Dark matter gets an even bigger question mark

Tue, 06/22/2010 - 11:56 — Ben Gilliland

Has Jupiter been leading science astray?

In 1998 astronomers had a bit of a shock when it was revealed that our universe was not behaving as it ought. They had believed that since the Big Bang hurled our universe into existence, its expansion must, inevitably, have been gradually slowing down. It came as no small surprise then when it was revealed that its expansion was actually accelerating and that we seem to be missing some 96 per cent of its matter.

To explain this curiosity, cosmologists summoned up a mysterious, invisible and undetectable force, called ‘dark energy’, and a barely detectable, invisible material called ‘dark matter’ (see next page). And everyone lived happily ever after (except for those who disagreed and thought it was all just imaginary bunkum). Until now.

One astrophysicist (who fits into the bracketed category above) had taken a second look at the data from one of the telescopes used to establish the existence of these dark materials – the Wilkinson Microwave Anisotropy Probe (WMAP). WMAP detects the radiation afterglow of the Big Bang and creates a temperature map of the universe as it appeared just 380,000 years after its birth. Since the temperature fluctuations it detects are so small, scientists use Jupiter’s microwave emissions to calibrate the data and cancel out any instrument distortions.

For the past three years, Tom Shanks, of the University of Durham, has been examining these maps and recalibrated the data using distant microwave-emitting galaxies that appear in the WMAP data itself. He found that, using these new sources, the map of this background radiation contained far fewer fluctuations and was much smoother. Since the size of these fluctuations is key in calculating the existence of dark matter and dark energy, the findings could eliminate the universe’s dark side altogether. It could also mean that the entire mathematical framework currently used to explain the universe – the Standard Model – is wrong and science could have been travelling down a false path for quite some time.

Fortunately WMAP’s successor, Europe’s Planck spacecraft, has already begun creating a new, far more detailed map of the cosmic background radiation (CMB), which should help shed some light on the universe’s dark side.

How science became seduced by the dark side

Bang goes the theory

At the beginning of the 20th century astronomers thought they had the universe figured out – it had always been just where it was and was immutable and unchanging. Then Einstein did some calculations that showed him the universe ought to be collapsing under the force of gravitational attraction. He didn’t like this much so he inserted an extra equation called the ‘cosmological constant’ (a force that opposes the force of gravity) and made the universe nice and static again.

All was fine again until a pesky American fellow called Edwin Hubble made observations that proved that galaxies were actually moving away from us and that the universe was expanding. Einstein threw out his ‘cosmological constant’ calling it his ‘biggest blunder’.

Hubble’s discovery led astronomers to conclude that the universe had begun in a Big Bang in which all matter was born and flung out into the cosmos.

Part of our universe is missing

At the end of the 20th century, astronomers thought they had the universe figured out – it was expending out from the Big Bang and, like a ball thrown from a hand, the momentum of that expansion was slowing down.
Then, in 1987, observations of supernovae revealed an inconvenient truth – far from slowing down, the expansion of the universe was actually accelerating.
Furthermore, to rub salt into the wound, it was revealed that there just not enough matter (stars, galaxies and cosmic dust) in the universe to account for its observable properties.
Some of this missing matter (22 per cent of it) was attributed to so-called ‘dark matter’ which, although unobservable directly, can be detected by its gravitational effect on the matter that we can see.

Not all wimps fear the dark

The best candidate for dark matter, is a particle called a WIMP (Weakly Interacting Massive Particle) these particles pretty much do what it says on the tin – they interact very weakly with normal matter and are massive. The fact that they hardly interact with ‘normal’ matter explains why they are difficult to detect and the fact that they are pretty massive, accounts for the missing mass.

Old dog with a new trick

However, this still left 74 per cent of the universe’s mass unaccounted for so, after scratching their heads for a while, cosmologists dug into Einstein’s kit bag and pulled out his ‘cosmological constant’. They dusted it off, gave it a greater ability to counteract the force of gravity and new coat of paint, and called it ‘dark energy’.
Put simply, dark energy is the cost of having space – in that a volume of space must possess an intrinsic energy – and, since Einstein proved that energy and mass are related (E = mc2 ), then that energy must have a gravitational effect which, in this case, is a repellent effect – dark energy pushes galaxies apart. It would also account for the universe’s missing mass.

Neither but aether

Before Einstein’s relativity did away with it, scientists believed that the universe has permeated by an all pervading aether – an invisible fluid-like medium that light waves travelled through.
In 2008, physicist HongSheng Zhao, resurrected the aether and called it ‘dark fluid’. Zhao argues that neither dark matter or dark energy really exist, but that they are actually just an undiscovered facet of gravity that operates at very large scales. He says that the fabric of space acts like a fluid, which can coagulate, compress or expand. Where there is matter, the fluid slows down and coagulates - amplifying gravity and giving the illusion of the presence of a mysterious dark matter-like material.