"Thus indeed, as though seated on a royal throne, the sun governs the family of planets revolving around it," Nicolaus Copernicus wrote in his revolutionary De revolutionibus orbium coelestium (1543).
Our species has many times confused reality with illusion. One of our most outrageous illusions was the old notion that we are at the center of the Universe. The Copernican or Cosmological Principle is a fundamental concept in cosmology that states that there are no "special" observers. For example, the Aristotelian model of our Solar System, that was still used in Medieval times, placed our tiny, lovely blue planet at the very center of the Solar System. This unique and very special position was wrongly assigned to our beloved rocky and watery home, because it appears to us that everything circles around the Earth. Nicolaus Copernicus (1473-1543) demonstrated for the first time that this view is an illusion and that, in reality, the Sun is at the center of our Solar System with the Earth, like all the other planets, circling the Sun. "At rest in the middle of everything is the Sun," Copernicus wrote.
The importance of Copernicus' work cannot be over-stated. His great and then-revolutionary insight challenged the dogmatic and literal interpretation of the Scriptures, shook the very pillars of the traditional moral beliefs of his era, and, last but not least, devastated humanity's precious Earth-evolved common sense. The upshot, of course, was that there was extreme opposition to Copernicus' reported revelations. However, hisheliocentric theory was ultimately begrudgingly swallowed by the world's "natural philosophers", and their reluctant acceptance eventually put to rest the general uproar against Copernicus. With Copernicus, our conceited species lost forever its dream-like notion that it somehow held a privileged place in a Universe where there is, in reality, no privileged place!
However, human life, as well as any intelligent life that may exist on other worlds, actually does play a very special role in the cosmic scheme of things. Conscious living creatures enable our Universe to be aware of itself. If observers did not exist anywhere in the Cosmos, all of its fantastic denizens, all of its mysterious and nonsensical attributes, would go forever into the oblivion of the unknown and unknowable. The late Cornell University astrophysicist, Dr. Carl Sagan, said: "We are a way for the Cosmos to know itself."
We are stardust come to life!
In spite of the alluringly secretive nature of our weird and mysterious Cosmos, scientists have nevertheless acquired the means to open new windows on its hidden character. This is often accomplished (very simply) by using new and more sophisticated technologies when they emerge, and also by just doing what good observers are supposed to do--the purpose of the observer is to observe! In astronomy, the opening up of new vistas within the electromagnetic spectrum frequently results in new and exciting revelations about the Universe's current attributes, past evolution, and general contents. Indeed, the final decade of the 20th century saw a great number of new and exciting discoveries in astrophysics. Until recently, it was thought that our entire Universe consisted only of the matter that we could see--only familiar atomic matter composed of a nucleus of protons and neutrons surrounded by a cloud of electrons. Now we know that this is far from the case. In fact, the familiar atomic matter of which stars, planets, and people are made, is the runt of the cosmic litter. A mere 4% of the matter-energy content of the Universe is made up of familiar atomic matter. The rest of it--96%--is composed of invisible and mysterious stuff. In fact, 22% of the Universe is composed of dark matter, which is thought to be made up of some as yet unidentified exotic particles that do not interact with light, and are therefore invisible--and the existence of dark matter was unknown until the 20th century! We believe that it is there, however, because it does interact gravitationally with ordinary atomic matter, and we can see these gravitational effects. The dark matter forms an immense web--the Cosmic Web--which is invisible to our human eyes. However, we can see the brilliantly starlit galaxies and clusters of galaxies dancing around in this web, outlining for us what we cannot see, like sparkling dewdrops outlining the web of some enormous spider.
The lions-share of the matter-energy content of the Universe--74% of it--is made up of the mysterious dark energy, a bizarre substance that is causing our Universe not only to expand--but to actually accelerate in its expansion! The existence of the dark energy was unknown until 1998. Up until that time, scientists thought that the Universe was slowing down in its expansion.
When our Sun dies, it will go with relative gentleness into that good night by softly puffing out its newly formed batch of heavy ordinary atomic elements into space. Stars, both large and small, create heavier elements out of lighter ones in a process termed stellar nucleosynthesis. Hydrogen, helium, and small quantities of lithium were formed in the Big Bang birth of our Universe almost 14 billion years ago. All of the rest of the elements of the Periodic Table were formed in the hearts of our Universe's stars, or in the supernova explosions that heralded their demise. Massive stars die in supernova explosions, that spew their newly forged batch of heavy elements into space. Smaller stars, like our Sun, go with more of a whimper than a bang. Our Sun's corpse will be a dense little object termed a white dwarf; its shroud an exquisitely beautiful planetary nebula, a luminous cloud of varicolored gases. Stars of solar-type usually die with relative peacefulness, and with great beauty--when they are solitary stars like our Sun, that is. Something very different, however, can happen when a solar-mass star is a member of a binary system, and there is another star involved in its death throes. In that case, the relatively small star goes supernova, just like the big guys. This results in what is termed a Type Ia supernova.
