The universe
The universe is all of space and time [a] and their contents. [10] It comprises all of existence , any fundamental interaction , physical process and physical constant , and therefore all forms of energy and matter , and the structures they form, from sub-atomic particles to entire galactic filaments . Space and time, according to the prevailing cosmological theory of the Big Bang , emerged together 13.787 ± 0.020 billion years ago, [11] and the universe has been expanding ever since. Today the universe has expanded into an age and size that is physically only in parts observable as the observable universe , which is approximately 93 billion light-years in diameter at the present day, while the spatial size, if any, of the entire universe is unknown. [3] Some of the earliest...