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What is Spin? | Quantum Mechanics

Looking Glass Universe
400K subscribers
1.2M views 10 years ago
Follow up video:    • Is Spin Angular Momentum afterall? ('What ...   Research assignment: Teach me about spin. Below there are suggested questions, recommended sources and my social media accounts: QUESTIONS: Questions that require less research: 1. This is our first real example of quantization, the phenomena that gives quantum mechanics it’s name. Here’s what it means. In the classical case of magnets going through a Stern Gerlach machine, the magnets can end up any where in the range. But in quantum mechanics, its can only be exactly up or down, these discrete values rather than a continuous range in between. This sort of quantization really bothered physicists. Can you understand why? And is there any classical physics phenomenon that also has sort of quantization? 2. Do you think that eventually all quantities in physics can be explained in terms of deeper physics? Are there any examples of quantities that later on did get explained th …...more
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What is Spin? | Quantum Mechanics
30KLikes
1,218,453Views
2015Jul 30
Follow up video:    • Is Spin Angular Momentum afterall? ('What ...   Research assignment: Teach me about spin. Below there are suggested questions, recommended sources and my social media accounts: QUESTIONS: Questions that require less research: 1. This is our first real example of quantization, the phenomena that gives quantum mechanics it’s name. Here’s what it means. In the classical case of magnets going through a Stern Gerlach machine, the magnets can end up any where in the range. But in quantum mechanics, its can only be exactly up or down, these discrete values rather than a continuous range in between. This sort of quantization really bothered physicists. Can you understand why? And is there any classical physics phenomenon that also has sort of quantization? 2. Do you think that eventually all quantities in physics can be explained in terms of deeper physics? Are there any examples of quantities that later on did get explained through a more encompassing theory? 3. How can you use the Stern-Gerlach machine to measure spin in the ‘forward-backward’ direction? 4. Why do half the particles go left, half right at 4:24? Questions that (probably) require research: 5. What are bosons and fermions? What’s spin got to do with it? If you really want to get into it, read ch 4, volume 3 of The Feynman Lectures: http://www.feynmanlectures.caltech.ed... 6. Electrons are so-called spin 1/2 particles. Are there any other spin types? What determines what spin a particle will have? 7. How does spin relate to the Pauli exclusion principle? 8. Explain how the Stern-Gerlach machine works 9. Is light polarization a type of spin? What are arguments for and against this? What spin does a photon have (spin 1/2, spin 1 etc)? 10. Why is it that charged particles moving causes magnetic fields- according to Einstein? (Look up relativity and electromagnetism) 11. What’s wrong with saying the electron is infinitely small? What experiments measure the electrons size? Are protons also infinitely small? 12. Find other reasons we don’t believe electrons are actually spinning. (An interesting one is about rotating a spin particle 360 degrees, and not getting back the exact same wavefunction.) 13. a) What is the Bloch Sphere, and why can we use it to represent spin? How do you visualise the spin left state on it? how about spin forward? (http://comp.uark.edu/~jgeabana/blocha... , note that a 2-level system is any particle that only has two options when measured (eg only up or down). |0) and |1) are the generic labels we’ll put on these options) b) Also, How do you write spin forward in terms of up and down (i.e. |forward)=a|up)+b|down))? You will probably need to look this up, so it’s useful to know the spin “up/down”ness is usually called spin in the z direction, spin “left/right”ness is spin in the x direction, and spin “forward/backward” is spin in the y direction. You can figure this out by looking at the Bloch sphere. 14. Magnetic Resonance Imaginging (MRI) is an important clinical technic that completely relies on manipulating spin. Explain it! http://www.scholarpedia.org/article/M... 15. What happens to the electrons if you put them into the Stern-Gerlach machine and then slowly rotated from up and down to side and side, do some of the electrons switch places? (Thank you Majoofi) 16. Why aren't there magnetic monopoles? (Thanks Culwin) 17. What is isospin? Why is it that, even though it hasn't got the units of angular momentum, it still 'formally acts like spin?' according to Wiki? (Thanks Hythloday71) RECOMMENDED SOURCES ON SPIN The Feynman lectures, Volume 3: http://www.feynmanlectures.caltech.ed... Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particle Physics- Eisberg and Resnick, the chapters of angular momentum and spin. This is a good one if you already know basic classical electromagnetism. Don't buy it, just visit your local university library and just read it there. Sneaking a Look at God's Cards - Ghirardi. This is one of my favourite quantum books. It talks about the Stern-Gerlach experiment. Wikipedia or Scholarpedia. These are always a good place to start- though sometimes they can throw you into the maths. Don't panic if you don't get all of it. Just try to glean the main idea, and that's more than enough to report here. Hopefully then others can help with any details that were confusing. The Story of Spin. Thank you Michael Sommers for the recommendation. I haven't read it, but it seems good! Hard to find though.   / 1.  . A Veritasium and Minute Physics video about electromagnetism! Thanks EnellGmz for reminding me about it.    • How Special Relativity Makes Magnets Work   SOCIAL MEDIA: Twitter: @Looking_glass_u Facebook www.facebook.com/LookingGlassUniverse Tumblr http://looking-glass-universe.tumblr....

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Looking Glass Universe

400K subscribers