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A Dark Energy Option Challenged

Having a constant named after you ensures a hallowed place in astronomical history, and we can assume that Edwin Hubble would have been delighted with our continuing studies of the constant that bears his name. It was Hubble who showed that the velocity of distant galaxies as measured by their Doppler shift is proportional to their distance from the Earth. But what would the man behind the Hubble Constant have made of the ‘Hubble Bubble’? It’s based on the idea that our region of the cosmos is surrounded by a bubble of relatively empty space, a bubble some eight-billion light years across that helps account for our observations of the universe’s expansion.

The theory goes something like this: We assume that the Hubble Constant should be the same no matter where it is measured, because we make the larger assumption that our planet does not occupy a special position in the universe. But suppose that’s wrong, and that the Earth is near the center of a region of extremely low density. If that’s the case, then denser material outside that void would attract material away from the center. What we would see would be stars accelerating away from us at a rate faster than the more general expansion of the universe.

The Hubble Bubble is an ingenious notion, one of the ideas advanced as an alternative to dark energy to explain why the expansion of the universe seems to be accelerating. If you had to choose between a Hubble Bubble and a mysterious dark energy that worked counter to gravity, the Bubble would seem a safer choice, given that it doesn’t conjure up a new form of energy, but the observational evidence for the Bubble is lacking, and now the idea has been hobbled by new work by Adam Riess (Space Telescope Science Institute) and colleagues.

Deflating the Bubble

Riess used data from the new Wide Field Camera 3 (WFC3) aboard the Hubble Space Telescope to measure the Hubble Constant to a greater precision than ever before. The value the team arrived at — 73.8 kilometers per second per megaparsec — means that for every additional megaparsec (3.26 million light years) a galaxy is from Earth, it appears to be moving 73.8 kilometers per second faster away from us. The uncertainty over the figure for the universe’s expansion rate in the new observations has now been reduced to just 3.3 percent, reducing the error margin by a full 30 percent over the previous Hubble measurement in 2009.

The new precision is thanks to Wide Field Camera 3, which helps the scientists study a wider range of stars to eliminate systematic errors introduced by comparing the measurements of different telescopes. The team compared the apparent brightness of Type Ia supernovae and Cepheid variable stars to measure their intrinsic brightness and calculate the distances to Type Ia supernovae in distant galaxies. Riess calls WFC3 the best ever flown on Hubble for such measurements, adding that it improved “…the precision of prior measurements in a small fraction of the time it previously took.” Further WFC3 work should tighten the Constant even more, and even better numbers should be within range of the James Webb Space Telescope.

This work is significant because as we tighten our knowledge of the universe’s expansion rate, we restrict the range of dark energy’s strength. The Bubble theory arose because scientists were looking for ways around a dark energy that opposed gravity. But the consequences of a Hubble Bubble are clear — if it’s there, the universe’s expansion rate must be slower than astronomers have calculated, with the lower-density bubble expanding faster than the more massive universe that surrounds it. Riess and team have tightened the Hubble Constant to the point where this lower value — 60 to 65 kilometers per second per megaparsec — is no longer tenable.

Lucas Macri (Texas A&M University), who collaborated with Riess, notes the importance of the study:

“The hardest part of the bubble theory to accept was that it required us to live very near the center of such an empty region of space. This has about a one in a million chance of occurring. But since we know that something weird is making the universe accelerate, it’s better to let the data be our guide.”

Riess, you may recall, is one of the co-discoverers of the universe’s accelerating expansion, having demonstrated that distant Type Ia supernovae were dimmer than they ought to be, an indication of additional distance that had to be the result of faster than expected expansion. Meanwhile, it’s extraordinary to realize how much the Hubble instrument has helped us pin down the value of the Hubble Constant, which had seen estimates varying by a factor of two before the telescope’s 1990 launch. This NASA news release points out that by 1999, the Hubble telescope had refined the value of the Hubble Constant to an error of about ten percent. Riess’ new work continues the 80-year measurement of this critical value and promises more to come.

