Loop Quantum Big Bounce
Quantum geometry prevents the singularity. Our Bang is the bounce of a contracting predecessor.
Placeholder for a 3D visualisation of Cyclic & Bouncing Cosmologies. The interactive scene will land in Phase 3. There is no absolute beginning. Our universe is the latest phase in an eternal cycle. Variants disagree on the mechanism: a conformal transition (Penrose), a quantum bounce (LQC), a brane collision (Ekpyrotic), or a dilaton-driven bounce (Pre-Big Bang).
In one sentence
A previous contracting universe bounced, quantum geometry prevented the collapse from becoming a singularity.
The claim
Loop Quantum Cosmology applies the quantized spacetime geometry of Loop Quantum Gravity to the early universe. At classical extremes, when density approaches the Planck scale, spacetime cannot be treated as smooth. Quantum geometry takes over, and predicts that infinitely high density cannot occur.
Instead of collapsing into a singularity, a contracting universe reaches a maximum density and "bounces" back into expansion. Our Big Bang was not the absolute beginning, it was the bounce point.
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.
Predictions
- Quantum bounce at Planck density
- Modified CMB power spectrum at large angular scales
- Pre-Bang contracting universe phase
Evidence
- Mathematically consistent with LQG framework
- Singularity-free without ad hoc assumptions
Counterpoints
- Effects only at Planck scale, not currently testable
- LQG itself is incomplete
- CMB corrections sub-dominant to cosmic variance
Variants in this family
▸Go deeperTechnical detail with proper terminology
In LQC, the classical FRW equations get quantum corrections at high density. The modified Friedmann equation includes a term -ρ²/ρ_crit, where ρ_crit ~ 0.41ρ_Planck.
When density approaches ρ_crit, the Hubble parameter goes to zero and reverses sign, this is the bounce. The bounce happens at densities ~10⁻³ ρ_Planck, comfortably within the regime where LQC corrections are valid.
References
- EstablishedBojowald (2001). Phys. Rev. Lett. 86, 5227
- EstablishedAshtekar, Pawlowski, Singh (2006). Phys. Rev. Lett. 96, 141301
- EstablishedAshtekar & Singh (2011). Class. Quantum Grav. 28, 213001
Also appears in
This variant answers questions in other chapters too. It is canonically housed here.
Spotted an error? Have a source to add?
Prefer email?
You can also send a prefilled email with the variant URL already filled in.