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Conformal Cyclic Cosmology (CCC) vs Ekpyrotic Cyclic Universe

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Cyclic & Bouncing Cosmologies· within family

	Conformal Cyclic Cosmology (CCC) Speculative	Ekpyrotic Cyclic Universe Speculative
Proposed	2005	2001
Key figures	Roger Penrose	Paul Steinhardt, Neil Turok, Justin Khoury, Burt Ovrut
In one sentence	A previous "aeon" existed. Its conformally smooth heat-death geometry became our Big Bang.	Our universe was born from a collision between two parallel brane\|branes, and the collision repeats every trillion years.
Predictions	Concentric CMB rings (Hawking points) Smooth conformal transition, no [[singularity]] Massless [[dark matter]] required at aeon boundary	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
Where it breaks	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.	Requires [[string theory]] and extra dimensions Brane-collision mechanism not fully derived Has its own initial-conditions problem
Key unresolved problem	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.	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.
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Conformal Cyclic Cosmology (CCC)

2005 · Speculative

Ekpyrotic Cyclic Universe

2001 · Speculative

Proposed

2005

2001

Key figures

Roger Penrose

Paul Steinhardt, Neil Turok, Justin Khoury, Burt Ovrut

In one sentence

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

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

Predictions

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

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

Where it breaks

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.

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

Key unresolved problem

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.

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.

Reader vote

No votes yet