Compare · Before the Universe

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

Cyclic & Bouncing Cosmologies· within family

	String-Gas Cosmology Speculative	Pre-Big Bang (Gasperini-Veneziano) Speculative
Proposed	1989	1993
Key figures	Robert Brandenberger, Cumrun Vafa	Maurizio Gasperini, Gabriele Veneziano
In one sentence	String-Gas Cosmology proposes that the Big Bang was the dynamics of a gas of fundamental strings, with cosmic structure emerging from string thermodynamics.	In string cosmology, a weakly-coupled contracting phase preceded the Big Bang, driven by the dilaton field.
Predictions	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	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
Where it breaks	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	Pre-Bang gravity-wave spectrum not yet detected Mechanism of the bounce remains incompletely understood Less developed than LQC bounce
Key unresolved problem	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.	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.
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String-Gas Cosmology

1989 · Speculative

Pre-Big Bang (Gasperini-Veneziano)

1993 · Speculative

Proposed

1989

1993

Key figures

Robert Brandenberger, Cumrun Vafa

Maurizio Gasperini, Gabriele Veneziano

In one sentence

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

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

Predictions

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

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

Where it breaks

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

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

Key unresolved problem

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.

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.

Reader vote

No votes yet