Preface
Some 350 years ago, in his Discorsi e Dimostrationi
Matematici [Galilei], Galileo Galilei discussed whether or not light
propagated with a finite though very high velocity, or with infinite speed,
instantaneously. The question was an
open one then, with prominent proponents for either position. For example, René Descartes argued on
philosophical grounds that light dispersed itself into all of space
instantaneously, whereas Galileo was more inclined toward the idea of a finite
velocity. In fact, he even reported
about an early experiment, which, however, would have to be refined and
performed again to reach a definite conclusion.
"Sagredo: ... However, of which kind, and how high might we
estimate the velocity of light? Is the
appearance instantaneous, momentaneous, or, like other movements,
temporal? Could one decide this
experimentally?
Simplicio: Daily experience teaches
us, that the spreading of light be instantaneous; if in a large distance the
artillery performs shooting exercises, we see the glare of the flame without
time delay, while the ear perceives the sound only after some considerable
time.
Sagredo: Oh, Mister Simplicio, from this well known attempt one
can conclude nothing but that the sound takes more time than the light; in no
way can one conclude that the light be momentaneous, and not temporal, if only
very fast. Also another observation
does not teach more: immediately when the sun appears on the horizon, we see
its rays; but who tells me, that the rays do not arise earlier at the horizon
than in my eyes?
Salviati: The low power of
decision of those and other similar processes evoked the thought in me, if one could
not in some way decide with certainty, whether the illumination, i.e. the
spreading of light, be really instantaneous: for, already the rather quick
propagation of sound leaves one to suppose that the one of light can only be
very fast. And the experiment, which I
considered, was the following: Of two persons each one holds some light in a
lantern or something similar to it, namely so, that each one can cover or
uncover the light with the hand; then they place themselves opposite to each
other within a short distance, and they practice to cover or uncover their
lights for the other: namely so, that, if the one sees the other light, he
immediately uncovers his; such correspondence is being mutually repeated
several times, so that soon without error upon uncovering of the one follows
the uncovering of the other, and, if the one uncovers his light, he will also
soon see the one of the other. Having
practiced within a short distance, the two persons separate with their lanterns
up to 2 or 3 miles; and by performing their experiment at night, they observe
carefully, whether the answering of their signal occurred in the same tempo as
before, wherefrom one could conclude whether the light was propagating
instantaneously; for if this were not the case, then in a distance of 3 miles,
that is, on a path of 6 miles to and fro, the delay would have to be fairly
well recognizable. (... )
Sagredo: A beautiful, sensible experiment; but, tell us, what
has resulted from the performance of it ?
Salviati: I have done the
experiment only within a short distance, within less than one mile, from which
no conclusion yet can be made about the instantaneity of light; but if it is
not momentaneous, it is at least very fast, even almost momentaneous..." [Galilei, pp. 39f]
The well-known measurements of Olaf Römer in 1675
eventually established that light propagates with a finite speed. However, the distances involved in the
calculations were not a few miles, but literally cosmic ones, making use of the
fact that the eclipses of the Galileian moons of Jupiter are time delayed once
by a considerable amount if measured twice in a year: once, when the earth is
on the same side as Jupiter, and half a year later. Thus, in the latter case,
the light from Jupiter has to travel an additional 2 Astronomical Units
(distances sun-earth) before reaching the earth. Olaf Römer in this way
determined the velocity of light as about 220,000 km/sec, not too far off
today’s 299,792,458 m/sec [Simonyi]. Elements of Galileo's experiments on the
speed of light are echoed in two main theories of the twentieth century, i.e.,
the theory of relativity, and quantum mechanics. First, Galileo's experiment was concerned with the simultaneity
of light flashes perceived by two independent observers, and with the possible
(though not achieved) obstruction of that simultaneity. And Albert Einstein began his arguments for
a theory of relativity with a discussion of simultaneity as established via
emission and reception of light by two independent observers. Second, the phenomenon of quantum mechanical
nonlocality today puts us in a similar situation as Galileo's facing a
"practically instantaneous" speed of light: the well-known "EPR
type"-experiments (based on the seminal paper by [Einstein et al.]), and
an increasing number of similar ones, all seem to indicate that in the presence
of two independent observers' apparatuses, the effects of operations on one
observer's apparatus are detectable "practically simultaneously" on
the other observer's apparatus. What a
Salviati and a Sagredo may have done with light lanterns 350 years ago may be
very similar to what Alice and Bob could do today with quantum communication
devices: (at least in retrospect) observing a "practically
instantaneous" change in a state of light upon predefined manipulations
over distances of miles, whereas with a much finer resolution in time one could
eventually show that the effects of state manipulations really propagate with a
very high, but finite speed.
