Spacetime or space-time refers to the mathmatical physics model relating time and space into a continuum.  There is both contention and fascination with this space-time contiuum concept much of it started with Einstein era physics of the early 20th century.  In Gravity, Mass Momentum by Jason Jarvis a discussion of gravity, mass momentum, and a re-evaluation of spacetime continuum limits are discussed.  Also discussed is gravity in detail as it pertains to Earth, Jupiter, and the origin of Earth as body N.