Physicists Closing in on Understanding the Primordial Universe

Article written: 14 Aug , 2012
Updated: 23 Dec , 2015

Photo of the ALICE detector at CERN. Photo courtesy of CERN.

Slamming barely nothing together is bringing scientists ever-closer to understanding the weird states of matter present just milliseconds after the creation of the Universe in the Big Bang. This is according to physicists from CERN and Brookhaven National Laboratory, presenting their latest findings at the Quark Matter 2012 conference in Washington, DC.

By smashing ions of lead together within CERN’s lesser-known ALICE heavy-ion experiment, physicists said Monday that they created the hottest man-made temperatures ever. In an instant, CERN scientists recreated a quark-gluon plasma — at temperatures 38 percent hotter than a previous record 4-trillion degree plasma. This plasma is a subatomic soup and the very unique state of matter thought to have existed in the earliest moments after the Big Bang. Earlier experiments have shown these particular varieties of plasmas behave like perfect, frictionless liquids. This finding means that physicists are studying the densest and hottest matter ever created in a laboratory; 100,000 times hotter than the interior of our Sun and denser than a neutron star.

CERN’s scientists are just coming off of their July announcement of the discovery of the elusive Higgs boson.

“The field of heavy-ion physics is crucial for probing the properties of matter in the primordial universe, one of the key questions of fundamental physics that the LHC and its experiments are designed to address. It illustrates how in addition to the investigation of the recently discovered Higgs-like boson, physicists at the LHC are studying many other important phenomena in both proton–proton and lead–lead collisions,” said CERN Director-General Rolf Heuer.

According to a press release, the findings help scientists understand the “evolution of high-density, strongly interacting matter in both space and time.”

Meanwhile, scientists at Brookhaven’s Relativistic Heavy Ion Collider (RHIC), say they have observed the first glimpse of a possible boundary separating ordinary matter, composed of protons and neutrons, from the hot primordial plasma of quarks and gluons in the early Universe. Just as water exists in different phases, solid, liquid or vapor, depending on temperature and pressure, RHIC physicists are unraveling the boundary where ordinary matter starts to form from the quark gluon plasma by smashing gold ions together. Scientists are still not sure where to draw the boundary lines, but RHIC is providing the first clues.

The nuclei of today’s ordinary atoms and the primordial quark-gluon plasma, or QGP, represent two different phases of matter and interact at the most basic of Nature’s forces. These interactions are described in a theory known as quantum chromodynamics, or QCD. Findings from RHIC’s STAR and PHENIX show that the perfect liquid properties of the quark gluon plasma dominate at energies above 39 billion electron volts (GeV). As the energy dissipates, interactions between quarks and the protons and neutrons of ordinary matter begin to appear. Measuring these energies give scientists signposts pointing to the approach of a boundary between ordinary matter and the QGP.

“The critical endpoint, if it exists, occurs at a unique value of temperature and density beyond which QGP and ordinary matter can co-exist,” said Steven Vigdor, Brookhaven’s Associate Laboratory Director for Nuclear and Particle Physics, who leads the RHIC research program. “It is analogous to a critical point beyond which liquid water and water vapor can co-exist in thermal equilibrium, he said.

While Brookhaven’s particle accelerator cannot match CERN’s record-setting temperature conditions, scientists at the U.S Energy Department lab say the machine maps the “sweet spot” in this phase transition.

Image caption: The nuclear phase diagram: RHIC sits in the energy “sweet spot” for exploring the transition between ordinary matter made of hadrons and the early universe matter known as quark-gluon plasma. Courtesy of the U.S. Department of Energy’s Brookhaven National Laboratory.

John Williams is a science writer and owner of TerraZoom, a Colorado-based web development shop specializing in web mapping and online image zooms. He also writes the award-winning blog, StarryCritters, an interactive site devoted to looking at images from NASA’s Great Observatories and other sources in a different way. A former contributing editor for Final Frontier, his work has appeared in the Planetary Society Blog, Air & Space Smithsonian, Astronomy, Earth, MX Developer’s Journal, The Kansas City Star and many other newspapers and magazines.

