Temperature Across the Universe
Living in Boston, I like to think that I get to experience the full extremes of temperature, from freezing February nights to muggy summer days. However, the temperature range in Boston is nothing compared to the Universe at large, where the temperature today easily ranges thousands of degrees between regions of empty space to the center of stars. By looking at the story of the temperature of the Universe, we can see how we went from a hot and uniform temperature to the thermal diversity we see today and can come to better understand the power of temperature.
You could say the Universe is full of thermal diversity, but this wasn’t always the case. Once upon a time, moments after the big bang, the Universe was uniform in temperature and hotter than we can imagine. Just as lowering the temperature causes water to freeze and turn into ice, the cooling of the Universe as a whole since the big bang has fundamentally changed the structure of matter, leading to where we are today. During the big bang, the temperature of the Universe was a whopping 10¹⁹ Celsius, or 33 trillion times hotter than the temperature of the hottest star ever discovered.
Approximately 100 seconds later, the Universe was 10 billion times cooler and cool enough for protons and neutrons, the building blocks of atoms, to coalesce into the first atomic nuclei. These nuclei don’t form the first hydrogen atoms until about 400,000 years later when the universe cools from 1 billion degrees Celsius to a few thousand degrees celsius and electrons can stably orbit a nucleus.
Fast forward another four billion years to when our solar system forms, and the temperature is now approximately -269 Celsius on average but full of the thermal diversity that comes from stars, just like our Universe today.
The Universe we see today when we gaze up at the stars is the product of billions of years of cooling and full of a thermal diversity that boggles my mind. Just like a fresh cup of coffee left on a counter, the Universe has been cooling ever since the big bang, and this process has led to the world we inhabit today. By taking the time to ponder the role of temperature in the Universe we can better appreciate the same thermal forces that impact our daily lives and recognize that when we’re feeling cold on a bitter Boston February day, we are just like the Universe as a whole, radiating heat out into space.
