The complexity of machines, expressed in terms of Φm, rises to illustrate increased utilization of power density by human-built devices during the cultural-evolutionary phase of cosmic evolution. That rise has been dramatic (shown here over 3 orders of magnitude) within only the past few human generations as technological civilization has become increasingly dependent upon energy. Note that the timescale for this graph is much, much briefer than any of the previous figures—here, roughly the past century of natural history—so it represents only a miniscule part atop the master curve graphed in Figure 2.
