Classical laws previously ruled out any time travel possibility.

Evidence

However, as has been described in earlier chapters, the classical laws were superseded by quantum laws based on the uncertainty principle. — Hawking, Stephen, A Brief History of Time, 290

Categorization

• corroborated: 2 independent passages support this claim — Hawking, Stephen, A Brief History of Time, 290
• XREF: connects to: The chronology protection conjecture might prevent time travel effects. — Hawking, Stephen, A Brief History of Time, 305

Broader Connections

• The chronology protection conjecture might prevent time travel effects. #qualifies (0.70) — Hawking, Stephen, A Brief History of Time, 305