Jul 27, 2022

Our universe is constantly undergoing an expansion phase which is accelerating in nature. There are several theories in the scientific literature that have been formulated to explain features of this accelerating expansion, one of which is cosmic inflation proposed by theoretical physicist Alan Guth in the late 1970s and later developed by Andrei Linde, Paul Steinhardt and others [1, 2, 3].

It is well suggested by the theory that the epoch of inflation lasted from 10^{−36} seconds to sometime between 10^{−33} and 10^{−32} seconds after the Big Bang. But in order to articulate the events following the Big Bang admirably, one needs to have a full-fledged quantum theory of gravity, which is still a substantial challenge for physicists.

Now our current picture of the universe is well approximated by the de Sitter framework, named after the Dutch astronomer Willem de Sitter. The de Sitter picture also provides a solution to Einstein’s field equations of general relativity. Making use of this framework, physicists from Kyoto University's Yukawa Institute for Theoretical Physics (YITP) have come up with a new method to describe the expansion phase in the de Sitter universe [4]. The new method essentially uses the infamous holographic principle to elucidate the same, mathematical details of which can be found in their publication.

The basic formalism of the holographic principle is that it expounds a two-dimensional framework for the actual three-dimensional picture and it encodes the relevant information of the latter. The authors of the new study thus utilized this idea to approximate the expansion of the 3D universe in de sitter space. This work also results out to be the first instance of a two-dimensional Conformal Field Theory (CFT) that employs a positive cosmological constant.

The reader would perhaps be interested to know here that conformal field theory is generally a class of quantum field theories and has been well incorporated into Juan Maldacena’s gauge-gravity duality which is famously known as the Anti-de Sitter/ Conformal Field Theory (AdS/CFT) correspondence among theoretical physicists. The AdS/CFT is essentially a duality between two physical theories - quantum field theories and gravitational theories and simplifies the calculations of hard problems. This is made possible because of the fact that gravitational theories are weakly interacting in nature and hence calculations which are otherwise hard to address in strongly interacting quantum field theories become easier to tackle in the former. In other words, because of the connection between the two theories, the addressing of a certain problem from one theory could be made in a different theory wherein the same problem becomes easier to solve.

It would be interesting to see how this new progress by YITP physicists is employed to understand applications of the holographic principle to other scenarios of gravitational physics. As the lead author says, "A special feature of our proposed model is to use a negative cosmological constant to account for gravity on anti-de Sitter space, thus highlighting the importance of the holographic principle for de Sitter gravity."

The idea of the holographic principle which originally stems from the work of physics Nobel laureate Gerard ’t Hooft and Leonard Susskind has become one of the cornerstones of modern physics and it is perhaps wise to say that the entire establishment would simply collapse without this principle.

With this new advancement in the ability of holograms to carve out the intricate properties of our universe, which is well approximated by the de Sitter picture, it has become quite certain that the holographic principle is one of the prime features of any contender for a quantum theory of gravity.

Physicist Nassim Haramein has provided an extension to the holographic principle which is termed the generalised holographic approach and is essentially based on a statistical entropy and thermodynamics approach of a surface-to-volume holographic ratio. It would be interesting to see how Nassim’s theory accounts for phenomena wherein the principle comes in handy, for example in the workings of black holes. Certainly, there are a lot of things to be uncovered and a coherent narrative of everything including the utilization of the generalized holographic theory and its role in the unification of forces would be contained in Nassim’s new paper which is soon to be published.

References

[1] Alan H. Guth, “Inflationary universe: A possible solution to the horizon and flatness problems”, Phys. Rev. D **23**, 347 (1981). doi: 10.1103/PhysRevD.23.347

[2] James M. Bardeen, Paul J. Steinhardt, and Michael S. Turner, “Spontaneous creation of almost scale-free density perturbations in an inflationary universe”, Phys. Rev. D **28**, 679 (1983). doi: 10.1103/PhysRevD.28.679

[3] A. D. Linde, “Chaotic inflation”, Phys. Lett. B (1983). https://doi.org/10.1016/0370-2693(83)90837-7

[4] Yasuaki Hikida et al, Holography in de Sitter Space via Chern-Simons Gauge Theory, *Physical Review Letters* (2022). doi: 10.1103/PhysRevLett.129.041601

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