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venerdì 16 gennaio 2015

Dark Matter the "Operating System" of the Universe

DEAP-3600, maybe the most sensitive dark matter detector yet, was installed last year more than a mile underground in a nickel mine in Ontario. Its spherical array of light sensors points inward, toward a core full of liquid argon. The hope is that dark matter particles striking argon atoms will trigger tiny flashes of light. Credit: Photograph by Robert Clark/National Geographic; © National Geographic

In conjunction with the release of National Geographic's January 2015 issue of its magazine, Timothy Ferris discusses the hunt for dark matter and dark energy in this Q+A tied to his feature "A First Glimpse of the Hidden Cosmos Why do dark matter and dark energy so easily capture the imagination?

Ferris: The human mind is attracted to seemingly significant questions that might plausibly be answered in the near future — within, say, a decade or a generation from now. Dark matter and dark energy certainly seem significant: Scientists estimate that they amount to 95 percent of all the matter and energy in the observable universe. And they might be solvable within a reasonable amount of time. So they're more intriguing than relatively intractable mysteries like, "What is time?," or "What existed prior to the big bang?" For something so elusive, we seem to know quite a bit about the influence of dark matter and dark energy. What are the biggest gaps in knowledge?

Ferris: Little is known about dark matter and dark energy except for their influence on the stuff that we can perceive. Dark matter interacts gravitationally with observable matter. Astronomers studying the dynamics of galaxies and clusters of galaxies find that they contain much stronger gravitational fields than could have been generated by the glowing stars and nebulae that are seen there. They call this unknown substance matter because it generates gravitational force, and dark since it emits no light. Other than gravitationally, dark matter interacts little if at all with the visible elements of the universe. Scientists imagine that dark matter will turn out to be one or more of the exotic, but as yet unconfirmed, materials envisioned by supersymmetry and other advanced physics theories. But one can imagine a great deal. It remains for experiments to see whether such hypotheses apply in the real world.

Dark energy is even more mysterious. The term refers to whatever it is that is causing the cosmic expansion rate to accelerate. So you could say that dark matter is nothing but a gap in human knowledge — a name tag pasted on a gap. If dark energy is a property of space itself, a quantum theory of the vacuum may be required before researchers can make sense of it. Such an account is often called a quantum theory of gravity, since Einstein's general relativity depicts gravitation as due to curvatures in space. What research into these phenomena seem to be the most promising?

Ferris: About a dozen dark-matter detectors are currently operating at various locations around the world. Either they will detect dark matter or they won't. In either case they will add to the sum of human knowledge. As Thomas Edison used to say, there's great value in learning what doesn't work.

Current research into dark energy consists mainly of observations aimed at refining measurements of how rapidly the universe is expanding and for how long the expansion rate has been accelerating. If you haven't yet identified the beast in the woods at least you can measure its footprints Dark matter and dark energy have had a profound impact on the evolution of our universe, something well illustrated in your article's "timeline" — can you explain the deep history of that influence?

Ferris: Dark matter did the lion's share of work in assembling galaxies and creating the large-scale cosmic structures observed today. Were it not for dark matter, the universe would look quite different today. It might not even be inhabitable.

Dark energy appears to be a property of space, and may have been responsible for the rapid initial expansion of space without which our universe wouldn't be here at all. Its current acceleration certainly influences the future of the cosmos, although the nature of that influence cannot accurately be predicted until scientists understand what dark energy is and how it behaves. If dark energy is the same field or set of fields that got the universe expanding in the first place, you could say that our universe owes its existence to dark energy.

The observable universe consists almost entirely of space. Even stars, planets and human beings are mostly space: Take away the space inside each atom and molecule and each of us could fit ourselves into a pocket pillbox. So if dark energy is indeed a property of space, understanding it would be important in the sense that one cannot understand rain, snow and steam without knowing what water is. What is the future for the search for the universe's most mysterious, and yet influential, components?

Ferris: A candidate dark-matter particle may be found in the near future. A few experimenters think they've already seen evidence of it. But there may be more than one variety of dark matter. We'll see.

Coming to grips with dark energy looks like both a longer haul and a bigger potential payoff. Several major avenues in theoretical physics, from the familiar "standard model" to exotica like string theory, strongly suggest that there is a great deal more to the universe than meets the eye. The path to glimpsing just how strange and extensive nature really is may lie through investigations of dark energy.

National Geographic: First Glimpse of the Hidden Cosmos  January 15, 2015

Is dark matter the "operating system" of the Universe? Tom Broadhurst, an Ikerbasque researcher at the UPV/EHU's Department of Theoretical Physics, thinks it is. He has participated alongside scientists of the National Taiwan University in a piece of research that explores cold dark matter in depth and proposes new answers about the formation of galaxies and the structure of the Universe. These predictions, published in the prestigious journal Nature Physics, are being contrasted with fresh data provided by the Hubble space telescope.
In cosmology, cold dark matter is a form of matter the particles of which move slowly in comparison with light, and interact weakly with electromagnetic radiation. It is estimated that only a minute fraction of the matter in the Universe is baryonic matter, which forms stars, planets and living organisms. The rest, comprising over 80%, is dark matter and energy. 
The theory of cold dark matter helps to explain how the universe evolved from its initial state to the current distribution of galaxies and clusters, the structure of the Universe on a large scale. In any case, the theory was unable to satisfactorily explain certain observations, but the new research by Broadhurst and his colleagues sheds new light in this respect.
As the Ikerbasque researcher explained, "guided by the initial simulations of the formation of galaxies in this context, we have reinterpreted cold dark matter as a Bose-Einstein condensate". So, "the ultra-light bosons forming the condensate share the same quantum wave function, so disturbance patterns are formed on astronomic scales in the form of large-scale waves".
This theory can be used to suggest that all the galaxies in this context should have at their center large stationary waves of dark matter called solitons, which would explain the puzzling cores observed in common dwarf galaxies.
The research predicts the soliton of dark matter in the centre surrounded by an extensive halo of dark matter in the form of large "spots", which are the slowly fluctuating density waves. This leads to many predictions and solves the problem of puzzling cores in smaller galaxies.
The research also makes it possible to predict that galaxies are formed relatively late in this context in comparison with the interpretation of standard particles of cold dark matter. The team is comparing these new predictions with observations by the Hubble space telescope.
The results are very promising as they open up the possibility that dark matter could be regarded as a very cold quantum fluid that governs the formation of the structure across the whole Universe.
This is not Thomas Broadhurst's first publication in the prestigious journal Nature. In 2012, he participated in a piece of research on a galaxy of the epoch of the reionization, a stage in the early universe not explored previously and which could be the oldest galaxy discovered. This research opened up fresh possibilities to conduct research into the first galaxies to emerge after the Big Bang.
The Daily Galaxy via
Image credit, dark matter halo at top of page:

Dark Matter --Is It the "Operating System" of the Universe? January 01, 2015

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