Electromagnetic radiation is not currently a significant factor in intergalactic space expansion due to its low energy density, which is much smaller than that of dark energy. In the early universe, radiation had a more substantial impact on expansion dynamics, but this is no longer the case. Beam-powered propulsion, which involves radiation pushing against objects, does not relate to the expansion of the universe itself. The energy densities of different substances in cosmology, such as matter, radiation, and dark energy, behave differently as the universe expands, with radiation density decreasing more rapidly than that of dark energy. Overall, the discussion emphasizes that while electromagnetic waves permeate space, their influence on cosmic expansion is negligible compared to dark energy.