- #1

Thuring

I haven't figured out why space is usually described in terms of only 3 spatial dimensions rather than six: x,y,z, Tx, Ty, Tz. For instance spin needs angular motion, as does torque. Torque is not along the z-axis, for instance, like the cross-product would lead one to believe, but "around" the z-axis. In spacecraft structural dynamics, we always use 6 dimensions in order to describe torque and bending. Without rotation, a pinned interface would be the same as a fixed interface. Once you get the problem in terms of vectors and matrices, the math is the same with 3 or 6 dimensions.

Perhaps physics assumes that particles are points, so a rotation is meaningless (except spin is used as well as particle angular momentum). If only 3 dimensions is required for a particular application, fine, but it should be ADMITTED that the other 3 are simply being ignored. (Yes, I know 10 - 11 are used for string theory.) Perhaps, the rotations may be considered compacted dimensions. :-)

I must be missing something ...