Dark Energy Measurement Sheds New Light on Universe's Expansion

Jul 15, 2010 by Kelen Tuttle and Adam Mann
In this optical and X-ray image of galaxy cluster Abell 2219, X-ray brightness from the Chandra X-ray observatory (pink) is superimposed on an optical image showing the distribution of starlight and galaxies in the cluster. The very hot gas that fills the cluster shines brightly at X-ray wavelengths. (Image courtesy Anja von der Linden et al.)

(PhysOrg.com) -- Through observations of massive galaxy clusters, scientists have made the most precise measurements to date of the effects of dark energy and gravity on cosmological scales. This work is an important step toward understanding why the expansion of the universe is accelerating. Something is pushing our universe apart, faster and faster, with each passing moment, and future work using similar methods should determine whether that something is dark energy or a change in the way gravity works on cosmological scales.

The analysis, contained in four papers published this month in the , was led by a team based at the Kavli Institute for Particle Astrophysics and Cosmology, located at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University.

Clusters of galaxies, the largest gravitationally bound objects in the universe, began forming about 10 billion years ago. Because it takes a long time for light from the farthest reaches of the universe to arrive at Earth, the most distant clusters appear as they did when they were much younger, while the closest ones look more their actual ages. By looking at clusters both near and far, researchers were able to study the evolution of clusters and deduce how changes in the universe over billions of years helped shape their growth. The results offer insights into the forces that made the universe we see today.

"As space expands faster and faster, it becomes more difficult for gravity to pull matter together and form structures such as ," said lead author Adam Mantz, a researcher at NASA's Goddard Space Flight Center and former graduate student at KIPAC. By observing clusters at a range of distances, the researchers found that the present-day universe contains fewer clusters than would be expected if the expansion of the universe weren't accelerating.

"At the same time," Mantz said, "whatever is causing the acceleration leaves a distinctive fingerprint on the resulting cosmic structure." Searching for a match to that fingerprint, the researchers compared their observations of galaxy clusters with various models of dark energy, a form of energy theorized to permeate all of space and drive the universe's accelerated expansion. Although the general idea of dark energy is relatively well accepted, there are a variety of models that try to explain what it is and how it works, and a detailed understanding remains elusive.

By combining their observations of galaxy clusters with other cosmological data, the scientists made the most precise dark energy measurements to date. The new measurements are consistent with the simplest model, in which dark energy is a "cosmological constant"—an energy field that is uniform throughout space and time. The idea of a cosmological constant was introduced by Albert Einstein in 1917, but soon fell out of favor. In recent years, the idea has become popular again as a way of explaining the accelerating expansion of the .

The observations also weigh against so-called “modified gravity" models, in which gravity is either stronger or weaker than predicted by Einstein’s Theory of General Relativity. The new results show that the growth of cosmic structure is consistent with the predictions of General Relativity, supporting the view that dark energy drives cosmic acceleration.

“Measuring the histories of both cosmic expansion and structure growth allows us to start to distinguish between different and modified gravity scenarios,” said co-author David Rapetti of KIPAC, who is leading efforts to constrain modified gravity models.

Building on previous work that had examined only small patches of sky, the new study used data from the ROSAT satellite and NASA's Chandra X-ray observatory, which record X-rays emitted by the hot, multi-million-degree plasma that fills galaxy clusters.

"By searching the entire sky for this X-ray emission, we have identified the rarest and most massive clusters, which provide the cleanest and strongest cosmological signal," said Harald Ebeling of the University of Hawaii's Institute for Astronomy, a coauthor on the papers. In addition to its large data set, the research incorporates modeling advances that make the results more robust.

Over the past decade, observations of supernovae, the cosmic microwave background and , as well as earlier X-ray observations of clusters, have all pointed to an accelerated expansion. Independently detecting the effects of acceleration on the growth of clusters provides an important consistency check.

"The suite of cosmological observations probe different physical systems, so the agreement between them is very encouraging," said co-author Steven W. Allen, associate professor of physics at KIPAC. "The combination of high quality and complementary observations offers our best chance to understand cosmic acceleration."

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Parsec
4.4 / 5 (10) Jul 15, 2010
Having several independent lines of evidence with consistent results strongly increases my confidence in the reality of dark energy.

I must say however I would be a lot more comfortable to discover that this was a global conspiracy to suck more salary money because I do not like dark energy. It messes with my simple view of the universe.

