New Technique Could Track Down Dark Energy

Article written: 21 Jul , 2010
Updated: 24 Dec , 2015


From an NRAO press release:

Dark energy is the label scientists have given to what is causing the Universe to expand at an accelerating rate, and is believed to make up nearly three-fourths of the mass and energy of the Universe. While the acceleration was discovered in 1998, its cause remains unknown. Physicists have advanced competing theories to explain the acceleration, and believe the best way to test those theories is to precisely measure large-scale cosmic structures. A new technique developed for the Robert C. Byrd Green Bank Telescope (GBT) have given astronomers a new way to map large cosmic structures such as dark energy.

Sound waves in the matter-energy soup of the extremely early Universe are thought to have left detectable imprints on the large-scale distribution of galaxies in the Universe. The researchers developed a way to measure such imprints by observing the radio emission of hydrogen gas. Their technique, called intensity mapping, when applied to greater areas of the Universe, could reveal how such large-scale structure has changed over the last few billion years, giving insight into which theory of dark energy is the most accurate.

“Our project mapped hydrogen gas to greater cosmic distances than ever before, and shows that the techniques we developed can be used to map huge volumes of the Universe in three dimensions and to test the competing theories of dark energy,” said Tzu-Ching Chang, of the Academia Sinica in Taiwan and the University of Toronto.

To get their results, the researchers used the GBT to study a region of sky that previously had been surveyed in detail in visible light by the Keck II telescope in Hawaii. This optical survey used spectroscopy to map the locations of thousands of galaxies in three dimensions. With the GBT, instead of looking for hydrogen gas in these individual, distant galaxies — a daunting challenge beyond the technical capabilities of current instruments — the team used their intensity-mapping technique to accumulate the radio waves emitted by the hydrogen gas in large volumes of space including many galaxies.

“Since the early part of the 20th Century, astronomers have traced the expansion of the Universe by observing galaxies. Our new technique allows us to skip the galaxy-detection step and gather radio emissions from a thousand galaxies at a time, as well as all the dimly-glowing material between them,” said Jeffrey Peterson, of Carnegie Mellon University.

The astronomers also developed new techniques that removed both man-made radio interference and radio emission caused by more-nearby astronomical sources, leaving only the extremely faint radio waves coming from the very distant hydrogen gas. The result was a map of part of the “cosmic web” that correlated neatly with the structure shown by the earlier optical study. The team first proposed their intensity-mapping technique in 2008, and their GBT observations were the first test of the idea.

“These observations detected more hydrogen gas than all the previously-detected hydrogen in the Universe, and at distances ten times farther than any radio wave-emitting hydrogen seen before,” said Ue-Li Pen of the University of Toronto.

“This is a demonstration of an important technique that has great promise for future studies of the evolution of large-scale structure in the Universe,” said National Radio Astronomy Observatory Chief Scientist Chris Carilli, who was not part of the research team.

In addition to Chang, Peterson, and Pen, the research team included Kevin Bandura of Carnegie Mellon University. The scientists reported their work in the July 22 issue of the scientific journal Nature.


17 Responses

  1. Lawrence B. Crowell says

    This should work. Dark energy is due to a quantum vacuum effect on spacetime which basically magnifies structures not gravitationally bound. So this is a scaling factor which should preserve this information and remain detectable.


  2. jimhenson says

    supermassive black holes produce the quantum vacuum effect that makes galactic visible matter accelerate by dark energy. Charged particles like cosmic rays, dark matter, and black holes do not expand space. neutral hydrogen will show a huge expansion for the universe, but not if they mapped ionized hydrogen nuclei, negative cosmic rays, and positive cosmic rays mostly formed by supernovas having strong magnetic fields and shock waves that accelerate particles. Dark energy has a negative sign, and gravity is positive. Both forces are not neutral, and are inseperable. One weakens the other gets stronger. why should we expect dark energy to rule “the universe” throughout eternity now that it has taken over? they are likely making an observation and description of evidence, but to say dark energy exists and is expanding the universe faster and faster forever and is a good theory is utter nonsense

  3. Lawrence B. Crowell says

    Dark energy is positive, but the pressure is negative. This is the equation of state which is often stated as w = -1. The negative pressure is what accelerates the universe outwards.

    Dark energy is associated with the cosmological constant, or what Einstein called his constant meant to keep the universe static. If was found the universe was not static, so Einstein abandoned it as his “greatest blunder.” However, it is found the universe is accelerating outwards, and for certain values of the cosmological constant one recovers this result. The scale parameter of the universe expand exponentially as

    a ~ exp(sqrt(L/3)t).

    for L the cosmological constant.


  4. Aodhhan says

    Pressure is an effect, not a cause. To claim the universe is expanding because high pressure is moving to areas of low pressure… you have to be able to show there is an area of low pressure (or at least there is a difference between our universe and where it is going). You also need to show what is causing the higher pressure and the lower pressure. I.e. on Earth, pressure is caused by either air rising or falling; your lungs have a sudden loss of pressure because your diaphram contracts to increase intercostal space.

