Word
Gems
What is a
man but the sum of his thoughts?
Chemistry
& Physics
- Nick Herbert's
- Quantum
Reality
... Quantum theory works like a charm: it correctly predicts all the quantum facts
we can measure plus plenty that we can't (such as the temperature of the sun's interior)
or do not care to (the electron's "piano attribute," for instance). This theory
has passed every test human ingenuity can devise, down to the last decimal point.
However, like a magician who has inherited a wonderful magic wand that works every
time without his knowing why, the physicist is at a loss to explain quantum theory's
marvelous success.
What does it mean to "explain" a theory? Just imagine what one would
like to know about the magician's wand, namely the hidden reality responsible for its
magical operation. Quantum theory is more than a lucky gift out of the blue; this theory's
unprecedented predictive power suggests that it makes contact with some real features of
the physical world. An "explanation" of quantum theory would tell us what sort
of world we live in that allows such a curious wave-mathematical technique to foretell
this world's gestures in such precise detail.
- Quantum
theory resembles an elaborate tower whose middle stories are complete and occupied. Most
of the workmen are crowded together on top, making plans and pouring forms for the next
stories. Meanwhile the building's foundation consists of the same temporary scaffolding
that was rigged up to get the project started. Although he must pass through them to get
to the rest of the city, the average physicist shuns these lower floors with a kind of
superstitious dread.
- ...
Physicists' reality crisis consists of the fact that nobody can agree on what's holding
the building up. Different people looking at the same theory come up with profoundly
different models of reality, all of them outlandish compared to the ordinary experience
which constitutes both daily life and the quantum facts.
Physicists
differ over which parts of this theory they will take seriously and which parts they will
ignore as empty formalism having no counterpart in the real world. Which different picture
of quantum reality you end up with depends on what parts of quantum theory you take
seriously.
In
this chapter ... I examine how the eight major quantum realities arise from the selective
emphasis of certain features of quantum theory and the neglect of others.
Quantum Reality #l: The Copenhagen interpretation, Part I.
There is no deep reality.
The
Copenhagen interpretation, developed mainly by Bohr and Heisenberg, is the picture most
physicists fall back on when you ask them what quantum theory means.
- Copenhagenists
do not deny the existence of electrons but only the notion that these entities possess
dynamic attributes of their own.
Although
an electron is always measured to have a particular value of momentum, it is a mistake,
according to Bohr, to imagine that before the measurement it possessed some definite
momentum.
- The
Copenhagenists believe that when an electron is not being measured, it has no definite
dynamic attributes.
Quantum
theory was developed almost solely by Europeans. J. Robert Oppenheimer, one of the few
Americans to have participated in Bohr's Copenhagen Institute, here explicitly denies the
existence of the major attributes with which classical physics described a particle's
external motion:
- "If
we ask, for instance, whether the position of the electron remains the same, we must say
'no'; if we ask whether the electron's position changes with time, we must say 'no'; if we
ask whether the electron is at rest, we must say 'no'; if we ask whether it is in motion,
we must say 'no.'" ...
Quantum Reality #2: The Copenhagen interpretation, Part 11.
Reality is created by observation.
Expanding
on the Copenhagen interpretation's special role for M devices, Quantum Reality #2
emphasizes the observer's special status in a quantum world. Of quantum theory's many
elements, the observer-created reality school stresses the quantum meter option--the
observer's ability to intervene in reality by freely selecting which attribute he wants to
look at. In waveform language, the meter option amounts to freedom to choose the waveform
alphabet in which an entity's proxy wave will be expressed: whether the traffic noise
shall be made from piano or tuba (or whatever) waves. By your choice of what attributes
you look for, say believers in observer-created reality, you choose what attributes a
system will seem to possess...
If one accepts that common phenomena like the rainbow are observer-created, one should not
be so surprised by such claims made on the electron's behalf. An electron after all is
surely stranger than a rainbow. Wheeler takes observer-created reality a step beyond
rainbows with what he calls a "delayed-choice experiment." In such an
experiment, the observer creates not only present attributes of quantum entities, but also
attributes that such entities possessed far back in the past, which by conventional
thinking existed long before the experiment was conceived, let alone carried out...
