The physics of portals

Fuckin' portals - how do they work?You heard it like me, someone just asked about the physics of Aperture Science's neat Portal Gun. I'll try to give an account of what we know from the material that Aperture recently made available and from what can be deduced from demonstrations of the product.

Unfortunately I've been unable to get any additional information or confirmation of my findings from Aperture themselves as the only person I was able to contact, a Mrs. Glados, told me on the phone that "all the persons who are still alive are currently unavailable, but as you seem to have an interest in doing science, I'd be happy to show you around our test chambers. We are open 24/7. I hope you like orange. Can you bring some cake? I don't want to lie to you: we seem to have run out."

So let's get going, shall we? Here's how the gun works:

The Portal Gun (source Aperture Science)

The central part of the Portal Gun is a miniature black hole with a Schwarzschild diameter of a few centimeters. Now black holes this size usually radiate strong amounts of Hawking radiation, resulting in their rapid evaporation. This is counterbalanced by an extraordinarily simple device, in the form of a cooling fan that blows evaporated virtual particles back onto the black hole's horizon.

Above and below the black hole, there are two ring singularity rings that can be made to rotate one way or another in order to communicate angular momentum to the black hole (this is why operating the gun while moving creates the impression that it is being gently pulled out of your hands, by gyroscopic effect). Making the hole rotate results in the event horizon opening up and revealing the ring singularity inside.

The fan is then sped up suddenly behind the singularity to blow part of it forward into the portal intake manifold, focused by the three quantum shaping prongs that you can see moving around the front end of the gun when firing a portal. The focalization is necessary but not sufficient, as the singularity needs to be stopped by a surface charged with Z bosons. This is why Aperture is building special panels for their test chambers, the only surfaces that can stop portals in place. Whenever you attempt to fire a portal on a different surface, the portal continues its course through space unaffected while the dye is stopped by the wall and produces a spray of color at the impact point. This of course makes portal guns unusable in practice outside of a specially equipped test facility.

It's worth mentioning at this point that it is a trivial cosmetic detail that orange or blue dye is injected around the singularity at the precise moment when it passes through the intake manifold. The dye then enters into the gravitational orbit of the ring singularity and remains there as long as the portal remains active, creating the rotating colored shimmer that we all know and love.

Now here is the tricky part: when you fire the second half of the portal, it is emitted as a second ring singularity that rotates counter to the orientation of the first one and most importantly while being entangled with it. It is this quantum gravitational entanglement that does the job of bridging space-time on both sides of the portal. Contrary to common belief, Aperture's portals work by creating a quantum tunneling channel between two locations and not at all by creating a wormhole. Creating wormholes requires considerably more energy, making the process unsuitable to the construction of portable devices. Furthermore, as Black Mesa recently showed, we do not know how to control which universe the other end of the wormhole comes from.

It is often asked whether portals are limited to connecting points in space or if they could permit time travel like wormholes do. Well, if you can find a way to aim in the direction of the past or future, which are unfortunately orthogonal to the three dimensions of space that we are familiar with, then yes, it is possible. Good luck with that.

Now that we understand how the gun works, we can look at the energetic consequences of punching tunnels into space. One thing that all people who have operated a portal gun report is that if they create a portal between two places that present a potential gravitational energy gradient (in layman terms, different altitudes), there is wind coming out of the top portal and entering the bottom portal. This wind gets stronger with the altitude difference.

This is very easy to understand as the difference in potential energy between the two ends of the portal manifests itself like any potential energy gradient: by a force from highest to lowest potential.

That leads us to an interesting point which is that air is affected by portals in exactly the same way that we or any massive object such as a weighted cube is. If for example you punch vertically aligned portals on the floor and ceiling of a test chamber, the air in the room will start falling through, creating a strong wind that will blow downwards, attracting passers by in virtue of the Venturi effect.

Another amusing consequence is that falling through such a portal pair, you can reach speeds much higher than the normal terminal velocity in the same conditions of pressure and temperature.

A gravitational turbine, as used by Aperture ScienceThis effect is actually used by Aperture Science to produce the considerable energy that their testing facility consumes: weighed cubes are left to fall between two portals in a tall well, and a turbine harvests the gravitational energy transformed into kinetic energy along the way.

Now of course the next question is where does this energy come from? Well, the portal itself carries little energy and it doesn't seem to decay as energy is harvested. Many speculations have been made about this but the most plausible explanation seems to be as follows.

