Geocentrism

A debate is always the best way to start one's day. In my first post, I wish to present a few brief refutations to all points Garrett has raised, and then present a few reasons why I am not a galactocentrist myself.Refutations1. IdeologicalNow, Garrett here is right. In scientific inquiry, we do start off saying "We are probably not special" and go from there. The reason for this should be obvious to all readers: if we did not start at this point and instead started with the assumption that what we observe was unique and special to us, then the impetus to explain and investigate odd phenomena vanishes. So we begin with the assumption we are not unique, but that does not mean that one cannot present evidence that we *are* unique, and indeed, this is what Garrett will now try and do.2. Galaxy densityFor this section, my opponent takes a visualisation of SDSS (Sloan Digital Sky Survey) results and tries to infer that the lower galaxy redshift density at higher redshift implies we are the centre of the universe. Whilst I could argue that higher density does not implied being physically central in the universe, this is not needed as lowering density is simply a result of Garretts lack of familiarity with cosmological surveys. Very simply stated, the graph Garrett presented shows successfully redshifted galaxies. The further out we go, the fainter the galaxies are and the lower the success rate on redshifting. When given a slightly larger telescope and looking out at higher redshifts (SDSS isn't a deep field survey, it has a median redshift of 0.1 - you can read about the survey on Wikipedia for corroboration [1]), you can see for yourself the fade off in the image presented by Garrett (which occurs around z=0.7 - redshift is denoted by a z) is simply because of redshifting difficulties: The above image is from the 2df QSO surey quasar survey, which goes up to z=13 [2].To hammer this point home, imagine you are standing in the middle of a relatively sparse forest, idenifying trees around you. You look at each tree you can see and try and identify it visually, and plot your result on a piece of paper. After finishing, you look down and realise you've managed to identify far more trees in your immediate vicinity than trees further out that you had to squint at. This is perfectly expected from any location in the forest, and anyone trying to claim that because of that plot they are at the centre of the forest would probably receive a few skeptical glances.3. Great wallI am really liking this debate, as it is helping me distil a good amount of cosmological information. So what Garrett has pointed out as "Concentric Density Spheres" in the SDSS diagram are the known result of Baryon Acoustic Oscillations [3] that give rise to large scale structure in the universe. In particular, Garret his highlighted the Sloan Great Wall [4], which is named because it was discovered by the SDSS. What Garrett is shown though is just a helpful cherry picking of the data which supports his view, because when we zoom out a little more, we clearly see galacitc filaments are not concentric spheres, and indeed we aren't even in one of the more impressie superclusters. The above image is based on physical data [5], the below is a simulation of mass distribution showing the structure of filament at extremely large scales [6]. Notice the lack of concentric spheres or indeed any obvious focal point that one could claim is the "center" of the universe. Unfortunately for Garrett, these images and their lack of any centre point merely reinforce the position that our galaxy is not special or unique in its location.4. Fingers of GodFingers of God are not indications of a central position in the universe, they are a well understood observational phenomenon that would be seen from any viewing direction [7]. To give a brief explanation, redshifting works by measuring recession velocity. In galactic clusters in which galaxies are orbitting each other and being pulled around, the objects recession velocity is a combination of both the expansion of the universe and it's perculair velocity (how it is moving relative to the cluster). Now, galaxies moving towards us in the cluster appear to have a lower recession velocity, and galaxies having a perculiar velocity away from us appear to have a higher recession velocity. Given that redshifting directly converts recession velocity to distance, those changes in recession velocity cause the cluster to become elongated, and we call those "Fingers of God" (don't ask me why). One could redshift those clusters from any direction, from any other galaxy, in every case we would find a finger of god. In fact, I would easily argue that NOT observing fingers of god would be far stronger evidence of us being unique, because it would mean that all galaxies would have to only be moving tangentially to us (no perculiar velocity), and that would be inexplicable. Why I am not a galactocentristThere are three main reasons I want to talk about. 1: we do not have available evidence for it, so we have a scope problem. 2: it makes no sense in spacetime models and 3: it would falsify modern cosmological models, and we have a vast amount of data supporting them.1. ScopeNotice, if you will, that the evidence Garrett has been using is only up to z=0.7. Indeed, this is the region we have the most data for, by orders of magnitude. However, z-0.7 corresponds to a bit less than 10 Glyr in radius. The size of the observable universe is around 47 Glyr in radius, so we are looking at a volume of less than 1% of the observable universe. This worse when we realise that the universe itself is, to best calculation, at least 250 times the volume of the Hubble sphere (250 is the lower bound for a closed universe, the upper bound is infinite) [8]. So this means that at the very most, we are looking at a volume of <0.003% of the universe and trying to say "See, we are in the middle of it". We simply do not have the data to form such a conclusion. Imagine that even if the arguments Garrett presented were valid, we would only have grounds to say that we appear to be the focal point of our immediate galactic neighbourhood. It could be possible that there are many such focal points and "concentric spheres of density" in the universe around different points. My mental pictures for this is that Garrett is trying to show we focus of an antlion trap and therfore the world, but is currently not considering the fact that a singular antlion trap is rarely the case. I hope to talk about the other two points in my next argument.ConclusionGarretts arguments for galactocentrism are founded on minunderstandings of basic observational cosmology and have been soundly refuted. Furthermore, even if incontrovertible evidence arose that we were the focus of our galactic neighbourhood, the sheer size of the universe means that continuing the conclusion out to being the focus of the universe will be unjustified. In my next argument, I will explain how a central point is geometrically nonsensical under the Minkowski space-time metric and why galactocentrism is a hypothesis that directly contradicts modern cosmology and thus cannot be considered individually.[1] http://en.wikipedia.org...;[2] http://www.physics.usyd.edu.au...[3] http://en.wikipedia.org...[4] http://en.wikipedia.org...[5] http://rand0m1y.blogspot.com.au...[6] http://scienceblogs.com...[7] http://en.wikipedia.org...[8] http://arxiv.org...