The paper is Riess et al., “A 3% Solution: Determination of the Hubble Constant with the Hubble Space Telescope and Wide Field Camera 3,” Astrophysical Journal Vol. 730, Number 2 (April 1, 2011). Abstract available.


Comments on this entry are closed.

  • redpeace March 15, 2011, 10:03

    Always interesting to read your blog. Had to comment on this to give you credit for this line:

    “…now the idea has been hobbled by new work…”

    Your allusion to a “Hobbled Hubble Bubble” forced me to comment. Intentional or not, kudos to you.

  • Paul Gilster March 15, 2011, 10:28

    Thanks! Hey, had almost written about ‘Hubble Bubble Trouble,’ but I decided that went too far… Appreciate the comment, redpeace.

  • Scott G March 15, 2011, 11:10

    The idea of an expanding universe doesn’t seem all that far-fetched to me (well, no more so than gravity). It actually seems more plausible than the extremely remote likelihood of being at or near the center of a vast ultra-low density region in space.

    On the other hand, what is a bit difficult for me to comprehend is the idea that this expansion is accelerating. In fact, correct me if I’m wrong, but the expansion of the universe is expected to become so strong in the distant future that matter itself will be torn apart. So what mechanism could be responsible for that? That’s the unsatisfying part to me…

  • Marc G Millis March 15, 2011, 11:12

    Several years ago, when helping one of my daughters with a science project, I saw a quote from Hubble to the effect that he did not ascribe to the expansion interpretation of his red-shift observation. He preferred that other scientists would hold off on making conclusions until other corroborating data came in. In the meantime, he wanted to just focus on the observations as they were: unexpected redshifts versus distance. I wish I would have recorded where that statement came from, because I’ve wanted to use it several times since.

    On a related vein, I wonder if any of you have ever run calculations for how long we’d have to wait before we could corroborate the expansion hypothesis with parallax distance measurements, or some other means that did not use the same set of assumptions. I have not run those numbers, but have often wondered about it.

    To be clear, I am NOT advocating that we dismiss the expansion hypothesis, but merely reminding ourselves that it is a ‘hypothesis.’ The redshifts are the observed effect. If other readers know of corroborating evidence for the expansion hypothesis that uses a different measurement technique, I’d appreciate knowing about it. This is one of those questions buried deep in my to-do list that I’ve not dug into. If any of you have, I’d appreciate the help.

    Thanks, Marc

  • Mark Presco March 15, 2011, 13:39

    I have often wondered if photons can decay, or slow down in frequency over time. Thus, the farther away the star, the more red shifted it would appear.

    The current model assumes photons are immortal, affected only by relative motion or space-time expansion.

    Has anyone addressed this issue?

  • Paul Gilster March 15, 2011, 13:54

    Mark, good question. The Wikipedia has an article on the ‘tired light’ hypothesis. Here’s the opening paragraph — the full article (linked below) has details on the history of the idea:

    Tired light is a class of hypothetical redshift mechanisms that was proposed as an alternative explanation for the redshift-distance relationship as alternatives to the Big Bang and the Steady State cosmologies, both of which proposed that Hubble’s law was associated with a metric expansion of space. The concept was first proposed in 1929 by Fritz Zwicky, who suggested that photons lose energy over time through collisions with other particles. Alternative models of gravity that do not produce an expanding universe sometimes appeal to tired light to explain Hubble’s Law. Today, tired light is remembered mainly for historical interest, and almost no scientist accepts tired light as a viable explanation for Hubble’s Law.


  • Paul Gilster March 15, 2011, 14:03

    Re Marc Millis’ question re Hubble and what his views on the Hubble Constant were, this is interesting. It’s from Marcia Bartusiak’s wonderful The Day We Found the Universe:

    For the most part, Hubble remained focused solely on his observations, leaving theory to others. ‘The interpretation,’ he told de Sitter at one point, ‘should be left to you and the very few others who are competent to discuss the matter with authority.’ Hubble obviously had some serious doubts about what it all meant. ‘It is difficult to believe that the velocities are real — that all matter is actually scattering away from our region of space,’ he told a Los Angeles Times reporter in 1929. In the very first paragraph of his discovery paper on ths subject he referred to the velocities of the galaxies as ‘apparent.’ He maintained this conceit for the rest of his career. As long as various theoretical explanations were under scrutiny, he didn’t want to be caught on the wrong side. He was never comfortable in the robe of a theorist and so published his data in such a way that the measurements could remain unsullied, no matter what the interpretation. ‘Not until the empirical sources are exhausted, need we pass on to the dreamy realms of speculation,’ he mused. This attitude rubbed off on his loyal helpmate as well. ‘I have always been rather happy that…my part in the work was, you might say, fundamental; it can never be changed — no matter what the decision is as to what it means,’ said Humason.