I know how climate deniers feel I guess. But I will go with the data, regardless of how I feel about it. Probably why I also believe in AGW.
yyz
4.7 / 5 (10) Jul 15, 2010
"Having several independent lines of evidence with consistent results strongly increases my confidence in the reality of dark energy."

Couldn't agree more! As multiple lines of evidence began to converge, it became much harder to explain away the observations. DE is not pretty, elegant or expected, but we need to deal with what is. I partially blame the 'dark' part of the monniker, as dark matter 'deniers' had another term to rally against (regardless of the difference between DM and DE). Maybe quintessence will win out: http://en.wikiped...physics)
Pete83
4.7 / 5 (7) Jul 15, 2010
Just wanted to add I agree with you two strongly as well! Nobody really wanted to admit this 10 years ago, but the cosmological constant is back in what seems to be such a very strong way. It's hard to deny it's existence when you look back far enough and you begin to end up with blue shift, because you are looking back to a time when gravity was winning for a short while.

Astrophysics is just too much fun.
Caliban
3 / 5 (4) Jul 15, 2010
Well, it may, or may not be, a cosmological "constant", given that there appears to be, and has been, some variability over time.

At any rate, there is either some fundamental aspect of the visible universe that has not been perceived and defined, or there is another aspect that is truly undetectable, and will therefore have to be infered before it can be incorporated.

YYZ's quintessence or zero-point field both seem like useful starting points. ZPF I prefer, because it's energy input increases as the volume of space increases- if I understand the concept, that is.

I have hopes that this will lead to the discovery of a universal energy source. Limitless "free" energy would solve an abundance of key problems for humanity.
rwinners
1.9 / 5 (8) Jul 16, 2010
...
At any rate, there is either some fundamental aspect of the visible universe that has not been perceived and defined, or there is another aspect that is truly undetectable, and will therefore have to be infered before it can be incorporated.


With the 'dark' stuff so completely undefined (ok, assumed as matter/energy we cannot see or understand), I have a very hard time taking anything that the cosmologists say about the "universe" seriously.
Personally, I think the 'more salary' or perhaps 'more grants' idea is pretty close to the fact.
You can't just 'infer' stuff to fit. If dark 'stuff' exists, what are it's properties, other than those that scientists grant it in order to make their calculations work?
Frankly, when we get beyond the local group of galaxies, cosmology is as much like science fiction as science fact.
Parsec
3.7 / 5 (6) Jul 16, 2010
rwinners - science always proceeds in fits in starts. Neutrinos were postulated solely because of unexplained missing mass in certain nuclear reactions involving the weak force. Just because something is not currently understood doesn't mean that its properties cannot be inferred indirectly. In the case of dark matter and dark energy we now have a lot of completely unrelated ways that we can tell something is happening, and as time proceeds we will learn more.

Only small minds limit themselves to imagining what is known as the entirety of what there is to know.
bluehigh
2.1 / 5 (7) Jul 16, 2010
DM and DE are mere untested unsubstantiated wild guesses. Recent reputable research has also shown that many of the ways we deduce the existence of the dark side may be due to flaws in measurements.
Yes indeed it is the small minded that refuse to accept that someones research grant is due for renewal.

frajo
4.7 / 5 (6) Jul 16, 2010
While I agree that there are no better explanations than those of the current standard cosmological model for the known observations I permit myself to be a bit more demanding.

I'm not satisfied as long as the list of explanations for the known astrophysical/cosmological phenomena is much shorter than the list of unsolved problems. To be honest, we have to encompass the list of all unsolved problems in physics, not just of the astrophysical ones.

I'm afraid the explanations presented up to now might be "insular" in that they allow to understand only isolated problems but block us from looking at "the whole picture", combining answers to the hierarchy, the homogeneity, the missing mass, the number of quark-lepton generations, the generation of mass for the elementary particles, the baryon asymmetry, the vacuum energy, the dark flow problems and many more.
kevinrtrs
1 / 5 (10) Jul 16, 2010
Just to let those with open minds know that the Bible has about 17 references to God "stretching out the heavens".
So though most of you wouldn't be believers in the Bible, it should certainly give you some food for thought.
Isn't it just rich that the "dark" energy cannot be seen?
By the way [most of] the verses in the Bible all seem to state the that the action of stretching was a once off thing and that the act has been completed. So we might just be seeing the effects of that stretching at the moment. here's some verses: Psalms 104:2, Isaiah 40:22, Isaiah 42:5, Isaiah 45:12, Isaiah 51:13 , Jeremiah 10:12 , Jeremiah 51:15, Zechariah 12:1.

