In a scenario where three people are allowed to choose between two options, the total number of possible outcomes is 2^3, or 8. Of these 8 outcomes, there will be 1 where everyone chooses option A, 3 where two people choose option A, 3 where one person chooses option A, and 1 where no one chooses option A.

The Monty Hall Problem (Monty Hall)

Problem

On a game show, the host offers the contestant the choice of 3 doors. Only 1 door holds a prize. After the contestant's initial choice the host (who knows where the prize is, but does not try to deliberately help or hinder the contestant) opens one of the other doors to show that it is empty. He then offers the contestant the choice of switching their choice to the remaining closed door. Is this a good idea, and what are the odds of them winning the prize if they switch?

This problem is famous for the dramatic misunderstandings of probability it causes. In one famous case, Marilyn Vos Savant (the woman with the highest recorded IQ in America) was asked by a reader of her newspaper column what the correct choice was. Vos Savant gave the correct answer, but she was then "corrected" with wrong answers by multiple people writing in, including doctoral researchers in Mathematics, the Deputy Director of the Center for Defense Information, and a Research Mathematical Statistician from the National Institutes of Health. Many later wrote apologies when multiple simulations revealed that vos Savant was correct.

The answer is simply this: if you switch, you will win the prize if your original choice was wrong. With three doors, the chance of your original choice being wrong is 2/3. So switching is a good idea and doubles your odds of winning.

Everything else in the problem is misdirection. Alternative interpretations and other odds, such as 1/3 (because there are three doors) or 1/2 (because after a door is opened there are 2 left) are incorrect.

The original Monty Hall, the host of the actual game show (Let's Make A Deal) where this appeared, was interviewed and admitted he was unsure of the probabilities himself, but he also added that the problem does not actually represent the original game show: as implied by the name "Let's Make A Deal", after the door was opened, Monty would offer the contestant increasing cash prizes in exchange for not switching.

Zero Time Dilemma

After the Control Room escape, the game announcer plays a Monty Hall game with 10 doors and the prize being the gas mask that is needed to survive the room flooding with CO2. Note that the "host" is not Zero, as the player may not believe them to be a neutral party. The chance of picking the correct door by switching is now 90%. The game plays this fairly, so it is possible by a 10% chance to switch to the wrong door, and the game has a death ending for this circumstance.

Prisoner's Dilemma (Ambidex)

Problem

Two prisoners are accused of a joint crime. They are held in separate cells and cannot communicate with each other. The police tells each prisoner individually that they may betray the other prisoner by confessing to the crime. If both prisoners confess, both will be jailed for 8 years. If neither do, they will be jailed on a lesser charge for 2 years. But if one prisoner confesses and the other does not, the confessor will be set free for cooperation and the non-confessor will be jailed for 10 years. As one of the prisoners, what should you do?

Initially it seems that confessing is the "safe" option since it avoids the 10 year possibility. However, the other prisoner is certain to think that too and thus both will confess, resulting in 8 years in jail. Therefore, it seems better not to confess. The other prisoner will work this out too and you will get only 2 years. However, if you can work out that the other prisoner will not confess, then confessing is the better choice because you will be set free. But the other prisoner can work this out too, and so on..

Zero Time Dilemma

This problem was the focus of the AB game in Virtue's Last Reward and makes a lesser appearance in Zero Time Dilemma. The version in ZTD has a very important difference: a single successful betrayal guarantees escape for the betrayer and death for the sucker. Contrary to what the characters say, this makes betrayal a much better idea in this version of the game than it was in Virtue's Last Reward, where a single betrayal would not result in escape and would result in distrust in future rounds.

Butterfly Effect

The Butterfly Effect is a term from chaos theory which describes a system which, although governed by scientific principles which should be deterministic, is impossible to predict because tiny variations in the input - often too small to observe - have dramatic effects on the output. It was coined by Edward Lorenz with regard to a scientific model for predicting the weather in which he discovered that even minor rounding errors in the inputs would produce dramatically different outputs. This was likened to "A hurricane is started by a flap of a butterfly's wing weeks ago in the other side of the ocean." Note that Lorenz only coined the term; he was not the first to observe the effect. Also, it was Lorenz's model of the weather that exhibited the phenomenon - that is, a human constructed deterministic mathematical model. It is known that the actual weather is very difficult to predict, but it is only theorized that the Butterfly Effect is the reason why. A more common example of the Butterfly Effect is rolling a dice; the laws of physics continue to fully govern the dice, but it is practically impossible to measure all the forces it receives while being rolled, and any of these may affect the number shown.

