1. Dark Energy: Hopes and Expectations
Mario Livio
Space Telescope Science Institute
Use for title page without text, add HST, JWST. Keep timeline

2. What Causes Cosmic Acceleration?
Dark Energy?
Standard General Relativity?
Alternative Theories of Gravity?

3. Dark Energy or Alternate Gravity?
High redshift supernovae observed with HST, and currently envisaged to be further investigated by wide-field observations from free space.
(JDEM)
Can be tested by experiments in the lab and on the lunar surface.

4. Inert vacuum energy (cosmological constant)
Dark Energy
Inert vacuum energy (cosmological constant)
Two main problems:
Why is V not much larger? Requires cancellation to unreasonable precision.
Why now? ( ~ M) The “Nancy Kerrigan Problem”

5. Possibility of Multiverse?
Landscape
scenario
String theory suggests that ~ vacua may exist.
Inflation may produce an ensemble of pocket universes.

6. Possibility of Multiverse?
Fundamental Theory
All constants determined uniquely.
Examples of past successes:
Particle masses in QCD
Electroweak theory
Allows universes with an ensemble of values of at least some non-fundamental parameters.
Examples of past non-fundamental quantities:
Number of planets in the Solar System
Shapes of snowflakes

7. Can A Multiverse Explain the Value of V?
If V can take a broad range of values in the multiverse, then complexity can arise only in some subuniverse. In general V /3 is constrained.
For a flat probability distribution:
Principle of mediocrity: Is our universe typical?

8. Typical Objections
Against the scientific method? Not everything should be observable or falsifiable. Rather, if the theory is testable in the observable universe, we should be prepared to accept its predictions in the unobservable parts.
No predictions? Not exactly true, statistical predictions.
End of physics? No. Rather, modification of expectations. E.g. in mathematics: Gödel’s theorem, computational complexity.
Supports religion-like arguments? Absolutely not!
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