Where did the antimatter go?

A young Pakistani scientist at CERN explores the fundamental questions about the mysterious elusive material

Zeeshan Ahmad April 04, 2021


In the words of one researcher, science is not meant to cure us of mystery. Instead, he argues, it is supposed to reinvent and reinvigorate.

For us lay people, science remains a mystery sans reinvention. For reasons mundane and existential, most of us shy away from asking the fundamental questions. Perhaps it is due to our own shyness, even fear, that many of us hold such awe for those who dare go intellectually where the rest of us are unwilling or incapable of going.

Speaking of awe and mysteries, there are a handful of places around the world that evoke both while capturing our collective imagination. If I mention the European Organisation for Nuclear Research, it may or may not mean anything to most of us. But, if I use the acronym CERN, many may find their thoughts transported to the world of Dan Brown, of scientific intrigue and where the impossible becomes possible.

Speaking still of mysteries, and of CERN, there is the question of antimatter, a material many of us may confuse with the similar sounding yet wildly different concepts of dark matter and dark energy. Beyond our own mysterious understanding of it, lie the antimatter mysteries that the scientists who study it reinvent and reinvigorate in their attempts to understand it.


As luck, or perhaps fate, would have it, one of them is Pakistani. Who better to demystify both what we know at the moment about antimatter and what working at CERN entails.

Demystifying antimatter

For Muhammad Sameed, a life’s yearning for understanding has led to a dream come true. The 32-year-old Islamabad native is among a mere handful of Pakistanis who would think themselves lucky for a chance to work at CERN. What is more in Sameed’s case, he is physicist involved in studying antimatter particles at one of the world’s premier physics research organisations.

At CERN, Sameed is part of the ALPHA experiment, an acronym that stands for the Antihydrogen Laser Physics Apparatus. Just recently, the ALPHA collaboration effort succeeded in cooling down antihydrogen particles – the simplest form of atomic antimatter – with laser light.

Speaking with The Express Tribune, the young scientist began by admitting that the wider scientific community had perhaps contributed to some of the public misunderstandings about antimatter. “I think it is us physicists’ fault for giving such similar names to such different concepts,” he said when asked about the difference between antimatter, dark matter and dark energy.


Taking his own crack at remedying that, he explained: “Before we explain antimatter, it is important remember what matter is, at the subatomic level.”

Most of us learn about atoms and how they are made of electrons, protons and neutrons in school. “But that is where the general awareness ends,” said Sameed. “If you look deeper, while electrons are fundamental particles – they belong to a family of particles called leptons – protons and neutrons are not. Those two are made up of two more kinds of fundamental particles: the quarks and the gluons, which bind them.” He added that all matter that surrounds us and that we can interact with is made of particles from two families, namely quarks and leptons. Both families consist of six kinds of particles each.

According to Sameed, we have known all of this since the early part of the previous century, when quantum mechanics was developed. “Where does antimatter come in? It was first articulated in a theoretical study by physicist Paul Dirac,” he shared.

Dirac, while solving a quantum mechanics equation, arrived at two solutions, one positive and the other negative. “The positive one corresponded to the electron. Dirac initially disregarded the negative solution, but later used it to hypothesise the existence of ‘antielectrons’,” Sameed explained. “He made that prediction in 1928, and just four years later, an American experiment actually discovered it.”

How was the discovery made, you wonder? “We have all these particles from outer space that pass through our planet,” said Sameed. “If we apply a magnetic field to them, we can determine which direction these particles turn in. If electrons turn to one side, particles with the opposite charge would turn in the other direction.”

The physicist shared that since the discovery of the antielectron almost 90 years ago scientists have discovered an antimatter counterpart to each regular matter particle we know of. “The story we physicists should be telling people is that not only is antimatter real, but that these are particles are found in nature,” he said. “The real question is this: we know from equations and experiments that when matter is produced – in a lab or after the Big Bang – an equal amount of antimatter is produced. So how is it that ‘regular’ matter became so dominant in our universe and why is there so little antimatter occurring in nature?”


