The ‘Little Bang’ Helping Physicists Study the Infant Universe

In order to comprehend the circumstances that led to the world as it is today, scientists are trying to recreate the quark-gluon plasma, an early form of matter.

A bang launched everything into life at the beginning of our universe. But it's unclear what took place after that. Scientists believe that a hot, soupy mixture of two basic particles called quarks and gluons, moving through space as a plasma, likely existed before atoms or even the protons and nuclei that make up an atom formed. Additionally, a group of scholars are attempting to rewrite history because no one was present to witness the creation of the universe.

They have basically produced a "Little Bang" using the Relativistic Heavy Ion Collider at Brookhaven National Laboratory and are using it to investigate the characteristics of that quark-gluon plasma. The discoveries will contribute to the improvement of cosmologists' still hazy understanding of the early universe and how the oozy, blistering condition of baby matter cooled and formed into the planets, stars, and galaxies of today.

According to scientist Rongrong Ma, who works with the Solenoidal Tracker at the Relativistic Heavy Ion Collider, or STAR, a detector dedicated to studying the quark-gluon plasma, "we think about a microsecond after the Big Bang, the universe was in this stage." Therefore, if we can learn from experiments about the characteristics of such matter, that will help us comprehend how the cosmos developed.

The duration of this plasma stage is unknown to scientists; it may have ranged from a few seconds to millions of years. Knowing its characteristics could help define the physics of the most extreme cosmic settings. It might even still exist today in the dense centers of neutron stars or be created when super-high energy particles collide with Earth's atmosphere.

Since observatories can only observe the cosmic microwave background—the first light to appear from the dense early universe a hundred thousand years after the Big Bang—their ability to research the early universe is limited. Everything prior to that is a dark period of astronomy, both physically and metaphorically. Nuclear physicist Jaki Noronha-Hostler of the University of Illinois at Urbana-Champaign notes that theoretical models can fill in that void, but detectors like STAR "allow you to experimentally understand a system that's very similar to the Big Bang."

Furthermore, quarks and gluons are never discovered alone in nature, which makes it challenging to research them separately. According to Helen Caines, a physicist at Yale University and spokesman for the STAR experiment, "We can't just pluck one out and examine it." Protons, neutrons, and more unusual matter like upsilon, pion, and kaons are instead trapped in composite forms. However, the separation between these compound particles blurs at high enough temps. Caines adds, "And that is the quark-gluon plasma." The quarks and gluons in this area are still contained within a certain volume, but they are no longer joined together. In reality, she claims, the term "plasma" may be a little misleading because it actually functions more like a fluid and moves.

Physical Review Letters published a paper in March by Brookhaven researchers describing their creation of the quark-gluon plasma for a moment in time by accelerating two streams of gold nuclei almost to the speed of light and slamming them into one another. Then came the smart part: they calculated how hot the post-Big Bang plasma would have been using this impact.

In order to accomplish this, they had to search for upsilons, which are a result of Brookhaven beam impacts but weren't actually present at the beginning of the universe. A quark and its antimatter counterpart are bonded together to form an upsilon in one of three ways: in a closely bound "ground state," or in two excited states, one of which is looser than the other. The gold atoms are abundant in each of these three forms when they are slammed together.

The goal, according to Caines, is to use these fragments as a gauge. These upsilons can be destroyed in a plasma similar to the one that might have existed microseconds after the Big Bang; interactions with unbound quarks and gluons will reduce them to their most elementary components. Furthermore, each jurisdiction has a unique "melting point." The quark-antiquark couples that are more loosely linked would require less energy to disintegrate, while ground-state upsilons would require the most energy and the highest temperatures. Therefore, simulating post-Bang plasma conditions and noting how many upsilons of each state remained would provide information about the temperature during the universe's creation.

Due to the fact that the temperature of the quark-gluon plasma is inextricably connected to its density, pressure, and viscosity, this would then provide scientists with information about other aspects of the plasma. A mathematical formula that describes all of the characteristics of the plasma, how they interact with one another, and how they change over time is what scientists refer to as an equation of state.

The structure of the quark-gluon plasma is special: It has a circumference similar to that of a proton, according to Noronha-Hostler, and is both incredibly hot and small. It therefore defies the rules that govern how fluids behave. She claims that while we can write down formulae, we cannot answer them. Cosmologists can infer how long the universe must have been in this soupy state by understanding this behavior, as well as what physical processes led to a transition into the more recognizable protons, neutrons, and other particles that make up matter today.

The first test was performed in 2012 using the Large Hadron Collider at CERN, which can accelerate electrons to velocities that are 25 times greater than those attained at Brookhaven. This was actually the second time that scientists had conducted such a test. Scientists can fine-tune theoretical models of the early universe by studying the plasma at lower energies to better understand how its characteristics rely on temperature. According to Brookhaven physicist David Morrison, who was not engaged in the research, "In the field that we're in, you really want to do things at a range of energies," However, the lower temperature state created at Brookhaven is closer to what the system may have looked like when the quarks and gluons started to combine. Hotter plasma is a superior probe for earlier in the cosmos.

This time, following the impact of gold atoms in the STAR detector, the researchers tallied the number of upsilons they observed in each state and compared it to the expected number, prior to the plasma melting the upsilons. About 60% of the upsilons in the ground state and 70% of those in the intermediate state were discovered to be gone and likely dissolved. The most weakly bound quark and antiquark duo upsilons appeared to be entirely gone.

The STAR team's earlier observations, which established an upper limit on the temperature required to create the plasma: at least a trillion degrees, were supported by their recently acquired data. (That is almost a million times hotter than the sun's core.) This temperature was maintained by their atom breaking for just 10-23 of a second.

In order to determine whether the particles with the loosestly bound quark-antiquark pair genuinely disappeared or simply survived at rates too low to be identified, the STAR team is preparing to repeat their upsilon measurement at Brookhaven with about 20 times more data. Within the next month, the facility will also activate a separate detector dubbed sPHENIX. The 1,000-ton device, which is centered on an ultracold, superconducting magnetic core, will enable more accurate study of this melting phenomenon. Morrison, a representative for the sPHENIX partnership, claims that "This STAR paper had hundreds of upsilons." "Tens of thousands will be measured,"

When attempting to comprehend the characteristics of the quark-gluon plasma, upsilons are ultimately just one piece of the jigsaw, according to Ma. In addition, physicists can observe individual quark collisions, examine photons coming from the plasma, or attempt to ascertain the kinds and rates of other particles produced by the explosions of gold atoms. These various observations will assist physicists in linking events they are already familiar with to theories for those they are not. To create a complete picture of the quark-gluon plasma, Ma explains, "we try to put all these together, using a multi-messenger approach for a theory that can explain everything."