In the last few years it’s become generally accepted knowledge that our universe is full of mysterious dark matter which has mass but is not obviously visible to us. A fringe of physicists have even made controversial claims that they have observed this dark matter in experiments, but now a new experiment makes this claim seem more unlikely.
The concept of dark matter comes from observations about the expansion of the universe. Physicists have plenty of evidence that the universe is expanding outwards thanks to the movements of stars within galaxies and the ways that matter clumps together. However, observations from the Hubble telescope in the early 1990s showed that in the distant past, the universe was expanding more slowly than it is now. Before this, it was expected that the rate of expansion of the universe would slow over time as matter got further and further apart and the gravitational forces between bodies became weaker. But the Hubble evidence showed that there must be a lot more matter in the universe than previously expected to create the increase in expansion rate that was observed.
This extra matter that must exist in the universe was termed “dark matter,” and the search to identify it has been on ever since. Earlier this year, an experiment in Italy called DAMA/LIBRA claimed to have detected dark matter in the galactic halo using social iodide crystal detectors. The crystals of sodium iodide should produce a tiny spark of light when a dark matter particle collides with them, which is what DAMA/LIBRA observed. However, the latest experiment on the topic from South Korea has failed to detect the signal that DAMA/LIBRA found.
The South Korean experiment is called COSINE-100 and used the same type of detector as DAMA/LIBRA, and is the latest in a series of experiments which have failed to replace the DAMA/LIBRA observations. There is a possibility that the difference in results between the two labs is due to yearly variations in the rate of collisions, with them occurring more at some times of the year than others. But most physicists are skeptical of the DAMA/LIBRA data: “I think this is one more nail in the coffin,” astrophysicist Dan Hooper of Fermilab told Science News.
The latest findings from the COSINE-100 experiment are published in Nature.
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