Dark Matter Either Exists, or It Doesn't

"Dark Energy and Dark Matter Might Not Exist, Scientists Allege "
Space.com (June 13, 2010)
Dark Matter Either Exists, or It Doesn't
"Dark matter and dark energy are two of the most mind-boggling ingredients in the universe. Ever since these concepts were first proposed, some astronomers have worked feverishly to figure out what each thing is, while other astronomers have tried to prove they don't exist, in hopes of restoring the universe to the more understandable place many would like it to be.

"A new look at the data from one of the telescopes used to establish the existence of this strange stuff is causing some scientists to question whether they really exist at all. Yet other experts are holding firm to the idea that, whether we like it or not, the 'dark side' of the universe is here to stay.

"Dark matter is a proposed form of matter that could make up 22 percent of the universe's mass-energy budget, vastly outweighing all the normal matter, like stars and galaxies. Astronomers can't observe dark matter directly, but they think it's there because of the gravitational pull it seems to exert on everything else. Without dark matter, the thinking goes, galaxies would fly apart...."

Literary allusions to the Star Wars movies aside, this is a pretty good article.

There's a short overview of what dark matter and dark energy are - why some cosmologists and physicists think they exist - and why some now don't. The reason, as I see it, that there isn't a consensus is that we've got a fairly large set of data about the universe. Some of it is very precise, some isn't so precise: not wrong, just 'fuzzy.' Like some aspects of the microwave background radiation.

Slice and dice the data one way, you get support for the idea that dark matter exists. Run it through a virtual Cuisinart another way: and dark matter isn't so obvious.

This sort of thing is nothing new. Around 340 years ago, phlogiston was a pretty good way to explain combustion. It was a hypothetical substance present in materials that can burn. As it turns out, phlogiston doesn't exist. But until we learned more about matter, it was a model that made sense.

Which is about where we're at with dark matter today.

Related posts:

• "Dark Flow: This Universe on the Move?"
  (March 18, 2010)
• "Looking for Dark Matter, Deep Under Minnesota"
  (February 26, 2010)
• "Dark Matter, Dark Energy, Galaxies, Mathematics and Observations"
  (January 17, 2010)
• "Lemming Tracks: Dark Matter, Dark Stars, and Keeping Up"
  (December 21, 2009)
• "Like, Far Out! Offbeat Galaxies"
  (August 6, 2009)
• "Dark Matter, the Gruber Foundation's Cosmology Prize, and Cephid Variables"
  (June 8, 2009)

Dark Flow: This Universe on the Move?

"Weird 'Dark Flow' Seen Deeper Into the Universe Than Ever"
Space.com (March 17, 2010)

"The puzzling migration of matter in deep space – dubbed 'dark flow' – has been observed at farther distances than ever before, scientists have announced.

"Distant galaxy clusters appear to be zooming through space at phenomenal speeds that surpass 1 million mph. The clusters were tracked to 2.5 billion light-years away – twice as far as earlier measurements.

"This motion can't be explained by any known cosmic force, the researchers say. They suspect that whatever's tugging the matter may lie beyond our observable universe.

"The notion is a controversial one because it has only been measured by one group of scientists in one set of data so far.

"'We understand why this idea is so annoying at times,' said study leader Alexander Kashlinsky at NASA's Goddard Space Flight Center in Greenbelt, Md. 'In fact, part of the motivation for our ongoing project was precisely to rule it out. But it is in the data, we don't see it going away.'..."

Research results like this being "controversial" doesn't mean they're wrong. Or right. Continental drift was "controversial" in this sense, until enough measurements were made, precisely enough, to show that the 'solid earth' we stand on is moving. (Normally, we don't notice it. Sometimes, we do. ("Chile City Moved 10 Feet West: Change Happens" (March 10, 2010))

This dark flow seems to be moving in the direction of Centaurus and Hydra, in our sky's southern hemisphere.

I can see how this research has raised eyebrows. The article summarizes what they did:

"...The new study is based on a larger data set of about 1,500 galaxy clusters and CMB measurements taken over five years by space and ground-based telescopes. The researchers say their new results strengthen indications that the dark flow is real...."

Astronomers and cosmologists have long ago come to terms with the idea that the five visible planets aren't the only things that move around: Although using the Big Bang's afterglow as a frame of reference seems to be something new. We haven't been able to, until fairly recently.

