Scientists have either found clear evidence that dark matter exists, have shown we can pretty much rule out dark matter, or have found a big old bunch of “probably”.
To cut an expanding story short, dark matter is the name given to what’s assumed to make up the large proportion of the universe that isn’t made up by physical objects as we currently understand them. It’s very existence is something of a hypothesis that’s used to explain some of the measurable effects that scientists attribute to dark matter. The image above (copyright NASA/ESA/Richard Massey) shows an inferred distribution of dark matter in one area of space, based on observed gravitational effects.
The latest news comes from a European collaborative project known as CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) based in the Gran Sasso National Laboratory in Italy. Researchers there use detectors to measure particle experiments conducted as close to absolute zero as can be achieved. The experiments involve lumps of calcium tungstate, with the detectors measuring both the light and sound created by interactions.
According to findings published this week, the researchers have found 67 such events that they believe can only be explained by the Wimps theory. That’s the idea that dark matter involves weakly interacting massive particles, which work in a way that means they don’t readily interact with what we currently understand as matter.
The BBC notes the results have been classed as having a four sigma level of certainty. That’s a stage at which its unlikely to be down to chance, but one step away from being so unlikely that it’s deemed a “discovery.”
The CRESST results follow on from similar studies at the Cogent experiement in Minnesota. They found that their results vary in line with the seasons, backing a theory that the solar system moves through a halo of dark matter, with the effects on the Earth depending on its current location.
The news follows reports from the NASA satellite FERMI that bring dark matter into question. The satellite tracked positrons in space — the antimatter version of the electron. The problem is that the level of positrons suggests that whatever we are calling “dark matter” must have a certain mass. But this mass is at least twice what has been found in what’s been suspected as dark matter in experiments back on Earth. And the CRESST experiment suggests dark matter may actually have a lower mass than previous theories.
Discover Magazine’s Sean Carroll sums up the current situation best: “either the universe is really messing with us by making dark matter more complicated than we might have thought (but still accessible to our experiments), or searching for dark matter is really hard and the experiments are still fighting with unknown sources of error. Or both!”