Paul P. Mealing

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Wednesday, 8 July 2009

Quantum Mechanical Philosophy

Following on from my last post, Subjectivity: The Mind’s I (Part 1), I read Paul Davies’ Other Worlds, for a couple of reasons. One, Hofstadter mentioned it in his ‘reflections’ that I referred to in that post, plus, I had recently come across it and already put it aside with the intention of re-reading it anyway. Also the subject of the post led me to contemplate the philosophical ramifications of quantum mechanics (hence the title), and Davies’ book was a good place to start.

As it turned out, I hadn’t read it, even though I’ve owned it for over 20 years, and I was confusing it with another one of his books, The Ghost in the Atom, which was a compilation of BBC interviews transcribed and published in the same decade (1980s). So, logically, I read them both.

Both of these were published in England before Davies came to Australia, where he wrote a string of books on philosophy and science: The Cosmic Blueprint (about chaos theory), The Mind of God (about cosmology), God and the New Physics (much the same territory as Dawkins’ The God Delusion, only written 20 years earlier, but with more depth in my view and a different emphasis), About Time (about time in every respect), The Origin of Life (about microbiology), and these are just the ones I’ve read. He now lives in America, as an astro-biologist with Arizona State University, and has since published The Goldilocks Enigma (about John Wheeler’s conjecture that the universe effectively exists as a cosmological-scale, quantum-phenomenal loop, and to whom Davies dedicated the book). This is arguably his best book, philosophically, because it entails a lifetime’s contemplation on science, epistemology and ontology.

At the top of my blog, I have scribed a little aphorism, which some may see as a definition for philosophy, but I see as a criterion. If you want a definition, I refer you to an earlier post: What is philosophy? (March 08) To quote: ‘In a nutshell, philosophy is a point of view supported by rational argument. A corollary to this is that it requires argument to practice philosophy.’ But in reference to my criterion, as well as my definition, Davies fulfils both of them admirably. It is impossible to read Davies without challenging your deepest held beliefs, especially about reality, the universe and our place in it. No, he’s not a science ‘heretic’, far from it: he just writes very well on difficult subjects about which he has a lot of knowledge.

The Ghost in the Atom (1986), has 2 authors credited: J. Brown and P.C.W. Davies. Brown was ‘Radio Producer in the BBC Science Unit, London’, whereas Davies was ‘Professor of Theoretical Physics [at] the University of Newcastle upon Tyne’. The book was a collection of radio interview transcripts (edited) of some very big names in physics: Alain Aspect, John Bell, John Wheeler, David Duetsch, David Bohm; and these are just the ones I’ve heard of. It also included: Rudolf Peierls, John Taylor and Basil Hiley; whom I hadn’t heard of. The interviews have been edited, but I get the impression from the book’s Forward that the text may actually contain more material than was originally put to air. I assume Davies was the interviewer in the programme, and he tended to play devil’s advocate to whomever he engaged. The book is a treasure, if for no other reason than some of these great minds are no longer with us.

In my encounters on the blogosphere, I’ve come across more than a few people who seem to think that philosophy has largely been overtaken by science, and any distinction is at best, academic, and at worst, irrelevant. But there are fundamental differences, as I recently pointed out in a comment on another post, The Mirror Paradox (July 08): science often deals in right and wrong answers, whereas philosophy often does not.

In a more recent post (Nature’s Layers of Reality) I made the point that ‘quantum mechanics is where science and philosophy collide, and philosophy is still all at sea.’ Quantum mechanics is arguably the most empirically successful meta-theory ever, so it’s been inordinately successful as a sieve for right and wrong answers. But philosophically it conjures up more questions than answers. (Davies makes the exact same point, albeit with more authority, in The Goldilocks Enigma.)

In The Ghost in the Atom, Rudolf Peierls argues for the traditional Copenhagen interpretation, largely formulated and promoted by Niels Bohr, and, right at the start, Peierls bridles at the word ‘interpretation’, because, as far as he was concerned, there are no alternative ‘interpretations’. He also baulked at the word, ‘reality’, or at least, in the context of the discussion. To him, physics can only give a description, and, in the case of quantum mechanics, ‘reality’ is a misnomer.