What's really bothersome, I think, about dark flow is that it shouldn't exist. Sure, things like planets, stars, and clusters of galaxies move in relation to each other: but all those (relatively) small things should average out to zero. That Big Bang microwave radiation is - or should be - a sort of stationary reference. Everything we observe is a sort of debris from that cosmic explosion.

Or we're living in a garbanzo bean in somebody's microwave oven - which I rather doubt. Old idea, from the days when we were discovering electrons, where some imaginative writers played with the idea that stars and planets were the electrons and nuclei of atoms in a bigger universe.

Back to the article:

"...'It looks indeed that the entire observable universe is moving with respect to the CMB radiation,' Kashlinsky told SPACE.com. 'We can now say that more confidently than our initial supposition.'

"The researchers think dark flow may be caused by structures that lie beyond the horizon of our own universe. As odd as that may sound, some cosmologists think that our universe is actually only a bubble of space-time that was created during a period of rapid cosmic expansion, called inflation, after the Big Bang. Other bubbles may also have been created where inflation took place at a different rate, and perhaps something in one of the other bubbles is tugging at our universe...."

Like I said, dark flow is a bit bothersome, in part because if it exists one of the simpler explanations is that there's another 'universe' off in the general direction of Centaurus and Hydra.

Which changes the idea of other universes existing from an intriguing subject for informed speculation to a serious hypotheses that has to be tested. And that is a lot more work than building elegant mathematical models that don't have to conform to observations.

It'll be interesting, to me at least, to see where this line of research leads.

I've used this quote before:

"Not only is the universe stranger than we imagine, it is stranger than we can imagine." (Sir Arthur Eddington English astronomer (1882 - 1944))

Probably so, but that won't keep us from trying.

Related post:

• "It's Just a Comic Book? Yes: But the Science Behind it is Stranger"
  Drifting at the Edge of Time and Space (December 4, 2009)
• "Physicists Visualize Extra Dimensions (Caution! Geeky Content!)"
  (May 23, 2009)
  • That's "dimensions" - not "universes"
    • In physics and cosmology, there's a difference
• "That's the Size of It: Local Galaxies to Quarks"
  (February 21, 2009)
• "It's About Time, Entropy, and Other Universes"
  (June 4, 2008)

More:

• "The Science Behind Marvel Comics' New Cosmic Tale"
  Space.com (December 4, 2009)

---

The December 4, 2009, Space.com article uses a Marvel Comics release as the starting point for a discussion of quantum energy and logical extrapolations from what we're discovering about how the (observable) universe works. The part that ties in with this post:

"...Other universes, space-time tears

"One consequence of quantum physics is the 'many-worlds interpretation,' which suggests a virtually infinite number of universes exist, altogether comprising every possible outcome to every event — including, perhaps, the truly horrifying possibilities seen in 'Realm of Kings.'

"But how would one adventure to another universe? The answer could be increasingly familiar tears in the space-time continuum known as wormholes. Einstein proposed that mass and energy curve space-time, creating the force we know as gravity. One consequence of his theories is that enough mass or energy concentrated in one place can warp space-time enough to create distortions allowing shortcuts in space, travel back in time and even voyages to other universes.

"The main problem with any concept involving wormhole is keeping them open enough for travel, as they naturally want to slam closed and form black holes. However...."

Looking for Dark Matter, Deep Under Minnesota

"Elusive Dark Matter May Be Hidden on Earth"
Space.com (February 25, 2010)

"Scientists are hot on the tail of one of nature's most elusive substances, the mysterious dark matter that is thought to make up the bulk of the universe. Many scientists think dark matter might even be hiding right under our noses here on Earth.

"Dark matter is especially tricky to find because of its dark nature. In fact, scientists don't know what it is. It doesn't emit or reflect any light, so the most powerful telescopes have no hope of spying it directly. It has been thought to exist since the 1970s based on observations of gravity's effects on large-scales, such as among and between galaxies – regular matter can't account for the amount of gravity at work.

"And dark matter doesn't often interact with most other matter, scientists theorize. One idea is that it flies right through the Earth, your house, and your body without bouncing off atoms...."

That last paragraph in the excerpt represents a huge improvement over quite a bit of media coverage of dark matter research. It took me a while - years back now - to learn that that "dark matter" wasn't simply material that wasn't illuminated - and wasn't hot enough to glow at observable wavelengths.

And yeah, dark matter really is exotic. So is dark energy.

If either exist.

Dark matter may be the 20th century's phlogiston. But as more and more data is crunched, it's looking like dark matter and dark energy exist.

