HAZ-3: Tidal limits on a traversable throat

The throat is large, and the exotic matter bill (STA-2) scales with it.

Kind: constraint · Family: HAZ (Hazards) · Last reviewed: 2026-09-12

The result

Tidal constraints on a human-traversable wormhole. Morris and Thorne require the tidal acceleration across a two-metre body to stay at or below one Earth g, which bounds the radial and lateral tidal terms by about (10^8 m)^-2 at the throat. The throat radius bound this gives scales with the traveller's speed through the throat; at one percent of c it is about 500 km

What it forbids or costs

The throat is large, and the exotic matter bill (STA-2) scales with it

Escape hatches

Slow traversal; designs with the tidal terms tuned down at the price of more exotic matter

Who it bites

Physics proposals

• VIOLATES: Gao, Jafferis and Wall: traversable wormholes via a double-trace deformation (2017). The opening $\Delta V \sim h G_N / R^{D-2}$ is Planck-scale and the wormhole is open for less than a Planck proper time (Freivogel et al.); a crossing quantum is blueshifted to $1/\Delta V$, so no macroscopic body passes, let alone one within a one-g tidal bound.
• VIOLATES: Passage through the Kerr interior (Carter 1968). The tidal bound is met at the horizons of a hole above about $3 \times 10^4$ solar masses, but at the inner horizon the traveller meets the exterior's entire future blueshifted by $e^{\kappa_- v}$ and a curvature that grows to Planckian scale, which no throat design can tune down.
• SATISFIES: Maldacena, Milekhin and Popov: traversable wormholes in four dimensions (2018), and the humanly traversable sequel (2021). Maldacena and Milekhin impose a $20g$ tidal bound on a half-metre body and derive $r_e > 1.5 \times 10^7$ m; the throat is boost-invariant so the $\gamma \sim 10^{12}$ traveller feels nothing extra, though any stray photon is a $\gamma^2$-boosted hazard.
• SATISFIES: Morris, Thorne and Yurtsever: the wormhole time machine (1988). The wormhole is a Morris–Thorne throat built to the one-g tidal bound; moving a mouth at high speed does not change the tides through the throat.
• SATISFIES: Morris–Thorne traversable wormhole (1988). The paper imposes the one-g tidal bound over a 2 m body and derives the throat-size and speed constraints from it; at $0.01c$ the throat must be at least 500 km, which is the register's number.
• SATISFIES: Visser's thin-shell wormholes (1989). Through a flat face the tidal forces are exactly zero, better than the one-g bound; the edges, where curvature is a delta function, are lethal and are to be avoided, which the design allows.

