The concept of matter being "destroyed" due to the expansion of the universe is a subject of ongoing scientific investigation and debate. Currently, the prevailing understanding in cosmology is that matter itself is not destroyed but rather becomes increasingly separated from us as the universe expands.
According to the current model of cosmic expansion, the space between galaxies is stretching, causing the distances between them to increase over time. This expansion is governed by the properties of dark energy, a hypothetical form of energy that is thought to be responsible for the accelerated expansion of the universe. As the expansion continues, galaxies that are sufficiently far away from us may eventually move beyond our observable universe. This means that the light or other signals from those distant galaxies will no longer reach us, leading to their exclusion from our observable universe.
However, it is important to note that even though we cannot observe or interact with matter beyond our observable universe, it does not necessarily imply that the matter itself has been destroyed. It simply means that due to the expansion of space, the distance between us and that matter has become so vast that any information or signals from it can no longer reach us.
Our current understanding suggests that matter is conserved, meaning it cannot be created or destroyed but can only change forms or be redistributed. So, while matter may become inaccessible to us as the universe expands, it is generally considered to persist in some form elsewhere within the cosmos.