Compare · The Dark Universe

Coupled Quintessence vs Holographic Dark Energy

Dark Energy Candidates · within family

	Coupled Quintessence Frontier	Holographic Dark Energy Frontier
Proposed	2000	2004
Key figures	Luca Amendola	Miao Li, Andrew G. Cohen, David B. Kaplan, Ann E. Nelson
In one sentence	Coupled quintessence links the dark energy field directly to matter, so the two exchange energy, dark matter in many versions feels a fifth force, and dark energy stays present through the matter era.	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	During matter domination the field keeps a small, nearly constant share of the total energy density, unlike uncoupled quintessence, which quickly becomes negligible. The [[cosmic microwave background]] spectrum tilts at large angles, and its acoustic peaks shift position and change height. In Amendola's original model, matter clumps less on scales of about 8 Mpc/h today than in uncoupled models; the size and sign of the effect depend on the coupling chosen. Dark matter particles attract each other more strongly than gravity alone predicts, through a fifth force set by the coupling.	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	Already in 2000, the data limited the dimensionless coupling to at most 0.1, so any effect on cosmic history must be small. Pettorino notes that the Planck plus Hubble Space Telescope preference comes mostly from the Hubble tension and may reflect systematics in one data set. When Planck is combined with BAO, supernova, and lensing data, interacting dark energy is fully consistent with a [[cosmological constant]] and shows no compelling coupling (Di Valentino et al. 2017).	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 evidence problem: hints of a nonzero coupling come mostly from the Hubble tension, and they weaken when more data sets are combined.	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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Coupled Quintessence

2000 · Frontier

Holographic Dark Energy

2004 · Frontier

Proposed

2000

2004

Key figures

Luca Amendola

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

In one sentence

Coupled quintessence links the dark energy field directly to matter, so the two exchange energy, dark matter in many versions feels a fifth force, and dark energy stays present through the matter era.

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

During matter domination the field keeps a small, nearly constant share of the total energy density, unlike uncoupled quintessence, which quickly becomes negligible.
The [[cosmic microwave background]] spectrum tilts at large angles, and its acoustic peaks shift position and change height.
In Amendola's original model, matter clumps less on scales of about 8 Mpc/h today than in uncoupled models; the size and sign of the effect depend on the coupling chosen.
Dark matter particles attract each other more strongly than gravity alone predicts, through a fifth force set by the coupling.

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

Already in 2000, the data limited the dimensionless coupling to at most 0.1, so any effect on cosmic history must be small.
Pettorino notes that the Planck plus Hubble Space Telescope preference comes mostly from the Hubble tension and may reflect systematics in one data set.
When Planck is combined with BAO, supernova, and lensing data, interacting dark energy is fully consistent with a [[cosmological constant]] and shows no compelling coupling (Di Valentino et al. 2017).

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 evidence problem: hints of a nonzero coupling come mostly from the Hubble tension, and they weaken when more data sets are combined.

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