UBC physicists make atoms and dark matter add up

Physicists at the University of British Columbia and TRIUMF have proposed a unified explanation for dark matter and the so-called baryon asymmetry -- the apparent imbalance of matter with positive baryon charge and antimatter with negative baryon charge in the Universe.

The visible appears to be made of , and each of these atoms carries a positive baryon charge equal to total number of protons and neutrons in its nucleus.

However, since the discovery of antimatter in 1932, researchers have wondered why the Universe doesn't hold a neutral baryon charge--requiring as much negatively charged antimatter as positively charged matter.

This net of particles over antiparticles remains one of the biggest unsolved mysteries in physics.

"We've proposed a matter formation scenario where the positive baryon number of visible atoms is in balance with the equal and opposite negative baryon number of ," says Kris Sigurdson, an assistant professor of Physics and Astronomy at UBC, who worked with colleagues at TRIUMF, Canada's National Laboratory for , and researchers at Brookhaven National Laboratory in the US, on the theory.

"This links the formation of atoms and dark matter and helps resolve the baryon asymmetry mystery, as the total dark plus visible baryon balance of the Universe is restored."

The proposal was published November 19 in the journal .

Observations of the the big bang's afterglow, the , by the WMAP satellite now show about 4.6 per cent of the Universe (by density) is comprised of atoms, with about five times more dark matter (23 per cent).

The cosmic balancing act proposed by the researchers may explain why the measured densities of dark matter and atoms differ only by a factor of five.

The researchers also predict an entirely new method to detect dark matter.

"Occasionally a dark-matter antiparticle may collide with and annihilate an ordinary atomic particle, releasing a burst of energy," says Sigurdson. "While extremely rare, this means dark matter might be observed in nucleon decay experiments on Earth that look for the spontaneous decay of protons."

Dark matter - first hinted at nearly 80 years ago - is an elusive material inferred to exist from measurements of its gravitational effects on visible matter in galaxies, background radiation, and the Universe as a whole. It interacts very weakly with ordinary matter and, while playing a key role in our Universe, is almost undetectable.


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Citation: UBC physicists make atoms and dark matter add up (2010, November 29) retrieved 25 August 2019 from https://phys.org/news/2010-11-ubc-physicists-atoms-dark.html
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Nov 29, 2010
Cute, making 'matter' and 'anti matter' almost unable to interact...

But why should antimatter 'condense' into dark matter rather than engage in mutual Annihilation with 'normal' matter ??

To be valid, this implies that something very, very weird is going on...

Uh, one outré possibility may be that macro-quantities of anti-matter are much more stable to annihilation than isolated nucleii-- Analogous to way neutron decay is inhibited when bound to appropriate number of protons...

Nov 29, 2010
Maybe there is a simpler explanation - we see repelling thermodynamical noise of EM field (CMB), but we have also other interactions and corresponding fields - they are much more difficult to observe, but doesn't equipartition theorem say that their degrees of freedom should also thermalize to 2.725K?
Some of them could interact weaker and so be filled only in active regions like galaxies, explaining dark matter halo?

About matter-antimatter asymmetry, because of CPT symmetry, we need some SYMMETRY BREAKING MECHANISM - such that the situation with equal amount of matter and anti-matter is statistically unstable - that the system wants to get out of such situation (CPT: in any direction).
So what we need is that the more matter, the easier matter is produced (and the same for antimatter) - for example that baryons are a bit easier produced in presence of other baryons (opposite direction to proton decay).

Nov 29, 2010
hey quick question to everyone

Observations of the the big bang's afterglow, the cosmic microwave background, by the WMAP satellite now show about 4.6 per cent of the Universe (by density) is comprised of atoms, with about five times more dark matter (23 per cent).



if 5% is baryonic matter and 25% is dark matter what is the other 70% ??

nuetrinos???

Nov 29, 2010
El_Nose: The rest is supposed to be Dark Energy.

Nov 29, 2010
If the visible matter in the "visible sector" is balanced with anti-matter/dark matter in the hidden sector, why the one to five ratio between baryonic and dark matter?

Nov 29, 2010
What proof is there that 1/2 the universe is not antimatter? Galaxy clusters may be either matter or antimatter with an equal number of both.


Isotropy...basically.

Also if galactic clusters had a mix of the two...well it wouldn't be huge fireworks, but let's just say we'd know it.

Nov 29, 2010
@Question: My conjecture: even the intergalactic medium has some gas passing through it, so between a cluster of matter galaxies and a cluster of anti-matter ones, there should be a zone of annihilation. These would probably appear as diffuse sheets of gamma ray source rather than any particular burst

Nov 29, 2010
What proof is there that 1/2 the universe is not antimatter? Galaxy clusters may be either matter or antimatter with an equal number of both.

There's the existence and near perfect smoothness (1 part in 100,000) of the CMB. Due to this smoothness, there simply wasn't anywhere for antimatter to hide from normal matter to avoid annihilation, so there can't be too much of the stuff lying around.

Nov 29, 2010
Once again, the evolutionary uber-paradigm raises its Machiavellian head: matter - 1, anti - 0.

Nov 30, 2010
To BREAK this matter-antimatter (CPT) SYMMETRY, the natural way is to do it on STATISTICAL LEVEL - search for mechanism which make symmetric state unstable.
It's like - why our life use practically only L-aminoacids against symmetry?
It's because the more L-life there was, the more material for L-life there was available ... and so it produced more and more L-aminoacids shifting the balance ... the symmetric situation with the same amount of L and R life is statistically unstable and so one of them just had to practically completely dominate.
And analogously we should look for matter-antimatter symmetry breaking - that for example in presence of baryon/lepton, there is a bit larger chance to produce another baryon/lepton than anti-version ... and by CPT conservation, in presence of anti-baryon/lepton, it's a bit more probable to produce another anti-baryon/lepton - making that the Universe had to choose one side of this symmetric hill ...

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