Heisenberg: Physics and Philosophy - book review

This week, I've been reading 'Physics and Philosophy' by Werner Heisenberg. Heisenberg was one of the leading lights of the Quantum Physics generation in the early twentieth century. He was the prime discoverer of the Uncertainty Principle; that it is impossible to know both the velocity and position of a subatomic particle at the same time.

I'll say, straight away, that 'Physics and Philosophy' is a dry read; the book is never going to succeed as a mainstream popular science book. Heisenberg writes like a physics professor giving a church sermon, but he also writes with an air of calm authority. He isn't polemicist or a demagogue. There's no sign that he has an axe to grind. As a result, the book reads as a benchmark of sober thought on the philosophical implications of what physicists discovered in the early twentieth century.

During his book, Heisenberg stays very much in the middle ground of the philosophical interpretations of quantum physics. He never concludes that the mind is required for matter to appear out of the quantum realm, unlike Wigner and Von Neumann, but neither does he follow the lead of Einstein and doggedly advocate the Classical Physics viewpoint of an external reality that is present and real all the time, whether we observe it or not. Instead, he talks calmly about what he thinks we can reliably conclude from the experimental evidence and the mathematics, and how that is elegant and beautiful and sufficient just by itself.

Two passages stood out for me in the book. Here's the first (from page 43):

Natural Science does simply describe and explain nature; it is part of the interplay between nature and ourselves; it describes nature as exposed to our methods of questioning. This was a possibility of which Descartes could not have thought, but it makes the sharp separation between the world and the 'I' impossible. If one follows the great difficulty with which even eminent scientist, including Einstein, had in understanding and accepting the Copenhagen Interpretation of quantum theory, one can trace the roots of this difficulty to the Cartesian partition. This partition has penetrated deeply into the human mind during the three centuries following Descartes and it will take a long time for it to be fully replaced by a really different attitude to the problem of reality.

Heisenberg goes on to say:

When Einstein has criticised quantum theory, he has done so from the basis of dogmatic realism. This is a very natural attitude. Every scientist who does research feels that he is looking for something that is objectively true. His statements are not meant to depend on the conditions under which they can be verified.

Heisenberg goes on to point out that the mathematics is the basis for the theory; its elegance and simplicity, at least in comparison to the phenomena that it describes, shows that it represents a truth to the nature of reality. Because of this, there is no need for a Dogmatic Realism, one propped up by assumptions based on a desire for reality to be a certain way. The Copenhagen Interpretation may not have been to Einstein's taste, but for Heisenberg, its mathematical elegance was sufficient for it to ring true.

The second passage I enjoyed was Heisenberg's thoughts on fundamental particles. On page 106, he discusses the post-war developments of cyclotrons, particle colliders, and how they were used in the discovery of many subatomic particles. He then says:

These results seem, at first, to lead away from the idea of the unity of matter, since the number of fundamental units of matter seems to have again increased to values comparable to the number of different chemical elements. But this would not be a proper interpretation. The experiments have, at the same time, shown that the particles can be created from other particles, or simply from the kinetic energy of such particles, and they can again disintegrate into other particles. Actually, the experiments have shown the complete mutability of matter. All the elementary particles can, at sufficiently high energies, be transmuted into other particles, or they can simply be created from energy or annihilated into energy, for instance into radiation. Therefore, we have here actually the final proof of the unity of matter. All the elementary particles are made of the same substance, which we may call energy or universal matter; they are just different forms in which matter can appear.

The last sentence is very interesting. Heisenberg makes it clear that he believes that all 'matter' is really just an outward form of energy. In this way, the particles seem a little like the colours of a rainbow. In other words, we see a rainbow's colours and identity them with names, but fundamentally, they are simply different manifestations of a single energy source, light. Why didn't Heisenberg conclude that, fundamentally, there is no matter, only energy in different manifestations? Why did he call energy 'universal matter', rather than matter 'universal energy'? It's a topic for much further discussion.

Overall, I did enjoy 'Physics and Philosophy' and I admire Heisenberg's careful, intelligent views. I can't recommend the book to a general audience but for someone interested in studying the views of famous twentieth century physicists in depth, I heartily recommend it.