Kevin Simler goes on to explain that he was talking about biological and social phenomena and he’s not sure about physical phenomena.
Why do planets exist? You might think that gravity is a positive feedback mechanism. The larger a planet gets, the more it attracts other mass. I think that this is correct for black holes, but not quite correct for gravity in the Newtonian regime: a planet attracts other matter, but this gives it the energy to fly away again. I think a more fundamental mechanism is electro-magnetism making matter “sticky.” It gives matter internal degrees of freedom, so that energy can be dissipated as heat, allowing inelastic collisions in which matter aggregates into larger bodies. Dark matter has gravitational interaction but not EM interaction, so it doesn’t form planets, but only a diffuse density field. But why is it denser around galaxies? If galaxies attract dark matter, that suggests that gravity is enough to provide positive feedback all on its own. For that matter, the existence of galaxies suggests that.
He also mentions mountains. Mountains seem to exist, or at least mountain ranges. They are caused by tectonic plates. I guess that plates exist because of positive feedback causing them to merge. But whatever reason, mountain ranges do not exist because of a positive feedback phenomenon to which they contribute; they are side effects of tectonic plates.
Do mountains exist? What does it mean to exist? I can give a precise description of “the point of highest elevation within 10 miles,” (or 10 feet!) which must exist without reason. Such indexical descriptions identify features, but do not suggest that they should have reasons for existing, or a shorter description. Most mountains look like they are differentiated from their neighbors as the result of noise and we should not expect reasons for their individual existence. Whereas mountain ranges are a more natural category and we should expect more definite explanations. That explanation is the collision of specific plates, which appear causally prior. Also, plates are much older than the mountain ranges on their borders. Plates might exist because of positive feedback causing them to grow, in which case the particular plates exist because of noise in their seeding a long time ago.
Kevin Simler goes on to explain that he was talking about biological and social phenomena and he’s not sure about physical phenomena.
Why do planets exist? You might think that gravity is a positive feedback mechanism. The larger a planet gets, the more it attracts other mass. I think that this is correct for black holes, but not quite correct for gravity in the Newtonian regime: a planet attracts other matter, but this gives it the energy to fly away again. I think a more fundamental mechanism is electro-magnetism making matter “sticky.” It gives matter internal degrees of freedom, so that energy can be dissipated as heat, allowing inelastic collisions in which matter aggregates into larger bodies. Dark matter has gravitational interaction but not EM interaction, so it doesn’t form planets, but only a diffuse density field. But why is it denser around galaxies? If galaxies attract dark matter, that suggests that gravity is enough to provide positive feedback all on its own. For that matter, the existence of galaxies suggests that.
He also mentions mountains. Mountains seem to exist, or at least mountain ranges. They are caused by tectonic plates. I guess that plates exist because of positive feedback causing them to merge. But whatever reason, mountain ranges do not exist because of a positive feedback phenomenon to which they contribute; they are side effects of tectonic plates.
Do mountains exist? What does it mean to exist? I can give a precise description of “the point of highest elevation within 10 miles,” (or 10 feet!) which must exist without reason. Such indexical descriptions identify features, but do not suggest that they should have reasons for existing, or a shorter description. Most mountains look like they are differentiated from their neighbors as the result of noise and we should not expect reasons for their individual existence. Whereas mountain ranges are a more natural category and we should expect more definite explanations. That explanation is the collision of specific plates, which appear causally prior. Also, plates are much older than the mountain ranges on their borders. Plates might exist because of positive feedback causing them to grow, in which case the particular plates exist because of noise in their seeding a long time ago.