Why aviolicide is a poor choice

A Field Guide to Time Travel in Fiction

I have a surfeit of annoying habits. Chortling through exorcism movies may be the worst, but a close second is ranting at incoherent movies about time travel. Why? Let's boil it down: killing your grandfather (aviolicide) should be inconveniently suicidal. Time travel has made it an administrative problem and a narrative delight. If he dies before the conception on which your existence depends, you cannot be there to kill him. This is a considerable burden to place on a man in carpet slippers.

I love time-travel fiction. I have also written a novel which obliges me to have opinions about it, and have now included that novel in a survey of other people's work. The possibility of a conflict of interest has occurred to me. Mea culpa. I have dealt with it by mentioning it early, which seems to be the accepted procedure.

The grandfather test is useful because it asks a small, brutal question of a very large invention. What happens if the traveller prevents the cause of the traveller? A machine may occupy an entire laboratory, but its lights tell us nothing about the answer. Before getting in, I would like to know whether the past can change, whether the visit was always part of it, or whether I have bought a ticket to somebody else's history.

We need a brief tour of the alternative views of the past.

In a fixed history, such as I employ in Proximal God Ascension, my visit already belongs to the account. I may discover that I caused the event I came to prevent. I may even discover that my attempt to prevent it was indispensable. This is irritating for me but consistent for the story. The restriction applies to the whole history, including what I choose and what I manage to do. It need not employ a supernatural attendant to knock the gun out of my hand.

Overwrite stories have a different difficulty. History had one form; now it has another. What orders those two versions? If the replacement takes time, which time is it taking? The events within a history already have their dates. The succession of histories requires additional bookkeeping, and a revision which unfolds needs an additional clock. This is the meta-time problem, usually left outside with the coats.

Marty's photograph in Back to the Future begins deleting his family while his memory retains them. His body follows its own timetable. I find the sequence gripping, which is mildly embarrassing given the complaint I am making. The film has arranged for three remnants of the old history to receive the correction at different speeds. An overwrite model can stipulate protected memories and surviving travellers; it still owes us a consistent account of the exemptions. The butterfly explains why a change might spread. It does not explain why the hero remembers a world which no longer produced him.

Branching offers a remarkably economical answer to that last difficulty, provided one does not count the universes. I arrive in another history and kill its grandfather. My own origin remains intact elsewhere. There is no contradiction in this arrangement, although the bereaved may feel that logical consistency has received more attention than they have.

The trouble begins when the traveller describes the result as changing the past. In a branching model, the original history remains. If I find a world in which my wife survives, the wife who died in the world I left has not been restored to her family. Whether the surviving woman and the dead woman count as the same person needs an account of identity. Finding the former does not, by itself, reverse the latter's death. A story can confront this honestly. The Peripheral makes the unequal relationship between histories a means of exploitation, with people at the less fortunate end of the connection paying for somebody else's opportunities.

The multiverse becomes an indulgence when it supplies whatever the plot has spent. Death, defeat and an inconvenient piece of continuity can each be referred to another universe. Existence is only the first permission being requested. We also need to identify the relevant world, reach it and perhaps get home again. Each capability needs its own premise. Saying 'multiverse' explains the journey about as well as saying 'aviation' explains why my wardrobe has arrived in Paris.

I find the human-choice version particularly rant-inducing. I consider tea or coffee, and reality is apparently obliged to furnish both decisions with a cosmos. My hesitation has acquired an astronomical construction budget. I am sufficiently self-involved to find this attractive, but I would struggle to defend it even to someone paying for the coffee.

A human decision has no privileged position in the physical account. In decoherence-based Everettian descriptions, approximately autonomous macroscopic histories emerge through interactions between physical systems. Those interactions did not wait for a conscious observer, much less for me to become indecisive. A choice belongs within the process; it is not a special instruction to manufacture worlds. Even accepting that interpretation supplies no known method for browsing the results.

There is room here for serious speculation, and considerably more room for fiction. My objection is to the invoice being passed to quantum mechanics. A screenplay cannot borrow the respectability of a theory while quietly adding a branch selector, a return ticket and a replacement for everyone it has killed. These are substantial purchases.

The word 'quantum' is beginning to look less like an explanation than a Hollywood credit card.

Nor does extravagance automatically make a story bad. Gerrold makes proliferating selves the substance of The Man Who Folded Himself; the excess is what he is examining. The useful distinction is whether the alternative histories create consequences the work is prepared to inhabit, or simply remove consequences it has become tired of accommodating. An infinite supply of worlds can still leave one person with an irreversible loss. I would like the story to remember that person.

A closed loop raises a separate objection, which is often bundled into the grandfather paradox because one paradox evidently looks much like another at a distance. Suppose I take a published score into the past and hand it to the composer, who copies and publishes it. Eventually I buy the edition and make the journey. Every delivery has an explanation. The composition does not. I have found an unusually efficient way of avoiding the work of writing music.

