# Holographic Dark Energy and Quantum Entanglement

## TL;DR

This paper reviews holographic dark energy models, introduces quantum entanglement as a thermal energy source for dark energy, discusses their observational consistency, and addresses theoretical issues through action principles and equations of motion.

## Contribution

It proposes a novel connection between quantum entanglement and dark energy, and resolves key theoretical problems in holographic dark energy models.

## Key findings

- Holographic dark energy aligns with observational data.
- Problems like non-locality and causality are addressed.
- Quantum entanglement may underlie dark energy phenomena.

## Abstract

In this paper, we briefly review the holographic dark energy model and introduce the idea that dark energy is a kind of thermal energy related to the quantum entanglement of the vacuum across a cosmic future event horizon. The holographic dark energy model comes from a theoretical attempt to apply the holographic principle to the dark energy problem and follows the idea that the short distance cut-off or ultraviolet (UV) cut-off is related to the long distance cut-off or infrared (IR) cut-off. The IR cut-off relevant to dark energy is the size of the future event horizon. This model gives a holographic dark energy comparable to the observational data. Though this model is in good agreement with observational data, some problems (non-locality, circular logic, causality problem, $\it etc.$) exist due to the use of the future event horizon as a present IR cut-off. These problems of the holographic dark energy model are considerably resolved using action principle and equations of motion. Finally, we discuss the relation between quantum entanglement and dark energy which is connected to the more fundamental relation between entanglement and gravity.