I finally got a little time to address some of the concerns of Stephen
Jones and Brian Harper concerning the analogy that I drew between
Feynman's work reformulating quantum mechanics in terms of path integrals
(which provides a natural explanatory mechanism for Hamilton's Principle
of Least Action in classical mechanics) and Darwin's work which explains
biological change in terms of variation and selection. I'm sorry for the
length of this post. Since it has been so long since the last posts on
this thread I thought that I ought to provide the (by now forgotten)
context by quoting from other posts more extensively than I normally would
have done.
On 14 Apr 1997 Stephen Jones wrote:
>[...]
>DB>My point was that Feynman's work takes away the mystery and shows
>>the optimality to be automatically a natural consequence of a
>>mindless quantum dynamics which treats all possible paths equally
>>without an overt appeal to such a necessary Designer.
>
SJ>Of course neither Feynman nor you actually know that this is
>"mindless". This theist at least believes that all laws of nature
>are ultimately grounded in the mind of God.
I think you are reading more into my use of the term "mindless" than I
intended. Notice the word "overt" in my above quote. I, too, believe
that "all laws of nature are ultimately grounded in the mind of God". My
use of the term "mindless" was in reference to the physical interference
effect, first discovered by Feynman, which naturally selects the least
action path for a classical-like system (i.e. one whose total elapsed
action was huge compared to Planck's constant) from the plethora of all
other competing conceivable paths -- each contributing on an equal footing
to the complex probability amplitude for a physical process. The
mathematical mechanism for this selection process is mindless in the same
sense that the production of any interference pattern from any wave-like
phenomenon is mindless. The concept of a mind does not enter the
mathematical description for how the effect works. All the scientific
physical laws of nature are mindless in this sense. They do not make any
*explicit* reference to a mind in their formulation. Whether or not a
Mind is behind the very existence of those laws or not is a metaphysical
and religious issue, not a scientific one. I suspect that many atheists
would appeal to the very (apparent) mindlessness, universality, and
inexorableness of natural law to support their religious beliefs. Of
course this is then just a case of atheists using science to do a bit of
"natural theology" and is the process of stretching science into scientism.
SJ>In any event, the theist would merely ask why is there "optimality"
>which is "automatically a natural consequence of a ... quantum
>dynamics which treats all possible paths equally"?
I think you mean here that the theist would treat the very existence of
natural law (and all of nature as well) as a brute fact that science
cannot explain and appeal to the existence of God as a ground for such
existence. If so, then I have no argument with you here. We should be
cautious though. Just because the current state of science (at any stage
of development) may some unanswered questions we should not be quick to
make a God-of-the-gaps appeal and say that God is overtly necessary to
fill them. Rather we (scientists who are theists) should look at such
gaps in the fabric of scientific explanations of natural phenomena as
places to do further scientific research to see if we can find out some
"mindless" natural scientific explanation for the mysterious phenomenon--
all-the-while confident that any such explanation and mechanism (and
indeed all that exists) owes its very existence to God who has created
and sustains all things (albeit in a manner that seems to usually be
consistent with natural law--which itself may be seen to be a reflection
of God's faithfulness).
>DB>In the biological analog the Darwinian mechanism provides a
>>natural(istic) explanation for the biological designs, their
>>adaptations, quasi-optimalities, and their occasional
>>suboptimalities, again without explicit reference to an underlying
>>intelligent Designer.
>
SJ>Darwin *claimed* to provide a "natural(istic) explanation
>for...biological designs" but even among biologists there are many
>who disagree that his explanation is adequate as a general theory.
> <SNIP>
Good point. I'm not a biologist and don't pretend to be able to evaluate
the various claims of sufficiency and of insufficiency of the Darwinian
mechanism as an explanation for the appearance (and extinction) of all the
various forms of organisms throughout geological time. This seems to be
one point where my analogy is uneven. Feynman's explanation of Hamilton's
Principle of Least Action has both intellectual beauty *and* mathematical
rigor. Darwin's explanation of biological change has intellectual appeal
but has not been fully demonstrated in actual practice in many instances.
This may be partly due differences in how scientists (must) approach
biology and physics. In physics the phenomena are simple enough for the
theories to provide a one-to-one correspondence between the physical
phenomena (or at least their statistics) and a mathematical description.
Biology is too complicated in most instances for such mathematical rigor.
Here sweeping theoretical explanations can be expected to have their gaps,
and there are expected to be cases where the theory may be less than
compelling. In any event (modern synthetic versions of) Darwin's theory
plays a paradigmatic role in biology as grand in its explanatory scope as
quantum mechanics plays in physics, even if there is a mismatch in the
levels of mathematical rigor and verification across the analogy.
