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However, the most interesting property of your spacetime tube isn't its bulk shape, but its internal structure, which is remarkably complex. Whereas the particles that constitute the Moon are stuck together in a rather static arrangement, many of your particles are in constant motion relative to one another.
Consider, for example, the particles that make up your red blood cells. As your blood circulates through your body to deliver the oxygen you need, each red blood cell traces out its own unique tube shape through spacetime, corresponding to a complex itinerary through your arteries, capillaries and veins with regular returns to your heart and lungs. These spacetime tubes of different red blood cells are intertwined to form a braid pattern (Figure 11.4, middle panel) which is more elaborate than anything you'll ever see in a hair salon: whereas a classic braid consists of three strands with perhaps thirty thousand hairs each, intertwined in a simple repeating pattern, this spacetime braid consists of trillions of strands (one for each red blood cell), each composed of trillions of hairlike elementary-particle trajectories, intertwined in a complex pattern that never repeats. In other words, if you imagine spending a year giving a friend a truly crazy hairdo, braiding his hair by separately intertwining not strands but all the individual hairs, the pattern you'd get would still be very simple in comparison.
Yet the complexity of all this pales in comparison to the patterns of information processing in your brain. As we discussed in Chapter 8 and illustrated in Figure 8.7, your roughly hundred billion neurons are constantly generating electric signals ("firing"), which involves shuffling around billions of trillions of atoms, notably sodium, potassium and calcium ions. The trajectories of these atoms form an extremely elaborate braid through spacetime, whose complex intertwining corresponds to storing and processing information in a way that somehow gives rise to our familiar sensation of self-awareness. There's broad consensus in the scientific community that we still don't understand how this works, so it's fair to say that we humans don't yet fully understand what we are. However, in broad brushstrokes, we might say this: You're a pattern in spacetime. A mathematical pattern. Specifically, you're a braid in spacetime-indeed one of the most elaborate braids known.
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Max Tegmark (Our Mathematical Universe: My Quest for the Ultimate Nature of Reality)