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Wednesday, 25 July 2012

Watching the Lie algebra su(3) at work

Just as in the post on su(2), we may attempt to visualize the effect of the su(3) rotations
tx=i2(010100000)ty=i2(0i0i00000)tz=i2(100010000)ux=i2(000001010)uy=i2(00000i0i0)uz=i2(000010001)vx=i2(001000100)vy=i2(00i000i00)vz=i2(100000001)
As already noted vz=tz+uz, leaving only eight linear independent generators. The resulting animation is shown in Fig. 1.

Fig. 1: The Lie algebra su(3) at work
The red, green and blue symbols mark three unit squares [(0,0), (1,0), (1,i), (0,i)], one in each of the three complex planes which constitute the three-dimensional complex space. The animations show the motion of the three squares when rotated by Tx=1+αtx, Ty=1+αty, etc.; here, α denotes the (infinitesimal) rotation angle. Note that it requires an accumulated rotation of 4π for the squares to return to their original position.

When we examine the right-most three (sub-)figures of Fig. 1 it actually can be seen that Vz corresponds to the combined effect of Tz and Uz. E.g. the anti-clockwise rotation of the blue square generated by Tz and its clockwise rotation generated by Uz cancel out causing it to remain fixed when Vz is applied.

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