>DB>In both cases the existence of such a Designer may be suggested to
>>the theist by the data, but the atheist doesn't feel (and doesn't
>>need to feel) the force of the suggestion.
>
SJ>Disagree. As Romans 1 points out, it is normal and natural even for
>atheists "to feel the force of the suggestion", ie. "the existence
>of...a Designer". The agnostic Paul Davies admits that there "...is
>for me powerful evidence that there is 'something going on' behind it
>all. The impression of design is overwhelming" (Davies P., "The
>Cosmic Blueprint", 1995, p203).
>
>Or atheist Pagels:
><SNIP>
The invisible qualities of God that Romans 1 (v. 20) says are clearly
visible are His "dunamis" (power) and His "theiotEs" (divinity, deity,
divine majesty, or godhead). It doesn't say anything about His
intelligent designs being such an apparent attribute. Just because Davies
and Pagels are impressed by the suggestion of teleology found in nature
doesn't mean that all atheists are necessarily similarly impressed. I
think Dawkins and Dennett may be considered as counterexamples.
SJ>Atheists have to work hard at denying intelligent design!
I suspect that they would bring up theodicy problems of suffering,
injustice and seeming suboptimal design in many organisms as arguments
that theists work hard to find an imaginary intelligent caring god to
comfort them in a cold brute world.
On 21 Apr 1997 Brian Harper wrote:
BH>I think its really difficult, for me anyway, to view the principal
>of least action in the same way its originators did. For example,
>it would never even occur to me to think that particles were actually
>engaged in a conscious act of figuring out which path minimizes
>the action. What is amazing to me is that the action is minimized,
>regardless how its accomplished.
>
>It isn't that often that I agree with Steve Jones on something ;-)
>but I agree with his reply:
>
>>SJ>In any event, the theist would merely ask why is there "optimality"
>>which is "automatically a natural consequence of a ... quantum
>>dynamics which treats all possible paths equally"?
Well, I'm glad that my post helped you and Steve to reconcile on
something. My comment to Steve's quote here is already given previously
above.
BH>This is exactly what I had in mind when I said I thought that Feynman
>had merely replaced one mystery by another (perhaps greater)
>mystery. Of course, this surprise could be due to ignorance of
>quantum mechanics.
I see this as just another case of a brute mystery being explained as a
natural automatic consequence of deeper underlying laws of nature. This
is the natural way science progresses. Consider the following examples:
Before the Renaissance the Ptolemaic geocentric cosmology was in vogue for
obvious phenomenological reasons. The model was not without its
unexplained mysteries however. For one, how could there be such an
enormous rigid celestial spherical shell with stars embedded in it which
rotated about the earth in a manner which kept it in tact? Or for
another, why is it that the superior planets always undergo retrograde
motion when they just happen to be in opposition to the sun? Why should
the gearing of their epicycles and their referants be such that these
motions stay synchronized with the sun's position? For that matter, why
should the inferior planets' motions also be synchronized with the sun?
Natural automatic explanations of these mysteries were given by the
Copernican heliocentric cosmology. The unified motion of the celestial
sphere is merely an apparent artifact of the earth's rotation. The stars
are not tied to each other by a dark shell; they are just sitting out
there at distances too far for their proper motions to be detected. The
retrograde motion of the outer planets is naturally synchronized with the
sun's apparent position because it is an artifact of the earth passing in
front of them as it orbits the sun on an inside orbit.
Later on Kepler discovered his famous laws of planetary motion. These laws
explained certain anamolies in the motions of the planets using the bare
Copernican circular orbit model. But it was a mystery as to why the
planets should orbit in ellipses with the sun at one focus, why they
should sweep out equal areas in equal times, why their orbital period
should be proportional to the 3/2 power their orbit's size.
Later Newton explained Kepler's laws as natural automatic consequences of
his universal law of gravitation combined with his three laws of motion.
This unified all celestial and terrestrial mechanics under a single
theoretical framework. Newtonian physics as successful as it is is not
without its mysteries. Why should F = ma? Why is the law of gravity a
1/r^2 force rather than something else? Why is the gravitational force on
a body always proportional to the mass of that body? How can there be
magical instantaneous action at a distance?
Later Hamilton's principle naturally explained Newton's laws of motion as
just automatic artifacts of the deeper principle that physical systems
always move in such a way as to minimize the elapsed action. It was a
mystery though as to why nature conspired to always be so efficient as to
always magically minimize the action.
