Sunday, April 23, 2017

Holographic Universe: Computing the Cosmological Observables

Sketch of timeline of the holographic universe. Credit Paul McFadden.

In the beginning of 2017, a team of researchers has presented the first observational evidence that our universe could be a hologram. In a paper published Jan. 27 in the journal Physical Review Letters, the scientists described their tests of a class of holographic models for the very early universe against cosmological observations. It now turns out that the most challenging part of this study was to compute the observables and compare them with observations.

The researchers, from the University of Southampton (UK), University of Waterloo (Canada), Perimeter Institute (Canada), INFN, Lecce (Italy) and the University of Salento (Italy) have found substantial evidence supporting a holographic explanation of the universe. It could mean that all the information, which makes up our 3D ‘reality’ (plus time) is contained in a 2D surface on its boundaries.

The team tested a class of holographic models for the very early universe against cosmological observations and found that they are competitive to the standard cold dark matter model with a cosmological constant of cosmology. The very early universe is the ideal place to look at because its physics requires a theory that combines general relativity and quantum mechanics and holography is such framework.

“We now have a wealth of observational data from this period which one can use in order to test our theories. In particular, the Planck mission (ESA space observatory) has observed the cosmic microwave background, the afterglow of the Big Bang, with unprecedented accuracy. This ancient radiation contains information about the physics of the very early universe and our task was to compute the prediction of the holographic theory against these observations,” Kostas Skenderis of Mathematical Sciences at the University of Southampton, UK, one of the co-authors of the paper told

First of all, Skenderis and colleagues formulated the holographic theory in precise mathematical terms. However, what was more challenging, they needed to compute the cosmological observables using this theory and compare them with observations.

“The holographic framework was developed through the years and the specific model that we tested was proposed several years ago in work I did with Paul McFadden (University of Southampton). The main challenges for the current work was to compute the observables and compare them with observations,” Skenderis said.

Although the new results may seem like a breakthrough in our understanding of the universe, this study is just one of the first steps to find more convincing evidence supporting the hologram theory. It is an on-going program and the scientific community is just in the beginning. The researchers now need to better understand the structure and the mathematics that underlie the holographic theories and further confront them against observational data. 

In particular, there is part of current data regarding the cosmic microwave background that no current theory can explain very well (the so-called large angle anomalies) and the next step should be to compute the predictions of the holographic theory and compare them against these observations.

“Current observational data are not sufficient to discriminate between this holographic model and more traditional theories for the early universe based on cosmic inflation. Further analysis and new data could rule out this model. On the other hand, if this model stands the test of time then our results would mark a pivotal moment,” Skenderis concluded.

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