I'm throwing around a rough concept in my head and wonder which effect it would have on the present world. How would the world as we know it change if this technology were invented (and nothing else changed)?

Imagine that we discover a way to build portals through space that connect distance points in space, similar to Stargate or many others. Imagine that in this case, a membrane appears between two otherwise remote locations. It has a slight outwards pressure, so you need to apply some force to cross the barrier (no such thing as being sucked in, and no interchange of air, sound, temperature, etc.)

I'm wondering about details of this. The technology connects two points in space, as if the distance between them were zero. Obviously, they would have to be defined relative to each other (space has no absolute dimensions). Would they vibrate or shift in relation to each other and by how much? Which effect would an instant transition to a different place on the surface of earth have? Air pressure differences are an obvious issue, but what about rotation? Would you really arrive head-down, spinning rapidly, as naive assumption leads me to believe? What else could go wrong, especially to living beings? Would there be serious damage if, for example, gravity goes into different directions in different parts of your body for the short time of passing through the portal?


  • The portals are intended to only connect space. No matter disassembly, teleportation, re-arrangement of wave functions or something. They are really just portals, nothing more fancy.
  • My intended story is earth-today-as-we-know-it-plus-portals - so interstellar travel is not my concern. Any "relative to" things would be relative to earth or to one of the portals.
  • Effects like energy conservation or energy generation through potential energy are discussed at length in other questions and are likewise not my concern.
  • $\begingroup$ This is your fictional technology; just define the rules however you need to to make the story interesting. $\endgroup$ – Frostfyre Nov 16 '16 at 13:23
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    $\begingroup$ Of course I could solve any problem just with handwaving. But I'd like to think about this from a hard SciFi perspective, and see which problems would arise, which would be simply annoyances and which are in serious need of a solution, how that solution would be like or if it would prevent application of the tech at all (or maybe limit it to non-living objects only). $\endgroup$ – Tom Nov 16 '16 at 13:25
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    $\begingroup$ the way you describe your portal, i think it would be perfectly feasible to treat the portal as the reference. so, up, down, etc are relative to the portal, while the portal should have something like a defined "up". As a result, setting up the target portal upside down would annoy any travellers... $\endgroup$ – Burki Nov 16 '16 at 15:00
  • $\begingroup$ See also this and this. $\endgroup$ – JDługosz Nov 17 '16 at 0:14
  • $\begingroup$ If this question is science-based, here is something to consider. If the only handwaving is the connection of space, the membranes within the portals will still transfer temperature, pressure, etc. Increasing outward pressure intelligently to regulate what goes through requires significantly more handwaving. $\endgroup$ – Zxyrra Nov 17 '16 at 3:51

One concept that comes up a lot in this sort of world (think Portal, Neal Asher's Polity series or Niven's Ringworld etc) is momentum.

Portal states, "Speedy thing goes in. Speedy thing comes out," allowing interesting effects as momentum is conserved relative to the plane of the portal.

In the Polity series, momentum energies are dissipated in the arrival Runcible, and a failure here tends to equal R.U.D.

And in Ringworld, plates couldn't be placed too far apart round the ringworld, or the momentum differences would kill you. Even minor differences required energy sinks to cool.

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    $\begingroup$ Niven further expanded his thoughts in The Theory and Practice of Teleportation (obooksbooks.com/2015/3975.html). Well worth reading for anyone wanting to think about any sort of teleportation/portal stories. $\endgroup$ – Ghotir Nov 16 '16 at 17:12
  • $\begingroup$ Maybe you could put down a few of the core thoughts from that into an answer here? $\endgroup$ – Tom Nov 16 '16 at 18:01
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    $\begingroup$ @Tom It's a "casual conversation" on a number of issues related to teleportation - but I'm not sure a summary would do it justice. It's also not a very long read (five or so pages, if I recall correctly). It does (briefly) dip into things like conversation of momentum, not letting two things occupy the same space, etc. I didn't feel it warranted a full answer - but I wouldn't be upset if someone else made an answer out of it. (I'm here to help/learn, not to earn online rating points.) $\endgroup$ – Ghotir Nov 16 '16 at 20:46

This is entirely up to you, but allows for some entertaining effects if you want it to.

Say your speed and rotation are maintained, what are they maintained relative to? The gate? The centre of the galaxy? Any arbitrary other point?

If you pick something other than the gate, then you go in at a maneuvering speed and come out on the other side of the galaxy somewhere between 420-480 km/s relative to the local star.

As is typical for spiral galaxies, the orbital speed of most stars in the Milky Way does not depend strongly on their distance from the center. Away from the central bulge or outer rim, the typical stellar orbital speed is between 210 and 240 km/s (470,000 and 540,000 mph). Wikipedia.

The only logical answer to make the gate work in practice is that speed relative to the gate is maintained. You can worry about the difference in energies when you've worked out how much energy is needed to actually translate a ship across the galaxy. After that, changing the speed of the ship by a mere few hundred km/s is probably a minor detail.

