Electrons DO NOT Spin
PBS Space Time・2 minutes read
Quantum mechanics explores mysterious concepts like quantum spin and angular momentum conservation through experiments with spinning objects and magnetic fields. Properties like quantum spin influence matter behavior, demonstrated by the Stern-Gerlach experiment with silver atoms, with implications for entropy, entanglement, and the universe's low initial entropy during the Big Bang and cosmic inflation.
Insights
- Quantum spin, a unique angular momentum possessed by electrons, plays a fundamental role in influencing the behavior of matter and magnetic fields, distinct from classical rotational motion.
- The concept of entropy, whether in the form of Von Neumann entropy representing extractable information or thermodynamic entropy reflecting energy distribution, sheds light on the early universe's low entropy state at the Big Bang, hinting at intricate entanglement and gravitational dynamics that shaped its evolution.
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Recent questions
What is quantum spin?
Quantum spin is a unique angular momentum possessed by electrons, influencing matter and magnetic fields. It is a fundamental property of particles, not physical spinning like wheels.
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Summary
00:00
"Quantum Spin: Essential Angular Momentum in Particles"
- Quantum mechanics involves many strange phenomena, with quantum spin being a particularly perplexing concept.
- The conservation of angular momentum is demonstrated through experiments involving spinning objects and magnetic fields.
- Electrons in iron cylinders align their spins due to external magnetic fields, leading to rotation and conservation of angular momentum.
- Despite not physically spinning like wheels, electrons possess a unique angular momentum known as quantum spin.
- Quantum spin is a fundamental property of particles, influencing the behavior of matter and magnetic fields.
- The Einstein de-Haas effect, observed in iron cylinders, showcases the spin-like properties of electrons.
- The Zeeman effect, discovered by Peiter Zeeman, demonstrates the splitting of energy levels in atoms under magnetic fields.
- Wolfgang Pauli's rejection of classical rotation for electrons led to the concept of quantum spin as an intrinsic angular momentum.
- The Stern-Gerlach experiment with silver atoms revealed the quantized and directional nature of electron spin.
- Spinors, mathematical objects describing particles with quantum spin, play a crucial role in quantum mechanics and the conservation of angular momentum.
14:23
"Entropy in Universe: Information, Expansion, Entanglement"
- Von Neumann entropy differs from thermodynamic entropy by representing the information contained in a system and extractable in principle, as opposed to information lost to the system through entanglement with the environment. Classical entropy, on the other hand, is hidden beneath the system's properties but can potentially be extracted.
- The low entropy at the Big Bang is attributed to the universe being extremely compact, hot, and dense, with gravitational degrees of freedom largely unoccupied. Despite the extreme smoothness indicating high matter entropy, the low gravitational entropy prevailed, suggesting early universe particles were likely entangled.
- The early universe's extreme expansion during cosmic inflation may have separated entangled regions but maintained internal thermal equilibrium without maximal entanglement within the regions themselves. This implies that the universe, or at least our portion of it, possibly began unentangled and at low entropy, even while at thermal equilibrium.
