Compare · The Dark Universe

Holographic Dark Energy vs Phantom Energy

Dark Energy Candidates · within family

	Holographic Dark Energy Frontier	Phantom Energy Frontier
Proposed	2004	2002 / 2003
Key figures	Miao Li, Andrew G. Cohen, David B. Kaplan, Ann E. Nelson	Robert Caldwell, Marc Kamionkowski, Nevin Weinberg
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.	Phantom energy is dark energy with equation of state w less than -1. Its density grows as space expands, rather than staying constant or diluting, driving a runaway acceleration that ends in a Big Rip.
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.	An equation of state w less than -1, with the dark energy density increasing over cosmic time rather than staying constant or diluting. A future Big Rip: the scale factor diverges in finite time, unbinding structures from clusters down to atoms in a fixed sequence. A measurably different expansion history from quintessence: at the same value of w today, phantom energy was less dense in the past, quintessence denser. A crossing of the phantom divide (w = -1) visible in the reconstructed w(z) from combined supernova, BAO, and CMB data.
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.	A canonical scalar field cannot reach w less than -1; phantom energy requires a non-canonical kinetic term, a ghost field with negative kinetic energy, which is unstable as a quantum field theory because the vacuum decays. Phantom energy violates the dominant energy condition (rho + p less than 0), which most physicists regard as a serious warning rather than a feature. The Big Rip is avoided if the apparent w less than -1 is instead a modified-gravity effect or a supernova-calibration systematic; no measurement yet establishes a genuine phantom-divide crossing.
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 instability problem: making the equation of state w drop below -1 needs a field with negative energy (a ghost), which would make empty space fall apart into runaway particles.
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Holographic Dark Energy

2004 · Frontier

Phantom Energy

2002 / 2003 · Frontier

Proposed

2004

2002 / 2003

Key figures

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

Robert Caldwell, Marc Kamionkowski, Nevin Weinberg

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.

Phantom energy is dark energy with equation of state w less than -1. Its density grows as space expands, rather than staying constant or diluting, driving a runaway acceleration that ends in a Big Rip.

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.

An equation of state w less than -1, with the dark energy density increasing over cosmic time rather than staying constant or diluting.
A future Big Rip: the scale factor diverges in finite time, unbinding structures from clusters down to atoms in a fixed sequence.
A measurably different expansion history from quintessence: at the same value of w today, phantom energy was less dense in the past, quintessence denser.
A crossing of the phantom divide (w = -1) visible in the reconstructed w(z) from combined supernova, BAO, and CMB data.

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.

A canonical scalar field cannot reach w less than -1; phantom energy requires a non-canonical kinetic term, a ghost field with negative kinetic energy, which is unstable as a quantum field theory because the vacuum decays.
Phantom energy violates the dominant energy condition (rho + p less than 0), which most physicists regard as a serious warning rather than a feature.
The Big Rip is avoided if the apparent w less than -1 is instead a modified-gravity effect or a supernova-calibration systematic; no measurement yet establishes a genuine phantom-divide crossing.

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 instability problem: making the equation of state w drop below -1 needs a field with negative energy (a ghost), which would make empty space fall apart into runaway particles.

Reader vote

No votes yet