Effective Cosmological Constant and Dark Energy

Abstract: Two very different methods are used to estimate the magnitude of the effective cosmological constant / dark energy (for the present cosmic epoch). Their results agree with each other and are in agreement with observations. One method makes use of unimodular gravity and causal set theory, while the other one employs arguments involving spacetime foam and holography. I also motivate and discuss the possibility that quanta of (both) dark energy (and dark matter in the Modified Dark Matter model) are extended/non-local, obeying infinite statistics, also known as quantum Boltzmann statistics. Such quanta out-number ordinary particles obeying Bose-Einstein or Fermi-Dirac statistics by a factor of $\sim 10^{30}$.