Nick Herbert

Known As:

Sep 7, 1936.
Pittsburgh, Pennsylvania, USA
Leading quantum physicist

1. The Quest for Reality

The essential point in science is not a complicated mathematical formalism or a ritualized experimentation. Rather the heart of science is a kind of shrewd honesty that springs from really wanting to know what the hell is going on!

Saul-Paul Sirag

In the seventeenth century Galileo, Newton and other natural philosophers discovered that an enormous body of physical facts could be encompassed in a few mathematical formulas. For instance with only three mathematical laws Newton could explain all motion in heaven and on Earth. Why should mathematics, developed primarily to keep track of human business transactions, have anything at all to do with the way the non-human world operates? Nobel laureate Eugene Wigner refers to this magical match between human mathematics and non-human facts as "the unreasonable effectiveness of mathematics in the natural sciences." This "unreasonable effectiveness," writes Wigner, "is a wonderful gift which we neither understand nor deserve."

Although mathematics originates in the human mind, its remarkable effectiveness in explaining the world does not extend to the mind itself. Psychology has proved unusually resistant to the mathematization that works so well in physics.

The German philosopher Immanuel Kant was deeply impressed by Newton's mathematical method and sought to explain its success as well as to understand its limitations. Kant began his analysis by dividing knowledge into three parts: appearance, reality, and theory. Appearance is the content of our direct sensory experience of natural phenomena. Reality (Kant called it the "thing in itself") is what lies behind all phenomena. Theory consists of human concepts that attempt to mirror both appearance and reality.

Kant believed that the world's appearances were deeply conditioned by human sensory and intellectual apparatus. Other beings no doubt experience the same world in radically different ways. Scientific facts - the appearances themselves - are as much a product of the observer's human nature as they are of an underlying reality. We see the world through particularly human goggles. Kant felt that the participation of human nature in the creation of appearances explained both the remarkable ability of human concepts to fit the facts and the natural limits of such abilities.

Our concepts appear to match the facts, according to Kant, because both facts and concepts have a common origin - the human condition. Insofar as human nature is entwined with the appearances, human concepts will be successful in explaining those appearances. Because we can only explain those aspects of the world which we ourselves bring to it, the nature of deep reality must remain forever inaccessible. Man is fated to know, either directly or through conceptualization, merely the world's appearances and of these appearances only that part which is of human origin.

[...] another difference separates researchers into the nature of reality: the pragmatist/realist division. A pragmatist believes only in facts and mathematics and refuses in principle to speculate concerning deep reality, such questions being meaningless from his point of view. Sir James Jeans, the distinguished physicist and astronomer, sums up this pragmatic orientation: "The final truth about a phenomenon resides in the mathematical description of it; so long as there is no imperfection in this, our knowledge of the phenomenon is complete. We go beyond the mathematical formula at our own risk; we may find a model or picture which helps us understand it, but we have no right to expect this, and our failure to find such a model or picture need not indicate that either our reasoning or our knowledge is at fault. The making of models or pictures to explain mathematical formulas and the phenomena they describe is not a step towards, but a step away from, reality; it is like making graven images of a spirit."

A realist, on the other hand, believes that a good theory explains the facts because it makes contact with a reality behind those facts. The major purpose of science, according to the realists, is to go beyond both fact and theory to the reality underneath. As Einstein, the most famous realist of them all, put it, "Reality is the real business of physics."

The pragmatist treats his theory like a cookbook full of recipes which are useful for ordering and manipulating facts. The realist sees theory as a guidebook which lays out for the traveler the highlights of the invisible landscape that lies just beneath the facts.

Most physicists are complex mixtures of pragmatist and realist, at once both optimistic and pessimistic about their chances for making solid contact with deep reality. [...]

2. Physicists Losing Their Grip

No development of modern science has had a more profound impact on human thinking than the advent of quantum theory. Wrenched out of centuries-old thought patterns, physicists of a generation ago found themselves compelled to embrace a new metaphysics. The distress which this reorientation caused continues to the present day. Basically physicists have suffered a severe loss: their hold on reality.

