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Contact: the Machine and the tunnel system (Sagan 1985, Zemeckis 1997)

The wormhole that Carl Sagan asked Kip Thorne to make legal: a chain of tunnels between stars, built by somebody older than the aliens who send the plans.

Kind: fiction · Loophole: L3 · Notability: N1 · Coherence: F3 · Causality: C-silent · Last reviewed: 2026-09-12

The drive as depicted

Sagan's novel Contact (Simon and Schuster, September 1985) has no ship of its own [HIGH] S3. A radio message from the direction of Vega carries plans for a device the humans call the Machine, a five-seat craft built around a dodecahedron, and the transit happens when the Machine is activated with its five passengers aboard on 31 December 1999 [HIGH] S3. Part III of the novel, titled "The Galaxy", carries the journey: chapter 19 "Naked Singularity", chapter 20 "Grand Central Station" and chapter 21 "Causality" [HIGH] S3. In chapter 19 the dodecahedron drops into a tunnel and the passengers argue about what they are inside; the physicists Eda and Vaygay debate whether it is a black hole or a naked singularity while the craft makes several hops between star systems, one of them at Vega, before docking at a station near the centre of the galaxy [MED] S3. The tunnel system is not the work of the beings who sent the message. They explain that they found it, that it was built by an earlier civilisation and that they maintain and use it without understanding its makers, which is the novel's answer to the question of who paid for the engineering [MED] S3.

The cost the novel does state is a mismatch of clocks. The travellers experience roughly a day of transit and conversation; the observers on Earth see the Machine's dodecahedron drop through the rings and come to rest, with the whole event lasting about twenty minutes and the craft never appearing to leave [MED] S3. The passengers' video recordings come back blank, wiped, the text suggests, by the Machine's magnetic fields, so there is no physical proof of the journey [HIGH] S3. The novel then moves the burden of proof into mathematics, with a pattern found deep in the digits of pi in chapter 24, "The Artist's Signature" [HIGH] S3.

The 1997 film, directed by Robert Zemeckis and released on 11 July 1997, keeps the shape and changes the numbers [HIGH] S3. The Machine is a set of counter-rotating rings with a spherical pod at the centre, the dodecahedron demoted to a cage around the sphere [HIGH] S3. Ellie Arroway travels alone, sees a radio-array-like structure at Vega and other systems, lands on a beach that matches her childhood drawing and meets an alien wearing her dead father's face [HIGH] S3. From outside, the pod fell straight through the rings into the safety net; her recorder holds only static, but eighteen hours of it, which is the film's version of the novel's clock mismatch and the fact that lets the audience keep believing her [HIGH] S3. The film's dialogue calls the tunnels wormholes; neither the novel nor the film gives the tunnel a metric, a throat radius or an energy source, and neither says what holds it open.

Origin and lineage

This is the one work in the catalogue with a physics paper as its offspring, and the paper says so in its own text. Morris and Thorne, Am. J. Phys. 56, 395 (1988), §I.C: they were "stimulated to find" their traversable wormhole solutions in the summer of 1985, when Sagan sent one of them a prepublication draft of Contact and "requested assistance in making the gravitational physics in it as accurate as possible"; Sagan, on receiving their preliminary description, incorporated the solutions into the novel at the galley proof stage [HIGH] S1. That sentence is the lineage. Sagan's draft had sent his heroine through a black hole; Thorne's objection was that a Schwarzschild throat pinches off before anything can cross it, and his replacement was a wormhole held open by matter with negative energy density, the "exotic matter" of the 1988 paper [MED] S3 (Thorne's own account in Black Holes and Time Warps, 1994, final chapter, which this catalogue has not read directly; the popular retellings on which the [MED] rests are listed under Sources). Sagan, by the same accounts, put the exotic matter and the engineering on a vanished earlier civilisation so that the novel need not explain them [MED] S3.

The physics dossier is Morris and Thorne 1988, and its sequel, the Morris, Thorne and Yurtsever time machine, was written within months of it. The Einstein–Rosen bridge is the black hole Sagan first reached for and Thorne rejected. The film's wormhole descends from the same paper through the novel; no source found for this catalogue names Thorne on the 1997 film's production [MED] S3. The documented person linking the 1997 film to Interstellar is the producer Lynda Obst, executive producer of Contact and producer of Interstellar, whom Sagan introduced to Thorne [MED] S3, which is why the lineage page for the two films and the paper is one page.

Lineage: Physicists in the writers' room; Sagan asks Thorne for a legal wormhole.

Which loophole, and why

L3, a shortcut. Nothing in Contact moves faster than light through the space it is in. The Machine drops into a tunnel whose two ends are in different star systems and comes out the other end; the transit between hops is a fall, not a flight, and the novel's physicists spend the trip trying to name the geometry they are inside [MED] S3. The cousin is Morris and Thorne 1988, whose bill is negative energy density at the throat in an amount that scales with the throat's radius, a total mass beyond engineering, a route that has to be laid in advance and a time machine the moment one mouth is moved. The novel pays the third of those explicitly, by making the tunnels the work of an older civilisation, and is silent on the rest.

The rules it keeps

That is enough for F3: a stated set of limitations (fixed tunnels, inherited infrastructure, a clock mismatch, no evidence) applied the same way in every instalment, with the physics named but never priced. It is not F4 because the story is built around the cost of belief, not the cost of the wormhole; the exotic matter that made the novel possible is never on the page as a constraint the characters must live with.

