The Ekyprotic Universe

[Manthor]

http://www.physics.princeton.edu/~steinh/npr/

What is the Ekpyrotic proposal?

The model is based on the idea that our hot big bang universe was created from the collision of two three-dimensianal worlds moving along a hidden, extra dimension. The two three-dimensional worlds collide and ``stick," the kinetic energy in the collision is converted the quarks, electrons, photons, etc., that are confined to move along three dimensions. The resulting temperature is finite, so the hot big bang phase begins without a singularity. The universe is homogeneous because the collision and initiation of the big bang phase occurs nearly simultaneously everywhere. The energetically preferred geometry for the two worlds is flat, so their collision produces a flat big bang universe. According to Einstein's equations, this means that the total energy density of the Universe is equal to the critical density. Massive magnetic monopoles, which are overabundantly produced in the standard big bang theory, are not produced at all in this scenario because the temperature after collision is far too small to produce any of these massive particles.

Quantum effects cause the incoming three-dimensional world to ripple along the extra-dimension prior to collision so that the collision occurs in some places at slightly different times than others. By the time the collision is complete, the rippling leads to small variations in temperature, which seed temperature fluctuations in the microwave background and the formation of galaxies. We have shown that the spectrum of energy density fluctuations is scale-invariant (the same amplitude on all scales). The production of a scale-invariant spectrum from hyperexpansion was one of the great triumphs of inflationary theory, and here we have repeated the feat using completely different physics.

The building blocks of the ekpyrotic theory are derived from superstring theory. Superstring theory requires extra dimensions for mathematical consistency. In most formulations, 10 dimensions are required. In the mid-1990's, Petr Horava (Rutgers) and Ed Witten (IAS, Princeton) argued that, under certain conditions, an additional dimension opens up over a finite interval. Six dimensions are presumed to be curled up in a microscopic ball, called a Calabi-Yau manifold. The ball is too small to be noticed in everyday experience, and so our universe appears to be a four-dimensional (three space dimensions and one time dimension) surface embedded in a five-dimensional space-time. This five-dimensional theory, called heterotic M-theory, was formulated by Andre Lukas (Sussex). Ovrut and Dan Waldram (Queen Mary Westerfield College). According to Horava-Witten and heterotic M-theory, particles are constrained to move on one of the three-dimensional boundaries on either side of the extra dimensional interval. Our visible universe would be one of these boundaries; the other boundary and the intervening space would be hidden because particles and light cannot not travel across the intervening space. Only gravity is able to couple matter on one boundary to the other. In addition, there can exist other three-dimensional hypersurfaces in the interval, which lie parallel to the outer boundaries and which can carry energy. These intervening planes are called ``branes," short for membranes. The collision that ignites the hot big bang phase of the ekpyrotic model occurs when a three-dimensional brane is attracted to and collides into the boundary corresponding to our visible universe.

[Bottlestein]

^ This isn't new BTW. Heterotic M Theory has already been replaced partially. Closed Timelike Curves under HM were giving all sorts of stupid results regarding conservation laws.

Re the monopoles: I wouldn't put too much stock in the "temperature" calculations from the Cosmic Microwave Background. Hell, the first polarization measurements of the CMB started just about an year ago. I am sure we will see massive divergence of calculated temperature from the "off the cuff" predictions of the 1990's.

The only thing Heterotic M does is explain dark energy without too much divergence from the Standard Model at high energies. But we already know the Standard Model should not work at high energies, so...whoops!

[starslayer]

Re the monopoles: I wouldn't put too much stock in the "temperature" calculations from the Cosmic Microwave Background. Hell, the first polarization measurements of the CMB started just about an year ago. I am sure we will see massive divergence of calculated temperature from the "off the cuff" predictions of the 1990's.

Mind expanding on this a bit more? I assume you mean calculating the temperature of the very early universe from the temperature of the CMB, is that correct? Why would the polarization of the CMB photons be important at all for that, considering that, to my knowledge of physics, it should be essentially random?

[Bottlestein]

^ After photogenesis - you are correct that CMB polarization should not affect the temperature calculation. (Photogenesis being when the universe first became transparent to photons). We expect the polarization to be random assuming the universe had no multipole moments before photogenesis. This is the key assumption. Since photons are the carrier for the EM force, before photogenesis there can't be large scale alteration of multipoles. But, if before photogenesis, multipoles had already existed on a large scale in the universe (due to the charge properties of quarks or some such mechanism), then the initial energy during photogenesis must be recalculated. This, in turn, will change our expectation values for the existence of monopoles.

[starslayer]

Aha, that makes sense. Thanks, Bottlestein.