Later Einstein showed how seeming instantaneous actions at a distance are
only apparent and are artifacts of the speed of causation (i.e. the speed
of light c) being so large compared to ordinary motions. His Equivalence
Principle showed why gravitational forces are proportional to a body's
mass. Such forces are locally just an artifact of a locally accelerating
reference frame and gravitational forces behave (on a local scale) just
like other accelerated frame-induced fictitious forces such as the
centrifugal force and the Coriolis force. Einstein showed how Newton's
1/r^2 force law of gravity is an automatic limiting case of gravitation
being due to matter curving the "fabric" of spacetime with the ostensibly
gravitating bodies really just following "straight lines" (geodesics) in
the curved spacetime manifold. Newton's force law comes out when the
curvature effect is asymptotically small. Einstein's theory of
relativity (both special and general) is not without its mysteries. Why
does matter (actually the stress-energy-momentum tensor for matter) curve
spacetime? Why does spacetime have 4 dimensions with its distinctive 3 +
1 space-time split? These questions are still not answered in any
satisfactory way yet, although progress is continuing to be made (by
investigating such arcana as various compactification schemes and the low
energy limit of superstring theories of everything).
In view of the historical process of the further development of physics we
see Feynman's contribution as another example of a deeper theory
explaining the mysteries of a shallower level theory. Feynman has
explained the mysterious Hamilton's Principle in terms of the automatic
working of quantum dynamics, but quantum theory has its own share of
mysteries as well. Why should nature obey the laws of quantum mechanics
anyway? Just how do quantum measurements take place? (There has been
significant recent progress on this last question though.)
Thus we see that the natural progress of physical science is to explain a
series of mysteries which are inexplicable at one (more phenomenological)
level as the natural automatic ("mindless", if you will) workings of a
deeper level process or mechanism. The deeper level mechanism has its own
set of unexplained (but fewer) mysteries though. Even if that "holy
grail" of physics is ever obtained--a unique self consistent "theory of
everything" which naturally explains all physical phenomena--even then--
there would still be the unexplained (at the scientific level) mystery as
to why this scheme of things is actually realized. Why is there existence
at all? Ultimately the end of science is metaphysics and religion. My
own take on the matter is that ultimately things are as they are because
that is God's plan and purpose (back to teleology here). An atheist would
presumably have a different answer here. The atheist might even be
content to leave the fact of existence as just a brute fact to be accepted
(rather than assume the existence of a god to explain that brute fact).
>>DB>In the biological analog the
>>Darwinian mechanism provides a natural(istic) explanation for the biological
>>designs, their adaptations, quasi-optimalities, and their occasional
>>suboptimalities, again without explicit reference to an underlying
>>intelligent Designer. In both cases the existence of such a Designer may be
>>suggested to the theist by the data, but the atheist doesn't feel (and
>>doesn't need to feel) the force of the suggestion.
>
BH>First of all, I agree with your overall assessment in the last
>sentence above. I think Pascal said it best when he wrote:
>"There is enough light for those who desire only to see, and
>enough darkness for those with a contrary disposition".
I like this quote.
BH>I had a kind of knee jerk reaction against your analogy with
>Darwinian evolution that I've had a hard time putting into
>words. Probably I'm reading too much into the analogy,
Yep.
BH> but
>here are some objections:
>
>1) We've emphasized here the differences between the Newtonian
>view and the principle of least action and quantum mechanics.
>Yet, Darwinian evolution is very mechanistic and Newtonian.
>Perhaps I better explain this a little since "mechanistic"
>can mean different things. Mechanistic as a world view means
>generally that everything is, in the end, reducible to the
>motion of elementary particles [as a sidelight, I recall that
>Dennett defined mechanistic as algorithmic, but this is not
>the usual definition].
Actually, Newtonian physics does not adequately describe or explain the
behavior of elementary particles. Quantum theory excels at this instead.
BH> The Newtonian view is best illustrated
>by an example. The acceleration of the mass center of a collection
>of particles is proportional to the sum of the *external* forces
>acting on the system. The evolution in time of the system is
>determined by factors external to the system. As a world view
>this is rather pessimistic. No free will, we are pushed here and
>there by external forces. Darwinian evolution fits very well into
>the Newtonian world view. Species adapt and evolve due only to
>selection imposed by external factors.
Don't forget that selection is only half of the process. There is the
matter of variation as well. The variation is produced internally (but
influenced by both external and internal factors). Any pessimism inherent
in the Newtonian world view is also present is in any other scientific
vision where the system's behavior is governed by natural law. The
Schroedinger equation of quantum dyanmics is just as deterministic as
Newton's F = ma. Indeterminism and uncertainty only enters quantum theory
when measurements (or measurement-like processes) are made.
