Magic portals are a familiar trope of fantasy worlds, especially in paper & pencil and computer games. They make a lesser appearance in science fiction settings (like Stargate) but don’t forget wormholes are basically portals. And they happen to feature in my current project where, like most other folks, I ignore the aspect of portals I’d like to discuss today: momentum compensation.
Let’s start with a thought experiment: an instantaneous, magical doorway connects Quito to Jakarta, places pretty much on the equator and on opposite sides of the earth. Step through the portal and, voila, you go from Quito to Jakarta. Pretty cool, eh? Except the rotational velocity of a person at the equator is 1000 miles per hour. And two points at opposite sides of the globe are actually moving at 2000 miles per hour with respect to each other. Pop through that magic gateway and you appear in Jakarta moving at 2000 miles per hour. Assuming you didn’t first vaporize from friction with the air, you would smash into the nearest solid object with the same energy as a loaded tractor-trailer moving at 100 miles per hour. That would be the end of you, but it would be so swift, it would merely be an unfortunate end, rather than a painful one.
Clearly, the portal needs to not only move you, it needs to impart the appropriate velocity at arrival, which means it has to instantaneously change your velocity by 2000 mph, which is a G force of infinity. It’s an even faster death but you now arrive as goo. (Or a burst of gamma rays if it really was nearly instantaneous.) Okay, maybe the teleport “magic” also accelerates you without splattering you. But it would be an interesting little fact, a nice touch of verisimilitude, if your teleportation device actually allowed a reasonable amount of time for you to match velocity. Maybe instead of moving instantaneously from place A to place B, you take a second. Let’s do the math… that’s about 80Gs, still not too good for flesh and blood (or really anything but a strong, solid object). But dial it back to about a minute for the transit and now you’re in the realm of a G, noticeable but quite tolerable. Make it ten minutes and its a tenth of a G, a fairly minor force.
Of course, it takes energy to accelerate you to that speed. This energy is on par with what it takes that tractor-trailer to go from 0 to 100mph, probably the energy content of 1-2 gallons of gas. This energy is also required even if you walk, fly, boat or drive from one side of the planet to the other but 1-2 gallons of gas (or the equivalent) is pretty insignificant compared to the energy needed to overcome friction and other losses on the more conventional journey. In case you are wondering, a gallon of jet fuel will move the average passenger about 10-15 miles in a jetliner so to fly halfway around the world would take about 1200 gallons. The energy required for teleportation is notable because it is a fair amount of energy needed in a short period of time (i.e., high power) but in magnitude, while 1-2 gallons of gas can make a big boom if detonated at once, it isn’t a vast amount of energy. Of course, there would presumably be energy required to create and sustain the portal but since the physics for portals is somewhat vague, I don’t know what that would be.
Suffice it to say that the portal probably ought not be instantaneous (unless over short distances) and requires some way to match the teleported object or person’s velocity to the destination milieu without disintegrating said object or otherwise causing issues. And while the energy required for this compensation is much less than the energy required to move a person by conventional means to the same place, it can still be a fair amount of energy in a short period of time. I.e., teleporters might require a major power source.
So where does that leave the author? Most people ignore the issues and the trope is so well established, I see no need to change that. However, especially in a science fiction story where readers sometimes like those crunchy science bits, it might actually make an interesting aspect to the device, especially if someone uses it as a weapon: disable the momentum compensation, pop a 2 ton pallet of cargo through the teleporter, and you have a nice kinetic energy weapon that’s going to destroy anything in the vicinity of the receiver. Could make for an interesting 23rd century terrorist incident. Or the momentum compensation can be the reason you give for why teleportation takes minutes rather than seconds (on a planet) or hours/days/weeks for interplanetary and interstellar travel, where the velocities are, of course, much higher than on the surface of the Earth.
Finally, time travel is another type of portal. In addition to the problem of where to place the exit portal, there’s the presumably even larger delta-velocity to deal with. For instance, you’re travelling 65 million years back in time, even if you know precisely where the Earth was that long ago, do you know where the level of the land was at that time and place as well? I doubt it: better to travel back in a space ship and pop out in the vicinity of where the Earth was and then land on it, assuming you match velocity so that you are moving at a rate relative to the Earth that allows a landing, and not a velocity that pops you out of the solar system in three minutes at a speed that will fry you from radiation resulting from collisions with intra-solar dust.
All this talk about energy and velocity compensation seems a bit too much for most fantasy settings, although for certain “harder” fantasy settings or urban fantasy it could be a nice addition. Maybe a portal opens in Washington, blasting the city with explosive kinetic projectiles (strangely analyzed to be organic tissue) until the alternate reality on the farside of the portal figures out how to get the velocity compensation right: the explosions were actually unfortunate ambassadors: the US isn’t under attack, someone is just trying to come through a portal and say ‘hello’!
As with other similar issues I’ve raised, my point is not to say you can’t use teleportation (again, I’m using it in my current project and don’t worry about any of this). Instead, I’m just tossing out some ideas that might prove of use in your own stories. I must confess I haven’t read much science fiction in the last few decades; I’m sure this has already occurred to other authors; but here’s my take on it.
- Physicists set new record for quantum teleportation with matter qubits (phys.org)
- Stargate (1994) – This must be the beginning of a beautiful franchise (meangoblin.com)
- Science Fiction Musings (mishscifimusings.wordpress.com)