    At any rate, there is no definitive answer to what is going on… only theories.

    What is always odd to me, is even though we see many galaxies moving at fantastic speeds, they do not appear to be distorted. If there was some “great vacuum” effect, they would elongate (even more so than a group of objects within an atmosphere), just like anything else which is caught in a powerful vacuum.
    This tells me, whatever dark energy is, objects are “riding” on the dark energy (or whatever) instead of being pulled.

    Say a glop of “Jell-O” is your galaxy. If you use a vacuum as dark energy to move it, it will elongate, and even pull apart.
    However, if dark energy is some object like paper, and you put the jell-o on it, and move the paper around, the glob of jell-o maintains it’s shape, and even allows the gravity effects of nearby galaxies to work on each other to continue to merge as normal.

  5. Aodhhan says

    One of the only things we know, which the objects in our universe could be ‘riding’ on is the fabric of spacetime. We also know gravity has a huge effect, and interacts with spacetime. At the same time, (shockingly) gravity is the force we know the least about, and it is far different from the other forces.
    So could the expansion of the Universe be because of gravity, could the expansion just be an affect of what happens to the fabric of spacetime after “a universe” is created? There is even a possibility of another force althogether.

  6. Aodhhan says

    Until we find something else, the “giggle test” for any theory is Einstein’s relativity. If it doesn’t fit in there, it isn’t going to be taken seriously.
    What is cool, is this is a good time to study the Universe. Hopefully soon, the LHC will be up and running without problems and they can continue the search for Higgs. Fact is, all physicists are waiting patiently for this to take place. If we find the Higgs, then we feel fantastic about the standard model. If we don’t find Higgs… then all Hades will break loose.

  7. Lawrence B. Crowell says

    Unfortunately you appear to have some gaps in your understanding. I went to rewatch one of Susskind’s lectures on general relativity last week. His manner of presentation is very good. I found he has now a lecture series on cosmology

    In here some of these questions can be answered.

    Dark energy does induce a frame dragging of particles. This frame dragging is due to the dynamics of spacetime, which has a w = -1 or negative pressure term associated with the vacuum.


  8. Jon Hanford says


    Great that you bring up Susskind’s lecture series which should be of interest to some here at UT. I viewed the series last year and was impressed with the presentation (but, hey, it’s Lenny Susskind). Alex Fillipenko has a series of lectures online (Intro to General Astronomy) that necessarily covers a lot of ground:

    “A description of modern astronomy with emphasis on the structure and evolution of stars, galaxies, and the Universe. Additional topics optionally discussed include quasars, pulsars, black holes, and extraterrestrial communication, etc.”

    Both are great resources for those with an interest.

  9. stan9fos says

    The GBT is an amazing sight; if you ever get the chance to see it in person. Went last year, and as soon as the tour bus stopped at the GBT site, the whole thing proceeded to turn completely around on its base, giving us all an awesome show. Doesn’t happen on command for the tour buses, we just lucked out. They say it’s the largest movable object in the world.

  10. Lawrence B. Crowell says


    I went there to relisten to some of his lectures on general relativity and found he now has these cosmology lectures and a number of lectures on quantum entanglement as well. Lenny’s lectures are on the advanced undergraduate to first year graduate level.

    I see that Fillipenko’s lectures end with interstellar travel. That might be interesting to listen to. i wrote a short book on the physics of sending spacecraft to other stars.

    I presume the Robert Byrd GBT is in West Virginia. The guy certainly knew how to bring the bacon home there. The telescope appears to be the most mechanically complicated one I have seen.


  11. jimhenson says

    Holographic dark energy expansion is a description of entropic kinetic gravity says Koelman, Li, Wang. Temp and Entropy describes kinetic gravity and event horizons. All horizons are fractally self-similar, where the smallest part contains the whole and vice versa. Our perceived location of universal expansion of only 4% visible matter is a quantum field effect information boundary that we observe in two configurations simulataneously. The boundary is the area of the horizon, where entropy S is less then or equal to A / 4 . Four proportional planck areas of information entropy is on a black hole event horizon. borders between one smaller and higher dimension is at a boundary location where the Bousso bound horizon induced entropy relates to size, mass and volume by surface area A. Kashlinksky of nasa believes a giant black hole singularity exists at 150 billion light years distance causing the dark flow and is possibly a gigantic event horizon where time and the incoming acceleration of visible matter slows down in the universe.

  12. Torbjorn Larsson OM says

    The usual “negative energy” comments can’t hide that this is a new and promising observational technique.

    LBC, thanks for the lecture tip!

    but to say dark energy exists and is expanding the universe faster and faster forever and is a good theory is utter nonsense

    The theory where dark energy belongs to is a theory because it predicts observation.

    It is a very good theory because it has eliminated all competition (for now) and is “the standard cosmology”.

    It is your failed description which is “utter nonsense”.

    Pressure is an effect, not a cause.

