Physics & Philosophy (Penguin Classics)

Loved this book that exposits physics and philosophy (what used to be called natural science), from one of the leading theoretical physicists of the last century. We may have made a mistake in our materialistic view of the world, our apparent sense of rationality driven by subject-object boundaries that have taken place in the last 4 centuries since Newton. This has been a subject of intense interest to me last few years and this book was like having a conversation with a friend with similar interests. There are no pretensions, no hiding behind abstractions - just simple, plain speak from the scientist who formulated the uncertainty principle.My notes -• Strange ideas in relativity - time dilation and length contraction, curved spaces and black holes. There is no absolute universal time and no concept of simultaneity in the universe• The deepest philosophical problem with theory of relativity is the possibility that the universe came into existence at a finite moment in the past and with it were born not just matter and energy but also space and time (Time may not stretch back to all eternity)• Its easy to see what the theory predicts (quantum mechanics) but hard to understand what it “means”• Heisenberg’s uncertainty principle - all physical quantities observed are subject to unpredictable fluctuations, their values are not precisely defined. Uncertainty in position x Uncertainty in momentum = Planck’s constant (So there’s a trade-off in precision when measuring one over the other). The particle simply does not posses simultaneously precise values of position and momentum (with respect to us, the observers - akin to ‘if a tree falls in a forest…’ problem)• Uncertainty in physical processes (markets/thermodynamics) is due to missing information rather than a fundamental limitation as in quantum particles• The popular model of atom with electrons circling the nucleus is badly misleading as its impossible to know precise trajectory of electron from point A to point B• Two quantum systems initially identical may go on and do different things (all else remaining equal) - its still not complete anarchy as these different things can be defined by probabilities• quantum mechanics is a statistical theory - definite predictions about ensembles but not of individual systems• weather prediction is also statistical mechanics - but chance element is “inherent” in quantum systems, rather than our limited grasp of information of variables• Einstein hoped that beneath the quantum chaos might lie a familiar deterministic dynamic (hence “god does not play dice”). Heisenberg and Bohr strongly opposed Einstein on this• EPR paradox - A system of two particles that interact and fly apart that carry information of the other - by measuring one particle, it would be then possible to know either position of momentum of the other - speed of light prohibits such measurement as information cannot carry faster than “c”- heart of the conflict between Einstein’s classical worldview (dogmatic realism) and Heisenberg and Bohr’s uncertain one• In classical world, our observations do not “create” reality - merely “uncovers” reality. According to Copenhagen interpretation of quantum mechanics, there’s no objective reality in the quantum world - nothing is well-defined. It is our observations that create the reality we perceive (An electron is not a “thing”, as a billiard ball may be)• Bohr’s principle of complementarity - same system can display apparently contradictory properties - like electron behaving as both a wave and a particle - this ambiguity is not contradictory but is complementary faces of a single reality - its up to the experimenter to expose the aspect he so chooses to (position vs momentum, wave vs particle) - so observation/experiment is a crucial part of the observation - the transition from the possible to the actual happens in the act of observation• Our language is limited by our real-world and limits our imagination. any attempt to explain what really happens in the quantum world is thus limited by our limits of imagination based on the real-world we observe (hence intuition doesn’t work!)• Blackbody radiation, photoelectric effect, electromagnetic waves - were some of the earliest precursors that led to definition of quantum theory• Asking the right question is frequently more than halfway to the solution of the problem (well stated is half solved)• Quantum properties arise due to our deficiency in knowledge of the electron, than as an inherent property of the electron (same as in weather systems - epistemology vs ontology)• Thales of Miletus in 6th Century BC thought Water was the fundamental material. Anaximander, pupil of Thales denied it could be water or any known substance. He taught the primary substance was infinite, eternal and ageless - Being and Becoming - the primary substance infinite and ageless was “Being” and it degenerates into various forms (“Becoming”) leading to endless struggles and returns back into that which is shapeless and characterless (Sort of Hindu philosophy, sort of pre-empted big bang)• Throughout history we have had an obsession to find the fundamental particle - we thought it was water (Thales), then air (Anaximenes), then fire (Heraclitus), pluralism from monism (earth, water, air and fire) of Empedocles, an infinitely small seed from which everything was made of (Anaxigoras) - sort of precursor to atom, and so on• Modern physics is closer to Heraclitus - replace “fire” with “energy” - that which