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Dark Matter

M

Mighty_Emperor

Gone But Not Forgotten
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I can't seem to find a dark matter thread although there is a dark energy one which is similar:

http://www.forteantimes.com/forum/showthread.php?s=&threadid=12277

so..........

August 30, 2004


Scaled-Up Darkness

Could a single dark matter particle be light-years wide?
By George Musser


SMALL GALAXIES such as NGC 3109 are rarer and less compacted than they would be if matter clumped freely, perhaps because colossal particles that might be the universe's "missing mass" resist clumping.

In 1996 Discover magazine ran an April Fools' story about giant particles called "bigons" that could be responsible for all sorts of inexplicable phenomena. Now, in a case of life imitating art, some physicists are proposing that the universe's mysterious dark matter consists of great big particles, light-years or more across. Amid the jostling of these titanic particles, ordinary matter ekes out its existence like shrews scurrying about the feet of the dinosaurs.

This idea arose to explain a puzzling fact about dark matter: although it clumps on the vastest scales, creating bodies such as galaxy clusters, it seems to resist clumping on smaller scales. Astronomers see far fewer small galaxies and subgalactic gas clouds than a simple extrapolation from clusters would imply. Accordingly, many have suggested that the particles that make up dark matter interact with one another like molecules in a gas, generating a pressure that counterbalances the force of gravity.

The big-particle hypothesis takes another approach. Instead of adding a new property to the dark particles, it exploits the inherent tendency of any quantum particle to resist confinement. If you squeeze one, you reduce the uncertainty of its position but increase the uncertainty of its momentum. In effect, squeezing increases the particle's velocity, generating a pressure that counteracts the force you apply. Quantum claustrophobia becomes important over distances comparable to the particle's equivalent wavelength. Fighting gravitational clumping would take a wavelength of a few dozen light-years.

What type of particle could have such astronomical dimensions? As it happens, physicists predict plenty of energy fields whose corresponding particles could fit the bill--namely, so-called scalar fields. Such fields pop up both in the Standard Model of particle physics and in string theory. Although experimenters have yet to identify any, theorists are sure they're out there.

Cosmologists already ascribe cosmic inflation, and perhaps the dark energy (distinct from dark matter) that is now causing cosmic acceleration, to scalar fields. In these contexts, the fields work because they are the simplest generalization of Einstein's cosmological constant. If a scalar field changes slowly, it resembles a constant, both in its fixed magnitude and in its lack of directionality; relativity theory predicts it will produce a gravitational repulsion. But if the field changes or oscillates quickly enough, it produces a gravitational attraction, just like ordinary or dark matter. Physicists posited bodies composed of scalar particles as long ago as the 1960s, and the idea was revived in the late 1980s, but it only really started to take hold four years ago.

Two leaders of the subject are Tonatiuh Matos Chassin of the Center for Research and Advanced Studies in Mexico City and Luis Ureña López of the University of Guanajuato. At a workshop at the Central University of Las Villas (UCLV) in Cuba in June, they described how scalar particles can reproduce the internal structure of galaxies: when the particles clump on galactic scales, they overlap to form a Bose-Einstein condensate--a giant version of the cold atom piles that experimenters have created over the past decade. The condensate has a mass and density profile matching those of real galaxies.

That inflation, dark energy and dark matter can all be laid at the doorstep of scalar fields suggests that they might be connected. Israel Quiros of UCLV argued at the workshop that the same field could account for both inflation and dark energy. Other physicists have worked on linking the two dark entities. "As my senior colleagues used to say, 'You only get to invoke the tooth fairy once,'" says Robert Scherrer of Vanderbilt University. "Right now we have to invoke the tooth fairy twice: we need to postulate a yet to be discovered particle as dark matter and an unknown source for dark energy. My model manages to explain both with a single field."

But all these models suffer from a nagging problem. Because the wavelength of a particle is inversely proportional to its mass, the astronomical size corresponds to an almost absurdly small mass, about 10-23 electron volts (compared with the proton's mass of 109 electron volts). That requires the laws of physics to possess a hitherto unsuspected symmetry. "Such symmetries are possible, although they appear somewhat contrived," says physicist Sean Carroll of the University of Chicago. Moreover, the main motivation for big particles--their resistance to clumping--has become less compelling now that cosmologists have found that more prosaic processes, such as star formation, can do the trick. Still, as physicists cast about for some explanation of the mysteries of dark matter, it is inevitable that some pretty big ideas will float around.
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http://www.sciam.com/article.cfm?chanID=sa004&articleID=00084A33-908A-111B-87CB83414B7F0000
 
Mr Snowman's House. The Unified Theory of Everything.

