No, I Am Not Desecrating Shabbos
Yesterday, I took my 15th plane flight so far this summer, this time not for work but instead joining a family vacation. I am now further from Israel than I have ever been in my life. This presented an interesting question when I recited mincha yesterday: Should I face east or west? I had flown from the east to get here, but the shortest journey home would be to travel west to get back home.
This may (but not necessarily) relate to a vastly more significant halachic question: Am I desecrating Shabbos by writing this on my computer? Certainly some Poskim would say so!
Here is the background: As we fly west from Israel, we keep moving the hour back, so as not to outpace the sun. But if we were to constantly do that, we could end up arriving back in Israel at an earlier time and date than having left it! Hence, the need for an international dateline. But where is the halachic international dateline?
This is a famous and complex question that I certainly can't do justice to in a blog post. But I will outline the issues and mention the factors that are relevant from a rationalist Jewish viewpoint.
There are three well-known approaches to this question, the first of which has two variants. The first approach is based on an inference from the words of the Baal HaMaor, which are in turn an inference from the Gemara in Rosh HaShanah relating to when the new moon can be seen. This is a very technical discussion, but the bottom line is that according to this view, the day begins six hours (90°) east of Jerusalem. According to the strict interpretation of this, followed by the Brisker Rav, China and parts of Russia and Australia would be west of the halachic dateline, i.e. people in those places would observe Shabbos on what the rest of the world considers to be Sunday.
A variant on this approach is that of the Chazon Ish. He considers it unreasonable for the halachic dateline to bisect a country - it would mean that your next-door neighbor could be keeping Shabbos on a different day than you! Hence, he says that contiguous land of China, Russia and Australia should be incorporated to their western parts. According to this, only places such as New Zealand would be keeping Shabbos on what the rest of the world considers Sunday.
Some, however, would entirely reject these approaches. This is because they consider the inference from the Baal HaMaor's inference to be either technically incorrect, or unsuitable for resolving a question that Chazal were not addressing.
A second approach is that of Rav Yechiel Michel Tucazinsky. He bases himself of the Gemara's statement that Jerusalem is the navel, i.e. center, of the world. This is understood to mean that it is the Prime Meridian. Accordingly, the halachic dateline is 180° east/west of Jerusalem. This is extremely close to the secular international dateline - the significant difference being the Hawaiian islands. These would on the western side of the halachic dateline rather then the eastern side, and thus eleven hours ahead of Israel rather than thirteen hours behind; accordingly, Shabbos would be on Friday.
But while it may seem intuitive to use this Gemara to resolve the question, it is problematic. The meaning of the Gemara's statement that Jerusalem is the "navel" of the world is not at all clear. Even if it is making a geographic rather than spiritual statement, it was stated at a time when the conception of world geography was very different. In fact, when the Americas were discovered, R. David Gans felt that this Gemara posed a problem, and felt forced to explain it as a geo-cultural statement that Jerusalem is the center of the civilized world (or something like that; it's a long time since I saw it).
A third approach is that of Rav Isser Zalman Meltzer and Rav Zvi Pesach Frank. They are of the view that there is no halachic Prime Meridian and thus no unique halachic international dateline. Rather, one simply follows what the rest of the world considers to be the day of the week. It would seem that this would be the correct approach from the rationalist perspective.
However, there is one further wrinkle. What about being choshesh lechol hedeyos - being concerned for all opinions? After all, we are talking about Shabbos - a very serious matter! Perhaps Jews in eastern Australia should avoid melachah on Sunday, and Jews in Hawaii should avoid melachah on Friday?
The answer to this also relates to rationalist vs. mystical approaches to Judaism. According to the mystical approach, there is a metaphysical reality to Shabbos, an objective spiritual state that is "out there". Hence, one would probably want to make absolutely sure to be in line with it, and one would take into account other views; after all, they might be right. According to the rationalist approach, on the other had, there is no independent metaphysical reality to Shabbos. Rather, Shabbos attains its status as a result of how we conduct ourselves.
Of course, there is much more to be said on topic, but I'll have to sign off here. Shabbat shalom!