# Simultaneity

Simultaneity is the property of two events happening at the same time.

• In mathematics, a system of equations or a set of simultaneous equations share variables; a solution is a set of variable values for which all these equations are satisfied simultaneously.
• In modern physics two events may be simultaneous with respect to a time event as follows:
A central event (0,0) is used to anchor a spacetime plane {(x,t) in RxR} = ST where x measures distance in units of 30 centimeters and t measures time in nanoseconds. Space events satisfy |x| > |t| and the time events satisfy |x| < |t|. Now a space event e is simultaneous with the origin (0,0), with respect to a time event z, if e and z are hyperbolic-orthogonal points in ST. Two events g and h in ST are simultaneous with respect to z if their difference g - h in ST is hyperbolic-orthogonal to z.

• Simultaneity in Music (http://www.toysatellite.org/iolini/thesis2.html) by Robert Iolini. Extract from a Master of Arts thesis entitled Simultaneity in Music. Macquarie University. Sydney. Australia. February 1998.

• Art and Cultures
• Countries of the World (http://www.academickids.com/encyclopedia/index.php/Countries)
• Space and Astronomy