whats spin?

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whats spin?

Postby papernuke » Sun Sep 17, 2006 3:52 am

I was reading my Elegant Universe book, and i came across this word (and entire chapter) and i didn't know what it meant, can somone tell me?
"Civilization is a race between education and catastrophe."
-H.G. Wells
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Postby jinydu » Sun Sep 17, 2006 4:35 am

As far as I know, spin is a property that a quantum particle can have. I should be able to answer your question thoroughly once I take a more advanced quantum mechanics course.
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Postby Hugh » Sun Sep 17, 2006 5:06 am

Here are some pages at Wikipedia with regards to spin as it applies to physics: http://en.wikipedia.org/wiki/Spin_%28physics%29 and http://en.wikipedia.org/wiki/Spin_quantum_number.
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Postby Nick » Sun Sep 17, 2006 12:34 pm

I always wondered; when it says spin, does that mean the particle is actually spinning? Or is it describing something else.
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Postby jinydu » Sun Sep 17, 2006 2:53 pm

irockyou wrote:I always wondered; when it says spin, does that mean the particle is actually spinning? Or is it describing something else.


As far as I know, the particle is not actually spinning.

I do know that the picture of a particle moving through space is itself incorrect; a system of particles is described by a wavefunction, not a collection of points flying through space.
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Postby batmanmg » Sun Sep 17, 2006 6:19 pm

well as far as i've read its talking about angular momentum. which means spin... so im not sure weither they are just trying to confuse me or if im just not getting it...
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Postby houserichichi » Mon Sep 18, 2006 2:17 am

Spin is an internal angular momentum. It doesn't actually spin because we think of point particles as "points"...they have no axes to spin around on.
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Postby PWrong » Mon Sep 18, 2006 3:04 pm

I suppose in string theory they could actually be spinning.
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Postby thigle » Tue Sep 19, 2006 3:03 pm

i believe that what we perceive and conceptualise as matter, do indeed have an internal jitter, in internal teeming motion. only when the conceptualisation is too rigid, like in the case of 'point particles model', it seems inadequate.

particles do not exist. it is just a model that we apply on a certain scale. however, that which we project our model of nonexistent particles onto, does spin, if we change our model from static idea of atom or particle, or a given something, to a spherical standing wave. the whole of space teems, jitters. so every 'point' performs spherical rotation - spin.

matter is just undulation in the fabric of space.

if Dirac was right then what we call particles do spin. their axies are object-centered, with just a point of their intersection that stays invariant.

this is one of best info on spin i read ever:

from page 3634 on, in tony smith's webBook. google "tony smith physics", you find tony's home, down at the end of the page is his whole website as a pdf file. it has 100mb, but it's well worth it. http://www.valdostamuseum.org/hamsmith/TonySwebBook.pdf

btw, houserichichi, did you already skim through his ideas (you said you plan to do so)
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Postby PWrong » Tue Sep 19, 2006 5:01 pm

Does an electron with positive spin actually have a different wavefunction to one with negative spin?

In stationary states (which are the only quantum systems I've studied), there is a time dependence to the wavefunction. You could say the wavefunction "rotates" in the complex plane. The higher the energy, the faster it rotates. But this doesn't depend on the quantum spin number.
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Postby thigle » Wed Sep 20, 2006 5:09 pm

i don't know. how do you express wavefunction ?

when you say wavefunction rotates in CP, do you mean that its graphing in CP rotates over time ? what does the direction of such rotation depends on ?
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Postby PWrong » Wed Sep 20, 2006 5:19 pm

i don't know. how do you express wavefunction ?

Assign a complex number to every point in spacetime. That's the wavefunction for a particle. When you talk about "spherical standing waves" it's the wavefunction that does the standing and waving. As for my own question, I was hoping someone like house or jinydu would know the answer.

when you say wavefunction rotates in CP, do you mean that its graphing in CP rotates over time ? what does the direction of such rotation depends on ?

You multiply the wavefunction by e^(i E t / h)
Are you familiar with the complex plane? Start with a point on the complex plane (the value of the wavefunction), and rotate it counterclockwise around the plane by an angle given by E t / h. This is the new value of the wavefunction after a time t.
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