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 Post subject: David where are you?
PostPosted: Mon Jun 04, 2007 4:25 am 
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Can String Theory Explain Dark Energy? [indent]A new paper by Cambridge physicist Stephen Hawking and Thomas Hertog of CERN (hertog@mail.cern.ch) suggests that it can. The leading explanation for the observed acceleration of the expansion of the universe is that a substance, dark energy, fills the vacuum and produces a uniform repulsive force between any two points in space -- a sort of anti-gravity. Quantum field theory allows for the existence of such a universal tendency. Unfortunately, its prediction for the value of the density of dark energy (a parameter referred to as the cosmological constant) is some 120 orders of magnitude larger than the observed value.

In 2003, cosmologist Andrei Linde of Stanford University and his collaborators showed that string theory allows for the existence of dark energy, but without specifying the value of the cosmological constant. String theory, they found, produces a mathematical graph shaped like a mountainous landscape, where altitude represents the value of the cosmological constant. After the big bang, the value would settle on a low point somewhere between the peaks and valleys of the landscape. But there could be on the order of 10500 possible low points -- with different corresponding values for the cosmological constant -- and no obvious reason for the universe to pick the one we observe in nature.
Some experts hailed this multiplicity of values as a virtue of the theory. For example, Stanford University's Leonard Susskind in his book "The Cosmic Landscape: String Theory and the Illusion of Intelligent Design," argues that different values of the cosmological constant would be realized in different parallel worlds -- the pocket universes of Linde's "eternal inflation" theory. We would just happen to live in one where the value is very small. But critics see the landscape as exemplifying the theory's inability to make useful predictions.
The Hawking/Hertog paper is meant to address this concern. It looks at the universe as a quantum system in the framework of string theory. Quantum theory calculates the odds a system will evolve a certain way from given initial conditions, say, photons going through a double slit and hitting a certain spot on the other side. You repeat your experiment often enough and then you check that the odds you predicted were the correct ones.
In Richard Feynman's formulation of quantum theory, the probability that a photon ends up at a particular spot is calculated by summing up over all possible trajectories for the photon. A photon goes through multiple paths at once and can even interfere with its other personas in the process. Hawking and Hertog argue that the universe itself must also follow different trajectories at once, evolving through many simultaneous, parallel histories, or "branches." (These parallel universes are not to be confused with those of eternal inflation, where multiple universes coexist in a classical rather than in a quantum sense.) What we see in the present would be a particular, more or less probable, outcome of the "sum" over these histories. In particular, the sum should include all possible initial conditions, with all possible values of the cosmological constant.
But applying quantum theory to the entire universe -- where the experimenters are part of the experiment -- is tricky. Here you have no control over the initial conditions, nor can your repeat the experiment again and again for statistical significance. Instead, the Hawking-Hertog approach starts with the present and uses what we know about our branch of the universe to trace its history backwards. Again, there will be multiple possible branches in our past, but most can be ignored in the Feynman summation because they are just too different from the universe we know, so the probability of going from one to the other is negligible.
For example, Hertog says, knowledge that our universe is very close to being flat could allow one to concentrate on a very small portion of the string theory landscape whose values for the cosmological constant are compatible with that flatness. That could in turn lead to predictions that are experimentally testable. For example, one could calculate whether our universe is likely to produce the microwave background spectrum we actually observe. [/indent]
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PostPosted: Mon Jun 04, 2007 9:03 am 
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Down here Bergle..........down here on the floor.

Good grief Charlie Brown............dark matter, dark energy, mass-less particles and a whole lot more including inflation theory. Sounds like some kind of nightmare, yikes.

A repulsive force, an attractive force, sounds a little bit confused to say the least.

String theory and Dr. Kaku.........and all those cool dimensions, no wonder I can't find my glasses.

Multiple pasts and multiple futures and if you pour enough gravy on it they will never know what they are eating.

You might get the idea that I do not agree about all the invisible dimensions and all the invisible particles. Well, I don't agree.

First the universe is expanding, but the rate of expansion is slowing and then the universe is still expanding but the rate of expansion is accelerating. But this accelerative expansion is something fairly new as it only started to accelerate some 5 billion years ago. Before that the rate of expansion was slowing, right after inflation and continuing up until 5 billion years ago.

Amazing isn't it. And all of this started with a singularity.

But, no one knows exactly what gravity is or energy for that matter, but never mind we have our dark matter and our dark energy and our mass-less particles to account for enough of it that we can ignore the rest.

Question; is the ratio of energy per unit of mass the same for all materials? Is it even possible that the ratio of energy per unit of mass could be the same for all materials?

Is energy a resistant force? Is it even possible that energy could be a resistant force?

Is gravity a force, an actual force itself? Is it possible that gravity is simply a dynamic response to an underlying force of energy which we have yet to acknowledge or accept?

Is time not different for all systems in motion? If so, does this not indicate an infinite multiverse? An infinite number of parallel universes all existing simultaneously?
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PostPosted: Tue Jun 05, 2007 12:57 am 
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Well ole Wilbur seems to imply gravity is a secondary force...as sort of newtonian reaction to another primal state existing in that locality..i think.....
Like a magnetic field forms around a wire when you switch on the current.
Its the current that causes the magnetic effect.He theorized that electromagnetics,and gravity were functions of another force....
berg
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