When you look in the refrigerator, you expect to feel cold. Similarly, astronomers looking billions of years into the past of the Universe expect to see intense heat there. A team of Japanese researchers recently confirmed this fundamental assumption with incredible accuracy, providing one of the most compelling pieces of evidence in favour of the modern theory of cosmic evolution.
Is it possible to measure the temperature of the Universe as it was billions of years ago? Previous measurements existed for the very early Universe and for the present day, but the intervening history remained largely unexplored. Therefore, a group of scientists from Keio University managed to take these complex measurements. Instead of studying cosmic microwave background radiation in its current state, they focused on light from a distant quasar. This light has been travelling towards us for 7 billion years, and on its way it interacted with the same background radiation, but in the distant past.
The Universe was hotter
By analysing archive data from the powerful ALMA observatory in Chile, scientists have discovered characteristic traces of this interaction in the light of the quasar. This has allowed them to determine the temperature of the cosmic background 7 billion years ago with unprecedented accuracy. It was 5.13 K (-268 °C), which is almost twice as high as the current value of 2.7 K (-270.45 °C). This is direct confirmation that the Universe has indeed been cooling over the billions of years of its expansion.
This measurement is not just an interesting fact with a difference of a few degrees Kelvin. It is a fundamental test of the standard cosmological model, the basis of our understanding of the Universe. This model assumes that as the cosmos expands, it should continue to cool.
The work of Japanese scientists has filled this gap with extraordinary precision. The data obtained almost perfectly matches theoretical predictions. To draw an analogy, it is as if meteorologists not only predicted rain, but also determined the temperature of each drop with precision down to the degree. Such confirmation greatly strengthens our confidence that we correctly understand the main stages of the evolution of the cosmos from the Big Bang to the present day.
Earlier, we reported on how the Universe would die.
According to Science Alert
