The Forever War: collapsar jumps (Haldeman 1974)
Fling a ship at a collapsed star and it comes out at another one at the same speed; the jump is free, the approach costs decades, and the decades are the novel.
Kind: fiction · Loophole: L3 · Notability: N2 · Coherence: F4 · Causality: C-owns · Last reviewed: 2026-09-12
The drive as depicted
Joe Haldeman's The Forever War (St. Martin's Press, 1974; serialised in Analog from 1972) states its physics in the first chapter, in the voice of the physics student William Mandella [HIGH] S1. Twelve years before the story opens, the collapsar jump had been discovered: an object flung at a collapsar with enough speed reappears elsewhere in the galaxy, and the formula predicting where was found quickly. The object follows the same "line", which the text glosses as an Einsteinian geodesic, that it would have followed had the collapsar not been there, until it meets another collapsar field, where it reappears repelled at the same speed with which it approached the first, and "Travel time between the two collapsars … exactly zero" [HIGH] S1 (chapter 1). Haldeman adds, in the same paragraph, that this made work for the mathematical physicists, who had to "redefine simultaneity, then tear down general relativity and build it back up again" [HIGH] S1. Ships are followed by a drone a couple of million miles behind so that someone comes back to report if the ship hits a portal planet, the bits of debris that orbit collapsars, at .999 of light speed [HIGH] S1.
The training-base collapsar Stargate is described in chapter 2 as a perfect sphere about three kilometres in radius, suspended forever in gravitational collapse, its surface falling toward its centre at nearly light speed with relativity propping it up; Mandella, as a physics student, worries about the tidal stress of having one end of the ship a kilometre from the other at the surface, and the passengers are told they will feel nothing and free-fall all the way [HIGH] S1. The jump itself is never wrong in the novel. Everything else is. To reach the next collapsar the ship accelerates to relativistic speed and decelerates again; a campaign that takes a few months by the ship's clock takes years by Earth's, and the book keeps the account. After the first campaign Mandella finds he has been in the army ten years though it felt like less than two, and the text names the reason as time dilation: even with the jumps, travel between stars eats the calendar [HIGH] S1. A commodore explains that an enemy ship met after nine years of dilation comes, in an engineering sense, from the future, because it has had the intervening years of development [HIGH] S1. Mandella notes that the only known way to send a message faster than light is to carry it physically through successive jumps, so nobody knows how many jumps a given enemy garrison is from its home or what it has learned [HIGH] S1. Lovers separated into different ships, even leaving minutes apart, will arrive on Earth decades apart, because the geometry of the jumps piles up years between them [HIGH] S1. The war lasts over a thousand years by Earth's calendar and a few years by Mandella's, and ends when the two sides have been talking past each other for centuries [HIGH] S1.
Origin and lineage
Haldeman took degrees in physics and astronomy at the University of Maryland in 1967 before being drafted, and the novel is his Vietnam [HIGH] S2 (Synthese, 2021, on the novel as a thought experiment). "Collapsar" was the working name for what became the black hole in the late 1960s, and the novel's Stargate, a sphere of three kilometres' radius with a surface frozen in collapse, is the Schwarzschild picture as taught at the time: the horizon as a surface where infall appears to freeze [HIGH] S1. The jump is the Einstein–Rosen bridge and the Kerr interior passage as popular astrophysics of 1970 had them, a collapsed star as a door to elsewhere, before Morris and Thorne showed that a horizon-free throat needs exotic matter and that a Schwarzschild throat pinches off. The velocity-preserving rule is Haldeman's own, and it is what makes the book work: because the ship must arrive fast and leave fast, every jump is bracketed by relativistic legs, and the relativistic rocket supplies the dilation. Haldeman's statement that simultaneity had to be redefined is the earliest acknowledgement in this catalogue that an instantaneous jump is a problem for special relativity, though he does not say what the redefinition was. The lineage runs outward into every novel since that keeps the dilation, and GRADING.md names Haldeman as an F4 example.
Which loophole, and why
L3, a shortcut with natural fixed endpoints. The ship enters one collapsar and leaves another with zero elapsed time; the endpoints are the collapsars that exist, discovered and named, not built. The cousins are the Einstein–Rosen bridge, whose finding is that the Schwarzschild throat pinches off before anything crosses, and Morris and Thorne 1988, whose bill for a throat that stays open is negative energy scaling with the throat radius, mass beyond engineering, a pre-laid route and a time machine on assembly. Haldeman pays the pre-laid route by using natural collapsars, states the causality problem in a sentence and never mentions the energy, because in 1974 the energy bill had not been written.
The rules it keeps
- Same speed in, same speed out. The velocity-preserving rule is stated in chapter 1 and never broken; it is why every jump costs a relativistic approach and departure [HIGH] S1.
- Zero transit, dilated legs. The jump is instantaneous and the legs between collapsars are dilated; the novel keeps the calendar (ten years for two, twenty-seven for a career, centuries for the war) and builds every relationship and every battle on it [HIGH] S1.
- No faster-than-light message. Information moves only by ship through jumps, so orders, news and intelligence arrive years late and enemy garrisons are of unknown vintage [HIGH] S1.
- The enemy comes from the future. Time lag turns dilation into a military problem: whoever has spent less time on relativistic legs has had more calendar time to develop, and the commodore's briefing says so [HIGH] S1.
