Why Philosophy of Physics is Awesome!

Niels MartensWhy Philosophy of Physics is Awesome!Oxford Philosophers of Physics

Philosophy of SpaceIs space real?Einsteins Relativity TheoryTime slows down!Space contracts!Cosmology/Big BangEmergent Space(time)Leibniz-Clarke CorrespondenceSpace exists!It makes sense to talk about empty spaceEven if there is no play tonight, the theatre is still there All talk about space is reducible to talk about relations between particlesCompare with family relations

NewtonClarke

LeibnizSUBSTANTIVALISMRELATIONALISM`Leibniz shifts: space must be relational

`Newtons bucket: lets 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 nonlocalErnst MachLets use your left and right handsImmanuel KantThere is a difference between your right and left handThe relationalist explains the different handedness of two objects via relationsWhat about a single hand in an empty universe?EarmanHanded laws of naturePhilosophy of Quantum Mechanics

Philosophy of Quantum MechanicsMetaphysics: What does the world look like according to quantum mechanics?Quantum informationProbability/determinism/free willInterpreting Quantum MechanicsDoes light (and everything else in the world) consist of particles? Or waves?Photo-electric effect (Einstein Nobel Price): particlesDouble split experiment: wavesDouble slit experiment

Double slit experiment

Double slit experiment

Double slit experiment

Double slit experimentDoes 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

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.

Schrdinger (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 beabsurd to have a large object - like a table - being here andsomewhere else at the same time!We never see tables in superpositions!Schrdingers cat

Ways outInstrumentalismMeasurement `collapses the wavefunctionIf 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 wavefunctionPilot-wave theoryMany-worlds interpretation

Questions?