Can a model of quantum gravity from holography explain cosmic acceleration?

Theoretical physicists have long struggled to devise a complete theory of gravity that could explain quantum mechanical phenomena unlike existing models. Such a theory could collectively explain many complex physical and cosmic phenomena observed over the past few decades.

Researchers at the University of Maryland and the University of British Columbia recently conducted a theoretical study exploring the possibility that holography, an approach to quantum gravity that includes some of the features of conventional holograms, could be used to explain quantum mechanical phenomena. their paper published in physical review letterIntroduces theoretical arguments that can suggest a link between observable cosmic phenomena and the physics underlying wormhole spacetime.

“Provising a theory of gravity that includes the physics of quantum mechanics has been a major forefront area of ​​theoretical physics for decades,” Mark Van Raamsdonk, one of the researchers who conducted the study, told Phys.org. “This is necessary to truly understand the physics of black holes and the Big Bang and to make progress towards a fully integrated theory of physics.

“We now have a fully coherent model of quantum gravity through an approach called holography, where the physics of gravity is encoded in a simpler, lower-dimensional non-gravity quantum system. Holographic gravity theory has taught us a lot about the physics of black holes. “However, so far there has been no significant progress in understanding realistic cosmic spacetime with the Big Bang.”

A key goal of recent work by Van Raamsdonk and his colleagues has been to describe cosmological space-time physics using a holographic approach. Spacetime is essentially the combination of the three dimensions of space and the first dimension of time into a single four-dimensional manifold, underpinning phenomena such as the Big Bang and the expanding universe.

“We argue that these models can explain the fact that the expansion of our universe is accelerating, but in a different way than is commonly assumed,” Van Raamsdonk said. “The most common explanation, referred to as the Lambda-CDM (cold dark matter) model, is that there is a positive ‘cosmic constant’, a kind of dark energy that always has the same density throughout the universe. We argued that the holographic model can also explain the cosmic acceleration naturally, but through dark energy whose density changes with time.”

The holographic model suggests that at some point the density of dark energy decreases below zero, reaching a negative value. This can eventually cause the cosmic slowdown and eventual re-collapse, which is sometimes referred to as the “Big Crunch”. Van Raamsdonk and his colleagues therefore suggest that these models may provide a different perspective on cosmic acceleration.

“We observed that the quantum gravity model arising from holography can naturally explain the cosmic acceleration in a new way. The changing dark energy ends up being negative,” said Van Raamsdonk. “We’re not sure if our universe works this way, but it’s something we can find out from cosmological observations.”

The team’s recent work provides new perspectives that may contribute to a theoretical understanding of unresolved cosmological problems. Van Raamsdonk and his colleagues have already conducted additional studies comparing their predictions with available cosmic observations.

“We compared the model’s prediction (decreasing dark energy) with what we see from direct observations of the expanding universe to see if it’s consistent,” Van Raamsdonk added. “Together with my student Chris Waddell, we looked at the most recent redshift versus brightness data for Type IA supernovae. These observations can tell us quantitatively what the expansion of the universe has looked like over the past 6 or 7 billion years. It doesn’t tell us conclusively whether dark energy is decreasing, but we find that most models that fit the data reasonably well now show that dark energy is decreasing.”

In their next study, the researchers want to better understand the physics of the cosmic microwave background and what the kinds of models they devised will predict regarding the distribution of galaxies in the universe. These predictions can then be compared to recent observations.