👉 The null fluid, also known as the vacuum of space or the interstellar medium's low-density region, is a theoretical concept representing the absence of matter in vast regions of space. Unlike a true vacuum, which is an idealized state with zero particles and energy, the null fluid accounts for the extremely low density of matter and radiation found in these expansive voids. It's not a complete absence but rather a region where particle density is so minimal that the effects of gravity and electromagnetic interactions are negligible. This concept helps physicists understand the behavior of matter and energy in the universe's most sparsely populated areas, contributing to theories about dark matter, cosmic expansion, and the large-scale structure of the cosmos.
