As the dawn of the twentieth century approached the horizon of human comprehension, mans classical understandings of matter and energy were about to be turned upside down. The instigation of this tumult first occurred in the mind of one German physicists, Max Plank, who was trying to figure out inconsistencies posed against classical notions of physics by the property of certain element to emit energy. This property, referred to as radioactivity and discovered in 1896 by French physicist Henri Becquerel, would set the stage for an epoch of profound discoveries resulting in the advancement of the human understanding of reality at a theretofore unparalleled pace.
Early in the 19th century, James Dalton etched in stone the notion, just as Democritus had predicted two and a half millennia before, atoms were the simplest and indivisible constituents of all matter. Likewise, the debate between Newton's particle theory and Huygens’ wave theory of light energy, based solely on the rectilinear propagation, refraction and reflection of light observed to that point, was concretely decided when the properties of interference and diffraction were discovered. Light was a wave traveling through a medium like the ripples on a pond when a stone is thrown into it. Or so the paragons of physics and chemistry had concluded towards the end of the 19th century. Interestingly, Plank himself was an adamant adherent to the classical notions of physics and didn’t realize the more profound implications of his theory.
Plank’s theory basically proposed that light (energy) was absorbed and emitted by atoms in discrete energy packages Plank called “quanta,” derived from the Latin term “quantus” meaning how much. The theory, proposed by Plank in 1901, was the first steak in the ground that would erect a whole new way, a quantum way, of looking at reality. Unfortunately, Planks theory was just a bit too radical for every other physicist of the day, save one young upstart who received his Doctor of Physics degree from the University of Zurich in 1905, Albert Einstein.
That same year, Einstein would write four papers outlining his special theory of relativity, redefining the nature of light and relationship of space and time. In the first of these papers Einstein used Plank’s Constant “light quanta” to describe the photoelectric effect. In the paper, Einstein coined the term photons to label Plank’s discrete energy packages. Einstein received his Nobel Prize for the photoelectric effect in 1921, because the rest of his theory of special relativity was not yet well understood, and even less bolstered by any proofs. At that point, Einstein's thoughts were a little bit too far out there for most physicists to grasp, except perhaps one of his own students, Leo Szilard.
Meanwhile, Plank and Einstein were not the only physicists making new discoveries. In 1911, physicist Earnest Rutherford from New Zealand made a profound discovery while performing experiments in a Canadian Laboratory. It turns out that atoms were not so indivisible after all as Rutherford established they were comprised of smaller components distinguished by the positive and negative electrical charges they carried. Two years later, the Danish physicist Niels Bohr would build on Rutherford’s atomic model with his own theory of atomic structure.
Bohr incorporated Plank and Einstein’s notion of light quanta or photons to explain the transitions of electrons to higher and lower energy levels. When an electron absorbs a photon it moves to a higher energy level and when an electron releases a photon it drops to a lower energy level. Bohr’s theory went a long way in explaining the electro-chemical properties of elements and also defined the basic posit of quantum theory concerning the exchange of energy and matter.
British astronomer Sir Arthur Eddington had proven Einstein's posit that light photons are particles with mass making them subject to gravitational effect, even if their mass was immeasurable. This kind of squelched a lot of notions about wave mechanics even if their were a lot of holes in the description of electrons and protons as particles, because these particles sometimes did things better defined in terms of wave mechanics theory.
In the 1920’s there was a growing group of physicists who began to subscribe to and investigate quantum theory. Among them was one German physicists Werner Heisenberg. In 1927, Heisenberg offer the posit that would become known as the uncertainty principle: “it is impossible simultaneously to determine exactly both the position of an object and its momentum.” IF you think about it, this proposition suggest an error in Einstein’s theory of relativity and famous E=mc2 formula. Einstein strongly objected to Heisenberg's posit, issuing his famous quote in response to it “God does not play dice with the universe.”
Even if the Heisenberg uncertainty principle seemed to take exception with relativity—it really doesn’t— it did provide some much needed solutions to some other problems and confirmed the wave/particle duality of protons electrons and photons unifying the basic constructs of quantum theory. But the glue that would pull the elemental constructs of quantum mechanics together awaited the resolution of a little anomaly on the more traditional side of the physics fence concerning atomic structure and the atomic weight of elements. As early as 1920, Rutherford had proposed the idea of a third and yet to be identified component of atoms. By then, enough was known about protons and electrons to know that in aggregate the number of them in any element did not add up to the known empirical atomic weight of the element. In 1932, an associate of Rutherford, James Chadwick, discovered the elusive particles, labeling them “neutrons” as they exhibited no electrical charge.
