F6, fascinating stuff. Dark energy driving the universe apart. 74% of the universe, dark matter 22%, so the ordinary energy and matter we see is left with a measly 4%.
Does it follow that each of us is 96% dark, too? Seems it follows, and, lol, sure fits some.
I know we are more space than matter, which is just as hard to fathom.
So much we don't know. Thank the Flying Spaghetti Monster ..
Author Christian Marinoni says the idea turns estimating the Universe's shape into "primary school" geometry.
While the idea of the Earth being flat preoccupied the first philosophers millennia ago, the question of whether the Universe itself is flat remains a debatable topic.
The degree to which the Universe is curved has an effect on what astronomers see when they look into the cosmos.
A telescope on or near Earth may see an image of a celestial object differently from how the object actually looks, because the very fabric of space and time bends the light coming from it.
Christian Marinoni and Adeline Buzzi of the University of Provence have made use of this phenomenon in their technique.
Dark prospect
The current model of cosmology holds that only 4% of what makes up our Universe is normal matter - the stuff of stars and planets with which we are familiar, and that astronomers can see directly. Continue reading the main story
“Once you measure the abundance of matter and energy in the Universe, you have direct information on its geometry; you can do geometry as we learn in primary school” Christian Marinoni University of Provence
The overwhelming majority of the Universe, the theory holds, is composed of dark matter and dark energy. They are "dark" because they evidently do not absorb, emit and reflect light like normal matter, making direct views impossible.
Dark energy - purported to make up 73% of the known Universe - was proposed as the source of the ongoing expansion of everything in the cosmos. Astronomers have also observed that this expansion of the Universe seems to be accelerating.
Even though gravity holds that everything should attract everything else, in every direction astronomers look there is evidence that things are in fact moving apart - with those objects further away moving faster.
Dark energy is believed to pervade the essence of space and time, forcing a kind of "anti-gravity" that fits cosmologists' equations but that is otherwise a mysterious quantity.
"The problem is that we do not see dark energy because it doesn't emit light, so we cannot measure it by designing a new machine, a new telescope," explained Professor Marinoni.
"What we have to do is to devise a new mathematical framework that allows us to dig into this mystery," he told BBC News.
It relies on measuring the degree to which images of far-flung astronomical objects are a distortion of their real appearance. The authors originally suggested a spherical object would work.
The way the image is distorted should shed light on both the curvature of the Universe and the recipe of matter, dark matter and dark energy it is composed of.
The problem until now has been to choose an object whose real, local appearance can be known with certainty.
Professor Marinoni and Dr Buzzi's idea was to use a number of binary galaxies - pairs of galaxies that orbit each other.
The idea was checked using data from the Sloan Digital Sky Survey
Since nature shows no preference for the direction these galaxies would be orbiting one another, a look across the whole sky should spot the full spectrum of orbital planes - up, down, left, right, side-on and so on.
Put all of them together and they should approximate a sphere.
The team formed a kind of average of all of those binary galaxies, and corrected for the varying speeds at which the galaxies might be orbiting each other.
The calculation also takes into account the relative proportion of dark energy in the Universe.
The equation was then juggled until the collection of binaries did indeed look like a uniform mix of directions.
The results suggest that the Universe is made up of about 70% dark energy.
"In general relativity, there is a direct connection between geometry and dynamics," Professor Marinoni explained, "so that once you measure the abundance of matter and energy in the Universe, you have direct information on its geometry; you can do geometry as we learn in primary school."
The team's conclusions suggest the Universe is indeed flat - an assumption first put forth by Albert Einstein and seemingly confirmed by more recent observations but that remains one of the most difficult ideas to put on solid theoretical footing.
Alan Heavens, a theoretical astrophysicist at the University of Edinburgh, said that the strength of the result lies in that it requires few assumptions about the nature of the cosmos.
"The problem that Marinoni and Buzzi have attacked is to see if we can get another, rather clean way of working out what the geometry of the Universe is without going through some fairly indirect reasoning, which is what we do at the moment," Professor Heavens told BBC News.
"They get complete consistency with [results from] existing methods, so there's nothing surprising coming out - thankfully - but it's a neat idea because it really goes rather directly from observations to conclusions."
However, while the abundance of dark energy seems on an ever-firmer footing, its nature remains a mystery.
"I don't think it can tell us in a lot of detail what the dark energy is," Professor Heavens said. "I think it's probably not precise enough - certainly not yet."
Some theorists think that dark energy and cosmic acceleration are a failure of general relativity on very large scales, larger than superclusters.[citation needed] However most attempts at modifying general relativity have turned out to be either equivalent to theories of quintessence, or inconsistent with observations.[citation needed]
Alternative ideas for dark energy have come from string theory, brane cosmology and the holographic principle, but have not yet proved[citation needed] as compellingly as quintessence and the cosmological constant.
On string theory, an article in the journal Nature described:
String theories, popular with many particle physicists, make it possible, even desirable, to think that the observable universe is just one of 10500 universes in a grander multiverse, says [Leonard Susskind, a cosmologist at Stanford University in California]. The vacuum energy will have different values in different universes, and in many or most it might indeed be vast. But it must be small in ours because it is only in such a universe that observers such as ourselves can evolve.
