Origin and Structure of the Universe

It's a big jump from the beginnings of the quantum theory to the structure of the universe, but the seeds to understanding this structure were sown there. The formation, structure and evolution of the universe is studied in the science of cosmology. Below I present a brief history of cosmology and show why many of the recent advances in our understanding of our universe comes from our understanding of the tiniest constituents of matter.

A brief history of astronomy
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As evidenced by prehistoric carvings made in bone 30,000 years ago and by Stonehenge in Neolithic times (2000 – 1400 BC), man has measured the skies for a long time. A significant change in this avocation occurred in about 600 BC in Ionia (a scattering of islands in the Aegean Sea) and the mainland of Greece and Turkey, when the cosmos became something that was governed by rules that could be understood and reasoned, rather than something unfathomable and capricious. Thales of Miletus accurately predicted the eclipse of 585 BC and began to piece together a model of the World. There followed Anaxagoras who pronounced (although it is not absolutely clear, as most of his writings are lost) that the earth is round, as could be surmised by its shadow on the moon during a lunar eclipse. Earlier, Pythagoras came to the same conclusion, but for more mythical reasons – if the Gods made the World they would surely have used perfect figures - spheres - from which to construct the World. To better understand heavenly motions Plato (who was more enamored with reasoning rather than observation as a means to understanding the cosmos) instructed his students to seek out the circular (another perfect figure) motions of the planets. (Plato's use of the word “circular” was to haunt future astronomers for 2,000 years). 

The next few hundred years produced many advances. Among them: Aristotle proposed a model of the World with the elements Earth, Air, Fire and Water residing inside the Moon’s orbit, 55 spheres that carried the planets, and an outer sphere that carried the stars. Beyond that was the domain of the Prime Mover, which caused the rotations of the stars; Eratosthenes measured the size of the earth; Hipparchus measured the distance to the Moon and Sun, and their sizes (to varying degrees of accuracy), and devised a method of calculating planetary motions using epicycles (circles superimposed on circles).  In the second century AD, Ptolemy, the last of the great Greek thinkers, improved on the model of Hipparchus which, in its Arabic translation The Almagest, became the guide to heavenly motions for the next 1,500 years. 

The middle ages saw reconciliation between the teachings of Aristotle and Christian doctrine as taught by the Holy Roman Church, thanks primarily to the work of Thomas Aquinas. In the sixteenth century, two radical ideas arose – the first by Nicolaus Copernicus who proposed a Sun-centered world; the second by Giordano Bruno that the stars are other suns like ours, complete with planets and their inhabitants, and, by implication, that our Sun has no preferred location. Copernicus died in 1543, shortly after his work was published; In 1600 Bruno was burned as a heretic for his efforts. Shortly after, three men would change the nature of astronomy, and science in general, into a form we still use today. 

The three were Galileo Galilei, Tycho Brahe and Johannes Kepler. 

Galileo, with the aid of the newly invented telescope, confirmed the Copernican system (among other accomplishments); Tycho brought unprecedented accuracy the art of observational astronomy; Kepler, using Tycho’s accurate data, finally broke the bonds imposed on his predecessors by Plato’s problem (remember the circles he instructed his students to use?), and established the true nature of planetary motion. In Kepler’s formulation the planets moved around the sun in elliptical orbits, with the sun at one of the focal points of the ellipse. This greatly simplified the solar model and established once and for all that, in science, the data should dictate the theory rather than the other way around. 

In the year of Galileo’s death (1642), Isaac Newton was born. In his monumental work, The Principia, he, among other things, formulated his equations of motion and set forth his theory of gravity. The former was instrumental in the beginnings of the industrial revolution; the latter put Kepler’s work on solid theoretical ground and allowed the calculation of planetary motion to almost any desired degree of accuracy. Using his law of gravity we can, for example, predict that on 24 July in the year 3991 there will be a total eclipse of the sun beginning at 22:20 O’clock (Universal Time), and it will last 7 minutes, 18 seconds (a particularly long eclipse). The power of Newton’s laws should be obvious. 

Newton’s law of gravity was replaced by Einstein’s theory of relativity in 1916. This theory, based on the principle of equivalence, replaces the gravity of Newton with a geometry of space and time, distorted by the presence of massive objects (e.g. stars and galaxies). With the general theory came a new era in astronomy (and astrophysics), providing us with a mathematical tool to combine with the telescope and map the evolution of the universe – cosmology becomes an “exact” science. 

When Einstein formulated his general theory, the accepted model of the universe was one that was more or less unchanging – the “steady state” model. To his dismay Einstein found his theory predicted an expanding universe and so added a “cosmological constant” to avoid the expansion problem.  In 1929, Edwin Hubble, using the 100-inch telescope on Mt. Wilson, detected the expansion the theory predicted, and the “Big Bang” model of cosmology was born. Einstein, after the expansion of the universe was discovered, called his cosmological constant (added to exclude expansion) his "greatest blunder". 

The big bang model predicts a universe that began some 12 billion years ago, from an infinitesimal kernel that grew to become the universe we know today. The Big Bang stands on strong theoretical and observational ground. Principal evidence for its validity is: Olber’s Paradox (Why is the sky dark at night?); The expansion (as evidenced by galactic red shift); the helium abundance of the universe (about 25% of matter in the universe is Helium – much more than could have been produced by stellar processes); the cosmic background radiation (measured at 2.7K, a number consistent with a 12 billion year expansion); a small but appropriate variation in that radiation, accounting for a non-uniformity necessary for the formation of galaxies). The model is consistent with theory, but the future is not clear. Theory predicts three possible expansions: one that continues to expand; one that eventually stops and then contracts; and one that lies in between – expands to a steady state. 

