The problem with anti-matter

 

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The problem with anti-matter, put simply, is that it doesn't hang about. As soon as an anti-matter particle comes into contact with a particle of matter, both annihilate in a burst of energy.

How then do we explain the existence of so much matter? Everywhere we look in the universe (and as far back in time as we can go by looking out across the lightyears of deep space), we see only matter.

The earth around us, the stars and galaxies, are all made almost exclusively of matter.

Representation of an antihydrogen atom (top), a positively charged antielectron, or positron, orbits a negatively charged antiproton Anti-matter (top) is the mirror image of matter

The existence of anti-matter was first suggested by the theoretical physicist Paul Dirac in the 1930s.

Working on a theory to combine quantum mechanics with Einstein's special relativity, he realised his equations predicted a corresponding anti-particle for every particle in existence - identical in every respect, but with an opposite electrical charge. So for every proton there is an anti-proton, and for every electron there is an anti-electron, or positron.

That is fine in theory, but it presents a problem: If our current understanding of the laws of physics tells us that as much matter as anti-matter must have been created in the Big Bang, then where has all the anti-matter gone?

One theory is that there must have been some minute discrepancy in the amount of matter and anti-matter created. When all the annihilations between matter and anti-matter particles had occurred (an event that took less than a second) what was left was all the matter that we see around us.

But is that right? Scientists working on the Alpha project at Cern are trying to find out by isolating and studying particles of anti-hydrogen.

Prof Jeffrey Hangst: "Anti-matter catches on because it's real... half the universe has gone missing."

Writing in the journal Nature Physics last November, the team announced that they had succeeded in creating anti-hydrogen particles in a series of overlapping magnetic fields.

At the time they managed to trap 38 anti-atoms for just 172 milliseconds. Now, by leaving their trap running, the same team report (again in Nature Physics) that they have managed to hold on to 19 antihydrogen atoms for 1,000 seconds.

"The question is really very simple," according to the lead author of the report Professor Jeffrey Hangst from Aarhus University.

Artist's conception of an anit-hydrogen atom being released from the trap after 1,000 seconds An artist's conception of an anit-hydrogen atom being released from the trap after 1,000 seconds

"Do matter and antimatter obey the same laws of physics? The Big Bang theory says there should have been equal amounts of matter and anti-matter at the beginning of the universe, but nature somehow took a left turn and chose matter, and we don't know why".

The length of time antimatter atoms hang around is important because it gives scientists the opportunity to study them in greater detail.

"A thousand seconds is more than enough time to perform measurements on a confined anti-atom" says co-author professor Joel Fajans from the University of California, Berkeley.

"It's enough time for the anti-atoms to interact with laser beams or microwaves. It's even enough time to go for coffee."

Working between cups of coffee, the team will now try to tease out the minute discrepancies between hydrogen and antihydrogen atoms that could account for the preponderance of matter over anti-matter in the universe.

 
Tom Feilden Article written by Tom Feilden Tom Feilden Science correspondent, Today

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