The problem with portals is that they tend to breach the laws of thermodynamics. Just place the exit over the entrance in a gravitational field and watch what happens.


This question seems a little too opinion based (you can create any problem you want with the portals by changing how you define how they work), but here are some ideas.

Problems with Dimensional anchor portals

You can visualize this being like a tunnel (with walls) made on Earth to connect 2 points to reduce the distance. (This is technically subspace travel, but since we don't even know if subspace exists, this could make the distance zero). So 2 obvious problems.

1) The energy to move these portals is similar to trying to move the tunnel. You have to move the tunnel (gate) AND force the Earth (space) out of the way.

2) Because these portals CAN'T move (not with our available power at least), and everything in space is moving, it would only be a relatively short amount of time before the portal moved too far. (Can't say how fast because technically, that requires knowing where the 'center of the universe' is. Which is different from the center of the Big Bang)

However, on gate force close, you would be forced out of one end (or crushed by the collapse if you're in the middle of it)

Problems with Mater Relay Portals

This kind of portal is just as matter enters one end of the portal, it gets broken down, sent to the other portal, and reconstructed. This is the most dangerous of them all since...

1) It is like a molecular grinder. If your acceleration as you pass through changes by even a micron, you will basically be atomic dust on the other side. Or you stop going through and you are now cut in half at the subatomic atomic level. Organics would need die as the beating of their heart just rips them to dust as they go through. Even drones would die if they did not enter while completely turned off and it's parts locked down.

Problems with Handwavium Portals

As you probably guessed, this is the portal that connects 2 points in space, and just says 'they are just two locations with a door between them now'. As you seem to already know...

1) Pressure differences can create strong winds between portals. Even with a 'membrane', it would have to strong enough that we can't enter without getting to hyper-sonic speeds first (and not die from deceleration upon hitting that membrane)

2) No one can really say what would happen if it closed while you passed through, but I will say it will at least hurt. A lot. At LEAST as much as a door closing on your face.

3) Gravity differences as you pass between the two points could be enough to kill you. I want to say 5G difference max for acceptably survivable.

Problems with all Portals

1) You remember conservation of energy? You know Work energy (Force X Distance)? No one can afford the power to send even a grain of sand through a portal so say goodbye to the law of conservation of energy (or make the portals so close to each other that it's like why bother?) Don't forget the energy to distort space itself. That probably only requires all the energy in the known universe plus some.

2) Because of the last point, what happens if it's destroyed? Where does that energy go? Everyone dies?

3) Politics. Handwaving all the problems, you know how much a key asset these portals are? Everyone will either want to control, or destroy them. So roll out the tanks, it's time for the Great Universal War!

4) Religion. Somehow, I just know a religion will pop up around these portals. Thankfully these crazies are rare and easily to keep away from.


I'm not so bearish on this idea as some of the other commentators.

In Loop Quantum Gravity (the smaller of one of a couple main efforts to develop a theory of quantum gravity), one of the core concepts is that fundamentally space-time is made of points connected to other points and that notions like "locality" and the number of space dimensions are only "emergent" properties of space-time at a macroscopic level that arise from points that have links to each other in common being perceived as being close to each other.

So, at a macroscopic level, space-time seems to have three spatial dimensions, to have well defined locality, to be smooth and to be continuous, but really, space-time is a network of discrete discontinuous points with ill defined dimensionality, in which it is entirely possible for a point to have a direct connection to another point light years away, even though most of its connections, on average, will be very near by.

In LQG, the true formulation of the speed of light is not in terms of distance per time in a continuous space, but in space-time points traveled per time whose average apparent distance from each other is well defined, but which actually have variable apparent distances from each other according to a well defined probability distribution that is reflected in the fact that accurate quantum mechanical calculations for the travel of a photon, for example, require not just consideration of all possible paths from point A to point B, but also a range of speeds above and below the speed of light (which is just a most probable average speed) that in an LQG version of quantum gravity may reflect scenarios in which the same number of space-time points are traversed in a given time frame, but the distances between them only produce the speed of light, on average, rather than exactly replicating it.

So, in a universe with non-local space-time connections, there is no intrinsic difference between going from one side of an atom to another through an apparently local connection of space-time points, and going from Earth to a distant galaxy. Both could involve the same number of space-time hops.

These non-local connections and the very notion of gravity itself, in some versions of LQG, are deeply related to the quantum mechanical phenomena of "entanglement" which allows particles whose wave functions collapse at greatly separated locations in time and space but once shared adjacent points in space-time to continue to act in a corrolated fashion.

