One of the great mysteries
of modern physics is why antimatter did not destroy the universe at the
beginning of time. To explain it, physicists suppose there must be some
difference between matter and antimatter – apart from electric charge. Whatever
that difference is, it’s not in their magnetism, it seems.
Physicists at CERN in
Switzerland have made the most precise measurement ever of the magnetic moment
of an anti-proton – a number that measures how a particle reacts to magnetic
force – and found it to be exactly the same as that of the proton but with opposite
sign. The work is described in Nature.
“All of our observations
find a complete symmetry between matter and antimatter, which is why the
universe should not actually exist,” says Christian Smorra, a physicist at
CERN’s Baryon–Antibaryon Symmetry Experiment (BASE) collaboration. “An
asymmetry must exist here somewhere but we simply do not understand where the
difference is.”
Antimatter is notoriously
unstable – any contact with regular matter and it annihilates in a burst of
pure energy that is the most efficient reaction known to physics. That’s why it
was chosen as the fuel to power the starship Enterprise in Star Trek.
The standard model predicts
the Big Bang should have produced equal amounts of matter and antimatter – but
that’s a combustive mixture that would have annihilated itself, leaving nothing
behind to make galaxies or planets or people.
To explain the mystery,
physicists have been playing spot the difference between matter and antimatter
– searching for some discrepancy that might explain why matter came to
dominate.
So far they’ve performed
extremely precise measurements for all sort of properties: mass, electric
charge and so on, but no difference has yet been found.
Last year, scientists at
CERN’s Antihydrogen Laser PHysics Apparatus (ALPHA) experiment probed an atom
of anti-hydrogen with light for the first time, again finding no difference
when compared with an atom of hydrogen.
But one property was known
only to middling accuracy compared to the others – the magnetic moment of the
antiproton. Ten years ago, Stefan Ulmer
and his team at BASE collaboration set themselves the task of trying to measure
it.
First they had to develop a
way to directly measure the magnetic moment of the regular proton. They did
this by trapping individual protons in a magnetic field, and driving quantum
jumps in its spin using another magnetic field. This measurement was itself a
groundbreaking achievement reported in Nature in 2014.
Next, they had to perform
the same measurement on antiprotons – a task made doubly difficult by the fact
that antiprotons will immediately annihilate on contact with any matter. To do it, the team used the
coldest and longest-lived antimatter ever created.
After creating the
antiprotons in 2015, the team were able to store them for more than a year
inside a special chamber about the size and shape of a can of Pringles.
Since no physical container
can hold antimatter, physicists use magnetic and electric fields to contain the
material in devices called Penning traps.
Usually the antimatter
lifetime is limited by imperfections in the traps – little instabilities allow
the antimatter to leak through.
But by using a combination
of two traps, the BASE team made the most perfect antimatter chamber ever –
holding the antiprotons for 405 days.
This stable storage allowed
them to run their magnetic moment measurement on the antiprotons. The result
gave a value for the antiproton magnetic moment of −2.7928473441 μN. (μN is a
constant called the nuclear magneton.) Apart from the minus sign, this is
identical to the previous measurement for the proton.
The new measurement is
precise to nine significant digits, the equivalent of measuring the
circumference of the Earth to within a few centimeters, and 350 times more
precise than any previous measurement.
“This result is the
culmination of many years of continuous research and development, and the
successful completion of one of the most difficult measurements ever performed
in a Penning trap instrument,” says Ulmer.
The universe’s greatest game
of spot the difference goes on. The next hotly anticipated experiment is over
at ALPHA, where CERN scientists are studying the effect of gravity of
antimatter – trying to answer the question of whether antimatter might fall
‘up’.
Via CosmosMagazine
"whether antimatter might fall ‘up’"
ReplyDeleteI would really doubt that...
It is doubtful, but everything has to be checked.
DeleteA kind of "anti-gravity" repulsion would explain the acceleration of the expanding universe.
DeleteWho said there is an up or down, isn't that from our perspective ?
DeleteMaybe the the split between matter and anti-matter during the Big Bang happened at the precise moment that space itself went through the initial expansion, therefore separating the matter and anti-matter enough that they couldn't interact.
ReplyDeleteI think "up" or "down" is not validly labeled just from our perspective. Apples keep falling when no one is watching, and happy deer keep finding them on the ground, closest to the source of gravity, not up in the sky.
ReplyDeleteSo OK 28105wsking, That was exactly my question. Although you say the apple falls to the ground and the deer loves them, that's fine. I was just making a statement who in the world defined up from down or sideways. I'm waiting on your explanation!
DeleteThis comment has been removed by the author.
ReplyDeleteObservation point, a stable or predictable viewing platform to gain perspective of an event or action....it does not matter if their is an up or down, it is a point of reference to meter or discern an affect
ReplyDelete