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Robert McNees

@mcnees.bsky.social

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Professor and physicist. Black holes, quantum gravity, cosmology. Rocky Top. Tar Heel. Reposts are spooky action at a distance. These are my views, not my employer's. Just terrible at this.

  1. Throughout his adult life, Hamilton reportedly struggled with alcohol. He abstained for two years after embarrassing himself at a meeting. But he took it up again after colleagues teased him for drinking water. Supposedly, excessive drinking brought on his fatal attack of gout. (15/n)

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  2. For the longest time, he couldn't. Until one day he had a flash of insight while walking across a bridge with his wife:

    i² = j² = k² = i j k = -1

    He stopped and carved his formula for quaternions right there on the bridge. There's a plaque there now! (13/n)

    Image: Wikipedia

    Color photo of a weathered stone plaque that reads "Here as he walked by on the 16th of October 1843, Sir William Rowan Hamilton in a flash of genius discovered the fundamental formula for quaternion multiplication..."
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  3. Eventually he became fixated on the idea of endowing triplets of numbers with a similar structure to that of complex numbers. But he was stuck, and it was agony. Each morning, at breakfast, his children would ask "Well, Papa can you multiply triplets?" (12/n)

    Ref: Piaggio, Nature 152, 1943

    The passage reads
"...about 1819, but never published, seems to have anticipated some of Hamilton's work. Hamilton struggled with the difficulty for fifteen years, sustained in the later stages by the sympathy of his family.
"Well, Papa, can you multiply triplets ?"
was his breakfast greeting from his two little sons, aged eight and nine, and he had to shake his head sadly and reply that he could only add and subtract them. But on October 16, 1843, when he was walking..."
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  4. Around the same time, Hamilton read a paper that treated complex numbers as pairs of real numbers, or "algebraic couples."

    He was intrigued, and for years considered ways of using and extending these quantities in his study of mechanics, optics, and other fields. (11/n)

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  5. There's a beautiful sort of geometry underlying all this that is known as symplectic structure. It's a rich field of mathematics. This formulation of classical mechanics was central to early formulations of quantum mechanics. (10/n)

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  6. Once you know the "Hamiltonian" H of the system –– in most of the examples we teach physics students it is essentially the total energy –– the q's (positions) and p's (momenta) evolve according to a simple pair of equation. (9/n)

    Hamilton's equations for the time evolution of a generic momentum p and position q for some degree of freedom of a mechanical system. The first equation reads "p dot is equal to minus the derivative of the Hamiltonian with respect to q", while the second equation reads "q dot is equal to the derivative of the Hamiltonian with respect to p." In both cases "dot" means the time derivative of the quantity.
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