Now, the fictional side of this when you get to a macroscopic sized gate based upon current technology is that in LQG and with respect to the quantum mechanical phenomena that seem to be a good fit for this kind of space-time, non-locality is a phenomena that generally happens on a one point in space-time just big enough for a single photon or quark or electron to occupy at a time basis, not on a macroscopic basis where everything averages out and creates the spatially three dimensional world in which concepts like locality and a smooth space-time and perfectly invariant speed of light seem to describe reality.

Essentially, without to much handwavium, the advanced technology that creates the gates would have to figure out how to get all of the space-time points and fundamental particles that make up the gate into a single unified quantum state with a parallel entangled set just like it, and then once the entanglement is established, to ove the gates far apart from each other. And, you would have to devise some way for this intensely coordinated collection of gillions of fundamental particles in two main clumps at the side of each gate, to do so in such a manner that someone passing through it is neither assimilated into the gate's coordinated wave functions itself, nor disrupts the epic feat of quantum mechnical coordination.

Realistically, even in the most far out versions of LQG (assuming that this proves to be correct rather than the alternatives), at best, it would merely be possible to exchange very low bandwidth information across non-local space-time connections that scientists discovery that send photons to known non-local destinations through non-locally connected space-time points, rather than any macroscopic gate.

But, probably the closest to theoretically possible science way to imagine such a technology would be to think about the interior of the gate (the frame of the gate would contain the "active ingredient interior" of it, so you could move it around) as some sort of near perfect Bose-Einstein condensate entangled with another near perfect Bose-Einstein condensate (each of which can only exist sustainably in very extreme conditions) in another gate.

Perhaps, somehow people and thinks can cross unscathed because passing through happens in such a tiny time frame, perhaps on the order of 10^2 units of Planck time (which are 5.39 × 10^-44 s each), that macroscopic objects don't have time to be assimilated and destroyed by the gate before the macroscopic object is through and recovering from the infinitessimally small journey in terms of space-time point hops traversed. It is a quick journey because you literally aren't travelling very far, you just have an inaccurate perception of the true nature of locallity which you developed over the course of your evolution of other primates because pondering such things for too long is not a good recipe for long term species survival when the universe that you have a sensory capacity to perceive is much difference from this under natural conditions.

Sure, it may seem infeasible, but we can at least conjure up the most plausible potential physical theory of the gates given what we have imagined is within the realm of possibility while doing it as little injustice as possible.


You can go with the Stargate answer - up, down, velocity, etc are defined by the ARRIVAL gate, not the departure gate. You pass through the first membrane, become an undifferentiated mass of data potentiality, then get rematerialised (reconstructed from the data) by the second gate.

The question to resolve is - where does the energy come from to materialise all that matter (E=mc squared and all)?

If the energy comes from the limitless potentiality pool between the gates, then you have just added energy to the system at the arrival end, so there will probably be some local shock-wave, sound, or heat wave. On the other hand, if you are pulling energy from the surrounding area to materialise the objects, you will have a snap frost every time something comes through the gate. (Stargate did the latter effect in the movie and about the first three episodes of Season 1, then just stopped it without explanation.)

  • $\begingroup$ I specifically do not want to do any matter-disassambly handwaving. My portals actually connect points in space, nothing else. Sorry if that isn't clear enough. $\endgroup$ – Tom Nov 16 '16 at 14:27
  • $\begingroup$ If you don't use matter-disassembly handwaving, and you have objects where half of outside Gate A and the other half is outside Gate B, then those objects are going to be ripped apart unless Gate A and Gate B have matched orbits (with regard to the central point of the Universe). The first atoms to pass through the gates would be ripped away if the velocity differential were as small as 10km/hr (think gravel rash when you come off a push-bike), then the next atoms, then the next. Effectively, anything sent through would be vaporised if the gates weren't completely matched in velocity. $\endgroup$ – Jnani Jenny Hale Nov 16 '16 at 14:35
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    $\begingroup$ @JnaniJennyHale There isn't some central point around which all matter in the universe orbits; what would that even mean? Motion is entirely relative, I think even Newton would agree with that, and Einstein certainly would! What we need to worry about here is momentum relative to the gate - would one half of the object have a velocity relative to the arrival gate that didn't match the other half's velocity relative to the departure gate? I'm not sure there's any fundamental reason why it would. $\endgroup$ – IMSoP Nov 16 '16 at 14:39
  • $\begingroup$ @IMAoP - I know. It was hyperbole to demonstrate to the OP why direct physical connection won't fly. $\endgroup$ – Jnani Jenny Hale Nov 16 '16 at 14:48
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    $\begingroup$ There are two gates. The object approaches Gate A. Let's say it is person, and they insert a finger. Let's say Gate B is exactly on the opposite side of the world, on the equator, so while Gate A is moving east at approx 1000 miles per hour, Gate B is moving at the same speed in the opposite direction. The fingertip strikes the side of the gate at about 2000km/hr. Our traveller pulls back in pain, to see the finger missing about half a cm off the top. $\endgroup$ – Jnani Jenny Hale Nov 16 '16 at 14:54

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