Spin



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Topic: Science > Physics
User: "tetrahedron"
Date: 06 Jan 2005 08:18:36 PM
Object: Spin
Puppet_Sock wrote:

tetrahedron wrote:

1) Does anyone have an explanation of the differences among particles
with different spin?


Sure. Here's the capsule version. Spin has to do with what
representation of the rotation group the particle sits in.
Let's see if we can work with that a bit.

Thanks. This explains the rotation description.
Bjoern Feuerbacher wrote:

What is not intuitive about "intrinsic angular momentum"?

I can't see how the "definition" agrees with the "description".

So far, I've only come across two kinds of intuitive definition of
spin. The first way was to consider a particle with spin 1 an object
that returns to the same appearance when it undergoes a complete
rotation, spin 2 when half a rotation was enough to return to the
starting look (or was it 2 rotations?),


Half.

What about spin-1/2 and spin 3/2 fermions?
Etc. I'm particularly interested in particles with spin 0: I get the
impression these must behave in a weird (totally asymmetric) way.


Where do you get that idea from?

spin * #rotations = 1
Or does the spin-0 particle simply look the same in every
circumstance? Besides some mesons, I don't know of any such particle
physically observed.

(locally/globally)?


I don't see what the behaviour of spin 0 bosons has to
do with the handedness with the universe, and also don't
understand what you mean with "local" and "global" handedness.

Me either, I'm trying to broaden my understanding and find
connections.
Best regards
.

User: "Bjoern Feuerbacher"

Title: Re: Spin 07 Jan 2005 04:31:16 AM
tetrahedron wrote:

Puppet_Sock wrote:

tetrahedron wrote:

1) Does anyone have an explanation of the differences among particles
with different spin?


Sure. Here's the capsule version. Spin has to do with what
representation of the rotation group the particle sits in.
Let's see if we can work with that a bit.



Thanks. This explains the rotation description.

Bjoern Feuerbacher wrote:

What is not intuitive about "intrinsic angular momentum"?



I can't see how the "definition" agrees with the "description".

The angular momentum is the generator of rotations. Does that help in
any way? Probably not, since you apparently are not that well versed in
QM (well, this is also true already in classical mechanics,
so perhaps you have nevertheless heard it).
[snip]

Or does the spin-0 particle simply look the same in every
circumstance?

Yes.

Besides some mesons, I don't know of any such particle
physically observed.

Some atoms and nuclei. IIRC, the helium atom is the easiest
example.
[snip]
Bye,
Bjoern
.


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