A hypothetical question, but perhaps nonetheless illustrative of underlying principles : If by some method, humanity [or some non-human force] managed to stop the rotation of the Earth around its axis, would Shabbos still need to be kept?

Suppose the rotation was stopped on a Tuesday (GMT). Would we view days as progressing based on clocks, or would we view the day as forever standing still based on the Sun never setting?

  • 2
    very related: judaism.stackexchange.com/questions/9250/… – Loewian Aug 5 '19 at 21:36
  • What about the opposite case, where the rotation speeds up? Yaakov experienced קפיצת הדרך and immediately davened Maariv; he didn’t wait until however many hours he skipped passed before he davened. – DonielF Mar 18 '20 at 14:29

The Gemorrah rules that Shabbos comes by itself and it not dependent on a Beis Din, contrary to Moadim which are dependent on Kiddush HaChodesh כדאיתא בב"ב קכ"א.

I understand that "Beit Din" in the Gemorrah means our acting as a result of astronomical phenomena. For example, Yom Tov can only come a certain number of days after the Beis Din has ascertained that there was indeed a New Moon. This applies even nowadays, according to the Gemorrah in Rosh HaShannah. What the Gemorrah says about Yom Tov and Beis Din would be analogous to our acting due to a certain number of rotations of the earth. The Gemorrah means that Shabbos comes independant of astronomical phenomena. Therefore the answer that Shabbat comes independent of astronomical phenomena is valid.

Answer #2: Also, even if your question were at least a ספק, it isn't worse than what the Shulchan Aruch in Siman שדמ deals with (what to do if you find yourself in the desert and you aren't sure what day Shabbos is). You still have to keep Shabbos m'Chumrah. In your case, you know for sure when the last Shabbos was.

  • Shabbos comes by itself because the Earth rotates about its axis. If the Earth isn't rotating, how can Shabbos come? – Daniel Aug 6 '19 at 13:20
  • Answer 2 isn't addressing this case. That's where the day changes and you don't know which is Shabbat. This is about when the day doesn't change: how do you count 7 days? – Double AA Aug 6 '19 at 15:29
  • @Meuchedet : How you count days would seem to be, in fact, very relevant. If the Earth is spinning, counting a day is easy - Sun comes down and up to the same point in the sky, one day has passed. But if the Earth is not spinning, what does counting a day mean? Is it just waiting until 24 hours pass...But why 24? If the Earth slowed down its rotation rate, we probably wouldn't still count days using 24 hour increments - it seems our notion of what a "day" depends on the apparent position of the Sun, and not on an absolute time period. – user9806 Aug 7 '19 at 22:11
  • 1. If what you are saying is true then the Gemorrah in Bava Basra would say something else! The Gemorrah in Bava Basra (and other places) says that you do not determine when the Kedusha of Shabbos is -- Shomayim does. What you are saying applies to the Kedusha of Yom Tov (that Beis Din halachically determines) -- not of Shabbos. – Meuchedet Aug 8 '19 at 8:45
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    @Meuchedet : The Shulchan Aruch says to count days to determine when to keep the next Shabbos. How is this counting to be done? It's a simple question. Even if Shabbos is determined "min shamayim", it is still up to humans to keep it, and to do that they need to know when it is. And that involves humans counting days. – user9806 Aug 9 '19 at 21:49

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