Quantum Reality #3: Reality is an undivided wholeness.
The contention of David Bohm and others that despite its obvious separations the world
is a seamless whole is related to Bohr's notion that quantum attributes are not localized
in the quon itself but reside (like the position attribute of a rainbow) in "the
entire experimental arrangement." Certain features of quantum theory imply that this
innocent expression "entire experimental arrangement" may have to include not
only activities in the immediate vicinity of the quon's actual detector but actions
arbitrarily remote in time and space from the detection site. Ultimately the whole
universe may be implicated in a simple measurement, in the selection of a single quon's
observed attributes...
Quantum Reality #4: The many-worlds interpretation.
This quantum reality, first dreamed up by Hugh Everett in 1957 while a Ph.D. candidate
under John Wheeler, takes the quantum measurement problem seriously and solves it in a
bold and flamboyant manner.
The measurement problem can be expressed in many ways. Everett saw it like this: the
orthodox ontology treats measurement as a special kind of interaction, yet we know that
measurement interactions cannot really be special since M devices are no different from
anything else in the world. How, then, asks Everett, can we strip the measurement act of
its privileged status and achieve within physics that democracy of interactions which
certainly prevails in nature?
Bohr, for instance, assigns special status to measuring devices, conferring on them a
classical-style actuality not possessed by the atomic entities under their scrutiny. Von
Neumann, on the other hand, does not consider M devices special: be describes them in
terms of possibility waves just like atoms. However, the price von Neumann has to pay to
purchase this equality of being is the necessary elevation of the measurement act to
special status. Unlike any other interaction in nature, measurement has the power to
collapse the wave function from many parallel possibilities (the premeasurement
superposition of possibilities) to just one (the actual measurement result).
Following von Neumann's picture of quantum theory, Everett represents everything by proxy
waves, but he leaves out the wave function collapse. When a quantum system encounters an M
device set to measure a particular attribute, it splits as usual into many waveforms, each
corresponding to a possible value of that attribute. What is new in Everett's model is
that correlated to every one of these system wave functions is a different M-device
waveform which records one of these attribute values. Thus if the measured attribute has
five possible values, the quantumentity-plus-measuring-device develops into five quantum
systems, each with a different attribute value paired with five measuring devices each
registering that value. Instead of collapsing from five possibilities to one actual
outcome, the quantum system in Everett's interpretation realizes all five outcomes.
To account for the stubborn fact that no one has ever seen one M device turn into five,
Everett makes a not-so-modest proposal. The apparatus actually does split into five
different parts, says Everett, but each part occupies its own parallel universe. A
human being--one of Everett's critics, for instance--dwells in just one of these universes
(at a time) and cannot perceive the other four. Likewise the inhabitants of the other four
universes are not aware of their parallel partners.
The "ordinariness" of quantum facts in spite of the real existence of multiple
universes is accounted for in Everett's model by the fact that each human observer
perceives only a single universe. We do not know why human perception is limited to such a
small sector of the real world, but it seems to be an unavoidable fact. We are not
directly aware of these alternate worlds, but our own universe would not be the same
without them.
Everett's quantum theory without collapse describes the world as a continually
proliferating jungle of conflicting possibilities, each isolated inside its own universe.
In that world (which we might call super reality) one M device splits into five. However,
humans do not happen to live in super reality but in the world of mere reality, where only
one thing happens at a time.
- We can picture Everett's super reality as a continually branching tree of
possibilities in which everything that can happen actually does happen...
Everett's many-worlds interpretation of quantum theory, despite its extravagant
assumption of numerous unobservable parallel worlds, is a favorite model of many
theoretical physicists because of all quantum realities it alone seems to solve the
measurement problem with no arbitrary canonization of the process of measurement. In
Everett's picture all measurement devices and measurement acts are fundamentally of the
same nature as all other devices and acts. Strictly speaking, there are no
"measurements" in the world, only correlations.
