Our Mathematical Universe: My Quest for the Ultimate Nature of Reality

by Max Tegmark

For example, about three-quarters of your body weight is water molecules, which get replaced every month or so, and your skin cells and red blood cells are replaced every few months. In spacetime, the trajectories of these particles joining and then leaving your body make a pattern reminiscent of the familiar silk strands attached to a corncob. At both ends of your spacetime braid, corresponding to your birth and death, all the threads gradually separate, corresponding to all your particles joining, interacting and finally going their own separate ways (Figure 11.4, right). This makes the spacetime structure of your entire life resemble a tree: at the bottom, corresponding to early times, is an elaborate system of roots corresponding to the spacetime trajectories of many particles, which gradually merge into thicker strands and culminate in a single tubelike trunk corresponding to your current body (with a remarkable braidlike pattern inside as we described above). At the top, corresponding to late times, the trunk splits into ever-finer branches, corresponding to your particles going their own separate ways once your life is over. In other words, the pattern of life has only a finite extent along the time dimension, with the braid coming apart into frizz at both ends.