Niels Martens DPhil Candidate Philosophy of Physics Oxford University Why Philosophy of Physics is Awesome!

Phil of Physics Quantum (info) Thermodynamics/ Statistical Mechanics Gravity, Space, Time & Space-time Specific sciences Phil of Biology Phil of Mind Phil of Physics Phil of Mathematics Philosophy of Science Epistemology Scientific method Specific sciences (Anti)-realism Metaphysics

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Oxford Philosophers of Physics

Philosophy of Space

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

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’ All talk about space is reducible to talk about relations between particles Compare with family relations Newton Clarke Leibniz SUBSTANTIVALISMRELATIONALISM

“Leibniz shifts”: space must be relational Principle of Sufficient Reason

Immanuel Kant: Let’s use your left and right hands 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?

“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

Philosophy of Quantum Mechanics

Metaphysics: What does the world look like according to quantum mechanics? Quantum information Probability/determinism/free will

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

Double slit experiment

Does each 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 a (probabilistic) interference pattern!  Photons are waves (and electrons, and protons, and all other matter) 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. 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!

Schrödinger’s cat

Ways out Instrumentalism (or the shut-up-and-calculate school) Measurement `collapses the wavefunction’ If you measure with a big apparatus, you will find the particle or cat in one specific location/state: the probability of that location/state depends on how big the wave is at that point. Consciousness `collapses the wavefunction’ Pilot-wave theory Many-worlds interpretation

Questions?