If you snap your fingers in a small room with the
appropriate acoustics, you will hear an echo of the "snap" almost
immediately. If one considers this from
a perceptual point of view, this experience may even be somehow surprising: it
is, for a moment, as if your body were extended in a "medium" that
reacts on your snapping with an echo so immediately afterward that it seems to
still belong to your bodily action, as if you had hit the wall with a long
stick in your hand. Somehow you are -
via the "medium" of the air - connected to the wall, and in a simple
experiment like when snapping your finger you become aware of this
"connection." In other words, we are often not aware of the media
that surround us, because they are always there and therefore filtered away by
our perpetual routines. Only when in
unusual circumstances, like in the mountains, for example, where echoes can
take seconds to return, do we become aware of these echoes, and, therefore, of
the finite velocity of sound. Rather
different considerations hold for the velocity of light. Bodily no more, but only under very
particular experimental situations, with very high resolutions in time, can we
experience that it is not infinite.
What, then, about the manipulation of quantum states? Could not they also occur in a
"medium" that connects all participants' apparatuses, and that upon
the appropriate manipulations becomes modified such that the effects of this
modification spread "practically instantaneously," but nevertheless
with some finite speed?
Such an option is actually being considered here in
this book. It will be shown that,
rather surprisingly, with the re-introduction of the concept of a quantum
"medium" (or "aether"), which contradicts neither the
theory of relativity nor quantum theory, in effect a unification of both
theories can be envisaged. The blind
Galileo, when snapping his finger, could have roughly told the size of a room
he was brought into by making use of the principle of echo orientation as we
know it also from bats or certain fish.
In abstract terms, this principle tells us that some localizable entity
may permanently emit and receive waves in a medium, where the incoming ones
provide information about the surroundings of said entity, which are then used
to guide its further movement. Here is
where cybernetics comes in: the circular causality between a "perceptual
entity" and its "environment." With the quantum cybernetics
aimed at in this book I try to elaborate a corresponding "perceptual"
model of quantum systems.
I would like to thank those scholars who have
massively influenced my thinking and who, throughout the years, and in numerous
discussions, helped to shape my understanding of quantum theory, and of science
generally: Heinz von Foerster, Daniel Greenberger, Franco Selleri, Jean-Pierre
Vigier, and Anton Zeilinger. Although
I've had the opportunity only once in each case, I also gratefully remember
stimulating discussions on the idea of quantum cybernetics with David Bohm and
John Bell. I am also most thankful for
reading and providing comments on the first draft of this book to Helmut Erber,
Siegfried Fussy, Richard Gordon, Peter Holland, Helmut Rauch, Herbert Schwabl,
and Johannes Werner. Fritz Bergler,
Peter Ferschin, Joseph Hartmann, Elisabeth Kopf, and Werner Korn have been of
invaluable help in preparing the illustrations. Furthermore, I thank Tom von Foerster for the very fine
collaboration with Springer-Verlag. And
finally, I am most grateful to Angelika, my other half of the sky, for sharing
with me the elating experience of this month's total solar eclipse, and much
more.
GG
Vienna, Austria
August 1999
1
By the time he wrote the Discorsi, Galileo
was placed under house arrest; he was already blind and had only a few more
years to live, but it is obvious from the following that in principle he
considered an experimental decision possible.