if i might add:
".... all phenomena are shunya, or empty of inherent existence ...." -- is not limited to 'certain schools of Mahayana'. while i might quite possibly be mistaken on this point, to the best of my knowledge, this is a tenet of the Buddha's teaching which is accepted -- if, perhaps, not emphasized -- by most Buddhist sects.
this thesis is taken to the point of stating that: 'the Universe itself has been constantly expanding from & contracting to, nothingness (or sunyatta), in all its manifestations; and this process has been going for a period beyond even the knowledge of the Buddhas themselves. it is postulated that the Univers has been creating itself from nothingness, expanding to an unstated extent & collapsing back to nothingess; then back to expansion, etc.; going through this process over & over again, perhaps ad infinitum.
(Universe taken to mean: all of existence - 'Sansara'; and infinity taken to be: a period of time which no living being can travel - in thought, meditation, or imagination - not even a Buddha.)
http://www.buddhistlibraryonline.net/en/the-teachings/suttapitaka/dighanikaya/pathikavaggapali/27-dn27-agganna-sutta/61-Agganna.html
http://www.buddhistlibraryonline.net/index.php
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