18.07.2014 Views

John Stillwell - Naive Lie Theory.pdf - Index of

John Stillwell - Naive Lie Theory.pdf - Index of

John Stillwell - Naive Lie Theory.pdf - Index of

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

8.8 Discussion 185<br />

deform the path to a single point—because the path creates a full twist in<br />

the arm, which cannot be removed by varying the path between the initial<br />

and final positions.<br />

However, traversing (a deformation <strong>of</strong>) the path again, asshownin<br />

the last three pictures, returns the arm and hand to their initial untwisted<br />

state! The topological meaning <strong>of</strong> this trick is that there is a closed path<br />

p in SO(3) that cannot be deformed to a point, whereas p 2 (the result <strong>of</strong><br />

traversing p twice) can be deformed to a point. This topological property,<br />

appropriately called torsion, is actually characteristic <strong>of</strong> projective spaces,<br />

<strong>of</strong> which SO(3) is one. As we saw in Sections 2.2 and 2.3, SO(3) is the<br />

same as the real projective space RP 3 .

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!