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> This is about what we can measure, not what we already have. That is not so, this discussion started with a claim that we already have observational proof th

> This is about what we can measure, not what we already have. That is not so, this discussion started with a claim that we already have observational proof that distinguishes between the two scenarios. I have already suggested that the Hubble constant could, in principle, be measured without cosmological assumptions, but we do not, AFAIK, have good enough data, and you have not offered anything to alter that opinion. >... look at how the redshift of a star changes over time instead of staying static. Up until now, you have been very vague about what sort of measurements you have had in mind. This is getting closer, but under which scenario does the redshift stay static? > This is that part where I see a breakdown in your logic... All you are doing here is disagreeing with the conclusion; you have not offered any refutation of the argument that leads to it. The reason for me saying "the relevant differences must be causally dependent on what form the expansion takes" is that if they were not, then they would not be the sort of differences that could be used to choose between the alternatives. And if they were so dependent, then the mapping from what we observe from here to what would be observed there also has that dependency. > It's very possible that we can make measurements on Earth that would tell us exactly how our telescopes would differ from a distant galaxy. There is something very confused here, but I cannot figure out what it is. I can say that my point does not have anything to do with "how our telescopes would differ from a distant galaxy." > Note that the proposition "We can only get this data by going to another galaxy and using telescopes there." is not part of this scenario. Actually, Swebs' original claim was pretty much that, as it could accurately be paraphrased as "we have seen, with our telescopes, that, when observed from a different galaxy, the expansion also seems to have originated there." You seem to have put yourself into the position of defending a claim that you do not actually believe in. Note that there are some conditionals here that you have to be careful of. What I said was that there are certain claims that, if they were made, would result in a circular argument. I did not say that Swebs had made those claims, as he had not done so; I wrote it in an attempt to forestall a trip down a dead end (so much for that!)

Dylan16807 7y ago
There's definitely some deep miscommunication going on. I'm just going to try to clarify a couple parts... > All you are doing here is disagreeing with the conclusion; you have not offered any refutation of the argument that leads to it. The reason for me saying "the relevant differences must be causally dependent on what form the expansion takes" is that if they were not, then they would not be the sort of differences that could be used to choose between the alternatives. And if they were so dependent, then the mapping from what we observe from here to what would be observed there also has that dependency. It's circular if we assume the form of the expansion. If the real form influences our measurements, and we use that to figure out what telescopes would show, which lets us calculate the real form, then nothing is circular. > Actually, Swebs' original claim was pretty much that, as it could accurately be paraphrased as "we have seen, with our telescopes, that, when observed from a different galaxy, the expansion also seems to have originated there." You seem to have put yourself into the position of defending a claim that you do not actually believe in. No, those are very different statements. "We can tell from here what telescopes would show" could be part of a valid argument. "We need to go there to know" is not necessary. > There is something very confused here, but I cannot figure out what it is. I can say that my point does not have anything to do with "how our telescopes would differ from a distant galaxy." I'm talking about the "none of our telescopes have observed the universe from the perspective of a distant galaxy" stuff. Okay, look, this is clearly not working. If you want to format your argument as a numbered chain of logical statements, I can probably give you a response you'll understand. Otherwise I'm giving up. Big blobs of paragraphs are not conducive to debating whether there "must" be certain assumptions.
- mannykannot 7y ago
  I had written a long response to your various points, but this seems to get to the crux of the matter: > It's circular if we assume the form of the expansion... Yes. > ...If the real form influences our measurements, and we use that to figure out what telescopes would show... In what way is that not exactly the sort of circularity that we just agreed about above, given that the real form is the issue to be decided?
  - Dylan16807 7y ago
    > In what way is that not exactly the sort of circularity that we just agreed about above, given that the real form is the issue to be decided? Because measurements are not assumptions. If we use assumptions about UEOS/UEIS to figure out what telescopes show, and use that as evidence for UEOS/UEIS, that's a circular argument. If we use measurements to figure out what telescopes show, without any assumptions about UEOS/UEIS, and then use that as evidence for UEOS/UEIS, that's not a circular argument. (And obviously there are always some assumptions when being sufficiently pedantic. It's an assumption that the sun still exists, etc. That's why I'm specifically saying "assumptions about UEOS/UEIS".)
    - mannykannot 7y ago
      > If we use assumptions about UEOS/UEIS to figure out what telescopes show, and use that as evidence for UEOS/UEIS, that's a circular argument. Exactly, and that is what my comment to Swebs was intended to forestall (I have already made this point, several posts back.) That comment, being a reply to Swebs, must be read in that context (obviously, as you had not even joined the thread yet), and in that post, Swebs was making an argument that UEOS/UEIS has already been settled by observation. In other words, the resolution of UEOS/UEIS was, in fact, the conclusion that Swebs was claiming to have observational proof of. Using a pre-existing resolution of UEOS/UEIS to deduce what observations might be made elsewhere simply didn't enter into the discussion, as in that case, the issue being debated would have already been resolved. > Because measurements are not assumptions. I don't have measurements, Swebs didn't have measurements (though he thought he did), and it has become clear that you don't have measurements either. Maybe someone does, but they have not yet shown up in this discussion.