That, or something that acts like them does.

I'm a little more-than-usually interested in this particular line of dark matter research: some of it's going on here in Minnesota, in the Soudan mine.

Putting a dark matter detector deep underground shields it from the sort of radiation and particles that are zipping around - and through - us all the time here on the surface. With 700 meters of shielding, there's a better chance of sorting out dark matter interactions with the detector from the background noise.

Dark matter isn't, apparently, just something that's 'out there.' It - or something that acts just like it - is in a cloud of stuff that's part of our Milky Way galaxy. Astronomers detected and mapped it, from its effect on the orbits of stars around our galaxy's center.

Looks like it's shaped sort of like like a rounded-off, and squashed, American football: It's a spheroid where the 'height,' 'length,' and 'width' are all different.

The odd thing is that, although it's clearly centered on the visible core of our galaxy - its longest axis is as right angles to the Milky Way's plane.

But that's another topic.

Related posts:

• "Dark Matter, Dark Energy, Galaxies, Mathematics and Observations"
  (January 17, 2010)
• "Lemming Tracks: Dark Matter, Dark Stars, and Keeping Up"
  (December 21, 2009)
• "Like, Far Out! Offbeat Galaxies"
  (August 6, 2009)
• "Dark Matter, the Gruber Foundation's Cosmology Prize, and Cephid Variables"
  (June 8, 2009)

More:

• Cryogenic Dark Matter Search (CDMS)
  University of California, Berkeley
• Soudan Underground Laboratory
  Cryogenic Dark Matter Search (CDMS), Experiments and Facilities

Dark Matter, Dark Energy, Galaxies, Mathematics and Observations

"Mystery Behind Galaxy Shapes Solved"
Space.com (January 11, 2010)

"Galaxies come in many shapes and sizes, but until recently astronomers have been at a loss to explain why.

"Now scientists have used dark matter theory to predict the menagerie of galaxies found in the universe. Their new model reproduces 13 billion years' worth of cosmic evolution, resulting in a surprisingly accurate tally of the different kinds of galaxies we see.

" 'We were completely astonished that our model predicted both the abundance and diversity of galaxy types so precisely,' said researcher Nick Devereux of Embry-Riddle University in Arizona...."

The article does a pretty good job of explaining the basics of how galaxies are sorted out by shape: and what the latest mathematical model is.

The bottom line:

"...Researchers created a new supercomputer model, based on observational data and the "Lambda Cold Dark Matter" theory of the universe. This theory suggests that about 72 percent of the cosmos is made of up a mysterious force called dark energy, while another 23 percent is composed of an invisible type of matter called dark matter. That leaves only 4 percent of the universe made of normal, visible matter, including all the stars and planets that we see...."

And, despite that "solved" in the headline, the scientists are still firmly connected to the space-time continuum:

"...'These new findings set a clear direction for future research,' Devereux said. 'Our goal now is to compare the model predictions with observations of more distant galaxies seen in images obtained with the Hubble [Space Telescope] and those of the soon-to-be-launched James Webb Space Telescope.'..."

Right now, it looks like dark matter, and dark energy, work very well as explanations for why the universe looks the way it does now. Not all that long ago, a substance called phlogiston was a pretty good explanation to explain why fire works the way it does. Then, in 1772, tests demonstrated that something called oxygen was involved. As it turns out, phlogiston doesn't exist.

But it worked for quite a while as an adequate model to explain combustion.

Dark Matter, Dark Energy, Galaxies, Mathematics and Observations

It's looking more and more like dark matter and dark energy really exist. Or, if they don't, that something that acts a whole lot like them does.

But: "Solved"? What we've got now is a better explanation - and one that can be tested.

Related posts:

• "Lemming Tracks: Dark Matter, Dark Stars, and Keeping Up"
  (December 21, 2009)
• "Like, Far Out! Offbeat Galaxies"
  (August 6, 2009)

Vaguely-related piece:

• "Once it Was Believed / Now We Know"
  Brian's Attic (2003)

Background:

• "Dark Energy, Dark Matter"
  Astrophysics, Science, NASA

Lemming Tracks: Dark Matter, Dark Stars, and Keeping Up

"Mystery Swirls Around 'Dark Stars' "
Space.com (December 21, 2009)

"When the very first stars lit up, they may have been fueled by the dark matter that has long eluded scientists.

