SH
Stephen Hawking's Radical
Philosophy of Science
By Michael Shermer
Big Questions Online, November 23, 2010
Edited by Andy Ross
Out of an incomprehensible number of data signals pouring in from the
senses, the brain forms models of faces, tables, cars, trees, and every
conceivable known and imagined object and event. It does this through
something called neural binding. Downstream neural inputs converge as they
move upstream through convergence zones. You end up perceiving a whole
object instead of countless fragments of an image.
At any given
moment there are hundreds of percepts streaming into the brain from the
various senses. All of them must be bound together for higher brain regions
to make sense of it all. Large brain areas such as the cerebral cortex
coordinate inputs from smaller brain areas such as the temporal lobes, which
themselves collate neural events from still smaller brain modules. This
reduction continues all the way down to the single neuron level.
The
models generated by biochemical processes in our brains constitute reality.
None of us can ever be completely sure that the world really is as it
appears, or if our minds have unconsciously imposed a misleading pattern on
the data. I call this belief-dependent realism. In my forthcoming book, The
Believing Brain, I demonstrate the myriad ways that our beliefs shape,
influence, and even control everything we think, do, and say about the
world. The power of belief is so strong that we typically form our beliefs
first, then construct a rationale for holding those beliefs after the fact.
According to Stephen Hawking, not even science can pull us out of such
belief dependency. In his new book, The Grand Design, co-authored with
Leonard Mlodinow, Hawking presents a philosophy of science he calls
model-dependent realism. The authors assume that our brains form models of
the world from sensory input, that we use the model most successful at
explaining events and assume that the models match reality, and that when
more than one model makes accurate predictions we are free to use whichever
model is most convenient.
According to Hawking and Mlodinow, there is
no concept of reality that is independent of a picture or a theory. There is
no privileged position in the universe. There are just models. It is not
possible to understand reality without having some model of reality, so we
are really talking about models, not reality. The way around this apparent
epistemological trap is called science.
The tools and methods of
science were designed to test whether or not a particular model or belief
about reality matches observations made not just by ourselves but by others
as well. Even when two models appear to be equally supported by
observations, over time we accumulate more precise observations that tell us
which model more closely matches reality.
Hawking and Mlodinow argue
that a model is good if it is elegant, it contains few arbitrary or
adjustable elements, it agrees with and explains all existing observations,
and it makes detailed predictions about future observations that can falsify
the model if they are not borne out.
Nearly all scientific models can
be parsed in such a manner. In the long run, we discard some models and keep
others based on their validity, reliability, predictability, and perceived
match to reality. I believe there is a real reality, and that we can come
close to knowing it through the lens of science.
AR I agree, though we
should be clear that the last sentence — belief in a real reality (RR, as
opposed to a profusion of unreal VR models) — is an assertion of faith.
By John Leslie
The Times Literary Supplement, December 8, 2010
Edited by Andy Ross
Stephen Hawking and Leonard Mlodinow
The Grand Design
New answers to the ultimate questions of life
Bantam, 200 pages
Roger Penrose
Cycles of Time
An extraordinary new
view of the universe
Bodley Head, 320 pages
Hawking and Mlodinow declare that philosophy is dead. Then
they make bold philosophical claims. For example, they say that "though we
feel that we can choose what we do", we are "governed by the laws of physics
and chemistry", so we can't.
Their quantum theory is controversial
too. They say only observations can terminate quantum superpositions in
which seemingly contradictory situations are combined: "the unobserved past
is indefinite". That's bold philosophy.
Hawking and Mlodinow propose
a many-branched universe. All branches are equally real. The observer splits
or branches. Most quantum cosmologists don't accept that all branching
depends on observations or that observations you make on a system in the
present affect its past. The authors say this is proved by delayed choice
experiments.
They say that in the beginning, quantum chaos ruled.
Time began only once the world arrived. Our universe is a fluctuation like a
bubble in boiling water, but with no energy. Gravitational energy is
negative energy that counterbalances all the rest. Total energy is zero. So
there is no need for God. Bubble universes just fluctuate into being.
