In parshah Tazriah (Leviticus 13), the Schrödinger cat 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 wavefunction back in the university, I would have surely discovered it by reading this parshah!
A Jewish person with a skin lesion or boldness (present company excluded) is brought to a priest (kohen) who examines it for symptoms of tzara’as. If the priest finds the lesion suspicious, he quarantines the person for seven days. At this point, the patient is possibly tameh (impure, i.e., afflicted with tzara’as) or tahor (i.e., pure, healthy). To translate this into the language of quantum mechanics, the person is in a state of superposition of two states – tomeh and tahor  – just like the unfortunate Schrödinger cat. It takes a kohen-priest to collapse the wavefunction of the quarantined person and to proclaim him pure (tahor) or unclean (tomeh).
Just as “establishing witnesses” (eidim ki’um) establish the reality (e.g., marriage), as contrasted with “clarifying witnesses” (eidim bi’ur) who merely clarify the situation, the kohen here does not merely diagnose a patient, but he establishes the reality by proclaiming the patient healthy (pure, or tahor) or afflicted (unclean, or tameh). It’s all up to the kohen. In certain situations, a kohen may choose not to put a person in the uncomfortable state of superposition (the sense of compassion apparently not shared by quantum physicists). For example, during holidays, or if the suspected person is a newlywed, the kohen may choose not to examine the person so as not to ruin the festivities. (Note another similarity with quantum mechanics, which is the only epistemic theory, unlike classical physics, which is ontic. An ontic theory concerns itself with the state of nature (the ontology). An epistemic theory concerns itself with a state of knowledge (the epistemology). In quantum mechanics, we study the state of knowledge of the observer. Here too, it is only the knowledge of a kohen-priest that matters.)
We find another example of how a kohen collapses the wavefunction in the story of the afflicted house. When a kohen is brought to examine a house afflicted with a suspicious “mold”, the kohen quarantines the house for seven days to see if the “mold” spreads further or not. At this stage, the house is in a state of superposition of being pure (tahor) or unclean (tomeh). The kohen returns a week later to examine the house, and if he finds that the “mold” spread and, therefore, is malignant, before pronouncing the house unclean, the kohen orders all furniture and kelim (e.g., pans and pots) to be taken out of the house and only then he pronounces it to be unclean. Had he made his diagnosis when the kelim are still in the house, they would have all become unclean as well. The kohen, therefore, orders the evacuation of the house to avoid making all furniture and other kelim unclean. After all, it is up to him – he is the one who creates reality by collapsing the wavefunction of the house.
Let us return now to the metzora – an unfortunate Jew afflicted by tzara’as. After he or she has been isolated from the rest of the society by being sent outside the camp, it comes the time for healing – a purification process performed by the kohen who first pronounced the person tomeh. In parshah Metzora (Lev. 14:4-7), the procedure of purification is described as a mysterious ritual involving taking two alive, clean birds, slaughtering one over a stream of water, dipping the other (alive) bird into the blood of the slaughtered bird and sending it free into an open field. What does it all mean? Here is where the Schrödinger cat meets angry birds.
Let us recall here two goats selected for sacrifice in the Beth HaMikdash (the Holy Temple in Jerusalem) on Yom Kippur – one goat chosen by a lot would be sacrificed to God, and the other – the so-called scapegoat – sent to Azazel. These two goats become entangled. If one of the goats dies or becomes unfit for sacrifice, both have to be replaced. Similarly, the two birds in parshah Metzora are entangled. The gematria of the Hebrew word for bird (tzippor) is 376, the same as shalom. The slaughtering of one of these birds represents the broken piece – the absence of shalom. It is precisely the absence of shalom caused by lashon harah that causes the tumah (impurity) of tzora’as – the word “tumah” literally meaning absence. According to Arizal, the two brains (chokhmah and binah) of the evil Nukva of Atzilut are called “the two birds.” These are not happy birds; these are angry birds. Their message is powerful and frightening!
The sages say that the spiritual affliction of tzara’as is the result of lashon harah – evil talk or talebearing. The word metzora (the one afflicted with tzara’as) is said to be a short form for motzeh shem rah (slander). Rashi tells us that, just as birds twitter and chirp all the time, a talebearer, who is habitually engaged in idle chatter, ends up slandering or just talking unfavorably about another person. Therefore, measure for measure, to purify a person, birds who twitter all day are taken.
