When colliding ions, the scientists create a fireball that recreates the initial conditions of the universe at temperatures in excess of several thousand billion degrees. In contrast to the Universe, the lifetime of the droplets of QGP produced in the laboratory is ultra short, a fraction of a second In technical terms, only about seconds. Under these conditions the density of quarks and gluons is very large and a special state of matter is formed in which quarks and gluons are quasi-free dubbed the strongly interacting QGP.
The experiments reveal that the primordial matter, the instant before atoms formed, behaves like a liquid that can be described in terms of hydrodynamics. They rely on studying the spatial distribution of the many thousands of particles that emerge from the collisions when the quarks and gluons have been trapped into the particles that the Universe consists of today.
This reflects not only the initial geometry of the collision, but is sensitive to the properties of the QGP. It can be viewed as a hydrodynamical flow. The degree of anisotropic particle distribution - the fact that there are more particles in certain directions - reflects three main pieces of information: The first is, as mentioned, the initial geometry of the collision.
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The second is the conditions prevailing inside the colliding nucleons. The third is the shear viscosity of the Quark-Gluon Plasma itself. Shear viscosity expresses the liquid's resistance to flow, a key physical property of the matter created. No matter the initial conditions, Lead or Xenon, the theory must be able to describe them simultaneously.
If certain properties of the viscosity of the quark gluon plasma are claimed, the model has to describe both sets of data at the same time, says You Zhou.
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The possibilities of gaining more insight into the actual properties of the "primordial soup" are thus enhanced significantly with the new experiments. The team plans to collide other nuclear systems to further constrain the physics, but this will require significant development of new LHC beams. You Zhou emphasised. Materials provided by Faculty of Science - University of Copenhagen. Note: Content may be edited for style and length.
Science News. The answer to that question, the classical reasoning went, should determine our Universe's fate. It must expand or contract, dependent on what's inside it and in what amounts. To know which one was correct, all we had to do was measure how fast the Universe was expanding, and how that expansion rate changed over time. Physics would determine the rest.
While matter and radiation become less dense as the Universe expands owing to its increasing volume, dark energy is a form of energy inherent to space itself. As new space gets created in the expanding Universe, the dark energy density remains constant. It was one of the great quests of modern astrophysics. Measure the rate at which the Universe was expanding, and you know how the fabric of space is changing today. Put those two pieces of information together, and the way the expansion rate both is and also has changed allows you to determine what the Universe is made out of, and in what ratios.
To the best of our knowledge, informed by these measurements, we've determined that the Universe is made of about 0. This quest, which began as early as the s for some, got an unexpected answer in the late s. The expanding Universe, full of galaxies and complex structure we see today, arose from a smaller, hotter, denser, more uniform state in the past.
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There must be some new form of energy driving the current phase of accelerated expansion, beyond the known matter and radiation. So if dark energy dominates the expansion of the Universe, what does that mean for our fate? Here are the five possibilities. Dark energy is an expansion-dominating cosmological constant. This is the default option given the best data we have today. While matter becomes less dense as the Universe expands, diluting as the volume expands, dark energy represents a non-zero amount of energy inherent to the fabric of space itself.
As the Universe expands, the dark energy density remains constant, causing the expansion rate to asymptote not to zero, but a positive value. This leads to an exponentially-expanding Universe, and will eventually push away everything that isn't part of our local group. The Big Rip scenario will occur if we find that dark energy increases in strength, while remaining negative in direction, over time. Dark energy is dynamical, and grows more powerful over time.
Dark energy appears to be a new form of energy that's inherent to space itself, implying that it has a constant energy density. But it could also be changing over time. One possible way it could be changing is that it could be strengthening in magnitude, which would cause the Universe's expansion rate to speed up over time. Not only would more distant objects appear to accelerate away from us, they'd do so at an increasing rate. In the final moments of the Universe, subatomic particles and the fabric of space itself would get torn apart.
This "Big Rip" fate is a second possibility. While the energy densities of matter, radiation, and dark energy are very well known, there is still plenty of wiggle room in the equation of state of dark energy.
It could be a constant, but it could increase or decrease in strength over time as well. Dark energy is dynamical, and decays over time. How else could dark energy change? Instead of strengthening, it could weaken. Sure, the expansion rate is consistent with a constant amount of energy belonging to space itself, but this energy density could be dropping, too. If it decays away to zero, it could lead to one of the original possibilities expressed above: the Big Freeze. The Universe would still expand, but without enough matter and other forms of energy to recollapse. If it decays away to become negative, however, it could lead to another of the possibilities: a Big Crunch.
The Universe could be filled with energy intrinsic to space that suddenly switched signs and caused space to recollapse.
While the timescale for these changes is constrained to be far longer than the time since the Big Bang, it could still occur. The different ways dark energy could evolve into the future. Remaining constant or increasing in strength into a Big Rip could potentially rejuvenate the Universe, while reversing sign could lead to a Big Crunch. Dark energy could transition into another form of energy, rejuvenating the Universe.