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    Cosmic Bubble Theory Of Universe Expansion Ruled Out
    By News Staff | March 15th 2011 04:00 AM | 10 comments | Print | E-mail | Track Comments
    Researchers say they have ruled  the cosmic bubble theory, an alternate theory on the nature of dark energy, after recalculating the expansion rate of the universe to unprecedented accuracy.

    The universe appears to be expanding at an increasing rate and some believe that is because the universe is filled with a dark energy that works in the opposite way of gravity. One alternative to that hypothesis is that an enormous bubble of relatively empty space eight billion light-years across surrounds our galactic neighborhood. If we lived near the center of this void, observations of galaxies being pushed away from each other at accelerating speeds would be an illusion.

    This
    cosmic bubble hypothesis has now been invalidated because astronomers say they have refined their understanding of the universe's present expansion rate.   The Hubble observations were conducted by the SHOES (Supernova Ho for the Equation of State) team that works to refine the accuracy of the Hubble constant to a precision that allows for a better characterization of dark energy's behavior. The observations helped determine a figure for the universe's current expansion rate to an uncertainty of just 3.3 percent. The new measurement reduces the error margin by 30 percent over Hubble's previous best measurement of 2009. 

    The value for the expansion rate is 73.8 kilometers per second per megaparsec. It means that for every additional million parsecs (3.26 million light-years) a galaxy is from Earth, the galaxy appears to be traveling 73.8 kilometers per second faster away from us.

    Every decrease in uncertainty of the universe's expansion rate helps solidify our understanding of its cosmic ingredients. Knowing the precise value of the universe's expansion rate further restricts the range of dark energy's strength and helps astronomers tighten up their estimates of other cosmic properties, including the universe's shape and its roster of neutrinos, or ghostly particles, that filled the early universe.

    "We are using the new camera on Hubble like a policeman's radar gun to catch the universe speeding," said
    Adam Riess of the Space Telescope Science Institute (STScI), who led the research. "It looks more like it's dark energy that's pressing on the gas pedal."

    Bursting the Cosmic Bubble

    Dark energy is one of the greatest cosmological mysteries in modern physics.  Albert Einstein conceived of a repulsive force, called the cosmological constant, which would counter gravity and keep the universe stable, but abandoned the idea when astronomer Edwin Hubble discovered in 1929 that the universe is expanding.   Evidence for dark energy didn't come along until 1998, when two teams of researchers (one led by Riess) discovered it.

    The idea of dark energy was so far-fetched, many scientists began contemplating other strange interpretations, including the cosmic bubble theory. In this hypothesis, the lower-density bubble would expand faster than the more massive universe around it. To an observer inside the bubble, it would appear that a dark-energy-like force was pushing the entire universe apart. The bubble hypothesis requires that the universe's expansion rate be much slower than astronomers have calculated, about 60 to 65 kilometers per second per megaparsec. By reducing the uncertainty of the Hubble constant's value to 3.3 percent, Riess reports that his team has eliminated beyond all reasonable doubt the possibility of that lower number.

    "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," explained Lucas Macri, of Texas A&M University in College Station, a key collaborator of Riess. "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."


    Using stars as "cosmic yardsticks" measuring the universe's expansion rate is a tricky business. Riess' team first had to determine accurate distances to galaxies near and far from Earth. The team compared those distances with the speed at which the galaxies are apparently receding because of the expansion of space. They used those two values to calculate the Hubble constant, the number that relates the speed at which a galaxy appears to recede to its distance from the Milky Way. Because astronomers cannot physically measure the distances to galaxies, researchers had to find stars or other objects that serve as reliable cosmic yardsticks. These are objects with an intrinsic brightness, brightness that hasn't been dimmed by distance, an atmosphere, or stellar dust, that is known. Their distances, therefore, can be inferred by comparing their true brightness with their apparent brightness as seen from Earth.

    ngc 5584
    The blue glow of young stars trace the spiral arms of galaxy NGC 5584 in this image. Thin, dark dust lanes appear to be flowing from the yellowish core, where older stars reside. The reddish dots sprinkled throughout the image are largely background galaxies. Credit: NASA, ESA, A. Riess (STScI/JHU), L. Macri (Texas A&M University), and Hubble Heritage Team (STScI/AURA)

    Among the most reliable of these cosmic yardsticks for relatively shorter distances are Cepheid variables, pulsating stars that dim and fade at rates that correspond to their intrinsic luminosity. But Cepheids are too dim to be found in very distant galaxies. To calculate longer distances, Riess' team chose a special class of exploding stars called Type Ia supernovae. These stellar explosions all flare with similar luminosity and are brilliant enough to be seen far across the universe. By comparing the apparent brightness of Type la supernovae and pulsating Cepheid stars, the astronomers could measure accurately their intrinsic brightness and therefore calculate distances to Type Ia supernovae in far-flung galaxies.