Einstein objected to suggestions of observer-created reality in quantum theory by
saying that he could not imagine that a mouse could change the universe drastically simply
by looking at it. Everett answers Einstein's objection by saying that the actual
situation is quite the other way around. "It is not so much the system," Everett
says, "which is affected by an observation, as the observer who becomes correlated to
the system." The moral of Everett's tale is plain: if you don't want to split, stop
looking at attribute-laden systems.
...In the conventional single-universe model of things, something with a very small
probability is effectively impossible: it will never happen. However, in the
Everett picture everything that can happen does happen. If life on Earth is
possible at all, then it is inevitable-in some corner of super reality. In
Everett's bountiful multiverse, every little "could be," no matter how
improbable, gets its time to shine.
Quantum Reality #5: Quantum logic. The world obeys a
non-human kind of reasoning.
In 1936 John von Neumann and Harvard mathematician Garrett Birkhoff proposed a new
approach to quantum theory which they called quantum logic. An entity's "logic"
means how its attributes combine to make new attributes.
The attributes of classical objects follow a familiar pattern called Boolean logic after
George Boole, an Irish schoolteacher who first codified the structure of ordinary
reasoning. Birkhoff and von Neumann show that because quantum attributes are represented
by waveforms, they combine according to a peculiar "wave logic." ...
Quantum Reality #6: Neorealism. The world is made of ordinary
objects.
The bottom line of many quantum experiments consists of a pattern of tiny flashes on a
phosphor screen. Is it so obvious that such a simple phenomenon--the basis of all TV
images--can be explained only by resorting to some bizarre quantum reality? Watching those
little flashes of light appear on the screen one by one, it's easy to imagine that they
are actually caused by little objects--by real electrons with position and momentum
attributes all their own. This common-sense notion that the ordinariness of direct
experience can be explained by an equally ordinary underlying reality is the basis for a
quantum reality I call neorealism. Neorealists claim that the familiar objects that make
up the everyday world are themselves made of ordinary objects; they believe, in
short, that atoms are "things." This straightforward view of
the world's real nature has been generally dismissed by establishment physicists as
misguided and hopelessly naive.
Werner Heisenberg, for instance, considered this way of thinking as outmoded as the
idea of a flat Earth:
- "The ontology of materialism rested upon the illusion that the kind of
existence, the direct 'actuality' of the world around us, can be extrapolated into the
atomic range. This extrapolation, however, is impossible . . . Atoms are not things."
Not only was neorealism rejected by Heisenberg, Bohr, and other founding fathers of
quantum theory as well as most of the scientific rank and file, it was condemned by the
New Physics' foremost mathematical authority. World-class mathematician John von Neumann,
in his quantum bible, considered the claims of the neorealists and conclusively rejected
them. Von Neumann showed that because quantum theory represents attributes by waveforms,
it makes predictions which no collection of ordinary objects can duplicate.
In other words, if quantum theory is correct, neorealism is impossible. This
conclusion, known as von Neumann's proof, strengthened the case for the prevailing
Copenhagen view, considerably dampened physicists' enthusiasm for neorealist heresies, and
effectively closed off research into object-based models of the world for more than twenty
years...
Quantum Reality #7: Consciousness creates reality.
The first person to suggest that quantum theory implies that reality is created by
human consciousness was not some crank on the fringes of physics but the eminent
mathematician John von Neumann. In his quantum bible Die Crundlagen, the most
influential book on quantum theory ever written, von Neumann concludes that, from a
strictly logical point of view, only the presence of consciousness can solve the
measurement problem. As a professional mathematician, von Neumann was accustomed to boldly
following a logical argument wherever it might lead. Here, however, was a severe test for
his professionalism, for his logic leads to a particularly unpalatable conclusion: that
the world is not objectively real but depends on the mind of the observer...
