The universe began with a big bang singularity due to general relativity.

Evidence

there must have been a big bang singularity provided only that general relativity is correct and the universe contains as much matter as we observe. — Hawking, Stephen, A Brief History of Time, 100

Categorization

• corroborated: 2 independent passages support this claim — Hawking, Stephen, A Brief History of Time, 100
• XREF: connects to: The existence of the universe raises questions about its origin. — Hawking, Stephen, A Brief History of Time, 341