- By Pallab Ghosh
- science reporter
image Source, SackmeisterK/Science Photo Library
Artwork: Shortly after the Big Bang that created the universe, matter and antimatter existed in equal amounts
Scientists have made an important discovery about antimatter – a mysterious substance that was abundant at the beginning of the universe.
Antimatter is the opposite of matter, which stars and planets are made of.
Both were created in equal quantities in the Big Bang that created our universe. Although matter is everywhere, its opposite is now extremely difficult to find.
The latest study has shown that both respond to gravity in the same way.
For years, physicists have been struggling to discover their differences and similarities, in order to explain how the universe originated.
The discovery that antimatter rose up instead of falling in response to gravity would have destroyed everything we know about physics.
They have now confirmed for the first time that antimatter atoms fall downwards. But far from being a scientific impasse, it opens the door to new experiments and theories. For example, does it fall at the same speed?
During the Big Bang, matter and antimatter should have canceled each other out, leaving nothing but light. Why they didn’t is one of the great mysteries of physics and uncovering the differences between the two is the key to solving it.
Somehow matter triumphed over antimatter in those first moments of creation. How it responds to gravity could be important, according to Dr. Danielle Hodgkinson, a research team member at CERN in Switzerland, the world’s largest particle physics laboratory.
“We don’t understand how our universe came to be matter-dominated, and that’s what motivates our experiments,” he told me.
Engineers are adding liquid helium to the system to keep the antimatter at minus 270 Celsius, the lowest possible temperature, close to absolute zero
Most antimatter exists in the universe transiently, only for a few seconds. So to carry out the experiments, the CERN team needed to make it stable and long-lasting.
Professor Jeffrey Hangst has spent thirty years painstakingly building a facility to create, trap, and then drop thousands of atoms of antimatter from subatomic particles.
“Antimatter is the coolest, most mysterious thing you can imagine,” he told me.
“As far as we understand, you and I could create a universe just like ours out of antimatter,” Professor Hangst told me.
“It’s inspiring just to address; this is one of the most fundamental open questions about what this stuff is and how it behaves.”
What is antimatter?
Let’s start with what matter is: Everything in our world is made of it, of tiny particles called atoms.
The simplest atom is hydrogen. The Sun is mostly made of this. The hydrogen atom is made up of a positively charged proton in the center and a negatively charged electron revolving around it.
With antimatter, the electric charges are opposite.
Take antihydrogen, which is the antimatter version of hydrogen used in CERN experiments. At its center is a negatively charged proton (the antiproton) and a positive version of the electron (the positron) orbiting it.
These antiprotons are produced by collisions of particles in CERN’s accelerator. They arrive in the antimatter laboratory through the pipe at a speed close to the speed of light. It is too fast to be controlled by researchers.
The first step is to slow them down, which the researchers do by sending them around a ring. This depletes their energy until they can move at a more manageable pace.
The antiprotons and positrons are then sent into a giant magnet, where they mix to form thousands of atoms of antihydrogen.
The magnet creates a field, which traps the antihydrogen. If it touched the side of the container it would be instantly destroyed, because antimatter cannot interact with our world.
When the field is turned off the antihydrogen atoms are freed. Sensors then detect whether they have fallen over or under.
Some theorists have predicted that antimatter might fall upwards, although most, notably Albert Einstein in his general theory of relativity more than a hundred years ago, said that it should behave just like matter and fall downwards. .
Researchers at CERN have confirmed with the greatest certainty ever that Einstein was right.
But just because antimatter doesn’t fall up, doesn’t mean it falls down at the same rate as matter.
For the next steps of the research, the team is upgrading their experiment to make it more sensitive, to see if there are slight differences in the rate at which antimatter falls.
If so, it could answer one of the biggest questions of all: how the universe came into being.
The results have been published in the journal Nature.