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A new model to explain the present accelerated expansion of the universe has been proposed. Contrasting existing models, this model does not need any form of dark energy or modified gravity approaches. Nonetheless, there is a price to pay: we require a partner anti-universe whose time flow is oppositely linked to our universe.

There are robust arguments supporting this concept. From a quantum theory standpoint, it is natural for the cosmos to be created in pairs. Recently, Boyle et al suggested that the cosmos does not violate CPT (Charge, Parity, and Time reversal symmetry)spontaneously, but rather, the cosmos post the Big Bang is the CPT image of the cosmos before it, pointing towards a partner anti-universe.

**Recent results **

In a fresh paper published in Gravitation and Cosmology, key concepts from quantum theory, like relative entropy, and from general relativity, like the null energy condition, which corresponds to the positive energy condition, were used. Findings suggest that the cosmos naturally expands in an accelerated manner.

Relative entropy, which needs two states, in this case, corresponds to the cosmos and its partner anti-cosmos. Accelerated expansion appears inevitable in a cosmos created in pairs that respect the null energy condition. This result is quite astounding and readers acquainted with Hawking’s area theorem may notice some similarities. The area theorem also deals with causal horizons and needs the null energy condition to hold.

In the present model, the causal horizon corresponds to the Big Bang. The results apply alike to the partner anti-universe.To sum up, the accelerated expansion of the cosmos is a perplexing subject that continues to inspire scientific efforts. Building on prevailing theories, this new model offers an explanation putting to use standard concepts from quantum theory and general relativity, without any need for elusive dark energy.

The results show that accelerated expansion is but natural for a cosmos created in pairs. Furthermore, studying causal horizons can expand our understanding of the universe. The beauty of this idea lies in its naturalnessand simplicity, setting it apart from prevailing explanations.

**Physicists have proposed alternative explanations to explain the accelerated expansion**

Physicists have proposed alternative explanations to explain the accelerated expansion. Those include quintessence and modified gravity theories, including scalar-tensor-vector gravity. Furthermore, explanations beyond four dimensions, such as the braneworld scenarios in the Dvali-Gabadadze-Porrati (DGP) model, alter gravity at large distances due to the influence of a higher-dimensional bulk on our four-dimensional brane, and variable brane tension.

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