The mean temperature of the Universe was more than 2 million Kelvin… At t = 1 x 10 -43 seconds, the universe was incredibly small, dense and hot. Scientists hope to discover the link between quantum and classical physics, which will give us a lot more information about how the universe works. The universe was born with the Big Bang as an unimaginably hot, dense point. a few billion degrees kelvin, maybe 10 billion K. This is called the hadron era, when the universe's age was between 0.1 … The key? When the Universe was one year old, it was much hotter and denser than it is now. When the Universe was one year old, it was much hotter and denser than it is now. This homogenous area of the universe spanned a region of only 1 x 10 -33 centimeters (3.9 x 10 -34 inches). Tiny messengers with information about the early universe, known as neutrinos, that have passed freely through the detritus of the universe since the very beginning. The temperature was only (!) The mean temperature of the Universe was more than 2 million Kelvin… The PTOLEMY project, based at Princeton University, explores the origins of the universe less than a second after the Big Bang.