Space itself does not expand but the distance between physical bodies increase due to dark energy:

Space itself is not a physical entity in the same sense as matter or objects. Space is a mathematical and conceptual framework used to describe the relationships and distances between physical bodies. 

When we talk about the expansion of the universe, we are referring to the observed phenomenon where the distances between galaxies and clusters of galaxies increase over time. This expansion is described mathematically using various parameters and metrics.

While the term "stretching" is often used in the context of describing the expansion of the universe, it is important to understand that it is not a literal stretching of physical space, as space itself is not a physical substance. Rather, it is an expansion of the distances between physical objects within the conceptual framework of space.

The driving force behind the expansion of the universe is thought to be dark energy, which is a hypothetical form of energy that is thought to permeate the universe and contribute to its accelerated expansion. Dark energy is postulated to exert a repulsive gravitational effect, causing galaxies and clusters of galaxies to move apart from each other.

Observational evidence, such as the redshift of distant galaxies, supports the notion of the expanding universe, but is not a literal stretching of physical space, as space itself is not a physical substance. This redshift is interpreted as a result of the expansion of space, causing the light from distant objects to be stretched to longer wavelengths. 

• The expansion of the universe refers to the increase in distances between physical objects within the conceptual framework of space.

• The term "stretching" is indeed used as a metaphorical description of the expansion of the universe. It helps to convey the idea that the distances between galaxies and clusters of galaxies increase over time, resulting in the observed redshift of light from distant objects.

• The driving force behind the accelerated expansion of the universe is commonly attributed to dark energy, a theoretical form of energy that is postulated to permeate space. Dark energy is hypothesized to exert a repulsive gravitational effect, causing the expansion of the universe to accelerate and leading to the increased separation between galaxies.

• Observational evidence, including the redshift of light from distant galaxies, supports the concept of an expanding universe. The redshift is a result of the stretching of the wavelength of light as space expands, and it provides valuable insights into the dynamics of the universe.