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The Cosmological Constant
Theories of Lambda and maybe not lambda

Basic Idea: theorists are very puzzled. Measurable by gravity which is not well understood force.


  • Don't know how to calculate it
  • Size seems unnatural relative to gravitational scales
  • Seems many contributing effects
  • Size relative to other energy densities changes with time, why comparable to other scales today?

Methods to try to explain it (courtesy J. Lykken)

  • give up
  • anthropic
  • some unrecognized symmetry
  • existing hierarchy
  • dynamics
  • original counting wrong
  • strings:
    • some models of the universe
    • ways to get lambda small with arguments of type above

Analogy with inflation

  • quintessence--same thing happening now?
  • scalar field description
  • link to inflation using same field

Some references.

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