  • Ronald March 15, 2011, 14:08

    My question here, which no one may be able to answer yet, is: will this acceleration continue or is it also possibel that it will level off and that at a certain point the universe will expand with level or even decreasing speed?

    BTW, from what I have read, the universal expansion is only at the level of superclusters, i.e. the superclusters (of galaxies) are moving away from each other. Within one supercluster the galaxies are staying together, gradually even moving toward eachother as a result of their gravity.

    There was an interesting article in Scientific American, by Lawrence M. Krauss and Robert J. Scherrer, March 2008, about the future of the (observable) universe: eventually, in some 100 gy orso, all galaxies within one supercluster will have merged into one supergalaxy. The different superclusters/supergalaxies will have moved beyond eachothers light horizon, and will be out of view for eachother.

    At the same time the hydrogen reserves of the universe will have been reduced (by about half? I am not sure how much), helium and heavier elements increased correspondingly.
    Nearly all stars will be red and orange-red dwarves (half solar mass and smaller), because of their vastly longer life-spans and their much more common formation. Solar type stars and larger will have become very rare.

  • Eniac March 15, 2011, 21:24


    But suppose that’s wrong, and that the Earth is near the center of a region of extremely low density. If that’s the case, then denser material outside that void would attract material away from the center.

    Spherical shells do not exert a gravitational force in their interior, so it is hard to see how this bubble theory would “attract material away from the center”. Unless, perhaps, something more complex relating to general relativity is at work?

  • Ron S March 15, 2011, 23:06

    Marc: “…corroborate the expansion hypothesis with parallax distance measurements,…”

    I don’t think this is possible. Parallax is only usable for short distances and the expansion has to be measured between objects that are not gravitationally bound to each other. Everything within our galaxy (and even further to nearby galaxies) is gravitationally bound. Therefore the cosmologists’ attention on superclusters.

    Or perhaps I misunderstood your point.

  • Scott G March 16, 2011, 9:16

    Marc Millis asks: If other readers know of corroborating evidence for the expansion hypothesis that uses a different measurement technique, I’d appreciate knowing about it.

    This 2010 paper might provide some insight into your question — “Possible direct measurement of the expansion rate of the universe” (Shi Qi, Tan Lu) — http://arxiv.org/abs/1001.3975

    An excerpt:

    Measuring the expansion rate of the universe along the redshift has been one of the most important scientific objectives in cosmology since the discovery of the expansion. It is usually pursued by measuring the distances at different redshifts, which, in turn, could be done with the data of the standard candles like the type Ia supernovae (SNe Ia), Gamma-ray bursts (GRBs) or the standard rulers from cosmic microwave background (CMB) and baryon acoustic oscillations (BAO). …

    On the other hand, despite of the difficulties, some proposals have been presented for directly measuring the expansion rate of the universe, for example, through the measurement of radial BAO, the relative ages of passively evolving galaxies, the temperature and polarization anisotropies of the CMB, or the redshift drift (the so-called Sandage-Loeb test). In this paper, we propose another method to directly measure the expansion rate by measuring the changes of the flux of extremely stable sources.

  • David March 16, 2011, 19:32

    Marc The best evidence would be the cosmic microwave background radiation measuremenst which show the universe just closed and thus it is assumed that Dark Energy is what does that. Plank should give us more details .
    I do know Frank Tipler thinks it is a cosmolgical constant as Einstein thought and later rejected. However He thinks we can use it as fuel and thus we would have a collaspsing closed universe instead of an ever expanding universe that is closed

  • Rob Henry March 17, 2011, 5:02

    David, you idea of an ever expanding universe that is closed is new to me. Knowing little about general relativity, I thought that the elliptic geometry needed for closure was synonymous under its precepts with an eventual big crunch. Do you also know if there can be a big crunch if our universe has a gross hyperbolic geometry?

