Dark Energy Detectives


We start the night’s work early with an inter-continental tele-conference before dinner. After dinner, we prepare the software and telescope until sunset, when the hunt begins. Working through the night (and through a few pots of coffee and bags of cookies), we emerge a few hundred images closer to understanding dark energy and its effects on the celestial objects deep in the night sky. Just after sunrise, we hit the hay, but our minds often keep crunching numbers or sifting puzzles that arose during our observations, as the work from our night bleeds into our dreamscape.

The Dark Energy Survey recently embarked on a five-year mission to better understand the universe. It’s not a starship, though, it’s an international collaboration using the Blanco telescope in Chile to study the effects of dark energy on the evolution of the universe through a variety of probes — supernovae, baryon acoustic oscillations, weak gravitational lensing, and counts of galaxy clusters.

Dark Energy Detectives is a blog that accompanies the project, and it’s well worth reading to get a sense for what it’s like to do modern astronomy. (Hat tip Nick Suntzeff.) The entries are engaging and well-written, mostly by Brian Nord from Fermilab. We’ve progressed quite a bit since Galileo’s time; we no longer peer through the eyepiece and sketch what we see. Actually there’s not much peering through eyepieces at all, it’s all done by electronics. But you still need to stay up through the night and coax the telescope through it’s targets. And I’m sure Galileo enjoyed more than a few cups of espresso and bags of biscotti along the way.

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12 Responses to Dark Energy Detectives

  1. Bob Zannelli says:

    Dr Carroll has written a very useful paper on the cosmological constant which clarifies a lot of issues, he certainly speaks with some authority on dark energy. I wonder if Dr Carroll would be kind enough to offer his take on the class of dark energy models that go under the name of holographic dark energy.

  2. John Duffield says:

    Interesting. But I noted the “Comments off”. I wasn’t keen on that. IMHO a blog only comes to life when it’s a two-way conversation, with people talking TO you rather than AT you. I mean, did you see this? “So how can we see these galaxies? The cluster (galaxies, dark matter and all) has distorted space time: the light will still travel in a straight line, but this straight line is now in curved space.” I’m gagging to say something about that. But I can’t. It really takes the edge off it.

  3. Bill Bunting says:

    I have great admiration for the work you are all doing. And gratitude.

    My 15 year old the other day, piqued by the suggestion in a current action movie that a pressure pack spray could annul the danger of nuclear contamination, announced that her future science focus will be on nuclear physics.

    You just can’t pick where that moment of inspiration will arrive from.

  4. John Duffield says:

    I should explain myself I suppose. See this article on the Baez website where you can read this: “Similarly, in general relativity gravity is not really a `force’, but just a manifestation of the curvature of spacetime. Note: not the curvature of space, but of spacetime. The distinction is crucial”.

  5. I have a question: If our images of distant galaxies are captured through electromagnetic telescopes, could it be that the photons emitted by those galaxies have actually decayed, perhaps millions of years ago?

  6. Lars Viklund says:

    A question:
    I have learned that empty space is teeming with activity at the planck scale. Matter coming in and out of existence all the time.
    Since space is a pretty big place, there must be enormous amounts of matter in existence at any given moment due to this activity.
    Is it possible that this can have something to do with dark matter & dark energy?

  7. John Duffield says:

    Lars: space has its vacuum energy, but that doesn’t actually mean that matter pops in and out of existence. However this energy is effectively “dark”, and I think it’s reasonable to say it’s something to do with dark energy.

    It may be something to do with dark matter too. Most cosmologist would say that dark matter consists of particles of some unknown type. People have tried to detect them for many years, but have been unsuccessful. But note that a concentration of energy causes gravity. Matter only causes gravity because it is a concentration of energy. If spatial vacuum energy was not uniformly distributed, it would have a gravitational effect. One example of this that we’ve known about for nearly a hundred years is a gravitational field. On page 185 of the Doc 30 Foundation of the General Theory of Relativity, Einstein says this: “the energy of the gravitational field shall act gravitatively in the same way as any other form of energy”. This isn’t nearly enough to account for the dark matter that is thought to be present. But see Inhomogeneous and interacting vacuum energy by Josue De-Santiago, David Wands, and Yuting Wang. IMHO it is still possible that dark matter doesn’t actually consist of particles.

  8. Tienzen (Jeh-Tween) Gong says:

    The dark energy mystery can be easily resolved by answering the two questions below.

