Analog Science Fiction & Fact Magazine
"The Alternate View" columns of John G. Cramer 
Previous Column  Index Page  Next Column 

The Universe as a Watermelon

by John G. Cramer

Alternate View Column AV-137
Keywords: cosmology cosmic microwave background radiation WMAP quadrupole anomaly spheroidal universe
Published in the May-2007 issue of Analog Science Fiction & Fact Magazine;
This column was written and submitted 12/17/2006 and is copyrighted ©2006 by John G. Cramer.
All rights reserved. No part may be reproduced in any form without
the explicit permission of the author.

 

This page now has an access count of: Hit Counter

Nicholas Copernicus, who first proposed the heretical theory of a heliocentric universe with the Sun at its center and the Earth demoted to just one of the planets in orbit around it, was absolutely certain that the orbits of the planets must be perfect circles.  They had to be, because they were the creations of a perfect God, and a circle is the most perfect of geometrical objects.  When Johannes Kepler, after spending most of his career trying to make sense of the meticulous planetary observations of Tycho Brahe, concluded that the orbits of the planets were not circles but ellipses, the discovery sent shock waves through the community of natural philosophers.  The discovery led Newton and others to arrive at the inverse square law of gravitational attraction.

A paradigm shift similar to this one has just occurred in observational cosmology.  The “surface” from which the cosmic background radiation was emitted may not be a sphere.  This discovery is the subject of this column.


About 400,000 years after the initial Big Bang, when the era of exponential inflation was over, things settled down to a slower and steadier rate of expansion.  As more space became available for the energy in it, the universe was cooling things down.  The early universe was a nearly perfect “liquid plasma” saturated with energy, in which quarks behaved as free particles.  As the cooling progressed, the only strongly interacting particles around, quarks, organized themselves into composite mesons, protons, and neutrons.  By some process that remains obscure, there was a slight excess of protons and electrons over their antimatter equivalents (antiprotons and positrons).  During the high-density stages of the early universe, essentially all of the antimatter paired off with its matter counterparts to annihilate, leaving behind the slight excess of matter particles as “the only game in town”.  The cooling universe was a “soup” dominated by free electrons and protons.  In this environment, a photon of light could travel only a short distance without being absorbed by interacting with one of the free charged particles.

Later, the negative electrons and positive protons tended to pair off, forming neutral hydrogen atoms.  In the process, the dominance of free charged particles, which easily absorb photons, was being replaced by light-transparent neutral atoms.  The “soup” of the universe was changing from murky black to crystal clear.

The photons that were present in that era had energies that were characteristic of light emitted from an object (the universe) with a temperature of about 2,900 K.  (Here, K means “kelvin” and specifies the absolute temperature in Celsius degrees above absolute zero.)  As long as the universe was murky black, they were caught in a “ping-pong match” of repeated emission and re-absorption.  However, the growing transparency of the universe released them from this trap, and they became free photons.  Those photons have been traveling through the universe ever since, and we detect them today as the cosmic microwave background radiation (CMB).

However, as the universe expands and space itself stretches, the wavelengths of these CMB photons were also stretched until they are microwave photons characteristic of a very cold object with a temperature of 2.73 K instead of visible light photons characteristic of a hot object with a temperature of 2,900 K.  We observe these CMB photons today as microwaves emitted from a “surface” that has not existed for 13 billion years. Parts of that surface were a bit hotter than other parts, and these tiny energy variations show up as variations in the intensities of these microwaves, revealing the structure of the hot surface of the Universe at 400,000 years of age.


The Wilkinson Microwave Anisotropy Probe (WMAP) was launched into a high orbit on June 30, 2001 from a Delta II 7425-10 rocket at Cape Canaveral .  It used a lunar gravity-assist to put it in orbit at the L2 point of the Sun-Earth system, 940,000 miles behind the Earth, with the Sun on the other side.  It detects CMB in five frequency windows between 23 and 94 GHz within two linear polarization channels.  The square root of the observation solid angles of the five frequency windows are 0.88o, 0.66o, 0.51o, 0.35o, and 0.22o, respectively, for the lowest to highest frequency. These small-angle measurements of the CMB allowed mapping a of the power at a very small angular scale, where the “ringing” of the early universe shows up.