Conservation of energy, as everyone knows, is not a principle in itself but rather is a consequence of the laws of physics being the same at all points in time. Ergo, all you have to do is to break the laws of physics in order for energy to stop being conserved. And you'll have to admit that a persisting quantum tunneling device is as weird as it gets.

The effect of this is that constants such as the fine structure constant or the gravitational constant are probably varying slightly as more stuff gets dumped into portals, possibly resulting eventually in atoms failing to retain electrons, galaxies to dissolve or the Sun to transform into a black hole. But don't worry too much, that should take at least a few centuries to happen if my calculations are right.

Well, this is it in a nutshell. I'm going to take questions now.

Archived comments

  • Skywalker said on Saturday, April 23, 2011

    Very cool and informative article! I just read "Physics of the Impossible" by Michio Kaku, which has a chapter about Teleportation. If I understood correctly, the time of his writing teleportation is possible on the atomic level, but teleporting larger objects will take many more years, perhaps centuries, due to the difficulty of maintaining coherence for large collections of atoms. At the end, he qualifies teleportation of complex molecules, perhaps even a virus or a living cell as a Class I impossibility. Teleporting larger objects (such as humans) is qualified as a Class II impossibility (which means it might take a few centuries before we are able to create and use portals like in the game). In any case, I hope your calculations are right :)
  • Willseph said on Wednesday, April 27, 2011

    Can you build me a portal gun? I locked my keys in the car.
  • James Bliss said on Wednesday, April 27, 2011

    A recent anecdotal report indicates that a vegetable (namely, a potato) impaled upon one of the three quantum shaping prongs does not affect the performance of the Portal Gun. Is this report in line with your explanation? Can you explain why this has no effect?
  • roncli said on Wednesday, April 27, 2011

    Looks like Mrs. Glados has commented on - and commended - your work. :)!/GLaDOS_2/status/61835900354691072
  • Wilson said on Wednesday, April 27, 2011

    "The central part of the Portal Gun is a miniature black hole with a Schwarzschild diameter of a few centimeters." I recently read "The Physics of Stargates" by Enrico Rodrigo. According to him, a black hole with a 3-centimeter Schwarzschild radius is three times as massive as the entire earth. "Above and below the black hole, there are two ring singularity rings..." "Aperture's portals work... not at all by creating a wormhole." Actually, according to the Rodrigo book a naked rotating ring singularity DOES form a wormhole connection to another universe. So I'm not sure that the portal gun could work as you've described.
  • bleroy said on Wednesday, April 27, 2011

    @Skywalker: portals do not work by quantum teleportation either: so-called teleportation really amounts to cloning the quantum state of an object, not transporting it to a different place. @Willseph: I'm afraid that would cost you a little more than what that car of yours is worth. @James: I'd like to see it reproduced before I give an opinion: we're trying to do science here. @Wilson: I'm afraid your understanding of quantum gravity leaves a lot to be desired.
  • thomas de jong said on Monday, May 2, 2011

    kun je met deze info echt een portaal geweer maken
  • christian chambers said on Saturday, February 22, 2014

    portal paradox time: A| if you take a wall and shoot a portal on it, then shoot a portal on an unattached wall. put the unattached wall piece with the portal and push it through the wall. or put a rod. what would happen? would multiple portals of one color appear, and if you go through the portal on the attached wall would you split into multiple versions of your self or clone? B| take two portals and and shoot them parallel to each other. get a rope or some belts and tie them together. increase the distance between the two portals. what would happen? C| put a portal on the floor and one on the ceiling. take a rod and hold it about half way. bind it to another small rod, then release it. what happens. and also if possible move the portals together and apart. what happens?
  • bleroy said on Saturday, February 22, 2014

    A. You could say that this is no different from mirrors facing each other, or cameras looking at a screen projecting what they see, or a Larsen effect, and that you'd get an infinite pattern of portals, but that would be naive. What would really happen is a curious case of cosmic censorship: the energetic cost of pushing the second portal into the first one diverges. The energy differences involved in moving objects through the portals being taken from the portal energy itself, not only would it take infinite energy to push the second portal in, but before you could even start, the portals would evaporate. B. The rope extends to the limits of its elasticity, then breaks. This is no different from tying a rope around a circle that can extend. C. Not sure what you mean. Whatever you drop into such a portal configuration accelerates until is reaches terminal velocity. Also, don't assume that moving portals has zero energy cost.