What happens inside an atom? What’s the secret of the atom? Two different teams of scientists believe they found the answer. Researchers are competing to prove their theory. However, which solution could be correct?
An atom is the smallest component of an element, characterized by a sharing of the chemical properties of the element and a nucleus with neutrons, protons, and electrons. No one knows how these protons and neutrons behave inside an atom. On the outside, an atom’s protons and neutrons have exact sizes and shapes; however, inside a nucleus, protons and neutrons look much more significant than they should be.
To explain that peculiar discrepancy, physicists have developed two theories. Both competing groups of scientists believe their hypothesis is correct; however, they agree that the right answer must come from a field beyond their own.
Gerald Miller, a nuclear physicist at the University of Washington, says the nucleons are limited in their movements and don’t have much energy, based on old researches. However, later studies show how beams of electrons bounced off the iron in a way that was very different from how they bounced off free protons. That was a surprise; the particles should have bounced off in much the same way as protons.
For unknown reasons, protons and neutrons inside heavy nuclei act as if they are much larger than when they are outside the nuclei. A group of researchers have discovered this by accident and named this phenomenon the EMC effect. However, it contradicts current theories of nuclear physics.
The force inside a nucleon is potent, so strong that it overshadows the strong force holding nucleons to other nucleons. The cross-section for deep inelastic scattering from an atomic nucleus is different from that of the same number of free protons and neutrons.
Hen and Miller worked together on this research, and according to Hen, most physicists now accept the theory of the EMC effect.
Ian Cloët, a nuclear physicist at Argonne National Laboratory in Illinois, believes that Hen’s work is incomplete. “I think the EMC effect is still unresolved,” said Cloët. “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. “We now think that the explanation must be coming from QCD itself.”
QCD stands for quantum chromodynamics —the theory of the strong interaction between quarks and gluons, the fundamental particles that make up composite hadrons such as the proton, neutron, and pion.
Although QCD equations are complicated to solve, it’s possible to answer some questions which at the moment offer a different explanation from the EMC effect. The Nuclear Mean-Field Theory.
“The picture that I have is, we know that inside a nucleus are these very strong nuclear forces.” These are “a bit like electromagnetic fields, except they’re strong force fields. 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.
The question is, which theory dominates the secret of the atom?
“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.”