the correct komi number has puzzled Go players for centuries, now we might finally have a chance to figure out the right answer (although not without some reservations). over the last 5 decades, komi has consistently been raised to keep the game more leveled between white and black (black makes the first move, so has the advantage). historically, there was no komi, and people kept an even game by always playing even number of games with each player switching sides after each game.
for whatever reason, it's no longer feasible in modern pro game (not to mention that this could result in no winner if each player wins half the game), so komi was introduced. at first at 5.5, and steadily climbed higher to 7.5 at present. In pro game, even a change of 1 is considered a big deal, so from 5.5 to 7.5 is hardly trivial.
Now with alphago playing "perfect" games against itself, we might finally be able to put to rest the debate of the correct komi (the Japanese Go associations for decades have kept meticulous records of every professional game, in order to find the correct komi).
There is a big "but" though. The correct komi at Alphgo Zero's level might not be the correct komi for human level players (AlphaGo is estimated to be 2-3 handicaps above human play; this is a bigger gap between the average pro player and the best amateurs).
Indeed, the change from 5.5 komi to 7.5 komi also had a lot to do with the change in play style rather than simply zooming in on the "correct" komi number. In the 70s and 80s, predominant play style was more conservative, and 5.5 might well be the correct komi for the time (defined as resulting in 50:50 chance of winning for either side). As play style shifted to become more aggressive and confrontational (actually fueld somewhat by the introduction of komi), it was discovered that komi needs to be raised to keep chances of winning at 50:50.
To make an analogy, suppose one is playing a casino game of chance that gives the house a slight advantage (similar to the first mover advantage for black in go). If one only makes small bets, the house will end up winning only a small amount. in other words, the player needs to be compensated by a small amount to make the game "fair".
If however one makes big bets (i.e. more aggressive game play), then the compensation needs to be bigger too, to make the game "fair", even if the underlying probabilities have not changed.
following this logic, while 7.5 komi is fair for Alphago vs. alphago games, it might not be the right number for human games. I suspect it might be samller for humans.... if only we could calibrate Alphago to the average human level and generate millions of self-play games...