PAIRING UP: The orientation of binary galaxies, which ought to be random, can help reveal distortions caused by the expansion of the universe.
Image: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)
-
The Best Science Writing Online 2012
Showcasing more than fifty of the most provocative, original, and significant online essays from 2011, The Best Science Writing Online 2012 will change the way...
Read More »
In the late 1990s, two teams of astronomers stunned the scientific community with the finding that the universe is accelerating in its expansion, somehow overpowering the constant pull of gravity that should be slowing it down. The culprit pressing the cosmic accelerator goes by the name "dark energy," which is an appropriately enigmatic moniker for something that remains so poorly understood.
"We have an amazingly simple picture of the universe," says Princeton University astrophysicist Michael Strauss. "Of course, we don't understand that picture—we don't know what dark energy is, and we don't know what dark matter is." Dark matter, a mysterious entity of longer standing, is some invisible but common substance that reveals itself only through its gravitational pull.
But dark energy—whatever it is—is there, according to a number of measurements taken in the years since its influence was first detected. Now a pair of researchers at the University of Provence in France has added to the body of evidence by confirming dark energy's presence through an independent test that verifies the impact of cosmic parameters on the appearance of pairs of distant galaxies. The research appears in the November 25 issue of Nature. (Scientific American is part of Nature Publishing Group.)
Determining where a distant object lies in space takes a bit of work, because the universe lacks clear distance markers. Astronomers and cosmologists can infer the three-dimensional position of a star or galaxy by measuring its redshift, which reveals not the actual distance to the object but how much its emitted light has been stretched by its recession from us within an expanding universe. Then, with a few assumptions about the curvature and contents of the universe, they can reconstruct the positions of those objects from redshifts. (Space can have positive curvature, like the surface of a sphere, or negative curvature, like the surface of a saddle. Only in a flat universe does space obey all the standard geometry-class rules—the angles of a triangle add up to exactly 180 degrees and parallel lines never meet.)
Decades ago, researchers realized that if they could observe some spherical distribution of objects in the distant universe, they could use any apparent distortion in that sphere to determine the universe's geometry and contents. After all, only with the correct parameters that convert redshift to position would the reconstructed distribution be spherical. The test was proposed in 1979 by Charles Alcock, now at the Harvard–Smithsonian Center for Astrophysics, and the late Bohdan Paczynski, who was a professor at Princeton until his death in 2007. The researchers "pointed out that if you're looking at the distribution of galaxies, and you're looking at the wrong cosmology, you're going to end up with a distorted mess," Strauss says. "Things that would otherwise be round look distorted."
University of Provence cosmologist Christian Marinoni and graduate student Adeline Buzzi, the study's authors, took a new approach to the Alcock–Paczynski test, concentrating on the individual alignment of hundreds of galactic binaries. The orientation of those gravitationally bound pairs of galaxies should be completely random, as viewed from our vantage point within the solar system. "Those galaxies have no idea that you're there watching them, so it's just some random variable," Strauss says. Imagine two points on opposite sides of a sphere—rolling the sphere around reveals all the different orientations a pair of galaxies might take for any particular observer, from a head-on arrangement to a vertical stacking to any flavor of tilt.
But the geometry and expansion of the universe can distort the apparent orientations; without the proper corrections for the universe's makeup and shape, the orientation of galactic binaries will look warped. "The apparent orientation is biased because we measure orientation not with a compass or with a ruler but with redshift," Marinoni says. And redshift depends on just how the universe is expanding.
By tweaking the universe's geometry and the nature of its dark energy, the researchers corrected the picture until the galactic couples were indeed pointed in all directions, as would be expected. With those tweaks, Marinoni and Buzzi confirmed two tenets of the current cosmological model: that the universe is a flat space and that it is dominated by a dark energy, which makes up roughly two-thirds of the universe, that looks a lot like Albert Einstein's famed cosmological constant. (The rest comes primarily from dark matter, with ordinary matter—atoms and molecules—contributing just 4 percent or so to the total makeup of the universe.) "You have a distorted image of these couples, but when you put in the good, flat curvature of the universe, and the good amount of dark energy, then immediately you recover the isotropic [symmetrical] arrangement of these couples," Marinoni says.