BH> This is not the only
>view of evolution of course. The self-organizational view is
>directly opposed to this. The "self" in self-organization
>emphasizes that the key factors in producing evolutionary
>change come from within the system. External factors play a small
>role.
>
>summary: Darwinian evolution lends itself readily to the Newtonian
>worldview, Quantum Mechanics does not.
Left to itself (i.e. unobserved and unmeasured) a quantum universe is just
as bleak as a Newtonian one. A Newtonian universe may have some wiggle
room for free will through chaos and a quantum one has some such wiggle
room through the undetermined results of measurement-like processes. The
processes of Darwinian variation and selection may also have some wiggle
room via the details as to how the variation is generated and through the
vagaries of the selection process.
>2) You mentioned "mindless quantum dynamics". Two points here.
>First, my layman's interpretation of QM was that it had returned
>"mind" to the universe. One sees this point emphasized so often
>in popular level discussions of QM.
Many popular discussions of quantum theory *do* overdo it on the "mind"
aspects. I think most serious physicists consider most such popular
treatments to be essentially new-age propaganda. There is a school of
interpretation of the quantum mechanical measurement problem where "mind"
and "consciousness" enters the discussion. In this *minority*
interpretation the consciousness of a conscious observer "reduces the wave
function" of the system when the result of a measurement becomes indelibly
registered in the observer's consciousness. Even in this interpretation
the consciousness of the observer merely plays an essentially mechanical
(--yet random) role in mysteriously collapsing the wave function. What I
refer to here is mostly the work of Wigner in the early 60s, esp. "Remarks
on the Mind Body Question" in *The Scientist Speculates__An anthology of
partly-baked Ideas*, (1961-2) where Wigner proposes the famous "paradox of
Wigner's friend". In this article Wigner extends the measurement theory of
London & Bauer *La Theorie de l'Observation en Mecanique Quantique* (1939)
which proposes that the mental activities of conscious observers cause a
physical interactions (not contained in the Schrodinger equation) which
can collapse a quantum wave function. These ideas of Wigner and London
and Bauer go *well* beyond the "mere" Copenhagen Interpretation (CI) of
the quantum measurement problem and are not what one usually thinks of
when the CI is the topic. Their ideas are decidedly "heterodox"
extensions of the "orthodox" CI and are related to the CI much like how
the distinctive theology of the Jehovah's Witnesses or the Mormons is
related to the doctrines of "mere" Christianity contained in the Apostles'
and Nicene creeds. The CI associated with Bohr doesn't refer to conscious
minds at all but rather to the principle of "Complementarity" and
emphasizes a fundamental role of the entire global experimental apparatus
which behaves *classically* when performing measurements. I think the CI
is still rather popular among physicists, whereas the consciousness-based
theories (speculations) of Wigner and London and Bauer are much less widely
held (among physicists if not among new-age gurus).
My own views on the "quantum measurement problem" are mostly found in the
book by Roland Omnes, *The Interpretation of Quantum Mechanics*, Princeton,
(1994) and in an article by Wojciech Zurek, "Decoherence and the Transition
from Quantum to Classical", *Physics Today*, Oct. 91. This view emphasizes
the importance of tiny uncontrollable interactions between a system and its
environment which destroy the quantum coherence of a pure quantum state and
irreversibly create a classical-like mixed state effectively causing
measurement-type events inadvertently to happen nearly all the time. Part
of the founding background formulation for such views is in the work of
(ASA member) Robert Griffiths on "Consistent Quantum Histories", J. Stat.
Phys. 36, 219 (1984) & Am. J. Phys. 55,11, (1987). This "decoherence"
interpretive framework seems to be becoming evermore popular among
physicists as it becomes more widely known and understood. This view does
not split the universe into 2 fundamentally different kinds (quantum systems
and their classical measuring apparatus) of entities like the CI does, nor
does it postulate many unobservable worlds, nor does it assume hidden
variables. It is actually quite sober.
> Second, some time ago
>Bill Hamilton [no, not *that* Bill Hamilton, the one at GM ;-)]
>made a point I had always thought rather obvious, namely that
>physical mechanisms, chemical reactions etc. are always mindless.
>Yet, in writings of many atheists one sees this (obvious) point
>emphasized. One wants to say: "my haven't you come a long way
>with your world view, you've figured out that chemical reactions
>are mindless ;-)". Methinks they really want to imply more than
>this though. They want to say there is no mind behind the chemistry.
