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The accelerated expansion of the current universe, believed to be driven by mysterious dark energy, is one of the biggest puzzles in our understanding of the cosmos. The Standard Model of cosmology, called Lambda-CDM, explains this expansion as a cosmological constant in Einstein’s field equations. However, the cosmological constant itself does not have a complete theoretical understanding, especially with regard to its very small positive value.

To explain the accelerated expansion, physicists have proposed alternative explanations such as quintessence and modified gravitational theories, including scalar-tensor-vector gravity. Additionally, explanations beyond four dimensions, such as the brane world scenarios in the Dvali-Gabadadze-Porati (DGP) model, alter gravity at large distances due to the effect of higher-dimensional volume on our four-dimensional brane and variable brane tension.

My new model

In my work, I propose another model to explain the current accelerated expansion of the universe. Unlike existing models, this does not require any form of dark energy or modified gravity approaches. However, there is a price to pay: we need a partner anti-universe whose timestream is oppositely related to our universe.

There are strong arguments to support this concept. From the point of view of quantum theory, it is natural for the universe to be created in pairs. Recently, Boyle et al proposed that the universe does not spontaneously break CPT (charge parity and time reversal symmetry), but rather the post-Big Bang universe is the CPT image of the universe before it, pointing to a partner anti-universe.

Latest results

In a recent article published in Gravity and Cosmology, I used key concepts from quantum theory, such as relative entropy, and from general relativity, such as the zero-energy condition that corresponds to the positive-energy condition. My findings show that the universe is naturally expanding at an accelerated rate.

The relative entropy, which requires two states, in this case corresponds to the universe and its anti-universe partner. Accelerated expansion seems inevitable in a universe created in pairs that respect the zero-energy condition. This result is quite surprising, and readers familiar with Hawking’s area theorem may notice some similarities. The area theorem also deals with causal horizons and requires the zero energy condition to hold.

In our model, the causal horizon corresponds to the Big Bang. The results apply equally to the partner anti-universe.

To summarize, the accelerated expansion of the universe is a challenging topic that continues to drive scientific efforts. Building on existing theories, my model offers an explanation using standard concepts from quantum theory and general relativity, without the need for elusive dark energy.

The results show that accelerated expansion is natural for a universe created in pairs. Moreover, studying causal horizons can deepen our understanding of the universe. The beauty of this idea lies in its simplicity and naturalness, which sets it apart from existing explanations.

This story is part of the Science X Dialog, where researchers can report findings from their published scientific papers. Visit this page for information about the Science X Dialog and how to participate.