OK. As far as I understand it, quantum physics tells us that there is a kind of parallel universe (but not in the strictest sense - more like a sub-universe) which co-exists with our own, sort of like the static foundation of a universe of linear time (like rolling a ball along a table where the ball is our physical universe and the table is the static quantum ether, as it were).

Now, let's look at dark energy. It is proposed that dark matter and energy exists in huge quantities, but do not actually interact with our universe in any substantial way (apart from when anomalies occur cf. most Forteana). I'm thinking that dark matter is pretty much the manifestation of the sort of separate quantum ether providing some kind of structure to our universe, similar to the way in which the frame of a house projects from the foundations and we live and move around it, unless somethng drastic happens and we decided to expend a lot of energy in changing the shape of the house. It is important that the house is not easily changed, otherwise it could fall apart after one blow from Mr Wolf. Likewise with dark matter and energy; they are not easily detectable or manipulated, for in the grand design, it would surely be folly to allow the very fabric of space and time to be manipulated as such.

As an interesting side note, I was perusing with some alacrity the interesting hypotheses that surround morphogenetics. However, I soon slowed down and developed a more sombre regard, once I realised that there is a possibility that these morphogenetic fields and dark energy could be one and the same. Given the large amount of life which undoubtedly inhabits the universe (don't argue), then is it possible that these redundant energy fields are the solution to the mystery of the unseen energies which elude us so?

You saw it here first. 8)
 
"As far as I understand it, quantum physics tells us that there is a kind of parallel universe..."

That's an unusual view, AFAIK - neither Copenhagen nor Many Worlds. Where do you get it?

"It is proposed that dark matter and energy exists in huge quantities, but do not actually interact with our universe in any substantial way "

Yes they do! That's the point of 'dark matter', it's supposed to supply all the missing graviational attraction that can't otherwise be accounted for.
 
- ""As far as I understand it, quantum physics tells us that there is a kind of parallel universe..."

That's an unusual view, AFAIK - neither Copenhagen nor Many Worlds. Where do you get it? " -

- "(but not in the strictest sense - more like a sub-universe) which co-exists with our own, sort of like the static foundation of a universe of linear time (like rolling a ball along a table where the ball is our physical universe and the table is the static quantum ether, as it were). " -

I hate "short-quoting"; please don't do it. The latter half of the paragraph kind of alludes to what I'm trying to get at.

- ""It is proposed that dark matter and energy exists in huge quantities, but do not actually interact with our universe in any substantial way "

- Yes they do! That's the point of 'dark matter', it's supposed to supply all the missing graviational attraction that can't otherwise be accounted for. -

Ah! Yes, my mistake. I should have left dark matter out of the non-interaction element. It's dark energy that I'm alluding to when I talk about non-interactive energies, although of course, it could be argued that dark matter acts in the same way, but as my equations are not yet complete, I cannot say for certain.
 
Anybody have the feeling that dark matter will be the next centuries DNA?

If we understand this, we will understand everything - cried the geneticists

Remember the thoughts about the Human Genome Project, if it was decoded we'd have miracle cures?

Sadly, they were wrong.
 
rjm said:
Remember the thoughts about the Human Genome Project, if it was decoded we'd have miracle cures?

Sadly, they were wrong.
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Give it a chance, the run-in time for new drugs can be anything up to 15 years, it's barely 5 since they sequenced the genome and the clinical implications are still at a very early stage.
 
http://www.newscientist.com/article.ns?id=dn6933
Dark matter clouds may float through Earth
18:00 26 January 2005
NewScientist.com news service
Maggie McKee
Small clouds of dark matter pass through Earth on a regular basis, suggest new calculations. The clouds may be remnants of the first structures to form after the big bang and could be detected by future space missions.

Dark matter interacts gravitationally with normal matter and appears to be seven times more abundant in the universe. But physicists do not know what the mysterious matter is made of or exactly how it is distributed through space.

Nonetheless, they have devised a number of hypothetical dark matter particles that were created in the big bang. These particles formed the universe's first structures, where mysterious "quantum seeds" caused matter to clump more densely in certain spots. Dark matter slid into these spots which grew into structures that merged to become giant clouds - or haloes - with millions or trillions times more mass than the Sun.

Previous computer simulations have modelled these giant haloes, which appear to surround galaxies and clusters of galaxies. Now, Jürg Diemand, a physicist at the University of California in Santa Cruz, US, and colleagues have modelled the very first clouds to clump together in the early universe - relatively puny structures with only the mass of the Earth.

For their study, they used the leading candidate for dark matter, a particle called a neutralino which has the mass of about 100 protons and interacts only weakly with normal matter. Their predicted energies and motions made them settle into structures about 30 million years after the big bang. The structures took the shape of flattened spheres or cigars with diameters about 4000 times the distance between the Earth and Sun.

