Spacelike
A four-vector a_mu is said to be spacelike if its four-vector norm satisfies a_mua^mu>0.
One should note that the four-vector norm is nothing more than a special case of the more general Lorentzian inner product <·,·> on n-dimensional Lorentzian space with metric signature (1,n-1). In this more general environment, the inner product of two vectors x=(x_0,x_1,...,x_(n-1)) and y=(y_0,y_1,...,y_(n-1)) has the form
| <x,y>=-x_0y_0+x_1y_1+...+x_(n-1)y_(n-1), |
whereby one defines a vector a to be spacelike precisely when <a,a>>0.
Geometrically, the collection of all spacelike vectors lie in the open subset of R^n formed by the exterior of the light cone.
See also
Light Cone, Lightlike, Lorentzian Inner Product, Lorentzian Space, Metric Signature, Negative Lightlike, Negative Timelike, Positive Lightlike, Positive Timelike, TimelikePortions of this entry contributed by Christopher Stover
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References
Misner, C. W.; Thorne, K. S.; and Wheeler, J. A. Gravitation. San Francisco, CA: W. H. Freeman, p. 53, 1973.Ratcliffe, J. G. Foundations of Hyperbolic Manifolds. New York: Springer-Verlag, 2006.Referenced on Wolfram|Alpha
SpacelikeCite this as:
Stover, Christopher and Weisstein, Eric W. "Spacelike." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Spacelike.html