Universe’s expansion rate contradicts dark energy data

Please consider donating to Behind the Black, by giving either a one-time contribution or a regular subscription, as outlined in the tip jar to the right or below. Your support will allow me to continue covering science and culture as I have for the past twenty years, independent and free from any outside influence.

The uncertainty of science: New measurements of the universe’s expansion rate, dubbed the Hubble constant, contradict theoretical predictions based on previous data.

For their latest paper, Riess’s team studied two types of standard candles in 18 galaxies using hundreds of hours of observing time on the Hubble Space Telescope. “We’ve been going gangbusters with this,” says Riess.

Their paper, which has been submitted to a journal and posted on the arXiv online repository on 6 April, reports that they measured the constant with an uncertainty of 2.4%, down from a previous best result2 of 3.3%. They find the speed of expansion to be about 8% faster than that predicted based on Planck data, says Riess. [emphasis mine]

I highlight the number of galaxies used to get this data because I think these scientists, are being a bit over-confident about the uncertainty of their data. The universe has untold trillions of galaxies. To say they have narrowed their uncertainty down to only 2.4% based on 18 is the height of silliness.

But then, the lead scientist, Adam Riess, recognizes this, as he is also quoted in the article saying “I think that there is something in the standard cosmological model that we don’t understand.”



  • Mitch S.

    There are lots of galaxies but maybe not “trillions”.

    “an acceptable range is between 100 billion and 200 billion galaxies, Mario Livio, an astrophysicist at the Space Telescope Science Institute in Baltimore, told Space.com.

    – See more at: http://www.space.com/25303-how-many-galaxies-are-in-the-universe.html#sthash.UDM9uTYy.dpuf

  • Edward

    From the article: “‘I think that there is something in the standard cosmological model that we don’t understand,’ says astrophysicist Adam Riess”

    One of my teachers liked to say “don’t confuse the map for the territory.”* I think that Riess has done just that. We should absolutely understand any model that we use, otherwise it cannot be a reliable model. What I think Riess meant is that there is something about reality that we don’t understand, and the model needs to be modified. The something that we don’t understand could even be missing from the current model — as Dark Energy was, only a few years ago — rather than being something in the model, as Riess suggested.

    * https://en.wikipedia.org/wiki/Map%E2%80%93territory_relation
    Am I being pedantic? Yeah, probably. Does this make me imperfect? Yeah, it adds to my imperfections. But I haven’t been perfect since I was 27-years old.

  • Local Fluff

    The nice thing with physics is that everything you can conclude from what you know is true always everywhere. The reason they observed 18 galaxies instead of only one, is to bring down the noise of the measurement. It’s got to do with the telescope, it’s not that some galaxies are special in this respect. 18 is plenty.

  • “18 is plenty.”

    This is the same answer that Wendy Friedman gave me in 1995 when she used Hubble, soon after it was launched, to measure the rate of the Hubble constant using a handful of Cepheid variables in the Virgo cluster and got a constant of about 80 km per second per megaparsec, with a margin of error of only 17 km plus or minus. I asked her in a phone interview, isn’t her sample awfully small to be so sure. She said that one sample in Virgo was plenty. I persisted, noting that it seemed premature to be so sure from this one data point. She actually got a little annoyed with me, a mere science journalist, for doubting her.

    Now, using only 18 galaxies, the number they have come up with 73.03 km per second per megaparsec, with a plus or minus of 1.79 kilometers. This number is higher than theoretical predictions of around 67.and 69 km per sec per megaparsec. Note that the predictions are significantly different than Wendy Friedman’s number from around 1995.

    So, which is it? The first Hubble number? The predictions? Or this new data from 18 galaxies?

    I am sorry, but 18 galaxies is not enough. There are too many other variables that can make this result exceedingly uncertain. You need a bigger sample to be sure.

  • D K Rögnvald Williams

    Sample size is certainly important, but much astronomical measurement rests on assumptions, which sometimes prove incorrect, as well as technological sources of error.

  • Phil Berardelli

    I had the pleasure of meeting Riess about 10 years ago when I was covering astronomy. This was long before he became a Nobel Laureate for his work on dark energy. I found him to be a passionate scientist and a modest man. Yes, 18 galaxies represent a minuscule sample among several hundred billion. Furthermore, the “standard candles” (type Ia supernovae) have occasionally shown up exhibiting unexpected characteristics. So the best we can conclude so far is that the universe’s expansion seems to be accelerating at a rate still to be determined, and the unseen force called dark energy seems to be responsible. I regard Adam’s latest paper as an attempt to refine the rate of acceleration, which no doubt will continue to be altered as measurements grow more comprehensive and precise. And my guess is if further research conclusively pushes the rate either faster or slower beyond current calculations, Adam would embrace the result.

  • David M. Cook

    I’ll never forget watching Project Universe back in the ’80s and being astounded at the methods used to gauge the size of space. “That’s it?!?” I exclaimed. “Variable stars?, Standard candles? You’ve got to be kidding me?!!?” I realized just how delicate were the foundations for some scientific conclusions. What an epiphany!

  • pzatchok

    What if some areas are moving faster than other areas?

    Sort of like a rubber sheet being stretched out from the center.

    We are measuring areas in the middle of the sheet and only guessing at the exact distance the outer edge is from the center.

    I am sure its been asked. But at what rate of spin would the universe have to have to produce the same centripetal effect we are attributing to the expansion rate of dark mater? And is that even possible?


    Everything else spins why not the universe?

  • Wayne

    Interesting thoughts! & yes, that question has been asked.
    (Not disagreeing with you as such, just attempting to clarify a little– would enjoy *more* of your thoughts along these lines.)

    However, from my understanding (& fully granted, this is WAY above my pay-grade but a strong personal interest) there is no “center” of the Universe & we are not ‘it.’ (It seems as-if there would be, but there is not.)

    The rubber sheet analogy is only good for sorta illustrating space-time curvature, as a starting point. But that analogy lacks the “3 dimensions + time” which is “Space-Time.”

    As I understand it as well, “space” is expanding between the various Galaxies & not within the Galaxies. (That is, within a galaxy matter is bound to itself & space itself is not expanding.)

    As for the “outer edge,” of the Universe, we are confined to viewing only the visible part, which only came about when the Universe expanded to a (spherical) point where photons were able to be liberated from the primordial particle ‘soup.’ There is reason to believe the “actual” size of the Universe is perhaps twice-three times that of the visible portion.

    It appears our theories are a bit more “tidy” than actual reality is turning out to be, but that having been said, I personally believe we are on the right track.

    tangentially– do some research on the geometric concepts of “light-cones,” where the speed of light is set at “1” and all photons move at 45 degree-angles through “space-time.” I’ve found, personally, that if I can get a grip on that & add in the dimension of Time, things make a lot more sense. (not that they are more “clear,” but they make a lot more sense!)

    as a starting point: http://casa.colorado.edu/~ajsh/sr/centre.html
    (covers the paradox of special-relativity & light-cone geometry)

    -further tangent:
    Think of a Black Hole, as a singularity where all the light-cones are folded in & over on themselves—nothing escapes, because of the geometry of space-time at those points.

  • Local Fluff

    I thnk that the cosmology actually says that space expands differently in diferent places. Empty space expands faster than space occupied by matter or energy. But this physics is way beyond me.

  • Wayne

    Local Fluff:
    I believe you are largely correct in part. The Physics is way over my pay-grade as well, but I just take the Math as given, and concentrate on the Concepts, makes it easier for me to take it all in & try to get a grip on it all.

    This is fairly enlightening & newer, but not as new as the Riess Paper…. (Starts out with translation, but not to worry– the talk itself is in English.)

    “Why is the Universe so Big and Old?”
    Dr. John Ellis at UCM. 1-21-16

    –Combination “public” & “technical” lecture.

    Ellis does a good job of thoroughly walking you through everything. I’m very (extremely) picky on these type of lectures myself, & only recommend material I’ve watched more than once & conforms with everything else I already know. (That may be my downfall, but while the Internet is filled with “physics” & “cosmology” lectures, the subset of high-quality material is considerably less.)

  • Wayne

    “matter tells space-time how to curve, and curved space-time tells matter how to move”
    -Everything you ever want to know about Gravity Probe B & testing Einstein’s universe…


Leave a Reply

Your email address will not be published. Required fields are marked *