Zero Time Dilemma

In ZTD, the "butterfly" is replaced by a Snail and repeatedly invoked by Zero II:

Eric's mother, jogging in the park, came to a fork in the road and saw a snail on one of the two paths, and decided to jog down the other path to avoid disturbing it.

Because she chose this path, she was murdered by the young Mira who was waiting in hiding on the path.

Because Eric's mother was dead, Eric was raised and traumatized by his father.

Akane Kurashiki's father was falsely accused of the murder and arrested, and wrongly executed.

Because of the death of her husband, Akane's mother committed suicide, leaving Akane and her brother Aoi Kurashiki as orphans.

It is implied that as a result of their being orphans, Akane and Aoi were taken into care in an institution linked to Cradle Pharmaceutical and consequently forced to participate in the First Nonary Game.

The need to close the time loop created by Akane in the First Nonary Game resulted in Zero Escape: Nine Hours, Nine Persons, Nine Doors .

. A taxi driver, who had originally been supposed to pick up Akane's father, failed to pick him up (because he had been arrested for murder) and instead picked up someone else, a surgeon. The taxi was involved in a car accident which resulted in the surgeon's death, meaning that Sean missed out on an operation that could have cured him. In the hospital he meets Delta, who sees him as an example of the unfairness and randomness of life and thus a justification for his actions in the future.

It is thus implied that the snail triggered the events of the entire Zero Escape series; however, there is no explanation of how the snail caused the nuclear terrorist mentioned by Delta to exist, who provides the motivation for Zero Escape: Zero Time Dilemma and thus also for Zero Escape: Virtue's Last Reward. Furthermore, Delta would have been already alive for several hundred years when the snail appeared, thus requiring the snail to exist as part of the stable time loop necessary for him to be born.

It is also arguable that this represents the Domino Effect rather than the Butterfly Effect because human choices are involved at each step of the process (whereas the butterfly effect referred to a fixed mathematical model).

The Experience Machine (Q)

Problem

If you have the opportunity to enter a Virtual Reality machine which will give you continuous pleasurable experiences, which will be identical to reality from your point of view, is it a rational choice to do so? Can it be a rational choice not to? In consideration of the problem the parameters of the machine may be altered; for example, you may be able to have your friends and relatives plugged in too, or may be able to have children while inside the machine (either virtual children, or physical ones actually via artificial insemination carried out by the machine).

This problem was created by Robert Nozick in 1974 as a thought experiment to attack the notion of ethical hedonism - the idea that doing something which makes a person happy or gives them pleasure must be right. The Virtual Reality machine by definition makes a person happy but it does not seem right to suggest that it would be ethical for everyone to be plugged into it. The most well known modern interpretation is in The Matrix series of movies, but the concept existed in sci-fi books long before Nozick wrote it up.

Zero Time Dilemma

This problem is briefly alluded to in the Q section, in which the character is given the opportunity to transfer his consciousness into a virtual reality which will simulate a utopian version of his life had he been cured in hospital. However, since the alternative offered by Zero is death, it may not fully represent the same ethical problem.

Non-Lethal Predation Benefit

Zero Time Dilemma

In several places in Zero Time Dilemma reference is made to the phenomenon of The Piranha in the Koi Tank. The claim made is that if Koi Carp are transported alone, they fight each other and many or all will be dead by the end of the journey. To transport them successfully it is necessary to add a single piranha to the tank; the effect of this is that all of the koi focus on avoiding the piranha rather than fighting each other, and all survive. This theory is the reason for Brother including Mira as a player in the Second Nonary Game.

This phenomenon is fictional. Koi Carp do not naturally fight each other when transported if they are given sufficient space; and placing the Koi, or any kind of fish, under unavoidable stress for a long period is likely to result in death from heart failure or immune system failure, caused by their system being strained by maintaining a panic state for that period of time.

There are, however, examples at a evolutionary level of species indirectly benefiting from the presence of predators, usually by adapting to avoid those predators but having the adaptation become directly useful as a result of later changes in the environment.

Schrödinger's Cat

Problem

A cat is placed in a box with a small vial of poison, a radioactive source, and a Geiger counter that is attached to a hammer. If the Geiger counter ever detects the radioactive source, it will shatter the vial, releasing the poison which kills the cat. The box cannot move, cannot be seen through, and any sound inside will not escape. After an hour, the observer goes to inspect the cat's fate. This moment, before the fate of the cat is revealed, is a paradoxical assumption of the cat's current state where it has an equal chance of being alive or dead. As such, the cat is in a state where it is both alive and dead.

