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
- some unrecognized symmetry
- existing hierarchy
- original counting wrong
- 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