null geodesic

A Dictionary of Astronomy | 1997 | 478 words | Copyright

null geodesic A path or geodesic joining two events in space-time along which the separation is zero. The separation in space-time can be zero even if the two events actually occur at different points in space. This apparent contradiction can arise because in the formula for determining the separation of events in space-time, the time interval between the events has the opposite sign to that for their distance apart in space. Light in a vacuum travels along a null geodesic.

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