preBig

PreBig is not a standardized encyclopedia term, but in cosmology it is commonly shorthand for the pre-Big Bang concept, especially within string theory–inspired models. The pre-Big Bang scenario, developed in the 1990s by Gasperini and Veneziano, envisions a phase of the universe that precedes the conventional Big Bang. In this framework, the early universe starts from a cold, flat, weakly coupled state and evolves through a dilaton-driven phase in which the cosmic scale factor increases in a quasi-inflationary way in the string frame.

One central issue is the graceful exit problem: connecting the pre-Big Bang phase to the standard radiation- and matter-dominated expansion without introducing a singularity or pathologies. The proposed resolutions vary from higher-curvature corrections to non-perturbative string effects, but a universally accepted mechanism has not emerged.

Predictions depend on the model, but typical features include a distinctive spectrum of primordial fluctuations and gravitational waves, often with a blue tilt, meaning higher amplitudes at higher frequencies. These signatures are challenging to observe and are not currently established by data, leaving the scenario as an alternative to inflation rather than a replacement.

Because it relies on physics beyond the Standard Model and general relativity, pre-Big Bang cosmology remains speculative, and it is considered a minority view within the broader cosmological community. It continues to be explored in theoretical work on quantum gravity and string cosmology, with researchers examining possible observational tests and theoretical consistency.

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