Cloud encounters
"We estimate that lots of these small clumps can still survive in the Milky Way," says Diemand. Perhaps a million billion of them drift around the large dark matter halo that is thought to enclose our galaxy. Such a cloud may float through Earth every 10,000 years in an encounter lasting about 50 years.

But the phantom clouds do not affect the Earth, says Diemand. Their relatively wispy densities mean they could only nudge our planet out of its normal orbit by less than a millionth of a metre per second.

Still, they may leave behind observable signatures. When two neutralinos hit each other, they are predicted to produce a jet of other particles, as well as gamma-ray photons. Detecting these photons may be difficult, given the unknown way in which neutralinos produce light in the clouds, but it is theoretically possible, say the researchers.

Indeed, a NASA detector called EGRET (Energetic Gamma Ray Experiment Telescope) turned up about 200 gamma-ray sources during the 1990s whose origin could not be identified, and Diemand thinks some of these may arise in small dark matter clouds.

Detected by movement
But Andrew Zentner, a cosmologist at the University of Chicago in Illinois, US, and not part of the team, questions that suggestion because most of EGRET's sources lie within the disc of our galaxy. The models suggest that the small dark matter clouds should be peppered throughout space, a point Diemand acknowledges.

But Zentner adds that the small clouds could in theory be detected using gamma rays generated as they float through the Milky Way's large dark matter halo. "It's like seeing an airplane fly across the sky," he told New Scientist.

A space telescope called GLAST (Gamma-ray Large Area Space Telescope), due to launch in 2007, will survey the entire sky at high sensitivity and may be able to turn up signatures from these clouds.

Even if it does not find them, says Zentner, their absence would shed light on the dark matter problem. That would indicate "that neutralinos aren't the dark matter, or that neutralinos might be dark matter but don't have the parameters we thought," he says.

Journal reference: Nature (vol 433, p 389)
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Ooooooooo... :)
 
Dark Matter Galaxy?

Summary - (Thu, 12 Jan 2006) Astronomers think they might have found a "dark galaxy", that has no stars and emits no light. Although the galaxy itself, located 50 million light years from Earth, is practically invisible, it contains a small amount of neutral hydrogen which emits radio waves. If astronomers are correct, this galaxy contains ten billion times the mass of Sun, but only 1% of this is hydrogen - the rest is dark matter.

Full Story -New evidence that VIRGOHI 21, a mysterious cloud of hydrogen in the Virgo Cluster 50 million light-years from the Earth, is a Dark Galaxy, emitting no star light, was presented today at the American Astronomical Society meeting in Washington, D. C. by an international team led by astronomers from the National Science Foundation's Arecibo Observatory and from Cardiff University in the United Kingdom. Their results not only indicate the presence of a dark galaxy but also explain the long-standing mystery of its strangely stretched neighbour.

The new observations, made with the Westerbork Synthesis Radio Telescope in the Netherlands, show that the hydrogen gas in VIRGOHI 21 appears to be rotating, implying a dark galaxy with over ten billion times the mass of the Sun. Only one percent of this mass has been detected as neutral hydrogen - the rest appears to be dark matter.

But this is not all that the new data reveal. The results may also solve a long-standing puzzle about another nearby galaxy. NGC 4254 is lopsided, with one spiral arm much larger than the rest. This is usually caused by the influence of a companion galaxy, but none could be found until now - the team thinks VIRGOHI 21 is the culprit. Dr. Robert Minchin of Arecibo Observatory says; "The Dark Galaxy theory explains both the observations of VIRGOHI 21 and the mystery of NGC 4254."

Gas from NGC 4254 is being torn away by the dark galaxy, forming a temporary link between the two and stretching the arm of the spiral galaxy. As the VIRGOH1 21 moves on, the two will separate and NGC 4254's unusual arm will relax back to match its partner.

The team have looked at many other possible explanations, but have found that only the Dark Galaxy theory can explain all of the observations. As Professor Mike Disney of Cardiff University puts it, "The new observations make it even harder to escape the conclusion that VIRGOHI 21 is a Dark Galaxy."

The team hope that this will be the first of many such finds. "We're going to be searching for more Dark Galaxies with the new ALFA instrument at Arecibo Observatory," explains Dr. Jon Davies of Cardiff University. "We hope to find many more over the next few years - this is a very exciting time!"

Original Source: PPARC News Release
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www.universetoday.com/am/publish/pparc_ ... ml?1212006
 
Gravity theory dispenses with dark matter

A modified theory of gravity that incorporates quantum effects can explain a trio of puzzling astronomical observations – including the wayward motion of the Pioneer spacecraft in our solar system, new studies claim.

