Has any sci fi ever tried to explain how conservation of momentum and energy would work with time travel or other similar teleportations? [closed]

Question

Where one just shows up in one point in time and space, whether through time travel or teleportation (one may argue any teleportation would involve time travel due to space-time relativity, but I think what's being asked is clear enough), has anyone ever tried to explain the conservation of energy and momentum in such scenarios?

Answer 1

Larry Niven's teleportation stories, beginning with the hard-to-find "By Mind Alone" (1966) (about psychic teleportation) and his "Flash Crowd" series (technological teleportation) all deal with issues of energy and momentum conservation. Niven wrote a non-fiction piece "The Theory and Practice of Teleportation" in 1969 as well; here's a link to Niven presenting the material that would later show up in that article.

In the stories, characters suffer disaster when they carry momentum from one reference frame to another (don't teleport out of a moving car), or people develop "momentum dampers" to balance out a large number of people's (technological) teleportations; energy conservation can result in overheating (as gravitational potential energy is converted to heat).

Quote from "By Mind Alone"

Pat would be all right. But Larsen was in for a surprise. We wouldn’t be changing any laws of physics. What Pat had run into was the law of Conservation of Energy. In teleporting a mile downhill she’d lost a good deal of potential energy. She’d gotten it back in heat: about seven degrees per mile.

And if that law held, so did conservation of momentum.

Some cops came along and pried me out of the car. A doctor told me how lucky I was, and I believed him, because all I had was two cracked ribs and four teeth knocked out on the steering wheel, which is why my smile today is so even and bright.

The next morning Larsen visited me at the hospital. He told me about Carol.

She’d teleported home. She’d appeared in the middle of her bedroom, four feet from a startled maid. The maid was in the hospital, suffering from shock.

Last night a jerking muscle woke me up to catch myself whispering, “Carol, come back. Come back.” I hope she doesn’t. It’s been six years since she rammed into a bedroom wall at sixty miles per hour, without even a seat belt to protect her. If she came back now, she’d be breaking another of God’s marvelously consistent laws. And you can’t do that.

Answer 2

One milieu that is worked out paying fairly close attention to conservation laws with respect to teleportation is the world of Qish in the stories "Displaced Person" and "Captives of the Slavestone" (both 1987) by Ian Stewart.

On Qish wormholes are grown in matched pairs by various plants and creatures. But potential and kinetic energy are strictly conserved; to enter a wormhole whose endpoint is at a location with greater gravitational potential energy (i.e. higher) requires supplying the necessary energy. A passage that loses potential energy will be accompanied by a commensurate gain of kinetic energy. Similarly with kinetic energy; moving away from the equator results in leaving a wormhole with excess kinetic energy due to the difference in angular velocity.

This is worked out in a number of different circumstances. For example, a pair of wormholes, entrances facing out, can be placed over someone's neck so that their head can be dislocated from their body. But if the head is raised too far above the body, blood pressure will not be enough to cross the potential energy difference to the head.

In another case, an animal will hunt by placing one end of a wormhole facing up on an elevated surface, and the other facing down on top of a pond in which it hides. The upper wormhole will thus appear to be a pool of water. An animal that attempts to drink will start to pass through the portal, and the ensuing conversion of potential to kinetic energy will suck the victim through the portal into the pond.

Answer 3

The Portal computer games implemented momentum-through-portals, and interacting with and exploiting these physics is a key part of the gameplay experience.

Notable aspects of portal-momentum explored during play include gravitational momentum-pumping (put a portal in the ceiling above one in the floor and pick up more momentum each time you drop through) and launching from an angled surface by putting one portal onto the surface and the other down a pit, then dropping into the pit.

Answer 4

E. E. "Doc" Smith's Lensman series, while not dealing with teleportation, but rather inertialess travel (called "free" travel in his books) has his spaceships matching intrinsic velocities with objects that they are interacting with upon resuming inertial flight (called "inert").

The "free" ships maintain the intrinsic velocity of the object they just left - usually a planet orbiting a star, so when they approach another planet, they stand off a distance and manually work out the relative velocities and match them so that they don't accidentally have a high-speed collision with the object when returning to inert travel.

Exactly how this is done is glossed over in the books, usually described similarly to the quote below (from First Lensman, Edward E. Smith, Pyramid Books, 1968):

The Chief Pilot was now at work, with all the virtuoso's skill of his rank and grade; one of the hall-marks of which is to make difficult tasks look easy. He played trills and runs and arpeggios—at times veritable glissades—upon keyboards and pedals, directing with micrometric precision the tremendous forces of the superdreadnaught to the task of matching the intrinsic velocity of New York Spaceport at the time of his departure to the I. V. of the surface of the planet so far below.

Occasionally objects and people are transferred between "Free" ships and put into the "Cocoon" which is a highly sprung armored room (from Second Stage Lensman, Edward E. Smith, Astounding Science Fiction November 1941-Feburary 1942):

Kinnison wrapped the package in heavy gauze, then in roll after roll of spring steel mesh. He jammed heavy steel springs into the ends, then clamped the whole thing into a form with tool-steel bolts an inch in diameter. He poured in two hundred pounds of metallic mercury, filling the form to the top. Then a cover, also bolted on. This whole assembly went into the "cocoon," a cushioned, heavily padded affair suspended from all four walls, ceiling, and floor by every shock-absorbing device known to the engineers of the Patrol.

The Dauntless inerted briefly at Kinnison's word and it seemed as though a troop of elephants were running silently amuck in the cocoon room. The package to be inerted weighed no more than eight ounces—but eight ounces of mass, at a relative velocity of fifty miles per second, possesses a kinetic energy by no means to be despised.

How people would cope with this is never mentioned, but it doesn't sound good to me.

Answer 5

Considered fairly carefully in the Night's Dawn trilogy by Peter F Hamilton. Adamist starships can jump multiple light years at a time, but retain their velocity relative to the universe so need to spend time realigning their vector and speed to account for galactic rotation and local motion of their destination.

Reality Dysfunction:

While the bitek craft could tailor their wormholes to produce a terminus at the required location irrespective of their orbit and acceleration vector, ships like the Lady Macbeth jumped along their orbital track without any leeway at all. It was that limitation which cost captains a great deal of time between jumps. The starship had to align itself directly on its target star. In interstellar space it wasn’t so difficult, simply a question of adjusting for natural error. But the initial jump out of a star system had to be as accurate as humanly possible to prevent emergence point inaccuracies from growing out of hand. If a starship was departing an asteroid that was heading away from its next port of call, the captain could spend days reversing his orbit, and the cost in delta-V reserve was horrendous.

The Naked God:

Earth’s sun orbits the galactic centre roughly once every two hundred and thirty million years, giving it an approximate velocity of two hundred and twenty kilometres per second relative to the core. Other stars, of course, have different orbital velocities, depending on their distance from the core, so their velocities relative to each other are also different.

[...]

The ZTT jump might provide a short cut across the interstellar gulf, but it cannot magically change inertia. A starship emerging from a jump has precisely the same vector it had when it started. In order to rendezvous with the planet or asteroid at its destination, its delta-v has to be altered to match. It’s a tedious process which uses up plenty of fuel;

Answer 6

Poul Anderson brings this up in World Without Stars (aka The Ancient Gods), noting that coming out of hyperdrive can leave you with a sizeable amount of relative velocity to correct, especially if you make an instantaneous jump to a distant galaxy where the differnce might be a considerable proportion of c.