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The Cosmological Constant

Basic Idea: When there is a cosmological constant the expansion of the universe accelerates, and inflation (an accelerated expansion) is desirable at least in early stages of the history of the universe. That is, it happened before, so maybe it could happen again.

Effects of dominance by lambda: Flatness, emptiness, horizons.
More generally result of inflation or accelerated expansion.

Motivation for inflation

  • observed homogeneity and isotropy
    including no weird heavy particles from high energy physics
  • combined with horizons and finite age-- need acausal behavior

Mathematically- acceleration depends on energy and pressure. Positive vacuum energy pushes out rather than attracting.

Particle physics and inflation

  • usual method to get inflation: some field gets stuck and gives approx constant energy density
  • scenario
    • inflation starts
    • inflation ends
    • (p)reheating
  • constraints:
    • timing :any time before bbn
    • extra bonus: generate initial conditions (particle creation)
  • "Who is the inflaton?" (not known)
    generic results both a strength and a weakness
    Current questions in the field today: quantum cosmology, reheating, theories which give inflation, reconstruction

Things of note:

  • Inflation may have happened via lambda--and if then why not now too?
  • Maybe all the potential energy didn't go into particles and so our current lambda is related to the earlier one
  • If lambda then was via a field maybe something that looks like lambda now is also via a field, and transient.
    Quintessence--a field that isn't quite acting like lambda but almost (loses energy with expansion but not as fast as e.g. matter).

    Some references.

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Comments or Questions? Contact jcohn@astron.berkeley.edu