    1. Where is the edge (boundary) of this universe?
    2. What is the outside of that edge (boundary)?

  9. Thomas Walsh says:

    Just a general related question: Einstein’s General Relativity equations contain the gravitational constant, G, and G has never been precisely measured (varies +/- 1.5% over many experiments and years) how can it be stated that GR is absolutely precise? Also, some ideas state that gravity was negative for a short period after the ‘big bang’; could G become negative today, also for a short period of time, in some processes? If G did became briefly negative in the black holes of galaxies, what that look like on the larger level?

  10. Hello Lars Viklund

    I would like to know the source of your learning that empty space teems with activity at the Planck Length level. My “belief” is that photons actually do have mass and that they do decay firstly into dark energy at minute size smaller than a Neutrino then clump into dark matter up the scale. Examples are; photons go into your eye and never come out and photons photosynthesise into plants which would not get heavier and more robust were it not for photonic absorption into matter at the Planck Scale. You would not be the mass that is you without conversion of photons into exotic particles of mass. I even understand that hydro-carbon fields in space photosynthesise photons. And if these examples are anything to go by, then yes, dark matter and dark energy are ubiquitous at different levels of clumping and time-maturity – you are less clumped now than the lump of coal you might become part of in two million years time. (By the way, if that lump of coal then conflagrates, it will unlock its absorbed photons from gravity and weight and release them back into energy and light – a flame is merely gravity in reverse?).

    I “believe” we are, and all mass is, dark cold matter and dark cold energy absorbing light and warmth; energising-outwards and looking-out from our own “inner” black holes. Instead of looking for black holes in the “uni”-verse, perhaps we should be turning our attention to an “ini”-verse.

    I accept this might be unscientific to some.

  11. Tienzen (Jeh-Tween) Gong says:

    Two of the greatest mysteries in physics today are dark mass and dark energy. What are they? Fortunately, we do have the Planck data (dark energy = 69.2; dark matter = 25.8; and visible matter = 4.82) now. The dark mass/visible mass ratio = 5.3526 and the number for the dark energy is 69.2. These are simple numbers. Any model which can *predict* these numbers will be a viable theory for the reality. With this Litmus test, these two mysteries are, in fact, resolved.

    For dark mass, see http://profmattstrassler.com/2013/09/16/a-quantum-gravity-cosmology-conference/#comment-86056

    For dark energy, see http://profmattstrassler.com/2013/09/19/am-i-misleading-you-about-string-theory/#comment-87311

  12. Tienzen (Jeh-Tween) Gong says:

    In my previous comment, I have given two links for the dark matter and the dark energy mystery issues. It will take one some efforts to go to those links. Yet, as great as these two mysteries are, they can be easily resolved with half page calculations, as we do have Planck data (dark energy = 69.2; dark matter = 25.8; and visible matter = 4.82) and the AMS02 data now. Since these are simple numbers, the *predictions* of a model for these numbers are very straightforward, no debate can come about.

    For dark matter, with the Pimple model (that is, every particles carry the same mass-charge, see http://tienzengong.wordpress.com/2013/09/19/barked-up-the-wrong-trees-m-theory-and-susy/ ), there are 48 matter particles (matter + anti-matter) while only 7 of them [the first generation matter (not anti-matter)] gives out lights (excluding e-neutrino). Thus, the dark mass/visible mass ratio = [41 (100 – w)% / 7] . The *w* is the percentage of the dark matter which does give out lights. According to the AMS02 data, it is between 8 to 10%. By choosing w = 9, the d/v ratio = 5.33 (while the Planck data shows d/v ratio = 25.8/4.82 = 5.3526). Details, (see http://prebabel.blogspot.com/2013/08/dark-matter-mystery-no-more-part-2.html ).

    For dark energy, it uses an iceberg model (see http://prebabel.blogspot.com/2013/03/planck-data-last-straw-on-higgs-back.html ). That is, the Time, Space and Mass (dark + visible) form an iceberg system, while the mass is the iceberg. And, they three take the *equal* share. So, the dark mass = [(33.3 – 4.82) x (100 -9)%] = 25.91 (while the Planck data is 25.8), with d/v ratio = 5.37. The 9% here is the melting ratio from the dark matter. Thus, the dark energy = 66.66 + [(33.3 – 4.82) x 9%] = 66.66 + 2.56 = 69.22 (while the Planck data is 69.2).

    One interesting thing here, the dark/visible ratio was calculated with two different pathways. Yet, the average [(5.33 + 5.375)/2] = 5.3527, exactly the same as the Planck data.

    With these calculations, the Nature is too simple than we can ever imagine. Yet, numbers are numbers, and there is no debate point for these.