A Riddle for Our Time – Astronomers Examine Cosmic History

Schematic of Cosmic History

A schematic of cosmic history.

In a newly published study, a team of astronomers call attention to a neglected riddle of the expansion of the universe: although cosmic acceleration might have started at any time, curiously it has happened in our own time.

One of the most remarkable successes of astrophysics in the last century was its discovery that the age of the universe as measured by its oldest stars was about the same as the age estimated in an entirely different way, from the recession of galaxies. Both came up with surprisingly long times – billions of years – providing reassuring confirmation that both were probably on the right track. But the two values were not identical and scientists very quickly realized a major discrepancy: the oldest stars were older than the universe itself. Refinements to the measurements and the models to resolve this contradiction were underway until 1998 when cosmic acceleration was discovered. It proved, in a single sweep, that the universe was actually much older than had been thought, and in particular, was older than the oldest stars.

But there was a riddle in the discovery: The motion of the universe is governed by matter, whose gravity tends to slow the expansion down, and by acceleration which speeds it up. Since the average density of matter in the universe steadily drops as the universe swells, in time it has a smaller and smaller value. Curiously, today it just happens to have almost exactly the same value (when expressed in the same units) as the acceleration parameter. Why? There was a second riddle too: The theoretical size of the acceleration parameter could be almost anything; indeed, basic quantum mechanical calculations suggest it should be vastly larger than it is. Why it is as small as we measure is a mystery.

CfA astronomers Arturo Avelino and Bob Kirshner have just published a paper calling attention to yet another riddle. The universe did not expand at a constant rate that was just the blend of these two factors. For the first nine billion years of cosmic evolution, contraction dominated and the universe gradually slowed its expansion. Since the relative importance of cosmic acceleration grows with time, however, for the past five billion years acceleration has dominated and the universe has sped up its expansion. Curiously, though, today the universe looks the same way it would have if it had always been expanding steadily at a constant rate (the rate required to prevent ultimate re-collapse). Although it sounds slightly similar to the original riddle, the authors describe why this new puzzle is actually different: We are living (apparently) in a privileged epoch; the other puzzles do not have this implication. The explanation(s) for these riddles is not yet known. If some specific new kinds of elementary particles exist, the scientists suggest, they could provide the answer, but for now, the only thing that is certain is that more observational research is needed.

Reference: “The Dimensionless Age of the Universe: a Riddle for Our Time” by A. Avelino and R. Kirshner, 25 August 2016, The Astrophysical Journal.
DOI: 10.3847/0004-637X/828/1/35

14 Comments on "A Riddle for Our Time – Astronomers Examine Cosmic History"

  1. I have always wondered about the period of inflation,,during which the volume of the universe grew at an apparantly implausibly rapid rate.

    Given that mass slows the passage of time,and that the entire mass of the universe was concentrated into a very small volume during the period of inflation,,was the passage of time slower during the period of inflation than it is today? Producing an illusion of inflation occuring incredibly quickly when judged against today’s clocks??

    • think about what you asked in your last sentence. Today’s Clocks?
      um time is only measured on earth by clocks. In space there is no such thing as time measurement. Time never stops but Man invented a way to track it. Our clocks are based on how long it takes Earth to make it’s way around the Star that sits above us. “Clocks” would be different on Mars as it takes longer then 24 hours to make it’s way around that star. So in space you can’t bring your watch on the way to Mars and calculate what time it is. That might be the time on Earth but………………………….

  2. If we believe that our World has started sometimes ago we are still in the position to decide which hypothesis, Lemaître’s or Gamow’s was closer to reality. There is an opinion that the problems in the standard cosmology could be solved by adjusting of details. Our suggestion is that we have to go back to the conceptions and use the observations accumulated since.

  3. And no one seems to consider (any more) that ‘time’ itself is a force.
    The expansive force, and the counter-force of gravity.

    Time is the force that keeps things and events separate, while gravity is the opposite.

    For every action there is an equal and opposite reaction…
    Gravity and Time are the opposing forces.

    The problem is, Time gains momentum as Gravity loses it. Hence, the accelerated rate of expansion as the universe ages.

    It would take very little extra force in the ‘inflation’ to tip the balance.
    All it would take is the small amount of force, that was the will of a certain thing.

