≡ Menu

Refined Parameters for an Expanding Universe

When it comes to matching what we know of the early universe, as seen in the Cosmic Microwave Background (CMB), with what we see today, astronomers have their work cut out for them. Edwin Hubble could demonstrate that the universe was expanding by studying the redshift of galaxies as they receded, but the rate of that expansion has been controversial. Now we have new work based on data from the Hubble Space Telescope as well as the Araucaria Project (about which more in a moment) that is helping us refine the Hubble constant (H0) to tighten the parameters on how the universe’s expansion is accelerating.

The result: The universe is expanding some 9 percent faster than we would expect based on observations by the European Space Agency’s Planck satellite, which mined data from the CMB from 380,000 years after the Big Bang. Exactly what drives this accelerated expansion — an enhanced interaction between matter and something we have yet to detect, ‘dark’ matter, or the as yet unknown form of energy likewise called ‘dark’ — no one knows.

Nonetheless, our cosmos is doing something that we need to explain. Nobel laureate Adam Riess (Johns Hopkins University and Space Telescope Science Institute) is lead researcher on this work. Riess’ Nobel came in 2011, shared with Saul Perlmutter and Brian Schmidt for demonstrating that the expansion of the universe was accelerating. We now firm up that discovery yet further. Riess says the chances of this observation being in error have dwindled from 1 in 3,000 to 1 in 100,000, adding “This disparity could not plausibly occur by chance.”

“This is not just two experiments disagreeing,” Riess added. “We are measuring something fundamentally different. One is a measurement of how fast the universe is expanding today, as we see it. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding. If these values don’t agree, there becomes a very strong likelihood that we’re missing something in the cosmological model that connects the two eras.”

Image: This illustration shows the three basic steps astronomers use to calculate how fast the universe expands over time, a value called the Hubble constant. All the steps involve building a strong “cosmic distance ladder,” by starting with measuring accurate distances to nearby galaxies and then moving to galaxies farther and farther away. This “ladder” is a series of measurements of different kinds of astronomical objects with an intrinsic brightness that researchers can use to calculate distances. Credit: NASA, ESA, and A. Feild (STScI).

Riess is working with a team called SHOES, for Supernovae, H0, for the Equation of State, which analyzed the light of 70 Cepheid variable stars in the Large Magellanic Cloud. Cepheid variables are ‘standard candles’ that brighten and dim at predictable rates, making it possible to measure the distance between galaxies. On the immediate level of data acquisition, the team was able to sharply reduce the time normally required for studying a Cepheid with Hubble (one star for every 90 minute orbit). Using a technique called Drift And Shift (DASH), Hubble can take quick ‘point and shoot’ images, considerably speeding the process.

With the Hubble data in hand, Riess combined them with observations from the Araucaria Project, which is an international collaboration studying the calibration of extragalactic distance, with considerable attention to Cepheid variables, RR Lyrae stars and other potential distance markers. The group has used eclipsing binaries to tighten our distance estimates to the Large Magellanic Cloud. The combined data helped refine the true brightness of the Cepheids.

Image: This is a ground-based telescope’s view of the Large Magellanic Cloud, a satellite galaxy of our Milky Way. The inset image, taken by the Hubble Space Telescope, reveals one of many star clusters scattered throughout the dwarf galaxy. Credit: NASA, ESA, Adam Riess, and Palomar Digitized Sky Survey.

We get a new estimate of 74.03 kilometres per second per megaparsec for Hubble’s constant, which means that for every 3.3 million light years further away a galaxy is from us, it appears to be moving 74 kilometers per second faster. This is a result of the expansion of the universe, and as mentioned above, is a figure 9 percent higher than the Planck observations of the early universe. The latter pegged the Hubble constant at 67.4 kilometres per second per megaparsec.

Consider the values we’ve determined for the Hubble constant in recent decades. A factor of two separated estimates of the constant in the days before the Hubble Space Telescope was available. By the late 1990s, the Hubble Space Telescope Key Project on the Extragalactic Distance Scale refined the value to within 10 percent. By 2016, with the discovery that the universe was expanding faster than previously calculated, the uncertainty dropped to 2.4 percent. What Riess and team have done is to reduce that figure down to 1.9 percent.

“The Hubble tension between the early and late Universe may be the most exciting development in cosmology in decades,” says Riess. “This mismatch has been growing and has now reached a point that is really impossible to dismiss as a fluke.”

And where do we go from here? From the paper (note the reference to gravitational waves, as well as to the supernovae used to extend distance measurements deeper into the cosmos):

A new feature in the dark sector of the Universe appears increasingly necessary to explain the present difference in views of expansion from the beginning to the present… Continued pursuit in precision in the determination of H0 is also needed to transition from the discovery of a difference to a diagnosis of its source. Additional observations of giants and pulsating stars in more hosts of SNe Ia [supernovae] are underway and should further refine H0. Less predictable but highly sought are contributions from gravitational wave sources as standard sirens (Schutz 1986; Abbott et al. 2017; Chen et al. 2018). Improvements in parallaxes from future Gaia data releases are also expected to continue to increase the precision of the distance ladder in the near term.