In each of the interviews, the discussion tended to centre around John Bell’s famous theorem and Alain Aspect’s consequential experiment, which affirmed Bell’s ‘inequality’ as it is called. This originally arose from a famous thought experiment proposed by Einstein and elaborated on by Podolsky and Rosen, so it became known as the Einstein-Podolsky-Rosen or EPR experiment. It examines the purported ‘action-at-a-distance’ phenomenon predicted by quantum physics for certain traits of particles or photons.

If you measure the trait of one of a pair of particles (of common origin), you instantaneously get the correlated result of its complementary partner, even though you couldn’t possibly know beforehand. In a very truncated nutshell, quantum physics says you won’t know what state either particle is in until you observe one of them or take a measurement of it, which will automatically affect the other particle, even if it’s on the other side of the universe. Einstein originally formulated this in a thought experiment to prove Bohr wrong, because, according to his own (proven) theory of special relativity, it should be impossible. John Bell worked out a mathematical theorem that would prove Einstein right or wrong, depending on a number of correlated outcomes. Alain Aspect then created a real experiment to test Bell’s theorem (made the thought experiment actually happen), which ultimately proved Einstein wrong and quantum theory correct. (This was long after Einstein had died, by the way.)

The various physicists, interviewed by Davies in The Ghost in the Atom, explained the outcome of Aspect’s experiment based on their (philosophical) interpretation of quantum physics. No one disputed the actual results.

John Wheeler, who was a protégé of Bohr’s, also defended the Copenhagen interpretation, but there was a subtle difference to Peirel’s interpretation as to what constituted an observation or a measurement. For Wheeler, the quantum ‘wave packet’ collapsed (into one state or another) when, for example, a photon changed the chemical composition of a film or set off a Geiger counter or a photon multiplier. But Peirel took Eugene Wigner’s extreme interpretation that the ‘collapse’ only occurred when the result was observed by a conscious observer. For Wigner, consciousness was intrinsically involved in forming ‘reality’, although Peirel argued that we can’t talk about ‘reality’ in this context, which was how he side-stepped the obvious conundrum this view posed (it verges on solipsism).

Wheeler took the more accepted or conventional view that quantum phenomena become ‘real’ when they interact with a ‘macro’ object. But Wheeler acknowledged that the choice of apparatus, or the preparation of the experiment affected the outcome. He argued that even if you made a ‘delayed-choice’ of what to measure, you would still get a quantum mechanical outcome. For example, in the famous Young double-slit experiment, if you measure or observe what goes through each slit, you won’t get the double slit interference that is observable when you choose not to ‘observe’ individual slits. Wheeler conjectured that this would still occur even if you made the measurement or observation after the photon or particle had traversed the slits, and he has since been proven correct. In other words, Wheeler is saying that you effectively create a causal effect backwards in time, quantum mechanically. But Wheeler goes further and conjectures that this would even happen on a cosmological scale if, instead of using 2 slits, you used a galaxy lensing light from a distant quasar to create interference or not. This is theoretically possible, if technologically impossible to confirm (at this point in time). It must be pointed out that this phenomenon does not allow communication backwards in time, so paradoxes of the sort that we often see in science fiction would not be possible, but it’s still very counter-intuitive to say the least.

David Deutsch defended the ‘many-worlds’ interpretation, originally proposed by Hugh Everett, which I referenced (via Hofstadter) in my last post. Deutsch’s interpretation is subtly different to Everett’s (in fact, many of the interviewees revealed the subtle variations that exist within this field) in that the worlds don’t bifurcate but are already in existence – not a huge step if there are an infinite number of them. But Deutsch did introduce a novel idea that the separate universes not only separate but also ‘fuse’, which is how he explained the interference.

In The Goldilocks Enigma (published 20 years later), Davies makes the observation that whilst the ‘multiverse’ started off as a quantum mechanical interpretation, it is now very popular amongst cosmologists in conjunction with the ‘anthropic principle’. Both Martin Rees (Just Six Numbers) and Richard Dawkins (The God Delusion) appropriate it to explain our peculiarly privileged existence in the overall scheme of things. Not just our existence, but the existence of life in general.

The most interesting interviewee, from my perspective, both now and when I originally read the book about 20 years ago, is David Bohm. I’m a great fan of Bohm’s, if for no other reason than he defied McCarthy, even though it meant that he spent the rest of his life in England. He wrote a book on philosophy in his later years (but prior to this interview) called Wholeness and the Implicate Order, which I’ve read. Bohm is a great mind but not a great writer, which is unfortunate for laypeople like me. The advantage of the interview is that someone, as knowledgeable and astute as Davies, can draw out the ideas and the elaboration of the ideas that you long to comprehend. But it helps, in this case, if one understands the implications of the Bell inequality.

