Thread: Portal 2 Ending Question (Spoilers)

During the battle with a rouge artificial intelligence unit the player places an orange portal within the facility (of course) and the only way of escaping becomes apparent by firing a blue portal to the moon. The pressures of the two obviously causes a suction towards the moon because of the pressure differential. (there are only two portals; orange and blue)

My question is this, if that portal were to remain linked to the moon and the pressure from the moon continuosly sucking the atmosphere of the earth, would this portal (roughly 10 meters in circumference (guesstimate)) be sufficient to drain all of the earths atmosphere into space? Akin to a space shuttle having a hull breach?

effectively, yes. The whole of the atmosphere would siphon off until the two sides of the portal were in equilibrium, much like the pressure difference found at the hole in the hull of a spaceship, or at the hole present at the bottom of a filled balloon.

Ahh thanks Arcane, I thought that it would.

Originally Posted by Quantime

During the battle with a rouge artificial intelligence unit the player places an orange portal within the facility (of course) and the only way of escaping becomes apparent by firing a blue portal to the moon. The pressures of the two obviously causes a suction towards the moon because of the pressure differential. (there are only two portals; orange and blue)

My question is this, if that portal were to remain linked to the moon and the pressure from the moon continuosly sucking the atmosphere of the earth, would this portal (roughly 10 meters in circumference (guesstimate)) be sufficient to drain all of the earths atmosphere into space? Akin to a space shuttle having a hull breach?

Who knows ?

What, in precise physical terms is a portal ? My sense is that it is a science-fiction gadget that is inconsistent with physics.

Physical laws are kinda like Pringles. It is hard to break just one law.

If a portal is something like a pipe there should be no problem. Gravity is what keeps the atmosphere from dissipating into space now.

Originally Posted by DrRocket

Originally Posted by Quantime

During the battle with a rouge artificial intelligence unit the player places an orange portal within the facility (of course) and the only way of escaping becomes apparent by firing a blue portal to the moon. The pressures of the two obviously causes a suction towards the moon because of the pressure differential. (there are only two portals; orange and blue)

My question is this, if that portal were to remain linked to the moon and the pressure from the moon continuosly sucking the atmosphere of the earth, would this portal (roughly 10 meters in circumference (guesstimate)) be sufficient to drain all of the earths atmosphere into space? Akin to a space shuttle having a hull breach?

Who knows ?

What, in precise physical terms is a portal ? My sense is that it is a science-fiction gadget that is inconsistent with physics.

Physical laws are kinda like Pringles. It is hard to break just one law.

If a portal is something like a pipe there should be no problem. Gravity is what keeps the atmosphere from dissipating into space now.

http://en.wikipedia.org/wiki/Portal_2

DrRocket i think you may enjoy that game actually

The Portal device projects a ovular hole onto a wall or other flat surface which can either be a blue or orange portal. Once firing this one can then fire the other colour and the two portals become linked.

So for instance if I fired a portal on the side of the white House in Washington DC and then portal outside the front gates I would be able to walk through the hole in the floor outside the gates and end up falling at a different angle off the side of the white house, and vice versa. With portals momentum, angle, speed and direction are all conserved.

With reference to my question one portal happens to be on the floor of a science lab so to speak, and then to escape the rouge artificial intelligence unit one fires a portal to the moon, the two then become connected, the portal on the moon happens to be facing you and the hole in the floor up at the sky so that when you look through the orange portal in the science lab you are actually looking up at space at a 180 degree angle relative from the moons surface from the blue portal. If you like here is the video that shows this:

Portal 2 Ending

Watch from about 04:07 to 05:38

Originally Posted by Quantime

With portals momentum, angle, speed and direction are all conserved.

Form the little I read on the Wikipedia page, momentum is not conserved. The page shows a diagram in which the person drops vertically into a portal and then comes out of another portal which is at a right angle to the first. If momentum were truely conserved, he would come out of the second with the eaxct same momentum as he had going in. IOW, instead of his velocity being from the right to left as he leaves the portal, it would still be downward.

Another example would be jumping into one portal at the equator and come out in another on the opposite side of the world. If momentum were conserved, you would find yourself moving at some 2000 mph relative to the ground when you exit. So either the portals don't obey the conservation of momentum or they store and release momentum in some way to achieve the desired effect.

Energy is obviously not conserved either, as shown by the link you gave. The Moon is at a much higher gravitational potential than the surface of the Earth is, and the pressure difference between Earth normal pressure and vacuum would not create enough energy to overcome that energy difference. The portals themselves would have to provide the additional energy from some other source.

So the answer to your question is that, according to the rules of the game, what is shown will happen.

Yes what I meant was the angle changes in accordance with what angle you went in.

...he would come out of the second with the eaxct same momentum as he had going in. IOW, instead of his velocity being from the right to left as he leaves the portal, it would still be downward.

Wouldn't the portal on the floor as it faces outwards from the wall, the angle of the blue portal is 180 degrees if you look at the floor, and 90 degrees relative to the orange portal on the wall In other words the second that the momentum gained from gravity is then conserved through the blue portal then out of the orange portal, seeing as the orange portal is at a 90 degree angle to the earth and gravity the momentum changes the second you leave the orange portal... is this what you meant? 'Momentum' being conserved is up until one enters the blue portal and leaves the orange portal, at which point momentum changes due to the new angle and the force of gravity being exerted on the player relative to their previous velocity out of the portal and the player is able to reach that platform.

Another example would be jumping into one portal at the equator and come out in another on the opposite side of the world. If momentum were conserved, you would find yourself moving at some 2000 mph relative to the ground when you exit. So either the portals don't obey the conservation of momentum or they store and release momentum in some way to achieve the desired effect.