The "Quantum Link"

The picture presented above arises from the compellation of observational evidence. As we use the big bang model to go back in time, the universe, like a movie running backward, becomes smaller and more compact, and so hotter (as does anything when compressed). As we approach the instant of creation the size is small indeed and the temperature is very hot (the size was 10^-20 times that of a proton; the temperature was 10³⁰ times what it is on Earth now). The time was 10^-43 seconds after the beginning. Under these conditions we exceed the very limits of our understanding of physics - prior to this neither matter, energy or nature itself existed in a way we can have knowledge of, and time and space were constantly being disconnected and reunited. At a temperature of 10³² K, microscopic black holes were constantly being created and annihilated under the action of the superforce, a single force that later disassociated into gravity and the grand unified force. 

As the temperature reduced (a result of the expansion) to about 10²⁷ K the grand unified force separated into the nuclear and electroweak forces. (The electroweak force later broke into the weak force and the electromagnetic force, thus forming, with gravity and the nuclear force, the four forces we know today). The time was 10^-35 seconds. While there was no matter prior this time and temperature, the vacuum of space contained energy (a consequence of quantum theory), and from this energy was created vast quantities of quarks and leptons, along with their antiparticles. This process was not unlike the transition that occurs when fog cools below the point at which its vapor turns into water droplets. As these particles were created, the resulting pressures caused the black holes to undergo an even more violent expansion (the inflationary period). As a result they either were either annihilated or forced to move away from each other. We have no knowledge of the history of any of them save one.

At 10^-12 seconds the temperature was 10¹⁵ K. The forces had separated into the four we know today. In this violent state matter and antimatter (the quarks, leptons and their antiparticles) were continually created and annihilated but, because of the decoupling of the electroweak force, the leptons separated into electrons, neutrinos and their antiparticles. (We still collectively call these leptons today). The quarks remained unchanged, as they are today. Gravitons and photons also were part of the mix. The gravitons were created during inflation. At the current lower temperature their production was drastically reduced, until they no longer were produced. As they could interact through the very small gravitational force they decoupled from the matter and photons. They still move through space and time today, the most ancient remnants of the early universe. The photons were created from particles and antiparticles which, driven by the high temperatures that prevailed, collided and were annihilated. These photons would quickly decay again into matter and antimatter, and the process continued. At this time there was continual creation and annihilation, without and permanent structure in evidence.

By the time the universe was a microsecond old (10^-6 seconds) the temperature had dropped to 10¹³ K. Quarks and antiquarks combined into protons, neutrons and their antiparticles. These particle-antiparticle pairs immediately combined and annihilated into photons, but the temperature was now such that the photons could not again combine to create new quarks or other particles, although they were still energetic enough to create electron-positron pairs. Of critical importance was the unbalance between quark and antiquark pair production that occurred during inflation: For every billion antiquarks a billion and one quarks were created. This fortunate circumstance resulted in the survival of one matter particle in a billion - these protons and neutrons make up the galaxies, stars, planets and puppy dogs that exist today.

(Older) problems with the theory

 The Horizon Problem: 

When the cosmic background radiation was created, the universe was millions of Ly in size. How could every part of this universe be so uniform if there was no way information could connect them?

The Flatness Problem:

The universe today has density close the critical density, which provides a flat universe (W=1). An open universe has W>1, and a closed one W<1. In the early universe, in order for the density to be so close to the critical density now, its density had to be extremely close to 1 (by 1 part in 10¹⁵) – Why is W so close to 1, given all the other possibilities?

The Structure Problem:

Although uniform on large scale, on a smaller scale (galaxies and clusters of galaxies) the structure is “lumpy”. Where did the structure come from?

Inflation:

In the very early universe (10e-34 sec to 10e-32 sec), a rapid expansion 100 fold took place. During this time the universe expanded by a factor of 10e25 or more.

Horizon: If radiation started before expansion, the universe was small enough to communicate (uniform temperatures could result).

Flatness: Just as the surface of a balloon gets flatter as it expands, inflation could impose a W = 1 that would remain after inflation. (An accelerating universe W>1 belies inflation).

Structure: If the universe was very small just before inflation, quantum effects would make its structure governed by probability considerations, and so a random structure could produce structure at the moment of inflation.

What do we know? 

The universe is controlled by two forces, electromagnetic and gravitational (plus two other forces that act over sub-atomic distances). It contains objects ranging in size from nucleons to galaxies (and the universe itself). These objects have masses ranging from that of the electron to that of galaxies. The chart shows the extent of our knowledge: In the lower left lies the realm of quantum effects. Here things do not have measurable sizes, but do have measurable masses. The edge of this region is less defined than the diagram suggests. In the upper left is the realm of the black hole. In this domain the combination of small size and large mass provide a density that can’t be supported by the structure of the objects that reside here, so gravity causes an unstoppable collapse. These two regions meet at the Planck Point (mass = 2x10^-5 grams, size = 2x10^-33 cm.). There are no distances less than the Planck size, because we have no physics to describe them. Any two objects with mass of 2x10^-5 grams and unit charge (that of the electron) have balanced gravitational and electromagnetic forces – they lie along the dotted line. Most astronomical objects lie near the black hole boundary – they are governed by gravity. The line marked “Constant Density” (and others drawn parallel) link vastly different objects with common density. Other common objects have similar ties – a book, the earth, a person and the sun have very similar densities.

How does this picture change?

Our theories dictate an expanding universe, but with an expansion slowed by the retarding force of gravity.  Recently, measurements made by the Hubble telescope strongly suggest that the rate of expansion is accelerating. How can this be so? We return to the general theory, and Einstein’s cosmological constant that provides the effect of anti-gravity. Empty space and exotic dark matter may combine to produce such an effect.

New telescopes and a gravity wave facility in Washington State will bring new discoveries.