Compare · The Dark Universe

Chaplygin Gas vs Holographic Dark Energy

Dark Energy Candidates · within family

	Chaplygin Gas Rejected	Holographic Dark Energy Frontier
Proposed	2001 / 2002	2004
Key figures	Alexander Kamenshchik, Ugo Moschella, Vincent Pasquier, Maria da Conceicao Bento, Orfeu Bertolami, Anjan Ananda Sen	Miao Li, Andrew G. Cohen, David B. Kaplan, Ann E. Nelson
In one sentence	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.	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.
Predictions	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.	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.
Where it breaks	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.	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.
Key unresolved problem	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.	The CMB problem: once CMB data are included, the fit drives w below -1 toward a Big Rip and the model falls behind ΛCDM.
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Chaplygin Gas

2001 / 2002 · Rejected

Holographic Dark Energy

2004 · Frontier

Proposed

2001 / 2002

2004

Key figures

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

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

In one sentence

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.

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.

Predictions

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.

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.

Where it breaks

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.

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.

Key unresolved problem

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.

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

Reader vote

No votes yet