- Collapsars are found. Aleph Aurigae, the first detected, and the alphabet of named collapsars after it; nobody makes one [HIGH] S1.
F4 on the GRADING.md definition and by its example: the novel names a real constraint (time dilation on relativistic legs, and the redefinition of simultaneity an instantaneous jump forces) and builds the whole story on its cost.
What it ignores
The energy and stability of the collapsar as a throat: the novel's Stargate is a frozen-star picture with no exotic matter, no throat radius and no answer to the pinch-off, because none of that was in the literature Haldeman had studied. The tidal question is raised in Mandella's worry and answered by assertion (free fall, nothing felt). On causality the book does not dodge and does not stay silent. It says in chapter 1 that the jump required simultaneity to be redefined and general relativity rebuilt, which is an admission that an instantaneous jump breaks the time-ordering of special relativity; it then adopts a working rule that no message can outrun a ship through the jumps, and uses the resulting ignorance as a weapon in the plot. That is C-owns: the implication is admitted in the text's own words and used. What the novel does not do is construct the loop; no two-collapsar time machine appears, and the "redefinition" is never spelled out, so the admission is one sentence and the use is structural.
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.
| Constraint | Verdict | Note |
|---|---|---|
| CAU-1 | ENGAGES | Chapter 1: the jump made physicists "redefine simultaneity" and rebuild general relativity. The text admits that an instantaneous transit is a problem for the time-ordering of special relativity and says so in the sentence that introduces the drive. |
| CAU-2 | SILENT | No chronology protection is named and no loop is built; the rebuilt relativity is asserted, not described. |
| CAU-3 | SILENT | The collapsars are fixed stars and nobody moves one; the two-mouth time machine never arises, and the book does not ask whether two collapsars in relative motion would give it. |
| CAU-4 | RULE | "Redefine simultaneity" is, read literally, the preferred-frame escape: the fiction asserts that simultaneity was re-fixed to make the jump consistent. The rule is stated in one clause and never elaborated, but it is the work's own answer. |
| CAU-5 | N/A | No entanglement signalling; the text says outright that the only faster-than-light communication is a carried message. |
| ENE-1 | SILENT | No energy condition is named; the collapsar is a frozen star and the jump costs nothing beyond the approach speed. |
| ENE-2 | SILENT | That beating light needs negative energy somewhere was proved in 1998 and is nowhere in the novel. |
| ENE-3 | SILENT | The quantum inequalities would price a throat three kilometres across held open forever; the book predates them and never touches the question. |
| ENE-4 | N/A | Warp-bubble pocket geometry. |
| ENE-5 | N/A | Not a Natário-class warp metric. |
| ENE-6 | SILENT | No source of negative energy is named. |
| ENE-7 | SILENT | A collapsar-to-collapsar shortcut is exactly the wormhole topological censorship forbids under the achronal ANEC; the theorem postdates the novel by two decades. |
| CON-1 | N/A | No warp bubble, so no bubble horizon. |
| CON-2 | RULE | The endpoints are natural collapsars, discovered and catalogued, and the ship must physically fly to one at sublight speed; nothing is created on a first flight. The rule answers CON-2 by making the infrastructure pre-existing rather than pre-laid. |
| CON-3 | N/A | No Krasnikov tube, though the novel's structure (fast jump, slow legs, decades lost) is the arithmetic the tube was invented to improve on. |
| STA-1 | N/A | Warp-bubble instability. |
| STA-2 | SILENT | The Stargate collapsar is a frozen star with a surface, not a throat threaded by exotic matter; what keeps the passage open is never described because in 1974 the question had not been asked. |
| STA-3 | SILENT | No time machine is built, so no chronology horizon is in view. |
| HAZ-1 | N/A | Warp deceleration burst. |
| HAZ-2 | N/A | Warp-bubble Hawking flux. |
| HAZ-3 | ENGAGES | Chapter 2: Mandella computes that one end of the ship a kilometre from the other at the collapsar's surface should set up tidal stress that tears it apart, and is told the passengers will feel nothing. The tidal question Morris and Thorne later bound is raised in the text and answered by assertion. |
| LOR-1 | ENGAGES | Ships approach collapsars at .9c and above and never exceed light speed; the whole novel is the price of that, kept in years. |
| LOR-2 | N/A | No tachyons. |
| LOR-3 | N/A | No signal in a medium. |
| LOR-4 | N/A | Neither the Scharnhorst effect nor the OPERA anomaly bears on a collapsar jump. |
| WRP-1 | N/A | Not a warp metric. |
| WRP-2 | N/A | Not a moving shell. |
| WRP-3 | N/A | No positive-energy warp claim. |
| MAN-1 | N/A | The ship never leaves the manifold; the geodesic language of chapter 1 keeps the jump inside ordinary spacetime. |
Sources
- S1 Haldeman, J., The Forever War (St. Martin's Press, 1974), chapters 1 and 2 for the collapsar jump, the Stargate description and the tidal worry; later chapters for the ten-year discovery, the commodore's briefing, the carried-message rule and the separation scene. Read in a digitised copy for this dossier.
- S2 "The Forever War: understanding, science fiction, and thought experiments", Synthese (2021), open access via PMC 8550122, for Haldeman's physics background and page-referenced quotations.
- S3 Wikipedia and reviews for publication history and the Analog serialisation.