Place in order the following events in the history of the universe. a. Planck era b. grand unified theory breaks c. today d. Big Bang nucleosynthesis e. electroweak breaks f. theory of everything breaks g. electron-positron pair annihilation h. formation of galaxies and stars i. recombination j. inflation

The Planck era marks the very beginning of our universe, occurring right at time zero, or the moment of the Big Bang. During this infinitesimally brief period, the universe was unimaginably hot and dense. To comprehend just how brief this era was, it's said to have lasted until the universe was about \(10^{-43}\) seconds old. Scientists believe that all the fundamental forces – gravity, electromagnetism, and the strong and weak nuclear forces – were unified. Understanding the Planck era is tricky since the laws of physics as we know them start to break down.

Big Bang nucleosynthesis refers to a critical period in the early universe, occurring roughly between 10 seconds to 20 minutes after the Big Bang. During this time, the temperature of the universe cooled enough from its initial incredibly high state to allow the formation of the first atomic nuclei. Primordial hydrogen, helium, and trace amounts of lithium were created. This process set the stage for all the elements we see in the universe today. Without Big Bang nucleosynthesis, the matter that forms stars, planets, and eventually life would not exist.

Following the recombination era, which allowed neutral atoms to form, the universe entered an era where gas clouds began collapsing due to gravity. This process led to the formation of the first stars and galaxies. Stars are born from dense clouds of gas and dust, which collapse under their own gravity and begin nuclear fusion in their cores. Galaxies formed through a combination of these star-forming regions merging and interacting. This formation period was pivotal in establishing the large-scale structure of the universe that we observe today. As galaxies and stars formed, they started to light up the universe, providing energy and building blocks for future star systems.

Inflation is a theory proposing that the universe underwent a rapid exponential expansion within a tiny fraction of a second after the Big Bang. This period of inflation is thought to have occurred between \(10^{-36}\) and \(10^{-32}\) seconds after the Big Bang. During inflation, the universe expanded faster than the speed of light, which helped to even out any irregularities and made the cosmos appear uniform on a large scale. It also explains why regions of the universe so far apart look similar to each other. Without inflation, the observable universe would be drastically different in structure and composition. The theory of inflation helps solve several important cosmological puzzles and is a key aspect in our understanding of cosmic evolution.