For one microsecond after the universe began, there were no stars, planets, or normal atoms. Instead, the universe was a hot, chaotic mix called quark-gluon plasma, where the basic parts of matter moved freely.
Now, researchers from the Niels Bohr Institute in Denmark have recreated this early environment. Using the Large Hadron Collider, they produced this ancient matter in a lab. They did this by colliding very small atomic nuclei, smaller than those used in past experiments.
The experiment happened near Geneva, Switzerland, in the Large Hadron Collider, the world's most powerful particle accelerator. This 27-kilometer machine includes the ALICE detector, where about 1,800 scientists from around the world work together. They create the extreme heat and density needed to turn protons and neutrons back into their original, free-moving state.
Because this early plasma cools and disappears almost instantly, scientists cannot see it directly. They study what happens after it breaks apart. By analyzing how particles scatter, they can learn about the plasma.
Emil Gorm Dahlbæk Nielsen, a researcher who worked on the study, compared it to seeing a shadow. "You can't see the object directly, but its shadow reveals its shape," he explained. "In the same way, the movement of the particles reveals the shape of the atomic nuclei at the start of the collision."
This high-energy method is a big change in nuclear physics. For years, scientists studied atomic nuclei using low-energy observations.
You Zhou, a professor at the Niels Bohr Institute who led the research, highlighted the new method's value. "Instead of studying nuclei at low energy, we make them collide at the highest energies we can create, and now we can read their shape from the imprint they leave," he said. Zhou mentioned that this work shows how small an atomic nucleus can be while still creating the early plasma.
This discovery is important because it helps us understand both atomic nuclei and the early universe. By learning how this extreme matter forms, scientists are getting closer to understanding how the early universe cooled and developed into the world we know today.