The statement that "space is a vacuum, so entropy will be 0" is not accurate. While space is indeed a vacuum in the sense that it lacks matter and energy, it is not devoid of physical properties or processes.
Entropy is a measure of the disorder or randomness in a system. In thermodynamics, it is commonly associated with the distribution of energy within a system. However, entropy is not strictly tied to the presence or absence of matter. It is a concept that applies to various physical systems, including those without matter, such as radiation fields.
When it comes to the expansion of the universe, the concept of entropy becomes more complex. The universe as a whole is often considered an isolated system, and the prevailing scientific consensus, supported by observations and theoretical models, is that the universe is expanding. This expansion is often described in terms of the metric expansion of space.
The entropy of the universe, in the context of its expansion, is a subject of ongoing research and debate. There are different perspectives on how entropy behaves in an expanding universe. Some theories propose that entropy increases as the universe expands, while others suggest that it remains constant or even decreases. These discussions involve considerations beyond the simple notion of matter distribution.
In summary, the expansion of the universe and the concept of entropy are complex topics in cosmology. While the vacuum nature of space does not imply zero entropy, it is important to recognize that entropy in the universe involves more intricate considerations and is not solely determined by the presence or absence of matter.