Open a bottle of soda too fast: the idea here is too much pressure differential. What John said: it creates bubbles that are too big to eliminate and now you have to wait for them to get re-absorbed before you can off-gas.
Not quite.
What you are talking about here is what you do to prevent bubbles from coming out of solution. When you look at a bottle of soda, you see no bubbles because there is sufficient ambient pressure with the cap on to keep them dissolved. Open the cap and the become exposed to the pressure in the environment. The pressure drops rapidly, allowing bubbles to form. Soda forms more and larger bubbles when it is opened on a mountain top because that gradient is even greater. That is why we do not ascend too fast, and that is why we do a safety stop, to keep the gradient between our tissues and our environment from becoming too great. That is classic dissolved gas theory for DCS prevention--keeping dissolved gas from coming out of solution.
That is not, however, what bubble theory is about. Bubble theory assumes bubbles already exist (and they do), and it tries to determine an ascent rate that will keep them from growing too large (or having too much total volume, depending upon the theory).
In both cases, the way to eliminate the nitrogen is by breathing a gas that has less nitrogen in it (in terms of partial pressure) than the nitrogen in the body. Every time you take a breath, you are inhaling N2 molecules, and some of them go into the body via the lungs and the blood, and some of them come out of the body through the blood and the lungs. When you have been doing this on the surface for a while, it all averages out--you have just as many coming in as going out. When you begin a dive to say 99 feet, you are suddenly putting 4 times as many N2 molecules in your lungs as in the body, so you have 4 times as many going in as coming out. Eventually it all begins to even out again. As you ascend, the partial pressure of the nitrogen you are breathing drops, so you have more coming out than going in. This drops the N2 in the tissues to safe levels so that we can continue to ascend and exit safely.
In dissolved gas theory, the best thing to do is to get as shallow as you can so that enough gas leaves the body and you do not have an unsafe gradient between the body and the surrounding environment. In bubble theory, that need is balanced with a theoretical need to stay deeper long enough to keep some of the bubbles that are already there from getting to be too big. How to make that balance work is the big question in decompression theory today.
In all cases, though, the bigger the gradient between the tissues and the inspired air, the faster the tissues will lose their N2. Technical divers breathe oxygen during their last stops because that maximizes the nitrogen gradient while there is still too much N2 present in the tissues to go directly to the surface.
Not quite: I open the cap on my TJ's sparkling spring water just a tiny crack and watch tiny bubbles form and hiss out. If I opened it all the way I'd need a new keyboard. It's different, granted, but similar in the too much pressure drop too fast sense.