Hawking and Mlodinow say M-theory is a theory of everything. It does not
dictate the strengths of forces, the masses of particles, or what types of
force and of particle exist. It implies that dimensions can become
compactified. How many curl up, and with just what sort of curling, varies
from universe to universe in perhaps 10 power 500 ways.
In our
universe four dimensions remain uncompactified. The way the others have
curled up produces the forces and particles we observe. The immense variety
of the universes explains how ours is fine-tuned for life. Almost all the
universes are lifeless.
Hawking and Mlodinow suggest that the laws
of M-theory are logically necessary. They say it is "a unique theory that
predicts and describes a vast universe":
1 Any set of laws that describes a continuous world
such as our own will conserve energy.
2
The energy of an isolated body surrounded by empty space is positive;
otherwise bodies could pop up anywhere.
3 The positive energy of the matter is balanced by negative
gravitational energy, so the universe creates itself from nothing.
4 M-theory is the most general
supersymmetric theory of gravity and a complete theory of the universe.
The Grand Design could survive without quite so many philosophical
claims.
Roger Penrose pictures a cyclic cosmos that
exists as "a succession of aeons, each appearing to be an entire expanding
universe".
Penrose is intrigued by the law of increasing entropy.
The flow toward disorder gives rise to eddies of increased local orderliness
such as plants and humans. Where did the initial low entropy come from?
According to inflation theory, the universe went through a brief period
of exponential expansion. Its size could have become greater by 10 power
100. Earlier disorder was smoothed away, but Penrose says we need a new
principle.
The principle concerns the big bang’s geometry. Penrose
says his proposal would force smoothness in a way more philosophically
acceptable than God placing a pin. Given the right geometry, what came out
of the bang would be almost evenly distributed. He explains that one sort of
entropy increases when gas distributes itself evenly, but gravitational
entropy increases through clumping.
Penrose then tells of the cosmic
cycles. The universe continues expanding and cooling, for what you might
think would be eternity. But to a photon, eternity is no time at all. All
the information in a black hole is lost when it evaporates through the
process discovered by Hawking. Immense ages after all black holes have
evaporated, the universe may contain no clocks. Then the universe could lose
its vastness. This would allow a smooth transition to a new bang.
Penrose tells an extraordinary story.
AR Penrose always tells an
extraordinary story. I'm still reading this latest one.
Concentric circles in WMAP data may provide evidence of violent
pre-Big-Bang activity
V.G. Gurzadyan, R. Penrose (GP)
arXiv:1011.3706v1
2010-11-16
Conformal cyclic cosmology (CCC) posits the existence of
an aeon preceding our Big Bang (BB), whose conformal infinity 'I' is
identified conformally with BB, now regarded as a spacelike 3-surface.
Black-hole encounters in that previous aeon would leave families of
concentric circles over which the temperature variance is anomalously low in
our CMB sky. These centers of these circles appear as randomly distributed
points in our CMB sky. Analysis of Wilkinson Microwave Anisotropy Probe
(WMAP) 7-year maps does reveal such concentric circles.
A search for concentric circles in the 7-year WMAP temperature sky maps
I.K. Wehus, H.K. Eriksen
arXiv:1012.1268v1
2010-12-06
GP claim to find evidence for violent pre-BB activity in
the form of concentric low-variance circles. We performed an independent
search for such concentric low-variance circles and compare the results
obtained from the 7-year WMAP temperature sky maps with those obtained from
lambda cold dark matter (LCDM) simulations. We do reproduce the claimed ring
structures observed in the WMAP data as presented by GP. But the results
from our simulations do not agree with those presented by GP. We obtain a
larger variance in our simulations, so that the observed WMAP sky maps are
consistent with the LCDM model.
No evidence for anomalously low variance circles on the sky
Adam Moss, Douglas Scott, James P. Zibin
arXiv:1012.1305v2
2010-12-15
GP claim to have found circles of anomalously low variance
in the CMB. These features are presented as evidence for their CCC picture
of the early universe. We repeated the analysis and confirm that such
variations exist in the temperature variance for annuli around points in the
data. But we expect this variation in a sky containing CMB anisotropies.