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18 Responses

  1. beyondEinstein says

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  2. lcrowell says

    There are connections between QCD and gravity. A gluon can form an entanglement with another gluon that is a graviton. The structure of QCD plasmas or QGP has then connections to black holes and anti-de Sitter spacetimes.

    It is not difficult to quantize weak gravity. This is usually written as a bimetric theory g_{ab} = ?_{ab} + h_{ab}, where ?_{ab} is a flat spacetime (Minkowski) metric and h_{ab} is a perturbation on to of flat spacetime. Gravitons enter in if you write the perturbing metric term as h_{ab} = ?_a?_b, or ?_a^c = ?_a?^c. The Ricci curvature in this weak field approximation is

    R_{ab} – (1/2)Tg_{ab} = ?h^t_{ab},

    with h^t_{ab} the traceless part of the metric, and ? the d’Alembertian operator. Which in a sourceless region this computes plane waves with the wave equation ?h^t_{ab} = 0. The two polarization directions of the graviton may then be interpreted as a form of diphoton, or two photons in an entanglement or a “bunching” as in Hanbury Brown-Twiss quantum optical physics.

    If we now think of extending this to a strong field limit there are the square of connection terms ?^a_{bc} in the Ricci curvature, or cryptically written as R ~ ?? + ?? where there is the appearance of the nonlinear quadratic term in the connection. This nonlinear term indicates the group structure is nonabelian, so the photon interpretation breaks down. The graviton in this case is a form of di-gluon, or gluons in a state entanglement or chain that has no net QCD color charge. This connects with the AdS_n ~ CFT_{n-1} correspondence, where for n = 4 the conformal field theory is quark-gluon QCD physics. Further D-branes have QCD correspondences and this takes one into the general theory I lay out. One does need to look at the references to learn more of the specifics. The quantum phase transition to entanglement states is given in the paper I wrote .

    These experiments with heavy ions are then extremely fundamental, reaching down to matters of quantum gravity and cosmology. This work should draw this connection between gravitation and quark-gluon or QCD physics.

    • Dav_Daddy says

      Hey LC, a little ot but does the graviton have any mass? I was curious because if the graviton is massless that would mean the gravitational would move at the speed of light, right?

      Assuming that is correct couldn’t that be why we have been unable to detect gravitational directly as of yet?

      • Peristroika says

        Gravitational is a noun?

      • Dav_Daddy says

        That should have read “gravitational waves.”

        Stupid auto correct on my new phone!

      • Torbjörn Larsson says

        Naively it has to be massless, its field interactions should have infinite range.

        It also helps with consistency with relativity when having lightspeed travel of field changes.

        I guess in the low energy theory the non-linearities of general relativity is greatly suppressed, so the backreaction from changing gravity on the gravitons mediating the change is not much of a feedback loop.

        In other words, gravity has to be, and is, weak. This is presumably why we haven’t detected its waves outside of pulsar observations (unambiguously but “indirectly” as the saying goes) and even less its particles as of yet.

        When you go to high energies and it all blows up in your face, I hear. That is probably why you see theorists making funny grimaces all the time.

      • lcrowell says

        Gravity is very weak because particle masses are very small. The Planck unit of mass, the mass of a quantum of a black hole, is m_p = sqrt{?c/G} ~ 10^{-5}g. Elementary particles are 19 to 22 orders of magnitude smaller in mass.

        If gravitons had mass Newton’s law of gravity would have a potential ? = GMme^{-ar}/r, which is the Yukawa potential.

      • lcrowell says

        Gravitons are massless, as are the gauge particle of quantum chromodynamics (QCD) called gluons, but they do have energy which is equivalent to mass. They just do not have a rest mass so they can exist in a frame as a stationary particle. A free graviton is then without mass and its degrees of freedom are transverse, or field oscillations perpendicular to the direction of propagation.

        The role of mass is though a bit strange with gravitons that are in some collective interaction or coherence like laser photons. Since gravitons are related to gluons, or are entanglement states of gluons, we can think of QCD and gluons. A hadron is a bound state of quarks, where gluons are the gauge particle mediating this interaction. Quarks have mass, but the up and down quark that compose protons are only around about 10MeV/c^2 in mass. So a proton has only 30MeV/c^2 of its 938MeV/c^2 mass as due to quark mass. The quark mass is determined by the Higgs field interaction. The rest of this mass is due to gluons that are self interacting in this confined vacuum state of the hadron. While the gluons are massless, they are confined in this region around 10^{-13} cm, which means this little bubble region has a mass. If one had a perfectly mirrored box with lots of photons in there, one could measure an effective mass increase of the box due to the photons inside. In this way the bound state of quarks and gluons has this effective mass.

