I do not claim to know that much, but how so? I have heard of so many people aging their beer in kegs... From what I have heard, they do this under a bit of pressure. You just need to check it on occasion to make sure the pressure hasn't dipped to far. How do people age their beer in kegs if they cannot seal them with CO2 and then age them?
Your beer will absorb Co2. How much Co2 it will absorb is based on pressure and temperature (Per the chart I linked above)
For instance:
Your un-carbonated beer will absorb twice its volume in Co2 if you apply 16 PSI at 60 degrees. This takes time. The volume of headspace in your keg is let's say 1/10th of the volume of the beer. If you apply 16 PSI to that headspace, your beer will absorb that Co2, lowering the pressure (Because you don't have a Co2 bottle feeding it more gas to keep up with the Co2 absorbed by your beer). Only once your beer has absorbed twice it's volume in gas, at that pressure and temperature, will it stop absorbing Co2 from the headspace. This is what we call "balanced".
Once balanced, you can remove the gas from the keg, and have "positive" pressure holding the lid tight. This is because your beer can't absorb any more Co2 when applied at 16 PSI, so that pressure remains in the headspace.
If the beer is under that balance, it will absorb the gas that's creating the pressure in the headspace. No more pressure to hold the lid shut.
Probably clear as mud...
Beer is like a sponge:
If I have a glass with 10oz of water in it and I shove a sponge into that glass of water, and the capacity of that sponge is 12oz, it'll absorb all of the water, and the sponge (Your beer) will be exposed to air.
If I want there to be water above the sponge (Co2 above the beer, in your case) I have to add more water (Co2) to the glass -
Until the Sponge is saturated, and can absorb no more water.
If I put the dry sponge in the empty glass, and throw 5 oz of water at it really fast, it's still going to absorb that 5 oz and be exposed to the air.
You have to saturate the beer with Co2 before it will quit absorbing it. Until that point, any Co2 you add to the headspace will be consumed by the beer.
Hell, now I'm just confusing myself