Though an anti–de Sitter (AdS) vacuum, corresponding to a negative cosmological constant (NCC), can be not responsible for the acceleration of the current Universe, it might coexist with one evolving positive dark energy component at low redshift, as well as with early dark energy around the recombination to solve the Hubble tension. In this paper, we investigate the scenario with one AdS vacuum around the recombination and one at low redshift, and from both current observational and theoretical perspectives preliminarily explore the possibility that the Universe experienced a landscape with multiple AdS vacua since matter-radiation equality.

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• Cosmic microwave background
• Cosmological constant
• Cosmological parameters
• Dark energy
• Quantum cosmology