# Bayesian probability

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## Wigner’s Friend Receives a Death Threat

It is related that on the day that Rabbi Yehuda HaNasi died, the Sages decreed a fast, and begged for divine mercy so that he would not die. And they said: Anyone who says that Rabbi Yehuda HaNasi has died will be stabbed with a sword. (Talmud, tr. Ketubot 104a)   We find an interesting example of the Wigner’s Friend paradox in the Gemara quoted above. The Gemara discusses the circumstances surrounding the death of Rabbi Yehuda HaNasi (Juda the Prince, knows simply as the Rebbi), one of the greatest sages of Israel, who compiled Oral Torah in the Mishnah. Why did the Sages issued a death threat to “anyone who says that Rabbi has died” promising that he “will be stabbed with a sword”? The medieval Talmudist Rabbi Bezalel Ashkenazi (1520-1592), in [...]

## Leprous Cats and Angry Birds

In the Torah portion Tazriah (Leviticus 13), the Schrödinger cat[1] gets leprosy. Well, it’s not really leprosy, it’s a mysterious supernatural disease called tzara’as, nowadays translated as psoriasis. And it’s not a cat, but a Jew who gets afflicted by tzara’as. In fact, cats, other animals, and even gentiles (i.e., non-Jewish humans) are immune to this spiritual malady. So why do I call a poor Jew afflicted with tzara’as a “Schrödinger cat”? Because he sure acts like one. Indeed, had I not studied quantum mechanics and had I not learned about the collapse of the wave function[2] back at the university, I would have surely discovered it by reading this Torah portion (parshah)! A Jewish person with a skin lesion or boldness (present company excluded) is brought to a priest (kohen), who examines it [...]