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A little over a decade ago astronomers discovered something astonishing. They were looking at exploding stars in the distant universe, and they noticed that not only is the universe expanding from its big bang origin, but its expansion is actually speeding up.
Scientists call the culprit behind this acceleration dark energy. It's a mysterious entity that fills the universe and pushes things apart. And there seems to be plenty of it: recent estimates say that the universe is more than 70 percent dark energy. That's a pretty extraordinary claim, and it demands extraordinary evidence.
A project called WiggleZ is helping to validate dark energy's existence. WiggleZ scientists have made a 3-D map of more than 150,000 galaxies near and far to trace the universe's evolution over time. [Chris Blake et al., "The WiggleZ Dark Energy Survey: The Growth Rate of Cosmic Structure Since Redshift z=0.9"]
The WiggleZ team looked at how readily galaxies clump together, how much space separates those galaxies, and how things have changed over the past seven billion years. They found that something is indeed driving things apart. And dark energy fits the bill nicely. So dark energy has passed an important reality check. But what is it? On that front, scientists remain in the dark.
—John Matson
[The above text is an exact transcript of this podcast.]
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22 Comments
Add CommentIs "dark matter" just the "ether" of our generation day?
Reply | Report Abuse | Link to thisClasen: this is dark energy, not dark matter. And, no: both "dark energy" and "dark matter" are essentially placeholders, for observations we can't yet explain. The idea of the "ether" was the opposite - an assumption about the fabric of the universe that turned out not to fit observations at all.
Reply | Report Abuse | Link to thisHow can a 3-d topological map of the near and very far, constructed from observations of recent and distant past EM emissions, represent the actual 4-d topology of observed objects? The universe has not been captured in a 'Polaroid Moment', yet astronomers seem to pretend that it has been...
Reply | Report Abuse | Link to thisThanks for the link to the research report - I look forward to reading it.
*"The action of dark energy is as if you threw a ball up in the air, and it kept speeding upward into the sky faster and faster," said Chris Blake of the Swinburne University of Technology in Melbourne, Australia.*
Reply | Report Abuse | Link to thisThis thinking is in the link:
http://www.nasa.gov/mission_pages/galex/galex20110519.html
Unfortunately, having reviewed the referenced research report, I have to admit that I understand almost none of it. IMO, it is an exceedingly parochial description of fitting 18 analytical models to their data to check its consistency with contemporary cosmological views. But, I can't really tell. The only thing I really got out of it was that 3-d topological maps of the spatial distribution of galaxies indicates that galaxies are becoming more densely clustered in time as the bubbles of space between them become larger. I deduced this from the statement:
Reply | Report Abuse | Link to this"One of the most important observational datasets for
addressing this issue is the large-scale structure of the galaxy distribution. The clustering within this distribution arises through a process of gravitational instability which acts to amplify primordial matter fluctuations. The growth rate of this structure with time is a key discriminant between cosmological models..."
That's about it for me. That gravitation would in time increase the relative localization of massive objects while the expansion of spacetime increases the intervening space between material structures composed of clustered galaxies does not surprise me at all, since the localized effect of gravitation diminishes with distance and the effects of expansion on spacetime accumulates, regardless of whether that expansion is accelerating or decelerating.
So, let me go back to the original type Ia SuperNovae studies that concluded that the expansion of the universe is accelerating. In simple terms, standard cosmological models that predicted galaxy distance from redshift agreed with the more reliable estimation of galactic distance based on type Ia SNe luminosity for more recent light emissions from nearby galaxies without using a cosmological constant parameter. However, more distant galaxies' distance estimates disagreed unless a cosmological constant was used to indicate acceleration.
If I understood correctly, it was the more ancient light emissions from more distant objects that indicated an increased rate of expansion. However, those more ancient light emissions from more distant, high-z objects represent the prevailing conditions looking back to the EARLIER universe, whereas the more recent light emissions from nearer, lower-z objects represent only more recent conditions of expansion.
From that perspective of the observational data, I can only conclude the the type Ia SNe data indicated that the expansion of spacetime has DECELERATED, as originally expected, not requiring any dark energy.
FYI - The WiggleZ home page is: http://wigglez.swin.edu.au/site/
Reply | Report Abuse | Link to thisAn overview: http://www.science.org.au/nova/115/115key.html
A related COSMOS article with links to other articles:
http://www.cosmosmagazine.com/news/4341/debate-over-dark-energy-reality-reignited
There is also another research report:
Reply | Report Abuse | Link to thisBlake et al, (2011), "The WiggleZ Dark Energy Survey: testing the cosmological model with baryon acoustic oscillations at z=0.6",
http://arxiv.org/abs/1105.2862
The aether of preEinsteinian Physics is the correct solution. We do not need to create science fiction to explain nonsense with nonsense. See Sciam March 2009:
Reply | Report Abuse | Link to thisEinstein's relativity theory is wrong nothing in this Universe can be explained with RT. NASA scientists cannot be so stupid to believe science fiction explanations.
Hartwig Thim
Good reply.
Reply | Report Abuse | Link to thisWeird viewpoint. Sorry.
Reply | Report Abuse | Link to thisBefore we accept the idea that dark energy exists do we not need to verify the expansion of the universe. If one applies Einstein's mass to Newtons equations, something I call the Newton-Einstein Relativistic Optic, one finds that the distance away from us will produce a red shift, and the farther away the greater the shift.
Reply | Report Abuse | Link to thisSo don't we first have to reconcile this conundrum?
