Comment by WorldMaker 16 hours ago
The other biggest fun trick of timezone math to a riddle like that would be the International Date line where a baby born on one side of it can be born on the "day before" by calendar reckoning despite being born 30 minutes after the other side of the line.
Yes, and if you ask any midwife, OB/GYN, or other person who routinely delivers babies, I'm sure you'll hear about plenty of born-on-different-days twins. One of my in-laws is a doctor who delivers babies; she has lots of stories, some of which she's restricted by HIPAA from sharing. But once a baby is born, the baby's birth date is public knowledge so she can share that info. So she often will tell her husband, "My patient is going into labor, I have to go to the hospital" without naming the patient. Then after the baby is born she'll say "Mrs. Smith's baby was born at 11 PM last night" because now it's a matter of public record who the mother was, whereas before it was protected by HIPAA. Next time I talk to her, I'll ask her if she's ever personally delivered any twins with different birthdays.
The timezones thing, of course, is just a way to have the younger twin be born "a year ahead" of the older twin by having their births be in two different timezones. Only practical way that would happen would be aboard a ship, because 1) babies born aboard an airplane would probably end up using the time zone of departure or of destination for their birth, and so twins would not be counted as being born in different time zones. And 2) any land-based transportation such as a car or a train would likely pull over (or in the case of a train, let the pregnant woman off at the nearest station) so that the woman giving birth doesn't have to do so in a moving vehicle. So a ship is the only moving vehicle where this kind of thing could likely happen, as there's no option of getting off in the middle of the ocean. It could happen while crossing time zones east-to-west, but crossing the International Date Line west-to-east makes more of an interesting thought experiment.
Yes, I've given this silly joke scenario way more thought than it really deserves. :-)
Yes, it's the same, the IDL just makes it easier for it to work, as otherwise the babies have to be born on either side of midnight while crossing the time zone line. With the IDL the birth time could be almost any time of day except for crossing over midnight and the joke would work.
Fraternal (not identical) twins, born aboard a ship traveling west to east across the Pacific. One of them officially born January 1st, 2016. The younger-by-30-minutes twin officially born December 31st, 2015. They'll have the hardest time persuading people that they're really twins once they're grown up.