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dark matter head

Physics is unique in the scientific world, in that its reliance on math means it tin come to a broad consensus on matters with very lilliputian evidence available. In Earth scientific discipline, a veritable mount of evidence can't fully coffin the issue of global warming, and even with the vast majority of scientists now convinced, a song minority still dissent. Yet in the case of physics and dark matter, a substance defined as being virtually immune to observation, there are no meaningful dark matter deniers left standing. Then what is dark matter, and how has physics come to such a powerful agreement on the thought that information technology makes upwards the vast majority of matter in the universe?

Matter, the regular kind that makes up the temper, the Dominicus, Pluto, and Donald Trump, interacts with the universe in a number of ways. It absorbs, and in many cases emits, electromagnetic radiation in the form of gamma rays, visible calorie-free, infra-red, and more. Information technology can generate magnetic fields of various sorts and strengths. And affair has mass, creating the force of gravity, the furnishings of which can be readily observed. All these things brand matter convenient to study, in particular its interactions with low-cal. Even a blackness hole, which emits no lite, blocks light past sucking information technology in — but what if the light coming from behind a black pigsty only passed right through, and on into our telescope lenses? How would weever have proven the existence of a black hole, in that instance?

In 2009, the Cryogenic Dark Matter Search published evidence of direct observation of dark matter, but the results are not definitive.

The Cryogenic Nighttime Matter Search.

That's the situation physicists face with dark thing. Dark thing does not seem to interact with the universal electromagnetic field in the slightest — that is, it does not absorb or emit light of any kind. In fact, dark matter seems only to interact with the universe as we can find it through a single physical forcefulness: gravity. So, in the example of our invisible black hole, we might have been able to notice it by seeing how light coming to us from a certain section of heaven was aptitude relative to our expectations, knocked slightly off course past passing close to an object bending the surface of the spacetime information technology's traversing. Adding up enough light-bending observations, scientists could probably figure out the position and even mass of the invisible singularity.

All the same, dark affair is harder to study than even that, because information technology does not come conveniently clumped into super-dumbo assurance like stars and blackness holes — that would exist far too like shooting fish in a barrel. Instead, the primary theory of dark matter says that information technology is made of hypothetical particles called Weakly Interacting Massive Particles (WIMPs), which are about also understood equally their catch-all name implies. WIMPs don't even seem to interact witheach other through anything more than gravity, pregnant dark matter does not fuse to form larger or more than circuitous molecules, and remains in a simple and highly diffuse gas-like state.

Thus, nighttime matter's gravitational touch is extremely spread out and, it turns out, can only be observed when we look at the large-scale distribution of visible thing in the universe — things like galactic super-clusters, and the corresponding super-voids. It's theorized that subsequently the Bing Bang, the backdrop of dark thing would accept led it to settle down far more quickly than regular matter, going from a totally uniform gas-cloud to a somewhat clumped network of smaller clouds and connecting tendrils. These tendrils can stretch across theuniverse; the distribution of dark matter soon after the Big Bang is thought to have directed where regular matter eventually collected, and thus where and how galaxies formed.

A simulation of the distribution of dark matter, made and rendered by a supercomputer.

A simulation of the distribution of nighttime affair, made and rendered by a supercomputer.

So, not simply is it invisible, only the effects of night matter'southward gravitational potential are and then physically sprawling that they're hard to measure. The light from a single star won't exist measurably aptitude by dark thing in reaching u.s., equally it was in passing our invisible black pigsty; that light might very well have originated, travelled through, and arrived all within the reach of a unmarried universal super-thread of invisible dark thing. So: how did physicists come up with the idea of nighttime matter in the offset place?

The answer is that gravity affects everything, at all scales, according to the same basic formulae. And then, scientists started to discover that every bit they took at larger and larger-scale looks at the universe, these gravity formulae delivered increasingly incorrect predictions. As early as the 1930s, Fitz Zwicky discovered that galaxies in the Coma cluster were moving as though they were subject to far more gravitational strength than could exist explained through a elementary accounting of the normal matter we could see. Decades later, Vera Rubin famously noted that stars in spiral galaxies rotate around the galactic center far faster than they ought to, leading to later studies showing that spiral galaxies must exist made up of about 6 times as much dark mass as the regular kind.

A map of the universal Cosmic Microwave Background radiation.

A map of the universal Cosmic Microwave Groundwork radiation.

But the really compelling evidence didn't come virtually until the advent of techniques like weak gravitational lensing, and the power to read the cosmic microwave background (CMB) radiation. Gravitational lensing allows a super, super, super large-scale version of watching light bend around our invisible blackness pigsty. It gets effectually the scale consequence with… more scale, watching how the nerveless lite from billions of clustered stars bends as it travels across big fractions of the diameter of the known universe. And a number of increasingly accurate CMB maps made betwixt the 1960'due south and the 2000'southward confirmed similar discrepancies in the movement of mass early on in the history of the universe.

Direct observation of WIMPs has been attempted, but never confirmed. In 2009, the Cryogenic Dark Matter Search published evidence of direct observation of dark matter, but the results are not definitive. All the evidence says right at present is that something very much like the mod conception of dark matter has to exist.

Calculations of exactly how much of this something would exist necessary to create the observed discrepancies have produced some… impressive figures. By modern estimates, the universe is only about 5% regular matter and energy, and about 27% dark affair, or more than five times as much. The remaining 68% of the universe is idea to be dark energy — a topic for another day. The signal is that our universe hasn't just been adjusted by the impact of night matter, it'southward beendivers by that impact. The Galaxy is what and where the Milky Manner is, due to the early gravitational influence of dark matter.

ATLAS is definitely the most visually imposing of the LHC experiments.

An upgraded LHC is our best bet to understand dark matter.

Of course, things are turning out to be slightly more complex than described higher up. Just months ago, one squad announced that dark matter may have been observed to interact with itself in some way during an enormous multi-milky way collision event. This could imply a much more rich sort of dark physics, perhaps nonetheless far as to create some sort of dark chemistry! Some physicists use the phrase "dark world," or fifty-fifty "dark sector," to describe this super big-scale conflicting universe that seems to exist nearly in parallel to our own.

The well-nigh probable candidate to produce further insight into dark matter is the Large Hadron Collider, which recently reopened after pregnant power upgrades. With experimental energies now exceeding xiii tera-electron volts (TeV), the new and improved LHC might but be able to smash particles together violently enough to provide real insight into WIMPs, or perhaps even disprove their existence. Finding nighttime affair was one of the main motivations for the upgrades; it'south an important area of study in physics, every bit astronomers go on to produce prove that our globe is only a fraction of cosmos.

Cheque out our ExtremeTech Explains serial for more in-depth coverage.