Well if we theoretically imagine a player falling towards the earth into the blue portal, then with the orange being on the other side of the world, the momentum is conserved and the player would be flung out of the orange portal up towards the sky at the same velocity as went in, until of course gravity slows down that velocity gradually. In the game itself if you have two portals on the floor no matter the velocity through one you go out at the same until gravity slows you down, eventually the second you leave one portal you are almost re-entering it right away as gravity had slowed you down.

The Moon is at a much higher gravitational potential than the surface of the Earth is, and the pressure difference between Earth normal pressure and vacuum would not create enough energy to overcome that energy difference. The portals themselves would have to provide the additional energy from some other source.

Thanks for that bit, thats the answer to my question

Originally Posted by Quantime

Yes what I meant was the angle changes in accordance with what angle you went in.

...he would come out of the second with the eaxct same momentum as he had going in. IOW, instead of his velocity being from the right to left as he leaves the portal, it would still be downward.

Wouldn't the portal on the floor as it faces outwards from the wall, the angle of the blue portal is 180 degrees if you look at the floor, and 90 degrees relative to the orange portal on the wall In other words the second that the momentum gained from gravity is then conserved through the blue portal then out of the orange portal, seeing as the orange portal is at a 90 degree angle to the earth and gravity the momentum changes the second you leave the orange portal... is this what you meant? 'Momentum' being conserved is up until one enters the blue portal and leaves the orange portal, at which point momentum changes due to the new angle and the force of gravity being exerted on the player relative to their previous velocity out of the portal and the player is able to reach that platform.

Let's forget gravity for a sec. Just imagine that he enters one portal in the down direction at 1 meter /sec and leaves the second which is at a right angle to the first. By the game rules, the speed is conserved, but not the momentum or velocity. This is because the person leaves the second portal with a velocity that is 90 degrees to the velocity at which he entered the first portal. If velocity and momentum were conserved between the two portals, he should leave the second portal with exactly the same speed and direction(down) as he entered the first, regardless of how the secound portal is oriented.

In other words, if momentum were conserved, the situation where you jump into one portal on the floor and pop back out of another on the floor would not be possible. In fact, portals would likely always have to be 180 degrees to each other. This restriction, however, would hamper the game too much so it is dropped in the game.

Another example would be jumping into one portal at the equator and come out in another on the opposite side of the world. If momentum were conserved, you would find yourself moving at some 2000 mph relative to the ground when you exit. So either the portals don't obey the conservation of momentum or they store and release momentum in some way to achieve the desired effect.

Well if we theoretically imagine a player falling towards the earth into the blue portal, then with the orange being on the other side of the world, the momentum is conserved and the player would be flung out of the orange portal up towards the sky at the same velocity as went in, until of course gravity slows down that velocity gradually. In the game itself if you have two portals on the floor no matter the velocity through one you go out at the same until gravity slows you down, eventually the second you leave one portal you are almost re-entering it right away as gravity had slowed you down.

imagine that you are looking down at the rotating Earth from above the North pole. The surface of the Earth on one side is moving in the opposite direction to the other. If momentum were conserved between portals, a person entering one portal would carry his velocity to the other and this velocity would be opposite to the direction the surface of the Earth at the exit portal. He wouldn't even clear the portal before being slammed into its edge. The game avoids this by not truely conserving momentum between portals.

The game, in fact, is a little inconsistent is how it treats conservation of momentum. For example:

Put a portal in the floor and the ceiling. Jump into the portal in the floor while moving East. You will come out of the portal in the ceiling also moving East and both West-East and up_down momentum is conserved.

Now put the exit portal on the floor and repeat the experiment. You will again exit the portal moving East. East-West momentum is conserved, but up-down isn't. The exit from the portal in the second experiment is not at the same orientation to the portal as it was in the first experment. (imagine rotating the first portal in the ceiling 180 degrees through its North-South axis.)

The Moon is at a much higher gravitational potential than the surface of the Earth is, and the pressure difference between Earth normal pressure and vacuum would not create enough energy to overcome that energy difference. The portals themselves would have to provide the additional energy from some other source.

Thanks for that bit, thats the answer to my question

Actually, it might not. I'm a little short on time right now, so I'll explain why in my next post.

Okay, to pick up whee I left off:


The reason that my response might not fully answer your question is that it assumes that the portals conserve gravitational potential energy. In other words, if the portals had to take potential energy into account, then the scenario mentioned would probably not work.

However, the examples I've seen from the game indicate that potential energy is ignored. Take for instance the following scenerio:

You are standing on a platform that is 100 ft above the floor. you wish to get to a platform 50 ft higher than you are. There is a third platform 50 ft lower than you are.
The game would allow you to do the following:
Put a portal on the floor that you can jump into from your platform. Put a second portal on the third platform.
Jump into the portal in the floor, picking up speed as you fall 100 ft. Leave the second portal going upward at the speed to entered the first, giving you enough speed for your trajectory to carry you to the 2nd platform, which is 100 ft above the exit portal.

If the portals conserved potential energy, this would not work, since you could not end up with more energy than you started with. So when you leave the exit portal you would only be moving fast enough to be carried 50 ft above it, or back to your original starting height. (the loss of exit speed in accounted for by the difference in gravitational potential between the two portal.)

Thus it is apparent the the game ignores gravitational potential difference between portals, and thus by the game's rules, the portal on the moon trick would work.

Put another way, you really can't use the laws of physics to determine what is to isn't possible in the game because the game play's a little loose with the laws of physics to begin with.

Ah now I understand, thanks for explaining that Janus I appreciate it.