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Dark Energy & Dark Energy & Cosmic HorizonsCosmic Horizons
Pim van OirschotPim van Oirschot
Table of ContentsTable of Contents
Part I: The standard model of Cosmology and its problems
Part II: Cosmic Horizons Part III: Melia’s Horizon
The standard model of The standard model of Cosmology and its Cosmology and its problemsproblems
Part IPart I
The Cosmological Constant The Cosmological Constant ProblemProblem
The cosmological constant can be interpreted as the energy density of the vacuum
Quantum Field Theory can predict a value for this energy density
We can compare this value with the value inferred from astronomical observations
The latter is 120 orders of magnitude smaller than predicted by Quantum Field Theory
The Expert’s OpinionThe Expert’s Opinion
Frank Wilczek The biggest and most profound gap in
our current understanding of the physical world
Sean Carroll One of the most perplexing
issues in theoretical physics
Michael Turner The biggest embarrassment
in theoretical physics
Dark EnergyDark Energy
A component that causes the expansion of the Universe to accelerate is referred to as Dark Energy
The cosmological constant is just one possibility
Dark Energy is characterised by its equation of state, w
w = -1 for the cosmological constant
Cosmic HorizonsCosmic Horizons
Part IIPart II
Particle Horizon
Harrison, Cosmology - 1981
Event Horizon
Horizons in an expanding Horizons in an expanding UniverseUniverse
The Robertson-Walker line element is conformally equivalent to the Minkowski metric
The conformal time
can converge, depending on a(t) For the concordance model:
Conformal ConvergenceConformal Convergence
The Hubble sphereThe Hubble sphere
Hubble’s law V = H D The Hubble sphere marks the
distance beyond which V exceeds the speed of light, c
We can see beyond the Hubble sphere
A Conformal DiagramA Conformal Diagram
Melia’s HorizonMelia’s Horizon
Part IIIPart III
A new type of A new type of “horizon”“horizon”
Observations should indicate that the equation of state of Dark Energy, w = -1/3
The Robertson-Walker line element should be written in static coordinates:
Notes on the “cosmic Notes on the “cosmic horizon”horizon”
1. The “cosmic horizon” has been defined before by Hawking as the apparent horizon of the Universe
2. We can see beyond the “cosmic horizon”, like we can see beyond the Hubble sphere
Another coincidence?Another coincidence?
Only in a Universe with
Only in such a Universe, is c times the age t always equal to the “cosmic horizon”
ConclusionsConclusions
A number of outstanding, fundamental questions concerning the standard model of cosmology remain unsolved.
Exploring the nature of Dark Energy might help us finding an answer to these questions
The theory of Cosmic Horizons is not in disagreement with the existence of a non-zero cosmological constant