Thanu Padmanabhan in Nautilus:
There are two tantalizing mysteries about our universe, one dealing with its final fate and the other with its beginning, that have intrigued cosmologists for decades. The community has always believed these to be independent problems—but what if they are not?
The first problem has to do with the existence of something called “dark energy,” which is today accelerating the expansion of the universe and will determine its final fate. Theorists tell us that the effects of dark energy can be explained by introducing a term into Einstein’s equations of gravity called the cosmological constant. But, for this explanation to work, the cosmological constant must have a very specific—and tiny—value. In natural units, the cosmological constant is given by 1 divided by a number made of 1 followed by 123 zeros! Explaining this value is considered one of the greatest challenges faced by theoretical physics today.
The second problem relates to another crucial number that shapes our universe, and is related to the formation of structures like galaxies and groups of galaxies. We know that the early universe, while being very smooth, also contained tiny fluctuations in density that acted as seeds for all the cosmic structures we see today. These fluctuations must have a specific magnitude and shape to be consistent with present-day observations. Understanding how these tiny fluctuations were created during the earliest stages in the evolution of the universe, and explaining their magnitude and shape, is an equally fascinating mystery in cosmology.
In the conventional approaches to cosmology, these two numbers—the numerical value of the cosmological constant and the magnitude of initial perturbations—are considered unrelated.