This is a bootstrap: information circulating without an independent point of invention. It need not contain a logical contradiction. A fact can depend on another fact which depends on the first without either being simultaneously true and false. Whether such a loop can be physically realised is another matter. Copying the music onto new paper also differs from sending the same watch round indefinitely. Wear, repair and the state in which the object returns must satisfy the loop's boundary conditions. Calling it self-consistent does not service the watch.

Heinlein tests how far a genealogy can fold into itself. In Behold the Man, Moorcock has a traveller enact the religious history that prompted the visit. The enacted narrative supplies its own historical support, an arrangement that ought to trouble anyone concerned with references. It does not follow that every cause of Christianity has been bootstrapped. The narrower claim is quite troublesome enough.

Hawking's chronology-protection conjecture addresses the physical opportunity for these excursions. It proposes that the laws of physics prevent closed timelike curves from appearing. His argument considers gravitational and quantum effects near their formation, including the possibility that the attempted time machine would be defeated by those effects. This remains a conjecture, rather than a general proof that every proposed route into the past is impossible.

There is an appealing economy to stopping the machine before the family argument begins. Chronology protection does not, however, mean that nature admits the traveller and then supervises the assassination attempt. A gun which jams, a bus which arrives early or a flowerpot which falls at the decisive moment belongs to a different sort of explanation.

Hawking did not propose a protection racket for elderly relatives.

Fiction can make history resistant. Leiber's compensating events and King's obstructive past give the universe ways to frustrate intervention; Willis's slippage restricts access. Their rules deserve examination on their own terms. A resistant past may still yield, and a consistent history can contain a perfectly ordinary gun jam without an intelligent cosmos arranging it. We should at least distinguish the mechanism from the outcome. 'He failed to shoot Grandpa' is evidence of a failed shooting, not yet a theory of time.

This is where my sympathy for the writer briefly exceeds my enthusiasm for the prosecution. A fixed history can offer a character choices whose consequences the character cannot escape. A resistant history can turn the past into an antagonist. Both are useful dramatic premises. The trouble comes when the work wants the rigour of the first and the convenient exceptions of the second, generally at the point where someone attractive needs rescuing.

We can cause most of these difficulties without transporting a person. Benford's Timescape sends information, and a single controllable bit sent into its own causal past is enough to make trouble. The Terminator is an expensive delivery system for a problem which fits in a message.

Imagine that tomorrow's machine sends YES to today if tomorrow's lamp is on, and NO if it is off. Today's receiver arranges for tomorrow's lamp to be off after YES and on after NO. There is no consistent binary answer. Something in the proposed arrangement must give: the signal, the control, the assumed history, or the claim that we can build this equipment at all. A branching or overwrite account can offer another arrangement, but it must explain where the received record and its sender belong. Removing the passenger has saved on casting without repairing the logic.

Information travelling from the past to the present is a different case. A read-only historical viewer, such as the chronoscope in The Dead Past, need not permit any intervention in earlier events. The grandfather paradox has no purchase on it. Privacy, on the other hand, is in dreadful trouble. An invention can ruin civilisation without once contradicting its own causes, which is a distinction inventors may not wish to advertise.

Reset loops keep information in a more selective fashion. If the world returns to exactly its earlier physical state, the brains in it return too. A remembered previous attempt is a difference. The story must preserve that difference somewhere, whether by protecting a brain, transferring a mind or exempting part of the world. 'Everything is identical except this new memory' is a perfectly intelligible fictional rule once the exception is admitted. 'Everything is identical, including the new memory' is not.

Groundhog Day grants retention and gets on with examining how a man might live. Edge of Tomorrow gives it an alien biological explanation; The First Fifteen Lives of Harry August develops a network out of recurring lives. The attempts accumulate in an order beyond the interval being repeated. I want to know what carries that accumulation and what can end it, but I do not require Bill Murray to spend the second act demonstrating a storage device. There are limits even to my patience with my own objections.

Consciousness complicates the vocabulary further. Sending an older mind into an earlier body requires some account of the younger occupant. Experiencing a life out of sequence, as in 'Story of Your Life' and its different cinematic adaptation, Arrival, need not involve that eviction at all. Foreknowledge still has to agree with action, or the story must explain how the known future can change. Learning a language does not provide tomorrow's memories by any established mechanism. The concession is substantial; what the work does with knowledge, choice and grief determines whether I am glad I made it.

Sometimes the apparent journey belongs to the telling. Time's Arrow reverses our experience of a life; Einstein's Dreams imagines different temporal arrangements. Neither obliges us to supply a machine moving between those arrangements. A change in narration is not automatically a change in spacetime. Authors have enough powers without my inventing additional ones on their behalf.

I should now submit my own contribution to the same inconvenience. Proximal God: Ascension uses an ontological Block, developed through the BEIPE framework in Occam's Ruler. I have called its entry 'Rigorous speculation' and awarded it five stars. There are more retiring ways to introduce one's work. In mitigation, the adjective has a published argument attached to it.