>This is a metaphysical conclusion, not a scientific one. To give
>what is likely a poor analogy, suppose you go into a factory and
>observe all the mindless mechanical behaviour of gears and pulleys
>etc. Of course, the gears are mindless and one can completely
>describe their behaviour in terms of mindless mechanical laws.
>This doesn't mean there's no mind behind the operation of the
>factory.
I agree with you, Steve, and Bill here. My use of the term "mindless" in
my previous post was only at the level that you and Bill discuss above.
Namely, the laws of nature are necessarily "mindless" (i.e. they have no
explicit reference to mental processes in their mathematical forumlation).
My use of the term should not be construed as to imply anything one way or
the other about whether or not there is a "mind behind the operation of
the factory" of the universe. I personally belief that there is such a
Mind.
>3) The type of "selection" going on with Feynman's result seems
>to me of a completely different sort than with Darwinian evolution.
>For example, let's just suppose for the moment that they really
>were analogous. Suppose that all the possible evolutionary
>paths that an organism might take were treated equally (instead
>of having to wait and hope for an advantageous, undirected mutation).
>And suppose further that this "equal treatment" or averaging process
>always resulted in some optimal solution comparable to minimizing
>the action in mechanics. Call me naive if you want :), but I think
>this situation lends itself to a vastly different view of evolution
>than one gets from the Darwinian view.
I think you *are* reading too much into my analogy here. I did not mean
to imply any similarity in the mechanisms of the saddle-point interference
selection effects that take place in Feynman path integrals that produce
a dominant amplitude for the least action classical path for processes
that have a minimum action huge compared to Planck's constant with the
mechanisms that take place for biological realm to produce mutations which
are then culled by natural selection. In the case of the quantum system
all conceivable classical trajectories are simultaneously "tried" and the
interference effect selects the one with least action. In the biological
case, only a few (ususally) slightly mutant strains (out of the space of
all conceivable variations) are tried at any given time in a population.
Also, in the biological case, the selection pressure tends, usually I
think, to come from the environment rather than from interference from the
competing variants themselves. My analogy was not meant to be taken very
far. My only suggestion was that Feynman's work showed how the behavior
of a classical system as described by Hamilton's Principle was an
automatic ("mindless") consequence of an underlying quantum dynamics, and
that *in this regard* it was like how the Darwinian mechanism of variation
and selection automatically ("mindlessly") produces (and goes a long way
in explaining) diversity of form and behavior seen at the macro level in
biology. I meant the analogy to function at a *paradigmatic* level, not a
detailed one. I didn't mean for either the explanation on the biological
side to be as air tight and rigorous as the physics side of the analogy is
(SJ's objection), and I didn't mean for the details of the corresponding
mechanisms to match (BK's objection #3). Actually if one wanted to push
for an analogy between the mechanism of biological natural selection and
quantum theory, I can think a different analogy connecting natural
selection to the quantum *measurement* problem which would have a closer
correspondence. One of the major theories (i.e. the "decoherence" view
mentioned above) for how quantum measurements get made (i.e. how the wave
function of a quantum system collapses) is that it does so through tiny
irreversible and uncontrollable interactions between the quantum system
and its environment. These interactions cause a decoherence due to a
dephasing between the various amplitudes for the various values of the
classical variable being measured. The result of such a decoherence is
a wavefunction that has collapsed to a classical-like state which produces
the value observed for the measured variable. Because the interactions with
the environment are random so is the result of the measurement-like process.
The probability for a given result of the measurement-like process is
determined by the original wave function amplitude for the quantum state
just prior to when the measurement-like process takes place. After this
process takes place the system definitely possesses the obtained value of
the measured property or attribute. In the biological case the raw
population of variants is like the previously unmeasured quantum state.
After natural selection operates on the population and some variant trait
becomes fixed in the population at a very high frequency then the resulting
population is like the wave function of the quantum state after the
measurement has taken place. In both cases the selection process is due to
an interaction with the environment, and in both cases the result of the
process becomes etched into the system as one of the defining attributes of
the system. A major difference (or failing of this analogy) is that the
prior biological population is usually considered to have gotten its
variation from a "random" mutational-type process and the selection aspect
is considered as more of a deterministic nonrandom one. In the quantum
system the prior range of potential values for the observed variable is
considered to have arrived to that state by the deterministic operation of
the Schroedinger equation, and the result of the quantum measurement
selection process is thought of as being a random one. Thus the roles of
chance and necessity are switched in the two cases.
David Bowman
dbowman@gtc.georgetown.ky.us
p.s. Writing this post has exhausted me and has taken far more time than I
should have allowed. I hope that I will not be called upon to defend or to
elaborate on large portions of it.