What it ignores

Contact never asks what a wormhole between stars does to the order of events. The clock mismatch is presented as a curiosity, a dilation-like discrepancy, and is never turned into the question the register asks first: a tunnel that beats light between Earth and Vega is, in some inertial frame, a tunnel into the past, and two such tunnels are a time machine with an assembly step (CAU-1, CAU-3). Chapter 21 is titled "Causality", and this catalogue could not verify from the text that the title refers to the time-ordering problem rather than to the aliens' account of their own ignorance about the builders [LOW] S3; on the evidence available the novel is silent, and the film is silent throughout. No instalment addresses chronology protection, the exotic matter at the throat, the quantum inequalities or the tidal bound. The absence is dated: no edition or adaptation of Contact engages the causality of its own tunnels as of 2026-09-12. Hence C-silent.

Constraint scoring

Every entry in the register, one row each, verdict from the fiction vocabulary in GRADING.md, with a note that says where in the work the engagement or rule occurs.

ConstraintVerdictNote
CAU-1SILENTThe tunnels deliver the Machine from Earth to Vega and the galactic centre faster than light through the space between; no instalment asks about the frame in which the arrival precedes the departure.
CAU-2SILENTChronology protection never arises; the novel has no time loop to protect against and the film has none either.
CAU-3SILENTThe tunnel mouths are fixed at the stars they serve, but no rule says they are immovable, and nobody in the work considers what moving one would do. The one-mouth round trip that makes a wormhole a time machine is never raised.
CAU-4SILENTNo preferred frame is stated. The clock mismatch (a day inside against twenty minutes outside) is reported as fact and never explained by a frame choice or anything else.
CAU-5N/AThe message from Vega arrives by radio at light speed and the Machine moves matter through geometry; no entanglement signalling is involved.
ENE-1ENGAGESBy Thorne's account the novel's tunnels are held open by exotic material with negative energy density, attributed to a lost earlier civilisation so that the text need not explain it; this is the reason Morris and Thorne looked for the solutions at all. The engagement is in the book's origin and the paper's §I.C rather than in a passage of the novel this catalogue could quote.
ENE-2SILENTThat a shortcut faster than light through flat space needs negative energy somewhere along the way is the result Olum proved a decade after the novel; Contact never states the principle, only inherits the tunnels that would require it.
ENE-3SILENTThe quantum inequalities bound how much negative energy can exist for how long; a tunnel wide enough for a dodecahedron, open long enough for a day's transit, is priced by them and the work never mentions the price.
ENE-4N/AThe Van Den Broeck pocket is a modification of a warp bubble, not of a wormhole.
ENE-5N/ANatário-class warp metrics are not involved; the Machine falls through a tunnel.
ENE-6SILENTThe Casimir effect is the only negative energy ever produced and it is tens of orders of magnitude short of any throat; the work never names a source for its exotic material beyond "somebody older built it".
ENE-7SILENTTopological censorship says a wormhole shortcut visible from outside needs the achronal ANEC to fail; the tunnels are exactly such a shortcut and the theorem, published in 1993, postdates the novel and is never touched by the film.
CON-1N/AThe warp-bubble horizon is a property of the Alcubierre class; there is no bubble here.
CON-2ENGAGESThis is the constraint the work answers on purpose: the tunnels are a pre-existing network built by an earlier civilisation and merely used by the senders of the message. Warp travel is infrastructure, and Contact makes it inherited infrastructure.
CON-3N/ANo Krasnikov tube; the tunnels are two-ended shortcuts, not a metric laid along a sublight outbound leg.
STA-1N/ASemiclassical instability of a superluminal bubble wall does not bear on a wormhole.
STA-2SILENTThe throat must be threaded by matter whose tension exceeds its energy density; this is the Morris and Thorne result the novel was the occasion for, and the text never describes what holds the tunnel open.
STA-3SILENTDivergence at a chronology horizon arises only once a wormhole is made into a time machine; the work never gets that far, so the question never comes up.
HAZ-1N/AThe deceleration burst is a warp-bubble hazard.
HAZ-2N/AHawking flux inside a superluminal bubble is a warp-bubble hazard.
HAZ-3SILENTMorris and Thorne bound the tidal acceleration across a human body at the throat and the bound sets the throat radius; the novel's travellers ride in comfort and the film's Ellie is shaken about, but neither version states a throat size or a tidal limit.
LOR-1RULENothing in the work is accelerated to light speed; the Machine's rings spin and the dodecahedron drops. The rule that the vehicle never flies fast is implicit in the design and is kept in both versions.
LOR-2N/ANo tachyons; the message is radio and the vehicle is a falling capsule.
LOR-3N/ANo wave in a medium is involved.
LOR-4N/ANeither the Scharnhorst effect nor the OPERA anomaly bears on a tunnel between stars.
WRP-1N/ANot a warp metric.
WRP-2N/ANot a shell of material moving inertially.
WRP-3N/ANo positive-energy warp claim is made.
MAN-1SILENTThe tunnels are not described as leaving the four-dimensional manifold; the passengers argue about singularities, not extra dimensions, and the film says only "wormhole".

Sources