    Well, cause and effect isn’t really pertinent to prediction and how it is tested. But this, that you can dig deeper, get more predictions and test it more thoroughly to understand it better is why people go on.

    After all, dark energy without an underlying theory is no worse than to have, say, things like “cause and effect” without the same. Luckily theories like special relativity dig deeper into the later “effect”.

    they do not appear to be distorted. If there was some “great vacuum” effect, they would elongate

    But the accelerated expansion is everywhere, since the big bang expansion is everywhere. In the later comments you seem to confuse these two separate mechanisms.

    Until we find something else, the “giggle test” for any theory is Einstein’s relativity.

    Indeed. And has been mentioned here on UT IIRC, dark energy and dark matter has allowed checking and expanding on GR to hitherto untested distances. This is an argument _for_ DE.

  13. jimhenson says

    the standard model can be disproved, try to explain why stars have been found that are spectroscopically older then the big bang, and why highly evolved merger structured galaxies existed so early after the big bang? many undesirable unanswered conclusions observations are derived from the standard model of cosmology where dark energy emerges. A fractal holographic universe needs no divine right of birth beginning 14.6 billion years ago. black hole singularities having more mass and gravity slows down time so that nothing in our 3D observational universe could ever permit us to see an object cross the event horizon of supermassive black holes. this would happen with us observing infalling matter into the massive 150 billion light year distant dark flow producing black hole. An observor located at the 150 billion distant black hole supergiant responsible for the dark flow sees the universe dark energy effects acting like gravity that weaken with distance pulling in less galaxies farther out and at a slower acceleration rate of time as compareably on earth galaxies expand slower nearer to us here on earth. This is the quantum field holographic principle where an observer simultaneously sees two events happening at the same time. It means that holographic entropic kinetic gravity is producing the observation and effects of dark energy and the universe can be considered as flattened space time which is a boundary area between black hole event horizons and a higher extra dimension.

  14. Lawrence B. Crowell says

    The problem of stars appearing older than the universe was solved. This was an apparent paradox or contradiction back in the early 1990s or so. I don’t recall how the controversy played itself out, but this is no longer an outstanding problem.

    Some of what you write has elements of reality in cosmological research, but other parts are strange. The distance of 70 billion light years to the CMB is a manifestation of frame dragging of comoving frames in general relativity. The manifold of space on a Hubble frame, where H = (a’/a) is constant through space, though not through time, is being stretched out like an enormous rubber sheet that has infinite elastic capacity.


  15. Torbjorn Larsson OM says

    Holographic dark energy expansion is a description of entropic kinetic gravity

    Now you are incoherent, contrary to your earlier comment you argue for an existing dark energy.

    Perhaps you think that a blanket barrage will score a hit; unfortunately that doesn’t lead to interesting comments. That you are uninterested in a discussion pales behind your inability to hold one.

    Okay, you fooled me once before this trolling. I will ignore your comments as much as they don’t engage the site.

    Only this blatant fallacy before I part:

    the standard model can be disproved,

    That is the whole point! Empiricism demands testability.

  16. Aodhhan says

    You are partially correct. The Standard Model does have some holes in it. Where in we’ve put in theories to plug these holes and make the math work, so the standard model is not totally fact. We know this, but in order to work we must accept some theories, and work to solve and/or prove they are correct or incorrect.
    This means we don’t believe it 100%, however we accept things for now and move on. Personally I hate the whole big bang/expansion plug, but it is something I accept for now, because the data we have so far works with it.
    Of course, everyone is patiently waiting for the LHC to get up to full power, and see if Higgs exists, and what else may show itself.

    LBC… I don’t have any gaps. I simply brought up another theory. There are a few where the math works. The fact you stated my theory has holes, and you are so antimate about what dark energy actually is (when NOBODY knows for sure) only solidifies my hunch in you being a poser. However, you are an expert at doing research and posting others work. Perhaps you’ll get to the point where you understand it.
    Although, I do like how you talk about the vacuum as being some wild cause; when it is in all theories… since it is the constant which must be used.
    Now, about your -1. The latest theory coming from the CMB, and using the data from WMAP allows the state of dark energy to differ from -1. The math works perfectly with the field equations of general relativity.

    Is it the right one? Who knows… nobody does.. yet.

  17. jimhenson says

    You don’t understand gravity but insist it makes detectable waves. You say that dark energy exists without an explanation except quoting Einstein. What we see as dark energy could be GRAVITY increasingly accelerating only visible matter towards a larger black hole singularity beyond our cosmic horizon. The differences between gravity and dark energy resolve, if mass slows time and the expansion the closer it gets to the monster event horizon we can never see anything enter just freeze. Therefore on earth under far less gravity redshifts increase expansion with distance and time runs faster. Gravity and dark energy would be the same mathematical force that comes from quantum field black hole effects dependent upon the LOCATION of the observer.there cannot be a maximum size for a black hole nor a minimum size so the universe is built on black and white holes called Einstein-Rosen bridges and the 2nd law of thermodynamics which states that everything including all your negative replies are to be trashed and degraded too.

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