dark matter

The WIMP (Weakly Interacting Massive particles) model has just not worked out: We understand how the Standard Model particles behave. We have solid predictions for how they should interact through all of the fundamental forces, and experimental confirmation of those theories. We also have extraordinary constraints on how they’re permitted to interact in a beyond-the-Standard-Model fashion. Because of our constraints from accelerators, cosmic rays, decay experiments, nuclear reactors and more, we’ve been able to rule out many possible ideas that have been theorized. When it comes to what might make up the dark matter, however, all we have are the astrophysical observations and our theoretical work, in tandem, to guide us. The possible theories that we’ve come up with include Read More ›

Twenty years ago, astronomers couldn’t find enough satellite galaxies orbiting the Milky Way. Now there seem to be too many. Some information seems to be missing. A possible solution is that many of these galaxies are dwarfs formed by dark matter: Most cosmologists believe that dark-matter particles are “cold,” meaning that they move slowly. Because of this, they can coalesce into numerous tiny halos, providing scores of places where dwarf galaxies can form. But “warm” or “hot” dark matter, which by definition moves faster, cannot coalesce so easily. In fact, hot particles wouldn’t be able to form mini-halos at all. So the sheer existence of these small galaxies is a sign that warm dark matter is likely not at play. Read More ›

From ScienceDaily: Astrophysical evidence suggests that the universe contains a large amount of non-luminous dark matter, yet no definite signal of it has been observed despite concerted efforts by many experimental groups. One exception to this is the long-debated claim by the DArk MAtter (DAMA) collaboration, which has reported positive observations of dark matter in its sodium-iodide detector array. The new COSINE-100 experiment, based at an underground, dark-matter detector at the Yangyang Underground Laboratory in South Korea, has begun to explore DAMA’s claim. It is the first experiment sensitive enough to test DAMA and use the same target material of sodium iodide. COSINE-100 has been recording data since 2016 and now has initial results that challenge the DAMA findings. Those Read More ›

A helpful list of the 11 biggest questions about dark matter starts with this: Originally, some scientists conjectured that the missing mass in the universe was made up of small faint stars and black holes, though detailed observations have not turned up nearly enough such objects to account for dark matter’s influence, as physicist Don Lincoln of the U.S. Department of Energy’s Fermilab previously wrote for Live Science. The current leading contender for dark matter’s mantle is a hypothetical particle called a Weakly Interacting Massive Particle, or WIMP, which would behave sort of like a neutron except would be between 10 and 100 times heavier than a proton, as Lincoln wrote. Yet, this conjecture has only led to more questions… Read More ›

Dark matter was first theorized a century ago and yet “ super-sensitive underground labs that can detect a particle just one-trillionth of one-trillionth of a square centimeter” haven’t found it. Some now think that the problem is that two different approaches to the search are in conflict: There are two methods that physicists use to discover dark matter, and they differ greatly. Particle physics focuses on the small-scale world — the subatomic properties of matter — whereas astronomy focuses on the large-scale world — faraway areas of the universe that we can probe with telescopes and signal detectors. Naturally, they use different approaches. “The language and tools we [physicists and astronomers] use tend to be quite different,” Peter, an assistant Read More ›

According to astrophysicist Ethan Siegel: Personally, I don’t expect these direct detection attempts to be successful; we’re stabbing in the dark hoping we hit something, and there are little-to-no good reasons for dark matter to be in these ranges. But it’s what we could see, so we go for it. If we find it, Nobel Prizes and new physics discoveries for everyone, and if we don’t, we know a little more about where the new physics isn’t. But just as you shouldn’t fall for the hyper-sensationalized claims that dark matter has been directly detected, you shouldn’t fall for the ones that say “there’s no dark matter” because a direct detection experiment failed. We are after the most fundamental stuff in Read More ›

Because the best theories have not identified dark matter after decades: Having been fooled once, scientists have to ask: Is dark matter the new ether? For decades, a few rogue scientists have stood hopefully at the edge of respectability, offering their theory called Modified Newtonian Dynamics, or MOND. Essentially, it says that physics doesn’t work as we know it at the largest scales. It says we’ve been drawing the wrong conclusions, and dark matter isn’t required to explain the universe. No one has managed to develop a theory of MOND that adequately explains the universe around us, but it occasionally gains converts simply because the competing theory of dark matter has a glaring flaw: we can’t find it. Perhaps we’re Read More ›

Modified gravity is a hypothesis (1983) that attempts to account for the gravitational pull that is otherwise attributed to dark matter (which has never been identified). From Sabine Hossenfelder, author of Lost in Math: How Beauty Leads Physics Astray, at : Which one is right? We still don’t know, though astrophysicists have been on the case since decades. Ruling out modified gravity is hard because it was invented to fit observed correlations, and this achievement is difficult to improve on. The idea which Milgrom came up with in 1983 was a simple model called Modified Newtonian Dynamics (MOND). It does a good job fitting the rotation curves of hundreds of observed galaxies, and in contrast to particle dark matter this model Read More ›