Paul Steinhardt in the same article criticizes string theory's explanation of dark energy stating "... Anthropics and randomness don't explain anything... I am disappointed with what most theorists are willing to accept".
Yet another, "radically conservative" class of proposals aims to explain the observational data by a more refined use of established theories rather than through the introduction of dark energy, focusing, for example, on the gravitational effects of density inhomogeneities, or on consequences of electroweak symmetry breaking in the early universe. If we are located in an emptier-than-average region of space, the observed cosmic expansion rate could be mistaken for a variation in time, or acceleration.
Another class of theories attempts to come up with an all-encompassing theory of both dark matter and dark energy as a single phenomenon that modifies the laws of gravity at various scales. An example of this type of theory is the theory of dark fluid. Another class of theories that unifies dark matter and dark energy are suggested to be covariant theories of modified gravities. These theories alter the dynamics of the space-time such that the modified dynamic stems what have been assigned to the presence of dark energy and dark matter.
Another set of proposals is based on the possibility of a double metric tensor for space-time. It has been argued that time reversed solutions in general relativity require such double metric for consistency, and that both dark matter and dark energy can be understood in terms of time reversed solutions of general relativity. .. with links .. AND .. MUCH MORE ..http://en.wikipedia.org/wiki/Dark_energy
chuckle .. am thinking that re lig ion is much simpler .. it stands still for one, until forced by science to expand it's horizons ..
Introduction Mysterious motion of the planets Mysterious motions of galaxies Invisible matter? Seriously? Other ways to "see" dark matter About the Authors Activity 1: Dark Matter Possibilities Activity 2: Dark Matter: Probing What You Can't See Resources
I explained that dark matter is this stuff that you cannot see, touch, taste, hear or feel, even with the most sensitive instruments. She looked suspicious. I added that most of the matter in the universe is dark matter. .. http://cdms.berkeley.edu/Education/DMpages/essays/ingredients.shtml .. She looked more suspicious. Getting a little desperate I confidently said the stuff is everywhere, even in our galaxy. Her face said she thought I was off my rocker. Out loud she asked, "How do you know this stuff really exists if you can't see it? Especially if there is so much of it!"?
In this image, dark matter (shown in blue) has become separated from luminous matter (shown in red) in the bullet cluster.
Image credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al
I realized then how poorly everyday life prepares one for understanding what the universe is made of. The Earth is a really exceptional place. Think about the kinds of things you encounter each day. You breathe air, which is mostly nitrogen and oxygen. You drink water, which is mostly oxygen by weight with some hydrogen. You eat food containing sugars composed of carbon, hydrogen and oxygen. The ground you walk on is composed of relatively heavy elements like silicon, iron and oxygen. It is natural enough to conclude the whole universe must be like this, a lot of heavy elements, a bit of hydrogen, and essentially no helium.
It is not.
The things you breathe, eat, and drink on Earth make up less than 1% of the sun. A star, like our sun, is about 75% hydrogen and 24% helium. Every object larger than a planet that we see in the universe is pretty similar to the sun in terms of its composition: mostly hydrogen, some helium, not much else.
So what about this dark matter stuff? Mom thought I was trying to change the subject so she gently reminded me to get to the point.
The point is that just as the materials commonly found on Earth don't represent what you observe in the sun, the materials that comprise the Sun don't represent all the matter there is in the universe. When you look at a galaxy the stuff that you see with a telescope is only a relatively small fraction of the stuff that is actually there. The stuff you can see—stars and gas—is made out of the same stuff as the sun; mostly hydrogen, some helium. The stuff you cannot see, called dark matter is...well, it is called dark matter. Nobody knows what it is.
About 80% of the matter in the universe is dark matter. .. http://map.gsfc.nasa.gov/m_uni/uni_101matter.html .. Describing a galaxy by saying it is made out of stars and gas isn't really accurate, in the same way that saying the sun is made out of helium isn't really accurate. Sure, there is some helium there, but most of the sun is not helium. Most of a galaxy is not stars and gas, it is dark matter.
Estimated distribution of dark matter and dark energy in the universe. Image credit: NASA
I was feeling pretty pleased with myself now. This seemed like a mighty fine explanation. Then Mom reminded me I still hadn't answered the big question: If no one has ever seen this stuff why do grownups (with Ph.D.s no less) believe this stuff exists?
The short answer is that the dark matter that we cannot see pulls, through gravity, on the matter that we can see. We "observe" the dark matter indirectly through the influence it has on ordinary matter.
You experience this sort of indirect detection in everyday life. As an example, imagine you are hanging a heavy picture on a wall. You need to put the nail into one of the wooden studs that supports the wall because the studs are strong and can support a lot of weight. Unless you have transparent walls you can't see the studs, so what do you do? One way to find a stud is to use a small magnet, moving it along the surface of the wall. When you pass over a screw attaching the wall to the stud, the magnet tries to stick to the spot, pulling on your hand a bit. You cannot see the screw but you can detect it by the pull it exerts on the magnet.
Mom would have been happier, I think, if I stopped there. But once she got me started there was no stopping. How can you not get excited about mystery stuff that permeates the universe? To understand in detail the evidence for dark matter a little history is useful.
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