Compare · Before the Universe

Pre-Big Bang (Gasperini-Veneziano) vs String-Gas Cosmology

← Back to Pre-Big Bang (Gasperini-Veneziano)

Cyclic & Bouncing Cosmologies· within family

	Pre-Big Bang (Gasperini-Veneziano) Speculative	String-Gas Cosmology Speculative
Proposed	1993	1989
Key figures	Maurizio Gasperini, Gabriele Veneziano	Robert Brandenberger, Cumrun Vafa
In one sentence	In string cosmology, a weakly-coupled contracting phase preceded the Big Bang, driven by the dilaton field.	String-Gas Cosmology proposes that the Big Bang was the dynamics of a gas of fundamental strings, with cosmic structure emerging from string thermodynamics.
Predictions	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	The number of large spatial dimensions is constrained by string dynamics (predicts three) Specific spectrum of cosmological perturbations from string thermodynamics Distinct signatures in CMB power spectrum that differ from inflation Relationship between primordial gravitational waves and density perturbations
Where it breaks	Pre-Bang gravity-wave spectrum not yet detected Mechanism of the bounce remains incompletely understood Less developed than LQC bounce	String theory itself has not been experimentally verified Specific predictions are model-dependent and not yet decisive The mechanism for emerging from the high-temperature string gas phase is not fully worked out
Key unresolved problem	The breakdown at the bounce: at the moment of greatest curvature the low-energy string equations stop working, and no one has an accepted replacement, so the switch from shrinking to expanding is not fully described.	The missing handoff: no one has fully worked out how the hot early string-gas phase, a dense tangle of vibrating strings, gives way to the ordinary expanding universe we see, so the link to observed physics is incomplete.
Reader vote	No votes yet	No votes yet

Pre-Big Bang (Gasperini-Veneziano)

1993 · Speculative

String-Gas Cosmology

1989 · Speculative

Proposed

1993

1989

Key figures

Maurizio Gasperini, Gabriele Veneziano

Robert Brandenberger, Cumrun Vafa

In one sentence

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

String-Gas Cosmology proposes that the Big Bang was the dynamics of a gas of fundamental strings, with cosmic structure emerging from string thermodynamics.

Predictions

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

The number of large spatial dimensions is constrained by string dynamics (predicts three)
Specific spectrum of cosmological perturbations from string thermodynamics
Distinct signatures in CMB power spectrum that differ from inflation
Relationship between primordial gravitational waves and density perturbations

Where it breaks

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

String theory itself has not been experimentally verified
Specific predictions are model-dependent and not yet decisive
The mechanism for emerging from the high-temperature string gas phase is not fully worked out

Key unresolved problem

The breakdown at the bounce: at the moment of greatest curvature the low-energy string equations stop working, and no one has an accepted replacement, so the switch from shrinking to expanding is not fully described.

The missing handoff: no one has fully worked out how the hot early string-gas phase, a dense tangle of vibrating strings, gives way to the ordinary expanding universe we see, so the link to observed physics is incomplete.

Reader vote

No votes yet