So many different theories are confusing me.
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Calilasseia wrote:First of all, the Big Bang theory was only intended to explain the behaviour of the universe once it was instantiated. What happened before this was never the remit of Big Bang theory.
Calilasseia wrote:
The idea of space-time coming into existence upon said instantiation, was in part a consequence of physicists not being in a position to develop ideas about what happened before, because the standard cosmological model at the time involved a singularity. Singularities constitute a sort of mathematical no-go area - they are, in effect, locations within a function domain for which the function in question ceases to be well-behaved, or worse still, ceases even to be defined. If you can't even define a function at a given point in the function domain, you can't really say much about how that function behaves at that point. The Big Bang singularity represented, in effect, a point where the functions representing the behaviour of physical systems cease to be defined. It was therefore thought that no progress beyond that point could be made.
Calilasseia wrote:
This view changed as a result of several developments. The one I'm best acquainted with is braneworld cosmology, which proposes that the universe was instantiated as a result of two branes colliding. This model requires that spacetime has always existed, and that as a result, the "t=0" of the Big Bang theory merely delineates the moment at which the instantiating collision occurred from the standpoint of the instantiated universe entity. Since that entity didn't exist beforehand, a "t<0" from the standpoint of that entity makes no sense, but does make sense from the standpoint of other entities that did exist beforehand.
Calilasseia wrote:
What makes braneworld collision particularly worth pursuing further, is that [1] it doesn't involve singularities (or, more rigorously, doesn't involve non-regularisable singularities - a quick look at complex analysis, and how singularities are treated therein, will explain how singularities can be regularised, provided they are of the correct type), and [2] provides a potential empirical test of the theory, Braneworld collisions, if they are genuinely responsible for instantiating universe-type entities, leave within those universe-type entities evidence of their having taken place, in the form of a particular spectrum of primordial gravitational waves. If that spectrum is observed (hence the expense being spent on LIGO etc), then this is an indication that braneworld cosmology is something more than mere speculation.
Macdoc wrote:I think you need to relieve Cali of this burden ..there is lots of good info on the web and open source courses
Macdoc wrote:I think you need to relieve Cali of this burden ..there is lots of good info on the web and open source courses
http://ocw.mit.edu/courses/physics/8-82 ... fall-2008/
http://www.openculture.com/physics_free_courses
and
have fun
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2016 GERALD WHITROW LECTURE
Dr Neil Turok (Perimeter Institute, Canada)
Universe
A spate of new observations are providing powerful clues about the laws of fundamental physics and the cosmos. The implications are revolutionary: the universe is astonishingly simple on the largest and the smallest observable scales, with great complexity in between. These findings contrast sharply with expectations from popular twentieth century paradigms including inflation, supersymmetry and string theory, which led many to take seriously the idea of a wild and unpredictable "multiverse" on large scales. Key "predictions" derived from that picture have been recently falsified, posing observational challenges to the paradigm which compound its many logical problems. In this talk I will discuss a new, and in my view more promising, approach to understanding the quantum nature and integrity of the universe.
Abstract
We study quantum cosmology with conformal matter comprising a perfect radiation fluid and a number of conformally coupled scalar fields. Focusing initially on the collective coordinates (minisuperspace) associated with homogeneous, isotropic backgrounds, we are able to perform the quantum gravity path integral exactly. The evolution describes a “perfect bounce”, in which the Universe passes smoothly through the singularity. We extend the analysis to spatially flat, anisotropic universes, treated exactly, and to generic inhomogeneous, anisotropic perturbations treated at linear and nonlinear order. This picture provides a natural, unitary description of quantum mechanical evolution across a cosmological bounce. We provide evidence for a semiclassical description in which all fields pass “around” the cosmological singularity along complex classical paths.
Quantum mechanics of a cosmological bounce.—For homogeneous, isotropic cosmologies, one can choose a Weyl gauge in which the metric is static and the scalars (φ, χ⃗ ) encode all of the dynamics. While the metric is nonsingular in this gauge, the theory is still problematic because the effective Planck mass, given by the coeffi- cient of R, can vanish, so that gravity becomes strongly coupled. Our strategy is to first identify this singularity in the quantum propagator, and then understand how to analytically continue around it. Our key assumption, which we shall test in various calculations, is that there are no singularities obstructing such a continuation. We set D = 4 unless otherwise stated.
(restoring the dimension D).
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Apologies for not replying sooner. I'm pleased to say that we will be publishing this talk in the near future. I will let you know when it's available.
Kindest regards,
Steven Pryer
IT and Information Manager
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