Bryce DeWitt
Neill Graham

One of the best-lept secrets of science is that physicists have lost their grip on reality.

News of the reality crisis hardly exists outside the physics community. What shuts out the public is partly a language barrier - the mathematical formalism that facilitates communication between scientists is incomprehensible to outsiders - and partly the human tendency of physicists to publicize their successes while soft-pedalling their confusions and uncertainties. Even among themselves, physicists prefer to pass over the uncomfortable reality issue in favor of questions "more concrete". Recent popularizations such as Heinz Pagels' Cosmic Code have begun to inform the public about the reality crisis in physics. In Quantum Reality I intend to examine how physicists deal with reality - or fail to deal with it - in clear and unprecedented detail.

Nothing exposes the perplexity at the heart of physics more starkly than certain preposterous-sounding claims a few outspoken physicists are making concerning how the world really works. If we take these claims at face value, the stories physicists tell resemble the tales of mystics and madmen. Physicists are quick to reject such unsavory associations and insist that they speak sober fact. We do not make these claims out of ignorance, they say, like anicnet mapmakers filling in terra incognitas with plausible geography. Not ignorance, but the emergence of unexpected knowledge forces on us all new visions of the way things really are.

The new physics bision is still clouded, as evidenced by the multiplicity of its claims, but whatever the outcome it is sure to be far from ordinary. To give you a taste of quantum reality, I summarize here the views of its foremost creators in the form of eight realities which represent eight major guesses as to what's really going on behind the scenes. Later we will look at each of these realities in more detail and see how different physicists use the same data to justify so many different pictures of the world.

Quantum Reality #1:
The Copenhagen interpretation, Part I
(There is no deep reality)

No one has influenced more our notions of what the quantum world is really about than Danish physicist Niels Bohr, and it is Bohr who puts forth one of quantum physics' most outrageous claims: that there is no deep reality. Bohr does not deny the evidence of his senses. The world we see around us is real enough, he affirms, but it floats on a world that is not as real. Everyday phenomena are themselves built not out of phenomena but out of an utterly different kind of being.

Far from being a crank or minority position, "There is no deep reality" represents the prevailing doctrine of establishment physics. Because this quantum reality was developed at Niels Bohr's Copenhagen institute, it is called the "Copenhagen interpretation." Undaunted by occasional challenges by mavericks of realist persuasion, the majority of physicists swear at least nominal allegiance to Bohr's anti-realist creed. What more glaring indication of the depth of the reality crisis than the official rejection of reality itself by the bulk of the physics community?

Einstein and other prominent physicists felt that Bohr went too far in his call for ruthless renunciation of deep reality. Surely all Bohr meant to say was that we must all be good pragmatists and not extend our speculations beyond the range of our experiments. From the results of experiments carried out in the twenties, how could Bohr conclude that no future technology would ever reveal a deeper truth? Certainly Bohr never intended actually to deny deep reality but merely counseled a cautious skepticism toward speculative hidden realities.

Bohr refused to accept such a watered-down version of the Copenhagen doctrine. In words that must chill every realist's heart, Bohr insisted: "There is no quantum world. There is only an abstract quantum description."

Werner Heisenberg, the Christopher Columbus of quantum theory, first to set foot on the new mathematical world, took an equally tough stand against reality-nostalgic physicists such as Einstein when he wrote: "The hope that new experiments will lead us back to objective events in time and space is about as well founded as the hope of discovering the end of the world is the unexplored regions of the Antarctic."

The writings of Bohr and Heisenberg have been criticized as obscure and open to many interpretations. Recently Cornell physicist N. David Mermin neatly summed up Bohr's anti-realist position in words that leave little room for misunderstanding: "We now know that the moon is demonstrably not there when nobody looks." (We will take a look at Mermin's "demonstration" in Chapter 13.)

