specialized search engines such as technorati digg and newsvine are sometimes called ____

Equivalently one can use a quadratic form of signature (-,+,+,+) and this is the convention used by Naber, but we will use the other convention here. It is by definition ordinary 4-space with a non-degenerate quadratic form of signature (+,-,-,-). Minkowski spacetime is the setting for special relativity. It is the time that is associated with the world line of the clock, and is intimately related to the arc length of that world line and thereby to the geometry of spacetime. The bottom line is that proper time is the only time that is measured by any (ideal) clock. This argument carries over unchanged to general relativity simply by a localization observation - the metric of GR is locally the Minkowski metric. Some of Rindler's perspective is also a part of this note. You can refer to that book for more detailed mathematics and to Essential Relativity, Special General and Cosmological by Wolfgang Rindler for a less mathematical and more physical treatment. It is largely based on the treatment given in the book The Geometry of Minkowski Space time by Gregory L. This explanation is based on a geometric treatment of special relativity. The purpose here is explain a bit about the geometry of Minkowski space and to show why 'proper time' defined in terms of the 'spacetime interval' has anything to do with what clocks measure.

Specialized search engines such as technorati digg and newsvine are sometimes called ____