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Comment by ramidarigaz | Hacker News Reader

Hmmm... I don't think your analogy is correct. There is a very solid reason that all the air in the room will never only be in one half of that room. It's a matter of pressure, not probability. I don't think the 'rogue' planets are subject to such things, and on a sufficiently long time scale, it could very well be possible for one to travel through our system.

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This is false, pressure is the result of atomic collisions with things contained within the gas as the atoms fly around at high velocity. It's extremely unlikely that a large percentage of a large number of oxygen atoms will randomly fly into the same area at once, but it's not completely impossible. It is governed by probability.

Refresher on pressure: http://littleshop.physics.colostate.edu/activities/atmos1/Wh...

Actually, the analogy is rather correct. They both describe highly improbable events.

The gas molecules in the air don't know anything about the room's overall pressure, and don't individually obey any "pneumatic" laws. Pressure, in essence, is just a huge amount of molecules bouncing off a surface.

The air in a room is usually very evenly distributed, because it would be extremely unlikely that all the molecules happened to be in the same half.

Here's a link that might explain it better: http://webs.morningside.edu/slaven/physics/entropy/entropy3....

In support of what the others have said, the reason that we say all of the air in a room will end up on one side is the second law of thermodynamics: entropy in a closed system only increases. That is statistical mechanics, which is very much a matter of probability. The probability that the second law of thermodynamics will be violated is so vanishingly small that we say it will never happen.

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