    And if ‘time’ was ‘slower’ in the early stages of the universe when matter was more localized, it would not matter in our perception of the time span – if everything were equal and opposite.
    In that case we should not expect to see an accelerating expansion.
    But we do, because everything is not equal.

    There is a force that is both external and internal that is not being taken into account by the scientific community.

    And that would be the force that actually caused the ‘Big Bang’.

    Because if everything was equal and opposite, every force countering another, nothing created nor destroyed – it would be equilibrium.
    Nothing would ever move – ever.

    There could NEVER be a Big Bang or a Big Crunch, or anything in between.
    There could be no expanding or contracting universe.
    It would just be a blob of nothing, and ever nothing.

  4. Perhaps or universe, following laws of quantum mechanics, only began accelerating since we began observing it,

  5. It’s time to admit that the background red shift is due to photon energy loss (through numerous processes) rather than expansion, which has led to more and more inconsistencies requiring the myriad fudge factors designed to make observation jive with theory. Electron-positron pair formation is actually all we need to populate the universe with matter — and doesn’t require the limitation of 13.7 billion years which is rapidly becoming untenable.

  6. The expansion is not simply an outward expansion, all things revolve in an orbit around a central nucleus, atoms, solar systems, galaxies, and even our own universe. I wonder if scientists have taken into account an expansion that is expanding outward as it also orbits the central nucleus of the expansion origination point? Taking into account the relative motion of the expanding rotation around this nucleus might explain some of the mystery.

  7. Tapir, at the time of inflation, which was in the mico seconds after the Bang, there was only energy, no mass, hence , no time dialation due to gravitational influences!!

    • Jim, actually energy and matter are the same – only in very different forms. This was one of Einstein’s great discoveries, which we are very familiar: e = mc2. Therefore, energy also has mass, albeit a massive amount of energy and only a relatively small mass. All the mass of the universe came from the initial energy of the Big Bang.

      Scientist theorize that under certain conditions (such as immediately following the BB), gravity can be massively repulsive, then rapidly weakens as it spreads out into the other hidden dimensions and becomes an attractive force…. I love reading about this stuff, but it can drive you cross-eyed at times.

  8. Blow up a balloon.
    Measure and contrast all periods of inflation.
    I didn’t say stop “blowing it up”….

  9. QUANTUM is the acronym for a quiz using abbreviations now to understand mathematics in jamaica

  10. Ever had a short snooze, but a long time duration dream?
    Also, the speed of light, taken in context of distance and time CANNOT be an absolute.
    Have a great day!

  11. It’s more like an infinitely large glass to put money in. Even a child would say… The universe is shaped like a glass? That is as ridiculous as dinosaurs made all of the oil.

  12. Madanagopal.V.C. | September 16, 2016 at 7:40 am | Reply

    AT the time of Big Bang birth of Dark Energy should have been 100%. This energy begot light energy of 4% which later on transformed into light matter like galaxies and stars. This light energy gave birth to all the bosons and fields like our four fields which are electro magnetic, gravitational, strong forces and electro weak forces that account for the birth of electrons, protons, neutrons, neutrinos and all their anti matter particles. Besides another Higgs field gave rise to mass of the matter through Higgs Bosons. This story apart Dark Energy also should have given rise to Dark matter the composition of which is still unknown. But this Dark Matter had been thrown apart to various distances which very well accounted for the gravitational lensing effect of distant galaxies, becoming core of stars and galaxies, and expansion of galaxies which are blown apart by their sheer strength against their gravitational force which always tend to collapse. Our Milky way itself contains good amount of Dark Matter in its core to keep its billion stars apart spiraling around in different radial trajectories. This concept only will explain why Dark energy is 72% Dark Matter is 24% and the remaining 4% being our light matter and visible universe. This concept may also explain why the expansion was slow at the beginning and now it is very fast for the past 13.7 billion years, when many stars and galaxies were formed to be foot balled to distances by the lumps of dark matter spread across, whereas the age of the universe is 15 billion light years. The initial slow down and subsequent hyperbolic expansion can thus be explained. Particles of Dark Matter and Bosons of Dark Energy are yet to found out by the future scientists. Thank You.

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