OK, you can now go ahead and shoot it down.
frajo
4.4 / 5 (5) Jul 16, 2010
OK, you can now go ahead and shoot it down.
You are not talking physics here. I don't mind when you try to reconcile scientific thinking with your religious thinking. But it is not scientific to draw scientific conclusions from non-scientific thinking. Thus, I don't shoot your comment down. I just note that your comment is OT.

PS: We could raise your comment onto the scientific level by moving over to the psychological needs of human beings.
Yellowdart
1.7 / 5 (11) Jul 16, 2010
"You are not talking physics here.


Eh, "stretching out the heavens" would have a physical process. It certainly suggested the universe was expanding or expanded long before we had the technology to prove it. No "reconciliation" is needed when it actually agrees with modern science.

Expansion, should cause clusters and galaxy's to fly apart, esp after billions of years. They havent. So we are left with two options at the present. One is that dark properties exist and they have been the missing force keeping the universe in its formation.

The other is that, the universe isnt that old. Which is that case means dark matter/energy isnt needed, and we have a solid understanding of gravity as it is. But thats no fun for most of you :)
loreak
5 / 5 (1) Jul 16, 2010
I like the idea of the ZPF, but doesnt the energy difference between what we see and what the ZPF would predict vary by many many orders of magnitude?
Skeptic_Heretic
5 / 5 (2) Jul 16, 2010
Personally, I think the 'more salary' or perhaps 'more grants' idea is pretty close to the fact.
You can't just 'infer' stuff to fit. If dark 'stuff' exists, what are it's properties, other than those that scientists grant it in order to make their calculations work?
Frankly, when we get beyond the local group of galaxies, cosmology is as much like science fiction as science fact.

You sound similar to those zealots who demanded the death of Bruno for insisting through inference that the Earth was not the center of reality.
Just to let those with open minds know that the Bible has about 17 references to God "stretching out the heavens".
So though most of you wouldn't be believers in the Bible, it should certainly give you some food for thought.
Or it could be a prosal reference to display inhuman power in an imaginary figure. IE: Zeus controls the lightning of the skies.
Skeptic_Heretic
4 / 5 (4) Jul 16, 2010
The other is that, the universe isnt that old. Which is that case means dark matter/energy isnt needed, and we have a solid understanding of gravity as it is. But thats no fun for most of you :)
Actually it would be fun for us if that was the case. We enjoy learning new things. The issue here is not that it woouldn't be fun, but that it wouldn't be reality.
jonnyboy
2.8 / 5 (8) Jul 16, 2010
IMHO, eventually they will come to the realization that the universe is being pulled apart by massive gravitational forces outside of our 13 billion year old "light bubble" and not pushed apart by some magical force.
Jigga
1 / 5 (5) Jul 16, 2010
Dark energy is rather trivial consequence of the two concepts: the omni-directional space-time expansion and constant speed of light. If the space-time expands, then the speed of light will decrease in it, which creates an illusion of accelerated expansion of space-time.

http://tinyurl.com/32pjchk

The same effect is responsible for the fact, the diameter of observable part of Universe is actually much larger, then the product of constant speed and universe age (~ 156 Gly instead of 13.7 Gly)

http://www.space....524.html
mrdualspace
not rated yet Jul 16, 2010
It is hard to find a documented cause/effect, that with such a monumental phenomenon, there must have been discovered a functional disparity between the observed luminance and the observed red shift that we could analyze for its validity. Mark well, there is only red shift and intensity. BTW what red shift function are they using?
I have my doubts that the universe could do any such thing.
jackpol
Au-Pu
2 / 5 (4) Jul 17, 2010
As far as something "pushing our universe apart faster and faster" is concerned all it requires is that space itself is slowly expanding and the rate of expansion is quite slight.
If space were to increase its volume by a miniscule 1 kilometer in all directions over a volume of space that was a 45,000 light year cube per second then by the time we observed matter at 13.5 billion light years distance it would be retreating from us at the speed of light.
Isn't that what we observe as a reality?
Whether this is a cosmological constant or something else I do not know but we do not have to look for something huge.
It will most probably be associated in some way with gravity. So in order to understand this we will need a better understanding of gravity.
So called dark energy is more likely to be an aspect of gravity than anything else.
So by all means let us keep looking for it, but let us look in the right places.
veepy
2.3 / 5 (3) Jul 17, 2010
When scientists measure acceleration of matter away from the center of our universe, do they automatically assume that there is only empty space outside our universe? What if matter lies around our universe that is so massive that it is responsible for the acceleration measured in our galaxy? Until we know more about what lies beyond the limits of our universe, it seems a little premature to assume that some unseen magical energy is causing this acceleration. The simplest solution is frequently more plausible.
HeloMenelo
1.5 / 5 (8) Jul 17, 2010
Veepy i agree, how could a conclusion be made
when everything that needs to me observed and measured cannot be observed and measured.