Many white dwarfs dwelling in our Universe exist in binary systems, where they are situated in close orbits with an ordinary, large main-sequence star that has not yet perished, and is still actively burning its supply of hydrogen fuel. Such a binary system, when it involves a white dwarf whose sister is an ordinary star, is a party waiting to happen. The fun begins when the dense white dwarf sucks off enough gas from its sister star to become heavy enough to reach the mass necessary to go supernova. When the white dwarf, or what was the white dwarf, "goes critical", the resulting runaway thermonuclear explosion completely destroys the dense stellar remnant in one spectacular Type Ia supernova blast. The entire process usually takes millions of years, with the vampire-like white dwarf mercilessly sucking up a steady stream of gas from its luckless sister and victim. Then it happens. The white dwarf can swallow no more, and it goes critical. The slow and relentless process--that reaches a sudden, dramatic, and catastrophic climax--erases most of the original variations among progenitor stars. Thus the spectra and light-curves of all Type Ia supernovae are almost identical. This makes Type Ia supernovae great "standard candles" that astronomers can use to measure distances.
In 1998, observations of Type Ia supernovae by the Supernova Cosmology Project at Lawrence Berkeley National Laboratory and the High-z Supernova Search Team suggested that the expansion of the Universe is accelerating. Since then, these observations have been confirmed by several independent sources. In addition, improved measurements of supernovae indicate that this acceleration is probably real, and not a mirage.
Because all Type Ia supernovae display very similar spectra and light curves, the two teams were able to track the history of the cosmic expansion and discover, to their amazement, that it was speeding up. As far back as 1938, the eminent scientist Walter Baade, working closely with the cantankerous "creative genius" Fritz Zwicky at the Mount Wilson Observatory in California, realized that supernovae, in general, were very promising tools for measuring the cosmic expansion. Their peak brightness seemed exceptionally consistent, and they were bright enough to be observed at very great cosmological distances. In fact, for weeks, a supernova can even outshine its entire host galaxy.
The 2011 Nobel Prize in Physics was awarded "for the discovery of the accelerating expansion of the Universe through observations of distant supernovae", with one half going to Dr. Saul Perlmutter of Lawrence Berkeley National Laboratory in California and the other half jointly to Dr. Brian P. Schmidt and Dr. Adam G. Riess. Dr. Schmidt is at the Australian National University Mount Stromlo Observatory, and Dr. Riess is at Johns Hopkins University and the Space Telescope Science Institute in Maryland.
An amazing series of events was set off by the Big Bang birth of our Universe, resulting almost 14 billion years later in literally everything we know of in the Cosmos, including ourselves. In the ancient Universe, the dark matter continued to clump together into ever larger and larger globs, and the so-called "ordinary" atomic matter followed it, somersaulting into halos of the dark stuff. Even though the gravitationally-bullying dark matter was far more abundant, the "ordinary" atomic matter had something of the cosmic last laugh. Although the "ordinary" atomic matter is the runt of the cosmic litter in comparison to the big guys--dark matter and dark energy--the atomic interactions of the "ordinary" matter brought our Universe to life. Though far less plentiful than the great masses of dark matter with its powerful and relentless gravitational pull, "ordinary" matter, after it had fallen deeper and deeper into dark matter halos, began to stick together to form objects composed primarily of atoms--the lovely and luminous stars blazing within majestic galaxies, the glowing gases that float around both between the stars and between the galaxies, and the dim planets--and their accompanying moons--that circle the beautiful, fiery stars. On at least one planet in our visible Universe (and very likely on many, many more), "ordinary" atomic matter evolved into the marvelous concoction that we call life. The dark matter was left to its bullying self to dominate the largest gravitational structures--the immense filaments of the Cosmic Web. But the atomic matter gave rise to us--and to other living creatures, both on Earth and wherever else they well may be, dwelling out there in the remote corners of of our Universe, on planets or on moons, made of atoms.