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