Stephen Hawking

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.

Sky Rings

Concentric circles in WMAP data may provide evidence of violent
pre-Big-Bang activity

V.G. Gurzadyan, R. Penrose (GP)

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

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

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

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.