This is meant to be Schrödinger's explanation of the flaws of quantum mechanics as an organic creature cannot be simultaneously alive and dead. However, this created Quantum Superstition where every possible quantum state can be represented as the sum of two or more other distinctive states. It helps to explain the Many Worlds interpretation every event junction simultaneously exists alongside the current observable timeline of events, even though they cannot be directly observed.

Zero Time Dilemma

In the Biolab, Q-Team are consulted by Zero II who explains that there are a series of vials that contain Radical-6. Radical-6 would kill them on its own, but Zero II explains that he is a clairvoyant and that he already knows which members of Q-Team infect themselves with R-6. Prior to their awakening in the Biolab, Zero injected Fanatic Bio R into the Q-Team members who would inject themselves. By Injecting R-6 into a FBR carrier, the two viruses cancel each other, completely curing an individual of the effects of both viruses. Q-Team is left with the decision to inject themselves with Radical-6 or not.

The observer, Zero II, already knows the result from the beginning, but the test subjects themselves are left in the quantum state where they are both infected and not infected. It is only when they "confirm" their condition by choosing to infect or not infect themselves. Regardless of the choice they make, the situation ends favorably and they are spared of the effects of both viruses.

Time Travel Paradoxes

Many-Worlds Interpretation

The Many-Worlds Interpretation is an explanation of quantum mechanics in which there exist many different planes of existence other than the one we observe. The Many-Worlds Interpretation is that every quantum possibility exists in a parallel universe, of which we experience only one. Though these universes are not readily observable, it does not discredit their existence or non-existence. Since any physical system may be subject to quantum possibility it follows that all possibilities exist within the parallel universes. (The question of whether human decision-making is a physical system raises a further paradox, since no property of a physical system corresponds to the traditional understanding or perception of human free will. It cannot be definitively said that all human decisions would be reflected in the many worlds, and if they are, it would require human decisions were either programmatic or random.)

For example, in our current history, the United States dropped the bomb on Hiroshima and in an infinite amount of other multiverses, this choice also occurred. However, there are an infinite number of them where the bomb was never dropped or perhaps was a dud upon impact. Even smaller variables such as the number of casualties as a result of this, the exact impact co-ordinates, and even right down to the precise atoms displaced by the impact of the bomb, change as well. While we cannot observe any of these parallel histories aside from the one we currently live now in, we cannot confirm nor deny the existence or non-existence of these alternate histories and futures.

It should be noted that the scientific many-worlds interpretation does not discuss or permit time travel to the past, and so does not offer any explanation for time paradoxes. "Multiple histories" exist only in the sense that the entire history of the world is modelled in its current state. The only scientific time travel is the speeding up and slowing down of time, which is proven and observed; actually travelling back into the past is generally considered impossible and were it possible, it would be impossible to avoid creating a paradox, since one could be created by even a slight movement of an atom.

Zero Time Dilemma

As with Virtue's Last Reward, the storyline of Zero Time Dilemma utilizes the Many-Worlds Interpretation using the multiple timeline/histories display through the Global Flowchart. This philosophy is utilized immediately at the start of the game, starting from the first Decision game's coin toss down to many possible routes where one team is killed off from the second choice. The Global Flow of events in the game best displays numerous parallel "universes" as it displays possible outcomes of every choice once the players have made a certain decision. As in much time travel fiction, the Many-Worlds Interpretation used is humanocentric - it heavily emphasizes choices made by humans, while in practice (for example) sub-atomic movement phenomena would be just as important and create just as many parallel universes.

(The original Nine Hours, Nine Persons, Nine Doors does not technically involve the many-worlds interpretation; although Akane may experience different endings to the story, she does so from a position of existing in the future and repeatedly editing the past. The story only requires additional timelines to exist in Akane's memory. The main story implies that there is a single timeline which must be satisfied, and that aligning to a changed past is a slow transition - which is not maintained in any of the other games.)

Zero Time Dilemma also reflects the free will paradox by having the critical decisions made by the player, who as an entity outside the universe in which the game characters exist, would not be subject to physical laws.