It's like putting on your fan running off your wall powersupply, you know the wall is supplying power to your fan.

You can't see the coal powerplant many miles away.

And compared to the universe's expansion, and our observational limit,
You don't even know what is there or what it is that could be driving the expansion. Because you cannot get to to there or observe anything outside our visible universe.
Thraxzer
not rated yet Jul 17, 2010
This is my first post ever, and I'm no physicist, but could it be possible that empty intergalactic space has a negative mass? Like an energy hole or something. What would be the implications?
Skeptic_Heretic
1 / 5 (2) Jul 17, 2010
This is my first post ever, and I'm no physicist, but could it be possible that empty intergalactic space has a negative mass? Like an energy hole or something. What would be the implications?

Interesting thought, but, if that was the case what causes negative mass? Is negative mass even possible? Effectively you'd have to find and define a measurable anti-gravity.

Implications would be that every calculation of motion in the universe would have to be entirely wrong resulting in no successful space flight.
Ober
2.3 / 5 (3) Jul 18, 2010
OK, here's some wild speculation for you to throw around.

I shall assume the universe is a sphere which moves forward in time. As it moves forward in time it expands.

Next the spherical universe is filled with VIRTUAL PARTICLES. Matter and anti-matter pairs, which pop into existence, then spontaneously annialate. We see evidence of this near black hole event horizons called Hawking radiation.

Recently software was created to 'CAD-like model' structures and calculate the Casimir force. For the first time, a REPULSIVE Casimir force was calculcated for the shapes computed.

So here's the idea. What if all the virtual particles are DARK MATTER. That is they don't really exist, but their presence can be felt.
These Virtual particles exert a pressure on everything. This is thus a repulsive force from every virtual particle on every other particle.

In a sphere with nothing outside it, this would cause an outward expansion.

As space expands, MORE VP's fill in the void.
Ober
1 / 5 (2) Jul 18, 2010
This creates even greater outward pressure, or an accelerating universe.

Black holes however, may get pushed along on this Universal Wind, taking their stars with them.

The further away a galaxy is, the greater the pairs of virtual particles exist between them, causing a greater repulsion between them. To an observer this appears as galaxies moving faster away from us, the further they are, ie RED SHIFT.

Now I'm unsure here, but black holes may thus appear as PRESSURE HOLES, in this virtual particle soup causing outward pressure.

The Casimir force involving a disc with a hole in the middle against a similar structure may repel or attract. Even though Casimir force is weak, summed over huge intergalactic space, it may be huge. What if galaxies and black holes are analogous to the disc and hole above.

What happens in areas of space where the virtual particle wind tries to apply pressure to a black hole. It might appear as an eclipsed area of spacetime.

What ya reckon?
FainAvis
1 / 5 (1) Jul 18, 2010
Suppose life evolved on a planet in one of those extreme redshifted galaxies. When they look out in one direction do they see no stars and galaxies out there, and looking toward us lots of stars and galaxies? Do they see the curvature of the edge of the universe like an expanding surface?
Skeptic_Heretic
3.8 / 5 (4) Jul 18, 2010
Ober, that isn't dark matter. That is a potential candidate for dark energy and is already being explored.

Secondly you make a rather horrid mistake. We have not observed Hawking radiation.
Jigga
1 / 5 (4) Jul 18, 2010
.. could it be possible that empty intergalactic space has a negative mass? Like an energy hole or something. What would be the implications?..
Technically yes, because space inside of our universe is of negative curvature (a sort of energy "bubble" or sphere interior) - whereas the observed objects are of positive curvature (a "spheres from outside" or "blobs").

