The current scientific understanding of the fundamental nature of the universe is based on the Big Bang theory and the observations and measurements made by astronomers and astrophysicists. According to this theory, the universe began as a hot, dense and infinitely small singularity around 13.8 billion years ago, and has been expanding and cooling ever since.

The composition of the universe is believed to be mostly dark matter and dark energy, which together make up about 95% of the universe's total energy density. Dark matter is a type of matter that does not interact with light or other forms of electromagnetic radiation, but is believed to exist because of its gravitational effects on visible matter. Dark energy, on the other hand, is a mysterious force that is causing the expansion of the universe to accelerate.

The visible matter in the universe, including stars, galaxies, and planets, makes up only about 5% of the universe's total energy density. This visible matter is made up of atoms, which are themselves composed of protons, neutrons, and electrons.

The structure of the universe is thought to be made up of clusters and superclusters of galaxies, which are distributed throughout the universe in a web-like pattern. The large-scale structure of the universe is influenced by the distribution of dark matter, which is believed to provide the framework for the formation of galaxies and galaxy clusters.

The ultimate fate of the universe is still uncertain, but current models suggest that the expansion of the universe will continue to accelerate due to the influence of dark energy. This could eventually lead to a "Big Freeze," where the universe becomes cold and dark as all the stars burn out and the expansion of the universe continues indefinitely. Alternatively, the universe could experience a "Big Crunch," where the expansion of the universe slows and reverses, leading to the collapse of the universe back into a singularity.