Spacetime foam
Abstract
The Einstein Lagrangian allows large fluctuations of the metric and topology of spacetime on scales of order of the Planck length. This foamlike structure can be described by introducing a Λ term as a Lagrange multiplier for the 4volume. The dominant contribution to the path integral seems to come from metrics which have about one unit of topology per Planck volume.
 Publication:

Nuclear Physics B
 Pub Date:
 November 1978
 DOI:
 10.1016/05503213(78)903759
 Bibcode:
 1978NuPhB.144..349H