Into the Primordial Soup

There is no reason to stop the extrapolation back in time at three minutes AB. We have a very good knowledge of the types of interactions expected in a universe of electrons, neutrons, protons, and photons, and so long as we can understand the relevant constituents of matter and its behavior at high temperature, we can reasonably speak of the evolution of the universe.

We know that neutrons and protons are not elementary particles, but rather, are made of quarks and gluons. At sufficiently high temperature and density the neutrons and protons themselves should melt. Earlier than a microsecond (one-millionth of a second) after the bang, the universe should have been a primordial soup of quarks and gluons.

The Known Ingredients in the Primordial Soup (circa four picoseconds AB)

Since our goal is to simulate the extreme conditions of the early universe, we must find a way to produce the corresponding temperatures in the laboratory. The most powerful tool for generating high temperatures is the particle accelerator. The accelerator is used to examine nature on the smallest scales and to discover the fundamental forces and particles. Accelerators are the world's most powerful microscopes. But the most powerful microscope is also a telescope, because by colliding particles at high energy we can recreate the environment of the early universe and understand how it evolved into the present universe.

The world's most powerful accelerator is Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois. Collisions of protons and antiprotons at Fermilab can produce temperatures of 3,000,000,000,000,000 K, which existed in the universe four picoseconds (fotir-millionth-millionth of a second) after the bang. We can study the early universe by recreating in terrestrial laboratories a little piece of the primordial soup. The ingredients of the primordial soup are the elementary particles produced and studied at accelerators.

The most abundant ingredients in the primordial soup were quarks and antiquarks. They are so numerous because there are six types of quarks and each type of quark comes in three ‘colors.’ The next most abundant particle species in the primordial soup was gluons, the carriers of the strong force. Quarks, antiquarks, and gluons make up 72% of the primordial soup. The electrons, muons, photons, and all the other elementary particles were the flavorful croutons in the primordial soup.

Contributed by: Dr. Edward Kolb