According to Sameed, all research into antimatter at CERN and other organisations is focused on this question: “What happened? Where did all the antimatter go?” One proposed explanation, he shared, is that antimatter has some as yet unknown property that converts it into regular matter in unequal amounts. “So by producing and trapping antimatter in a lab, we test it for various properties and whether those can explain what happened to most antimatter in nature. This has been the focus of research for the last 30 to 40 years.”

Cooling with lasers

Explaining the recent ALPHA experiment with laser cooling, Sameed began by explaining the choice of antihydrogen. “Hydrogen is the simplest atom we know of, with just one proton and one electron. Antihydrogen, similarly, is the simplest antiatom,” he said.

“You take an antiproton, get an antielectron to orbit it, and you should have an antihydrogen atom. But this is easier said than done,” he explained. “The main challenge with producing antihydrogen or any other antimatter particle is that if an anti-matter particle comes in contact with a regular matter particle, both are annihilated. So in order to capture anti-matter particles, you need to create perfect vacuum to ensure they don’t come in contact with matter particles.”

Sameed added that the challenge isn’t just limited to creating vacuum either. “You need to make sure that the container being used is designed in a way to ensure antimatter particles don’t come in contact with its walls. This is done using electromagnetic fields.”


Explaining how scientists study antimatter, Sameed began by explaining how regular matter particles would be studied. “Take a regular hydrogen atom which is in what we call a ‘ground state’ or normal state. If we shine a laser with a specific energy level onto that simple atom, its electron can jump into an ‘excited’ state.” He said that scientists have known about the effects of lasers on hydrogen atoms for a long time. “We know what frequencies can excite it. For our experiment, we thought to test the same on anti-hydrogen atoms. We wondered if it would react differently to regular hydrogen due to differences in energy levels or other properties. Perhaps our findings could help unravel some of the mystery around why there is so little antimatter in the universe?”

According to Sameed, the effects of lasers on antihydrogen were first tested in 2017. “We shined a laser with the same frequency as the one that excites electrons in a regular hydrogen atom on to an antihydrogen atom. The results suggest the effect on antihydrogen was more or less the same,” he said. “But one side effect that we uncovered at the time – and this had been predicted before the experiment – was that laser light can ‘cool’ particles.”

“Normally we use lasers to heat things, but if you shine a laser beam on an atom that is coming towards it, it has an effect of ‘slowing down’ the atom,” he added. “So our current experiment was the first time we tested this laser cooling principle on antimatter.”

Sameed further revealed that the next antimatter experiment being developed aims to study how it behaves under the influence of gravity from regular matter. “We know how gravitational forces work between regular matter. Our equations suggest the same interaction would be true between two objects made of antimatter. But, we want to find out what happens in terms of gravity when there is an interaction between matter and antimatter. At the moment, we don’t even have any strong theories to predict what will happen.”


Easier said than done

When Sameed explains the experiment, one may get the false impression that it is as easy as pointing a laser towards antimatter. But nothing could be further from the truth.

“For starters the laser we use is not the one used in laser pointers that most people know of. Ours is an ultraviolet laser, which is invisible to the naked eye and has a much higher energy level. It is not available commercially and is very difficult to manufacture, so we have to develop it in-house at CERN,” he said. The laser in question is also absorbed by air particles, Sameed added. “Not only must the beam travel through vacuum, it must be produced and aimed in vacuum as well.”

According to Sameed, firing a laser at antihydrogen is a very different challenge that firing it at regular hydrogen. “For normal hydrogen, we can shine the laser from any angle. But for antihydrogen, because the entire container is surrounded by special magnets to keep it from touching the walls, there is a very small access point for the laser itself.”

Commercial possibilities

Any innovative technology can open up opportunities beyond what those who developed it are sometimes able to appreciate. Speaking on this aspect, Sameed said: “We scientists develop such innovative solutions to satisfy pure curiosity and answer the fundamental questions about physics. But all research produces technological byproducts and sooner or later, they trickle down to R&D companies and eventually to wider society.”

Asked if he could foresee any antimatter applications used beyond research, Sameed said there was one example already in medical imaging, even if it was difficult to predict wider uses. “The PET or Positron Emission Tomography scanner. The positron is an anti-matter particle. It is essentially an anti-electron.”

