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Dark energy survey launches

The Dark Energy Camera photographs galaxies from its perch on the Blanco telescope in Chile.

The Dark Energy Camera photographs galaxies from its perch on the Blanco telescope in Chile.

Reidar Hahn/Fermilab

High in the Chilean Andes, a massive project to probe the nature of dark energy has begun.

The Dark Energy Survey (DES) launched on 31 August at the 4-metre Blanco telescope at the Cerro Tololo Inter-American Observatory. It is one of several new pushes to explore the physical properties of dark energy, the mysterious force that is driving the Universe to expand at an ever faster rate.

Over the course of 5 years, the DES will map 300 million galaxies over one-eighth of the night sky. Its backbone is a 570-megapixel digital camera (pictured), designed to capture sharp images of galaxies and galaxy clusters. Such high resolution is essential because the DES measures weak gravitational lensing, the phenomenon in which light from distant cosmic objects is subtly distorted by the gravity of matter between them and Earth.

Weak lensing can be hard to spot. A competing Japanese-led survey, which uses the Hyper Suprime-Cam in Hawaii, relies on even more detailed images, from an 870-megapixel camera. That camera is mounted on a larger machine, the 8.2-metre Subaru telescope, and so it can image fainter galaxies than the DES can. The DES covers more area on the sky, however. Both surveys aim to measure enough weak lensing to map matter across the Universe — a three-dimensional web that can reveal the fingerprints of dark energy through time.

Along with weak lensing, the DES has a couple of other tools in its arsenal. To beef up the matter map, it will count galaxy clusters at different distances from Earth. And it will probe for distant supernovae, whose otherwise reference light is dimmed as the Universe expands. This technique was originally used to discover the accelerating cosmic expansion, and netted its scientists the 2011 Nobel Prize in physics.

The DES also hopes to muscle in on the territory of studying sound waves in the early Universe. Its sky maps could reveal the effects of pressure waves frozen in place some 370,000 years after the big bang. Those results, in turn, could shed light on how the expansion rate of the Universe changed over time, presumably driven by dark energy.

But other approaches have a head start in this arena. The ongoing BOSS survey and its planned successor, BigBOSS, focus on taking spectra of these acoustic waves, known as baryon acoustic oscillations. BOSS has already mapped these cosmic ripples and provided some of the tightest constraints on dark energy through time.


  1. Report this comment

    James Dwyer said:

    If this study of a ‘dark energy’ effect (the acceleration of universal expansion) is based on the increasing distances between the large scale structure of matter comprised of relatively dense galaxy clusters, it infers that large scale voids separating material structures are increasing in size. If, in the presence of matter, gravity locally contracts spacetime and, in the absence of matter, spacetime expands, then it seems that by increasing the distance between large scales material structures the expansion of voided regions should increase universal expansion without any separate expansion force or energy. Expansion itself should produce the conditions that inherently accelerate universal expansion…

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    Reid Barnes said:

    This article says that the new project “is one of several new pushes to explore the physical properties of dark energy, the mysterious force that is driving the universe to expand at an ever-faster rate.” But how can the properties be explored with a theory that is based on self-contradicting non-Euclidean geometry? See the Note, Are We Ready for a Galaxy Formation Paradigm Shift?

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    Joao Carlos Barcellos said:

    We will make a new approach for an effect known as “Dark Energy” by an effect on gravitational field.

    In an accelerated rocket, the dimensions of space towards movement due to ‘Lorentz Contraction’ are on continuous reduction.

    Using the equivalence principle, we presume that in the gravitational field, the same thing would happen.

    In this implicates in ‘dark energy effect’. The calculi show that in a 7%-contraction for each billion years would explain our observation of galaxies in accelerated separation.

    Lorentz Contraction

    If we suppose that gravitational field contracts the space around it (including everything within), we can explain the accelerated separation from galaxy through this contraction without postulating ‘dark energy’.

    The contraction of space made by gravity would cause a kind of ‘illusion of optic’, seem like, as presented below, that galaxies depart fastly.

    The contraction of space would be equivalent to relativistic effect which occurs in a special nave in high-speed L.M.: With regard to an observer in an inertial referential stopped compared to a nave, the observer and everything is on it, including own nave, has its dimension contracted towards to movement of nave compared to a stopped observer (Lorentz Contraction).

    This means that the ‘rule’ (measuring instruments) within the nave is smaller than the observer outside of moving nave.

    The consequence is, with this ‘reduced rule’, this moving observer would measure things bigger than the observer would measure out of nave.

    An accelerated rocket and its continuous contraction

    In the same way, if we think of an accelerated increasing speed rocket, its length towards movement – compared to an inertial reference – will be smaller, and ‘rule’ within the nave will decrease continuously compared to this observer.

    We would think of ‘equivalence principle’ to justify that gravitational field would have the same effect on ‘rules’ (measuring instruments) as an accelerated rocket would do within the nave, but, now, towards all gravitational field and not, in the case of rocket, only at acceleration speed.

    I.e., the gravitational field would make that all rules within this field would be continuously smaller regarded to an observer outside of gravitational field and this would make, as we can see, these observers see things out of field be away fastly.

    Anyway, even if “equivalence principle” can’t be applied into a gravitational field to show that the space is contracting around it, we can take it as a new effect on gravitational fields and this would explain the ‘dark energy effect’.

    The “dark energy” through gravitational contraction:

    Let’s think what would happen if a light emitted by a star from a distant galaxy would arrive into our planet:

    Our galaxy, as well as distant galaxies, would be in continuous contraction, as seen before, due to gravity.

    A photon emitted by a star from this distant galaxy, after living its galaxy, would go through by an “empty” big space, without so much gravitational influence, until finally arrives into our galaxy and, lastly, to our planet.

    During this long coursed way (sometimes billion years), this photon would suffer few gravitational effect and its wavelength would be little affected.

    However, during this period, our system (our rules) would still decreasing due to gravitational field, and when this photon finally arrives here, we would measure its wavelength with a reduced ‘rule’ compared to what we had had at the moment when this photon was emitted from galaxy.

    So, in our measurement would verify if this photon had suffered Redshift because, with reduced rule, we would measure a wavelength longer than those was measured. The traditional explanation is “Shift for Red” happened due to Doppler Effect compared to galaxy separation speed!

    End of Dark Energy

    Farthest a galaxy is from viewpoint, more time this light will take to arrive us and more shrunken our ‘rule’ will be to measure this photon since it had been emitted; so it would be bigger than wavelength, which would induce us to think of faster galaxy separation speed.

    This acceleration (this new explanation, only visible) from distant galaxies took astronomers to postulate the existence of a “Dark Energy” would have a repulsive effect, seems like they are getting away faster.

    But if acceleration is due to our own scale reduction, this dark energy wouldn’t be necessary anymore, because what makes this separation accelerated is, actually, our own special contraction. This would be the end of dark energy.

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