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2013-09-29 13:19:49: We are about to start the very last session of the conference with Jeremy Butterfield giving the ‘rapporteur session’.
2013-09-29 13:41:18: First section: beyond spacetime, and beyond the Bronstein cube
Butterfield starts out from the so-called ‘Bronstein cube’:
This cube is too neat to adequately capture the situation in quantum gravity (QG), in several respects: the edges are often not well-defined, probably not unique, generally don’t commute. And it might not at all be what you want, i.e., perhaps we won’t need a quantization of gravity.
Consider three broad approaches: (A) strings, (B) loops and its ilk (including causal set theory), and (C) condensed matter approaches. But e.g. string theory doesn’t say, for instance, we should let $c$ be finite starting out from quantum Newton-Cartan theory, etc.
In sum, Butterfield concludes “the search for QG is like orienteering in a blizzard–without a map.”
2013-09-29 13:48:29: Second section: Halfway through the woods
So we have relativity and the quantum, but it may well be that the quantum will have to mend its ways more than relativity in an ultimate reconciliation, due to the “scandal of the measurement problem”. So Rovelli is right about that we are “halfway through the woods”, but there is a more detailed time-scale of relevant developments, such as the evolution of philosophy of physics since around 1970, which is now in seamless contact with foundations.
2013-09-29 13:54:53: Third section: What use philosophy?
What could be philosophy’s role, apart from scavenging on the carcasses of dead theories, be journalists or camp follower, or perhaps more in symbiosis (like pilot fish guiding the sharks…).
Examples of foundational work which can act as heuristics for future fundamental physics, such as Belot’s study of the Aharonov-Bohm effect, or Weatherall’s investigation of the relationship between Newtonian gravity and GR.
What are projects for the young? Previous examples of low-hanging fruit: Bell’s locality condition arises in Reichenbach’s philosophy, Manchak’s bringing to fruition of earlier considerations of work by Malament and Glymour.
2013-09-29 14:10:32: Fourth section: personal reflections
(1) Beware of beguiling words: one has to be careful not to be led down the garden path by nefarious doctrines such as Kantianism. So conceptual analysis has its limited place–but have it checked against empirically established results!
(2) The vacuum vs. zilch (cf Oliver and Smiley, Analysis): ‘zilch’ as a necessarily non-referring term, and its usefulness in philosophical discourse, and to avoid mystery mongering about the vacuum in QFT and LQG.
(3) Condensed matter approaches: challenges whether we have any grip on what the fundamental degrees of freedom are. Should we take it to be suspicious that some theories have remnants of less fundamental theories in them, such as the Ashtekar variables in LQG?
(4) Duality: Butterfield starts out from Belot’s appraisal that philosophers and physicists have different attitudes towards dual theories, where the former see two theories (because they reject verificationism) and the latter deny that (because they are moved by historical examples of dual pairs of theories who would then dissolve into a more general unified theories which was recognized as progress).
2013-09-29 14:31:15: Daniele Oriti: It’s good for physicists to know that philosophers can scavenge on the carcasses of their theories! And the Bronstein cube should have an additional dimension along which the number of degrees of freedom is increased, giving rise to collective phenomena.