The Short Version
No credible scientific source supports the assertion that parallel universes are a confirmed reality. The most authoritative sources — including the Stanford Encyclopedia of Philosophy and peer-reviewed literature — consistently describe parallel universes as a feature of certain theoretical interpretations (such as the Many-Worlds Interpretation) that lack direct empirical evidence. The strongest observational candidate, bubble-collision signatures in the cosmic microwave background, has not reached statistical significance. Stating their existence as fact conflates mathematical possibility with physical confirmation.