The new twist on the Alcock–Paczynski test was not simply a creative leap—Marinoni and Buzzi also had to correct for some pesky redshift effects that come from the galaxies' own velocities, independent of the universe's expansion. Marinoni likens the process to clocking a speeding car on an expanding street; cosmologists want to know not how fast the car is moving on its own but how fast the spreading street is carrying it along. Without correcting for the galaxies' own motions, which are known as peculiar velocities, the binary pairs tend to appear more elongated along an observer's line of sight.
So the researchers measured the orientation of 721 nearby, or low-redshift, galactic binaries in archival data from the Sloan Digital Sky Survey, calibrating them to account for the contribution of the galaxies' own velocities. Armed with the assumption that nearby galaxy pairs move in the same way as those in the distant universe, the researchers applied their calibration to 509 faraway, or high-redshift, galactic binaries from the DEEP2 redshift survey to isolate the true orientation of the distant pairs.
But that assumption leaves a little daylight in the new case for dark energy. If the distant galaxies have different peculiar velocities than the nearby galaxies, the researchers' results would be skewed. Still, the test is a new look at the curious phenomenon of dark energy, and its findings agree well with a mounting body of evidence from different perspectives. "Thus far, the picture has been pretty rosy, in that all the tests that have been done seem to fit together," Strauss says. "But the more tests you have, the better off you are."
See what we're tweeting about
24 Comments
Add CommentThe article states:
Reply | Report Abuse | Link to this"Armed with the assumption that nearby galaxy pairs move in the same way as those in the distant universe, the researchers applied their calibration to 509 faraway, or high-redshift, galactic binaries from the DEEP2 redshift survey to isolate the true orientation of the distant pairs."
It's not explained here that the light from the "509 faraway, or high-redshift, galactic binaries" was emitted into and traversed the hotter, denser conditions of the _early_ universe. In these conditions, why was it presumed that the peculiar velocities (relative to each other) of binary galactic pairs should be similar?
It would seem more reasonable that in a hotter, denser early universe that the independent relative velocities of gravitationally bound objects could be much greater than in the cooler, less dense more recent conditions of the universe.
As the article correctly states:
"If the distant galaxies have different peculiar velocities than the nearby galaxies, the researchers' results would be skewed."
IMO, all test results likely appear positive because they all presume a nearly identical set of unproven assumptions. All test results and the initial observation indicating universal acceleration could all be inversely interpreted.
I contend that the dark energy which is expanding the universe is the same energy which powers atoms. Quantum physics may explain how things work at that scale, but not why. And even at the atomic level, there is no perpetual motion.
Reply | Report Abuse | Link to thisWouldnt' dark energy a form of dark mass and dark mass a form of dark energy. Maybe anti-mass and anti-energy.
Reply | Report Abuse | Link to thisSo if the universe is flat what flatened it? and if it curves in on itself it would have to be a hollow tube except nothing could be in the hollow part not even nothing.
I posit here that dark matter originates in our senses. It is simply not a part of the world we can sense. http://www.youtube.com/watch?v=zPME9_iS28s
Reply | Report Abuse | Link to thisThe missing matter is the incompleteness of our senses. It is in our head.
Peter Reynolds
reflectogenesis@hotmail.co.uk
Interesting that the Universe is termed "flat"- this is a bit like the flat Earth scenario.
Reply | Report Abuse | Link to thisActually it's not quite flat, but because the entire Universe is a billion times bigger than the "observable Universe" (which lays within its own Cosmological horizon), then we perceive it as flat.
This and a lot more are all explained in the following published scientific articles.
Available online
1.An advanced dynamic adaptation of Newtonian equations of gravity. Physics Essays 21: 222-228.
http://dx.doi.org/10.4006/1.3027501
2. String quintessence and the formulation of advanced quantum gravity. Physics Essays 22: 364-377. http://dx.doi.org/10.4006/1.3182733
P.S. you can join the learned journal Physics Essays free for one year and get the articles free.