A rather dark corollary of the many-worlds interpretation is that the concept of stopping an event happening becomes meaningless. Thus, the characters in Zero Time Dilemma do not actually stop the release of Radical-6, they SHIFT their current consciousnesses to a timeline where it does not happen, but the path on which it does happen remains fully intact.

The Bootstrap Paradox

Main article: Bootstrap paradox

Problem

A person found a note on his bookshelf describing the procedures to build a time machine. He followed the procedure and built the time machine. Then he travelled back in time and placed the note on his bookshelf in the past. But where did the note (or the information on it) originally come from?

This is also known as a Causal Loop related to time travel as chronologically Event A leads to Event B. However, due to time traveling, what occurs as a result of Event B influenced what occurred in Event A. Because both events cause each other, which is the original event?

Zero Time Dilemma

This occurs several times in Zero Time Dilemma and is not explicitly invoked.

Diana and Sigma fall in love and sire twins in D-END: 2. Sigma names their daughter Phi in honor of Phi who they participated in the Decision Game with when they decide to copy their genetic data in the Transporter. However, the baby named Phi is the same Phi they worked with. Why did he name the girl Phi in the first place, having never met one before? (This is slightly more awkward because Sigma also met Phi after explicitly traveling into the future in Virtue's Last Reward , then traveled back.)

the same Phi they worked with. Why did he name the girl Phi in the first place, having never met one before? (This is slightly more awkward because Sigma also met Phi after explicitly traveling into the future in , then traveled back.) Phi comes to DCOM with a special brooch that is a memento of her deceased mother. She is incinerated in the D-END: 2 route and only her Brooch is left behind. Diana takes this brooch and later places it in the Transporter with her new infant daughter Phi to be a memento. This data travels back in time where it is used in 2008 when baby Phi is reconstructed alongside the brooch. Since the brooch is a reconstruction, when and where did Phi obtain the original incarnation of the brooch?

Brother is born in the complex as Sigma and Diana's son, but Sigma and Diana were only in the complex because Brother trapped them there, and only fell in love because they had to spend 10 months there. On top of that, Sigma only went to DCOM because he was trying to stop the spread of Radical-6, which Brother caused, and which was spread by Phi. So why did Sigma and Diana have twins inside the complex the first time, when Brother wasn't alive?

The Bootstrap Paradox has been called a plot hole in the Zero Escape series. Uchikoshi wrote a series of tweets in English to a fan who asked him about it:

Bootstrap Paradox(BSP) is one of my favorite paradox. However I don't think that BSP is a paradox. I think that the effect such as BSP as the most simple and elegant solution in the time loop story. There might be no beginning or end in all of the time. Just as there is no beginning or end on the surface of the earth. However, in Punchline, I purposely made a starting point. Because it's easier to understand for the audience. But I really think "it's more beautiful that starting point does not exist". Btw, in a time loop, so many multiple protagonists must be existing. Why is the protagonist in the story only the protagonist? In most cases, he is "who started the time loop" or "who broke out from the time loop" or "who ended the time loop". What is the difference between him and other protagonists? What is his specificity? Btw, you exist also in your past and future. Why are you in the present you on here now? In the next piece of my work, you might solve the mystery about this matter. The time river flows swiftly. And I think you are already boarding the ship on the river. Best regards :) -- Kotaro Uchikoshi

Experience Erasure Paradox

Problem

Marty McFly in Back to the Future originally was born to a low wage earning father bullied by his supervisor, Biff, while his mother was an overweight, depressed alcoholic. During the film, Marty travels to the past via Doc's time machine. While there, he alters the past by encouraging his father to stand up to a younger Biff. Returning to the present, Marty now has a rich, successful father who has become a science fiction author and his mother is fit and happy.

Even though the future changed, Marty still has memories of his past where he was raised poor and no new memories of being born rich. Yet Marty, in some form, must have lived through several years in which he was growing up in the rich family. What happened to this Marty? There are not two Martys when poor-Marty returns, so does rich-Marty die or disappear when poor-Marty arrives? Or does he get into the time machine at the same time poor-Marty does, stop his father punching Biff, and return to a poor family?

This is an extremely complex and subtle problem in time travel which is frequently not considered by most fiction.

Zero Time Dilemma

This was mentioned as a fan objection to the plot of Virtue's Last Reward, in which Sigma shifting to avoid death implied that he was swapping another Sigma into the dead body. It was also mentioned in the "Another Time End" of VLR, in which Tenmyouji asks if curing Radical-6 in the past would, in addition to preventing the disaster, also prevent all the good things that might have happened to the survivors afterwards. (In Zero Time Dilemma his theory is proven right: although the characters end up in a timeline where Radical-6 is not released, the timeline where it is released remains fully intact, and thus presumably he and Quark and the other survivors in Rhizome 9 remain there until the supplies run out.)

