I understand the atmospheric equilibrium concept... but not the why behind it. In other words, when you shoot a window out in space station what factors decide that the higher state of compression of the two burst out into the lower until a balance is established? Side note: A question popped into my head while typing the first question. What causes the atmosphere of our planet to stay put (remain stable)? I want to say gravity and temperature, but figured I'd throw it out there anyway.