# Bayesian probability

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## Gazing at the Shekhinah

In his commentary on this week’s Torah Portion, Yitro, Rabbi Chayim Vital, writing in the name of his teacher, the Ari-zal, states that Abel was punished for gazing at the Shekhinah—the divine presence.[1] But what relevance does this have to the Torah portion retelling the greatest event in Jewish history (and, indeed, the history of human civilization)—the Sinaitic epiphany—the giving of the Torah? This is the Torah portion, where we read the Ten Commandments. What is the relevance of the sin of Abel to the Ten Commandments? More generally, what is Abel’s connection to this Torah portion? That is easy to understand. The Torah portion Yitro starts with the story of Jethro (Yitro), Moses’s father-in-law, coming to Moses in the Sinai desert with his daughter—the wife of Moses—and her two children. Rabbi Chayim [...]

## 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 [...]

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