Spin

[Ishimura_]

Can someone explain to me, in layman's terms, what exactly particle spin is? This concept is elluding me...

from Wikipedia (http://en.wikipedia.org/wiki/Spin_(physics))

...as far as can be determined, these elementary particles are true point particles...

My issue is: How can a point particle spin, since there is no center to spin about?

 

[ramparts]

It's not spin the same way a ball spins, but rather a concept which is mathematically analogous to spin. We have a set of mathematical tools which we use to draw correspondences between classical concepts and particle concepts - for example, classical momentum and particle momentum.

Spin comes from angular momentum. A classical object has angular momentum from two components - orbit, and spin. For example, the Earth's angular momentum is dependent on its rotation on its axis and its orbit around the Sun. A particle can get angular momentum from orbits, but also has angular momentum from this second, intrinsic mathematical property. Since it's analogous to spin, that's the name we give it. Hope that helps.

 

[Gravity_Ray]

Can someone explain to me, in layman's terms, what exactly particle spin is? This concept is elluding me...

from Wikipedia (http://en.wikipedia.org/wiki/Spin_(physics))

...as far as can be determined, these elementary particles are true point particles...

My issue is: How can a point particle spin, since there is no center to spin about?

Why do you say "there is no center to spin about". A point particle is still "something". Called "fermions" for matter, and "bosons" for energy. They do exist, its just that right now we dont know how to split them further. But they do exist and they can spin about themselves.

That doesnt mean they "cant" be split further, just that right now we dont know how to split them further (the so called "God" particle and I hate that term because pretending to know the mind of God is stupid).

Depending on the spin that fermions have they can be electrons, positrons, and quarks which make up protons, neutrons and neutrinos.

Not sure if that helps you though.

 

[ramparts]

Erm, it's not true that fermions are matter and bosons are energy. Both are particles just the same. The fundamental difference is that bosons obey one kind of statistics, and fermions obey another. What this means is that multiple bosons can be in the same place at once, quantum mechnically speaking, while fermions with the same properties can't occupy the same space. For fermions (like electrons) that's the Pauli uncertainty principle you learned about in high school.

Now, there's a nifty little feature of the Universe that when you quantize spins, bosons are the particles with integer spins (0, 1, 2) and fermions are the guys whose spins end in 1/2 (1/2, 1 1/2, etc.).

Another feature (which I think you were thinking of) is that of all the fundamental particles we know, everything which we consider regular matter is a fermion, and every force carrier (like the graviton and the photon) is a fermion. I'm not sure if that's a hard and fast rule, and in quantum mechanics the difference between a force carrier and a "stuff" particle is a bit unclear to begin with. They're all particles, and the only difference is the spin.

 

[Gravity_Ray]

But I was just trying to simplify it for the OP per their request. When you get that far down the scale nothing is really following our rules very well. I mean not only can things occupy the same space, but the same thing can occupy more than one place. I'm not a teacher so I was speaking as a layman, maybe there is no laymans explanation that far down.

 

[SpaceTas]

You can also think of spin for massless particles like photons as the handedness of the polarization.