@SophistiCat
Hey, you’re making a lot of the same points I would make if I held your view. What’s your background?
The thing is, you need much larger scales in order to detect redshifting due to expanding space. On the scale of a galaxy gravitational attraction overcomes this effect.
It’s smart to distinguish frequency shifting from different sources. It’s standardly used to measure front-back motion within our own solar system, where inflation is negligible. The flip side is that the mechanics describing motion throughout the galaxy will entail increasingly precise frequency shifts. Seeing as we just observed gravity waves, I think it’s fair to suppose we’ll eventually measure EM waves precisely enough to notice a subtle climb in error for objects farther out with much longer orbital radii. Now, you’re right that the net effect of gravity is negative, meaning things fall back to us, whereas the Hubble data mostly concern galaxies in permanent recess, but that doesn’t mean the space in our galaxy isn’t expanding. The small but non-zero acceleration due to inflation may show up as error in our orbital mechanics. It does in principle, anyway. Adequate measurement is a technological question, and not one I feel we can confidently settle for all inquirers at all times.
I think you are underestimating the underdetermination of theory by evidence in general, and the autonomy of physical theories at different scales/energies in particular.
I have a deep appreciation for the Duhem-Quine Thesis and other literary hallmarks on this topic, so I get where you’re coming from. However, I think the success of science must come down to constraints imposed by the external world. A theory succeeds inasmuch as it conforms to nature, if I may risk sounding naive. So, while observation may not fix your theory, it will still reward theories that conform better to the world. In the case of inflation, I’m not saying other creatures would talk about it the way we do, but I’m not convinced they’ll fail to theorize around the same constraints.
I realize physical theory isn’t some grand, unified corpus with logical dominos from one end to the other. I’m just saying, I think rightly, that the reductive pattern in scientific progress tends to unify unrelated phenomena in unforseeable ways. Historical examples abound. I’m sure no one thought Mercury’s odd precession had anything to do with the effect of gravity on light.
You seem to understand this well enough. I guess I just find it more compelling. I think the trend will continue, and it seems immodest to rule out the possibility that scientific progress on the small scale will explain cosmological phenoma like inflation.
Oh no, nothing can rule out Last Thursdayism :) This is where other, non-empirical considerations come in.
Yeah, it’s basically a Cartesian demon. I don’t blame you for lashing out at it. Annoys me that it gets so much space still in the universities.