The Cosmological Constant Problems

  title={The Cosmological Constant Problems},
  author={Steven Weinberg},
The old cosmological constant problem is to understand why the vacuum energy is so small; the new problem is to understand why it is comparable to the present mass density. Several approaches to these problems are reviewed. Quintessence does not help with either; anthropic considerations offer a possibility of solving both. In theories with a scalar field that takes random initial values, the anthropic principle may apply to the cosmological constant, but probably to nothing else. 
Anthropic Approach to the Cosmological Constant Problems
There are now two cosmological constant problems: (i) why the vacuum energy is so small and (ii) why it comes to dominate at about the epoch of galaxy formation. Anthropic selection appears to be the
Cosmological constant problems and their solutions
There are now two cosmological constant problems: (i) why the vacuum energy is so small and (ii) why it comes to dominate at about the epoch of galaxy formation. Anthropic selection appears to be the
The cosmological constant puzzle
The accelerating expansion of the Universe points to a small positive vacuum energy density and negative vacuum pressure. A strong candidate is the cosmological constant in Einstein's equations of
X-Particle as a Solution for the Cosmological Constant Problem
The cosmological constant is a fundamental problem in modern physics, and arises at the intersection between general relativity and quantum field theory. In this paper we show how the cosmological
Is the Zero-Point Energy Real?
I consider the arguments to show that the vacuum energy density should receive a large contribution from the zero-point energy. This is the cosmological constant problem, as it was originally framed.
The Cosmological Constant Problem, an Inspiration for New Physics
We have critically compared different approaches to the cosmological constant problem, which is at the edge of elementary particle physics and cosmology. This problem is deeply connected with the
The cosmological constant problem and brane universes are reviewed briefly. We discuss how the cosmological constant problem manifests itself in various scenarios for brane universes. We review
The Solution of the Cosmological Constant Problem: The Cosmological Constant Exponential Decrease in the Super-Early Universe
The stage of a super-early (primordial) scale-invariant Universe is considered on the basis of the Poincare–Weyl gauge theory of gravity in a Cartan–Weyl space-time. An approximate solution has been
Installing of cosmological constant
An artificial scale of observable cosmological constant is dynamically related to its natural bare value due to an installation of relevant coherent state for the inflationary field in a finite


The Cosmological Constant Problem
Astronomical observations indicate that the cosmological constant is many orders of magnitude smaller than estimated in modern theories of elementary particles. After a brief review of the history of
Anthropic bound on the cosmological constant.
  • Weinberg
  • Physics
    Physical review letters
  • 1987
It is argued here that in universes that do not recollapse, the only bound on the cosmological constantlambda is that it should not be so large as to prevent the formation of gravitationally bound states, and it turns out that the bound is quite large.
Quintessence, cosmic coincidence, and the cosmological constant
Recent observations suggest that a large fraction of the energy density of the Universe has negative pressure. One explanation is vacuum energy density; another is quintessence in the form of a
Likely Values of the Cosmological Constant
In theories in which the cosmological constant takes a variety of values in different "subuniverses," the probability distribution of its observed values is conditioned by the requirement that there
Birth of inflationary universes
A cosmological model is proposed in which the Universe is created by quantum tunneling from ''nothing'' into a de Sitter space. The tunneling is described by a de Sitter-- p Hawking--Moss instanton.
Predictions from quantum cosmology.
  • Vilenkin
  • Physics
    Physical review letters
  • 1995
The picture that has emerged from this line of development is that a small closed universe can spontaneously nucleate out of nothing, where by ‘nothing’ I mean a state with no classical space and time.
Cosmology with a Time Variable Cosmological Constant
Description d'une cosmologie basee sur une constante cosmologique Λ decroissante avec le temps quand l'energie potentielle du champ scalaire φ possede une queue en loi de puissance V∼φ − α pour φ
Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant
We present spectral and photometric observations of 10 Type Ia supernovae (SNe Ia) in the redshift range 0.16 " z " 0.62. The luminosity distances of these objects are determined by methods that
Implications of the red-shift-number test for cosmology.
  • Loh
  • Physics
    Physical review letters
  • 1986
This Letter discusses the recent measurement of the number of galaxies versus red shift and flux for cosmological models with a nonzero cosmological constant ..lambda.. and pressureless matter. The