[lloeki]

For all intents and purposes, from the point of view of each chain, the other does not exists but it merely turns out their past are the same. IOW BTC is B2X (the money, not the unit) before the fork, and each one considers that its own blockchain is the Truth†. So:

    - from the BTC point of view, there is 1 BTC both before and after the fork
    - from the B2X point of view, there is 1 B2X both before and after the fork
    - at any one time the value of 1 BTC is whatever people want to exchange it for
    - at any one time the value of 1 B2X is whatever people want to exchange it for
    - it just turns out that BTC == B2X before the fork

Therefore the value of each one merely depends on how much people care to trade them for, and the fork may affect this value, both before and after. Both may crash, both may shoot through the roof, or anything in between independently. But yes indeed since they come from the same past, if T is the last common transaction on the blockchain, then in between T and T+1 your 1(BTC+B2X) == X$ just became 1BTC + 1B2X == Y$ + Z$ (which at that precise, immaterial, instant == X$ + X$) by virtue of the fact that they disagree about the validity of any transaction you may make on each chain, including ones that get $$ out of the system. Hence you can "double spend" the coin. But speculation may shortly thereafter make Y and Z stay == X$ + X$, or become X$ + 0$, or X/2$ + X/2$).

† Without replay protection, transactions may or may not be replayed, but the blockchains do differ.

[ricg]

So if the exchange price for BTC does not drop by the same amount of the exchange price for B2X, a fork essentially means money (dollars) is generated out of nothing and given to me as the owner of now 2 coins (one of each type)?

Or in the opposite case, a fork could mean I lose money, just because somebody else decided to create fork?

[corobo]

In fairness you could also lose money because it's Bitcoin and its value is all over the place, fork or no fork