Pre-Big Bang (Gasperini-Veneziano)

1993Maurizio Gasperini, Gabriele VenezianoSpeculativeAlso answers, Ch.02 The Origin of Our Universe2 primary sources, 2 established

String theory predicts a dilaton-driven contracting phase before the Bang.

Visualisation · Cyclic & Bouncing Cosmologies

string theory: A framework proposing that fundamental particles are tiny vibrating strings rather than points, requiring extra dimensions of space.
scalar field: A field with one value at each point in space, like a temperature map. The inflaton is one example.
inflation: A brief burst of accelerating expansion in the very early universe, smoothing out and stretching whatever existed before.
singularity: A point in a theory where quantities like density become infinite, signaling the theory has broken down.

§1 · The claim, in one sentence

In string cosmology, a weakly-coupled contracting phase preceded the Big Bang, driven by the dilaton field.

§2 · Why it might be true

The Pre-Big Bang scenario emerges from low-energy string theory. String theory includes a scalar field (a quantity with a single value at every point in space) called the dilaton, which sets how strong all the forces are. In the Pre-Big Bang model, the universe began in an empty, cold, weakly-coupled state with the dilaton at very negative values. The dilaton-driven dynamics led to accelerating expansion ("dilaton-driven inflation") that ended at a high-curvature bounce.

After the bounce, the universe entered the standard hot Big Bang phase. The asymmetry between the pre-Bang and post-Bang phases is a defining feature: cold and contracting before, hot and expanding after.

The family stance

A previous cycle, aeon, contracting phase, or alternate-brane state existed before our universe. The "before" is a physically connected predecessor, not nothing or another arena.

§2.5 · Evidence

Naturally derived from string theory low-energy action
Avoids singularity via high-curvature regime

§3 · What you'd need to test it

Specific tilted spectrum of gravitational waves (blue tilt)
Before the Bang, a quiet low-energy state described by string theory, where all the forces were very weak (a weakly-coupled string vacuum)
Universe is asymmetric across the Bang

§4 · Where it breaks

Pre-Bang gravity-wave spectrum not yet detected
Mechanism of the bounce remains incompletely understood
Less developed than LQC bounce

Go deeper

The Gasperini-Veneziano scenario uses the duality symmetries of string theory. The pre-Bang and post-Bang phases are related by scale-factor duality: a(t) ↔ 1/a(-t). The dilaton φ runs from -∞ to a finite value across the bounce.

The high-curvature bounce regime is where string-scale physics dominates and the low-energy effective action breaks down. Various proposed completions (loop corrections, string-theoretic completions) attempt to describe this transition, but none is universally accepted.

▸§5 · Who built it, and when(2 sources, 2 established)

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