Sidney Bludman
Departamento de Astronomía
Universidad de Chile
 

"Our Recently Accelerating Universe"
 

I. HOMOGENEOUS EXPANSION OF OUR UNIVERSE  

Review of Robertson-Walker Cosmology: We will review CMB, baryon oscilla­tion, supernova and weak lensing cosmographic measurements of the homogeneous expansion history H(z) of our universe, back to red-shift z = 1089. These obser­vations are consistent with either a static finely-tuned cosmological constant or a dynamic ‘dark energy’ mechanism, which itself may be material Dark Energy or low-curvature modifications of Einstein gravity (Dark Gravity). The homogeneous expansion measures only kinematic variables, and cannot fix the underlying dynamics driving the recent acceleration since z ≥ 0.5.

 II. ONLY GROWTH OF FLUCTUATIONS CAN RESOLVE COSMODYNAMIC DEGENERACY

The Dark Energy/Dark Gravity degeneracy in the homogeneous expansion ob­servations can only be resolved by observing the growth of cosmological fluctua­tions. However, because the ’dark energy’ evolution is now quasi-static at most, any dynamical effects on the fluctuation growth function will be minimal. Pro­jected observations may potentially distinguish static from dynamic ‘dark energy’, but distinguishing between dynamic Dark Energy and Dark Gravity will require a weak lensing shear survey more ambitious than any now projected. Dark gravity is also, in principle, observable in the solar system or in isolated galaxy clusters.  

III. OBSERVERS ROLE: WHY WE LIVE AT PRESENT TIME