Dark matter – Missing you already

Pivot Points is a monthly column by EuroScientist writer David Bradley.

It’s a moot point that perhaps only one of Einstein’s papers went through the modern scientific peer review process and I often wonder whether an email received from him today suggesting that he’s overturned Newton’s work with talk of warped space-time and wormholes wouldn’t simply fail at the first or second step of my “Fraudulent Invention Debunkifier” flowchart mentioned around this time last year on the Pivot Points column.

Indeed, as a lowly chemist by training I am often at a loss to distinguish the ludicrous from the luminous when I read fundamental physics papers, and that’s despite a year of undergraduate physics with my generation’s latterday Brian Cox – Professor Paul Davies who was at Newcastle University at the time but was swallowed up by the Australian brain drain during the scientifically crushing Thatcher years.

Anyway, ludicrous or luminous? In which camp does dark matter sit? It certainly isn’t luminous, it’s very name tells even a lowly chemist that much. But, does it actually exist? Einstein’s equations would suggest it might. Those various equations of general and special relativity have, of course, been validated on several occasions and gave us nuclear power, the atomic bomb (that’s the E = mc^2 bit that equates energy and matter with the square of the maximal speed of light as proportionality constant). Relativistic effects also help chemists understand why some heavy metal compounds are not the colour they should be but are shifted to lower or higher energy glows. And, we must take Einstein into account if Global Positioning System is to work correctly and preclude our vehicular immersion in duckponds or down blind alleys.

La Silla Telescope, European Southern Observatory

Speaking of blind alleys, it seems that new research from various powerful telescopes including the European Southern Observatory’s (ESO) La Silla Observatory, may have offered us an astronomical detour. The La Silla telescope sits on the edge of the Atacama Desert in the pure, almost unadulterated and certainly rarefied Chilean air viewing the darkest of night skies this side of the solar system, has spotted something odd about dark matter predictions.

Dark matter, you will recall, is a mystery. It is thought to account for some 83% of the mass of the universe (23% of the total mass-energy equation) but neither absorbs nor emits light or any other form electromagnetic radiation. As such, we cannot “see” it, hence the “dark” epithet, but it is matter and so its presence should be perceptible by observing its gravitational effects. The existence of dark matter would lead to a closed universe, the seemingly interminable expansion of which since the Big Bang, would actually slow given enough time and lead to a massive collapse back to a singularity in a Big Crunch. The discovery of evidence suggesting that the expansion of the universe is accelerating because of yet another mystery “substance, known as Dark Energy, scuppers the Big Crunch idea but does not preclude the existence of Dark Matter.

The ESO La Silla Observatory and others have looked at 400 stars up to 13000 light-years from the Sun.

“We used fluid dynamics, extensively used in Galactic dynamics, the Poisson and Jeans equations, valid for systems of collisionless particles to look at the spatial motion of the stars,” team leader Christian Moni Bidin of the Departamento de Astronomia, Universidad de Concepcion, Chile, told Pivot Points. They could relate velocities to the local gravity. “The movements of the stars in their orbits, caused by gravity, reflects the quantity of mass that is present,” he adds. Feeding the measurements in to the appropriate equations then allowed them to calculate the total amount of matter in the vicinity of the Sun. Unfortunately, for fans of Dark Matter, it seems that there is less total matter affecting the stellar movements than theory would suggest.

“The amount of mass that we derive matches very well with what we see – stars, dust and gas – in the region around the Sun,” says Moni Bidin. “But this leaves no room for the extra material – dark matter – that we were expecting. Our calculations show that it should have shown up very clearly. But it was just not there!”

If Dark Matter really does not exist, then the theories of galaxy formation and rotation that relied on this postulated mystery substance to explain certain phenomena, such as the speed of rotation of galaxies, might fall apart. Existing models of galaxy formation suggest that our galaxy, the Milky Way, is surrounded by a vast halo of dark matter and that there should most certainly be large quantities of the stuff surrounding the Sun. The missing evidence for Dark Matter might mean a rethink on the galactic halo effect, which could be too much of a stretch for some.

“Despite the new results, the Milky Way certainly rotates much faster than the visible matter alone can account for. So, if dark matter is not present where we expected it, a new solution for the missing mass problem must be found. Our results contradict the currently accepted models,” says Moni Bidin. If this lack of Dark Matter evidence is reproduced in subsequent studies and physicists continue to fail to find it in more local terrestrial evidence too, then maybe it is time to invoke my flowchart and check off another entry on the list of debunked ideas.

David Bradley

David is a freelance science writer with more than thirty years in science communication. His best-selling book, Deceived Wisdom is available now.
David Bradley

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