Fictional drives

• SILENT: 2001: A Space Odyssey (1968): the Star Gate. Bowman rides through in a pod and is delivered intact until the makers choose otherwise; tidal forces at a throat are never mentioned, and the film's corridor is visual, not dynamical.
• SILENT: Banks's Culture: the energy grid, infraspace and ultraspace (1987 onward). People are Displaced routinely (The Player of Games) through wormholes with no stated radius; the tidal bound applies to the throat and is never addressed.
• SILENT: Commonwealth: CST wormholes with trains through them (Hamilton 2004). Passengers and freight cross throats without tidal comment; a train-sized throat is within Morris and Thorne's bound at low speed and the novel never says so.
• SILENT: Contact: the Machine and the tunnel system (Sagan 1985, Zemeckis 1997). Morris 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.
• SILENT: Cowboy Bebop (1998): the astral gates. Ships and crews pass unharmed on every routine transit and the series never mentions any stress on a body or hull in the tunnel; the tidal bound is unaddressed.
• SILENT: Dune: the Guild navigators and folding space (Herbert 1965). The passage is called dangerous, which is why a navigator is needed, but no tidal force, throat size or physical hazard is ever named.
• SILENT: EVE Online: the warp drive (CCP Games, 2003). Ships of every size pass through gates without any statement of tidal limits.
• SILENT: Event Horizon (1997): the gravity drive. The crew are at the centre of a singularity the ship makes and the film shows no tidal effects at all; the tidal bound on a traversable throat is never engaged.
• SILENT: Homeworld: hyperspace cores and the Far Jumpers. The gates are traversed by capital ships without stated size limits or tidal effects; the row applies through the gates and is not addressed.
• SILENT: Interstellar: the wormhole near Saturn (2014). Morris and Thorne's tidal bound at the throat is not stated on screen; the Endurance shakes in transit and nobody is hurt, which is consistent with a large throat but is never argued. Tidal gravity is engaged elsewhere in the film, at Gargantua, and in the book's chapter on it.
• SILENT: Star Trek: transwarp, quantum slipstream and the other beyond-warp drives. Ships enter conduit apertures and the mycelial network without any statement of tidal limits; the Morris and Thorne bound is never mentioned.
• SILENT: Starfield (2023): the grav drive. Crews jump unharmed on every trip and nothing is said about stresses on bodies or hulls; the tidal bound is unaddressed. The magnetosphere damage is to the planet the drive was tested near, not to anything that jumps.
• SILENT: Stellaris: warp, hyperlane and wormhole (Paradox Development Studio, 2016). Fleets of any size pass through wormholes and gateways with no tidal limit stated.
• SILENT: The Expanse: the ring gates and the slow zone (Corey 2013 onward). Ships pass through rings a thousand kilometres wide without tidal comment; a throat that large would be comfortably within Morris and Thorne's bound, and the novels never say so.
• SILENT: Weber's Honorverse: hyper bands and Warshawski sails (1993 onward). Junction transits are described as stressful passages for a ship under sail with no radius or tidal figure given; the throat bound applies to the L3 secondary and is not addressed.
• ENGAGES: Farscape (1999): wormholes, and starburst as a separate thing. Transit is lethal to unprepared bodies: Peacekeeper pilots sent through in Prowlers are liquefied, and Crichton's survival is attributed to his module and his knowledge. The show never says "tidal", but it prices the throat in bodies.
• ENGAGES: No Man's Sky: the hyperdrive, warp cells and range. Black hole transit damages ship components on every use, the game's own statement that passing through the throat costs the ship; not Morris and Thorne's tidal bound, but the row's question, what the throat does to what passes, is answered by a repair bill.
• ENGAGES: Star Citizen: quantum drive and jump points. Interspace has walls that damage the hull on contact, masses that can kill a crew and a fatal early exit; "UEE Queries" and the 4.0 implementation price the tunnel in hull and lives, which is the entry's question answered in the game's own units.
• ENGAGES: The Forever War: collapsar jumps (Haldeman 1974). 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.
• ENGAGES: Wing Commander (1990) and the 1999 film: jump points. The film makes the gravity well itself the hazard: a ship that misjudges it is lost, and the Kilrathi command ship is destroyed because its mass cannot escape. It is a statement about mass and escape rather than about tides across a body, but it is the one place in the franchise where transit through a gravitational door has a physical cost.
• RULE: Guardians of the Galaxy Vol. 2 (2017): jump points. The fifty-jump rule is the film's answer to what transit does to a body: passengers are distorted and distressed by dose, stated by Yondu and shown in the montage. It is a rule about the traveller, not about tides at a throat, but it is the one place in the franchise where passage has a physical cost.
• RULE: Hyperion: the farcasters (Simmons 1989). A farcaster is a flat doorway with no interior; a person steps across a surface and there is no throat to be stretched in. The rule is implicit in every portal scene and is the thin-shell answer to the tidal bound.
• RULE: Outer Wilds (2019): Nomai warp cores. Living Nomai and the player fall through Brittle Hollow's black hole and warp through towers unharmed by rule; the game never mentions tides, and its natural black hole is survivable at its centre, which is a stated property of the world rather than an engagement with the bound.
• RULE: Stargate: the gate network (1994 film, SG-1 1997 onward). The dematerialisation rule (film; "Children of the Gods") means nobody crosses a throat as an extended body, so the tidal bound is answered by fiat: there is no body in the tunnel to be stretched.
• RULE: Super Dimension Fortress Macross (1982): the space fold. The fold carries a whole island and its sea intact, with the civilians in shelters surviving; the series' rule is that whatever is inside the fold radius crosses unharmed, and the danger of folding near a planet is to the fold's accuracy, not to the bodies inside.
• RULE: Thor (2011): the Bifrost. Travellers cross unharmed by rule, while the bridge left open at full power destroys the receiving world: the film has a stated rule that the throat is safe for a traveller and lethal as a beam, which answers the tidal question in its own vocabulary.

Sources

• Morris and Thorne, Am. J. Phys. 56, 395 (1988); the 500 km figure from Lemos, Lobo and Oliveira, Phys. Rev. D 68, 064004 (2003), arXiv:gr-qc/0302049, App. B ✓ (Morris and Thorne full text paywalled; constraint verified via Lemos et al. and Lobo, arXiv:0710.4474)