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e=mc². It’s probably the most famous equation in modern history, out-competing (these days) even Pythagoras’ Theorem. But, how many of you actually stop and think what it means? The e stands for energy, the m for mass.
In other words, energy and mass are interchangeable. That is, mass can be converted to pure energy (and vice-versa, although, as we’ll find, the reverse is a lot harder).
That’s where the c² comes in. C stands for the speed of light: 300,000,000 km/sec. Square that figure and you’ve got a really big number: 90,000,000,000,000,000.
So, as you’ve probably realised, converting even a tiny amount of mass results in a huge amount of energy.
Which is what happens in an atomic explosion: when atoms split or fuse, a very small amount of their mass is converted to pure energy. Big-badda-boom.
But that’s a firecracker compared to what happens when antimatter and matter come into contact. Both are converted 100 per cent into pure energy: really-big-badda-boom.
So it’s just as well that there’s so little antimatter around.
The question is: why?
Antiparticles are almost identical to their ordinary particle “twins”. They have the same mass, but carry the opposite charge.
For instance, an electron has a negative charge, while its antimatter sibling — called a positron — is positively charged.
Almost everything we see in the universe: you, me, the Moon, star and even the most distant galaxies, is made from ordinary matter. Yet, according to the Standard Model of particle physics, equal amounts of matter and antimatter should have been made during the Big Bang. Presumably there were, but almost all of it would have annihilated each other. Somehow, though, a lot more matter than antimatter was left over.
Curtin University theoretical physicist Igor Bray [said…] “But we have only a little bit of antimatter, and many, many orders of magnitude more ordinary matter.”
Yet despite years of scanning the observable Universe, we simply don’t see any sign of huge quantities of antimatter out there, Professor Bray said.
“It’s a huge puzzle … as to why there are different amounts of matter and antimatter.”
One mooted explanation to the missing antimatter problem is that gravity repulses antimatter.
If such “repulsive antigravity” was the case, some physicists theorise, antimatter made in the Big Bang might have been propelled into an anti-Universe populated by antiparticles, and therefore be missing in the Universe we observe.
Instead, recent experiments show that antimatter behaves under gravity just the same as ordinary matter.
[Professor Jeffrey Hangst] and his crew created a cloud of antihydrogen atoms in a “trap” inside their tall, pipe-like ALPHA-g device.
Magnetic fields held the antihydrogen atoms inside the trap, stopping them from colliding with the sides and annihilating.
Those magnetic fields at the top and bottom of the trap were then slowly removed, releasing the antihydrogen cloud.
As the anti-atoms dropped through the bottom or jiggled their way out the top, they hit ordinary matter and annihilated, producing flashes of gamma rays which were counted by sensitive detectors.
Around 80 per cent of the antihydrogen atoms fell downwards – the same as ordinary hydrogen in the same situation.
ABC Australia
Hydrogen and antihydrogen are ideal for the experiment, being electrically neutral, meaning that they are not affected by static electricity, only gravity.
The reason one in five of the atoms appeared to defy gravity is because atoms naturally ‘jiggle around’, enough that some of them could ‘shimmy’ out the top of the trap.
All very interesting, but why does antimatter, well, matter?
Well, for a start, antimatter weapons would put even H-bombs to shame. Luckily, then, antimatter is one of the most expensive substances on earth. A single gram would cost quadrillions of dollars.
But, as it turns out, the same technology that can produce tiny, tiny (and very expensive) amounts of antimatter at CERN’s “Antimatter Factory” has a very useful, peaceful application. If you’ve ever had a PET scan to detect cancer, you’ve benefited from antimatter-related technology. That’s because PET stands for Positron Emission Tomography.
PET scanners work by detecting radioactive decay in the feebly radioactive tracer isotope injected into the body. As the isotope decays, it emits a single positron. Then this particle is annihilated in a microscopic flash, which is detected by the scanner and used to create 3D images of the inside of the body.
