Today, the darkness of the night is studded with star light. But before the stars were born, did the light shine at the beginning of the universe?
The short answer is “No.” But the long answer reveals an extraordinary journey of light. Initially, early universe light was “confined” and took hundreds of thousands of years to escape. It then took about 100 million years for the stars to form.
By examining the velocity and direction of the galaxy moving, astronomer Edwin Hubble discovered that the universe is expanding. This 1929 discovery suggests that the cosmos was once small, and scientists ultimately calculated that the entire universe was concentrated in one infinitely dense point about 13.8 billion years ago.
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“The Big Bang created and expanded spaces with everything in the universe,” Andrew Layden, chairman of physics and astronomy at Bowling Green State University, Ohio, told Live Science.
The only way all the problems that make up the universe today can fit into a small place is if it was energy at the time,” Leiden said. Einstein’s famous equation E = MC2 revealed that energy and mass are interchangeable, Leiden explained.
As the universe expanded, the density of energy decreased and it cooled. According to the Las Cumbres Observatory, the first particles began to form within a second after the big bang. These included photons that made up light, as well as protons, neutrons and electrons that made up atoms. According to NASA, about three minutes after the Big Bang, the protons and neutrons were able to fuse to create a nucleus of atoms such as helium.
“Think of fog and dew,” Leiden said. “Particles in high energy state are dispersed like water in a mist, and when the energy is low enough, they can condense like droplets of dew.”
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However, photons of light were present from the first seconds after the Big Bang, but they still couldn’t shine across the universe. This was because early universes were so hot that “electrons were moving too fast for the nucleus to hold in their surrounding orbit,” Leiden said. “The universe was this extremely hot and thick soup.”
All electrons that moved freely in the early universe meant that light was not moving around very much. “During this time, the light was trying to move in a straight line, so it was constantly hitting an electron, so it couldn’t go too far,” Leiden said.
A similar situation can be seen in the sun, Urbana-Champaign cosmologist Srinivasan Lagunathan, a cosmologist at the University of Illinois, told Live Science. “You can imagine the photons of light produced by the nuclear reaction at the center of the sun trying to come out onto the surface of the sun,” he said. “The center of the sun is very hot, so there are plenty of free electrons. This means that light cannot move in a straight line.”
The distance from the center of the sun to its surface is approximately 432,450 miles (696,000 kilometers). The speed of light in a vacuum is about 186,000 miles per second (300,000 km/s), but in the sun “it takes about 1 million to 2 million years for light to escape from the center of the sun to its surface,” Lagunathan said.
However, about 380,000 years after the Big Bang, the universe’s expansion has cooled enough for the nuclei to be shining on electrons. “When that happens, all these electrons are no longer free,” Layden said. “This happens at around 3,000 Kelvins. [4,940 degrees Fahrenheit, or 2,725 degrees Celsius]the surface temperature of a cold reddish star. ”
In a short year, “everything goes from a hot, thick soup to a clear universe where light can move freely,” Leiden said. “At that moment, the first photon of the universe can escape.”
The typical light in the universe is near visible wavelengths of around 3,000 Kelvins, Layden noted. However, as the universe expanded for over 13 billion years, and the average temperature was cooled to about 2.73 Kelvin (minus 455 F, or minus 270 C), the universe’s first light extended to a longer microwave wavelength.
Astronomers first detected this remaining radiation from the Big Bang, known as the background of the cosmic microwave in 1964.
Analyzing these microwaves gave us a lot of insight. For example, gravitational pulls in galaxies can distort light. This is a phenomenon known as a gravity lens. Examining the amount of distortion experienced by the cosmic microwave background at various points in the sky will help scientists reconstruct the massive structures of the universe, namely the huge voids between the galaxy arrangement and the universe, Lagunathan said.
After the release of Light from the Big Bang, the universe went through what is known as the Dark Age of Space. Ultimately, millions of years later, the gravity of a cloud of gas led to these masses of material collapse into themselves.
“This created the first generation of stars, and there was a galaxy full of stars in the universe about a billion years after the dawn of space began,” Layden said.
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