The WMAP data on the CMB intensity as a function of direction is analyzed into “multipoles”, the frequencies at which the intensity varies as the angle changes.  The high frequency components of this analysis have produced very accurate values of the numerical constants that characterize our universe.  The lowest frequency multipole, the “dipole” component, tells us how much the CMB is skewed off center by the motion of the detector through the CMB.  It measures how fast and in what direction the Earth-Sun system is moving through the radiation, and acts as a sort of universal “speedometer”.

There has been an ongoing problem in understanding the second-lowest frequency multipole, the “quadrupole” component of the CMB radiation.  This component characterizes the degree to which the distribution is elongated (positive eccentricity) or squashed in (negative eccentricity) in some spatial direction.  The expected value, measured as a temperature variation of the average 2.73 K temperature of the CMB, is DT2=14.5 mK (i.e. micro-kelvin), while the expected value that would be consistent with the other measured multipoles and the standard inflation model of the early universe is DT2=35.4 mK.  This discrepancy is called the CMB Quadrupole Puzzle, and it has bee troubling astrophysicists and cosmologists ever since the WMAP data was first analyzed.

Recently, Leonardo Campanelli of the University of Ferrara and his colleagues Paolo Cea and Luigi Tedesco at the University of Bari (all in Italy) have provided a possible explanation for the small quadrupole moment of the CMB.  They hypothesize that the solution to the CMB Quadrupole Puzzle is that the “surface” from which the CMB was emitted 13 billion years ago was not perfectly spherical, but rather was slightly elongated in one direction, making the early universe slightly spheroidal, with a shape like a watermelon.  Their calculations show that this would have the effect of reducing the quadrupole moment of the CMB without affecting the higher frequency moments.  They calculate that an “eccentricity” e, the ratio of extra radius in the long direction divided by average radius, of e=0.0067.  In other words, the surface that emitted the CMB radiation was about 0.67% larger in one spatial direction than in the other two.

How could this be?  In a well ordered Big Bang, there should be no preferred spatial direction.  So how could the universe be slightly larger in one direction?  Campanelli and his colleagues provide an answer to this question.  The symmetry of the early universe could be broken by the presence of a uniform magnetic field.  A universe full for free charged particles would be highly conductive, freezing in the primordial magnetic field, which would diminish as the universe expands.  The charged particles of the early universe would move freely in the magnetic field direction, but would be deflected by magnetic forces if they moved in the two directions perpendicular to the field.  This would produce a shape asymmetry in the surface from which the CMB was emitted.  They also speculated on another mechanism that would create the asymmetry, the presence of a cosmic string, a sort of linear fracture in space, which could produce the observed asymmetry.  In any case, if the spheroidal shape of the early universe is actually the solution to the CMB Quadrupole Puzzle, it could have some interesting implications for cosmological calculations, all of which have assumed a spherically symmetric early universe.


This is a science fiction magazine, so let me engage in a bit of SF speculation.  I wonder if there is not another answer to the CMB Quadrupole Puzzle.  Naïve calculations indicate that our universe should contain a large number of magnetic monopoles (isolated “north” or “south” magnetic charges), yet none of these has ever been seen.  The inflationary model of the universe suggests that the number of monopoles was reduced because the monopoles from the Big Bang have a large number of universes in which to end up, not just one. There is even some reason to suspect that each universe contains exactly one magnetic monopole, which is the "nucleating agent" that caused it to "precipitate" from primordial space, like the dust particle at the heart of every raindrop.

So universes may form like bubbles in a freshly opened bottle of beer.  If that is so, perhaps they bump together.  Perhaps our universe is not spherically symmetric because it was “nudged” by one or more universes next door in the initial stages of its expansion.  And if they are that close, perhaps there is a path from one to another.

 


References

Ellipsoidal Universe:

"Ellipsoidal Universe Can Solve THE CMB Quadrupole Problem", I. Campanelli, P. Cea, and L. Tedesco, submitted to Physical Review Letters, September,2006, preprint astro-ph/0606266 .


Previous Column  Index Page  Next Column 

Exit to Analog Logo issue index .
 This page was created by John G. Cramer on 01/06/2007.