what is space

Space is a term that can refer to various phenomena in science, mathematics, and computing and generally encompasses the concept of an area or region. In classical physics, physical space is often conceived in three linear dimensions, while modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as spacetime. Outer space, commonly referred to simply as space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. It is a near-perfect vacuum containing a low density of particles, predominantly a plasma of hydrogen and helium as well as electromagnetic radiation, magnetic fields, neutrinos, dust, and cosmic rays. From our Earth-bound perspective, outer space is most often thought to begin about 62 miles (100 kilometers) above sea level at what is known as the Kármán line. Space is usually regarded as being completely empty, but the vast gaps between the stars and planets are filled with huge amounts of thinly spread gas and dust. Even the emptiest parts of space contain at least a few hundred atoms or molecules per cubic meter. Space is also filled with many forms of radiation that are dangerous to astronauts, such as infrared and ultraviolet radiation from the Sun, high-energy X-rays, gamma rays, and cosmic rays.