Observation of antihydrogen property reaffirms nature’s fundamental symmetry
According to our current models of physics we shouldn’t exist.
As far as we currently know you should not exist.
Key points
• Physicists at CERN have found the value of the Lamb shift in antihydrogen closely agrees with the value in hydrogen
• This reaffirms a fundamental symmetry of nature
• Yet it can’t tell us why we and the rest of the material universe exists when our current physics models say we shouldn’t
It’s nothing personal.
According to our current theories of physics, neither you, me, nor the entire material universe around us should exist.
That’s because 13.8 billion years ago, just after the Big Bang, every particle of matter, including what we’re made of, should have been annihilated by an equal amount of antimatter.
Yet here we are — in a universe where there’s a lot more matter than antimatter.
“We’re at a complete loss to explain that, and so we’re investigating everything about antimatter that we can,” said physicist Jeffrey Hangst of Aarhus University and spokesperson for CERN’s ALPHA experiment.
Matter vs antimatter
Matter is essentially the stuff that we and all the material universe is made of.
Antimatter is thought of as matter’s almost-identical twin — the same, except that it carries a different charge.
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For example, hydrogen has a proton and an electron, antihydrogen has an antiproton and a positron (the antiparticle of an electron).
Now, for the first time, Professor Hangst and colleagues at CERN in Switzerland have observed a property of the antimatter equivalent of hydrogen that had previously only been predicted.
They say the research, published in the journal Nature, reaffirms a fundamental symmetry of nature.
Why antihydrogen?
We’ve been studying in-depth the structure of hydrogen for over 100 years.
“It is no exaggeration at all to say that we learned quantum mechanics and atomic physics from hydrogen,” Professor Hangst said.
“It’s the thing we know the most about I would say in physics at every level.”
But it’s only been in the last few years that Professor Hangst and his colleagues have been able to do similar experiments with antihydrogen.
“First of all we had to learn how to produce it. And then we had to learn how to hold onto it. And we had to learn how to interact with it once it’s held. And we had to learn how to make more of it,” he said.
Every atom of antihydrogen that’s ever been studied has been produced, trapped and studied in ALPHA.
“Other people have tried and failed to do what we do,” Professor Hangst
Splitting energy levels within atoms
In this latest experiment, the team measured the energy differences between different excited states of antihydrogen in a vacuum.
When an atom of antihydrogen gets excited, its positron gets kicked to an orbital or energy level further out from the antiproton-containing nucleus of the atom.
When it returns to its original orbit it emits energy.
While our classical models only detail these big jumps between orbitals, there are other quantum effects.
“There are fluctuations in the vacuum, there are virtual particles that can appear and disappear,” Professor Hangst said.
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These quantum fluctuations can shift the energy of these levels by different amounts.
One such shift, called the Lamb shift after it was reported in atomic hydrogen in 1947, led to the field of quantum electrodynamics which describes the interactions between particles and light.
Professor Hangst and his colleagues were able to show that in antihydrogen the value of the Lamb shift closely agreed with the value in ordinary hydrogen.
“To be honest, nobody expected it to not be there, because there’s no alternative to quantum electrodynamics that would predict some difference between hydrogen and antihydrogen,” Professor Hangst said.
High levels of precision
This experiment really tested one of the most interesting predictions of quantum electrodynamics, said particle physicist Phillip Urquijo of the University of Melbourne, who wasn’t involved in the research.
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Dr Urquijo is working on a different experiment called Belle II that is looking for matter-antimatter asymmetries.
Both types of experiments require extremely high levels of precision and measurement techniques in order for a potential effect to be observed, he said.
“And [then] you may eventually be sensitive to the new particles that you’re looking for, [or] the new forces that you’re looking for,” Dr Urquijo said.
Until then the contradictions between our theories and the real world will continue to rankle.
“It’s always in the back of our mind that … there’s some mystery about antimatter that we simply can’t explain,” Professor Hangst said.
“Now, whether it shows up in what I do, or whether it shows up on the LHC [Large Hadron Collider] or some other experiment we’ve yet to devise, we just don’t know.”