Quantum Reality #2:
The Copenhagen interpretation, Part II
(Reality is created by observation)

Although the numerous physicists of the Copenhagen school do not believe in deep reality, they do assert the existence of phenomenal reality. What we see is undoubtedly real, they say, but these phenomena are not really there in the absence of an observation. The Copenhagen interpretation properly consists of two distinct parts: 1. There is no reality in the absence of observation; 2. Observation creates reality. "You create your own reality," is the theme of Fred Wolf's Taking the Quantum Leap.

Which of the world's myriad processes qualify as observations? What special feature of an observation endows it with the power to create reality? Questions like these split the observer-created reality school into several camps, but all generally subscribe to quantum theorist John Wheeler's memorable maxim for separating what is real in the world from what is not. "No elementary phenomenon is a real phenomenon until it is an observed phenomenon," Wheeler proclaims. Without a doubt, Mermin's description of the inconstant moon qualifies him for membership in the observer-created reality school.

The belief that reality is observer-created is commonplace in philosophy, where it serves as the theme for various forms of idealism. Bertrand Russell recalls his fascination with idealism during his student days at Trinity College: "In this philosophy I found comfort for a time... There was a curious pleasure in making oneself believe that time and space are unreal, that matter is an illusion and that the world really consists of nothing but mind."

Since pondering matter is their bread and butter, not many physicists would share Russell's enjoyment of matter as mere mirage. However, like it or not, through their conscientious practice of quantum theory more than a few physicists have strayed within hailing distance of the idealist's dreamworld.

Quantum Reality #3:
Reality is an undivided wholeness

The views of Walter Heitler, author of a standard textbook on the light/matter interaction, exemplify a third unusual claim of quantum physicists: that in spite of its obvious partitions and boundaries, the world in actuality is a seamless and inseparable whole - a conclusion which Fritjof Capra develops in Tao of Physics and connects with the teachings of certain oriental mystics. Heitler accepts an observer-created reality but adds that the act of observation also dissolves the boundary between observer and observed: "The observer appears, as a necessary part of the whole structure, and in his full capacity as a conscious being. The separation of the world into an 'objective outside reality' and 'us,' the self-conscious onlookers, can no longer be maintained. Object and subject have become inseaprable from each other."

Physicist David Bohm of London's Birkbeck College has especially stressed the necessary wholeness of the quantum world: "One is led to a new notion of unbroken wholeness which denies the classical analyzability of the world into separately and independently existing parts... The inseparabale quantum interconnectedness of the whole universe is the fundamental reality."

Quantum wholeness is no mere replay of the old saw that everything is connected to everything else, no twentieth-century echo, for instance, of Newton's insight that gravity links each particle to every other. All ordinary coonections - gravity, for one - inevitably fall off with distance, thus conferring overwhelming importance on nearby connections while distant connections become irrelevant. Undoubtedly we are all connected in unremarkable ways, but close connections carry the most weight. Quantum wholeness, on the other hand, is a fundamentally new kind of togetherness, undminished by spatial and temporal separation. No casual hookup, this new quantum thing, but a true mingling of distant beings that reaches across the galaxy as forcefully as it reaches across the garden.

Quantum Reality #4:
The many-worlds interpretation
(Reality consists of a steadily increasing number of parallel universes)

Of all claims of the New Physics none is more outrageous than the contention that myriads of universes are created upon the occasion of each measurement act. For any situation in which several different outcomes are possible (flipping a coin, for instance), some physicists believe that all outcomes actually occur. In order to accommodate different outcomes without contradiction, entire new universes spring into being, identical in every detail except for the single outcome that gave them birth. In the case of a flipped coin, one universe contains a coin that came up heads, another, a coin showing tails. Paul Davies champions this claim, known as the many-worlds interpretation, in his book Other Worlds. Science fiction writers commonly invent parallel universes for the sake of a story. Now quantum theory gives us good reason to take such stories seriously.


