> Our errors on these measurements come down to how accurately we can measure the distance to galaxy and its size, but the quasar is very obviously much smaller

> Our errors on these measurements come down to how accurately we can measure the distance to galaxy and its size, but the quasar is very obviously much smaller than the galaxy. I have no issue with this - my question is how much smaller? Which you then attempt to discuss - it is here that we can look at the assumptions you propose. > Looking for an upper limit, let's assume that the entire object changes at the same time; some process coordinates the change so that the whole thing gets brighter or dimmer at the same time. My question is (as we can't actually investigate the object directly) how valid is this assumption? Are there possible scenarios that would affect the association of data observed and the model we use to explain the observations. What if we use a different assumption about luminosity changes, does this affect the outcome of the size? It is a question that can be asked and in asking it may well lead to a better understanding of the data we observe. In asking it, it may also lead nowhere. from my perspective that is not a problem. Is there any situation in which the further parts get brighter before the closer parts? How would this affect the sizing determination? Our understanding of many of the phenomena we observe is limited at best. Asking questions is a first step. > Importantly, the object (at least the light producing parts of the object, the parts we care about) can't be larger than implied by the smear. If it was bigger, the smear would be bigger. A smaller object can have a bigger smear, by slowing changing over time, but a bigger object can't have a smaller one. Again, is this an actual valid truth or just an assumption we work with because we don't have a perspective that might say otherwise? It is an assumption we can start with - no problems with that. It is also an assumption that must be looked at when anomalies start appearing. > Quasars often change luminosity significantly on the order of weeks or days, so we know that they are no bigger than a few light-weeks or light-days across. A statement that relies on certain assumptions being true. If the assumptions are incorrect, the statement that follows will be wrong. I am not saying it is wrong, I am saying that we need to keep it in mind that the view is based on assumptions made and could change if the assumptions change. > Once you have those measurements you can compare with other measuring techniques and see if they agree. Sometimes changes will be made, but the errors are very very rarely 'huge'. At the kinds of distances and sizes we are talking about, light years are very tiny. Lokk at it this way, we have an estimation of the size of our galaxy and there is, maybe, a 25% difference between the larger estimate and the smaller estimate. We use this as a basis for estimating the sizes of other galaxies, as well as other measurement processes which depend on estimations of distance. There is enough anomalous data to suggest that our measuring techniques may be wrong by big margins. It is dependent on what data you use and what you ignore. > I don't disagree at all, but simply saying we need to reconsider our 'basis assumptions' doesn't do any of that. We need to look at the basis assumptions to see if there are things that should change. This is sensible. If it means continuing with them, okay. If it means changing them, then do so.