Yes, this article is consistent with my own hypothesis of what dark energy and dark matter really are. Both are phases of the quantum vacuum at different scales in the sense of wavelet transforms. Positive vacuum zero point pressure gravitating dark matter has a higher density of virtual fermion-antifermion pairs than virtual bosons. Anti-gravitating negative vacuum zero point pressure dark energy is the opposite. Therefore, dark matter does not consist of exotic real particles outside the vacuum whizzing through space and the LHC or any other detector will never find them as a matter of principle. This prediction is Popper falsifiable.
Reply | Report Abuse | Link to thisEureka 999 does not seem to understand what is meant by "flat". It's only the 3-Geometry that is flat on large scales in which the FRW metric is a good approximation.
Reply | Report Abuse | Link to thisReflectogenesis's comment is also not relevant to the physics. It is in Pauli's words "not even wrong." in my opinion.
Reply | Report Abuse | Link to thisI doubt the universe is flat. I suspect the curvature is small and hard to detect that's why it looks flat. Current observation puts the radius of curvature at greater than 70 billion lightyrs. But it does not rule out an infinite radius - a flat universe.
Reply | Report Abuse | Link to thisIf the universe is indeed flat, that would be mindboggling. It means the universe is bounded. It has an edge. Like a flat earth surface where you can "fall" off the edge. But the universe would be a 4 dimensional flat manifold.
I agree and suspect that we can only observe only a very small fragment of the universe, almost none of which actually lies on any contemporaneous surface, but then I also doubt that the expansion of the universe is actually accelerating.
Reply | Report Abuse | Link to thisI suspect it's much more likely that we simply do not have enough information to properly perceive the structure of what can be observed, or its temporal development. These shortcomings do not seem to be a detriment for astrophysicists...
Dr. Strangelove: "If the universe is indeed flat, ... it has an edge."
Reply | Report Abuse | Link to thisNot so. It could wrap around while still being flat. Wraparound allows you to make a finite unbounded space, even flat ones, like a video game where the sides of the screen are connected together. There are many ways to do such connections, leading to many flat topologies.
The flat torus is a good example of this.
"The flat torus is a specific embedding of the familiar 2-torus into Euclidean 4-space or higher dimensions. Its surface has zero Gaussian curvature everywhere. Its surface is "flat" in the same sense that the surface of a cylinder is "flat". In 3 dimensions you can bend a flat sheet of paper into a cylinder without stretching the paper, but you cannot then bend this cylinder into a torus without stretching the paper. In 4 dimensions you can."
In higher dimensions, there are even more possibilities.
http://en.wikipedia.org/wiki/Flat_manifold
http://en.wikipedia.org/wiki/Torus#Flat_torus
http://www.geom.uiuc.edu/~banchoff/script/b3d/hypertorus.html
I think it is plausible that at very high densities of matter, such as a galactic black hole, that gravity has a density limit of expression. Therefore, as one moves much further from the galactic black hole more of its gravity becomes expressed. Thus, the dark matter is only the much more massive galactic black holes. Suns would also have this phenomena, but a much smaller scale.
Reply | Report Abuse | Link to thisSo these researchers took a set of assumptions that essentially mean "our math is bad" and built a further expansion of the dark whatever. How nice. When you get the same observations from 200 light years away or you show me an actual piece is dark matter or power something with dark energy I'll believe it.
Reply | Report Abuse | Link to thisI'm not saying to stop researching it. If it is real then everything changes as far as human potential. That would be great. All I'm asking for is proper labelling. These researchers have made the dark stuff theory more plausible. They haven't proven anything.
copernicus - WTF? Where did you come up with the demonstratably false idea that a gravity well gets stronger the farther away from it you get? If you were correct then the accelerated expansion would not have been observed because expansion would be slowing.
Another way to account for the apparent acceleration of the galaxies or expansion of the universe is that the galaxies are simply falling (accelerating)toward the border of the universe.
Reply | Report Abuse | Link to thisThe finite universe is shaped like a hollow sphere with all its physical laws, matter and energy contained within the sphere. Beyond the border of the universe (the outer circumference of the "sphere") the laws of the universe (inertia, gravity, etc.) can no longer exert their influence to guide and govern, matter and energy. Beyond this border, the "laws of nature" do not exist, therefore nothing can exist, there is no gravity or inertia, etc.. Space itself does not exist.