Invented in 1957 by Hugh Everett, a Princeton graduate student, the many-worlds interpretation is a latecomer to the New Physics scene. Despite its bizare conclusion, that innumerable parallel universes each as real as our own actually exist, Everett's many-worlds picture has gained considerable support among quantum theorists because it resolves, as we shall see, the major unsolved puzzle in quantum theory - the notorious quantum measurement problem.

These four quantum realities should give you some feeling for the diversity of claims regarding the world's ultimate nature. While followers of Everett bear witness to uncountable numbers of quantum world, plus more on the way, students of Bohr and Heisenberg insist that there is not even one quantum world. In their struggle to gain firm footing amidst the slippery bricks of quantum fact, physicists have invented more realities than four. Keep your wits about you as we press on.

Quantum Reality #5:
Quantum logic
(The world obeys a non-human kind of reasoning)

Quantum logicians argue that the quantum revolution goes so deep that replacing new concepts with old will not suffice. To cope with the quantum facts we must scrap our very mode of reasoning, in favor of a new quantum logic.

Logic is the skeleton of our body of knowledge. Logic spells out how we use some of the shortest words in the language, words such as and, or, and not. The behavior of these little linguistic connectors governs the way we talk about things, and structures, in turn, the way we think about them. For two thousand years, talk about logic (in the West) was cast in the syllogistic mold devised by Aristotle. In the mid-nineteenth century, George Boole, an Irish schoolteacher, reduced logical statements to simple arithmetic by inventing an artificial symbolic language which laid bare the logical bones of ordinary language.

Boole's clear codification of the rules of reason jolted logic out of the Middle Ages and launched the now-flourishing science of mathematical logic. Outside the mathematical mainstream, a few creative logicians amused themselves by constructing "crazy logics" using rules other than Boole's. These deviant designs for and/or/not, although mathematically consistent, were considered mere curiosities since they seemed to fit no human pattern of discourse.

However, according to some New Physicists, one of these crazy logics may be just what we need to make sense out of quantum events. Listen to quantum theorist David Finkelstein calling for mutiny against the rules of Boole:

"Einstein threw out the classical concept of time; Bohr throws out the classical concept of truth... Our classical ideas of logic are simply wrong in a basic practical way. The next step is to learn to think in the right way, to learn to think quantum-logically."

As an exmaple of the usefulness of changing your mind rather than changing your physics, quantum logicians point to Einstein's general theory of relativity, which achieved in the realm of geometry what they propose to do with logic.

Geometry is the science of points and lines. For two thousand years only one geometry existed, its rules compiled by the Greek mathematician Euclid in his bestselling book The Elements, which once rivaled the Bible in popularity. The latest revival of Euclid's Elements is your high school geometry book.

Coincident with Boole's pioneer work in logic, a few adventerous mathematicians thought up "crazy geometries," games points and lines could play outside of Euclid's rules. Chief architect of the New Geometry was the Russian Nicolai Lobachevski along with German mathematicians Karl Gauss and Georg Riemann. Their cockeyed geometries were regarded, like non-Boolean logics, as high mathematical play, clever business but out of touch with reality. Euclidean geometry, as everyone knows, was the geometry, being after all, nothing but common sense applied to triangles and other geometric figures.

However, in 1916 Einstein proposed a radical new theory of gravity that demolished the Euclidean monopoly. Einstein, in opposition to Newton and everybody else, declared that gravity is not a force but a curvature in space-time. Objects in free fall are truly free and move in lines as straight as can be - that is, lines straight by the standards of a gravity-warped geometry. Einstein's theory has testable consequences: for instance the deflection of starlight grazing the sun (confirmed by Eddington in 1919) and the existence of black holes (according to astrophysicists, in the constellation Cygnus, black hole Cygnus X-1 resides). On Earth, where our common sense was formed, gravity is weak and space almost Euclidean; out near X-1, high school geometry flunks.

