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conservation laws

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Dreams of Pharaoh—a Lesson in Symmetry

In the Torah portion Miketz, Pharaoh sees two dreams. He wakes up agitated and calls on all wise men of Egypt to interpret his dreams. Nobody is able to come up with an acceptable interpretation, so they fetch Joseph from a prison and he successfully interprets dreams of Pharaoh—there will be seven years of plenty followed by seven years of famine. Joseph proceeds to instruct Pharaoh on how to prepare for the seven years of famine. In the previous posts, Interpreting Dreams and Joseph—the Master of Time—we already explained how Joseph was able to interpret dreams in terms of units of time and why Pharaoh appointed Joseph as the Viceroy of Egypt. This story, however, is still puzzling. Perhaps it can teach us more lessons… In Talmudic and Kabbalah literature, Joseph is called [...]

The Entangled Twins

Entanglement is often called the most baffling and the most quintessential aspect of quantum mechanics. What is entanglement, in a nutshell? Two particles born out of one reaction (or two particles that interacted through a collision) remain connected, no matter how distant from each other. A change in the status of one particle instantaneously causes a change in the status of the other particle. Einstein called it "spooky action at a distance." Entanglement is often associated with a certain symmetry and corresponding conservation laws. For example, the law of conservation of angular momentum requires that the spin (the quantum-mechanical analog of the angular momentum) of two entangled particles always point in the opposite directions. This means that, if two entangled particles have their spin in a state of superposition of Up (↑) and Down (↓) and we collapse [...]