The Light Of Other Suns

New short animation in the works !

Fournier's Fractal

I'm trying to find out more about an alternate solution to Olber's Paradox (the sky shouldn't be dark in an infinite eternal universe) : the structure is a fractal. Yes yes, the real Universe isn't a fractal, but it's a neat idea and fun to try and visualise.

Apparently some dude named Fournier found a fractal structure (sometimes it's called a "proto-fractal", not sure why) back in 1907 which allows large blank areas of sky, even though it's infinite in size. Couldn't find out much more than that but I did stumble upon an image of it, so it was easy to make a looping zoom animation.

I can't find much more in the way of fractals that would look more like the real sky that would also allow blank lines of sight. "Fractal cosmology" searches tend to turn up raving loonies or advanced mathematics I don't understand. Hmmm.

Dark matter in the inner Milky Way

So, as promised, I read through the original claim of evidence (not proof) of dark matter in the inner part of the Milky Way :
http://arxiv.org/abs/1502.03821
... and the "not even wrong" response :
http://arxiv.org/abs/1503.07813
... and the "your response was not even wrong"* response to the response :
http://arxiv.org/abs/1503.08784

* They didn't actually say that, but they could have done.

Cautiously, I generally find in favour of the response by McGaugh et al. McGaugh et al.'s most important claim is that the result of the paper is that there is clear evidence of dark matter only beyond 6 kpc from the galactic center, which is not a new or surprising result. This is probably correct. Ideas about whether this is really the case or not have, however, waxed and waned (http://iopscience.iop.org/0004-637X/483/1/103/fulltext/35135.text.html#fg1)

A google search for "Milky Way rotation curve" reveals differing claims as to whether the Milky Way requires dark matter in the inner regions or not, e.g. https://squishtheory.files.wordpress.com/2013/04/rotcurve.gif vs http://pages.uoregon.edu/jimbrau/BrauImNew/Chap23/6th/23_21Figure-F.jpg
Therefore the main claim of McGaugh et al. that the paper does not present a new or surprising result appears to be substantiated.

McGaugh also make the claim that this result "follows from any plausible circular speed and Galactocentric distance for the Sun", citing a textbook I don't have. The original authors claim that this statement is factually wrong. I don't know who's right about this.

McGaugh et al. claim that the paper is confusing with its use of the term "inner". However, this is not the case. It's clear the authors mean "closer to the center of the Galaxy than the Sun". McGaugh et al. also state the great care must be taken when combining multiple data sets; while true, this statement is disingenuous. While I've no idea if the author's methods are correct or not, it's abundantly clear that they haven't just thrown everything together willy-nilly.

McGaugh et al. correctly note that the press release about the letter (http://perma.cc/JJ4S-G42D) makes very strong assertions (proof of dark matter) which are not at all warranted by the paper. It is not "direct observational proof" at all, it doesn't automatically falsify all alternatives. It is simply evidence which is compatible with the dark matter model - nothing more, nothing less. The paper is far more ambiguous as to whether it's claiming a really novel result or just improved evidence - the press release is unequivocal that it's a brand new result.
http://arxiv.org/abs/1502.03821