Why Philosophy of Physics is Awesome!

1. Why Philosophy of Physics is Awesome! Niels Martens

3. Oxford Philosophers of Physics

4. Philosophy of Space • Is space real? • Einstein’s Relativity Theory • Time slows down! • Space contracts! • Cosmology/Big Bang • Emergent Space(time)

5. Leibniz-Clarke Correspondence • Space exists! • It makes sense to talk about empty space • ‘Even if there is no play tonight, the theatre is still there’ Newton Leibniz Clarke SUBSTANTIVALISM RELATIONALISM • All talk about space is reducible to talk about relations between particles • Compare with family relations

6. `Leibniz shifts’: space must be relational

7. `Newton’s bucket’: let’s look at science! • The relative motion between bucket and water is the same in picture 1 and 3, but the relative motion with respect to the stars is not! • Problem: physics becomes nonlocal Ernst Mach

8. Let’s use your left and right hands • Immanuel Kant • There is a difference between your right and left hand • The relationalist explains the different handedness of two objects via relations • What about a single hand in an empty universe? • Earman • Handed laws of nature

9. Philosophy of Quantum Mechanics

10. Philosophy of Quantum Mechanics • Metaphysics: What does the world look like according to quantum mechanics? • Quantum information • Probability/determinism/free will

11. Interpreting Quantum Mechanics • Does light (and everything else in the world) consist of particles? Or waves? • Photo-electric effect (Einstein  Nobel Price): particles • Double split experiment: waves

12. Double slit experiment

13. Double slit experiment

14. Double slit experiment

15. Double slit experiment

16. Double slit experiment • Does the photon (light particle) go through both slits at the same time? Can we measure which slit it goes through? • Even if you only send one photon through the slits, we still get an interference pattern! •  Photons are waves (and electrons, and protons) • You cannot say that there is a localised particle that goes through one of the two slits: there is a wave that goes through both slits: the photon is in a SUPERPOSITION of going through the left and the right slit at the same time

17. This is absurd! • So, at the smallest scale, our world consists of quantum waves: light, electrons, protons, everything is a quantum wave, meaning that the `particles’ are at several places at the same time. Schrödinger (Magdalen College Alumnus): This cannot be true. If it would be true, it should also apply to large objects (since they are made up out of small objects), and it would be absurd to have a large object - like a table - being here and somewhere else at the same time! We never see tables in superpositions!

18. Schrödinger’s cat

19. Ways out • Instrumentalism • Measurement `collapses the wavefunction’ • If you measure with a big apparatus, you will find the particle or cat in one specific place: the probability of that place depends on how large the wave is at that point. • Consciousness `collapses the wavefunction’ • Pilot-wave theory • Many-worlds interpretation

20. Questions?