game of life question


Let L denote the set of all points of the plane with integer coordinates
and let P denote the set of all subsets of L. Conway's game of life
determines a mapping T from P to itself. Call an element x of P timeless
if there is a sequence x0=x, x1, x2, ... of elements of P such that, for
every positive integer n, we have T(x(n)) = x(n-1).

Is there any characterization known of the set of timeless elements of P,
other than the definition?
--
Ignorantly,
Allan Adler <ara@xxxxxxxxxxxxxxxxxxxx>
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.
.

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