Einstein's lesson is plain to see, say the quantum logicians. The question of the world's true geometry is not settled by common sense but by experiment. Likewise with logic. For the rules of right reason, look not inside your own head but get thee to a laboratory.

Quantum Reality #6:
(The world is made of ordinary objects)

An ordinary object is an entity which possesses attributes of its own whether observed or not. With certain exceptions (mirages, illusions, hallucinations), the world outside seems populated with objectlike entities. The clarity and ubiquity of ordinary reality has seduced a few physicists - I call them neorealists - into imagining that this familiar kind of reality can be extended into the atomic realm and beyond. However, the unremarkable and common-sense view that ordinary objects are themselves made of objects is actually the blackest heresy of establishment physics.

"Atoms are not things," says Heisenberg, one of the high priests of the orthodox quantum faith, who likened neorealists to believers in a flat earth. "There is no quantum world," warned Bohr, the pope in Copenhagen; "there is only an abstract quantum description."

Neorealists, on the other hand, accuse the orthodox majority of wallowing in empty formalism and obscuring the world's simplicity with needless mystification. Instead they preach return to a pure and more primitive faith. Chief among neorealists was Einstein, whose passion for realism pitted him squarely against the quantum orthodoxy: "The Heisenberg-Bohr tranquilizing philosophy - or religion? - is so delicately contrived that, for the time being, it provides a gentle pillow for the true believer from which he cannot very easily be aroused. So let him lie there."

Despite their Neanderthal notions, no one could accuse neorealists of ignorance concerning the principles of quantum theory. Many of them were its founding fathers. Besides Einstein, prominent neorealists include Max Planck, whose discovery of the constant of action sparked the quantum revolution; Erwin Schrodinger, who devisred the wave equation every quantum system must obey; and Prince Louis de Broglie, who took quantum theory seriously enough to predict the wave nature of matter.

Dr. Broglie, a French aristocrat whose wartime involvement in radio swerved his research from church history into physics, fought for ordinary realism until 1928 when he converted to the statistical interpretation (another name for Copenhagenism). Twenty years later, however, influenced by David Bohm's neorealist revival, de Broglie recanted and returned to the faith of his youth [...].

Einstein, despite his numerous contributions to its success, never accepted quantum theory into his heart and stubbornly held to the old-fashioned belief that a realistic vision of the world was compatible with the quantum facts. During the thirties Einstein and Bohr engaged in an extended debate on the quantum reality question. Bohr argued that as far as reality was concerned, quantum theory was a closed book. By 1928 perceptive physicists had already grasped the theory's essence. Quantum theory would develop in detail but its principles would not change. Bohr's confidence has been upheld so far; fifty years later, physicists still follow the old rules.

Quantum theory is complete as it stands, said Bohr. It has no need of ordinary objects. Furthermore such objects cannot be added without spoiling its predictive success. Ordinary objects are not merely unnecessary luxuries in quantum theory, they are strictly impossible.

Einstein's strategy was to comfort Bohr with a series of thought experiments which aimed to show that quantum theory had left something out. He did not attempt to show that the theory was wrong, but by demonstrating that it was incomplete Einstein hoped to open the door for what he called "elements of reality."

As the winners tell the story, Bohr closed each of Einstein's loopholes, but in the minds of each the debate was never settled. Long after their arguments had ended, on the day Bohr died, his blackboard contained a drawing of one of Einstein's thought experiments. Bohr struggled with Einstein to the end.

Einstein too never gave up. In his autobiography he expresses his final thoughts on the quantum reality question: "I still believe in the possibility of a model of reality - that is, of a theory which represents things themselves and not merely the probability of their occurrence."

