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Dark energy theories demolished

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  • Dark energy theories demolished


    BY THOMAS KITCHING ON 12/13/17 AT 7:38 AM

    This article was originally published on The Conversation. Read the original article.

    There was much excitement when scientists witnessed the violent collision of two ultra-dense, massive stars more than 100 million light years from the Earth earlier this year. Not only did they catch the resulting gravitational waves—ripples in the fabric of spacetime—they also saw a practically instantaneous flash of light. This is exciting in itself and was the first direct evidence for a merger of neutron stars.

    But from a cosmologist’s perspective, the photo-finish of the gravitational waves and the flash of light has at a stroke demolished years of research into a completely unrelated problem: Why is the expansion of the universe accelerating?

    An artist imagines crashing neutron stars.MARK GARLICK/UNIVERSITY OF WARWICK

    It turns out that space and time are actually mutable, pliable, flexible and wiggly, rather than constant, fixed or immovable. This has been known since Einstein published his theory of general relativity, which explains how gravity warps spacetime. The subtle effects that this mutability causes need to be accounted for even in the GPS that makes your sat nav and iPhone work.

    One prediction of Einstein’s theory was that it should be possible for spacetime to have waves in it, like the surface of the sea. These would be visible if one could, for example, smash together two black holes … This prediction was dramatically seenin the first detection of gravitational waves by the LIGO experiment in 2015. The discovery opened up a whole new way to probe the cosmos, and was awarded the Nobel Prize for physics. Something is pushing galaxy cluster SDSS apart.K SHARON/TEL AVIV UNIVERSITY/E OFEK/CALTECH)/ESA/NASA

    The new detection of gravitational waves from the merger of neutron stars also has profound implications for our understanding of the universe. However for the cosmologists it was the flash of light 1.7 seconds after the gravitational waves that was the more intriguing observation. The cosmic speed camera

    The 1.7 second time delay is important because it means that the gravitational waves and the light waves had been travelling at almost exactly the same speed. In fact these are two of the most closely matched observed speeds ever: the two only differed by one part in 10 million billion.

    To put this into context, if the speed cameras on the road could measure speed differences this finely you would get a ticket for going 30.0000000000000001mph in a 30 miles per hour zone.

    Compared to the best measurements cosmologists were hoping for in the future, this is a factor of a million billion times better. Factoring in that the electromagnetic waves may have taken a bit of time to escape from the turmoil of a neutron star collision, for all intents and purposes the speed difference is zero.

    The International Dark Energy Survey's Dark Energy Camera captures galaxies in the nearby Fornax cluster, August 18, 2014.DARK ENERGY SURVEY

    Cosmology is in a bit of a pickle. We have a great model that can explain the evolution of the universe from a fraction of a second before the big bang, until now approximately 14 billion years later. The problem is that in order to explain all the observations, a mysterious energy called “dark energy” must be added to the models. Dark energy is a huge problem, it accounts for about 70 percent of all the energy in the universe, and we have absolutely no idea what it is.

    Dark energy is like an anti-gravitational effect that is pushing the universe apart and causing its expansion to accelerate. So to explain dark energy, cosmologists have attempted to change or replace Einstein’s theory to see if a new theory of spacetime could finally explain the effects of dark energy.

    One way that cosmologists tried to do this was by changing the speed in which gravitational waves and light traveled. There were many different theories that had this component—each with a peculiar name like quartic and quintic galileons, vector-tensor theories, generalized proca theories, bigravity theories and so forth. Without data any of the theories could have been correct, and there were many people hopeful that they could be the next Einstein or Newton. Where are we now?

    But now in a single observation from a single neutron star merger, a wide variety of these have now been consigned to the cosmological dustbin in a flurry of papers (here, here, here, here, here and here). So no new Einstein yet.

    In the absence of compelling data, it is still possible that we can update Einstein so we can account for dark energy. But the wiggles from the gravitational wave data has left very little wriggle room. An artist depicts the finished square kilometer array.SWINBURNE ASTRONOMY PRODUCTIONS/SKA PROJECT DEVELOPMENT OFFICE

    All the theories that have survived the pruning are much simpler than those that were allowed before; and the simplest theory, and the frontrunner, is that dark energy is the energy of empty space, and just happens to have the value we observe.