The work appears to rule out the need to invoke dark matter or another alternative gravity theory called MOND (Modified Newtonian Dynamics). But other experts caution it has yet to pass the most crucial test – how to account for the afterglow of the big bang.

Astronomers realised in the 1970s that the gravity of visible matter alone was not enough to prevent the fast-moving stars and gas in spiral galaxies from flying out into space. They attributed the extra pull to a mysterious substance called dark matter, which is now thought to outweigh normal matter in the universe by 6 to 1.

But researchers still do not know what dark matter actually is, and some have come up with new theories of gravity to explain the galaxy observations. MOND, for example, holds that there are two forms of gravity.

Above a certain acceleration, called a0, objects move according to the conventional form of gravity, whose effects weaken as two bodies move further apart in proportion to the square of distance. But below a0, objects are controlled by another type of gravity that fades more slowly, decreasing linearly with distance.

But critics point out that MOND cannot explain the observed masses of clusters of galaxies without invoking dark matter, in the form of almost massless, known particles called neutrinos.

Quantum fluctuations
Now, Joel Brownstein and John Moffat, researchers at the Perimeter Institute for Theoretical Physics and the University of Waterloo in Ontario, Canada, say another modified gravity theory can account for both galaxies and galaxy clusters.

The theory, called scalar-tensor-vector gravity (STVG), adds quantum effects to Einstein's theory of general relativity. As in other branches of physics, the theory says that quantum fluctuations can affect the force felt between interacting objects.

In this case, a hypothetical particle called a graviton – which mediates gravity – appears in large numbers out of the vacuum of space in regions crowded with massive objects such as stars. "It's as if gravity is stronger" near the centres of galaxies, Brownstein told New Scientist. "Then, at a certain distance, the stars become sparse, and the gravitons don't contribute that much." So at larger distances, gravity returns to the behaviour described by Newton.

Pioneer 10 anomaly
Brownstein and Moffat tested the theory in several ways. They estimated the gravitational change that occurs 46,000 light years out from the centre of a large galaxy and half that distance for a small galaxy. They applied these estimates to 101 observed galaxies, and found that both their theory and MOND could account for their rotations. "The point is that neither of the two theories had any dark matter in them," says Brownstein.

But the theories did diverge when the pair tested them against observations of 106 galaxy clusters. MOND could not reproduce the observed cluster masses but STVG accounted for more than half.

Furthermore, the team tested the theory against observations of NASA's 34-year-old Pioneer 10 spacecraft, which appears about 400,000 kilometres away from its expected location in the outer solar system. Brownstein says the theory fits observations of the so-called Pioneer anomaly (see New Scientist feature, 13 things that do not make sense), while MOND cannot address it because Pioneer's acceleration is above a0.

Big bang's afterglow
"At three different distance scales, we see answers that agree with experiment," says Brownstein. "They are claiming they can solve all the world's problems," agrees Sean Carroll, a cosmologist at the University of Chicago in Illinois, US. But these experiments are "not what most cosmologists would first think of if they were going to test a new theory of gravity".

He says any theory must also explain the development of large-scale structures in the universe, and most importantly, the afterglow of the big bang. Called the cosmic microwave background (CMB) radiation, this afterglow was produced about 370,000 years after the big bang when the first atoms formed and has been studied in great detail by satellites, such as NASA's WMAP probe.

"The dark matter model is not perfect, but it made a very specific prediction for the microwave background that seems to be coming true, and it fits galaxies and clusters and large-scale structure and gravitational lensing," Carroll told New Scientist. "Nobody would be happier than me if it turned out to be modified gravity rather than dark matter, but it's becoming harder and harder to go along with that possibility."

http://www.newscientistspace.com/article.ns?id=dn8631
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Source
Dark matter comes out of the cold
By Jonathan Amos
BBC News science reporter

Astronomers have for the first time put some real numbers on the physical characteristics of dark matter.
This strange material that dominates the Universe but which is invisible to current telescope technology is one of the great enigmas of modern science.

That it exists is one of the few things on which researchers have been certain.

But now an Institute of Astronomy, Cambridge, team has at last been able to place limits on how it is packed in space and measure its "temperature".

"It's the first clue of what this stuff might be," said Professor Gerry Gilmore. "For the first time ever, we're actually dealing with its physics," he told the BBC News website.

Science understands a great deal about what it terms baryonic matter - the "normal" matter which makes up the stars, planets and people - but it has struggled to comprehend the main material from which the cosmos is constructed.

