Compare · The Origin of Our Universe

Higgs Inflation vs Old Inflation

Inflationary Big Bang · within family

	Higgs Inflation Strongly supported	Old Inflation Historical
Proposed	2008	1980 / 1981
Key figures	Fedor Bezrukov, Mikhail Shaposhnikov	Alan Guth
In one sentence	Bezrukov and Shaposhnikov proposed in 2008 that the Standard Model Higgs field drove inflation, provided it couples strongly to the curvature of spacetime, using only the particles of the Standard Model.	Guth's original 1981 model proposed that exponential expansion is driven by a false vacuum state which decays via quantum tunneling into bubbles of true vacuum, solving the horizon, flatness, and monopole problems of the standard Big Bang.
Predictions	In the [[cosmic microwave background]], a spectral index n_s near 0.97 and a tensor-to-scalar ratio r near 0.003, almost independent of Standard Model parameters when the Higgs mass sits well above its critical value A lower bound on the Higgs mass, because the Standard Model must stay a consistent theory up to the energy of inflation If the Higgs mass sits within a few hundred MeV of that bound, n_s and r depend on the top-quark and Higgs masses, and r can be well above 0.003 A higher reheating temperature than in Starobinsky R-squared inflation, which gives slightly different n_s and r and a different allowed range for the Higgs mass	Spatial flatness with Omega close to 1 Homogeneous and isotropic large-scale universe Absence of GUT-scale magnetic monopoles at observable densities
Where it breaks	Barbon and Espinosa argued in 2009 that the effective theory stops being valid at the Planck mass divided by the coupling, far below the field values inflation uses Burgess, Lee and Trott found in 2009 that the Hubble rate during inflation sits close to the scale where the semiclassical treatment breaks down Linking the inflationary parameters to collider measurements needs extra assumptions about the unknown high-energy completion, as Bezrukov and collaborators acknowledge The predictions nearly coincide with Starobinsky R-squared inflation and with a class of supergravity attractor models, so CMB data alone struggle to single out the Higgs ACT data combined with Planck, lensing and DESI give n_s = 0.974 ± 0.003. Some 2025 analyses read this as slightly above the simplest Higgs-inflation value, a tension that depends on the data combination and the model's high-energy details	Bubble nucleation cannot percolate to fill all space if [[inflation]] lasts long enough to solve the horizon problem, leaving isolated bubbles in an eternally inflating sea. Where bubbles do collide, they produce large inhomogeneities incompatible with the observed smoothness of the CMB. The density perturbation spectrum produced by bubble nucleation does not match the nearly scale-invariant, Gaussian, adiabatic spectrum observed.
Key unresolved problem	The cutoff problem: the strong coupling to gravity lowers the energy at which the theory stops being reliable, so the flat plateau inflation needs depends on physics no one knows yet.	The graceful exit problem: bubbles of ordinary space form too slowly to ever join up and fill the universe, so they stay marooned as isolated pockets in a sea that keeps inflating around them.
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Higgs Inflation

2008 · Strongly supported

Old Inflation

1980 / 1981 · Historical

Proposed

2008

1980 / 1981

Key figures

Fedor Bezrukov, Mikhail Shaposhnikov

Alan Guth

In one sentence

Bezrukov and Shaposhnikov proposed in 2008 that the Standard Model Higgs field drove inflation, provided it couples strongly to the curvature of spacetime, using only the particles of the Standard Model.

Guth's original 1981 model proposed that exponential expansion is driven by a false vacuum state which decays via quantum tunneling into bubbles of true vacuum, solving the horizon, flatness, and monopole problems of the standard Big Bang.

Predictions

In the [[cosmic microwave background]], a spectral index n_s near 0.97 and a tensor-to-scalar ratio r near 0.003, almost independent of Standard Model parameters when the Higgs mass sits well above its critical value
A lower bound on the Higgs mass, because the Standard Model must stay a consistent theory up to the energy of inflation
If the Higgs mass sits within a few hundred MeV of that bound, n_s and r depend on the top-quark and Higgs masses, and r can be well above 0.003
A higher reheating temperature than in Starobinsky R-squared inflation, which gives slightly different n_s and r and a different allowed range for the Higgs mass

Spatial flatness with Omega close to 1
Homogeneous and isotropic large-scale universe
Absence of GUT-scale magnetic monopoles at observable densities

Where it breaks

Barbon and Espinosa argued in 2009 that the effective theory stops being valid at the Planck mass divided by the coupling, far below the field values inflation uses
Burgess, Lee and Trott found in 2009 that the Hubble rate during inflation sits close to the scale where the semiclassical treatment breaks down
Linking the inflationary parameters to collider measurements needs extra assumptions about the unknown high-energy completion, as Bezrukov and collaborators acknowledge
The predictions nearly coincide with Starobinsky R-squared inflation and with a class of supergravity attractor models, so CMB data alone struggle to single out the Higgs
ACT data combined with Planck, lensing and DESI give n_s = 0.974 ± 0.003. Some 2025 analyses read this as slightly above the simplest Higgs-inflation value, a tension that depends on the data combination and the model's high-energy details

Bubble nucleation cannot percolate to fill all space if [[inflation]] lasts long enough to solve the horizon problem, leaving isolated bubbles in an eternally inflating sea.
Where bubbles do collide, they produce large inhomogeneities incompatible with the observed smoothness of the CMB.
The density perturbation spectrum produced by bubble nucleation does not match the nearly scale-invariant, Gaussian, adiabatic spectrum observed.

Key unresolved problem

The cutoff problem: the strong coupling to gravity lowers the energy at which the theory stops being reliable, so the flat plateau inflation needs depends on physics no one knows yet.

The graceful exit problem: bubbles of ordinary space form too slowly to ever join up and fill the universe, so they stay marooned as isolated pockets in a sea that keeps inflating around them.

Reader vote

No votes yet