# A Science! Question \[Portal 2 spoilers\] **URL:** \ **Category:** Factual Questions\ **Created:** [January 13, 2012, 10:36am UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380 "2012-01-13T10:36:59Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [January 15, 2012, 12:17am UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/21 "2012-01-15T00:17:56Z")
> [@MikeS](#): > > See the [pertinent comment](http://ask.metafilter.com/197386/Thinking-with-Portals#2841398) in the Ask MetaFilter thread linked above (which I was the one who actually posted over there.) The flaw in your reasoning is that the molecules in Earth’s atmosphere aren’t moving nearly as fast as they would be if they had been “dropped from infinity”. I’m not sure speed of the molecules is sufficient, because speed is only related to temperature. What’s forcing the air out is pressure, which may not influence speed. > [@MikeS](#): > > The other thing that may be tripping you up is that portals don’t conserve energy; consider a situation where you fall through a portal on the floor and come out on the ceiling directly above it, in a loop. As far as I can tell, the game treats the gravitational acceleration vector field as discontinuous when you pass through a portal. Yes, it’s not consistent in the game. This depends on how realistic you want the scenario to be. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [January 15, 2012, 1:02am UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/22 "2012-01-15T01:02:08Z")
My vary vague memory here - it has been decades since I read the book. In Larry Niven’s Ringworld he describes a storm created by the atmosphere leaking down a huge crater - with a hole at its bottom - that has been created by a meteor impact onto Ringworld. Earlier in the book the protagonists observe the crater from the other side of Ringworld as they approach. The point being the Niven, in typical hard SciFi, noted that this damage would take a very very long time to actually rain the atmosphere. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 15, 2012, 1:21am UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/23 "2012-01-15T01:21:00Z")
> [@](#): > > I’m not sure speed of the molecules is sufficient, because speed is only related to temperature. What’s forcing the air out is pressure, which may not influence speed. It amounts to the same thing. Fundamentally, all a gas is is a bunch of particles moving around and occasionally colliding with each other or with the boundaries of their enclosure (if any). Nothing can happen in a gas faster than the thermal speed, and speeds will in general be less because the individual molecules aren’t moving in exactly the direction you want. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [January 15, 2012, 2:03am UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/24 "2012-01-15T02:03:28Z")
> [@Bryan\_Ekers](#): > > Well, assuming the portal is, say, two meters wide and the wind rushing through it is at hurricane speed (~150 km/h), the portal will evacuate 471,000 cubic meters of atmosphere an hour. The total volume of Earth’s atmosphere is about 17.5 x 10[sup]21[/sup] cubic meters, giving us about 4 billion years to find a big plug. I’m too lazy to check your math, but I hope you didn’t solve for zero, because we’d have to find a plug long before the atmosphere was completely gone. I’m guessing you’re off by an order of magnitude. ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [January 15, 2012, 5:24am UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/25 "2012-01-15T05:24:50Z")
What about energy? Would wayward cosmic beams of X get sucked through the portal, bypassing Earth’s atmosphere, and create some sort of localized radiation zone? ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [January 15, 2012, 9:44am UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/26 "2012-01-15T09:44:04Z")
> [@Chronos](#): > > It amounts to the same thing. Fundamentally, all a gas is is a bunch of particles moving around and occasionally colliding with each other or with the boundaries of their enclosure (if any). Nothing can happen in a gas faster than the thermal speed, and speeds will in general be less because the individual molecules aren’t moving in exactly the direction you want. The average speed refers to RMS, and doesn’t define a maximum. If what you said is true, why hasn’t the moon trapped an atmosphere? ---
**Author:** ![chorpler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chorpler/32/2888_2.png) [@chorpler](https://boards.straightdope.com/u/chorpler)\ **Post date:** [January 15, 2012, 5:34pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/27 "2012-01-15T17:34:08Z")
> [@Francis\_Vaughan](#): > > My vary vague memory here - it has been decades since I read the book. In Larry Niven’s Ringworld he describes a storm created by the atmosphere leaking down a huge crater - with a hole at its bottom - that has been created by a meteor impact onto Ringworld. Earlier in the book the protagonists observe the crater from the other side of Ringworld as they approach. The point being the Niven, in typical hard SciFi, noted that this damage would take a very very long time to actually rain the atmosphere. The hole causing the eye-storm was small, but there was also the much much larger Fist-of-God hole, which Louis Wu observed was large enough to let all the air out of the Ringworld fairly quickly if it hadn’t been way up outside the atmosphere. And then in Ringworld’s Children an ARM ship has an antimatter containment failure and blows a huge hole in the Ringworld that requires an enormous fusion-powered torus to temporarily block the air from leaking out … and can you believe some people don’t like that book?! ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 15, 2012, 8:26pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/28 "2012-01-15T20:26:01Z")
