  Ignoring the differences between countries, human reproductive and dispersal
behaviors can be described by some standardized models, so whether there is a
universal law of population growth hidden in the abundant and unstructured data
from various countries remains unclear. The age-specific population data
constitute a three-dimensional tensor containing more comprehensive
information. The existing literature often describes the characteristics of
global or regional population evolution by subregion aggregation and
statistical analysis, which makes it challenging to identify the underlying
rules by ignoring national or structural details. Statistical physics can be
used to summarize the macro characteristics and evolution laws of complex
systems based on the attributes and motions of masses of individuals by
decomposing high-dimensional tensors. Specifically, it can be used to assess
the evolution of age structure in various countries over the past approximately
70 years, rather than simply focusing on the regions where aging has become
apparent. It provides a universal scheme for the growing elderly and working
age populations, indicating that the demographics on all continents are
inevitably moving towards an aging population, including the current "young"
continents of Africa, and Asia, South America with a recent "demographic
dividend". It is a force derived from the "life cycle", and most countries have
been unable to avoid this universal evolutionary path in the foreseeable
future.