"These 'dark stars,' first born nearly 13 billion years ago, might still exist today. Although they would not shed any visible light, astronomers might detect these invisible giants — some 400 to 200,000 times wider than our sun and 500 to 1,000 times more massive — because they should spew gamma rays, neutrinos and antimatter and be linked with clouds of cold, molecular hydrogen gas that normally would not harbor such energetic particles.

"If scientists find these stars, they could aid the search to discover and identify dark matter. They could also help solve the mystery of why black holes formed much faster than expected.

"Scientists think unseen, as-yet unidentified dark matter makes up about 95 percent of all matter in the universe. They know it exists because galaxies rotate faster than can be explained by the visible matter within them...."

This is a quibble, but that last paragraph isn't, quite, accurate - as far as I can tell. It's a fact: The visible parts of galaxies spin too fast, assuming that the stuff we see is all that's in the galaxies - and that gravity is all that's pulling the visible matter toward the center of the galaxy.

Dark matter is a pretty good working model to explain the odd behavior of stars and gas clouds in galaxies. And, it may actually exist.

Or, although this is getting more and more unlikely, dark matter may join phlogiston as a reasonable explanation for otherwise-unexplained phenomena - which turned out to be wrong.

The Space.com article discusses the possibility that the first stars were powered by the conversion of dark matter into energy. At this point, it looks like these "dark stars" wouldn't have radiated visible light - but would have emitted gamma rays, as the 2nd paragraph said.

Articles of this sort often use the phrase "dark matter" without trying to explain what it is. Can't say that I blame the writers and editors for that. It's easier to say what it isn't, than what it is.

Dark matter isn't ordinary stuff that's not illuminated. In other words, a rubber ball doesn't become "dark matter" when you put it in a drawer.

Princton's WordNet defines dark matter this way: Dark matter is "a hypothetical form of matter that is believed to make up 90 percent of the universe; it is invisible (does not absorb or emit light) and does not collide with atomic particles but exerts gravitational force".

Then there's dark energy - but that's another topic.

Dark Matter, Dark Stars, Stuff That's Billions of Years Old: So What?

I'll admit that it's hard to see how pushing the envelope of knowledge about dark matter will make a difference in whether or not the New Orleans Saints make it to the Super Bowl this year.

Or keep the sidewalks shoveled this winter.

On the other hand, right now I'm using practical applications of wave and particle physics to write this blog.

Whether or not there turns out to be a practical application to research in physics and cosmology - and, eventually, I'm pretty sure there will be - I think there's value in the knowledge itself. It helps that I'm one of those people who is interested in the universe and how it works.

And, I'm glad there are resources like Space.com, where I can try to keep up with what's known, what scientists are discovering about how much they don't know, and observations that conform (or refute) established models to explain why things happen.

Like, Far Out! Offbeat Galaxies

"Speeding Stars Confirm Bizarre Nature of Faraway Galaxies"
Space.com (August 5, 2009)

"Stars in a distant galaxy move at stunning speeds — greater than 1 million mph, astronomers have revealed.

"These hyperactive stars move at about twice the speed of our sun through the Milky Way, because their host galaxy is very massive, yet strangely compact. The scene, which has theorists baffled, is 11 billion light-years away. It is the first time motions of individual stars have been measured in a galaxy so distant.

"While the stars' swiftness is notable, stars in other galaxies have been observed to travel at similarly high speeds. In those situations, it was usually because they were interlopers from outside, or circling close to a black hole.

"But in this case, the stars' high velocities help astronomers confirm that the galaxy they belong to really is as massive as earlier data suggested.

"Bizarre, indeed

"The compact nature of this and similar galaxies in the faraway early universe is puzzling to scientists, who don't yet understand why some young, massive galaxies are about five times smaller than their counterparts today...."

The article is a pretty good overview of an intriguing situation in astronomy, physics, and cosmology. Until the latest set of observations were made, there was a somewhat comfortable amount of uncertainty about exactly how massive these galaxies were and how far they are from us. It was possible to assume that the masses were lower than assumed, and the distances less.

That set of assumptions allowed existing theories of how galaxies - and the universe - developed to stand.

That was then, this is now.

"...'It's a bit of a puzzle,' [study leader and Yale University astronomer Pieter] van Dokkum told SPACE.com. 'We think these galaxies must grow through collisions with other galaxies. The weird thing is that these mergers must lead to galaxies that are larger in size but not much more massive. We need a mechanism that grows them in size but not in mass.'..."

