Ekpyrotic Cyclic Universe
Two parallel branes collide periodically, each collision is a Big Bang.
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
Our universe was born from a collision between two parallel branes, and the collision repeats every trillion years.
The claim
In the ekpyrotic model, our universe sits on a 3-brane in a higher-dimensional bulk. A parallel "hidden" brane lurks just nearby in the extra dimension. Slowly, over enormous timescales, the two branes are drawn together. When they collide, the released energy fills our brane with hot matter and radiation, that is our Big Bang.
After the collision, the branes separate, the universe expands and cools, and eventually dark energy dilutes it. Then the slow attraction begins again. The cycle repeats forever.
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
- Negligible primordial gravitational waves (r ≈ 0)
- Slightly red-tilted scalar power spectrum
- Each cycle ~10¹² years or longer
Evidence
- Resolves horizon and flatness problems without inflation
- Low tensor-to-scalar ratio prediction consistent with current data
Counterpoints
- Requires string theory and extra dimensions
- Brane-collision mechanism not fully derived
- Has its own initial-conditions problem
Variants in this family
▸Go deeperTechnical detail with proper terminology
In the cyclic model, the scalar field (a brane modulus) drives slow ekpyrotic contraction. The equation of state w = p/ρ greatly exceeds 1, suppressing anisotropies and curvature exponentially.
Quantum fluctuations during contraction generate a nearly scale-invariant spectrum of density perturbations, similar to inflation but with much lower tensor-to-scalar ratio.
References
- EstablishedKhoury, Ovrut, Steinhardt, Turok (2001). Phys. Rev. D 64, 123522
- EstablishedSteinhardt & Turok (2002). Science 296, 1436
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.