It is written of slanderers, “Their tongue is a sharp sword.” (Psalms 57:5) The frivolous use of tongue spills innocent blood. Hence the bird to be set free is dipped into the blood of a slaughtered bird.
The Zohar (Metzora p. 53b) says:
It is because of this that it is written, “Be afraid of the sword.” [One should] be afraid of slander, which is called by the name “sword”. And that states, “…for wrath brings the punishment of the sword,” what sword is being referred to? It is the sword of God, as we have learned that the Holy One, Blessed be He, has a sword and punishes the wicked with it. This is as is written in the verse “The sword of God is filled with blood…” (Isaiah 34:6)
The Talmud says: “Lashon harah kills three people: the person who says it, the person about whom it is said, and the person who listens to it.”. We are also told that sins of the subject of the gossip are transferred onto the gossiper.
This is indeed the message of the birds: the live bird, after being dipped in the blood of the slaughtered bird, is set free over the open field – it flies away thinking it is free, while in truth, it is forever entangled with the slaughtered bird and carries its blood on itself. So too is a person who casually utters unkind words about another person causing untold damage to that other person, to himself and to the one who listens. He goes off having forgotten the incident without realizing that he (or she) has entangled himself (or herself) with the subject of his (her) talebearing, that he (or she) now acquires the sins of that person and, indeed, carries the blood, as it were, of an innocent person upon whom the evil chatter brought harsh judgments. So I heard from a bird…
On a positive note, the birds used for purification are not only entangled with each other but together they are entangled with the metzora – a Jew suffering from tzara’as. By slaughtering one bird and sending away the other bird, the kohen removes tzara’as from the Jew and purifies him. This is why the word “metzora” also means motzi rah – remove evil. Nowadays, this procedure is no longer practiced, but, alas, lashon horah is. What is left, is the message of the angry birds. Next time we are about to open our mouths to speak of another person, let us pause and listen to the chirping birds – perhaps we will hear their message.
 Schrödinger cat is the subject of a thought (a.k.a, gedanken) experiment which finds a cat suspended in a state of superposition of being alive and dead. In this state, the cat is neither alive, nor dead, nor both, nor neither, but it is in a new state (C) – the state of superposition of being half alive (A) and half dead (B), which means that the cat has 50% probability of being found alive and 50% chance of being found dead.
 Wavefunction ψ describes probability distribution of finding a system in a particular state (e.g., a probability of finding a particle in a particular area of space). A collapse of the wavefunction is an ad hoc phenomenon collapsing the uncertainty cloud of the wavefunction into a single point – a single number obtained as a result of the measurement. (This phenomenon is often referred to as the Measurement Problem in Quantum Mechanics.)
 To express this in a formula using traditional Dirac bra-ket notations, let |A⟩ be the state of tohar and |B⟩ be the state of tameh, than the person is a state of superposition |C⟩, which is, roughly speaking, |C⟩ = ½ |A⟩ + ½ |B⟩.
 In quantum mechanics, when two objects, such as elementary particles, interact (e.g., collide) they become like one object in a sense that, henceforth, they are described by the same wavefunction. Such objects are called entangled and the phenomenon is called entanglement. The phenomenon of entanglement is one of the strangest animals in the quantum-mechanical zoo. The two particles that once collided and then flew apart in different directions remain entangled forever. If the two particles, for example, must have the opposite spin (say, when particle A has spin UP, particle B must have its spin DOWN), when we flip the spin of one of the entangled particles the other particle will change its spin instantaneously no matter how far apart the particles are (even though this may violate the special theory of relativity, because the entangled particles seem to communicate with a speed that is faster than the speed of light!).
 The fact that the Torah writes “birds,” (i.e. plural) already tells us that a kohen must bring two birds, which is the minimum plural number. Torah explicitly specifies the number “two” to teach us that the birds must be identical in their appearance, height, and monetary value (Talmud, Tractate Yoma 62b), which further hints that the two birds are entangled as they are indistinguishable.
 Erkin 15b.