So, the setup. For the purpose of this question, there's no difference between a wormhole, stargate or teleporter. They all do the same thing - move an object instantly over space.

Because I've been thinking about it, and there are some real interesting complications caused by conservation of energy, which would significantly effect the energy cost of use - and if you don't have an infinite energy source, that will hit the cost of use. Some examples I've thought of..


You would always teleport to either in atmosphere (for areobraking) or orbit. Even on the same planet, if you teleported from one side of the equator to the other you would still have a velocity equal to the rotation of the planet in the complete opposite direction. Read: SPLAT.

Factor in both planets rotational and orbital speeds and your best bet would always be to appear right at the start of an areobraking maneuver which captures and then de-orbits you in a loop or two.

But this would imply that there would be very few windows of travel where this lines up nicely at the same point. You could do it year round, if you didn't mind where you landed - which means that a "Star Port" wouldn't work very well. You'd end up with tourist windows at intervals, but I can't work out how frequently.

But moving between planets would be Stressful. And expensive in terms of travel pods. Worse, you've got Gravitational Potential Energy. Going from Earth to Mars will cost you the energy to move further away from the Sun (And the gravitational centre of the universe, but I'm fairly sure that over a few AUs that's going to be small). That energy cost is really non-trivial - so importing Mass is always going to be expensive. You can send a moonbase... but you'd be better off sending a small one and then the means to build a big one locally.

Worse, going inwards would generate energy. Probably instantly. If you could hold that energy, or use it to power an outwards move at the same time you would have a really weirdly different cost for moving inwards. But getting out would be hellishly expensive in energy. (Going to the surface of the sun generates small warhead levels of energy. Think 1-10KT, for meaningful trips)


I've not even tried the numbers for looking at an interstellar trip. Could we even match speeds well enough to not go zooming out the system and never achieve capture??

Anyway, I can have a stab at predicting what will be cheap and what would be expensive. What I'm having trouble with is... what impact will this have on people? Travel between worlds would be expensive. Which normally says "For the rich!". But travel back would be HARD. And they wouldn't have comforts there. Any sort of mass trade would be really hard and impractical I think...unless you traded up and down at the same time. But what would Pluto's colony have to trade? Would we end up dumping stuff at one end or the other, to help the numbers balance?

What does this do to the society? Who does this favour? Who does it harm? And if anyone wants to do more math for us, to give hard numbers - please do!!

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    $\begingroup$ Nitpick: in your example about teleporting to the other side of earth, the problem is conservation of momentum, not energy. $\endgroup$
    – Guran
    Apr 4, 2018 at 6:13
  • $\begingroup$ Good point, should have been conservation of everything. I blame the lack of coffee in my local spacetime. $\endgroup$ Apr 4, 2018 at 6:16
  • 1
    $\begingroup$ Yes, include conservation of caffeine. ;) $\endgroup$
    – Guran
    Apr 4, 2018 at 6:18
  • $\begingroup$ With potential energy differences, probably the most thermodynamically-compliant (read: inconvenient) is to have the machine need the energy difference for lower-to-higher, and the energy to turn into waste heat for higher-to-lower. Some of the waste heat could be turned into energy, but the biggest problem will be to get rid of it fast enough, without it ruining the machine and/or cargo. If you are unlucky, waste heat is dumped directly into the cargo. Humans probably won't survive an altitude differential of more than a few hundred metres without medical assistance... $\endgroup$
    – Eth
    Apr 4, 2018 at 15:51
  • $\begingroup$ What's the problem with making everything a two-way exchange transport? Worst case, that makes it twice as expensive if you have nothing valuable to transport back, i.e. only rocks. $\endgroup$
    – Karl
    Apr 4, 2018 at 16:56

2 Answers 2


If you look up the Larry Niven books in the teleporter universe, you find that this has at least in part been addressed. There are solutions for conservation of energy, conservation of momentum, et al.

The Alibi Machine (as an example) is a story in which conservation of energy is key to the solving of a whodunnit mystery. In the story, what happens is that potential energy is conserved through increase in (or reduction of) heat in whatever (including a person) is being teleported. Therefore, if you come from a high altitude down to a low one, you'll feel hotter on arrival.

Even airports have been turned into long distance teleportation terminals, with large mass canisters in the ocean, dampening momentum into wave energy so that the person being teleported any distance can have their current velocity matched to the new location. In one instance, someone feels themselves being pushed up off the arrival platform slightly because the inertial dampening system is slightly out of alignment for the source location.

Bottom line is that your concern is actually warranted and these problems would likely occur with large scale teleportation considerations. The trick will be to find ways to either bleed off (or add) momentum as needed to align for your needs. Instead of trying to design such a system myself, I'm going to advise that you seek out some of Mr Niven's fictionalised analyses directly; not only are they quite sound approaches, but they're a good read as well. :)

  • $\begingroup$ I'll have a look... but I suspect that he's allowed himself much more wriggle room than I would. $\endgroup$ Apr 6, 2018 at 15:37

Well, you see, the thing is that the stargates in the Stargate Universe DO have enforced conservation of energy.

You see, the reason why the stargates are made out of Naquada is that they build up & store significant amounts of energy upon activation, which is then used to establish and stabilize the wormhole. Unfortunately, the Law of Energy Conservation is in effect, so they can only run for 38 minutes before they run out of power. If they are kept running afterwards without a significant amount of power being provided, they go "boom" quite spectacularly.


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