In a paper published in the scientific journal Nature on Wednesday, Cornell alumni Muhammed Sameed ’11, and William Bertsche ’00 have begun to shed light on one of the universe’s darkest secrets — antimatter.
Antimatter is similar in many ways to the matter encountered in our day to day lives — it has mass, a magnetic moment and positive or negative charges. However, antimatter particles have the opposite charge of their matter counterparts, and when these two counterparts interact with one another they are both annihilated and produce energy.
As a result of this annihilation, these elusive particles are difficult to come by in nature, which is why Sameed and his colleagues utilize the technology at CERN, a European particle physics laboratory in Geneva, Switzerland, to capture particles of antimatter.
Sameed’s work is a part of the ALPHA experiment collaboration, which works to compare the nature of hydrogen and its antimatter counterpart — antihydrogen.
Specifically, the team at ALPHA makes use of a machine known as an antiproton decelerator. This machine uses magnetic and electric fields to slow down and capture the typically fast-moving antiprotons. These antiprotons can be combined with antielectrons — also known as positrons — to form the antimatter equivalent of hydrogen, the universe’s simplest element.
These antihydrogens are what Sameed and colleagues study as a model system for all antimatter, because it is the most simplistic system that can be created. Any time they make an observation in antihydrogen they compare it to what is known about hydrogen.
ALPHA’s most recent observations have confirmed the presence of a quantum phenomena known as Lamb-Shift in antihydrogen. This shift predicts the difference in energy between two energy levels for hydrogen, which is incorrectly predicted by the Dirac equation.
The Dirac equation aimed to reconcile the two governing laws of physics, Einstein’s Theory of General Relativity — which describes gravity— and the Standard Model of particle physics — which describes the other three fundamental forces of the universe, weak and strong nuclear interactions and electromagnetic forces.
A better understanding of the quantum-mechanical workings of antimatter particles could enable the group to study more complex properties of antimatter, including how antimatter particles interact with gravity in our matter-based Earth.
“We know that on planet Earth we know that if you have a normal matter hydrogen atom it will fall because the gravity of the Earth is pulling on it. Similarly if you had an anti-Earth and an antihydrogen we expect the same to happen,” said Sameed.
However, the effects of Earth’s gravity on antimatter particles are yet to be understood, but the group at ALPHA is designing experiments to observe the interaction between Earth’s gravity and antiparticles.
The reason physicists like those at ALPHA conduct research on the workings of antimatter is because it is fundamental to understanding the structure and creation of the universe.
“You always form matter and antimatter in equal parts, if this is true now it must have been true decades ago and basically at the beginning of the Big Bang,” Sameed said. “But our universe doesn’t show that — when we look out through a telescope you see galaxies made predominantly of matter particles and a very, very small amount of antimatter particles,”
If matter and antimatter must be formed in equal proportions, then there should be equal amounts of antimatter and matter in the observable universe — but this is not the case. According to Sameed, there are 10 billion matter particles for every one antimatter particle.
“Where did all of that antimatter go? Is there a specific property that somehow converts antimatter into matter or is antimatter in some far corner of the universe that we can no longer see?” said Sameed.
In order to answer these questions scientists like Sameed must understand how these particles function, so that they can piece together where the antimatter is in our universe and what role it played in the formation of the universe as we know it.
With improvements in technology and better understanding of the nature of antiparticles the group at ALPHA are able to probe the nature of antimatter more deeply, as they search for the quantum mechanical quirk that differentiates it from matter.
“The expectation is that the results should be the same, but there is a catch however. If all of the properties [of antimatter] were the same [as matter] then our universe should not exist, because it should have an equal amount of matter and antimatter atoms and everything should be annihilating with each other. So we know there must be some difference out there and we are trying to find out what that difference is,” Sameed said.
While the presence of Lamb-Shift is not the defining factor dividing matter and antimatter Sameed and colleagues have narrowed down the list of properties making antimatter special.