Few formulations of scientific theories are as memorable as Sir Isaac Newton’s when he proposed his theory of gravity in the 17th century after an apple is said to have fallen on his head as he sat under a tree. The theory has had a massive impact on the world of physics. Four centuries later, an international collaboration of scientists, including researchers from Calgary, are still investigating gravity — this time to observe its effects on antimatter.
One of physics’ most substantial questions is where antimatter exists or not in our universe. Scientists, in a massive international collaboration, have just published results from an experiment that marks an important advancement in the field of matter and antimatter research.
Researchers involved with the Antihydrogen Laser Physics Apparatus (ALPHA) collaboration that’s based at the European Organization for Nuclear Research (CERN), have observed the first-ever gravitational free-fall of antimatter, a significant step forward in understanding the nature of antimatter.
“The really big picture goal is that we have this big unsolved mystery in physics, which is what happened to the antimatter in the universe? Why do we see no antimatter? We think, based on our understanding, there should be equal amounts of matter and antimatter but we can’t find it.” said Timothy Friesen, a senior researcher on the ALPHA collaboration and an assistant professor of physics and astronomy at the University of Calgary who’s been working with ALPHA since 2009.
“ALPHA is looking very closely at antimatter we produce in the lab and studying the properties as precisely as we can to see if we can find a small difference because we know there’s something we don’t understand about antimatter,”
What is antimatter?
Antimatter is the counterpart of matter, which makes up our universe. Although theories in physics have long predicted that when we create matter we create antimatter, where this antimatter actually exists in our universe is a mystery not yet solved. By observing the characteristics of antimatter, such as the gravitational effects on antimatter, information is made available that may help scientists answer this question.
“Most people were convinced it would fall down,” said Robert Thompson, the associate vice president of research at the University of Calgary, a senior researcher and one of the founding faculty members with the ALPHA collaboration. “But when you push them on why they were convinced that, people, in this case [those] being physicists, it was a little harder for them to do it on a completely firm foundation,”
“Initially, we wanted to trap the anti-hydrogen atom and to hold onto it so we could study it. So that was the first proposal that we wrote, was to figure out how to do that” said Jeffrey Hangst, spokesperson and founded ALPHA in 2005. He added, “The next big milestone in this field was learn how to hold onto anti-hydrogen atoms after they were formed, and that was the original goal of ALPHA”
In 2010, ALPHA achieved its first two goals of making and storing anti-hydrogen, and since then has focused on understanding the characteristics of antimatter to compare them with matter.
“Our technical goal was to create, trap, and study anti-hydrogen, the simplest form of atomic antimatter. The high-level goal is to solve the riddle of antimatter,” said Thompson.
The experimental portion of the ALPHA-g experiment commenced in April 2022 at CERN’s laboratory in Geneva, Switzerland and ran 24 hours a day until November 2022. The goal was to understand the gravitational effects on antimatter and perform the first precision weight measurement of antimatter.
Trapping antimatter
“The idea is quite simple, said Hangst. “You form some anti-hydrogen atoms and you trap them in this vertical magnetic bottle. Then you release the magnetic field just at the top and the bottom of the trap to see what happens. If anti-hydrogen is attracted to the earth, more atoms will go out the bottom then the top. So it’s really just a counting game, you need to repeat this experiment enough times to believe in your statistics,”
The first results from the experiment, published on September 27, 2023, revealed that when interacting with gravitational forces, antimatter falls just as matter does.
“We’re talking gravity,” said Thompson. “We’re talking Newton sitting under an apple tree, with a matter apple falling onto the matter Earth, and it falls at a predictable rate. And we’re pretty confident that if you were on a world made out of antimatter, and you had an apple made out of antimatter, [it] would fall the same. An anti-apple would fall in the same direction as an apple.
Thompson also noted that an anti-apple may fall at the same rate of an apple, “But we don’t have the precision yet to confirm that. And that is still an important difference left to be confirmed.”
The next wave of discovery
The fact that antimatter falls may seem like a small discovery, but it marks a major advancement in the physics world, and will undoubtedly lead to a further understanding of our universe.
“This is the first time we’ve been able to do this test. It sounds simple to kind of drop antimatter, but it’s very hard because gravity is quite weak compared to electricity and magnetic forces,” said Friesen. “The next step is does it fall down in exactly the same way? So this is like the first big result and we hope to go further after this.”
Following the results from the ALPHA-g experiment, ALPHA hopes to focus on identifying if antimatter has the same optical characteristics as matter by studying if anti-hydrogen interacts with light the same way hydrogen does.
“We now have a starting point,” said Thompson. “Now that we know we can do the measurement, we can continue to refine it, and truly understand how gravity acts between matter and antimatter.”
They will also further investigate the relationship between antimatter and gravity next year, where they hope to measure if antimatter matter falls at the same rate as matter. ALPHA plans to continue investigating the properties of antimatter, continuing to make important discoveries to advance this field of research and the world’s understanding of matter and antimatter.
“I’m really proud of this team, it’s an amazing group of individuals who always deliver and who are always first — no one has ever beaten us to any milestone ever. We always get things done first,” said Hangst.