Universe

The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from sub-atomic particles to entire galactic filaments. Since the early 20th century, the field of cosmology establishes that space and time emerged together at the Big Bang 13.787±0.020 billion years ago and that the universe subsequently expanded. Today, the universe has expanded into an age and size that is only partially observable from Earth; while the spatial size of the entire universe is unknown, the smaller observable universe is approximately 93 billion light-years in diameter at present.