        Gravitons are I think entanglements of gluons, or what we might call gluon chains. Certain complex self interacting states of gluons can form effective mass states. Remember that gravity interacts with mass-energy, so gluons can be self-interacting — similar to gluons. In classical gravity there are some solution types that are intermediate to the near field solution, a black hole, and the far field solution as gravity waves. These type I and II solutions are complicated self-interacting solutions of the Einstein field equation. As gravitons these are coherent self-interacting gravitons that have an effective mass. These gravitons can then have a longitudinal field component and are an aspect of what is called f(R) gravity. J. A. Wheeler called some of these “geons,” and if the geon is sufficiently self-bound it can implode into a black hole. A black hole can be thought of as a condensate of particles or gravitons in a state that is completely self-confined.

        Quark-gluon plasmas produced by RHIC and the lead heavy ion collisions at the LHC can produce very transient states corresponding to black holes, or with tiny quantum amplitudes corresponding to black holes. These amplitudes are not large enough to generate a full bonifide black hole, as seen in previous fears of the LHC producing an Earth devouring black hole, but they should be sufficient to test these theories.


      • Wezley Jackson says

        Nice post. I do my best to try and understand… I really liked your observatioin – ” If one had a perfectly mirrored box with lots of photons in there, one
        could measure an effective mass increase of the box due to the photons

        From my novice knowledge level, it reminds me of the photoelectric effect – I am fascinated no end to learn that photons can translate to electrons by interaction with certain metalic substrate/s.. Although both massless particles, the electron is closely associated with matter states and helps me understand your analogies – I am fascinated by all the developments from LHC and appreciate you taking the time to explain – When I get time I will read your paper further – To be honest many of the denser equations ellude me but I definitely appreciate the thrust of the conclusion in your paper and have often considered similar cosomologies [albeit with not the same degree of education as you possess]

    • I’m a little confused… I’ve heard with the Higgs-like Boson announcement that now all the puzzle pieces per force carrier p[articles have been discovered, but I thought gravitons were still eluding ‘our’ searches… Or is it just Grav Waves that ‘we’ have still to detect? Or are they the same thing?

      • lcrowell says

        There is a prospect that we may find evidence for the quantum state of a gravity wave, or the graviton, before we detect a classical gravity wave from an astrophysical source. This would be a bit of an irony. There is indirect evidence for gravity waves with the Taylor-Hulst measurement of pulsar timing change. The Light Interferometry Gravity Detector (LIGO) is a huge Fabry-Perot plus Michelson-Morley interferometer that could detect gravitational radiation due to the collision of two black holes or black hole plus other object within about 50 million light years. There are plans to extend its sensitivity out to 300 million light years, if I remember the numbers right. It would be good to get this direct measurement of a classical gravity wave.

  3. Lord Haw-Haw. says

    The boundary line John Williams writes of is a little better explained by John Timmer on Ars Technica:

    Effectively the physics behind heavy ion collisions differ from proton-proton collisions, with lead collisions at the LHC the concept is to spread a lot of energy over a large volume to reveal phenomena that a focused energy collision would miss, in the case of the latter (i.e. proton-proton collisions) as much energy as possible is focused on a tiny area.

  4. Torbjörn Larsson says

    On another note, has the primordial WordPress engine or its implementation on UT changed lately?

    I get all these problems with the editor and flagging comments (say, as “like” comments) interacting with the browser security techniques and the browser interacting with the editor security techniques, which makes it tricky to respond on UT.

    It works fine as long as you only make short comments without errors. As soon as you pass onto the trickier stuff, the stuff gets tricky – more than usual.

  5. bugzzz says

    Naive related question: regarding astronomy, has anyone yet figured out how we can peer into the primordial plasma soup? Or does this still remain a problem in that we can only see back to the point in time where the plasma has sufficiently cooled to be transparent?

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