Simulated Gaussian CMB data contain such variations. GP have not found
evidence for pre-BB phenomena.
Quantum Mechanics
By Jeremy Bernstein
arXiv:1012.1020v1
Edited by Andy Ross
In January 1991, Rudolf Peierls published a paper in defence of measurement.
"I do not agree with John Bell," he wrote. "In my view the most fundamental
statement of quantum mechanics is that the wave function or more generally
the density matrix represents our knowledge of the system we are trying to
describe." The wave function collapses when this knowledge is altered. There
is no spooky action at a distance here. But what is the system about which
we have knowledge?
I think of this as a form of hidden variable
theory. Peierls rejects Bohmian mechanics because he says that it is a
hidden variable theory. In Bohmian mechanics what is hidden is the wave
function.
The collapse of the wave function is a
problem. Bohm made use of the notion of decoherence in 1951. In his
discussion of the Stern-Gerlach experiment, he writes down the entangled
wave function for the two spin possibilities. He then squares it to find an
expression for the probabilities of the two spin states. This contains cross
terms but he argues that in the presence of the magnetic field the phases of
these cross terms oscillate so rapidly that the terms effectively vanish and
we have the classical expression for the probabilities. This is decoherence.
Nothing in this mechanism has
projected out one of the two terms. That is what the measurement does. The
Schrödinger equation cannot describe the collapse of the wave function. That
is the measurement problem.
Bell went to CERN in 1960 partly to do
elementary particle theory and partly to work on accelerator design. Working
on the foundations of quantum theory was not in the job description. This he
did in his spare time. But in 1963 Bell spent a year at Stanford. During
this period he came up with his inequality. In 1969 John Clauser told him
that he had produced a generalization of Bell's inequality that might be
tested by using polarized light. In 1972 Clauser and Stuart Freedman
published the first experimental results and the flood gates opened.
Bell never had the slightest doubt that these experiments would confirm the
quantum theory. There was nothing special about the domain in which they
were being done, a domain in which all the predictions of the theory were
always borne out. But he certainly had no inkling of the reaction to this
work. The quantum Buddhists were let loose and are still out there.
The Theory of
Everything work that has most impressed me is that of Gell-Mann and Hartle.
Its ancestral origins are in an obscure paper by Dirac in 1933. Dirac put
much of the contents of this paper in subsequent editions of his book.
Feynman learned about it and made it the subject of his thesis. After the
thesis was published, the path integral formalism of quantum theory became
an attractive alternative. The Gell-Mann-Hartle interpretation is in this
spirit.
This approach offers a solution to the measurement problem
unless you insist that an explanation of the Born rule is part of the
problem. The wave function does not collapse but the other parts which
describe alternates to what is actually measured describe other histories.
All those unused paths may seem too much. But this is not what really
bothers me about this. It is the past.
I believe that the past is
classical while the future is quantum mechanical. Events in the past have
happened while events in the future will probably happen. Even some of the
founders appeared to think that there was something fishy about trying to
describe the past quantum mechanically.
The paper of Einstein,
R.C.Tolman and B. Podolsky entitled "Knowledge of Past and Future in Quantum
Mechanics" published in 1931 presents a gedanken experiment which purports
to show that if past events do not have a quantum mechanical uncertainty
then this will lead to a violation of the uncertainty principle for at least
some future events. This would seem to be a very profound conclusion. If you
believe in a quantum theory of everything then you cannot have a classical
past.
Here is the experiment. Imagine a triangle. A one corner of the
base there is a box with a shutter that emits some sort of particle or
particles when the shutter opens automatically for a short time. On one of
these openings two particles are emitted. One goes straight across the base
to a detector while the other travels around the two sides of the triangle
to the detector. They both move at constant speeds such that the one that
follows the longer path will arrive later. We have measured these distances.
We have also weighed the box before and just after the particles are
emitted. This tells us the total energy of the two emitted particles.
