Can the Thermodynamics of Black Holes Help Us Understand the Evolution of the Universe?
Black holes have taught physicists a profound lesson: horizons carry entropy, and this entropy is proportional to their area. When the same principle is applied to the horizon of the observable Universe, it provides a framework for deriving the equations that govern cosmic expansion.
But what happens if the relationship between entropy and horizon area is slightly modified, as suggested by some approaches to quantum gravity?
In two new research papers, PhD student Pranav Prasanthan, together with Dr. Hussain Gohar and Dr. hab. Vincenzo Salzano, investigates how such modifications could affect the evolution of the Universe and whether their predictions are consistent with observational data.
First study: How sensitive is cosmic evolution to quantum corrections?
Published in Physics Letters B, the first paper examines how small deviations from the standard horizon-entropy relation influence the history of cosmic expansion.
The results reveal a remarkable sensitivity: even a deviation of just 0.01% can lead to excessive or negative dark energy densities in the early Universe. Corrections associated with quantum entanglement remain viable only within a narrow parameter range, while the quantum-gravity corrections considered in the study are too small to produce observable effects.
Read the paper: Physics Letters B — First Study
Second study: What do observations tell us?
Published in the Journal of Cosmology and Astroparticle Physics, the second paper confronts these modified cosmological models with modern observational data, including Type Ia supernovae, galaxy surveys, and the cosmic microwave background.
The findings reinforce the stringent constraints identified in the first study. Some models predict a higher expansion rate for the Universe, potentially reducing the long-standing Hubble tension—the discrepancy between different measurements of the present-day expansion rate—by more than half.
However, a closer statistical analysis indicates that the standard cosmological model, ΛCDM, remains the better-supported explanation of the available data.
Read the paper: Journal of Cosmology and Astroparticle Physics — Second Study
Why does this matter?
Together, these studies demonstrate how profoundly the thermodynamic properties of space-time can influence cosmological models. By combining theoretical modifications inspired by quantum gravity with observational tests, the researchers identify tighter limits on which descriptions of horizon entropy remain physically viable.
The findings also highlight a fundamental challenge in modern cosmology: even theoretically motivated extensions of established physics must withstand the stringent demands of observational evidence.
Understanding the Universe may ultimately require us to understand the microscopic physics of space-time itself.