I've written before, how it's nice when data confirms an existing theory: but exciting and rewarding when data doesn't fit the mathematical models. (March 23, 2009)

The trick is to come up with a revised, or new, theory - a new mathematical model - and see if that matches the real world.

"How Strange, Small Galaxies Lost Their Stars"
Space.com (August 4, 2009)

"Close encounters of the galactic kind may explain the existence of an unusual type of dwarf galaxy, a new study suggests.

"So-called dwarf spheroidal galaxies are small and very faint, containing few stars relative to their total mass.

"These star-deprived galaxies appear to be made mostly of dark matter — an elusive form of matter detectable only by its gravitational influence. Dark matter outweighs normal matter by a factor of five to one in the universe as a whole.

"Astronomers have found it difficult to explain the origin of dwarf spheroidal galaxies...."

Again: observed data and current mathematical models don't quite agree. I'm enough of an old fogy to think that it's the theories that need to be changed.

This article is a look - quick, but pretty good - of another bit of the cosmological puzzle that researchers are working on today.

Some words about dark matter:

"Dark matter" and "dark energy" are phrases that come up now and then in articles about what astronomers, physicists, and cosmologists are thinking these days. Some of those articles seem to have been written - or edited - by someone who learned science by watching the Star Wars movies.

I like the Star Wars movies, by the way: but they're to physics and astronomy what the Terminator movies are to robotics: 'Any resemblance to real science or technology, off-the-shelf or in development, is purely coincidental.'

Where was I? Dark matter and energy, right.

Turns out, "dark matter" isn't just a way for an astronomer to say, "I can't see it." Dark matter and dark energy are pretty good ways of explaining some observed phenomena. If they exist, they're very odd stuff. Dark matter isn't unlit stuff of the sort that the sun and planets are made of; it isn't antimatter; and it's not black holes. As for what it is - that's a matter of some debate.

I found a fairly clear discussion of dark matter and dark energy on the NASA website.

Right now, some enthusiasts notwithstanding, dark matter and dark energy are convenient mathematical models. The models may describe something that's real, or not.

This wouldn't be the first time that additional research showed that a part of the universe 'discovered' by a theory wasn't really there. I remember phlogiston. That doesn't mean that chemistry and physics are a fraud: Just that we don't know everything there is to know. There may be better models than what we have today, which more accurately reflect the underlying reality.

More-or-less-related posts:

• "Lemming Tracks: All Betelgeuse, All the Time"
  (June 10, 2009) (list of related posts updated as they're written)
• "Colliding Galaxies Leave Debris"
  (June 9, 2009)
• "Star Explodes Too Early: Theory May Need Tweaking or Trashing"
  (March 23, 2009)
• "A Serious Search for Other Worlds, Life, and - Maybe - Extra-Terrestrial Intelligence"
  (May 29, 2009)
• " 'What's a Supernova?' - a Pretty Good Overview"
  (May 4, 2009)

Background:

• "Dark Energy, Dark Matter"
  Astrophysics, Science, NASA

Dark Matter, the Gruber Foundation's Cosmology Prize, and Cephid Variables

"Astronomer who found universe's number"
The Australian (June 8, 2009)

"ALMOST 20 years of painstaking intergalactic measuring using pulsating stars to calculate the age of the universe has brought a $US500,000 ($630,000) payoff for three astronomers, including Australian Jeremy Mould.

"Professor Mould, 59, of Melbourne University, is set to receive about $200,000 after he and two colleagues in the US and Britain were awarded the US-based Gruber Foundation's cosmology prize.

"The award recognises their work in discovering one of the most important numbers in astronomy - the rate at which the universe is expanding.

"Using data from the Hubble telescope, which was sent into orbit in 1990, the astronomers discovered over a period of 10 years almost 800 pulsating stars, known as Cepheid variables...."

If you're still reading this post, you're one of those people who really care that the universe is roughly 13,700,000,000 years old, and whether or not it's rate of expansion is increasing, decreasing, or staying the same.

None of which will help you find minestrone soup at the grocery, or which brand of toothpaste is best.

This article is a good overview of what the three scientists found, and what some current thoughts on what dark matter is and how it works.

I understand that dark matter is a viable way of explaining what astronomers have observed, now that we've been able to make more precise measurements of some features in the universe. And, the dark matter and dark energy models may reflect something that's real.

On the other hand, I remember phlogiston. There may be better models, which more accurately reflect the underlying reality.