Even though this question is inspired by the computer game Portal 2, I’d like to think it has a semi-factual answer. However, as we’re dealing with Science! rather than actual, real world Science, I figured GD was the place for it…
It goes without saying there’s a significant spoiler for the game ahead. If you haven’t played it and intend to, or haven’t finished yet, now would be an excellent time to stop reading and go and play the game.
If you’re not familiar with the Portal games, the idea is to solve a series of puzzles in a test chamber facility using a gun that basically shoots portals which allow you to “teleport” through one portal and appear out of the other one somewhere else in the room. Also the computer mainframe governing the test is insane.
Ok, with that out of the way, at the conclusion of the Portal 2, there is a sequence in which your character fires one portal on the floor underneath the villain and fires the other one onto the surface of the moon, effectively sucking the villain (and almost yourself) into space.
Now, here’s my question: Assuming the Portal technology in the game actually existed in real life, what would realistically happen if you created a Portal between somewhere on Earth and the surface of the Moon? Would Earth’s oxygen and atmosphere suddenly vanish into space? Something even worse? Or maybe even nothing at all?
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.
In order to complicate your maths a bit, I’d say the speed at which air rushes through the portal slows down as the Moon’s atmosphere starts building up (assuming the Moon’s gravity is high enough to actually keep one up and the air is not just sucked right into space - I do not know this). Which should give us even more time and eventually the pressure differential would even out.
Also, because someone’s bound to make that reference and we might as well get it out of the way: I’m in space. I’minspace. SPAAAAAAaaaaaaace !
Weird. I was thinking about asking this exact question but hadn’t got around to typing it yet. Thanks for saving me the effort.
One additional point I was wondering about - assuming the portal is on the side of the moon facing Earth and the geyser of air is fast enough to escape the moon’s gravity, would the air eventually fall back to Earth?
Also, is the volume escaping at the Earth portal end signficant enough to affect weather systems? Would you end up creating a permanent low pressure area?
I wouldn’t have thought so - the moon is a really long way away. To scale, if the moon was the size of a basketball, the moon would be about the size of a tennis ball, and 9 yards away. A little jet of gas on the moon isn’t going to make it all the way back to Earth significantly.
Statistically, of course, some small fraction of the gases will make it back to Earth just because they’re dispersing - and especially when the moon is nearly between us and the sun, as the solar wind will push it back toward us (in other cases, the solar wind will tend to prevent the gases making it back to Earth).
Whoa, the moon is the size of a basketball and the size of a tennis ball? This really is Portal physics!
Back to the OP, it just occurred to me that gravity doesn’t seem to go through portals. Otherwise, you would be pulled toward a wall portal with the other side in the floor. I was thinking that Earth’s gravity would act to counter some of the out-rushing force, but I guess it wouldn’t.
I still wish I could get one to replace my shower curtain.
Here’s a discussion from Ask MetaFilter on the exact same topic. Note in particular that the molecules of air that go through the portal are not, for the most part, moving fast enough to escape the Moon’s gravity, so the air wouldn’t be lost immediately. (It would probably slowly leak away into space, but not before hanging around for a bit.)
Which also means that any solid objects that got sucked through (like, say, Aperture Science Personality Construct Cores) also wouldn’t have enough energy to go into orbit.
And this question really could be in GQ. “How quickly would air flow from a 1 atm environment to vacuum, through a 2 square meter opening?” isn’t exactly a contentious question.
I wasn’t 100% sure whether or not the subject matter (It’s a computer game in which you have a teleportal gun, after all) was “serious” enough for GQ… works for me if it is though!
I have to say I’m surprised the effects probably wouldn’t be more serious, though… it just strikes me as one of those things which would have Severe Consequences, or at least more of an effect than opening the door into a wind tunnel.
There was a SyFi story written years ago, by Harry Harrison I believe, in which a “portal” had been accidentally created that was causing the atmosphere to be sucked into space. Various methods were used to disrupt the leak, but to no avail.
The main character offered to solve the problem if he could have legal rights to the area of the leak. This was granted and he solved the problem by creating two hemispheres that were raised into position and enclosing the portal.
Problem solved! He’d installed a valve on one of the hemispheres and was going to sell vacuum to recoup his costs.
“Speedy thing goes in, speedy thing comes out” - I haven’t done the calculations, but I believe atmospheric pressure at Earth’s surface is enough to force air through the portal and out of the moon’s gravity field. Think of it like this: if I drop an object from infinitely high altitude into Earth’s portal, it’ll have enough energy to escape the moon’s gravity, right? In other words, Earth’s gravity potential well is deeper than the moon’s.
For portals to work, I believe gravity fields (and their first derivatives) have to be consistent across portals - i.e. no perpetual motion machines. Maybe someone can come up with the implications of this.
See the pertinent comment 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”.
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.
I prefer the fact core to the space core. Who knew that one in six children will at some point in their lives be abducted by the Dutch?
I wonder if I might add another portal-related question to this thread…
I’m in a room 9 feet tall - I shoot a portal on the ceiling and another on the floor directly below it. I then take a steel rod that is a smidge longer than 9 feet and lower it through the portal in the floor.
It emerges from the portal in the ceiling and I adjust it into a vertical orientation. I then weld the bottom end of the rod to its own top.
What have I created? If I look through the portals, I now appear to have a rod of infinite length, or is it a 9 foot long ring that just happens not to be curved? What happens next?
The Moon’s gravity is not enough to hold any kind of atmosphere in the long run. The atmosphere would bleed off into nothingness, but it would take centuries, maybe longer, to do so. However, it would hold an atmosphere long enough that the concern you raise would begin to matter-- a rising atmospheric pressure would slow the escape of gas through the Portal.
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.
Thanks - yeah - I was trying to get my head around whether the apparent recursive nature of the thing made a difference, but that’s just a visual quirk.
