Column A Universe Veiled in Darkness – dark matter, dark energy and CERN

LAST TIME ANYONE checked, the Universe was approaching its 13.8 billionth birthday. While such long timescales mean it is safe to assume that not much has changed during our brief spell on Earth, the shifts in our understanding of the make-up of the Universe over time have been pronounced.

The study of the Universe (cosmology) as a scientific pursuit largely stretches back to the Greeks and the idea that everything was comprised of four elements: Earth, Water, Fire and Air. For a long time, it was believed that the Universe arranged itself around Earth in a nested onion-like structure of shells capped off by a solid dome consisting of fixed stars.

During the Renaissance, the Sun displaced the Earth as the centre of the Universe and in modern times the significance of the Sun has faded; it is simply one of another 100 billion stars in our galaxy, the Milky Way, which in turn is just one of potentially another 100 billion galaxies in the parts of the Universe we can observe. The numbers and possibilities, especially for life elsewhere, are breathtaking.

Scientists have pinned down the composition of the Universe

Technology, most notably satellite experiments, for example NASA’s COBE (awarded the Nobel Prize, 2006) and ESA’s Planck, in which NUI Maynooth plays a role, has permitted cosmology to enter an unprecedented era of precision measurements. As a result, scientists have pinned down the composition of the Universe.

The result is a simple exercise in classification amenable to any school-goer; 5 per cent of the Universe is known stuff (atoms, gas and plasma, planets, stars) and the remainder is anybody’s guess, but can be further decomposed into roughly 27 per cent dark matter and 68 per cent dark energy. Fame and big prizes await anyone who can shed light on either.

Except in the land of TV, where it has been hijacked by Sheldon Cooper and cohorts, or maybe Korea where there is a popular K-pop boy band, ‘Big Bang’ typically refers to the beginning and exponential expansion of the early Universe. As all objects with mass, humans, planets, stars, etc, attract each other and like to clump, the eventual fate of the Universe depends on the amount of stuff, or what physicists call “matter”, in it.

Too little and the Universe will expand forever, too much and it will re-contract into a big crunch.

Dark energy and dark matter

Now, the real surprise is that supernovae observations tell us that the Universe is not only expanding but that the rate of expansion is accelerating! So, some mysterious force of which have no experience to date is driving the Universe apart. This goes by the name dark energy and little is known about it.

On the other hand, dark matter is a more mundane affair, but still leads to considerable head scratching by scientists. As the name suggests, this type of matter does not emit light and its existence is inferred from gravitational effects, so we can be sure it has mass. Evidence for dark matter can be found in galaxies, including our own, the Milky Way, where the solar system sits in one of the arms.

One mystery surrounding spiral galaxies concerns the speed of outlying stars whose quick rotation cannot be accounted for simply through luminous matter. To explain this phenomenon one can either imagine that Einstein’s celebrated theory of General Relativity, part of the magic of GPS technology, is not universal and does not hold further out from the galactic centre. If one rejects this possibility, the only reasonable alternative is that dark matter corresponds to a not-yet-discovered type of subatomic particle. One plausible alternative to a new particle is the idea that dark matter could be lurking in black holes, but this has been ruled out.

The discovery of the Higgs’ boson

So, to recap, our Universe is old, it is expanding and 95 per cent of it corresponds to something we have little experience of in our day-to-day lives on Earth. By looking at the heavens we have identified the existence of dark matter, proposed it is a yet to be identified particle, a process which brings us back to terra firma and arguably the world’s most amazing feat of engineering hidden away beneath the Swiss-French border.

In its first run the Large Hadron Collider (LHC) at CERN has identified the Higgs’ boson, something physicists have been chasing for almost five decades. This for the LHC has merely been a warm-up exercise. After a short break in 2015 it will be cranked up to its full design energy and presents one of the best chances of discovering new particles that could account for dark matter.

Although Ireland is not a member of CERN, the Irish public will have upcoming opportunities to learn more about the fascinating work of CERN, which spans the fields of Engineering, Physics and Computing.

• The CERN travelling exhibition will be visiting the new UCD Science building from 9–28 Oct.
• To mark Maths Week 2013 TCD’s Mathematical and Physical societies will be co-hosting a public lecture on dark matter by Prof. B. Allanach (Cambridge) on 15 Oct.
• The following month, Nov 25, Prof E Gross (CERN/Weizmann) will be in town to give an account of his role in the discovery of the Higgs’ boson.

Eoin O Colgain is a theoretical physicist at University of Oviedo, Asturias, Spain. Follow him on Twitter: @ocolgain