Quantum Reality #7:
Consciousness creates reality

Among observer-created realists, a small faction asserts that only an apparatus endowed with consciousness (even as you and I) is privileged to create reality. The one observer that counts is a conscious observer. Denis Postle examines reality-creating consciousness in Fabric of the Universe. I include this quantum reality not only because it is so outlandish but because its supporters are so illustrious. Consciousness-created reality adherents include light/matter physicist Walter Heitler, already cited in connection with undivided wholeness, Fritz London, famous for his work on quantum liquids, Berkeley S-matrix theorist Henry Pierce Stapp, Nobel laureate Eugene Wigner, and world-class mathematician John von Neumann.

Hungarian-born von Neumann was the mathematical midwife for some of the twentieth century's most exciting developments. Wherever things were hottest, the brilliant von Neumann seemed to be there lending a hand. In the late forties he invented the concept of the stored-program computer; today's computer scientists refer to all computers from pocket calculators to giant IBMs as "von Neumann machines." In collaboration with Oskar Morgenstern, von Neumann laid the mathematical foundation for strategic game theory, on which much government and corporate policy in both the East and the West is based. He also worked on early robots and helped develop the atom bomb. In 1936 with Harvard mathematician Garrett Birkhoff he came up with the idea of quantum logic, but von Neumann's biggest contribution to quantum reality research was his book on quantum theory.

By the late twenties physicists had constructed a quantum theory that met their daily needs: they possessed a rough mathematical structure which organized the quantum facts. At that point von Neumann entered the picture, putting physicists' crude theory into rigorous form, settling quantum theory into an elegant mathematical home called "Hilbert space" where it resides to this day, and awarding the mathematician's seal of approval to physicists' fledgling theory.

In 1932 von Neumann set down his definitive vision of quantum theory in a formidable tome entitled Die Mathematische Grundlagen der Quantenmechanik. Our most general picture of quantum theory is essentially the same as that outlined by von Neumann in Die Grundlagen (The Foundations). Von Neumann's book is our quantum bible. Like many other sacred texts, it is read by few, venerated by many. Despite its importance it was not translated into English until 1955.

Many of the issues I discuss in Quantum Reality were first made public in von Neumann's book. For instance, there is von Neumann's proof that if quantum theory is correct, the world cannot be made of ordinary objects - i.e., the neorealist interpretation is logically impossible. Von Neumann posed, but did not solve to everyone's satisfaction, the famous quantum measurement problem which is the central issue of the quantum reality question. In addition, von Neumann was the first to show how quantum theory suggests an active role for the observer's consciousness. Physical objects would have no attributes, von Neumann said, if a conscious observer were not watching them.

Von Neumann himself merely hinted at consciousness-created reality in dark parables. His followers boldly took his arguments to their logical conclusion: if we accept von Neumann's version of quantum theory, they say, a consciousness-created reality is the inevitable outcome.

At the logical core of our most materialistic science we meet not dead matter but our own lively selves. Eugene Wigner, von Neumann's Princeton colleague and fellow Hungarian (they went ot the same high school in Budapest), comments on this ironic turn of events: "It is not possible to formulate the laws of quantum mechanics in a fully consistent way without reference to the consciousness... It will remain remarkable in whatever way our future concepts may develop, that the very study of the external world led to the conclusion that the conent of the consciousness is an ultimate reality."

Quantum Reality #8:
The duplex world of Werner Heisenberg
(The world is twofold, consisting of potentials and actualities)

Most physicists believe in the Copenhagen interpretation, which states that there is no deep reality (QR #1) and observation creates reality (QR #2). What these two realities have in common is the assertion that only phenomena are real; the world beneath phenomena is not.

One question which this position immediately brings to mind is this: "If observation creates reality, what does it create this reality out of? Are phenomena created out of sheer nothingness or out of some more substantial stuff?" Since the nature of unmeasured reality is unobservable by definition, many physicists dismiss such questions as meaningless on pragmatic grounds.

However, since it describes measured reality with perfect exactness, quantum theory must contain some clues concerning the raw material out of which phenomena spring. Perhaps using the power of imagination we can peer beneath this theory and make some shrewd guess about the background world against which our familiar world of solid observations stands.

