ABSTRACT
Fluctuations are key to life and ubiquitous in both physical and biological systems where atoms and molecules experience random motions. These kinds of fluctuations are of thermal origin, namely that the random motions occur because of a finite temperature. Another example is the fluctuations in the number of photons in a cavity in thermal equilibrium. However, there is a different type of fluctuation that is intrinsic and temperature independent and whose origin is quantum-mechanical. It is this latter that, defying the wildest imagination, is the origin of the large-scale structures of the Universe. How is this possible? In what follows the authors present the part of the answer within the framework of the inflationary scenario. The authors do this in order to stick to a chronological order of the evolution of the Universe. At the end of this chapter, they expand this answer to explain the tiny variations in temperature of the Cosmological Microwave Background.