The Bell inequality can be distilled into the mandatory abandonment of one of two highly-cherished and long-assumed ideas: objective reality or the impossibility of non-local communication. Objective reality requires no explanation. But non-local communication (usually short-handed as non-locality) means the ability to communicate at faster-than-light-speed, which breaches Einstein’s special theory of relativity. Hence the reason that Einstein originally created the thought experiment which led to Bell’s theorem.

In ordinary parlance, non-locality refers to an unseen and undetectable connection between 2 objects separated in space and time, which is a more intuitive concept to grasp. Einstein called it: ‘ghostly action-at-a-distance’; which provides the title of the book.

In effect, Bohm is willing to entertain the possibility of non-locality in order to hang on to objective reality. He calls it a ‘hidden variables’ theory, but it is also known as the ‘quantum potential’ theory. The labels are unimportant; it’s the ideas he has behind them that I believe are worth pursuing. Like Bohm, I find it the easiest interpretation to live with, philosophically.

To quote David Deutsch, when he was discussing David Bohm’s interpretation with Davies: ‘A non-local hidden variable theory means, in ordinary language, a theory in which influences propagate across space and time without passing through the space in between.’

I couldn’t have expressed it better myself, and neither, I suspect, could Bohm.

Basically, Bohm is saying that there is something hidden underneath that we have not uncovered, which is why he uses the term ‘implicate order’. He gives the analogy of folding up a piece of paper and drawing lines on it, then, when you unfold it, you get a pattern. In quantum phenomena we see the pattern but not the ‘order’ underneath. My own interpretation is that quantum phenomena may be the surface effects of a hidden (or multiply-hidden) dimensions. Instead of many ‘hidden’ universes perhaps there are ‘hidden’ dimensions, but I suspect you would really only need one.

If you take a box and unfold it into 2 dimensions, you get a cross. If you go off the end of one of the branches of the cross in 2 dimensions, you would end up on the opposite branch if you were in 3 dimensions. An extra dimension allows you to ‘cut’ through space and time. Bohm even entertains the heresy of heresies that backward communication may be possible (within limitations). Bohm doesn’t discuss extra dimensions; it’s just my mind trying to come up with a ‘physical’ interpretation that would allow both non-locality and objective reality (I’m really not familiar enough with the physics to conjecture further).

The last person interviewed in the book is Basil Hiley, who worked with Bohm on the ‘quantum potential’ theory. He has come up with a mathematical interpretation using Schrodinger’s equations, in conjunction with a ‘quantum potential’ that allows non-locality (a sort of ‘absolute space-time [like] a quantum aether’ to use his own description) and, to quote: ‘[from] the statistical results of typical quantum experiments you find that they are still Lorentz invariant’ (they obey Einstein’s relativity theory).

When Davies quizzed Hiley about Heisenberg’s Uncertainty Principle, Hiley attempted to explain it as a thermodynamic statistical effect. Davies then said, if that was the case, you wouldn’t need Planck’s constant, and Hiley said: ‘To me the value of Planck’s constant is not really relevant to quantum mechanics’, which is an extraordinary statement considering Planck’s constant is what initiated quantum theory in the first place. But to be fair to Hiley, he acknowledges this and makes the point that many people believe that if you brought Planck’s constant to zero you would get classical physics, but he asserts ‘nothing could be further from the truth.’

The value of Plank’s constant has always intrigued me: it places a limit on our ability to perceive the world. It also explains (to me) why quantum effects are scale dependent, though many people claim they are not, and mathematically that is true. But perhaps, and this is a big perhaps from someone as ignorant as me, Planck’s constant determines the hidden dimension, if there is one. This is pure speculation and obviously incorrect, otherwise, I’m sure, someone would have explored it well before now.

Addendum: There is a detailed discussion on this topic in Scientific American, March 2009 issue. The online version can be found here. Where the article has attracted 152 comments to date.



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Paul P. Mealing said...

Hi Aristiono,

Thanks for your comment.

I visited your site and read your 'Essential Step'.

All I can say in response is that I believe there are many paths, and everyone must find their own.

I sincerely wish you well in seeking your own path.

Regards, Paul.