  • David March 17, 2011, 10:21

    Rob while Geometry is usually destiny the dark energy throws a real curve(pun) into it. I belive it was a paper by Glen Starkman some years ago that showed even if the DE is a standard Cosmolgical Constant there is now way to really prove that it will act that way forever so the geometry could return and collapse the universe.If the constant didnt change you could have a closed universe that expands forever. If it was a changing dark energy and the CC becasme negative a gemetrically open universe could collapse!
    If this is all beginning to look like epicyycles in Geocentric cosmolgy you would not be alone I think that maybe why Mark Presco is looking at tired light theory!
    However if we could “burn” the CC like Tipler thinks (and others) then we have interstellar travel

  • kzb March 17, 2011, 14:20

    If our species happened to evolve several billion years in the future, we would see the Local Group of galaxies, or perhaps that would have merged into just one giant elliptical galaxy.

    Outside of that, nothing, because all other galaxies have receded beyond the light horizon. Our universe would consist of just one galaxy, albeit a large one.

    We would have no observations to give us the idea that the universe was expanding, and because of that we wouldn’t hypothesise a big bang beginning, nor dark energy.

    Makes you think doesn’t it?

  • Bounty March 17, 2011, 18:15

    Perhaps space is like the surface of water and we’re on a rising wave watching things around us fall away. All of course on a scale so large and long (time) that…. ok now I’ve gone cross-eyed.

  • James M Essig March 18, 2011, 13:09

    Grammatically Corrected Version.

    Hi Folks

    An absolutely beautiful thing regarding the Standard Big Bang Model and also new models that assume increased rates of expansion is that effectively superluminal travel away from the Milky Way Galaxy and even from our local group is definitively possible in theory.

    For instance, a space craft traveling at 0.5 C away from Earth such as a huge world ship or space zonde might travel 20 billion light years through space time, inertially, but by the time the 20 billion years time has ended, the spatial region in which it occupies would be receding at super luminal velocities from Earth.

    Say a huge sub-C inertially traveling space craft could contain a civilization that would survive 10 EXP 60 years of travel at only 0.5 C thus traveling [ 0.5 x (10 EXP 60)] light-years through space-time. The craft not taking into account the total time integrated lengthening of the spatial interval between itself and the remains of the Milky Way would be receding at [0.5 x (10 EXP 60)] C from the Milky Way Galaxy. This is [0.5 x (10 EXP 60)] [3 x (10 EXP 8)] [5.39 x (10 EXP – 44)] meters per Planck Time Unit = 808 million light years per Planck Time Unit, background time. In actuality, the recessional velocity and distance traveled would be many, many orders of magnitude greater yet due to universal space-time expansion as the craft traveled.

    I was talking with a friend of mind earlier this Winter about the effects of compounded distance traveled due to universal space-time expansion, we came to the conclusion, that regardless of whether or not other universes exist, perhaps our universe in terms of spatial extension, just goes on forever.

    I had a rather whimsical night-time dream a couple decades ago, really several in all, in which I dreamed that I was talking to some Saint or something while at the same time looking at a photograph of a galaxy with stars in the foreground. Although this was only a dream with no supernatural significance as far as I can tell, I asked the subject person in my dreams how big is the universe, to which the person replied, it simply goes on forever in spatial and temporal extent. I asked this person how fast can we travel, and the person answered, “The speed of light.”. But then I became concerned and bothered by the finite limit of C. The person then consoled my by telling me not to worry, because there is no limit to how far you can travel, and at the speed of light, there is no limit to the distance you can travel, even in one Planck Time Unit ship time. If I recall my dream correctly, I then said, “CooOOOOOL!”.

    This nocturnal dream has forever left a strong impression on me that I will never forget. Thus, since some of you folks who have been posting comments here at TZ-CD dreams as well as Marc Millis and Paul Gilster may be familiar with my love of conjecture about cosmic scale space travel concepts as well as extreme gamma factor concepts, I thought I would provide an explanation for my motives.

