I have been recently researching the topic of the expansion of the Universe. Specifically, the 1998 discovery by Saul Perlmutter that claims the Universe is expanding at an accelerated pace. From my understanding, the premise of this discovery was that the observed redshift of a Supernova 7 Billion Light years away was perceived to be receding at a slower rate than that of the redshift observed of a Supernova 1 Billion Light Years away. The conclusion was that the Universe was expanding at a slower rate 7 Billion years ago than it was 1 Billion years ago, thus an acceleration of expansion.
I also understand that two other teams had similar results based off different studies, Erick Guerra and Ruth Daly (Studied 14 radio galaxies indicating the mass of the Universe is 20% smaller than would be necessary to stop the expansion of the universe and cause a collapse back unto itself) and, Neta Bahcall and Xiaohui Fan (Studied the mass density of galaxy clusters and came to a similar conclusion).
I am curious as to what your thoughts are on the conclusion of this data. Specifically, do you have other theories as to why the accelerations of the two Supernovae were perceived to be receding at different rates? What else could cause our perception to show the varying expansion rates?
As a preface to my thoughts on the matter, I should state that I have not been researching this for long and have no background in the field, just a curious and wandering mind.
Anyway, I was wondering if the differing space environments at the time of the stars' destruction have an effect? E.g. The Universe was more dense at the time of the Supernova 7 Billion years ago than that at the time of the Supernova 1 Billion years ago. That being the case, 7 Billion years ago, when the Universe was expanding, the density of the Universe, in my mind, could have impeded the acceleration of expansion more so than the less dense Universe that the Supernova 1 Billion years ago was experiencing. This leads me to believe that the acceleration would be naturally increasing as the density continues to decrease over time.
Another question I have been pondering is the point of reference for the two differing Supernovae, which is Earth. Our Galaxy is also caught in the expansion of the Universe, so the rate at which we are moving would also have to be factored in. As well as the locations and directions of all three points of reference, Earth, Supernova 1, and Supernova 2. If Our Galaxy is expanding in a similar direction through space as that of Supernova 1 (7 Billion Years ago) and an opposite direction than that of Supernova 2 (1 Billion Years ago), then the obvious outcome would be that Supernova 2 would appear to be receding at a more accelerated rate than Supernova 1 due to the variance of our location in space in comparison to that of the observed points.
From my understanding, which is very minuscule, redshift does not allow the observer to determine the direction of expansion, just the speed and distance. I suppose given the variables, one can calculate the direction of expansion if given enough time to observe the Supernovae, but seeing as the observer only has approximately 18 days before a type 1a Supernovas light fades, that does not seem likely to me.
Any feedback is appreciated. Even if it is to tell me I am wrong. I enjoy hearing all perspectives.