    Another explanation that has survived is that it’s a Higgs-like field. The now famous Higgs boson is a manifestation of a “Higgs field”—the first “scalar field” observed in nature. This is a field that has a value at every point in spacetime, but no direction. An analogy would be a pressure map on a weather forecast (values everywhere but no direction). A wind map, on the other hand, isn’t a scalar field as it has speed and overall direction. Apart from Higgs, all particles in nature are associated with “quantum fields” that aren’t scalar. But like the Higgs, dark energy could be an exception: a ubiquitous scalar field pushing the universe apart in every direction.

    Thankfully we won’t have to wait long before new telescopes will test the remaining theories and a big piece of the cosmological puzzle will be completed.

    Thomas Kitching is Reader in Astrophysics, UCL

  • #2
    This is a really big and very important discovery. It destroys most of the theories about dark energy. So it will take the science about dark energy in a new direction.


    • #3
      When I first heard of Dark Matter and Dark Energy I ridiculed the notion. Glad I don't have to eat my hat. :)


      • #4
        Thanks again Lou


        • #5
          Discovery of neutron star collision is 'breakthrough' of 2017

          AFP Kerry SHERIDAN,AFP 7 hours ago This image released by the National Science Foundation shows an artist's illustration of two merging neutron stars (AFP Photo/A. Simonnet)
          Miami (AFP) - The world's first-ever detection of two faraway neutron stars colliding, causing a massive blast that rippled through the fabric of space and time, was judged the scientific breakthrough of 2017, the journal Science said Thursday.

          The smashup of the two ultra-dense stars observed on August 17 "confirmed several key astrophysical models, revealed a birthplace of many heavy elements, and tested the general theory of relativity as never before," said the report.

          The blast, which occurred 130 million light-years away, is the kind of event that produces as much as half of the universe's gold, platinum, uranium and mercury, experts said.

          Shockwaves ran through the scientific community when the discovery was announced in October, after being detected by gravitational wave sensors in the US and Europe, and some 70 telescopes and observatories around the world.

          Bangalore Sathyaprakash from Cardiff University's School of Physics and Astronomy recalled the moment as "the most exciting of my scientific life."

          The magazine's annual rundown of the top advances of the past year also included the discovery of a new kind of orangutan, Pongo tapanuliensis, with just 800 believed to live in an isolated Indonesian forest.

          Another was a second look at a skull unearthed from a Moroccan cave in 1961, showing that it was actually about 300,000 years old, a full 100,000 years older than early homo sapiens were previously known to exist.

          The findings have "reinvigorated the search for new fossils of our species's earliest members," said the report.

          The successful gene therapy trial in children with spinal muscular atrophy 1 (SMA1), the most common genetic cause of death in infants, also made the list.

          Eleven of the 12 babies who were infused with a high dose of intravenous AAV9 gene therapy -- carrying the gene for a missing protein -- "can talk, eat, and sit at least briefly on their own," it said.

          A genetic advance called base-editing that may help eliminate certain diseases also made the top 10, along with the approval of pembrolizumab (Keytruda) by Merck to kill a range of cancers based on their DNA rather than their location in the body.

          - 'Breakdowns' of 2017 -

          The journal, which is published by the non-profit American Association for the Advancement of Science in Washington, noted several "breakdowns" in the world of science this year, too.

          They included the "deeply dysfunctional" relationship the scientific community and between US President Donald Trump, who this year "renounced the 2015 Paris climate accord, rolled back many environmental rules, and called for deep budget cuts at key research agencies," it said.

          "It's a breakdown of epic proportions, with no obvious fix."

          Sexual harassment also roiled the scientific world, as more women were encouraged to speak out by the #MeToo movement that has swept through the worlds of entertainment and politics.

          Another low point was the failure of a $5 million project to save a small porpoise, called the vaquita, off the coast of Mexico.

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