makes all elementary particles, that which moves - causes all change in the world• Plato - prisoners in a cave thought experiment - men bound in a cave looking in only one direction with fire behind them see objects behind them and themselves only as shadows on the wall• Descartes - in “Discourse on method” - not believing senses, driven by doubt and thus thought - the famous “cogito ergo sum” - he thus made the triangle of “God-World-I” - separating and elevating God from the world - here on philosophy and natural science separated ‘res cogitans’ and ‘res extensa’ - me and my world - subject and object - cartesian division between self and the world - the world was then described by physics and chemistry and same applied to the mind led to concept of “free will” and that one can speak about the world without speaking about God or ourselves (God here in my opinion is nothing but probability) - we need to get back to “practical realism” of natural science from the “dogmatic realism” of modern physics concerning the material world.• Locke, Berkeley, Hume - empiristic philosophy - All knowledge is ultimately founded in experience (Locke). If all knowledge is founded in experience, there’s no meaning to the statement that things really exist (Berkeley). Hume denied induction and causation which when taken seriously would destroy the basis of all empirical science• If we attach symbols to phenomena, the symbols can then be combined by certain rules (as in math) and statements about the phenomena can be represented as combinations of symbols. Now, a combination of symbols that doesn’t comply with rules is not wrong but conveys no meaning (like complex numbers)• Kant - ‘Critique of pure reason’ - Our knowledge is in part ‘a priori’ and not inferred inductivity from experience - he also distinguished analytic (what follows from logic) and synthetic propositions (empirical knowledge)• It will never be possible by pure reason to arrive at some absolute truth• Space and time belonged both to newtonian mechanics and theory of relativity - in the former they were independent and in the latter, they were connected by Lorentz transofmration• Newtonian mechanics, theory of heat, electricity and magnetism, quantum theory - all arose as closed system of concepts with their own axioms - there may arise a 5th set in the future with theory of elementary particles• While chemistry can be understood as a limiting case of physics, biology and living organisms display a degree of stability that cannot be explained by physical and chemical laws alone - its the stability of process or function, rather than stability of form (as in atoms/crystals)• Some scientists were inclined to think psychology could be explained by physical and chemical phenomena - from quantum-theoretical standpoint, there’s no reason for such an assumption. Quantum theory does not allow a completely objective description of nature.• Every energy carries some mass with it but it is miniscule and that’s why it was not observed before *(E = mc^2 for intuition). The binding energy of particles in the nucleus of an atom is what shows up in their masses (and in the atomic bomb)• The concepts of space and time belong to our relation to nature, not to nature itself (Kant)• Every act of observation is by its very nature, an irreversible process• Matter in itself is not a reality but only a possibility (potentia) - Aristotle. The statue is potentially in the marble, before it is cut out by the sculptor• Our natural language and concepts of classical physics can only apply to phenomena for which velocity of light can be considered infinite - a mathematical language is necessary for everything else in the universe. With expansion of scientific knowledge, our language also expands and with it the word’s applicability in a wider sense (Eg. energy, electricity, entropy are widely used in different contexts in natural language)• Most fruitful developments frequently take place when two different lines of thought meetIt is always lovely when a scientist tries to unify disparate modes of thought, history, philosophy and is so open to ideas from different disciplines. This is like reading the diary of such a great scientist and if the topic of uncertainty/probability, subject-object boundaries, what makes up the fabric of reality and who we are, interests you, then this book is a must read. 11/10

I think every engineer, every student of science could benefit from the wisdom this book has to offer. The author goes back and forth between the development of quantum theory and its causal connection to the history of (mostly western) scientific thought process. For its size, it touches on many topics concerning not just science & technique but also its relationship with the 'human condition'. For someone studying quantum theory on their own, I would recommend this book as a well motivating precursor to more technical books.

Heisenberg explained the philosophical development in history that gradually gave rise to the scientific world view today we have. being neutral, he presented all the different perspectives of big figures of history and showed how they were similar or way form each other. the language he used was very technical which added to its good flavour. i really enjoyed reading it.

Variety of subjects

Brilliant readable book penned by one of the greatest 20th century quantum physicist.

Beautiful book from one of the great minds of the twentieth century.

Deserves to be re-read.

The book was folded in half to fit the box.