A unified theory of everything has long eluded scientists due to gravity being irreconcilable with the three other fundamental forces (electromagnetic, weak, and strong) described using quantum field theory (QFT).
The fundamental discrepancy between the unification lies in how the two theories are described. The gravitational field—described by Einstein’s theory of general relativity—is a manifestation of the very fabric of reality, spacetime.
On the other hand, the Standard Model uses principles of QFT to describe the electromagnetic, weak, and strong fields.
However, the fundamental difference is that these quantum fields are defined on spacetime. This means they exist as fields throughout spacetime, with a value associated with every point in it.
Thus, reconciling the two remains a gruelling challenge for scientists. Aalto University scientists have proposed a fresh perspective on gravity designed to integrate gravitational theory with the Standard Model.
A new approach to gravity
In the framework of the Standard Model, the three fundamental forces arise due to certain symmetries in their quantum fields. Each force has a unique symmetry pattern associated with it.
To develop a similar framework for gravity, the researchers introduce a new mathematical quantity called the spacetime dimension field. This entity has four symmetries that give rise to the gravitational field when applied to every point in spacetime.
In other words, gravity naturally emerges from the symmetries of the spacetime dimension field, just as we see with the other three forces in the Standard Model.
The researchers found that their unified gravity theory successfully produces a coherent framework for all four fundamental forces. Most importantly, their theory was proven to be renormalizable up to the first order, addressing one of the most pressing challenges with quantum gravity.
A renormalizable theory means that calculations using this theory yield finite, definable values. They can avoid infinities by adjusting a few parameters to get meaningful results. In this case, the framework appears to be renormalizable up to a certain number of terms in the equations, not completely.
Finally, the researchers showed that in the classical limit (not considering quantum effects), their theory reduces to the teleparallel equivalent of general relativity, which is a mathematically equivalent version of Einstein’s theory of general relativity.
This test is crucial because general relativity is the most accurate description of gravity seen at large scales, from laboratory experiments to black holes. Therefore, this proves that the theory produces the same results when observing gravity at the same scales.
Extending beyond first-order terms
While merely theoretical, this research offers a potential solution to the problem of quantum gravity, which has persisted for nearly a century. It offers a way to reconcile gravity and the Standard Model in a way that ensures that results are definable and meaningful.
“If this turns out to lead to a complete QFT of gravity, then eventually it will give answers to the very difficult problems of understanding singularities in black holes and the Big Bang,” said lead author Mikko Partanen from Aalto University in a press release.
The researchers plan to extend their theory to work beyond just the first-order terms, meaning that infinities can be eliminated throughout the calculations.
The theory provides a new perspective on a long-standing physics problem without introducing new parameters, suggesting that gravity can be understood as arising from the symmetries of a spacetime dimension field instead of the curvature of spacetime itself.
The findings of the study are published in Reports on Progress in Physics.