Occam’s Ruler: A reformation of physics without indulgences or imaginary friends.

A reformation of physics without indulgences or imaginary friends. Includes the BEIPE physics appendix.

AmazonPeter Merrens

The premise is that the Block exists complete. Entities are their entire spacetime extents, or streaks; BEIPE develops persistent informational structures as Worldline+s within the Mobifold. Nothing moves, including light. Denizens perceive differentiated portions of the structure and experience that perception as time. There is no objective succession in which the Block develops into a later version of itself. The distinction matters, however unhelpful it may be when describing a novel in a lift.

What looks like travel is therefore a relation within the complete object. An extent experienced out of chronological order has not arrived from outside to amend it. 'Grandpa lived, then I went back and killed him' asks the Block to have two successive versions. The word 'then' is doing illicit work. It introduces an external ordering which the premise does not contain.

The ancestry remains exact. If my existence depends on this man conceiving this child, the same complete account cannot also include his death before that conception while supplying no other account of my origin. Those conditions fail to describe an instance of the ontology. There is no contradiction which subsequently needs fixing, and no need for the universe to arrange a fortunate mechanical failure. Grandpa can put the gun-jamming service out of his budget.

That is what 'Resolved' means in the entry: the grandfather paradox is inapplicable.

I have not discovered how to perform a contradiction successfully.

Nor have I obtained this result simply by calling a timeline fixed. The claim concerns the nature of the complete object and what an apparent journey within it can mean. Other works admit Block-compatible readings; I do not acquire sole ownership of consistency by describing my premises at greater length.

The pressure moves to identity and agency. What is a person if the person is an entire extent? What is choosing like for someone whose deliberation and its consequences belong to the structure, but whose perspective is incomplete? The absence of historical revision does not dispose of those questions. They are part of the novel's difficulty, and rather more interesting to me than another elderly man narrowly missing a bus.

The BEIPE paper supplies axioms, definitions, an explicit ontology and proposed tests. Its entropic age is an ordering parameter, not a physical clock on which the Block runs. The five stars recognise that developed speculative foundation. They are not five experimental confirmations, and a systematic argument can still be wrong. Its application in a novel must also withstand the events I have written. I have provided the reader with an unusually convenient opportunity to check whether I observe the restrictions I recommend to everyone else.

The distinction between a good story and a coherent mechanism is worth retaining, particularly when a survey makes disagreement look so pleasantly tidy. I can admire a film while thinking its causal account is nonsense. I can also find a meticulously specified machine less interesting than the person who has missed the bus beside it. Physics, consistency and artistic persuasion answer different questions; forcing them into one mark would make the survey shorter and considerably less useful.

Superman enjoys a generous allowance because Christopher Reeve is in it. Reversing the apparent rotation of Earth is not an explanation of reversing history, but the scene has emotional force. Back to the Future makes us care about the disappearing photograph before we have properly examined its peculiar privileges. These are artistic achievements. My objection would arise if I were asked to accept the photograph as a scientific demonstration, or the Earth's rotation as a useful adjustment to a bereavement.

Interstellar deserves its credit for relativity. The differential ageing has real physical grounding. The later use of gravity to communicate into the sender's own causal past needs the additional speculative machinery of the film's higher-dimensional construction. Gravity normally connecting events does not license that particular connection. I have allowed four stars and retained the right to complain about the last part. Einstein has already supplied enough of the film to be excused responsibility for every message in a bookcase.

Truth, Educated Guesses, and Speculations in ‘Interstellar’

An excerpt from “The Science of Interstellar,” a new book by theoretical physicist Kip Thorne.

Science FridayKip Thorne

The physicist-novelists do not receive a general exemption either. Benford gives temporal communication the texture of scientific work. Hoyle asks what it might mean for different epochs to be neighbouring places. Forward tries to specify the apparatus, while Lightman considers what unfamiliar kinds of time would do to familiar human lives. Their different purposes deserve different judgements. A doctorate may improve the discussion; it cannot make an invented mechanism exist.

I am quite willing to accept an impossible premise. Fiction would become an impoverished occupation if we admitted only events which had cleared a laboratory. I become less willing when the story changes its terms after taking my attention. A traveller who can rewrite everything except the memory needed for the climax has acquired a very particular immunity. It may be a defensible rule, but the defence ought to precede the rescue.

The linked entries are judgements, with the limitations of judgements. They are not a claim to have freshly read or watched all 110 works, and a reading labelled 'open' should remain open. The dates and sources identify the versions and factual distinctions where these matter. They cannot turn an interpretation into a measurement. I have used stars because they are quick to read; their resemblance to precision should not be taken too seriously.

What I ask of these stories is that their restrictions have consequences. If the past is fixed, let somebody discover what that costs. If another world is available, remember the people left in this one. If memory survives a reset, make its survival matter. A work can earn a considerable indulgence by doing something with it. I have written a book myself; I am hardly in a position to close the account.

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