    Using the sharpness of the new Wide Field Camera 3 (WFC3) to study more stars in visible and near-infrared light, scientists eliminated systematic errors introduced by comparing measurements from different telescopes.

    "WFC3 is the best camera ever flown on Hubble for making these measurements, improving the precision of prior measurements in a small fraction of the time it previously took," said Macri.

    Using one instrument to measure the Hubble constant is like measuring a hallway with a tape measure instead of by laying a ruler from end to end. By avoiding the need to pick up the ruler and lay it back down, you can prevent mistakes. "The camera on Hubble, WFC3, is the best ever flown on Hubble for making these measurements, improving the precision of prior measurements in a small fraction of the time it previously took," Riess said.

    The astronomer hopes that Hubble will continue to be used in this way to reduce the uncertainty in the Hubble constant even more, and thus refine the measured properties of dark energy. He suggests the present uncertainty could be cut in two before Hubble gives way to improvements out of Hubble's reach but within the scope of the James Webb Space Telescope, an infrared observatory scheduled to launch later this decade.

    Chasing a runaway universe, Riess has been pursing dark energy for 13 years. He co-discovered the existence of dark energy by finding that distant Type Ia supernovae were dimmer than expected, which meant they were farther away than anticipated. The only way for that to happen, Riess realized, was if the expansion of the universe had sped up some time in the past.

    Until that discovery, astronomers had generally believed that the cosmic expansion was gradually slowing down, due to the gravitational tugs that individual galaxies exert on one another. But the results implied that some mysterious force was acting against the pull of gravity, shoving galaxies away from each other at ever-increasing speeds.

    Riess decided that one of the best ways to tighten the constraints on dark energy is to determine an accurate value for the Hubble constant, which he has been doing with the Hubble Space Telescope. That measurement, combined with others from NASA's Wilkinson Microwave Anisotropy Probe (WMAP), traces the universe's behavior from nearly the dawn of time to the present age. (WMAP showed the universe as it appeared shortly after the Big Bang, before stars and galaxies formed.)

    Riess is just one of many astronomers who, over the past 80 years, have been measuring and re-measuring the Hubble constant. The Hubble telescope has played a major role in helping astronomers precisely measure the universe, expansion. Before Hubble was launched in 1990, the estimates for the Hubble constant varied by a factor of two. In 1999, the Hubble Space Telescope Key Project on the Extragalactic Distance Scale refined the value of the Hubble constant to an error of about 10 percent.


    Riess' results appear in the April 1 issue of The Astrophysical Journal.

    Comments

    Is it possible that the dark energy used to explain the expansion of the universe is actually surrounding the universe and that it is acting as an attractive force outside our "bubble?

    The Stand-Up Physicist
    "Evidence for dark energy didn't come along until 1998, when two teams of researchers (one led by Riess) discovered it."

    This is a standard way to write about this issue, so is acceptable. It does bother me because it puts the cart - the hypothesis of dark energy - before the horse - odd acceleration.


    I like to focus on the problem. Gravity is all about universal attraction, always, always, always. So consistent is gravity! Think about how gravity would change the effect of the Universe over the lifetime of the Universe. Surely the cost of all that attraction would be the Universe would slow down, like we all do as we age.


    Like good scientists, the astronomers decided to check the reasonable hypothesis. This is not an easy hypothesis to check. That is why it took until 1998 to determine that not only were we not slowing down with age, but we are speeding up.  Get on our horse, and ride to assisted living. Our understanding how gravity works over the age and size of the Universe is wrong. I prefer blunt admissions of failure to hypothesis promotions. My Eeyore to another's Rabbit. 


    I would have titled the article "Cosmic Bubble Hypothesis Of Universe Expansion Ruled Out", reserving the word "Theory" for widely accepted, multiply confirmed areas of science. Again I understand this is a standard way to write, and is shorter, sounding less technical.
    Hank
    The issue is using a proper name.   String Theory is not obviously a theory but Brian Greene wisely made it the proper name so everyone says 'string theory' colloquially, seemingly putting it on a par with evolution or gravity, though more enlightened people know better.  Using theory as a name was popular in the 1970s.    They certainly feel like it is a theory if dark energy is, though in the text hypothesis is also used.
    The Stand-Up Physicist
    I am careful to always say "work on strings" and not the proper name. Probably because I am a fanboy of "Not Even Wrong", this is one subject where I part ways linguistically from what is clearly in wide use. Brian Greene is a promoter of work on strings, he is enlightened on the issue, but makes a strategic word choice that help the promotion work. In my own mind, I don't see how I could work on string theory that was yet a theory. I certainly could work on strings in the hope that it makes testable predictions.
    My own work remains a hypothesis, one that makes testable predictions. If anyone starts to call it a theory, I will whack them on the head. For me, the word theory should be reserved for only a few ideas in science. It is near the top of special words, along with experiment.
    An important theory that this measurement helps to confirm is that there IS a Hubble Constant, i.e. that the universe is expanding uniformly and at the same rate in all directions. Which is by no means a foregone conclusion - there are many cosmological models in which the expansion is anisotropic. But in fact Riess's data is self-consistent to within 3 percent and yields a unique value for the Hubble Constant.

