A higher-dimensional model can help explain cosmic acceleration without dark energy. Dark energy remains a puzzle in our understanding of the cosmos. The standard model of cosmology, Lambda-CDM, accounts for it by adding a constant term to Einstein’s field equation. This constant is very small and positive but lacks a complete theoretical understanding.
Physicists look for alternative explanations for cosmic acceleration. Earlier, I proposed that if our universe exists with an anti-universe running backwards in time, we can explain this acceleration without dark energy. In my new work, I developed the braneworld model, where our universe is a 3-brane immersed in a higher-dimensional bulk.
In this model, I started with a braneworld scenario where our universe is part of some higher-dimensional bulk. Each brane has a constant tension that plays a role in its dynamics. I used a variable tension brane model and promoted Newton’s constant G to a scalar field while keeping the 5D Newton’s constant fixed.
To make us comfortable, some modified gravity theories promote Newton’s constant G to a scalar field. This led to dynamics that mimic the standard Friedmann equation, but now the scalar field plays the role of matter fields in our universe, and matter effectively plays the role of dark energy.
Without using any cosmological constant term, I was able to explain dark energy with only two known fields: scalar field G and matter field. The results are published in Europhysics Letters.
After working on problems of dark matter and dark energy, I can say that either we accept general relativity as correct and live in a dark universe or we accept that we live in a higher-dimensional multiverse.
Regarding modified gravity theories, my intuition suggests that nature prefers beauty, simplicity, and symmetry, but these theories do not meet these criteria. It remains with observations to determine the truth, which hopefully will be known someday given our scientific advancement.
Source: https://phys.org/news/2024-08-higher-dimensional-cosmic-dark-energy.html