Editing Weyl's postulate (section)

{{Short description|Concept in cosmology}}
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In relativistic [[physical cosmology|cosmology]], '''Weyl's postulate''' stipulates that in the [[Friedmann equations|Friedmann model]] of the universe (a [[fluid solution|fluid]] cosmological model), the wordlines of fluid particles (modeling galaxies) should be ''hypersurface orthogonal''. Meaning, they should form a 3-bundle of non-intersecting geodesics orthogonal to a series of spacelike hypersurfaces (hyperslices).<ref>{{cite book|last=Peebles|first=Jim|date=1971|title=Physical Cosmology|publisher=Princeton University Press |isbn=9780691646961}}</ref>

Sometimes, the additional hypothesis is added that the world lines form timelike [[geodesic (general relativity)|geodesic]]s.