Is my understanding correct?
Weren't it for the internal resistance forces between particles in a solid object, the expansion of the Universe would continuously increase the distances between all of those particles, gradually "pulverizing" the solid. The size of a bar of steel remains constant though, and the manner in which it remains constant is through internal resistance forces, which imply internal stresses are present.
We don't fully understand this expansion actually. This is an effect measured from the CMB and from cepheids, so it's true for light travelling in vacuum. If there is a cosmological constant, it stretches the vacuum, but actually it is really a weak thing. It gets strong due to the super large scale of the universe. When you are in the cosmic webs, filaments, there the gravitational potential dominates over the effect of the cosmological constant. There the effect is extremely small, non measurable, maybe even zero depending on the true effective coupling between gravity and matter and lambda.