Einstein et al.:
"Let us now assume that the observer at O measures
the momentum of the first particle as it approaches along the [shorter] path
SO, and then measures its time of arrival. Of course the latter observation,
made for example with the help of gamma-ray illumination, will change the
momentum in some unknown manner. Nevertheless, knowing the momentum of the
particle in the past, and hence also its past velocity and energy, it would
seem possible to calculate the time when the shutter must have been open
from the known time of arrival of the first particle, and to calculate the
energy and velocity of the second particle from the known loss in the energy
content of the box when the shutter is opened. It would then seem possible
to predict beforehand both the energy and the time or arrival of the second
particle, a paradoxical result since energy and time are quantities which do
not commute in quantum mechanics."
"The explanation of the apparent
paradox must lie in the fact that the past momentum of the particle cannot
be accurately determined as described. Indeed, we are forced to conclude
that there can be no mechanism for measuring the momentum of a particle
without changing its value ... [Hence] the principles of the quantum
mechanics must involve an uncertainty in the description of past events
which is analogous to the uncertainty for the prediction of future events."
Freeman Dyson:
"I deduce two general conclusions from these
thought-experiments. First, statements about the past cannot in general be
made in quantum-mechanical language. We can describe a uranium nucleus by a
wave-function including an outgoing alpha-particle wave which determines the
probability that the nucleus will decay tomorrow. But we cannot describe by
means of a wave-function the statement, 'This nucleus decayed yesterday at 9
a.m. Greenwich time'. As a general rule, knowledge about the past can only
be expressed in classical terms. My second general conclusion is that the
'role of the observer' in quantum mechanics is solely to make the
distinction between past and future. The role of the observer is not to
cause an abrupt 'reduction of the wave-packet', with the state of the system
jumping discontinuously at the instant when it is observed. This picture of
the observer interrupting the course of natural events is unnecessary and
misleading. What really happens is that the quantum-mechanical description
of an event ceases to be meaningful as the observer changes the point of
reference from before the event to after it. We do not need a human observer
to make quantum mechanics work. All we need is a point of reference, to
separate past from future, to separate what has happened from what may
happen, to separate facts from probabilities."
AR I agree with Freeman
and Jeremy. The past is classical, the future is quantum mechanical, and the
boundary marks our epistemic location. In my formalism, the moving boundary
defines the present moment — the now — of the evolving subject of
the sequence of mindworlds that form the subject's world line. In this
formalism, time is an epistemic dimension that is represented as the height
of the tree in a logical formalism using modal or constructive logic and
that in my approach can also be represented as the growing ordinal axis of
the cumulative hierarchy.
Stephen Hawking, 70
By Martin Rees
The Times, January 7, 2012
Edited by Andy Ross
In my first week as
a graduate student at the University of Cambridge in 1964, I encountered a
fellow student, Stephen Hawking. Now he may be the most famous scientist in
the world. Stephen had won a first at the University of Oxford and went on
to Cambridge.
Within a few years of our meeting he was in a
wheelchair and his speech was a croak. But he quickly came up with a series
of insights into the nature of black holes and how our universe began. In
1974 he was elected to the Royal Society at the tender age of 32.
At
that time he worked, as I did, at the Cambridge Institute of Astronomy. I
would often push his wheelchair into his office and open an abstruse book on
quantum theory for him. He would sit hunched, motionless for hours. Within a
year he came up with his best idea, encapsulated in an equation that he said
he wanted on his gravestone. He had found a profound and unexpected link
between gravity and quantum theory. This has been hugely influential. One of
the main achievements of string theory has been to confirm and build on his
idea.
Stephen became the Lucasian Professor of Mathematics at
Cambridge, a chair once occupied by Isaac Newton, and held it for thirty
years until he retired in 2009.
In 1987 he lost his voice. He had
long since lost the ability to use a keyboard. But he was saved by
technology. He still had the use of one hand to spell out sentences for a
computer. These were then declaimed by a speech synthesizer. He has learnt
the art of brevity.
