Attempts at Solving the Coincidence Problem – seminar by Marina Cortês

In this excellent seminar, Marina told us about her group’s attempt to solve the coincidence problem of dark energy by allowing for multiple phases of acceleration. The coincidence problem is that it seems we live in a special time where (according to the ΛCDM model) the energy density of matter and dark energy is comparable. Since the energy density of matter decreases as a^-3 (where a is the scale factor) whereas that of dark energy is constant, the period of time where the two are comparable is very small when compared with the age of the universe, thus making the composition of the universe that we currently observe, where dark energy makes up about 70% and matter 30%, quite unlikely.

Fraction of total energy density of radiation (green), matter (blue) and dark energy (purple).

Although the Anthropic Principle has been suggested as a solution to this problem, Marina proposes another possible solution: that there were multiple phases of acceleration (MPA) in the history of the universe and we just happen to be experiencing one right now. Marina’s group have looked at the simplest possibility: the dark energy equation of state was equal to -1, as in ΛCDM, and at some point, its energy density dominated over matter, causing a period of acceleration. But the acceleration ceases when, for a period w becomes greater than zero, causing dark energy to dilute and allow matter to dominate again. Then it switches back to w=-1 and expansion accelerates again once dark energy dominates over matter. Thus there could have been another period of acceleration before this one, meaning we do not occupy a special point in time.

Marina told us that it is difficult to “hide” this period of acceleration and deceleration in the data we have, especially the CMB power spectrum, the shape of which is sensitive to the behaviour of dark energy. It is not the short period of acceleration which has the most effect but the period of dilution, which necessarily has to be quite long to allow matter to dominate again, which strongly affects the CMB through the integrated Sachs-Wolfe (ISW) effect.

Through Markov Chain Monte Carlo methods, Marina and her team investigated at what possible redshifts this could happen. The effect on the CMB by the ISW effect and the fact that extra periods of acceleration affect the distance to the surface of last scattering, seem to rule out low redshifts as candidates for a period of extra acceleration. They did, however, find that it was possible to “hide” an extra period of acceleration in the CMB during the radiation dominated era (z~300 to 3000).

It has been shown that the universe could have undergone another period of accelerated expansion and the CMB would not be altered. However, it seems that the only period during which this is possible is in the radiation dominated epoch.

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One Response to Attempts at Solving the Coincidence Problem – seminar by Marina Cortês

  1. Gravity is a pseudo-force on earth, but outer space is called “zero gravity.” All scientific organizations and their scientists, always comply with the big-bang theory, or they would not be funded and become discredited. I don’t believe that the CMB is the remnant of the Universe. The largest known collisions are galaxy clusters, which collide along intersecting cosmic plasma filaments, which are surrounded and confined by magnetic fields, and have an electric field component perpendicular. Moving charges in space obey Faraday’s law, and form magnetic and electric fields. Kip Thorne’s team shows that the warping and twisting of space, is the inertial angular momentum of magnetic field. Team member David Nichols says the rising of the ocean tides on earth from the moon, is the electric component. When you get electric shock from a plug, you can feel the pull and stretch because you are grounded to earth. Gravity I believe is interrelated to electricity and magnetism. Einstein developed relativity using a model of a charged sphere, with isolated charged points. Later, black holes were invented to replace point charges. Dark matter became necessary to keep the shapes of galaxies together, and prevent stars from flying away. In truth, the big-bang with dark energy too, is the accepted cosmological model, but is not believable by me. Vortex and Tendex forces they say will become a cosmology, and there work is accepted by relativity. The major problem with the big-bang to me is, what existed throughout eternity, before it happened? The singularity is unstable. After the big-bang, plasma physics quickly became imperative to operated before gravity could form the first atoms, which happened minutes later during the re-ionization epoch. A more logical explaination is that two or more entire superclusters, which take 90 billion years to form, collided along cosmic filaments. These huge explosion is still expanding our visible universe, and giving the effect of a cosmic redshifts and dark energy acceleration. There is evidence from NASA that the dark flow is a huge singularity 150 billion light years away. Why would the Universe has an absolute or minimum size to anything? A supercluster with huge voids, is connected together by cosmic filaments, the largest known is 1.3 billion light years long, called the sloan great wall. Galaxy clusters are connected into a filamentary structure, which big-bang theory says formed shortly after the big-bang. Recent BOSS studies of 14,000 quasars shows this plasma filamentary structure exists out to 12 billion light years scale view ! I assume myself that this filamentary structure extends beyond 100 billion light years too, and that the “Universe” cannot be described by anybody, because it is quite frankly “Emptiness” like all things are in nature. I believe that superclusters form “hyperclusters’ and so forth forever, and that the largest sized objects in the universe, are mere specks of dust and gas, and that the tiniest particles can be huge objects when nearby and compared viewed by tinier specks. SIZE is the great deceiver in the universe, and to call the Universe the absolute object of everything, and to say it came from the big-bang, cannot make sense to me. Thank you for allowing me to share my views on reality.
    Pat
    http://HologramUniverse.wordpress.com
    http://HolographicGalaxy.blogspot.com

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