Quantum mechanical fluctuations at the end of inflation

During the inflationary phase of the early universe, quantum fluctuations in the vacuum generate particles as they stretch beyond the Hubble length. These fluctuations are thought to result in the density fluctuations and gravitational radiation that we can try to observe today. It is possible to calculate the quantum mechanical evolution of these fluctuations during inflation and the subsequent expansion of the universe until the present day. The present calculation of this evolution directly exposes the particle creation during accelerated expansion and while a fluctuation is larger than the Hubble length. Because all fluctuations regardless of their scale today began as the vacuum state in the early universe, the current quantum mechanical state of fluctuations is correlated on different scales and in different directions.