Compare · Before the Universe

Ekpyrotic Cyclic Universe vs Conformal Cyclic Cosmology (CCC)

Cyclic & Bouncing Cosmologies· within family

	Ekpyrotic Cyclic Universe Speculative	Conformal Cyclic Cosmology (CCC) Speculative
Proposed	2001	2005
Key figures	Paul Steinhardt, Neil Turok, Justin Khoury, Burt Ovrut	Roger Penrose
In one sentence	Our universe was born from a collision between two parallel brane\|branes, and the collision repeats every trillion years.	A previous "aeon" existed. Its conformally smooth heat-death geometry became our Big Bang.
Predictions	Almost no primordial gravitational waves: the tensor-to-scalar ratio r, the strength of gravitational-wave ripples relative to density ripples, sits near zero (r ≈ 0) The spectrum of primordial density ripples is slightly stronger at large scales than small, a so-called red tilt Each cycle ~10¹² years or longer	Concentric CMB rings (Hawking points) Smooth conformal transition, no [[singularity]] Massless [[dark matter]] required at aeon boundary
Where it breaks	Requires [[string theory]] and extra dimensions Brane-collision mechanism not fully derived Has its own initial-conditions problem	Independent analyses find rings consistent with noise Requires massless dark matter, not established Community consensus is largely skeptical Bodnia et al. (2024) find no statistically significant low-variance circles or Hawking points in Planck/WMAP data using a ResNet18 ML pipeline, contradicting earlier Gurzadyan-Penrose claims.
Key unresolved problem	The missing derivation: the brane collision driving the model, two higher-dimensional sheets striking each other, has never been worked out from string theory's basic rules, so the bounce itself stays physically unspecified.	The missing fingerprint: other teams cannot find the predicted Hawking-point rings, faint circles in the cosmic microwave background, leaving CCC's one big observational claim statistically unsupported.
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Ekpyrotic Cyclic Universe

2001 · Speculative

Conformal Cyclic Cosmology (CCC)

2005 · Speculative

Proposed

2001

2005

Key figures

Paul Steinhardt, Neil Turok, Justin Khoury, Burt Ovrut

Roger Penrose

In one sentence

Our universe was born from a collision between two parallel brane|branes, and the collision repeats every trillion years.

A previous "aeon" existed. Its conformally smooth heat-death geometry became our Big Bang.

Predictions

Almost no primordial gravitational waves: the tensor-to-scalar ratio r, the strength of gravitational-wave ripples relative to density ripples, sits near zero (r ≈ 0)
The spectrum of primordial density ripples is slightly stronger at large scales than small, a so-called red tilt
Each cycle ~10¹² years or longer

Concentric CMB rings (Hawking points)
Smooth conformal transition, no [[singularity]]
Massless [[dark matter]] required at aeon boundary

Where it breaks

Requires [[string theory]] and extra dimensions
Brane-collision mechanism not fully derived
Has its own initial-conditions problem

Independent analyses find rings consistent with noise
Requires massless dark matter, not established
Community consensus is largely skeptical
Bodnia et al. (2024) find no statistically significant low-variance circles or Hawking points in Planck/WMAP data using a ResNet18 ML pipeline, contradicting earlier Gurzadyan-Penrose claims.

Key unresolved problem

The missing derivation: the brane collision driving the model, two higher-dimensional sheets striking each other, has never been worked out from string theory's basic rules, so the bounce itself stays physically unspecified.

The missing fingerprint: other teams cannot find the predicted Hawking-point rings, faint circles in the cosmic microwave background, leaving CCC's one big observational claim statistically unsupported.

Reader vote

No votes yet