(search - falling galaxies)
Another way to account for the apparent acceleration of the galaxies or expansion of the universe is that the galaxies are simply falling (accelerating)toward the border of the universe.
Reply | Report Abuse | Link to thisThe finite universe is shaped like a hollow sphere with all its physical laws, matter and energy contained within the sphere. Beyond the border of the universe (the outer circumference of the "sphere") the laws of the universe (inertia, gravity, etc.) can no longer exert their influence to guide and govern, matter and energy. Beyond this border, the "laws of nature" do not exist, therefore nothing can exist, there is no gravity or inertia, etc.. Space itself does not exist.
(search - falling galaxies)
Dark matter can be understood as the relict of light. Dark energy is not necessary if accepted the new theory of Vasily Yanchilin in his book "The Quantum theory of Gravitation (2003), which relates the speed of light to the potential of the total mass of the universe. As the latter is expanding that speed gets smaller and becomes zero at the edge of the universe, where speed an direction become undetermined. Mass limits the uncertainty which is well known for small particles in quantummechanics.
Reply | Report Abuse | Link to thisEinstein's old theory of general relativity is not valid according Yanchilin and this is evident from redshift. Photons leaving the sun, it was thought, have to overcome gravitational attraction while also the second is longer there. So the sum of both phenomenae should be measured but in reality only one is noted.
The Shapiro-delay, retardation of time for a far observer, gives another clue: As a particle the photon turns towards the sun in a parabolic way. That means it becomes richer in energy, because the other way there is redshift. The second is defined as a number of oscillations, a frequency of a chosen atom. Richer in energy euqals higher frequency and so the second near mass becomes smaller, not longer! As a wave the photon seaks a path with least energy, the so-called shortest optical route, which is realized with as big oscillations as possible and a number of these as small as possible. Then in own time on the clock of the
photon a minimum of time is spent.
If the photon would pass the mass linea recta then it has to overcome a larger distance because near mass the unit of length becomes smaller. A more curved parabole requires also a longer path, so the photon chooses in between. This has to be explained still mathematically and then results of a photon as a particle and the photon as a wave are to be compared, these will be the same.
Wow that's stupid
Reply | Report Abuse | Link to thisDURGADAS DATTA published a few very important theories in ASTRONOMY.NET in year 2002/2003. The papers are --MISJUDGEMENTS BY NEWTON ---2/ ETHER=GRAVITY =DARK ENERGY =FIVE GOD PARTICLES THEORY OF GRAVITOETHERTONS. 3/BALLOON INSIDE BALLOON THEORY OF MATTER AND ANTIMATTER UNIVERSES ON OPPOSITE ENTROPY PATH PRODUCING GRAVITOETHERTONS OR FIVE GOD PARTICLES AT THE COMMON BOUNDARY BY ANNIHILATION OF MATTER AND ANTIMATTER. Therefor our space is dark energy itself consisting of five GOD PARTICLES which is swirling and whirling and expanding due to more and more gravitoetherton injection into our universe and we are observing rotation of stars etc in this whirl but directly not detecting the particles except gravity etc. THIS GREAT GRAVITOETHERTONS SOUP IS NON UNIFORM FIELD DENSITY. As such EINSTEIN IS WRONG IN HIS POSTULATES. LIGHT SPEED IS VARYING AND NOT MAXMLIMIT FOR EVEN RELATIVITY. Actually monomagnetic coupling reaction of five god particles can be the source of four forces and one for mass creation. We know as explained by DATTA that GRAVITON pushes each molecule irrespective of molecular weight towards center of earth and we observe equal fall etc. Similarly weak force paticle WEACON REACTS WITH EACH MOLECULE IRRESPECTIVE OF MOLECULAR WEIGHT so that in AVOGADROS LAW we see equal molecule if condition kept similar. ACTUALLY this gravitoethertons are source of all constants and laws to a particular space and as the density is vaying we will see different constants and laws at different parts of the universe. FOR MORE READ THE THEORIES AVAILABLE IN --durgadas datta facebook--.
