I have this player with some portal based technology that wanted to build a moving base. His technology works like this: You need 2 portals connecting two spaces, both go in both ways, and conserve momentum. Furthermore, if you were to stick your arm through one of them, and then moved the other one through the air, your arm would follow without you putting any effort.

Illustration of the moving portals

Knowing this, he then built a couple of portal-rings. Erected a big pillar somewhere in his state, and put one of the portals at its base. Put the other somewhere, and built a whole dome that hung from the pillar. Since he only needed enough energy to move the portal-ring and those ignore most physical issues, he said he could move this whole dome at his will. At first I said no… The idea was cool and all, but I thought there would be friction to overcome and it would strain the main pillar too much. So he could move it… but very slowly. So… he slowly moved it out to space and said that there would be no problem then. And… I conceded. It was a game and it was a great idea.

In our game we assumed that since the dome was connected to earth through the pillar and portals, there was earth’s gravity in it, and since he could move the portal at will and the dome would just follow – being no resistance at all in space – he could move it at his top speed at the moment.

How would gravity function in the dome? Would we have a relatively vertical force of gravity like are we are used to? Or would gravity point towards the portal?

Illustration about gravity issues

Would the absence of friction really eliminate all strain on the pillar? Somehow I think that pulling all that mass can’t be free.

What improvements could be made to the formula to avoid these or other problems?


3 Answers 3


If anything, it would point directly towards the portal.

I am assuming that force is transmitted through the portal as well. For instance, if you open a portal from Earth to space with no dome, the air pressure difference would cause air to flow from the Earth portal to the space portal.

The best you can assume is a line of sight transmission of forces for a portal.

He could design the base with this in mind, put a large hemisphere in the middle to walk around on, it would be like walking on a very small planet with Earth gravity.

  • $\begingroup$ If the force of air pressure is transmitted, would gravity also be transmitted? This would eventually form a sphere of air around the portal when the pressure forces were balanced by gravity forces. $\endgroup$
    – Jim2B
    Commented Feb 11, 2016 at 5:03
  • $\begingroup$ @Jim2B Yeah, that's an interesting point. $\endgroup$
    – Samuel
    Commented Feb 11, 2016 at 5:15

It took me several readings to finally understand how this thing was actually supposed to work. Having the one portal at a pole and the other at a 'cap'/dome that gets pushed up by the pole as the first portal moves along the pole.

So the first problem with the current design is the portal should be at the top of the pole, not the bottom. Putting the pole at the bottom of the pole will have the pole 'fall' into the portal until it reaches gravitational equilibrium. and will happen fast, likely shattering through the dome at the other end.

The more intelligent scenario would be to put the ring at the top of the pole, and have the ring go DOWN the pole grown up under the dome. The farther down the portal goes on the pole, the higher the dome will travel. I would probably leave the second portal on the ground under the dome instead of attaching it to the dome or you will be inverting your pole and it will stand on it head under your dome.

This of course does mean that the pole/tower and the ground/foundation would need to be able to support the weight of the dome on at it's top. It also means that regular physics for moving the dome through the atmosphere would still apply. The only part that would be 'magic' would the part of 'moving' as much or as little of the pole under the dome as you want as fast as you want.

It would also give enemies 2 locations to attack your dome.

  • $\begingroup$ It seems I didn't explain it well enough! The portal on earth would be at the bottom of the pillar, yes, but it would be immobile. The other one is the one that we want to move. Like this, the Dome would always be resting on the pillar, that's resting on earth through the portal. Displacing the second portal around wouldn't make the pillar shorter nor longer, it would just... move the pillar, and the dome, in 3D wherever you want. And yeah, we now have two locations to deffend, but that was accounted for. $\endgroup$
    – Helwar
    Commented Feb 11, 2016 at 14:58
  • $\begingroup$ @Helwar That doesn't make any sense. If I understand it, you really just made a ufo and the pillar has nothing to do with it. Also if you put a portal AT THE BOTTOM of the pillar, it will FALL INTO THE PORTAL from gravity, it won't be standing on anything. $\endgroup$
    – bowlturner
    Commented Feb 11, 2016 at 15:24

Sooo... if you happen to know the television show Stargate, there is one episode that might be interesting for you ("A matter of time" I think the original name was).

They do have their own... portal (wormhole) which is connected to a black hole at the other side. They do experience a submission of gravity too. I wonder if they did use the same explanation in original as they used in my synchronized version, but is looks like their wormhole works like a lens for that gravity, pulling stuff towards it from all directions.

Sadly, most time stuff that does interact with it comes from in front of it... still, that would make your second picture the correct answer, but of course its open for debate if they did explain this correctly at all.

When looking that show, you may encounter even a graphic that shows how the time/gravity effect does spread in their case; this one does hint for your second approach too.

If take this to "mashup with currently known science" and we assume gravity force as something transmitted by higgs-bosons or some other particles, than they would certainly flow to your portal like water into a sink, so... I would vote for the second approach too.

But the gate does have one feature that is superior to your portals: it wont let air pass through, so you don't have to expect your oxygen to escape to the other side...

One last thing - having a sudden source of gravity of the power of a planet will surly shake things around if you throw it inside an asteroid belt. And I can't stop pondering what may happen if you start experimenting with this, like trying to build an anti-gravity device x) Like: if the caster place it upside-down, will you get an pushing-effect at the other side? If you place the "exit" in the same manner, things in font of it might move away from wherever they are pointing right now. Uh... well, Maybe another question: how to build an spaceship-engine by using this kind of gravity transmitting portal technology...


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