'Magic volume'

Astronomers cannot detect dark matter directly because it emits no light or radiation.

Its presence, though, can be inferred from the way galaxies rotate: their stars move so fast they would fly apart if they were not being held together by the gravitational attraction of some unseen material.

Such observations have established that dark matter makes up more than 95% of all cosmic material.


These are the first properties other than existence that we've been able determine
Prof Gerry Gilmore
Institue of Astronomy, Cambridge

Now, the Cambridge team has provided new information with its detailed study of 12 dwarf galaxies that skirt the edge of our own Milky Way.
Using the biggest telescopes in the world, including the Very Large Telescope facility in Chile, the group has made detailed 3D maps of the galaxies, using the movement of their stars to "trace" the impression of the dark matter among them and weigh it very precisely.

With the aid of 7,000 separate measurements, the researchers have been able to establish that the galaxies contain about 400 times the amount of dark matter as they do normal matter.

"The distribution of dark matter bears no relationship to anything you will have read in the literature up to now," explained Professor Gilmore.


If this 'temperature' for the dark matter is correct, then it has huge implications for direct searches for these mysterious particles
Prof Bob Nichol
Institute of Cosmology and Gravitation, Portsmouth

"It comes in a 'magic volume' which happens to correspond to an amount which is 30 million times the mass of the Sun.
"It looks like you cannot ever pack it smaller than about 300 parsecs - 1,000 light-years; this stuff will not let you. That tells you a speed actually - about 9km/s - at which the dark matter particles are moving because they are moving too fast to be compressed into a smaller scale.

"These are the first properties other than existence that we've been able determine."

Knowledge advance

The speed is a big surprise. Current theory had predicted dark matter particles would be extremely cold, moving at a few millimetres per second; but these observations prove the particles must actually be quite warm (in cosmic terms) at 10,000 degrees.

The most likely candidate for dark matter material is the so-called weakly interacting massive particle, or Wimp.


Scientists believe these are relic particles produced in the Big Bang.
They are predicted by certain theoretical extensions to the accepted description of matter and forces, the Standard Model of Fundamental Particles and Interactions. But also their presence would go a long way to explaining the structure and geometry of the Universe we observe.

Professor Bob Nichol, from the Institute of Cosmology and Gravitation at the University of Portsmouth, described the Cambridge work as "awesome".

"If this temperature for the dark matter is correct, then it has huge implications for direct searches for these mysterious particles (it seems [science] may be looking in the wrong place for them) and for how we thought the galaxies and clusters of galaxies evolve in the Universe.

"Having 'hotter' dark matter makes it harder to form the smallest galaxies, but does help to make the largest structures. This result will generate a lot of new research."

Big neighbours

Experimental crystal detectors placed down the bottom of deep mines are hoping to record the passage through normal matter of these hard to grasp dark matter particles.

Researchers would hope also that future experiments in particle accelerators will give them greater insight into the physics of dark matter.


The Cambridge efforts have produced an additional, independent result: the detailed study of the dwarf galaxies has allowed the scientists to weigh our own galaxy more precisely than ever before.
"It turns out the Milky Way is more massive than we thought," said Professor Gilmore.

"It now looks as though the Milky Way is the biggest galaxy in the local Universe, bigger even than Andromeda. It was thought until just a few months ago that it was the other way around."

The Cambridge University team expects to submit the first of its results to a leading astrophysics journal in the next few weeks.
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The Brownstein/Moffat theory has been heavily criticised recently. They can get the results they desire for galaxy rotation curves if and only if they have a 'constant' in the theory varying with the mass of the galaxy-i.e. a different theory for every system considered!

From the paper:

'The choice of K, which determines the strength of the coupling of B_{\mu\nu} to matter and the magnitude of the Yukawa force modification of weak Newtonian gravity,is based on phenomenology and is not at present derivable from the STVG action formalism.'
 
Just a quick question. Is it conceivable that each galaxy may need its own constant?
 
Cosmic smash-up provides proof of dark matter

A cosmic collision has supplied direct proof that dark matter really exists, astronomers say. The collision has allowed dark matter to be separated from ordinary matter, casting doubt on the idea that dark matter could just be an illusion due to a flaw in our understanding of gravity.

The pull of gravity from ordinary matter seems to be insufficient to hold spinning galaxies together, including our own. This and several other lines of evidence point to the existence of a mysterious form of invisible matter that exerts a gravitational influence on other matter and outweighs ordinary matter by a factor of about 6 to 1.

But it is not clear what the dark matter is, and some scientists have argued that modifying the laws of gravity set out by Newton and Einstein could explain the observations in question, without the need for dark matter (see Gravity theory dispenses with dark matter).

