Is empty space a pure vacuum?

Space is never completely empty. Although hydrogen, helium, and other lighter elements are widely distributed, interstellar space isn't a true vacuum.

Additionally, virtual particle/anti particle pairs spontaneously form in a vacuum as a result of quantum effects, and they quickly annihilate one another.

A region of space that is close to a mass object will be four-dimensionally curved, and particles in space-time that are not subject to external forces will follow geodesics.

Although vacuums are sometimes used interchangeably with empty space, they are not entirely vacuums because there are traces of particles and electromagnetic radiation in empty space, which are also referred to as vacuum fluctuations. These fluctuations are caused by the uncertainty that exists in quantum mechanics and lead to the spontaneous creation and annihilation of particle-antiparticle pairs.