Hubble Confirms Dark Energy’s Clout

Cosmology isn't my strong suit, but I remember exactly where and when it first sunk in that the universe was out of control. It was August 2000, and I was in Manchester, England, to cover the International Astronomical Union's XXIVth General Assembly.

Recipe for our universe
Here's the recipe for our universe, as presently understood. Ordinary or baryonic matter, the building blocks of atoms and molecules, accounts for less than 5% of all matter and energy. Our universe is dominated instead by unseen and mysterious dark matter and dark energy.
Sky & Telescope illustration
A parade of distinguished cosmologists weighed in on the recent revelation that the redshifts of the most distant supernovae could only be explained if the universe's expansion has been speeding up, rather than slowing down (as you'd expect due to its own self-gravity). This unexpected acceleration, they conjectured, must be due to some kind of force throughout space that opposes gravity itself on very large scales. It came to be called "dark energy."

The big thinkers still don't know what dark energy is, but they've come to accept its reality, thanks to key observational tests such as those from NASA's Wilkinson Microwave Anisotropy Probe (WMAP) mission.

There's also no consensus on what makes up the dark matter — invisible stuff whose gravity holds galaxies together. But it isn't anything like the "normal," proton-neutron-electron (baryonic) matter that we're familiar with.

Whatever their true nature, dark energy (symbolized as Λ) and dark matter must dominate everything else by a large margin for the universe to "work." For those of you keeping score at home, the composition of our universe must be very nearly:

  • 73% dark energy

  • 23% non-baryonic dark matter
  • 4% unseen baryonic matter
  • <1% visible matter (stars, nebulae, and so forth)

Map of dark matter
A reconstruction of how matter (mostly dark) is distributed in a field imaged by the Hubble Space Telescope. Colors indicate mass concentrations (blue is nearest, red is farthest), as derived from weak gravitational lensing of background galaxies.
NASA / ESA / P. Simon / T. Schrabback
The scales of scientific proof have just tipped more firmly toward this recipe. Yesterday a team of astronomers announced that the most distant galaxies appear misshapen due to weak bending, or lensing, of their light by the gravity of unseen dark-matter concentrations along the way. Led by Tim Schrabback (Leiden Observatory), the team used this gravitational lensing to "weigh" the distribution of mass in space over large distances. Not content with spot checks, the researchers included 194,000 galaxies out to a redshift (z)) of 5, corresponding to when the universe was less than a billion years old.

Dark energy: model vs. reality
A comparison of the mass map obtained from Hubble's COSMOS (left) survey with two simulated model maps. The statistical properties (the overall number of mass peaks and how they cluster) of the model dominated by dark energy is the best match for the Hubble observations.
NASA / ESA / J. Hartlap / P. Simon / T. Schrabback
As the team details in an article for the European journal Astronomy and Astrophysics, the galaxies' shapes and distribution only make sense if the universe is dominated by dark energy and cold dark matter — dubbed the ΛCDM cosmology. If you're up for the challenge, the full paper is here — or you can read the less-formidable press release here.

By the way, this work was made possible by a little-known but astounding effort undertaken with the Hubble Space Telescope called the Cosmic Evolution Survey, or COSMOS. From October 2003 to November 2005, HST's Advanced Camera for Surveys acquired 38-minute-long exposures of 575 overlapping fields, collectively covering a patch of Sextans a full 1.3° square.

COSMOS took 1,000 hours of Hubble time to acquire — making it even more ambitious than observatory's famous, but much narrower, "deep fields." At full resolution, the final image is 100,800 pixels on a side — imagine a page in Sky & Telescope 28 feet on a side and you'll get the picture (so to speak).

13 thoughts on “Hubble Confirms Dark Energy’s Clout

  1. John Umana

    Right – the expansion is accelerating rather than slowing down. The cosmos is 73% dark energy, but what does that mean? Dark energy is the repulsive force, what some have called ‘reverse gravity,’ that continues to drive the disparate regions of the universe apart. Most galaxies (other than those that are gravitationally bound) are pulling away from each other. The energy density in the universe in the form of dark energy is just the right amount to explain both the flatness of the universe (proved by WMAP) and the observed accelerated expansion, first observed in the early 1990’s by Saul Perlmutter and his team from observations of supernovae. Dark energy explains many cosmological observations at once, but what is it? ‘Reverse gravity’ may just be a play on words, as there is no such thing. What the WMAP and Hubble teams are observing as ‘dark energy’ is actually a force external to the physical universe that works upon it with a great deal of precision. Dark energy is not a force emanating from within the physical universe.

  2. John Umana

    Right – the expansion is accelerating rather than slowing down. The cosmos is 73% dark energy, but what does that mean? Dark energy is the repulsive force, what some have called ‘reverse gravity,’ that continues to drive the disparate regions of the universe apart. Most galaxies (other than those that are gravitationally bound) are pulling away from each other. The energy density in the universe in the form of dark energy is just the right amount to explain both the flatness of the universe (proved by WMAP) and the observed accelerated expansion, first observed in the early 1990’s by Saul Perlmutter and his team from observations of supernovae. Dark energy explains many cosmological observations at once, but what is it? ‘Reverse gravity’ may just be a play on words, as there is no such thing. What the WMAP and Hubble teams are observing as ‘dark energy’ is actually a force external to the physical universe that works upon it with a great deal of precision. Dark energy is not a force emanating from within the physical universe.

