(TMU) — Science has come a long way in the past few years. I still remember when the “Particle of God”, Higgs boson, was just a dream that needed to be confirmed after physicist Peter Higgs theorized its existence. In December 2013, after a lot of work done on the LHC built by CERN, Higgs’ theory was confirmed and he was warded with with the Nobel prize.
We have also learned more about subatomic particles recently, such as the two main types that exist: elementary and composite. Thirty-six fundamental particles, including antiparticles (same mass than the original but opposite physical charge; e.g electron-antielectron), exist. Twelve of these are force-carrying particles, and the other 24 are called “matter particles” and only interact with each other indirectly via the force carriers.
But it is still a mystery for scientists what really happens inside an atom. A healthy competition is being held regarding this: two groups of scientists presume they have the key to solving the mystery and both teams are working to prove their own vision is correct.
An atom is the smallest unit of ordinary matter that constitutes a chemical element, and every state of matter is composed of atoms. Electrons whiz around orbitals in an atom’s outer shell. There is a lot of empty space as well as a tiny nucleus, which provides most of the atom’s mass.
We have four fundamental forces working in the universe:
- Weak force
- Strong force
The strong force is the one bonding together the protons and neutrons inside the atom.
No one knows yet how these protons and neutrons behave inside an atom. Outside an atom, the nucleons (protons and neutrons together) have defined sizes and shapes. Each of them is made up of three smaller particles called quarks. The interactions between these quarks are so intense that no external force should be able to deform them. Scientists have known for many years that the theory now accepted of the atom is not quite correct because inside a nucleus, protons, and neutrons appear much larger than they should be.
Nucleons moving in little orbitals within the nucleus have very little energy, they are restrained by the strong force. In 1983, physicists from CERN noticed something strange: Beams of electrons bounced off iron in a way that was really different from how they bounced off free protons. Gerald Miller, a nuclear physicist at the University of Washington, told Live Science that that was unexpected because if the protons inside hydrogen were the same size as the protons inside iron, the electrons should have bounced off in much the same way.
Scientists came to believe it was a size issue. Researchers created a name for this phenomenon, the EMC effect, after the European Muon Collaboration.
Or Hen, a nuclear physicist at MIT, said that while quarks strongly interact within a given proton or neutron, quarks in different protons and neutrons can’t interact much with each other. The strong force inside a nucleon is so strong it eclipses the strong force holding nucleons to other nucleons.
“Imagine sitting in your room talking to two of your friends with the windows closed,” Hen said. The trio are three quarks inside a neutron or proton. “A light breeze is blowing outside,” he said.
That light breeze is the force holding the proton or neutron to nearby nucleons “outside” the window. Hen also said that experiments have shown that at any given time, about 20% of the nucleons in a nucleus are in fact outside their orbitals and instead they’re paired off with other nucleons. Due to these circumstances, the interactions between the nucleons are much higher-energy than usual. These interactions break down the walls separating quarks inside individual protons or neutrons.
The quarks making up one proton and the other quarks involved with the other proton start to occupy the same space, this causes the protons to stretch and blur, Hen said. After this, they grow a lot, but for very shorts periods of time. This produces the EMC effect previously mentioned.
Most physicists now accept this interpretation of the EMC effect but not everyone thinks this is how you would solve this problem. Ian Cloët, a nuclear physicist at Argonne National Laboratory in Illinois, said he thinks Hen’s work draws conclusions that the data doesn’t fully support.
“I think the EMC effect is still unresolved,” Cloët told Live Science. “If you use that model to try and look at the EMC effect, you will not describe the EMC effect. There is no successful explanation of the EMC effect using that framework. So in my opinion, there’s still a mystery.”
“What is clear is that the traditional model of nuclear physics … cannot explain this EMC effect,” he said.
QCD stands for quantum chromodynamics, the system of rules that govern the behavior of quarks. “We now think that the explanation must be coming from QCD itself,” Cloët also said. Nuclear physics would be ancient “technology” compared to quantum chromodynamics, but it also needs a lot more work to build.
The problem is that the complete QCD equations describing all the quarks in a nucleus are too difficult to solve, Cloët and Hen both said.
Modern supercomputers are about 100 years away from being fast enough for the task, Cloët estimated. And even if supercomputers were fast enough today, the equations haven’t advanced to the point where you could plug them into a computer, he said. )You can read more about the latest breakthroughs in quantum technology here.)
That suggests we need a different model, Cloët also said.
“The picture that I have is, we know that inside a nucleus are these very strong nuclear forces,” Cloët said. These are “a bit like electromagnetic fields, except they’re strong force fields.”
Clöet calls these force fields “mean fields” which actually deform the internal structure of protons, neutrons, and pions.
“Just like if you take an atom and you put it inside a strong magnetic field, you will change the internal structure of that atom,” Cloët said.
Scientists who support the mean-field theory think the sealed-up room Hen described has holes in its walls, with wind is blowing through that causes the quarks to stretch out.
In the end, researchers emphasized that the debate is friendly.
“It’s great, because it means we’re still making progress,” Miller said. “Eventually, something’s going to be in the textbook and the ball game is over. … The fact that there are two competing ideas means that it’s exciting and vibrant. And now finally we have the experimental tools to resolve these issues.”
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