> [@](#): > > The average speed refers to RMS, and doesn’t define a maximum. If what you said is true, why hasn’t the moon trapped an atmosphere? OK, I should have said that nothing _significant_ can happen at faster than the thermal speed. There will be a few outlier molecules that are significantly faster, but not enough to really matter on the macro scale. And just to be complete, I should also specify that I’m referring to neutral gases, not plasmas where magnetic effects can be significant and where most things happen at the Alfven speed. ---
**Author:** ![Munch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/munch/32/5281_2.png) [@Munch](https://boards.straightdope.com/u/Munch)\ **Post date:** [January 17, 2012, 7:41pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/29 "2012-01-17T19:41:53Z")
> [@appleciders](#): > > It is, I think, a nine foot long ring curved through whatever dimension Portals work through. It can’t be of infinite length, because if you pick it up and move it around, it weighs no more than it did when it was a simple rod. Would this transdimensional ring start to spin if you let go of it? What would restrict it from achieving near speeds approaching the speed of light? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 17, 2012, 7:53pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/30 "2012-01-17T19:53:26Z")
Portals of the sort in the game are impossible according to everything we know of science, so if they’re possible, then our knowledge of science is seriously flawed. Your questions cannot be answered without knowledge of that new physics, which is currently unavailable to us. ---
**Author:** ![Chessic\_Sense](https://avatars.discourse-cdn.com/v4/letter/c/7c8e57/32.png) [@Chessic\_Sense](https://boards.straightdope.com/u/Chessic_Sense)\ **Post date:** [January 17, 2012, 8:15pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/31 "2012-01-17T20:15:02Z")
> [@Chronos](#): > > It amounts to the same thing. Fundamentally, all a gas is is a bunch of particles moving around and occasionally colliding with each other _Occasionally?_ Only if [10 billion times per second](http://galileo.phys.virginia.edu/classes/152.mf1i.spring02/MolecularCollisions.htm) is “occasionally.” Without frequent collisions, you can’t have the Magnus effect. Hell, airplanes wouldn’t fly otherwise! Secondly, I think some of you are making a common mistake about Portal physics. If gravity were to pull you through a portal, there’s no reason to think it would pull you back in the other side. It would push you away from the exit portal. Think of it like this- if I had a floor and ceiling arrangement, and held and arrow facing down, and stuck it through the floor portal, where would it point when it came out the other side? Toward the floor, of course. That would be the gravity vector. So saying “you’re not sucked back in” doesn’t prove or disprove whether forces are transmitted through portals. As far as I know, we still don’t know. Thirdly, you don’t need to weld a pole together to get a self-sustaining rod. Just put a portal on the wall and one on the floor, such that they nearly intersect. Place a short rod through the hole, slanted toward the ceiling. It’ll come out of the floor portal pointing away from the wall. Then drop the rod. The part sticking out of the wall will drop toward the wall. The floor piece will slide toward the wall as well, eventually intersecting and holding itself up. ---
**Author:** ![Munch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/munch/32/5281_2.png) [@Munch](https://boards.straightdope.com/u/Munch)\ **Post date:** [January 17, 2012, 8:34pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/32 "2012-01-17T20:34:27Z")
> [@Chronos](#): > > Portals of the sort in the game are impossible according to everything we know of science, so if they’re possible, then our knowledge of science is seriously flawed. Your questions cannot be answered without knowledge of that new physics, which is currently unavailable to us. Really? I had no idea. Do hypothetical questions not exist either? ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [January 17, 2012, 9:58pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/33 "2012-01-17T21:58:49Z")
> [@Munch](#): > > Would this transdimensional ring start to spin if you let go of it? What would restrict it from achieving near speeds approaching the speed of light? Nothing at all; this is pretty much what it would do. There’s no such thing as conservation of energy in the world of Portal (see below). > [@Chronos](#): > > Portals of the sort in the game are impossible according to everything we know of science, so if they’re possible, then our knowledge of science is seriously flawed. Your questions cannot be answered without knowledge of that new physics, which is currently unavailable to us. I wouldn’t say that it’s as bad as all that. You’re basically doing classical mechanics with a constant gravitational acceleration field, along with some identifications (in the topological sense) of the space you’re looking at. I will certainly grant that there’s no useful notion of conservation of energy or momentum in this world, but that doesn’t mean we can’t do basic things like compute trajectories. > [@Chessic\_Sense](#): > > Secondly, I think some of you are making a common mistake about Portal physics. If gravity were to pull you through a portal, there’s no reason to think it would pull you back in the other side. It would push you away from the exit portal. Think of it like this- if I had a floor and ceiling arrangement, and held and arrow facing down, and stuck it through the floor portal, where would it point when it came out the other side? Toward the floor, of course. That would be the gravity vector. > > So saying “you’re not sucked back in” doesn’t prove or disprove whether forces are transmitted through portals. As far as I know, we still don’t know. See [this trailer, at about 1:55.](http://www.youtube.com/watch?v=GWzmL05OlYA&t=1m54s) There’s a brief clip of a security turret oscillating between two portals in the floor. I don’t think this would be possible unless the gravitational force field on one side of the Portal was at least somewhat insulated from the other side. Plus, let’s be honest: this is a computer game, and the simplest way to get an effect like this (in terms of computational overhead) is to not have to deal with the effects of gravity leaking through portals. It’s probably hard enough to simulate the physics of this world without having to recalculate the gravity field every time you move a portal. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 17, 2012, 10:23pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/34 "2012-01-17T22:23:22Z")