  3. B. Dodds

    Has anyone read the book,”The Electric Universe”.
    In the book it mentions ‘Birkeland currents’.
    Why do we assume the Universe is chaotic rather than a realm carefully engineered by a higher being(s)?
    The ‘ancients’ tapped into this electrical energy and opened stargates to other sectors of the galaxy.
    Unfortunately, a galactic core explosion set off the supernova in Vela.
    This cataclysm ended the Atlantean Golden Age.
    I’m not knocking dark matter, but I haven’t heard its’ mention in books about ancient civilizations.
    Is dark matter real, or just another ‘Coke’, ‘Pepsi’ catch-word?

  4. GoBackToYourHomelands

    It’s the Universe’s REPO ****SPIRIT****MAN & His KIN COMING…to take away all the INVASIVE TOYS that are intruding into the Sacred Space of the Universe…humans can’t even keep track of how they Trashed the Earth…they went OUT to TRASH Space Too!

    It’s the HOPI PROPHECY….that coincides with the Maya-Aztec One!!!!

    Is blessed I minded what my Elders told me growing up!

    Waves to the SACRED Famili UP IN SKY NATION!

    BLESSINGS, BLESSINGS, BLESSINGS!

  5. GoBackToYourHomelands

    It’s the Universe’s REPO ****SPIRIT****MAN & His KIN COMING…to take away all the INVASIVE TOYS that are intruding into the Sacred Space of the Universe…humans can’t even keep track of how they Trashed the Earth…they went OUT to TRASH Space Too!

    It’s the HOPI PROPHECY….that coincides with the Maya-Aztec One!!!!

    Is blessed I minded what my Elders told me growing up!

    Waves to the SACRED Famili UP IN SKY NATION!

    BLESSINGS, BLESSINGS, BLESSINGS!

  6. Ron Skurat

    OK, I’ve been wondering this for ages now – how exactly is dark energy quantified? Even when you use matter-energy equivalence, how do you compare a mass to an acceleration in the expansion of the universe? Is the estimate based on the acceleration being roughly equivalent to the effect of 3x the universe’s mass being “outside” it?

    In high school physics you learn that the interior of an empty shell of any given mass has no gravitational field – is this why they use the term “energy” rather than assuming the existence of extremely distant mass?

    Any cosmologists out there with a clue on this?

    Thx,

    Ron

  7. Major Tom

    @ Ron S

    I’m not a cosmologist but your question got me curious:

    The short answer is that dark energy is likely zero-point energy – i.e. it is a quantum property of all space arising from virtual particles.

    This implies that the ratio of pressure density to energy density is different than for photons.

    From http://www.calphysics.org/zpe.html


    According to relativity theory, energy is equivalent to mass as a source of gravity, thus zero-point energy should gravitate, which according to general relativity means producing a positive curvature in space-time. At first glance one might assume that if there is an enormous amount of zero-point energy underlying the universe, its effect would be to dramatically curve the universe to a minute size…

    Zero-point energy behaves differently. For ordinary radiation, the ratio of pressure to energy density is w=1/3c2, which is customarily expressed in units whereby c=1, and thus the ratio is expressed as w=+1/3. But for zero-point energy the ratio is w=-1. This is owing to the circumstance that the zero-point energy density is assumed to be constant: no matter how much the universe expands it does not become diluted, but instead more zero-point energy is assumed to be created out of nothing.

    A further peculiarity is that a ratio of w=-1 implies that the zero-point energy exerts a negative pressure which, counter-intuitively, leads to an expansion of space-time.

    Now – How does more zero-point energy get created out of nothing?

  8. Roger Miller

    Are these things being made up to explain possible errors in our fundamental laws of physics? We are creating 95% of the universe to explain the 5% that can be verified. Is there a more likely, simpler explanation? Why don’t we have a unified theory of relativity? Glass/water/passing thru a surface can bend light.
    Are we discibing an ant colony and we have only seen an ant?, An iceberg and we’ve never been below the surface?

  9. Arthur Riaf

    Years ago I read a book The Energy of the Vacuum. It seems there is alot going on in “empty space” Particules come and go in the vacuum of space all the time. They seem to come from nowhere and return there all on their own. No help from “GOD” or man needed. The experts used to call the unknown aspects of space the “ether” for lack of understanding what “it” was. Now we have a new unknown, and a problem either in our physics or our observations or our understanding of what we see. After 100+ years of studying the cosmos all we can claim is we know what 1% is? Thats pretty sad and we spent lots of money on this little peek around us. Are we sure we haven’t just been fooled by some other misunderstanding of what we see and have made a series of assumptions that have lead the scientific leaders to a wrong conclusion of how the universe really works or looks? My work in semiconductors has shown me time after time that intuition is a poor performer and most things are not as they appear and usually much more complicated than first thought. Good luck looking for that remaining 99% of our existance. Art

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