Werner Heisenberg was fully aware of the difficulties of attempting to describe the subphenomenal world: "The problems of language here are really serious," he said. "We wish to speak in some way about the structure of the atoms and not only about the 'facts' - for instance, the water droplets in a cloud chamber. But we cannot speak about the atoms in ordinary language." Although he realized the difficulty in doing so, Heisenberg was one of the few physicists to try to express what he saw when he looked into quantum reality.

According to Heisenberg, there is no deep reality - nothing down there that's real in the same sense as the phenomenal facts are real. The unmeasured world is merely semireal, and achieves full reality status during the act of observation: "In the experiments about atomic events we have to do with things and facts, with phenomena that are just as real as any phenomena in daily life. But the atoms and the elementary particles themselves are not as real; they form a world of potentiaities or possibilities rather than one of things or facts...

"The probability wave ... means a tendency for something. It's a quantitative version of the old concept of potentia in Aristotle's philosophy. It introduces something standing in the middle bewteen the idea of an event and the actual event, a strange kind of physical reality just in the middle between possibility and reality."

Heisenberg's world of potentia is both less real and more real than our own. It is less real because its inhabitants enjoy a ghostly quantum lifestyle consisting of mere tendencies, not actualities. On the other hand, the unmeasured world is more real because it contains a wealth of coexistent possibilities, most of which are contradictory. In Heisenberg's world a flipped coin can show heads and tails at the same time, an eventuality impossible in the actual world.

One of the inevitable facts of life is that all of our choices are real choices. Taking one path means forsaking all others. Ordinary human experience does not encompass simultaneous contradictory events or multiple histories. For us, the world possesses a singularity and concreteness apparently absent in the atomic realm. Only one event at a time happens here; but that event really happens.

The quantum world, on the other hand, is not a world of actual events like our own but a world full of numerous unrealized tendencies for action. These tendencies are continually on the move, growing, merging, and dying according to exact laws of motion discovered by Schrodinger and his colleagues. But despite all this activity nothing ever actually happens there. Everything remains strictly in the realm of possibility.

Heisenberg's two worlds are bridged by a special interaction which physicists call a "measurement." During the magic measurement act, one quantum possibility is singled out, abandons its shadowy sisters, and surfaces in our ordinary world as an actual event. Everything that happens in our world arises out of possibilities prepared for in that other - the world of quantum potentia. In turn, our world sets limits on how far crowds of potentia can roam. Because certain facts are actual, not everything is possible in the quantum world. There is no deep reality, no deep reality-as-we-know-it. Instead the unobserved universe consists of possibilities, tendencies, urges. The foundation of our everyday world, according to Heisenberg, is no more substantial than a promise.

* * *

Physicists do not put forth these quantum realities as science fiction speculations concerning worlds that might have been, but as serious pictures of the one world we actually live in: the universe outside your door. Since these quantum realities differ so radically, one might expect them to have radically different experimental consequences. An astonishing feature of these eight quantum realities, however, is that they are experimentally indistinguishable. For all presently conceivable experiments, each of these realities predicts exactly the same observable phenomena.

The ancient philosophers faced a similar reality crisis. For instance three ancient realities - 1. The world rests on a turtle's back; 2. The world is bottomlessly solid; 3. The world floats in an infinite ocean - led to identical consequences as far as anyone could tell at the time.

Likewise modern physicists do not know how to determine experimentally what kind of world they actually live in. However, since "reality has consequences" we might hope that future experiments, not bound by our current concepts of measurability, will conclusively establish one or more of these bizarre pictures as top-dog reality. At present, however, each of these quantum realities must be regarded as a viable candidate for "the way the world really is." They may, however, all be wrong.

The following video visualizes one of the most famous experiments in quantum mechanics, which will reveal with unequivocal clarity the seriousness as well as the madness of quantum reality: