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seen Jul 8 at 21:02

Jul
8
awarded  Supporter
Jul
8
comment Can I look at the sky and find the day of the week?
I've been thinking a bit, and yes, you're right. Suppose we have a star far enough from the others with a single planet orbiting around it and no other spatial bodies nearby. Then the planet has a perfect elliptical orbit. Now assume that a "year" consists of precisely 100 "days". If I drop you off on the planet twice with a difference of a "year", you'll see exactly the same (as the entire system is in the same state), but you need to give a different answer. For a deterministic method, that's a contradiction.
Jul
5
comment Can I look at the sky and find the day of the week?
Ok, it's not the index point that really bothers me. I understand that it's a cultural and religious issue, but that only affects shifting and there still remains an astronomical question beyond that. Let me propose another thought experiment to make it clear. I'll drop you off at several planets and each time you should tell me which day of the week it is. You can say whatever you want, but if I take you back to the same planet at some later time, you'll have to be consistent (e.g. if you said Wednesday first and I bring you back 100 “days” later, you should say Friday now). Can you do that?
Jul
4
awarded  Scholar
Jul
4
comment Can I look at the sky and find the day of the week?
I see. I hoped for a bit more, but it seems like I'll have to face the reality. :)
Jul
4
accepted Can I look at the sky and find the day of the week?
Jul
4
comment Can I look at the sky and find the day of the week?
By the way, I just realized that the Gregorian reformation didn't affect the days of the week at all, so we can use the Julian calendar as well.
Jul
4
comment Can I look at the sky and find the day of the week?
Ok, the first part is clear now, thank you, but I still don't get the second one. Perhaps I wasn't clear in the question. I accept that the days of the week are man-made, but that doesn't mean that they can't be absolute. For instance, the metre is an ad-hoc man-made unit of measurement, but today we define it as “the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second”. I wonder if there exists a similar definition for, say, Sunday.
Jul
4
awarded  Student
Jul
4
asked Can I look at the sky and find the day of the week?
Jul
3
awarded  Informed