Recently In October 2008, I ended up acquiring the domain name spinor.info on a whim. I was looking for something else when it happened. Usually, nice and short names like spinor are already taken, even under a relatively new top-level domain like .info. But, spinor turned out to be an exception. And spinor.info has a kind of a ring to it.
One reason I like the name is that spinors play such an important role in modern physics. To say that without spinors, matter would not exist is not an exaggeration. “Stuff” in physics comes in many forms, all defined by their properties under a coordinate transformation. For instance, light (electromagnetism) can be described by a vector field, which means that the basic quantity of electromagnetism transforms as a vector does when we change coordinates. Gravity is a tensor field; it transforms as a rank-2 tensor. The hypothetical Higgs boson that is supposedly responsible for giving mass to matter transforms like a scalar field.
But matter itself is different. Material particles cannot be represented by scalars, vectors, or tensors. Instead, they are represented by spinors. Loosely speaking, a spinor is the square root of a rotation, and that is exactly how a spinor behaves when we change coordinates; it transforms as the square root of a rotation. One immediate, rather counterintuitive consequence is that when you perform a full rotation of 360 degrees, a spinor only goes through half a rotation and becomes its own opposite; you need to go around twice, 720 degrees that is, to get back the original spinor.
Okay, I guess that sets the tone for what I am going to do here. On the other hand, for non-physicists, in this politically charged era, spin may mean something else altogether, so perhaps I am forgiven if I talk about things other than physics, too, in my Spinor Info web log. Which, incidentally, is a continuation of a Day Book that I have been maintaining continuously since 2002.
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