In those theories, the gravity from ordinary matter remains strong at greater distances than predicted by Newton and Einstein, which prevents galaxies from flying apart.

Isolated clouds
"A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," says Doug Clowe at the University of Arizona in Tucson, US.

Now, he and colleagues show that the universe does indeed appear to be dominated by dark matter. The conclusion is based on observations of a collision between two clusters of galaxies that separated dark matter from ordinary matter.

Astronomers were able to observe the gravitational influence of isolated clouds of dark matter for the first time – normally, this is impossible because dark matter and ordinary matter are too well mixed to observe the dark matter independently.

The astronomers observed an object called 1E0657-556, which was produced by two galaxy clusters that collided with one another 100 million years ago at 4700 kilometres per second.

Gravitational lensing
Most of the ordinary matter in such clusters is in the form of hot gas, which the astronomers were able to map out using NASA's Chandra X-ray Observatory. But the researchers found that the cluster's gravity field was not centred on the gas clouds.

The gravity field was measured using the Hubble Space Telescope and the European Southern Observatory's Magellan telescope and Wide-Field Imager. They observed the distortion caused by gravitational lensing, in which the cluster's gravity bends light from distant background galaxies.

The observations showed that the two clusters, which passed through each other in the collision and are now separate in space again, held onto their massive dark matter clouds. Their hot gas clouds, however, got entangled with one another in the collision and were left trailing behind the clusters of galaxies.

Watch an mpg video showing an artist's impression of the dark matter and ordinary matter getting separated.

Electromagnetic forces
The separation occurred because dark matter does not experience the same drag that stripped the gas from the galaxy clusters. That is because drag is caused by electromagnetic forces between atoms, and dark matter interacts with other matter only through the force of gravity.

Clowe says the results strongly support the existence of dark matter: "You cannot explain the result using altered gravity."

Sean Carroll of the University of Chicago in Illinois, US, who is not a member of the research team, agrees. "This result proves beyond a reasonable doubt that there really is such as thing as dark matter," he told New Scientist.

"The whole idea that modified gravity can do away with all dark matter is more or less ruled out," he says. But he says it is still possible that modified gravity could exist in addition to dark matter, even if the motivation for such theories has been reduced.

http://www.newscientistspace.com/articl ... atter.html
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Just a quick question. Is it conceivable that each galaxy may need its own constant?
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I beleive there are theories that the laws of physics may have been different in the early universe, so i suppose it's feasible, since we're viewing structures that existed millions or billions of years ago, that different constants do apply...
 
http://news.nationalgeographic.com/news ... atter.html

Late last month scientists working at NASA's Chandra X-ray Observatory announced that they had found proof of dark matter, the theoretical substance believed to make up more than a quarter of the universe.

But Glenn Starkman, a cosmologist at Case Western Reserve University in Cleveland, Ohio, is hitting back with a blast from the past.

He argues that dark matter might not exist and that the long-discredited substance known as ether is actually what influences gravity in the cosmos.

Dark matter is the prevailing scientific explanation for a puzzling phenomenon: Galaxies behave as if they contain much more mass than is visible to astronomers.

According to theory, dark matter is the invisible mass that accounts for this behavior, and the undetectable substance makes up five times more of the universe than the matter we can see.

Starkman's controversial counterproposal is that the presence of ether in the universe better explains the galaxies' behavior.

His theories were recently reported in the August 26 issue of New Scientist magazine.

"Galaxies spin faster than they should, given the amount of matter we see in them. The possibility we've gone with for a long time is that there's some unaccounted-for mass generating that extra gravity," Starkman said.

"But the other possibility is that the amount of mass we see generates more gravity than we thought. That's where ether comes in."

Ether Wind

The term "ether" is derived from Aether, the ancient Greek god of the upper sky and the personification of space and heaven.

The scientific concept of ether—a background medium that pervades the universe—has been around for hundreds of years.

Scientists once believed that ether was the substance that allows light to move through the universe, just as sound needs air or water to propogate.

Earth's motion through the ether, some physicists thought, would create a type of wind that bends light waves the same way that wind in the atmosphere bends sound waves.

But the theory was largely abandoned after an 1887 experiment by physicists Albert Michelson and Edward Morley.

Dubbed "the most famous failed experiment," the test was meant to gather data on the effects of this so-called ether wind. But the experiment showed that light propagation was not affected, suggesting ether wind did not exist.

Later, Einstein based his theory of special relativity on the idea that light can move through an ether-free vacuum.

Starkman's conception of ether, however, is very different from the outmoded 19th-century one—he thinks that ether affects the pull of gravity, not the movement of light waves.

