Compare · The Dark Universe

Holographic Dark Energy vs Chaplygin Gas

Dark Energy Candidates · within family

	Holographic Dark Energy Frontier	Chaplygin Gas Rejected
Proposed	2004	2001 / 2002
Key figures	Miao Li, Andrew G. Cohen, David B. Kaplan, Ann E. Nelson	Alexander Kamenshchik, Ugo Moschella, Vincent Pasquier, Maria da Conceicao Bento, Orfeu Bertolami, Anjan Ananda Sen
In one sentence	Holographic dark energy ties the dark energy density to the size of the cosmic event horizon, motivated by a limit from black hole physics on the entropy a region of space can hold.	The Chaplygin gas was proposed as a single exotic fluid that behaves like matter early on and like a cosmological constant later, replacing both dark matter and dark energy.
Predictions	An equation of state of about -0.90 today, for a dark energy fraction of 0.73 in the original model. For some values of its free parameter, the equation of state crosses -1 and turns phantom, a quintom-type behaviour. If the equation of state ends below -1, the expansion runs toward a Big Rip in the far future.	A single fluid that behaves like non-relativistic matter at early times and like a cosmological constant at late times, with an intermediate phase between. An effective cosmological constant whose value increases over time, as the 2001 paper states. No separate cold dark matter, since the same fluid must both seed structure and drive the acceleration. Oscillations or exponential growth in the matter power spectrum, the signature that later ruled the unified model out.
Where it breaks	Adding [[cosmic microwave background]] data drives the fit to c below 1, with w crossing -1 at more than 10 sigma, and makes the model significantly less favoured than ΛCDM (Li et al. 2025). Zhang and Wu (2005) found that simulated supernova data built from a pure [[cosmological constant]] still pushed the model into its phantom-crossing range. A phantom future ending in a Big Rip is a problem shared with phantom energy, and interacting versions of the model are studied partly to avoid it.	With dark matter kept separate, WMAP and supernova data force the generalized gas close to a cosmological constant, with its exponent below 0.2 (Amendola et al. 2003). As a unified model of dark matter and dark energy, only the limit that matches ΛCDM survives the data, so the surviving version makes no distinct prediction.
Key unresolved problem	The CMB problem: once CMB data are included, the fit drives w below -1 toward a Big Rip and the model falls behind ΛCDM.	The structure problem: a single fluid that drives the acceleration distorts the growth of cosmic structure, and only the version identical to ΛCDM fits the data.
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Holographic Dark Energy

2004 · Frontier

Chaplygin Gas

2001 / 2002 · Rejected

Proposed

2004

2001 / 2002

Key figures

Miao Li, Andrew G. Cohen, David B. Kaplan, Ann E. Nelson

Alexander Kamenshchik, Ugo Moschella, Vincent Pasquier, Maria da Conceicao Bento, Orfeu Bertolami, Anjan Ananda Sen

In one sentence

Holographic dark energy ties the dark energy density to the size of the cosmic event horizon, motivated by a limit from black hole physics on the entropy a region of space can hold.

The Chaplygin gas was proposed as a single exotic fluid that behaves like matter early on and like a cosmological constant later, replacing both dark matter and dark energy.

Predictions

An equation of state of about -0.90 today, for a dark energy fraction of 0.73 in the original model.
For some values of its free parameter, the equation of state crosses -1 and turns phantom, a quintom-type behaviour.
If the equation of state ends below -1, the expansion runs toward a Big Rip in the far future.

A single fluid that behaves like non-relativistic matter at early times and like a cosmological constant at late times, with an intermediate phase between.
An effective cosmological constant whose value increases over time, as the 2001 paper states.
No separate cold dark matter, since the same fluid must both seed structure and drive the acceleration.
Oscillations or exponential growth in the matter power spectrum, the signature that later ruled the unified model out.

Where it breaks

Adding [[cosmic microwave background]] data drives the fit to c below 1, with w crossing -1 at more than 10 sigma, and makes the model significantly less favoured than ΛCDM (Li et al. 2025).
Zhang and Wu (2005) found that simulated supernova data built from a pure [[cosmological constant]] still pushed the model into its phantom-crossing range.
A phantom future ending in a Big Rip is a problem shared with phantom energy, and interacting versions of the model are studied partly to avoid it.

With dark matter kept separate, WMAP and supernova data force the generalized gas close to a cosmological constant, with its exponent below 0.2 (Amendola et al. 2003).
As a unified model of dark matter and dark energy, only the limit that matches ΛCDM survives the data, so the surviving version makes no distinct prediction.

Key unresolved problem

The CMB problem: once CMB data are included, the fit drives w below -1 toward a Big Rip and the model falls behind ΛCDM.

The structure problem: a single fluid that drives the acceleration distorts the growth of cosmic structure, and only the version identical to ΛCDM fits the data.

Reader vote

No votes yet