The thing I find most difficult to comprehend when looking back in time billions of years via telescopes of various kinds, is if the data received now has been travelling for billions of years the universe must have been much smaller when its journey commenced. Our particular portion of space would also be much closer to the object being observed at that time. The more distant in time & space, the closer we would initially have been. Unless expansion is at an incredible rate, a substantial proportion of the speed of light, why has the radiation now being detected not long since passed us by? I have not put this particularly well but I hope an astronomer reading this understands what I am querying & is able to explain.
Reply | Report Abuse | Link to thisSmoot had measured the CMB and called it the "New Aether Drift", the Aether he had detected was not so new it was the old Lorentz Aether for which Maxwell wrote his euations. Andira, you think it is a "Weird viewpoint" the Nobel Comittee will also "appreciate" Andira's comment.
Reply | Report Abuse | Link to thisIn his famous speech Einstein gave on May 5th 1920 in Leyden he brought back the aether which is in his words essential for light propagation. Andira does not know that as well.
Reply | Report Abuse | Link to thisI think you've stated the issue very well, but then I'm not an astronomer. I've also pondered this question: the only solution I can imagine is that light emitted in our direction was detected long ago. The light we now detect from distant objects must have been directed elsewhere, having never been detected before now.
Reply | Report Abuse | Link to thisThat light not directed towards us is now reaching us seems to require that differences in the direction that light was emitted and the direction that our galaxy has been traveling account for our later interception of that light.
I can only imagine an example early spherical universe which was radially expanding (this concept is considered to be taboo). In this universe, galaxies are initially moving primarily in the local direction of radial expansion. However, as the universe expands, this initial radially directed expansion would become increasingly omnidirected, since its radial expansion necessarily introduces increasing lateral expansion of spacetime (between radii).
The galaxies are universally moving in somewhat different directions (along with varying 'peculiar' motions produced by localized gravitation).
Unlike galaxies, light is self-propagating, independently moving in its own direction. However, just as light can, in effect, be locally curved by gravitational effects, it should also be potentially redirected by spacetime expansion.
While the universe is now considered to be 'flat', that may largely be an effect of scale. The earlier, smaller universe could have been very curved. That curvature applied to expansion in conjunction with light's independent self-propagating direction could have imparted large scale, universal curvature to the path of distant light.
These factors could have combined to allow ancient light emitted from relatively nearby objects to reach us now. In addition, our determination of object distances is based only on effects impart to detected light during its traversal of expanding spacetime (redshift & luminosity). We actually can only derive the traversal distance of detected light: we only presume that distant light travels 'in a straight line' through expanding spacetime.
Now, that could radically affect our perception of our observations of the distant (ancient) universe! In this case, how representative would a spatial topographical model of galactic observations be? There certainly could be a developing structure imparted to the 'cosmic web', but we'd be a long way from understanding how that structure is configured.
But I'm not sure...
Carlyle,
Reply | Report Abuse | Link to thisThink of stretching out a rubber band, at a constant rate. Two points right next to each other on the band won't move apart very fast at all...but points farther apart on the band will move away from each other much faster - even though the overall stretching is constant! So yes, the light that has taken billions of years to reach us is from regions of space that were further from this one, at the time; they started out further away on the rubber band. And yes, that means that the edges of the observable universe are expanding away from us at close to the speed of light, whereas the distance between you and me is expanding at a rate too small to measure. It's a big place, this universe!
Love the placeholder idea. I've been calling them theories in response to the articles that call them discoveries, but placeholder is better.
Reply | Report Abuse | Link to thisSeems I read somewhere that the acceleration hasn't been constant, but supposedly started a few billion years ago. Anyone heard of an explanation for that curious event?
"A project called WiggleZ is helping to validate dark energy's existence."
Reply | Report Abuse | Link to thisIt seems to me that all the project is doing is confirming that existing observations are accurate. The term "dark energy" is nothing more than shorthand for a phenomenon that we don't understand, so pretending to validate its existence is pretty meaningless. It would be more appropriate to say that "WiggleZ is helping to confirm the phenomenon of the increasing speed of the expanding universe", but that makes for a pretty dull article.
I detest the terms dark energy and dark matter...
Stand in the bottom of a 100 foot deep well in Arizona. Now describe the Andes mountains as you see them. Until we get out among the stars all of our cosmological mumblings are pretty much the same fantasy as presented in my sentences above.
Reply | Report Abuse | Link to thisI have intuitive trouble with this concept that energy within the universe is pushing matter apart. It makes sense that matter would spread to fill the void beyond it's perimeter. I look at that as being sucked apart or pulled from the outside, not pushed from within. So the absence of matter and energy outside the perimeter is the force doing the sucking.
Reply | Report Abuse | Link to thisbtw, I'm not postulating a theory, just raising the point of what I don't understand in hopes that someone may help me see it better. Perhaps other laymen have the same problem.
Reply | Report Abuse | Link to thisHumans love to name things they cannot explain. Like fish in an aquarium they see a distorted view of the world, and they name the distortion as if that will help to explain it.
Reply | Report Abuse | Link to thisI think the "distortion" is due to the effects of gravity on photons. Photons have gravity, which makes the distortion more complex. I think dark matter is simply photons, which are in orbit around dark stars. Other photons, that have gravity, are in transit, but have gravity.
As photons travel from very far, mutual gravity causes a red shift as they separate in space. Since they have gravity, our measurement of how far they have come is distorted in angle. This means that the universe is not expanding. Calling the distortion "dark energy" is wrong. A better name is simply gravity distortion.
Instead of naming things, we should study photon gravity.