    This press release puts way too much emphasis on the 'cosmic bubble' idea! And misses the key point of Riess's work. According to an earlier story in the New York Times, they calibrated the Cepheid distance scale using the galaxy M106, where spectral lines of water vapor were found, which enabled an independent determination of its distance.

    vongehr
    Agree and don't quite agree. Yes, the bubble thing is not the main point, but it is also misrepresenting the issue to say that now inhomogeneous acceleration is somehow ruled out. Firstly: We know that the Hubble constant is space-time dependent (that is what makes bubble universes in eternal expansion possible in the first place) and that global expansion due to general relativity is indeed (and of course must be) consistent with what can be described as "local space production", after all, modern physics is local field theory.
    Secondly: The problem comes not from the anisotropy or inhomogeneity as such but from the wrong assumption of that expansion leads to frame dragging! There is no frame dragging at all if the Hubble constant is a constant (the so called big rip necessarily needs ever more accelerated expansion). The expectation of being able to measure anisotropic expansion if the Hubble constant is inhomogeneous is based on ill-conceived frame dragging (on that the local bubble pushes the outside away - but cosmic expansion does not push!).
    The bubble idea to explain dark energy seemed unlikely when I first heard of it a while back but now based upon the above analysis it is believed to be very unlikely, or close to impossible. Although I believe my own answer is correct as discussed below, in any event changing expansion rates of the universe (from Inflation to deceleration to acceleration again) also seems to me to be far-fetched like the bubble idea, even though this dark energy hypothesis is presently popular.

    The original and primary evidence for the dark energy hypothesis is/ was based upon type 1a SN data. Based upon a different cosmological model, the "pan theory" I took great pains and many weeks to reanalyze this supernova data concluding that the problem is with the Big Bang model via the Hubble distance formula which accordingly would need to be modified which would re-calculate somewhat different distances. Using an "e" factor modification based upon the alternative model, dark energy accordingly would be a misinterpretation of the data based upon somewhat inaccurate distance calculations. Even the expansion of the universe itself also disappears based upon this same model; the redshifts are otherwise explained. The related paper that I wrote of this proposal will not be released for maybe a year or longer since I am presently looking for a university affiliation so as to be able to distribute this paper in the mainstream arena, otherwise via non-mainstream journals/ publishers it would get little exposure or criticisms from mainstream practitioners.

    > Supernova Ho for the Equation of State

    I think it should be spelled "Supernovae, HO, [etc.]"
    By the way, isn't "ho" a vulgar feminine insult, in English?

    I never liked the bubble theory because it wasn't a local effect. Non locality in theories is not satisfactory unless it contains a description of how it propigates by altering the local microstates.

    The preference of dark energy is not acceptable as an alternative either, for the same reason that hidden variables are not embraced in quantum mechanics.

    Leading scholars have argued that theories should be built of things that can be observed or measusred. Dark energy and dark matter theories require about 15 things that have never been found in experiments. Proponents seem to be continually grasping at straws in the most nebulous of data sets.

    At the same time the physics commuinity has not produced a unified theory of the micostates in local space time.

    Without a descrioption of the vacuum, it seems silly to assume that we need dark physics. Dark energy is said to make up a large percent of the total energy, but there is no agreement about how much energy is contained in the universe. If dark energy was so strong, then it should have major influence on local events. There is no evidence of that type. Local physics on a human scale doesn't need a big new power source.

    As far as I am concerned, no one ever proved that the dark energy is not just another name for the vacuum potential, and the dark matter is not just another way to sescribe virtual particles in the polarized vaccum.
    .

    James Ph. Kotsybar
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    DARK ENERGY QUESTION

                                   -- James Ph. Kotsybar

     

    Could inflation have done more than we know,

    shortly after the Big Bang’s first salvo,

    and created a dense matter halo

    beyond the horizon where we can go?

     

    Beyond the horizon that we can see,

    is there a remote possibility

    of a most massive field of gravity

    that pulls the strings of our reality?

     

    Perhaps it’s just dense matter that’s the source,

    accelerating expansion perforce,

    and not some new and mysterious force,

    or change of gravity’s attractive course,

    as though we are bound by a black hole’s skin,

    that stretches space to surface dimension.