What is dark matter?
What is dark matter?
Physics is unique in the scientific world, in that its reliance on math means it can come up to a wide consensus on matters with very little show available. In Earth scientific discipline, a veritable mount of prove can't fully bury the issue of global warming, and fifty-fifty with the vast majority of scientists now convinced, a vocal minority still dissent. Yet in the case of physics and dark matter, a substance divers every bit being virtually immune to observation, in that location are no meaningful dark matter deniers left standing. And then what is dark matter, and how has physics come to such a powerful agreement on the thought that it makes upwards the vast majority of matter in the universe?
Matter, the regular kind that makes up the temper, the Sun, 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 light, infra-red, and more. It can generate magnetic fields of diverse sorts and strengths. And matter has mass, creating the force of gravity, the effects of which can exist readily observed. All these things brand matter convenient to written report, in particular its interactions with light. Even a black hole, which emits no calorie-free, blocks calorie-free by sucking it in — but what if the light coming from backside a black pigsty simply passed right through, and on into our telescope lenses? How would wee'er accept proven the existence of a black hole, in that instance?
The Cryogenic Dark Matter Search.
That'due south the situation physicists face with dark matter. Nighttime affair does non seem to interact with the universal electromagnetic field in the slightest — that is, it does not absorb or emit lite of any kind. In fact, night affair seems only to interact with the universe every bit we tin discover it through a single concrete strength: gravity. So, in the case of our invisible black hole, we might have been able to discover it by seeing how light coming to us from a certain section of sky 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 low-cal-bending observations, scientists could probably figure out the position and even mass of the invisible singularity.
Still, dark matter is harder to study than even that, because it does not come up conveniently clumped into super-dense assurance like stars and black holes — that would exist far besides like shooting fish in a barrel. Instead, the primary theory of dark matter says that information technology is made of hypothetical particles chosen Weakly Interacting Massive Particles (WIMPs), which are about equally well understood as their catch-all proper name implies. WIMPs don't fifty-fifty seem to interact witheach other through anything more than gravity, significant night thing does not fuse to form larger or more circuitous molecules, and remains in a simple and highly diffuse gas-like state.
Thus, dark matter's gravitational impact is extremely spread out and, it turns out, tin only be observed when we look at the big-scale distribution of visible matter in the universe — things similar galactic super-clusters, and the respective super-voids. Information technology'due south theorized that afterward the Bing Blindside, the properties of night affair would accept led it to settle downwards far more apace than regular affair, going from a totally compatible gas-cloud to a somewhat clumped network of smaller clouds and connecting tendrils. These tendrils can stretch across theuniverse; the distribution of dark matter shortly after the Big Bang is idea to have directed where regular thing eventually nerveless, and thus where and how galaxies formed.
A simulation of the distribution of nighttime matter, fabricated and rendered by a supercomputer.
So, not just is it invisible, but the effects of dark matter's gravitational potential are so physically sprawling that they're hard to measure. The light from a unmarried star won't be measurably bent by night matter in reaching united states, every bit it was in passing our invisible black hole; that light might very well take originated, travelled through, and arrived all within the attain of a single universal super-thread of invisible dark matter. Then: how did physicists come upward with the idea of dark matter in the start place?
The answer is that gravity affects everything, at all scales, according to the same basic formulae. So, scientists started to notice that as they took at larger and larger-calibration looks at the universe, these gravity formulae delivered increasingly wrong predictions. Every bit early on as the 1930s, Fitz Zwicky discovered that galaxies in the Coma cluster were moving as though they were subject to far more gravitational force than could be explained through a simple bookkeeping of the normal matter we could encounter. Decades later on, 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 be made up of about half dozen times as much nighttime mass as the regular kind.
A map of the universal Cosmic Microwave Background radiation.
But the actually compelling prove didn't come up almost until the advent of techniques like weak gravitational lensing, and the ability to read the catholic microwave background (CMB) radiation. Gravitational lensing allows a super, super, super big-scale version of watching light bend around our invisible black pigsty. It gets around the scale issue with… more scale, watching how the nerveless light from billions of clustered stars bends as it travels beyond large fractions of the diameter of the known universe. And a number of increasingly accurate CMB maps made between the 1960'due south and the 2000's confirmed similar discrepancies in the movement of mass early in the history of the universe.
Direct ascertainment of WIMPs has been attempted, but never confirmed. In 2009, the Cryogenic Dark Matter Search published evidence of directly observation of night thing, but the results are non definitive. All the evidence says right now is that something very much like the mod conception of dark matter has to exist.
Calculations of exactly how much of this something would be necessary to create the observed discrepancies accept produced some… impressive figures. By modern estimates, the universe is only about v% regular affair and free energy, and about 27% dark affair, or more than 5 times as much. The remaining 68% of the universe is idea to be dark free energy — a topic for another day. The point is that our universe hasn't but been adjusted by the impact of dark matter, information technology'southward beendefined by that affect. The Milky Mode is what and where the Milky way is, due to the early on gravitational influence of nighttime matter.
An upgraded LHC is our best bet to understand night matter.
Of form, things are turning out to be slightly more circuitous than described above. But months ago, i squad appear that dark matter may have been observed to collaborate with itself in some style during an enormous multi-galaxy collision event. This could imply a much more rich sort of dark physics, perhaps nevertheless far as to create some sort of night chemistry! Some physicists use the phrase "dark world," or even "dark sector," to draw this super big-scale alien universe that seems to exist almost in parallel to our own.
The near likely candidate to produce further insight into nighttime affair is the Big Hadron Collider, which recently reopened after significant power upgrades. With experimental energies now exceeding 13 tera-electron volts (TeV), the new and improved LHC might just be able to blast particles together violently enough to provide existent insight into WIMPs, or mayhap even disprove their existence. Finding dark thing was one of the main motivations for the upgrades; it'south an of import expanse of study in physics, every bit astronomers continue to produce bear witness that our globe is only a fraction of creation.
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Source: https://www.extremetech.com/extreme/212601-what-is-dark-matter
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