"With traditional gravitational models, you have a rubber sheet that curves wherever there's a large mass on it," he said.

In Starkman's theory of how ether works, "when ether is around, the rubber sheet gets softer. So when you put a large mass on the sheet, the effect of the mass goes out further."

Starkman's initial calculations show that ether's localized effects on gravity would account for the high velocities of galactic stars.

The next phase in his research will be to perform more detailed calculations to make sure his ether theory matches up with empirical evidence, such as the motion of planets within the solar system.

"It's important to do these experiments, because either we'll be able to rule dark matter out or we'll increase our confidence in it.

"At this point I don't think we can rule out either of the two [competing] theories," he said.

Challenging Einstein

Several high-profile theoretical physicists have lined up to support Starkman's theory, including Jacob Bekenstein, theoretical physics professor at Hebrew University in Jerusalem, Israel, and Andreas Albrecht, cosmologist and physics professor at the University of California, Davis.

Still, Starkman acknowledges that his theory is in its infancy and may not stand up to rigorous testing.

"We're offering an alternative to the dark matter theory—we're not saying it's wrong. If I had to bet today on which of these theories was correct, I might bet on dark matter."

Meanwhile, many other experts are sitting on the fence.

Michael Turner, an astrophysicist at the University of Chicago in Illinois, is intrigued by Starkman's theory, but he hesitates to accept it wholesale due to its troubling implications.

For example, the presence of ether would create holes in Einstein's theories of relativity, the widely accepted explanations for how light moves and gravity works (read an excerpt and see images from "Einstein and Beyond" in National Geographic magazine).

"It's early to tell whether this [ether] theory will really pass through the gate," Turner said. "When you change the theory of gravity, you could cause lots of problems elsewhere.

"It's an interesting Plan B, but we already have a pretty good Plan A."
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Hi all,
Sorry if this seems overlong and perhaps not entirely well explained, but I'm looking after me newborn and typing with one hand. However, what I'm proposing is an entirely serious idea, and one I'd like to bounce off other minds.
Here goes...(sorry for the length)
Spacetime and dark matter interaction hypothesis