Dylan16807 7y ago

There's definitely some deep miscommunication going on. I'm just going to try to clarify a couple parts... > All you are doing here is disagreeing with the conclusion; you have not offered any refutation of the argument that leads to it. The reason for me saying "the relevant differences must be causally dependent on what form the expansion takes" is that if they were not, then they would not be the sort of differences that could be used to choose between the alternatives. And if they were so dependent, then the mapping from what we observe from here to what would be observed there also has that dependency. It's circular if we assume the form of the expansion. If the real form influences our measurements, and we use that to figure out what telescopes would show, which lets us calculate the real form, then nothing is circular. > Actually, Swebs' original claim was pretty much that, as it could accurately be paraphrased as "we have seen, with our telescopes, that, when observed from a different galaxy, the expansion also seems to have originated there." You seem to have put yourself into the position of defending a claim that you do not actually believe in. No, those are very different statements. "We can tell from here what telescopes would show" could be part of a valid argument. "We need to go there to know" is not necessary. > There is something very confused here, but I cannot figure out what it is. I can say that my point does not have anything to do with "how our telescopes would differ from a distant galaxy." I'm talking about the "none of our telescopes have observed the universe from the perspective of a distant galaxy" stuff. Okay, look, this is clearly not working. If you want to format your argument as a numbered chain of logical statements, I can probably give you a response you'll understand. Otherwise I'm giving up. Big blobs of paragraphs are not conducive to debating whether there "must" be certain assumptions.

mannykannot 7y ago
I had written a long response to your various points, but this seems to get to the crux of the matter: > It's circular if we assume the form of the expansion... Yes. > ...If the real form influences our measurements, and we use that to figure out what telescopes would show... In what way is that not exactly the sort of circularity that we just agreed about above, given that the real form is the issue to be decided?
- Dylan16807 7y ago
  > In what way is that not exactly the sort of circularity that we just agreed about above, given that the real form is the issue to be decided? Because measurements are not assumptions. If we use assumptions about UEOS/UEIS to figure out what telescopes show, and use that as evidence for UEOS/UEIS, that's a circular argument. If we use measurements to figure out what telescopes show, without any assumptions about UEOS/UEIS, and then use that as evidence for UEOS/UEIS, that's not a circular argument. (And obviously there are always some assumptions when being sufficiently pedantic. It's an assumption that the sun still exists, etc. That's why I'm specifically saying "assumptions about UEOS/UEIS".)
  - mannykannot 7y ago
    > If we use assumptions about UEOS/UEIS to figure out what telescopes show, and use that as evidence for UEOS/UEIS, that's a circular argument. Exactly, and that is what my comment to Swebs was intended to forestall (I have already made this point, several posts back.) That comment, being a reply to Swebs, must be read in that context (obviously, as you had not even joined the thread yet), and in that post, Swebs was making an argument that UEOS/UEIS has already been settled by observation. In other words, the resolution of UEOS/UEIS was, in fact, the conclusion that Swebs was claiming to have observational proof of. Using a pre-existing resolution of UEOS/UEIS to deduce what observations might be made elsewhere simply didn't enter into the discussion, as in that case, the issue being debated would have already been resolved. > Because measurements are not assumptions. I don't have measurements, Swebs didn't have measurements (though he thought he did), and it has become clear that you don't have measurements either. Maybe someone does, but they have not yet shown up in this discussion.