> [@](#): > > Occasionally? Only if 10 billion times per second is “occasionally.” Without frequent collisions, you can’t have the Magnus effect. Hell, airplanes wouldn’t fly otherwise! A gas _can_ have frequent collisions, but it doesn’t _need_ to: Almost any level of collisions at all is enough to behave as a gas. In particular, the mean free path of an air molecule between collisions with other air molecules is macroscopic, but a volume of air smaller than that still acts like a gas in every sense. ---
**Author:** ![Munch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/munch/32/5281_2.png) [@Munch](https://boards.straightdope.com/u/Munch)\ **Post date:** [January 18, 2012, 2:11pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/35 "2012-01-18T14:11:47Z")
> [@MikeS](#): > > Nothing at all; this is pretty much what it would do. There’s no such thing as conservation of energy in the world of Portal (see below). So in the “real” world (where portals are theoretically possible), would friction with the air create enough heat to superheat the metal bar until…what? Either the bar melts or the air around it explodes? Could you create a giant super generator by wrapping the bar in copper coil? ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [January 18, 2012, 6:01pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/36 "2012-01-18T18:01:48Z")
Yeah, I would guess that it would heat up, melt, and then possibly break apart due to the [Plateau-Rayleigh instability](http://en.wikipedia.org/wiki/Plateau%E2%80%93Rayleigh_instability). I don’t think you could make a generator out of this, though; the magnetic flux through your copper coil is going to always be the same, and you need a change in flux to create an EMF. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 18, 2012, 9:02pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/37 "2012-01-18T21:02:58Z")
> [@](#): > > So in the “real” world (where portals are theoretically possible), would friction with the air create enough heat to superheat the metal bar until…what? Any sort of portal which would be possible in the real world would have to obey conservation of energy, and so you wouldn’t get the accelerating bar to begin with. If you had a portal connecting the Earth and the Moon, for instance, there would have to be an extremely strong gravitational field in the vicinity of the portal, such that it would take just as much energy to pass through the portal as it would to reach the Moon through normal space. ---
**Author:** ![Munch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/munch/32/5281_2.png) [@Munch](https://boards.straightdope.com/u/Munch)\ **Post date:** [January 18, 2012, 9:40pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/38 "2012-01-18T21:40:50Z")
> [@Chronos](#): > > Any sort of portal which would be possible in the real world would have to obey conservation of energy, and so you wouldn’t get the accelerating bar to begin with. If you had a portal connecting the Earth and the Moon, for instance, there would have to be an extremely strong gravitational field in the vicinity of the portal, such that it would take just as much energy to pass through the portal as it would to reach the Moon through normal space. My line of questioning picked up from applecider’s hypothetical question, which involved not a portal on Earth and a portal on the Moon, but rather a portal on the ceiling and a portal on the floor - thus a continuously falling pipe/bar that is continuously accelerating. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [January 18, 2012, 9:56pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/39 "2012-01-18T21:56:45Z")
> [@Munch](#): > > My line of questioning picked up from applecider’s hypothetical question, which involved not a portal on Earth and a portal on the Moon, but rather a portal on the ceiling and a portal on the floor - thus a continuously falling pipe/bar that is continuously accelerating. I think there’s some confusion here. In any world in which portals work as in the game, energy is not conserved. Or, equivalently, if energy is conserved, portals cannot work as they do in the game. A portal pair between the floor and ceiling violates conservation of energy just as much as a portal pair between the Earth and the Moon. So by the “real world” in Post #35, did you mean “a world in which energy is conserved” or “a world in which portals work as in the game”? Because you can’t have both. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 18, 2012, 10:37pm UTC](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380/40 "2012-01-18T22:37:21Z")
> [@](#): > > My line of questioning picked up from applecider’s hypothetical question, which involved not a portal on Earth and a portal on the Moon, but rather a portal on the ceiling and a portal on the floor - thus a continuously falling pipe/bar that is continuously accelerating Same problem, though. An object (it doesn’t have to be a continuous bar) falling through the portal-loop would gain speed while it’s away from the portal, and lose speed while actually going through it, in a way that would balance out overall (except you’d still lose some additional energy from friction and the like). Effectively, you’d have a funny-shaped flywheel or pendulum, where at any given time some mass is going “up” and some is going “down”, or where the same mass alternates going “up” and “down”. [Previous page](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380.md?page=1) [Next page](https://boards.straightdope.com/t/a-science-question-portal-2-spoilers/609380.md?page=3)