I've always wanted to understand how the Universe works. This is proving rather difficult, so I'm prepared to settle for knowing what it looks like.
Maybe a more interesting question to ask is : how accurate is the video ? Is this really what the Universe looks like ?
Well, no, it isn't. It's an approximation, but it's grounded in reality. Allow me to try and explain, because it's my blog and you can't stop me.
The complete, full HD video. Partially in 3D if you've got those
old red-blue glasses. The original can be seen here.
How do we know where all the galaxies are ?
We don't. Just looking at an image isn't always enough to tell what's a galaxy and what isn't. For example... THIS
isn't a galaxy. It's just a crummy old star cluster, and therefore useless. Whereas THIS
Just like with James Spader and Michael Shanks, there's no way to tell the two apart by just ogling them. But if we measure how fast their stars are moving, we can see that all is well with the star cluster, but the stars in the galaxy are moving way too fast. Without some invisible matter to hold them all together, they should all fly apart (unless we've got something very wrong, which is possible, but in the interests of time let's not go there). So galaxies have dark matter, and star clusters don't.
|Whereas distinguishing Spader / Shanks is simply hopeless.|
Still, the upshot is that identifying galaxies is tricky, and we can't be sure we've found them all. In fact, we know we haven't, because the Milky Way is big, bright, and in the way.
|And very pretty.|
How do we know how far away the galaxies are ?
We may not know exactly where all the galaxies are, but for those we do know about we generally have pretty good estimates of how far away they are - even though we can't directly measure the distances to other galaxies.
The only way we can directly measure the distances to astronomical objects outside of our own solar system is through parallax, where we see how much a star moves relative to the stars behind it. That's good for nearby stars, but for more distant objects we have to use other methods (calibrated on the ones we can get direct measurements for) to create a 'distance ladder'. And that lets us get pretty good estimates of how far away galaxies are.
|Full size image here.|
** Merging is even rarer - and considerably more unpleasant - for sumo wrestlers.
This is particularly bad in galaxy clusters, which are the equivalent not of sumo wrestlers, but a bunch of obese, angry rabid cats on a trampoline, possibly on fire - the Platonic ideal of chaos. Here, the velocity measurements tell us practically nothing about distance. Some galaxies are even coming toward us, which would give a meaningless, negative distance if we were silly enough to take Hubble's Law at face value. So the galaxy distances in the GIF are pretty good, but far from perfect. There's just no way around that, because better data doesn't exist.
No they don't. The images used are optical images from the Sloan Digital Sky Survey, but just because they were observed at similar wavelengths that we use to see with doesn't mean they look like what you'd see with your naked eye.
For starters, they're all much too bright. Think about what the Milky Way looks like on a clear, dark night. Does it really look like this ?
Hell no. The real thing looks beautiful, but nowhere near as bright or as colourful - not even in the darkest spot on the darkest night. Images like this are only possible with long exposures, or large telescopes. So out of necessity - because the video would show bugger all otherwise - the galaxies are shown much brighter than you'd really see them.
The colours aren't 'true' either. but that shouldn't bother you. Everyone perceives colour in a slightly different way - it's practically a subjective choice, rather than a measurement. And then, of course, some people are colourblind. The important point is that the colours are relatively correct - things which look bluer really are bluer than things which are redder.
|Left to right : 1) Raw image from the SDSS; 2) Galaxy as displayed in Blender without colour correction; 3) Galaxy displayed in Blender with colour correction.|
This makes a very dramatic difference indeed for the whole set of galaxies. Here's what they would look like if I hadn't done the correction :
|A Universe rich in stars, galaxies, flying spaghetti monsters, etc.|
What about the sizes of the galaxies ? Like brightness, these are exaggerated out of necessity, by about a factor of 40. That means that you can see the structures in many galaxies at once, without hoping that the viewpoint passes very close to them (otherwise you'd just see a bunch of small, uninteresting fuzzy blobs). However, as with colour, the relative differences are correct : a galaxy that looks twice as big as another really is twice its size.
One thing there was no need to compromise was the structures visible in the galaxies. Each of the 23,935 galaxies in the video is represented by an optical image of the actual galaxy seen at its location. This is pretty unusual - many of these large-scale videos often just use a few hundred template images. Here, there are unique images of every single blasted one. Don't believe me ? Here's the complete sample.
EDIT : This is from the original version of the post, which used a mere 11,710 galaxies. I can't be bothered to remake this.
|View this in full, terrifying detail here.|
I had a choice here. The first option was to carefully check all
Finally, we'll never know exactly what some galaxies really look like, because we're seeing them from a jaunty angle. We can correct for this to some extent, but only if we know the minimum and maximum dimensions of the galaxy. Which, for this sample, we don't. And if a galaxy is edge-on to us, there's nothing at all we can do except go home and cry.
In summary then, the video shows what you'd see if you had super-sensitive eyes and all the galaxies were forty times bigger than they actually are, with lots of errors. The large-scale structures of filaments and voids you see are correct, but not complete. That's a correctable problem, and one I might tackle at some point. But since downloading 11,000 images took about 8 hours, it can wait.