Stephen became an international celebrity and his
lectures have filled the Albert Hall. He has even featured in Star Trek. He
has done more than anyone else since Einstein to improve our knowledge of
gravity and he is one of the top ten living theoretical physicists.
Seventy Earth Years For Mr. Universe
The Sunday Times, January 8, 2012
Edited by Andy Ross
Stephen Hawking founded the Centre for Theoretical Cosmology in the
department of applied mathematics and theoretical physics at Cambridge
University and is lauded by his peers as our greatest living scientist. He
was Nuts magazine's 2011 "British bloke of the year", beating Daniel Craig
and David Beckham. When asked by New Scientist magazine last week what he
thought about most during the day, Hawking replied: "Women. They are a
complete mystery."
American theoretical physicist Kip Thorne: "When
Stephen lost the use of his hands and could no longer manipulate equations
on paper, he compensated by training himself to manipulate complex shapes
and topologies in his mind at great speed. That ability has enabled him to
see the solutions to deep physics problems that nobody else could solve, and
that he probably would not have been able to solve himself without his
new-found skill."
Hawking once said studying theology and philosophy
was a waste of time: "We need to find the answers to the questions of the
universe. Why is there something rather than nothing? Why do we exist? Why
does the universe follow this particular set of laws? Philosophy is now
dead. It has not kept up with modern developments in the sciences,
particularly physics. Scientists have become the bearers of the torch in our
quest for knowledge."
Hawking last week: "I have a beautiful family,
a successful career, I have written a bestseller — one can't ask for more."
Philosophy of Cosmology
By
Ross Andersen
The Atlantic, January 19, 2012
Edited by Andy Ross
In December 2011, a group of American philosophy professors set
out to establish the philosophy of cosmology as a new field of study. New
York University philosopher Tim Maudlin was a member of the group.
RA
Your group will pursue conceptual problems at the foundations of cosmology.
What are they?
TM The big bang state had to be a very low entropy
state, and there's a line of thought that says very low entropy is very
improbable. This is probably the most important question within the
philosophy of cosmology. One suggestion is that we live in a kind of bubble
universe, among lots of bubble universes, all very different from one
another. The anthropic principle says we will find ourselves in a bubble
that supports living beings.
RA Is the philosophy of cosmology a
translation of existing physics into more common language or concepts, or do
you expect that it will contribute to physics?
TM
I don't think
this is a translation project. This is all within the purview of a
scientific attempt to come to grips with the physical world.
RA
Stephen Hawking said last year that philosophy is dead because it has failed
to keep up with physics. Does your project hopes to address this?
TM Hawking is no expert in philosophy. The philosophy of physics has become
seamlessly integrated with work done by physicists. He doesn't know what
he's talking about.
RA Has physics neglected foundational questions?
TM Physics has avoided foundational physical questions since the
foundation of quantum mechanics. The problem is that quantum mechanics was
developed as a mathematical tool. Physicists understood how to use it as a
tool for making predictions, but without an agreement or understanding about
what it was telling us about the physical world. Now we're coming out of
that.
RA Time is considered to be a tricky problem for physics. Why
is that?
TM Some say time is real, others say time is an
illusion. I think none of the arguments are very good. Physicists for
almost a hundred years have been dissuaded from trying to think about
fundamental questions. The asking of fundamental physical questions is just
not part of the training of a physicist anymore.
RA Philosophers
might be uniquely suited to evaluating the probabilistic arguments for the
existence of life elsewhere in the universe. Do you expect philosophers of
cosmology to enter into those debates?
TM Life is a physical
phenomenon. The question of how likely it is that life will emerge connects
up to physics and cosmology. The question is how often life evolves into
intelligent life capable of making technology. What people haven't seemed to
notice is that on earth, of all the billions of species that have evolved,
only one has developed intelligence to the level of producing technology.
Which means that kind of intelligence is really not very useful.
AR That last sentence involves an obvious fallacy. The more natural deduction is that technological intelligence is expensive for an organism to develop and sustain, so only extreme evolutionary pressures will give rise to it. Its survival value is obvious from the billions of humans now raping the biosphere.
