What would you see in a time-lapse movie of the interstellar medium over hundreds of millions of years?

In a time-lapse movie of the interstellar medium over hundreds of millions of years, you would observe gas constantly changing form and moving at high speed. The interstellar medium is not a static environment; rather, it is a dynamic and complex region filled with various states of matter, including gas and dust that undergo continuous evolution due to processes such as star formation, supernova explosions, and galactic interactions.

Gas in the interstellar medium can be observed in different phases, such as hot ionized gas, warm neutral gas, and cold molecular gas. Over long periods, these gases can change in density, temperature, and composition as they interact with radiation from stars and other cosmic events. For instance, supernovae can compress nearby gas, leading to the formation of new stars, while stellar winds can disperse gas into surrounding regions.

These movements and transformations give rise to nebulae and can lead to significant changes in the structure and distribution of the interstellar medium, making it a lively and dynamic backdrop for the life cycles of stars and other celestial phenomena. Thus, the continuous motion and changing states of the gas are what would be depicted in a time-lapse visualization over an extensive timescale.