While Chadwick was discovering neutrons, Einstein's former student and now friend and colleague at the University of Berlin, Leo Szilard, was reading H.G. Wells novel “The World Set Free” published in 1914; fictionally predicting the development of an unimaginably powerful bomb and a war taking place in 1956 in which the major cities of the world would be destroyed with such bombs. As a physicist, Szilard wondered if such a bomb could be conceived by releasing the energy contained in the atom per Einstein's formula E=mc2. Einstein laughed at the idea calling it “foolish nonsense,” but from that point forward Szilard’s mind was often contemplating the idea of a nuclear chain reaction. Only a year later, after fleeing Germany to escape the wrath of Hitler and the Nazi’s Szilard figured out how to bring about a chain reaction. All that was needed was to find an element which when hit with a neutron would disintegrate into other elements while releasing a surplus of free neutrons which would strike other atoms and carry on the chain reaction. Ironically, his brainchild was the bastard offspring of none other than Lord Ernest Rutherford’s assertion that chain reactions were not in the realm of possibilities. On July 16, 1945, near Alamogordo in the New Mexico desert, Szilards impossible idea would become an awesome reality, and Einstein’s theory of relativity formula E=mc2 was unquestionably proven as the sky was illuminated with a quantum release of light energy 100 times brighter than the Sun.
A few years later, the energy force at the heart of the sun would it self be brought to Earth as the first thermonuclear fusion warhead was exploded at Bikini Atoll in the pacific ocean. Quantum mechanics had become a truly quantum reality, but there was much more to be learned. By this time, quantum physicists had discovered and quantified the electromagnetic force, the weak interaction that binds electrons and protons together to form neutrons, the strong interaction which holds protons and neutrons together in the nucleus, and of course, the gravitational force which Einstein had quantified in his general theory of relativity in 1915. The question now was, is there some unifying force which can explain all of these forces. It was a quandary that had occupied most of Einstein’s twilight years and that he never solved. It would be up to a new generation of quantum physicists to carry the mantle of discovery forward.
In 1968, at the Stanford Linear Accelerator Center (SLAC), a whole new quantum paradox was realized when the nucleus of an atom was blown to bits revealing for the first time that protons and neutrons were made of even smaller particles called “quarks” by the scientists who discovered them. Over the past fifty years much has been learned about the quantum reality or should we say quasi reality of subatomic particles and plasmas, and yet we are no closer to finding the unification of forces which now represent the holy grain of quantum mechanics. Physicists now suspect that gravity, rather than an independent force, is more likely a manifestation of the weak or strong interaction, just as electromagnetism has been linked to the weak interaction.
Theories have been proposed that imply heretofore unsubstantiated dimensions of reality, and are equally untested or supported in terms of any empirical evidence. String theory is one example, which goes to the extreme point of proposing an infinite number of parallel dimensions slicing time into infinitely small increments each representing one possible instant of reality amid a continuum of every other possible instant of reality. We may get the thumbs up or down on this bizarre new way of perceiving the quantum reality soon, as an experiment planned at the CERN supercolider will soon crash particles together at twice the speed of light, a feet up until recently thought to be impossible. Some have proposed the notion that the event might even create a small black hole which will then suck in the rest of the earth and solar solar system. More reasonable minds consider this an impossibility just like dimension jumping and time travel. But who knows what profound attributes of quantum mechanics sill await discovery. It was not so long ago that quantum mechanics it self was considered an absurdity by those subscribing to more classical notions of the physical reality.
There are still many questions without answers, an unknown number of pieces of the puzzle of quantum mechanics yet to be discovered. But what we know today and have learned over the past hundred years since Plank and Einstein first unveiled the quantum reality, unquestionably represents the greatest addition of understanding added to the continuum of human knowledge since our species first experience the cognitive capability to contemplate the universe around us, and our place within it. Considering, that by virtue of that knowledge we now possess weapons of mass destruction, which if unleashed to bring about the extinction of the species, the greatest question might be will we survive long enough for future generations to resolve the remaining quandary and assemble the remaining pieces of the puzzle of quantum mechanics?