What happens if two different groups have a definitive disagreement about the evolution of the bitcoin protocol? I have read is several places that the "majority" somehow would win, but is this really true, or could two different branches (A and B) of the blockchain (now tree) survive indefinitely in parallel?
I imagine that since the coins can be spent twice, once in each branch, they would somehow have their effective value halved. Suppose I'm a supporter of branch B, I would want to sell the A versions of my coins to buy more B-coins. The exact exchange ratio between the two new type of coins would depends on the relative size of the two communities. Is this scenario plausible, or is it economically unstable?