Consciousness-created reality (QR # 7) should not be confused with mere
observer-created reality (QR # 2). Quantum realists belonging to these schools make very
different claims. Any observer -- conscious or not -- has to make a choice of what
attributes to measure (quantum meter option), which determines into which waveforms the
quantum system will be analyzed. By his choice of what to measure, the observer will cause
the quon to take on position rather than momentum attributes, but he does not decide what
the value of this quon's position shall be. The quantum meter option can just as well be
exercised by an inanimate computer as by a human observer. The observer "creates
reality" here by choosing what kinds o f attributes a quon shall possess. (Observer
creation of the first kind.)
Consciousness-created reality goes one step farther. Consciousness selects (or at least
acts as the site for such a selection) which one of the many position possibilities
actually becomes realized. Thus the meter option selects what game shall be played
(position instead of momentum, for instance); consciousness actually deals out the cards
(this particular value of position). Consciousness "creates reality" by deciding
what particular attribute value shall materialize. (Observer creation of the second kind.)
According to Quantum Reality # 7, dynamic attributes, when not being observed,
exist as a wavewise superposition of possibilities; the universe acquires
definite values for these attributes only during a conscious observation. A mere machine
can't manufacture reality, in this view, unless it embodies some kind of awareness
analogous to our own; the measurement problem is solved by a ghost in the machine. This
quantum reality suggests that most of the universe most of the time dwells in a half-real
limbo of possibility waiting for a conscious observer to make it fully real.
During the eighteenth century the growing success of Newton's clockwork mechanics inclined
many philosophers to the belief that all phenomena, including life, mind, and spirit could
ultimately be explained as types of complex machinery. George Berkeley, bishop of Cloyne
in southern Ireland, outraged by scientific materialism, opposed it with strong
philosophical opinions of his own. Berkeley argued that mind is not a form of matter but
quite the opposite: matter does not even exist except as the perception of some mind.
Absolute existence belongs to minds alone-the mind of God, the minds of humans and other
spiritual beings. All other forms of being, including matter, light, the Earth, and stars,
exist only by virtue of some mind's being aware of them. In Berkeley's philosophydubbed
"idealism" because it emphasizes the primacy of ideas over things -nothing
exists unless it is either a mind itself, or is perceived by a mind. Esse est percipi
(To be is to be perceived) was the Irish bishop's motto concerning matter: "All those
bodies which compose the mighty frame of the world have no subsistence without a
mind."
Quantum idealism does not go as far as Berkeley's. According to Quantum Reality # 7, all
quons and their static attributes enjoy an absolute existence whether they are observed or
not. Only a quon's dynamic attributes, including the major external attributes position
and momentum, are mind-created. Thus all those entities "which compose the mighty
frame of the world" do certainly exist without the intervention of mind, but until
someone actually looks at them, these entities possess no definite place or motion. The
peculiar existential status of unobserved quons is the topic of my eighth quantum reality.
Quantum Reality #8: The duplex world of Werner Heisenberg.
No matter how bizarre the visions of quantum realities dancing in their heads, most
physicists agree that the results of measurements are truly real. Like ordinary people
(but unlike some philosophers), physicists cannot deny the evidence of their senses. The
indubitable reality of measurement results is a solid rock on which to found an empirical
science, or from which to launch speculative voyages into deep reality.
In most quantum realities the measurement act does not passively reveal some
preexisting attributes of quantum entities, but actively transforms "what's really
there" into some form compatible with ordinary experience.
- One of the main quantum facts of life is that we radically
change whatever we observe.
Legendary King Midas never knew the feel of silk or a human hand after everything he
touched turned to gold. Humans are stuck in a similar Midas-like predicament: we can't
directly experience the true texture of reality because everything we touch turns to
matter.
Many of the previous quantum realities have focused on what extra feature makes an
ordinary interaction into a measurement (macroscopic device, record-making observer,
conscious spectator, for example), but little has been said about the character of the
unmeasured state. Since most of reality most of the time dwells in this unmeasured
condition, which quantum theory represents by an uncollapsed superposition of
possibilities, the lack of such a description leaves the majority of the universe
(everything that's not currently being measured) shrouded in mystery.
