The concept of spacetime expanding in cosmology refers to the metric expansion of space itself. It is important to note that this expansion occurs on a large scale, affecting the vast distances between galaxies and clusters of galaxies, rather than on smaller scales, such as within our bodies.
While the universe as a whole may be experiencing an expansion, the forces that hold matter together, such as gravity and electromagnetic forces, are much stronger at smaller scales. These forces counteract the expansion on local scales, including within our bodies.
From a biological perspective, our bodies do undergo growth and development, but this is primarily driven by internal biological processes, such as cell division and tissue growth, rather than the expansion of spacetime. The expansion of the universe does not directly cause our bodies to expand in size.
Therefore, on a day-to-day basis, we do not experience any noticeable expansion due to the overall expansion of spacetime. Our bodies are primarily influenced by internal biological processes and the forces acting within our immediate environment.