The implication will be, massive objects would collapse by their gravity with increasing speed and the space-time would expand by its antigravity with increasing speed - which is basically what we are observing by now.
Jigga
1 / 5 (4) Jul 18, 2010
.. Do they see the curvature of the edge of the universe like an expanding surface?
They would observe distant galaxies redshifted in the same way, like we do. Which implies that no Big Bang occurred and expansion of space-time is a relative artifact of light dispersion, similar to dispersion of ripples at watter surface.

http://www.pitt.e...ples.jpg
Sferics
not rated yet Jul 18, 2010
If at the big bang, the universe existed as the thin surface of a bubble which holds all four familiar dimensions. In the center of the bubble an unknown vector dimension which is expanding outward from the point of the big bang as a radius. As the radius of this expanding vector increases so would the surface area of the skin of the bubble, thus our four dimensions in our observable universe would also expand at an accelerated rate. This could explain dark energy
trekgeek1
3 / 5 (4) Jul 18, 2010
Just to let those with open minds know that the Bible has about 17 references to God "stretching out the heavens".
So though most of you wouldn't be believers in the Bible, it should certainly give you some food for thought....

...By the way [most of] the verses in the Bible all seem to state the that the action of stretching was a once off thing and that the act has been completed. So we might just be seeing the effects of that stretching at the moment.


That's ridiculous. The Qur'an obviously eludes to the creation of the universe. It's not possible for two separate groups of people to overreach with their imaginations and conjure up ridiculous connections between metaphors and scientific observation after the fact. Is it?

Here's an idea, if it's all there in the bible, give science a break and you make the next breakthrough. Why study science if you have the answers? Also, cross check our quantum theory with the bible, see how we did.
kevinrtrs
1 / 5 (3) Jul 19, 2010
Why study science if you have the answers?

Like I said, "for those with open minds...."
Skeptic_Heretic
2.3 / 5 (3) Jul 19, 2010
Like I said, "for those with open minds...."
An open mind requires objectivity, something that you lack.
frajo
1 / 5 (2) Jul 19, 2010
An open mind requires objectivity
No, it doesn't. An open mind requires empathy, first of all. Objectivity doesn't help you to understand another being. It may help torturers and other war criminals to "refine" their methods, though.

I happen to know analphabetic people who are more open-minded than all those "objective" human experimenters of past and present times.
2Crazy2bTrue
not rated yet Jul 19, 2010
Dark matter, dark energy, dark gravity... See where all this darkness leads to, to an astronomers dark mood. And this is the point where we nono's can come in...

One thing is for sure in the universe, everything is on the move (often in orbit) somehow. Maybe on a more astronomical scale things are still in orbit but not in a three but in four dimensional space. Watch an hypercube rotating and see how space appears and disappears. This could give us un answer about what happens here. Something(s) are in orbit in hyperspace and as a result of this action (parts of) our universe are shrinking or expanding.

Work it out, boys and girls, I wish you the best.
Skeptic_Heretic
3 / 5 (2) Jul 19, 2010
One thing is for sure in the universe, everything is on the move (often in orbit) somehow. Maybe on a more astronomical scale things are still in orbit but not in a three but in four dimensional space. Watch an hypercube rotating and see how space appears and disappears. This could give us un answer about what happens here. Something(s) are in orbit in hyperspace and as a result of this action (parts of) our universe are shrinking or expanding.
That'd be 5d space, not 4d.
Ethelred
3 / 5 (6) Jul 19, 2010
Like I said, "for those with open minds...."


Keep an open mind. But not so far open that your brains fall out.

Since you think the world is VERY young I would say that you don't have an open mind since ALL the evidence is against that. Please do not ask people to keep an open when you adamantly refuse to even unlock the door.

Ethelred
sok
1 / 5 (2) Jul 19, 2010
Our Universe accelerates upward by the Dark Forces of Gravity. It falls up, up and away from itself and into every direction. It falls away from a center that is everywhere, and into a Dimension we can’t quite grasp, yet we still have time. In this Dimension we might experience the natural resting state of our Universe as one of ‘free fall’. But from the other end of a Greater Universe, along the axis of its Greater Dimension, our Universe still appears as a Big Bang. So go figure.
Skeptic_Heretic
2.3 / 5 (3) Jul 21, 2010
An open mind requires objectivity
No, it doesn't. An open mind requires empathy,
Certainly not. Empathy is the first method by which your mind becomes closed.
Objectivity doesn't help you to understand another being. It may help torturers and other war criminals to "refine" their methods, though.
What a low blow and intellectually dishonest statement from you. Objectivity allows one to define attributes of an item, person, process, etc without preconception. Your statement on torturers is also highly inaccurate. The greatest form of torture is emotional or mental, and in order to be effective at either you would require the ability to use your empathy to determine the most painful method of interaction. Again, I'm shocked that you would assert as you had above.