    The cool thing is that if our universe is completely open and will expand perpetually, even in the event that it is infinite in spatial extent and in spatial volume, it will continue to grow to ever larger infinite values in size.

    Perhaps nature will find a way or already has found a way to fill in the expanding space time with additional particles either created out of Dark Energy or perhaps from somehow reified zero point field energy.

    Perhaps there will be one, or than one, or even an unlimited number of future phase change events in which our universe will hyper-inflate again and again, and undergo additional symmetry breaking events. This would be bad news for us unless, … and I say unless, we can somehow teleport, transport, or otherwise by-pass the phase change condition and enter into the new era of our universe.

    Transferring our souls, or personalities if you will, to an embodying form of material that can survive the phase change whereupon we would be restored completely, body and soul once we are safely away from the phase change condition would be of help here. Ideally, the temporary embodying matter would be teleported into the new revamped state of the universe without passing through the phase change state so that the temporary embodiment of the transported personality as well as the temporarily embodying matter would not become corrupted in the phase change.

    The study of Dark Energy, previous symmetry breaking events and inflationary episodes, and the potential of future ones is an absolutely necessary science because at some point, in another cosmic era, our universe I believe is going to undergo another phase change. In the meantime, we will have to deal with a great rarefication of the mass energy content of our universe in the trillions of year to follow as well as stellar burnout.

    Part of the fun in all of these conjectured events for me is precisely the fact that they are mysterious and fraught with potential universal danger, but even more so, with possibilities for eternal evolution and progress that is currently veiled from our precise and detailed understanding.

  • kzb March 19, 2011, 13:31

    So where is the energy coming from to accelerate all this mass? The laws if thermodynamics somehow don’t count in this situation? What is more, the universe will tend to infinite energy content in the far future.

  • ljk April 18, 2011, 9:12

    Antigravity Could Replace Dark Energy as Cause of Universe’s Expansion

    by Vanessa D’Amico on April 18, 2011

    Since the late 20th century, astronomers have been aware of data that suggest the universe is not only expanding, but expanding at an accelerating rate. According to the currently accepted model, this accelerated expansion is due to dark energy, a mysterious repulsive force that makes up about 73% of the energy density of the universe. Now, a new study reveals an alternative theory: that the expansion of the universe is actually due to the relationship between matter and antimatter. According to this study, matter and antimatter gravitationally repel each other and create a kind of “antigravity” that could do away with the need for dark energy in the universe.

    Massimo Villata, a scientist from the Observatory of Turin in Italy, began the study with two major assumptions. First, he posited that both matter and antimatter have positive mass and energy density. Traditionally, the gravitational influence of a particle is determined solely by its mass. A positive mass value indicates that the particle will attract other particles gravitationally. Under Villata’s assumption, this applies to antiparticles as well. So under the influence of gravity, particles attract other particles and antiparticles attract other antiparticles. But what kind of force occurs between particles and antiparticles?

    Full article here:


  • ljk July 10, 2011, 22:16

    Did Edwin Hubble plagiarize?

    Giora Shaviv

    (Submitted on 3 Jul 2011)

    Recently Block published an astro-ph [arXiv:1106.3928 (2011)] insinuating that Hubble censored a prior publication of his famous and seminal discovery of the expansion of the universe.

    This issue was investigated by us in detail as part of the book: The Quest for Chemical Element Genesis and What the Chemical Elements Tell about the Universe (Accepted for publication, Springer Pub. Heidelberg, 2011.) Since the book is due in few months, we extract here the relevant parts.

    Our summary: We exonerate Hubble from the charge that he censored or ignored or plagiarized Lemaitre’s earlier theoretical discovery.


    11 pages 4 figures


    History and Philosophy of Physics (physics.hist-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

    Cite as:

    arXiv:1107.0442v1 [physics.hist-ph]

    Submission history

    From: Giora Shaviv professor [view email]

    [v1] Sun, 3 Jul 2011 10:09:28 GMT (261kb,D)