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Quantum entanglement is one of the most fascinating and mysterious phenomena in nature. It needs no interactions, or any sort of exchange for it to take place. It is possible, not against any rules of physics as far as we know, that all matter that was created in the early universe was in an entangled state.

The question is:

Is it possible to explain the uniformity and isotropy of matter in the universe, by means of quantum entanglement in the early 'days' of universe? If that could be possible, would it mean that there would be no need for the inflationary model any more?

If this problem has been researched in detail, any references posted will be appreciated.

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Wow! (+1), interesting idea! Another question is giving it a definite shape: how that entanglement, what observational consequences, etc. But as a starting point it seems to me brilliant! –  Eduardo Guerras Valera Apr 24 '13 at 0:52
    
+1, great and interesting question! –  Thriveth Aug 14 '13 at 9:08

3 Answers 3

I've found this paper: Cosmological quantum entanglement, of E. Martin-Martinez and N. C. Menicucci.
(last revised 19 Oct. 2012)

Abstract We review recent literature on the connection between quantum entanglement and cosmology, with an emphasis on the context of expanding universes. We discuss recent theoretical results reporting on the production of entanglement in quantum fields due to the expansion of the underlying spacetime. We explore how these results are affected by the statistics of the field (bosonic or fermionic), the type of expansion (de Sitter or asymptotically stationary), and the coupling to spacetime curvature (conformal or minimal). We then consider the extraction of entanglement from a quantum field by coupling to local detectors and how this procedure can be used to distinguish curvature from heating by their entanglement signature. We review the role played by quantum fluctuations in the early universe in nucleating the formation of galaxies and other cosmic structures through their conversion into classical density anisotropies during and after inflation. We report on current literature attempting to account for this transition in a rigorous way and discuss the importance of entanglement and decoherence in this process. We conclude with some prospects for further theoretical and experimental research in this area. These include extensions of current theoretical efforts, possible future observational pursuits, and experimental analogues that emulate these cosmic effects in a laboratory setting.

More recently (14 Aug. 2014): Entanglement in curved spacetimes and cosmology, of the same authors.

Abstract We review recent results regarding entanglement in quantum fields in cosmological spacetimes and related phenomena in flat spacetime such as the Unruh effect. We being with a summary of important results about field entanglement and the mathematics of Bogoliubov transformations that is very often used to describe it. We then discuss the Unruh-DeWitt detector model, which is a useful model of a generic local particle detector. This detector model has been successfully used as a tool to obtain many important results. In this context we discuss two specific types of these detectors: a qubit and a harmonic oscillator. The latter has recently been shown to have important applications when one wants to probe nonperturbative physics of detectors interacting with quantum fields. We then detail several recent advances in the study and application of these ideas, including echoes of the early universe, entanglement harvesting, and a nascent proposal for quantum seismology.

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One of the problems that inflation solves is the so-called horizon problem. The problem is that parts of the sky that don't appear to have been in causal contact have the same temperature. Inflation solves this problem because before the period of rapid expansion all parts of the sky were in causal contact.

Let us consider whether entanglement - which is long-distance correlation - can help us correlate patches of the sky that have the same temperature but don't appear to have been in causal contact. Unfortunately, we encounter an obstacle:

In order for two subsystems to be in an entangled state, they must have interacted (i.e. been in causal contact) in the past.

Without going through any detailed realization of your idea, I don't think it's going to get around the horizon problem. Entanglement couldn't explain how patches of the sky became entangled if they weren't in causal contact.

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Entanglement results when the system under consideration belongs to one quantum mechanical solution of the specific problem.

The inflationary period as introduced at the beginning of the Big Bang model is a quantum mechanical solution to the boundary problem of the very early universe. At those sizes and energy densities it is assumed that everything is described with a quantum mechanical model. Specific models, are used to check consistency with the cosmic background radiation and the density of galaxy clusters in the observable universe, more or less successfully.

The dominant quantum field theoretical model presently is the one with a scalar field :

According to inflation theory, the inflaton is a scalar field that is responsible for cosmic inflation in the very early universe. A quantized particle for this field is expected, similar to other quantum fields, called an inflaton. The field provides a mechanism by which a period of rapid expansion from 10−35 to 10−34 seconds after the initial expansion can be generated, forming the universe .

It is consistent with the observation. The aim is to explain the observations and this quantum mechanical model leads to inflation at the early universe, and the fields and particles it posits are by construction entangled.

It is possible that another quantum mechanical model might describe the homogeneity of the observations without leading to rapid inflation, but it would be by different fields and boundary assumptions; entanglement will exist in any quantum mechanical model.

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