1 / 38

Causality in Philosophy and Physics

Ponte di Legno 2003. Causality in Philosophy and Physics. Mark Fox Department of Physics and Astronomy University of Sheffield. Outline. Why ?. Aristotle’s four causes Causality in classical physics Causality in quantum physics Trying to make sense of it all. The four causes.

gwidon
Download Presentation

Causality in Philosophy and Physics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ponte di Legno 2003 Causality in Philosophy and Physics Mark Fox Department of Physics and Astronomy University of Sheffield

  2. Outline Why ? • Aristotle’s four causes • Causality in classical physics • Causality in quantum physics • Trying to make sense of it all

  3. The four causes • 1. MATERIAL • what is it made of ? • 2. FORMAL • what is the whole, the composition, the form ? • 3. EFFICIENT • what is the source of changes ? • 4. FINAL • what is the end, purpose ? • Physics, Book II, Chapter III Aristotle 384 - 322 BC

  4. An example 1. Material cause: Bronze (paper or wood would have decayed) 2. Formal cause: Sir John Franklin (ie not Queen Victoria, David Beckham) 3. Efficient cause: The sculptor, the crane operator who put in on the plinth 4. Final cause: Born in Spilsby, Arctic explorer Spilsby, Lincolnshire

  5. Another example 1. Material cause: sodium atoms 2. Formal cause: gaseous sodium in a discharge tube 3. Efficient cause: The electrical current 4. Final cause: Lab experiments, street lighting

  6. Causality in physics Material : atoms electrons, protons, neutrons quarks, strings Formal : macroscopic: solid, liquid, gas Microscopic: states of atoms, nuclei Wave function Y ? * Efficient : cause  effect Final: ? * N. Gisin, EQEC, Munich, June 2003

  7. Efficient causality EFFECT: tL / c Effect must come after the cause CAUSE: t = 0 L Signals cannot travel faster than light

  8. Magic EFFECT: t<L / c CAUSE: t = 0 L v Observer can see effect preceding cause

  9. Superluminal propagation ? Clear message for causalityPhysics in Action: December 2003 Experiment confirms that information cannot be transmitted faster than the speed of light Ever since Einstein stated that nothing can travel faster than light, physicists have delighted in finding exceptions. One after another, observations of such "superluminal" propagation have been made. However, while some image or pattern- such as the motion of a spotlight projected on a distant wall - might have appeared to travel faster than light, it seemed that there was no way to use the superluminal effect to transmit energy or information.

  10. Quantum philosophy ? “We live in a remarkable era in which experimental results are beginning to elucidate philosophical questions. In no domain have the results been more dramatic than in quantum mechanics.” Abner Shimony “The reality of the quantum world” Scientific American , January 1988

  11. m I r +Ze v -e Stern-Gerlach experiment (1924) non-uniform magnetic field atom beam Atomic magnet or Force  z Bz'

  12. Einstein-Podolsky-Rosen (1935) either special radioactive source or

  13. Interpretations Einstein’s approach or Bohr’s approach

  14. Bell’s theorem (1964) • John Bell, 1928 -1990 • Measure at different angles • Bohr and Einstein interpretations predict different results

  15.  D1(1) D2(1) D1(0) D2(0)  S   D1(1) D2(1) b a D2(0) D1(0) Modern EPR-Bell experiments with photons EPR S BELL

  16. or a' b' b a Aspect experiments (1981-2) switch switch PMT PMT   S filter filter PMT PMT Local hidden variables inconsistent with the results Einstein approach

  17. “Spooky”* action at a distance measurement t = 0 “The EPR experiment is as close to magic as any physical phenomenon that I know of, and magic should be enjoyed.” David Mermin, Physics Today, 1985(4), 38 * Einstein, letter to Max Born, 1947

  18. Quantum teleportation |y output ACME ALICE input |y BOB Quantum teleportation machine “Quantum information processing”

  19. |F+ |F- |Y+ |Y- Teleportation of photons in the lab classical information output photon |y BOB U BSM ALICE    Demonstrated with single photons across River Danube 2003 input photon |y EPR source

  20. Philosophical implications Two types of question: 1. If we cannot know what we have before the measurement is made, is it meaningful to consider objective reality existing independently of the observer ? 2. How do we preserve the notion of efficient causality with measurements producing effects instantaneously at space-time separated locations ?

  21. Bell’s assessment “Phenomena of this kind made physicists despair of finding any consistent space-time picture of what goes on on the atomic or subatomic scale. Making a virtue of necessity, and influenced by positivistic and instrumentalistic philosophies, many came to hold not only that it is difficult to find a coherent picture but that it is wrong to look for one - if not actually immoral then certainly unprofessional. Going further still, some asserted that atomic and subatomic particles do not have any definite properties in advance of observation. There is nothing, that is to say, in the particles approaching the magnet, to distinguish those subsequently deflected up from those subsequently deflected down. Indeed even the particles are not really there.” J.S. Bell, Journal de Physique (1981), C2, 41-61

  22. Is the moon there when nobody looks ? * “After we came out of the church, we stood talking for some time about Bishop Berkeley’s ingenious sophistry to prove the non-existence of matter, and that everything in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it, ‘I refute it thus’.” Samuel Johnson (1709-1784) from Boswell’s life of Johnson (year 1763) * A. Einstein

  23. Material or formal causality ? Does the act of observation create the reality ? • Wave function Y is the form of the system • Measurement “collapses the wave function” i.e. changes the form • Form is unknown prior to the measurement • Measurement does not create the matter ! • Teleportation of form not matter (N. Gisin, EQEC 2003)

  24. Efficient causality in quantum physics • No surprise that quantum physics does not agree with classical concepts of efficient causality. • Narrow definition of efficient causality resolves contradictions: •  No predictable effects prior to their cause •  No information-carrying signals travel faster than light • But is this satisfactory ? • Form (wave function) of the particle is extended (non-local). Measurement changes the form.

  25. Question for the philosophers Can a cause be simultaneous with its effect ? “Those causes which are particular and actual, are and are not simultaneously with the things of which they are causes.” Aristotle, Physics II, 3

  26. Summary • Many issues resolved by distinguishing clearly between matter and form • Concept of efficient causality in classical physics apparently at odds with quantum experiments. Resolve by narrowing definition of efficient causality • New subject of “quantum information processing” beginning to exploit non-locality

  27. Ponte di Legno 2003 The argument by designin Physics Mark Fox Department of Physics and Astronomy University of Sheffield

  28. Why ? Outline • Final causality • Teleology: the purpose of the universe • Design arguments in physics

  29. The four causes • 1. MATERIAL • what is it made of ? • 2. FORMAL • what is the whole, the composition, the form ? • 3. EFFICIENT • what is the source of changes ? • 4. FINAL • what is the end, purpose ? • Aristotle, Physics, Book II, Chapter III Aristotle 384 - 322 BC

  30. Final causality in physics • Does everything have a purpose, e.g. atoms, photons, galaxies, the universe ? If so, what is it ? • TELEOLOGY • Is intelligence necessary for final causality ? Theme of next conference ?

  31. The argument by designThomas Aquinas, Summa Theologiae I, q. 2, a. 3. • The fifth way is taken from things’ being directed. • We see that there are things that have no knowledge, • like physical bodies, but which act for an end. • This is clear in that they always, or for the most part, act in the same way, and achieve what is best. This shows that they reach their end not by chance but in virtue of some tendency. • But things which have no knowledge do not have a tendency to an end unless they are directed by something that does have knowledge and understanding. • An example is an arrow directed by an archer. • Therefore there is some being with understanding which directs all things to their end, and this, we say, is God.

  32. Design arguments in biology Why does evolution occur ? Can natural selection by chance mutation explain everything ? Can intelligent life evolve spontaneously Evolution of the eye

  33. The God of the gaps in a clockwork universe ? • Newton’s “proof” of the existence of God • Laplace (1798-1857): “We did not need that hypothesis”

  34. The anthropic principle Planet earth is ideal for humans. Is this just a co-incidence ? • What conditions are required for human beings to exist ? • Stable stars • Planets • Carbon atoms • water • surface temperature between 0 ºC and 100 ºC These conditions are very hard to achieve !

  35. Carbon nuclear resonance • Carbon is essential to life. Where does it come from ? • nucleosynthesis of heavy elements in stars • How does this occur ? (Salpeter, 1952, Hoyle 1954) (a) LONG lifetime (b) resonance at 7.7 MeV (c) 16O* level below 7.16 MeV prevents 12C + 4He  16O* Steps (a), (b), (c) depend critically on: me, mp, h, c, e …..

  36. Planet earth Is planet earth unique ? extra-solar planets: 119 planets 104 planetary systems 13 multiple planet systems • Life takes a very long time to evolve • Require stable conditions for billions of years • Importance of the moon

  37. Quantum theory to the rescue “Although the uncertainties introduced by the quantum picture are often stressed, this same quantum picture is absolutely vital for the stability, consistency, and intelligibility of the physical world. In a Newtonian world, all physical quantities like energy and spin, can take any values whatsoever... Hence if one were to form a ‘Newtonian hydrogen atom’ … every pair of electrons and protons that came together would be different. There could not exist a well-defined element called hydrogen with universal properties.” John Barrow Theories of everything: the quest for ultimate explanation (Oxford, 1991)

  38. The $6,000,000 question WHY ? Why is there matter at all ? Why isn’t there nothing ? Why is there energy in the universe ? meta - physics

More Related