Dear Rabbi Kornfeld,
The Gemara says that we keep yom tov sheini in case the goyim oppress us and we forget how to set the dates. Does the fixing of the calendar affect this in any way; if not why not-why can't we just look up when Rosh Chodesh is supposed to be? Is the chashash that everyone outside Eretz Yisrael will be unable to do so?
Gershon Dubin, Brooklyn NY
The Gemara to which you refer is itself referring to nowadays, when the calendar has already been fixed. Yet the Chachamim were afraid that the details of fixing it correctly might become forgotten.
Don't forget that at the time when this ruling was instituted, there were no printing presses and no written calendars. Just about everything in those days was still memorized. Consequently, the fear of which the Gemara is speaking is perfectly justifiable.
I have no doubt that when Mashi'ach comes and he presides over a Beis Din that is greater in wisdom and in numbers than the one that fixed the ruling of "Hizaharu be'Minhag Avoseichem ...",that one of the first things he will do is to negate the second day of Yom Tov (assuming anyone remains in Galus).
In the meantime, we will have to abide by the ruling of the Beis Din that initiated it.
Incidently, the Rambam too (Hilchos Kidush ha'Chodesh 5:5) states clearly that nowadays, people who live in Chutz la'Aretz really ought to observe only one day, and it is only due to the Takanas Chachamim that they observe two.
be'Virchas Kol Tuv,