Zero Time Dilemma explicitly acknowledges this problem. Brother is aware of it and it is part of the reason for his dislike of SHIFTers. In fact, the final dilemma presented by Zero II to the player in Zero Time Dilemma is to either allow themselves to die in the facility's self-destruction explosion or SHIFT their consciousness to the alternate history where they succeeded in the Coin toss at the start of the story. This will allow them to live on with the memories they have obtained with the Decision Game, but at the same time by SHIFT mechanics, they are forcibly making that history's versions of their consciousness die in their stead. Do they allow themselves to die noble deaths by not sacrificing "themselves" in an alternate history in the process, or do they reward themselves for surviving the ordeals and horrors they were put through in the Decision Game by sacrificing the lives of "themselves" who simply survived because of a coin toss - but in doing so destroy that happy ending?

Corollary

Akane's "swapping" model introduces an interesting corollary paradox which can arise in any system with multiple universes and defined differences between them - the Propagated Causality Paradox. In the example above let us call the previously-poor-but-now-rich Marty Marty1, and the previously-rich-but-now-poor Marty Marty2. When Marty1 and Marty2 swap the exchange is symmetric in a way that ensures there is no abrupt discontinuity in consciousness for either of the two; they both time travel at about the same time in their lives, in the same time machine, made by the same Doc Brown who is in the same circumstances. If Marty2 were not time travelling at the same time Marty1 is, then Marty2's experience would be of his conscious being abruptly ripped into the alternate universe where he is poor. By creating symmetry, this problem is avoided, but it creates a second problem.

Suppose that after returning and learning he is poor, Marty2 realizes what the problem is and decides to go back in time again to fix it. He arranges that he'll be easily able to return this time and prepares to travel back and make his father punch Biff. However, in order to be rich again he must swap back with Marty1. But Marty1 is not making any corresponding time trip, because he has no reason to. A symmetrical swap is impossible. This implies that somehow something must stop Marty2, but what and how?

(An alternate version of this paradox which does not relate to time travel comes from fiction with universes of "evil opposites". If everyone has an evil opposite, then to some extent births - and lesser, deaths - must be synchronized between the universes. If this synchronicity ever broke then the extra child would breed and within a few generations the evil universe would have a totally different population. This means that a hero whose goal is to have children with his girlfriend and to kill or imprison his evil opposite may find he cannot do both - if he is having children with his girlfriend, his evil opposite would need to be having children with his girlfriend's evil opposite, which he cannot do if he is dead or in jail. But what stops the hero?)

This paradox does not arise in Zero Time Dilemma because it is explicitly acknowledged that when a SHIFTer shifts, they rip their own alternate consciousness out of their destination universe and swap with it. But this can create another issue. At the end of the game, the consciousnesses of the group who won the coin flip are forcibly swapped into the bodies of those about to die by the destruction of the shelter. But they are still SHIFTers, and although they have not played the Decision Game, many of them (such as Akane and Junpei) are fully aware of their abilities. They are also in danger, the prerequisite for SHIFTing. So why don't they just immediately shift back again? Could a constant series of competing swaps result?

Two solutions to this problem are either:

The SHIFTers who came from the detonation sequence have SHIFTed more and thus, override the SHIFTing done by the SHIFTers who won the coin toss. Although not directly comparable to the Zero Escape franchise, a similar fan theory exists in Chrono Trigger called Time Bastard. The theory works by erasing time travelers with the least amount of "time travel" done, leaving only the time traveler that has done the most time travel left. The SHIFTers from the coin toss had no time to take in the situation they were just put in and before they could focus on the decision to SHIFT, they were killed by the explosion. Time is of course another valuable resource to consider in this exchange, so it stands to reason that the swapped mind from the safer timeline would have even less time to figure out they had to SHIFT than the SHIFTer from that timeline did.

With the many worlds interpretation though, another dimension is added to this paradox since the participants are given the choice not to SHIFT. Given that a universe exists where this choice was made, does it then follow that the group that won the coin toss still exists in some universe? Moreover, since new universes are endlessly created with each decision that is made, could a universe where the coin toss winners exist and one where they were forced out coexist within the many worlds model?