The universe bathes in a sea of light, from the blue and white flickering of young stars to the deep red glow of hydrogen clouds. Beyond the colors visible from human eyes, there are X-ray and gamma-ray flashes, powerful radio bursts and the faint, constant glow of cosmic microwave background. Space is filled with colors, seen and unseen, ancient and new. But of all this, there was one color that appeared before everyone else, the first color of the universe.
The universe began 1
At first, the temperatures were so high that there was no light. The space had to cool for a split second before photons appeared. After about 10 seconds, the universe entered the photonic age. Protons and neutrons cooled in the nuclei of hydrogen and helium, and the space was filled with plasma of nuclei, electrons and photons. At that time, the temperature of the universe was about 1 billion degrees Kelvin.
But although there was light, there was still no color. Color is something we can see, or at least some kind we can see. During the photon era, temperatures were so high that light could not penetrate the dense plasma. Color will not appear until the nuclei and electrons have cooled enough to bind to atoms. It took 380,000 years to cool so much of the universe.
Until then, the observable universe was a transparent cosmic cloud of hydrogen and helium for 84 million light-years. All the photons formed in the Big Bang were finally free to flow through space and time.
This is what we now see as a cosmic microwave background – the glow of light from a time when the universe could finally be seen. For billions of years, the radiance has cooled to the point that now there is a temperature below 3 degrees above absolute zero. When it first appeared, the universe was much warmer, about 3000 K. The early universe was filled with a bright warm glow.
We have a good idea of what this first color is. The early universe had an almost uniform temperature everywhere, and its light had a distribution of wavelengths known as the black body. Many objects get their color from the kind of material they are made of, but the color of the black body depends only on its temperature. A black body of about 3000 K will have a bright orange-white glow, similar to the warm light of an old 60-watt bulb.
People don't see the color very accurately. The color we perceive depends not only on the actual color of the light, but also on its brightness and on whether our eyes are adapted to the darkness. If we could go back to the period of this first light, we would probably perceive an orange glow like a fiery light.
Over the next few hundred million years, the pale orange glow will fade and blush as the universe continues to expand and cool. Eventually the universe will fade to black. After about 400 million years, the first shining blue-white stars began to form and new light emerged. As stars and galaxies emerge and develop, the cosmos begins to take on a new color.
In 2002, Karl Glasbrook and Ivan Boldry calculated the average color from all the light we see from the stars and galaxies today to determine the current color of the universe. It turned out to be a pale complexion, similar to the color of coffee with cream. They called the color "space latte".
Even this color will only last for a while. As the big blue stars grow old and die, only the deep red glow of the dwarf stars will remain, after all, after trillions of years, even their light will fade and the universe will turn into a black sea. All colors fade with time and time will bring us into the darkness.
But for now, the colors of the universe still paint us. And if you ever sit by the fire with creamy coffee as you look up into the dark night, know that you are bathed in cosmic colors. Past, present and future.
When was the first light in the universe?
Ivan K. Baldri et al. The 2dF Galaxy Redshift Study: Limitations in the History of the Formation of Cosmic Stars on the Cosmic Spectrum, The Astrophysical Journal (2002). DOI: 10.1086 / 339477
What was the first color in the universe? (2019, October 21)
retrieved 21 October 2019
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