actual volatility and implied volatility are kind of correlated but they don't have to be. Actual vol can go up, while implied goes down, or vice versa. the best thing that can happen if you buy a straddle (you can do this with any option btw) is for implied vol to go up, so you can sell it at a 'higher' price (in practice this will be 'lower' most of the time), in the meantime you will lose theta however, this you have to compensate by actually trading the underlying and making a profit there, it's the last part that is really the gamma scalping. So your total profit over time will be the sum of those three elements.