I started this idea a very long time ago, as a child, ever wondering whether I’d ever be able to travel to other planets and times, a la Dr. Who. I entertained fantasies of exotic engines, warp speed and so forth, until I began to think that there might be a way of doing it without accelerating. About a week ago, an idea came to mind that I have been bending backwards and forwards every way I can, and I can’t find a problem at the moment, apart from the fact it uses a form of matter that is only just on the verge of being described. What is more, my idea seems to resolve a whole raft of complex issues regarding astrophysics and quantum physics, plus some other issues relating to religion and philosophy. It also implies a way to travel that could cover infinite distances and times, but without breaking any laws of physics. I know this is an outrageously enormous claim; This is why I must put this idea into the public domain, where it must be pulled every which way to see if it’s just crackpot or not. Let’s begin.
My current round of thinking about this concept began with the question ‘what would a universe look like if it did not have time?’, the answer, quite obviously, being absolute bloody chaos; everything would happen instantaneously. However, it also implies that a universe without time could not have a cogent space, as distance of any kind implies time between events. In other words, a timeless universe is an absurdity – it could not possibly have shape or substance. Rather like the singularity that led to the Big Bang. So far, so basic; I also started thinking along the lines of ‘what does time and distance look like in a universe devoid of sentience?’ – I wanted to understand what the absolute definition of time is, rather than the mathematical limits of seconds, hours, days, months etc that we place upon time. I also asked myself ‘what would the universe look like if it were smaller/bigger?’
It was this last question that set me following the white rabbit down the hole, or rather, an extremely large, at least light-year-wide, invisible bunny through spacetime.
Dark matter and dark energy have become increasingly accepted features of the universe over the past few years, even though we don’t know what they are, how big they are, or what they’re doing loitering around, being invisible. Dark matter does not seem to interact with the visible universe; we can’t see it, touch it, taste it, hear it or weigh it, which pretty much renders an impossible thing. Yet it must be there, because the universe and the structure within could not possibly exist without it. It is a thing that we simply do not have the capacity of perceiving, yet we can infer its existence.
And it does not interact with the visible universe.
However, what it does do is interact with spactime, simply because it is a fundamental part of the universe, just like gravity, mass, and electromagnetism.
Now here’s the idea:
The universe is far, far smaller than we actually consider it to be.
The reason it looks larger is very simple: dark matter dilates spacetime.
In other words, dark matter somehow acts as a kind of lens, distorting the actual fabric of the material, visible universe.
How on Earth is this provable?
Well, I’m still working on that one, but a couple of thoughts come to mind. Basically, dark matter may pervade the universe, but it should clump in gravitational centres, i.e. in galaxies and around black holes. The greater the amount of dark matter, the larger (and longer) spacetime appears to be. In other words, someone standing at the heart of the galaxy would see space, and the distance between stars, as being far more stretched out than someone standing at a point outside a galaxy. Not only that, it would also appear older than it is. So, you could send some people off on unimaginably long journeys to the centre of our galaxy and outside it, the compare their experiences, although might take a teensy-weensy bit too long – by several million years. Or you could try bouncing some kind of signal towards a system towards the centre of the galaxy, and another equidistant towards the outside, and measure the length of time it takes the signal to return. If my idea is true, it should take marginally longer for the signal aimed at the heart of the galaxy to return. Or you could try with the Pioneer probe, now hurtling away from the solar system and into deep space. If my supposition is correct, then our solar system should appear smaller than it does to us as a spacecraft enters deep space and less dark matter.
Now, dark matter appears to consist of enormous structures – current ideas suggest that a single particle may be more that a light year in dimension – but this helps the notion of the way it dilates spacetime. Although it affects the visible, material universe, what it does not do is affect matter at the subatomic, quantum level, simpy because of its sheer size. This could explain ‘spooky action at a distance’, or the way subatomic materials appear to have an effect on other subatomic particles regardless of distance and time. This is because the distance and time are the byproduct of spacetime dilation through dark matter. Dark matter behaving as I suggest would also explain why the Universal Constant appears to have changed, and why the speed of light possibly isn’t what it used to be. In fact, they have remained the same; what has occurred, from our perspective, is movement of dark matter, giving the illusion of change.
What are the implications of what I’m suggesting?
I’d argue that they are possibly enormous. Firstly, it suggests that we are capable of travelling vast distances without expending much in the way of energy. Quite simply, if you understand what dark matter (and dark energy, too) is, and how it behaves in relation to the visible universe – how it moves, how it clumps and so forth – then, in theory, and with an extremely fast computer and an extraordinarily accurate map, you should be able to avoid it – in other words, to warp through ‘real’ spacetime, rather than the dilated version. In terms of the kind of vehicle you’d need to do this, think more in terms of the Tardis than the USS Enterprise. This is because you would be able to move through time as well as space – hence the need for a really good map.
It also gives an insight into certain philosophical and religious ideas that the universe we live in is an illusion – that’s because it is: Our sense of space and time is a necessary illusion. I say necessary, because our senses have evolved to perceive spacetime as it appears to be, in its dilated state. This also implies that the rate of dilation would be relatively constant.
One thing I also suspect is that, not only does dark matter clump, the amount of it in the universe gradually increases as the universe ages. This would gradually increase the rate of spacetime dilation, leading to the visible universe appearing bigger and older.
Anyway, that’s the idea, in short – I have a few more suppositions that can be added to that, some of which relate to other spheres of science, but I want to work them through. This is a serious idea, and I’d like other serious minds to look at it. If it’s wrong, please tell me and explain why it’s wrong. If it looks right, please test it to destruction.
 
gellatly68 said:
and I can’t find a problem at the moment, apart from the fact it uses a form of matter that is only just on the verge of being described.
Click to expand...

I'm not a science boffin, but isn't that potentially a big problem?
 
:D of course it is! It's a bloody enormous problem! However, the idea struck me as a highly interesting possibility, and one that deserves at least a cursory look from others better qualified. Dark matter appears to exist, and it must be a nonsense to say that it doesn't interact whatsoever with the visible, observable bit that we call the universe.
 
A very interesting post, gellatly. :)

One thing. I thought that dark matter did interact with the universe? As far as I understood it, and I haven't read anything about the subject for a long time, the existence of dark matter was inferred in order to explain the fact that the universe wasn't expanding faster than it already is? In other words, the gravitational attraction of dark matter is required to slow the expansion, ie, there is an interaction.

If I've mistaken anything in your post then please forgive, it's late and I'm a bit on the knackered side.

Nevertheless, a very interesting idea.
 
Dark matter is supposed to interact gravitationally with the universe, it is what supposedly keeps galaxies together. And according to Einstein´s theory of relativity, gravity slows time down. So an object moving through an area of dark matter would experience time slower than one that moved through an empty area I believe. Except I´m not sure there are such a thing as empty areas, dark matter might be rather homogenous.
 
Why is dark matter not all around us?
If we wave our hands around, why are we not wafting dark matter around?
Phlogiston? The Ether? Some of those old scientists unwittingly had it right, perhaps?
 
I don't click links! :mad:

You have to tempt me to know more, give me the gist...

I can end up going around in circles clicking bloody links. A total waste of my time. :evil:
 
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