Reply | Report Abuse | Link to thisI need help with this.if anyone would be a sport. I am by no means an expert in this field so this is where I can't grasp dark matter / energy.
Reply | Report Abuse | Link to thisThe scientific community comes out and announces dark matter. We know its there because we can see its gravity. But if this stuff is the opposite of matter (which is the description) than how can we expect it to have gravity - a common trait of all things matter.
And then their is energy. Why is it dark energy? Can't it just be energy? Where is it coming from? I don't know either but because we can't pinpoint a source we just name it and now it exists? Sounds like religion.
So I guess my question is to someone who follows this much better than me (and I have been trying for years) what the hell are we looking for? Are these claims backed by anything more than theory or are we just blindly explaining things away that could be far more interesting and meaningful than this invisble stuff that we thought we saw once because something was distorted in a gravitaional field across countless units of distance in space. I need schooling!
That certainly involves a substantial amount of internally conflicting assertions -- not that that necessarily invalidates anything you said, just that if any part of it is actually true, then we inhabit a most nonsensical universe indeed.
Reply | Report Abuse | Link to thisWhich, frankly, I have no problem with at all.
Anything that "originates in our senses" is nothing more than a psychotic projection, saying absolutely nothing about anything external to our own skin. Not particularly cosmological, in my view.
Reply | Report Abuse | Link to thisYeah, it confuses the wits out of me!
Reply | Report Abuse | Link to thisHowever, if it helps, the way I understand it is: the universe is seen to be expanding. Theories are constructed around the available observations. Alas, the theories cannot explain the observations unless a huge proportion of the mass 'needed' for the explanation is not detected. Theorists recheck and find nothing immediately wrong with the theory, so they posit that this mass actually exists, but is not detectable, hence 'dark'.
It's not exotic, weird or non-normal matter with strange properties, it's just that it is hiding somewhere where we cannot find it.
The "early" universe, seems to be the most ordered system imaginable. If this is correct, it was hot. Actually it was at zero temperature-an ideal degenerate nuclear matter. True, the top of the "sea" was "hot". If this is true, the temperature of the current universe (of the order of a few degrees Kelvin) is the true average temperature of the universe. Thus, we are really very close to the "homogenous", "isotropic", "ordered" and "low entropy" early universe. This closed system is utilizing more space-time, hence, increasing its entropy. The entropy is produced as non-existent space-time becomes available to the universe. The "future" is available only when it exists, which is "present". The more "past" we have, the more "entropy" the universe has. The "past" is not recoverable, hence, the "dead energy" in thermodynamics and principle of increase of entropy, and only forward asymmetrical "flow" of "space-time".
Reply | Report Abuse | Link to thisDurgadas Datta published a few ground breaking theories in ASTRONOMY.NET in year 2002. Variable gravity theory what he called -MISJUDGEMENTS BY NEWTON .. is proposed a non isotropic ,, non uniform universe of GRAVITOETHERTONS SOUP CONSISTING OF FIVE GOD PARTICLES AND APPEAR BEFORE US AS SPACE. This gravitoethertons as per theory of DURGADAS DATTA IN--BALLOON INSIDE BALLOON THEORY OF MATTER AND ANTIMATTER UNIVERSE IN OPPOSITE ENTROPY PATH .--tell us that these gravitoethertons are produced by annihilation of matter and antimatter at common boundary and injected into our universe as space of five god particles of non uniform density from place to place and produce gravity and laws. That is why a factor of permeability --P-- is introduced in NEWTONS LAW as in COULOMBS LAW. EINSTEIN is wrong by assuming UNIFORM UNIVERSE . We have to study the theories about how AVOGADROS LAW OR MENDELEEFS TABLE OR EVEN GRAVITY IS CREATED BY MONO MAGNETIC REACTION ON MOLECULES IRRESPECTIVE OF MOLECULAR WEIGHT. SO WE CAN EXPLORE OUR OBSERVABLE UNIVERSE WITH THESE NEW IDEAS.--SECRETARY HOME RESEARCH FOUNDER--DURGADAS DATTA.
Reply | Report Abuse | Link to this