Beyond that, CERN in general is responsible for developing a wide-range of technologies. “For instance, to trap anti-matter particles, we need strong magnetic fields. To produce those, we have to develop superconducting magnets which have various commercial uses as well. For instance, such magnets are used in hospitals in MRI scanners. A lot of technologies used in modern medicine were first developed in research centres like CERN,” Sameed revealed.

“Even on the software side, applications developed to track near-instant physical phenomenon have been co-opted by some financing trading companies which want to leverage the ability to process information in microseconds.”

Sameed added that all CERN research is open-source and accessible to anyone in the world. “You can contact our knowledge transfer centre and gain our research to use in reasonable ways.”

The value of research

According to Sameed, the side effects of research for research’s sake are undeniable. “We can see it over the last few centuries. The countries and regions that invested in fundamental research and technology, are the ones that are now global powers,” he said. “But we don’t even need to look at it philosophically. Just look at the Internet.”

Sameed pointed out that the World Wide Web was originally developed by CERN in the 1980s as a means to share information between physicists instantaneously. “The intention at the time was only to aid research. But it was made open source, and the effect of that simple choice in reshaping life can be seen today.”

Back to the future

How does one get to work at CERN? For Sameed, the yearning to become a scientist was sparked by one movie most of us watch and loved growing up. “I was five or six when I watched Back to the Future. I don’t think I understood much about the movie at the time, but I remember finding the character of Doc Brown fascinating,” he said. “I decided then that I would at least try to be a scientist when I grew up.”

In terms of background, Sameed admits he had an ordinary middle-class upbringing. “But I am lucky that my parents tried to provide me the best education possible,” he said. Still, CERN was beyond his dreams till the time he graduated A-Levels.

For Sameed, the path to a career in science opened with his elder brother’s academic pursuits. “He went to the US on scholarship to study chemical and biological engineering. That made me realise that I too could get in-depth education in physics abroad. Like him, I applied for a scholarship and was able to study physics at Cornell University. That really set the stage for me.”

The next chapter began when Sameed came across the example of another Pakistani who went on a summer internship to CERN. “He made me aware that there was a programme international students could apply for. I applied, with no hope of getting in, and originally I was rejected. But, some time later, they contacted me again and told me that I was a better fit for another department, and here I am.”


According to Sameed, he initially believed his recruiters at CERN had made an error. “But once I got here, I realised that I was no different from other students, from Europe or US or elsewhere. We Pakistanis are in no way inferior to other countries in terms of talent. All that is missing is awareness.”

When not busy participating in research, Sameed tries to do his part to raise awareness about opportunities for other Pakistanis at CERN. “Pakistan is now an associate member at CERN and what that means is that any Pakistani can apply for any job here. This is not limited to just positions for scientists and engineers, and involves things like administration and legal affairs, etc.”

Pakistan and CERN

According to Sameed, at the youth level, there is more awareness about CERN in Pakistan now. “In fact, Pakistan has one of the highest number of applicants to CERN,” he said. “But most of these are just student positions at the moment and for higher level positions, we are still lagging behind. In terms of Pakistanis who are at CERN for the long term, there may be four or five.”

Even so, Pakistanis appear to be highly valued at CERN, Sameed revealed. “Pakistani engineers have made a huge contribution to CERN and they are a very well respected community here. They always trust Pakistanis who make it to CERN to do a good job,” he said. “There is also immense pride for Pakistanis at CERN due to Dr Abdus Salam’s contributions, both to physics as a whole and to CERN during the time he spent here. One of the streets is even named after him,” he added.

Asked what advice he had for other young Pakistanis who choose a similar path, the physicist pointed out that there are many opportunities available, not just in CERN, but other high quality institutes. “Not only are Pakistanis eligible to apply, but they are looking for people from diverse backgrounds with talent,” he said. Even if you don’t have the confidence, I would say apply. Because you might think you’re not good enough, but the people who are recruiting may believe otherwise.”

Sameed reiterated that when he joined CERN, he realised he was as good as anyone else. “My hope for the future is that in addition to engineers, more Pakistani physicists will join as well.”




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