Werner Heisenberg was one of the few physicists who attempted to describe in
non-mathematical terms the "world-in-itself," that innocent existence quantum
entities enjoy before undergoing a measurement. Heisenberg's description is no full-hedged
model of reality, but just one man's attempt to convey in ordinary language the flavor of
the deep reality symbolized by a wave.
Heisenberg was acutely aware of the difficulty of trying to describe the quantum world in
words. "The problems of language here are really serious," he admits. "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." Heisenberg however did not let this difficulty render him
speechless. He realized that some words are better than others for describing the
unmeasured world.
Quantum theory according to the Copenhagen interpretation represents the world in two
different ways: the observer's experience is expressed in the classical language of
actualities, while the unmeasured quantum realm is represented as a wavewise superposition
of possibilities. Heisenberg suggests that we take these representations literally as a
model for the way things really are...
QUANTUM REALITY REPRISE
Most physicists use quantum theory as mere recipe for calculating results and don't
trouble themselves about "reality." However, it is hard to believe that this
theory could be so successful without corresponding in some way to the way things really
are.
Like the story of the blind man and the elephant in which each man imagines a
different animal according to which part he's holding, these eight quantum realities
result from different physicists each taking a part of quantum theory seriously and
identifying it with the "real reality" behind appearances.
Bohr, for instance, took the uncertainty principle seriously, using it to argue that quons
possess no dynamic attributes of their own. A quon's so-called attributes reside in the
relation between the entity itself and a "classical" measuring device.
Believers in observer-created reality take the quantum meter option seriously: exercising
this powerful option, the observer decides which kinds of attributes quantum entities will
seem to possess.
Quantum Reality # 3 (undivided wholeness) takes phase entanglement
seriously as a token of a real physical connectedness (the quantum connection) that
instantly joins each quon to every other.
Everett in his many-worlds interpretation takes the quantum measurement problem seriously:
he solves this problem by declaring that the wave function collapse is an illusion caused
by human inability to experience reality fully: we are unaccountably blind to all but a
single branch of a luxuriant tree of coexistent universes.
Quantum logicians (QR # 5) view incompatible attributes as the central
quantum fact: a new form of reasoning is needed in which the strange behavior of quantum
attributes appears perfectly natural.
Neorealists (QR #6) believe that the surface ordinariness of all quantum
facts (Cinderella effect)--the fact that every experiment must be described in classical
language--clearly suggests that reality itself is ordinary too.
Believers in consciousness-created reality take the quantum measurement problem seriously
and conclude that nowhere in mere quantumstuff is there a logical site for proxy wave
collapse: only the mind of the observer can fill the bill.
Werner Heisenberg's duplex universe (QR # 8) takes literally the proxy
wave representation of quantum entities as super positions of possibilities. Unmeasured
quantum attributes are just what quantum theory says they are: unrealized possibilities.
Because of the Cinderella effect--the stubborn ordinariness of quantum fact--we cannot
experience directly any of these strange quantum realities (with the exception of
neorealism). Although these realities make very different claims, they all predict exactly
the same facts. At present there's no way to decide experimentally among these alternative
visions of the way the world really is.
- When my son asks me what the world is made of, I confidently
answer that deep down, matter is made of atoms. However, when he asks me what atoms are
like, I cannot answer though I have spent half my life exploring this question. How
dishonest I feel--as "expert" in atomic reality--whenever I draw for
schoolchildren the popular planetary picture of the atom; it was known to be a lie even in
their grandparents' day.
Physicists cannot explain atoms to their children, not because we are ignorant but
because we know too much. The behavior of atoms is no longer a mystery. Quantum theorists
can confidently calculate the outcome of any conceivable atomic experiment. However, as we
see, the price physicists have paid for quantum theory's remarkable predictive power is
their inability to picture in plain language an image of the atomic world.
Thirty years after the publication of von Neumann's Die Grundlagen (1932) the
quantum reality question inspired heated debates among philosophers and physicists, but
little progress was made toward solving the problem of what sort of world we actually live
in.
Then, in 1964, a physicist named John Bell proved an important theorem which gave us a
new insight into deep reality...
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