The paper is Riess et al., “Large Magellanic Cloud Cepheid Standards Provide a 1% Foundation for the Determination of the Hubble Constant and Stronger Evidence for Physics Beyond LambdaCDM,” accepted at the Astrophysical Journal (preprint).


{ 25 comments… add one }
  • Robin Datta April 30, 2019, 15:24

    The expansion of the universe is attributed to a change in the scale of space, an expansion of space. It would seem that the more space there is, the more expansion is to be expected.

    Could the known universe be one bubble in a witches’ cauldron?

    • David Evans April 30, 2019, 18:36

      I prefer E. R. Eddison’s idea (in, I think, A Fish Dinner In Memison) that the universe is a bubble in a glass of champagne at a cosmic dinner party.

  • Larry Kennedy April 30, 2019, 19:07

    I’m unclear as to why this is news. We already knew the rate of expansion is accelerating. How is this different?

    • Paul Gilster April 30, 2019, 19:29

      Larry, you’re right, but what this does is to tighten up the parameters of the observation. The idea that the expansion is accelerating is not new, but the magnitude of it in comparison with the Planck data is interesting and confirms the original findings.

    • Antonio May 1, 2019, 3:27

      This is news because it confirms much more exactly that our computation of the Hubble constant is totally wrong. The explanation can be new physics not accounted for.

    • Alex Tolley May 1, 2019, 9:36

      My understanding of the issue is based on the UK’s “Sky at Night” episode (Is Cosmology in Crisis?) where the scientists examining this issue from both ends: measuring the constant through standard candles vs the CMB predictions, was that the differences was due to an issue with one or other (or both?) miscalculation. There was always a measurement error overlap that could reconcile the different approaches, but these errors are now so reduced that they clearly show 2 different values. The hope is that this means there is some new phenomenon to discover to explain the difference.

  • Alex T. May 1, 2019, 2:54

    Meanwhile standard candles that used to measure those huge distances all use Electromagnetic (EM) waves (light, radio).
    There is huge probability that there is something in EM waves (photons) properties that we still do not know. For example photons aging, i.e. photons slowly loose it’s energy during large time scale, that appears to observer like false red shift effect, or even worst case both real Universe expansion (but with much slower rate) combined with photon’s aging…
    All hopes to solve this problem – to use alternative “standard candles” (gravity waves etc.)

  • Alex T. May 1, 2019, 3:23

    What if the optical property of our Universe allow to us to see our own (may be very distorted) endless “tails” or reflections or self images millions-billions years ago ?
    The simple experiment : put two mirrors, when one mirror reflecting it’s own reflection in opposite – you will see the perfect example of endlessly expanding Universe :-)
    Suppose we can even calculate a virtual acceleration of this “expansion”. By the way, this option is going very well with “photons aging”

    • Harry R Ray May 1, 2019, 10:17

      If “photons aging” is a correct interpretation, then the implication is staggering! This means that you would have to EXPAND the Second Law Of Thermodynamics to include “light death” with “heat death” Recent observations of Bismuth and Xenon have proven that protons indeed DO decay. Is this true for photons as well? If so, the concept of entropy may need to be revised to make it a fundamental force, with its own corresponding boson, the entropon, instead of it just being a derived condition.

      • AlexT May 1, 2019, 15:02

        I am not sure that “photon’s aging” requires expansion of the Second Law Of Thermodynamics, probably there is some undiscovered yet interaction (forces) , for example between EM waves and space-time that cause energy loss/exchange or we can call it “light friction” :-)
        I do not see why this concept is less plausible than “Dark matter” or “Dark energy” concept.
        May be whole our Universe, i.e. everything we can observe – is located inside Event Horizon of some super-huge Black Hole…
        In this case the possibility to see our self’s “tail” or “back” – is not fantastic case.
        The question – which way we can recognize our own galaxy back , i.e. how it was looking a billions years ago? I am afraid – no way to check this case.

  • David May 1, 2019, 18:46

    Precision cosmology really has really given us a lot more questions.There are alternate theories popping up to explain these measurments. It seems that dark energy would have had to kick in earlier than we first thought.
    Also of course this mysterious force is pushing spacetime. Certainly a dream for interstellar travel….but just a dream as of now.
    Thanks for keeping us updated on cosmology.

  • Marc Millis May 2, 2019, 3:09

    So, if two different ways of measuring the same value give different values, then at least one of those techniques is wrong:
    ~ 67 km/s/Mps – via Plank satellite data on Cosmic Microwaves
    ~ 74 km/s/Mps – via observations of Large Magellanic Cloud

    These values are based on a combination of raw observational data and a string of assumptions on how to interpret those observations. I have more confidence in the raw data than on the assumptions.

    What confuses me is how to sort out the core nature from the assumptions – to deduce which of our assumptions are wrong. The situation is confounded because we often talk about the assumptions as if they are the phenomena. Take for example, Dark Matter – a hypothesis not a phenomenon. It started from observations that the rotations of galaxies do not match Newton or Einstein. Rather than question the limitations of Newton or Einstein on galactic scales, it was easier to invent invisible matter. And more to the point of this latest cosmological mismatch is the assumption that redshifts are entirely due to expansion.

    That habit of talking about the hypotheses as if they are the phenomena creates a confirmation bias, impeding our deciphering of the true correlations in nature. Instead, I would prefer that the conversations were anchored with the priority of the raw observations, and then listing more than just the prevailing hypotheses offered to explain the observations.

    • Ron S. May 2, 2019, 9:22

      Does tobacco cause lung cancer? We knew of the effects before knowing detailed chain of cause and effect. Unfortunately cosmology is full of these things, where we see effects but cannot nail down every step in the process or unambiguously identify a root cause. There is still much to learn. But we already knew that.

      As the authors have stated, there is either something terribly wrong with our understanding or interpretation of the raw data, in one, some or all experiments, or that something has changed during the evolution of the universe as it aged. We don’t know.

      Be careful about implying that because we have uncertainty that we should throw it all away. That way lies madness. Wild hypotheses are just that: wild. Relying heavily on the raw observations is no panacea since there is unavoidable ambiguity in what we are truly measuring. At least for now.

      I find these developments quite positive. Having our understanding and assumptions challenged helps us to progress and learn.

      • ljk May 2, 2019, 9:46

        If I remember my Zen correctly, when things start becoming confusing, that is when you are on the right path to understanding.

    • Alex Tolley May 2, 2019, 11:01

      If I understand what you are saying about the redshift, you are suggesting that maybe there are 2 parts to the redshift:

      1. The Doppler effect that stretches the wavelength from recessional velocity due to expansion.
      2. Some other effect that also causes wavelength stretching.

      The second effect results in incorrect recession velocity and hence expansion rate calculations.

      • Alex T. May 3, 2019, 3:38

        Even most traditional explanation of the Universe expansion require second factor (part) to the observable data – they use “Dark Energy” to save concept.
        There is number of possibilities that known to modern science , that can cause the EMW “red shift”:
        – relative motion speed difference
        – gravity
        – space expansion
        May be there is additional factors that can cause photons to loose the energy other than listed here.

        • Alex Tolley May 3, 2019, 11:49

          space expansion

          You mean something different than the plain expansion of the universe. The extra expansion that once was thought to cause the “Great Rip”?

          My sense is that cosmologists do recognize all these possibilities and more, they just cannot find a way to make the numbers work in a coherent, model driven way, to reconcile the different models.

          • Alex T. May 4, 2019, 3:26

            Alex, I only maid copy-past (about “red-shift”) from wikipedia here, to show that even super “conservative” explanation today requires to involve some “third/fourth/fifth” factor to build valuable theory.
            My opinion – present cosmology far from understanding what is really happening in our Universe. Example – content of discussed article and huge uncertainty of scientific data and our understanding of this data.
            For example , two alternative Hubble constant values, for the “recent” and “far” past of our Universe , can be mean exactly opposite things , than it is described in the article.
            The same numbers (if we exclude some local animality) can mean that Universe passed acceleration extremum , still expanding now, but now on the “right” way to shrink back to singularity.
            I am sure this finding can totally disprove the “Dark Energy” concept and need in thig concept.

  • Alex T. May 4, 2019, 3:12

    Everything is relative here.
    By the way, it is not so obvious as it seams to be from the first sight.
    But … the higher acceleration value in the relatively “recent” past, than in “far away” past , can mean exactly opposite things than described in this article!!!
    I.e. Universe sometime in “recent” past passed acceleration rise edge and probably now acceleration rise rate is decreasing , i.e. approaching zero acceleration point, after which it will begin to shrink.
    I suppose that acceleration measurements that done relatively farthest cosmic objects should give more correct the Earth / Universe acceleration numbers (for present moment) that “recent” one.

  • stephen May 5, 2019, 16:41

    We find an irregular distribution of galaxies, and many intergalactic voids, so the universe somehow became asymmetric.

    So maybe the universe is expanding at different rates in different directions. Regarding the curvature of the universe, it might be like a plate, a ball or a saddle. Could the universe have different curvatures in different directions?

    Dare I suggest the universe is shaped like a horse standing on a plate, with a saddle on its back, and a ball on the saddle…? Nah.

    • Alex Tolley May 5, 2019, 20:48

      Aren’t galaxies themselves moving asymmetrically, e.g. towards “The Great Attractor”. Is there any outside chance this hasn’t been taken into account, or is this irrelevant to calculating H0?

    • Alex T. May 6, 2019, 2:34

      Yes, we know almost nothing about the Universe shape(s).
      The fact that there is huge voids can be good sing that:
      – the Universe size is limited and
      – far away (billions light years) galaxies can be our own time delayed reflections in the huge gravitational mirror(s)/lens(es).

Leave a Comment