My God, it's full of galaxies

August 14, 2012 7:47 AM

A flight through the universe using data from the Sloan Digital Sky Survey. [single-link APOD]
posted by fantabulous timewaster (22 comments total)

[more outside]
posted by fantabulous timewaster at 7:47 AM on August 14, 2012 [4 favorites]

what is left at the center of the universe?
posted by Jondo at 7:58 AM on August 14, 2012

Well, I feel small.
posted by petrilli at 8:06 AM on August 14, 2012 [1 favorite]

Here is the press release which goes into more detail on this latest set of data that's been made available.
Am incidentally a very very small cog in the machine that produced this.
posted by edd at 8:09 AM on August 14, 2012 [1 favorite]

And against this infinite backdrop, the monkeys continue to squabble.
posted by seanmpuckett at 8:30 AM on August 14, 2012 [3 favorites]

I guess it's the parts where the camera orbits around a central point, but this is the first video like this that makes the foam structure really apparent without some kind of density overlay.
posted by cmoj at 8:33 AM on August 14, 2012 [2 favorites]

Ha, this was made by my co-worker! He is in the office next to mine. I'll alert him to this thread.
posted by capnsue at 8:33 AM on August 14, 2012 [2 favorites]

Since we seem to have a lot of SDSS people on board, I have a question about the Sky Survey: I'm assuming the positions of these galaxies, clusters, and filaments are taken as is -- but what if we took into account the finer, localized movements and velocities of each galaxy, and then used a simulation to extrapolate those movements over time?

Would the overall texture of our cosmic neighborhood change if these celestial bodies were bumped forward to the "now," compensating for light lag? Or are these movements relatively insignificant compared to the vast distances involved? Or is the idea of "now" just completely meaningless on such a huge relativistic scale?
posted by brownpau at 8:44 AM on August 14, 2012 [1 favorite]

My brain is broken. How large would an entity need to be to have that perspective? I mean, galaxies look like floating motes of dust.

Ever since seeing the starfield screensaver for the first time, I've wondered what it would look like to be flying through space (because I figured it wouldn't look like that). I'd like to see something from the perspective of a human. Would it just be an infinity of empty space?
posted by MsVader at 8:45 AM on August 14, 2012

Needs a "you are here" arrow.
posted by modernnomad at 8:53 AM on August 14, 2012

brownpau: The movements of each galaxy add or subtract to the redshift it has due to the expansion of the universe. The total redshift is what we measure, so the individual movements of galaxies cause us to slightly misplace them on the map (causing the fingers of God effect and Kaiser effect). It causes the denser parts of the map to line up with us. These extra movements can be really important to a cosmologist - you can extract quite a lot of information from them.
Also, the 'overall texture' changing is what a cosmologist would refer to as 'growth of structure' and it's also really important, although it's pretty slow still. It won't change the positions of voids and clusters much, but it changes how densely packed they are. The easiest way to get the gist of it is to look at a simulation video like this one. SDSS's BOSS survey looks out to about about z=0.7 (z is redshift), and earlier parts of SDSS cover down to z=0, so you can see how that fits in with timescale for the video which has z labelled.
posted by edd at 9:13 AM on August 14, 2012 [2 favorites]

How large would an entity need to be to have that perspective?

Well, the top comment on youtube (I know, I know) is: "If we say that that the "camera" in this video is spanning the distance of a milky-way sized galaxy in 1 millisecond, then it's travelling at 1,262,304,000,000,000 times the speed of light."

We'll get there someday! We only have to figure out how to get our GoPro camera to 1(c) first.
posted by yeti at 9:15 AM on August 14, 2012

I had some hilarious joke to make but that video completely wiped my mind. That's a lot of stars. A LOT of stars. And yeah, the foam structure really jumps out and demands an explanation.
posted by DU at 10:34 AM on August 14, 2012

Get Celstia (free) and install the sloan survey and you can fly through yourself. It's really cool to see how three dimensional everything is.
posted by jeblis at 11:07 AM on August 14, 2012 [1 favorite]

Celestia data plots are here.
I recomend the glactic redshift survey (pic)
posted by jeblis at 11:13 AM on August 14, 2012 [1 favorite]

I'd like to see something from the perspective of a human.

Go outside at n... I KNEW IT THE REPTILIANS ARE HERE
posted by cmoj at 3:54 PM on August 14, 2012

Yeti: "it's travelling at 1,262,304,000,000,000 times the speed of light."

I feel very naive saying this, but I suddenly have the feeling that light actually moves very slowly. Which then makes me wonder, why would nature's speed limit be so low?

I have nothing but intuition to go on here, but I suddenly have the feeling there must be something faster than light, or some way to travel faster than light.

I've often heard and said myself that an ant can never understand what it means to be human... Seeing things like this, that boil such vast concepts down to manageable experiences makes me feel like an ant getting a brief glimpse into being human.
posted by PigAlien at 9:29 AM on August 20, 2012

I feel very naive saying this, but I suddenly have the feeling that light actually moves very slowly. Which then makes me wonder, why would nature's speed limit be so low?

If you really want a head-scratcher, consider this: The big bang is believed to have happened 13.75 billion years ago. The observable universe -- that is, just the bit that is theoretically possible to see from any given point -- is 92 billion light years in diameter. Assuming we are the centre of the universe (we aren't, but whatever) that would mean all that junk got all the way out there from all the way in here at more than three times the speed of light.

How's that? Because space is expanding!

You can travel from a stationary point in a perfectly straight line at exactly the speed of light for exactly one billion years, then look back (as a billion-year-old space corpse) to realize that you're more than a billion light years away from where you started, not because you traveled faster than the speed of light, but because the space between you and that point got bigger all by itself.
posted by Sys Rq at 3:55 PM on August 20, 2012 [1 favorite]

(Of course, I may have totally misunderstood the whole concept of the metric expansion of space. It all kind of makes my brain hurt.)
posted by Sys Rq at 3:58 PM on August 20, 2012 [1 favorite]

No, Sys Rq, you've got it basically right. It's actually a little weirder than that. Because the expansion of space is accelerating, many of the galaxies in the SDSS are "unreachable": if we were to send a signal to one of those galaxies now, the expansion of the universe would speed up while that signal was in transit so that the galaxy would actually outrun our message. For the same reason, even if we continue to observe the universe for ever, we won't actually see much more of its volume than we have already. (I learned about these things from this surprisingly readable paper, read the caption to the first figure first; unfortunately the high-resolution Map Of Everything has disappeared from the internet recently.)

It does seem strange at first that Nature's speed limit is so slow. But if you think about it, there are really two options: the universe is most likely to be either very large or very small compared with the speed required to cross the universe during its lifetime. (The fine-tuned case, where the universe is exactly big enough for light to cross it once during its life, would be true only briefly before evolving to "very small.") The Earth is very small compared with this limit, which is what we are "used to"; a not-too-extraordinary person can now circumnavigate the Earth many times during his own life. It's certainly possible to imagine a universe that's similarly small: look off in a particular direction and, far away, you see the back of your own head. But that doesn't seem to be the case. I'm not completely sure it makes sense to be surprised by the "sluggishness" of light; I think that the alternative would probably be even stranger.
posted by fantabulous timewaster at 5:25 AM on August 23, 2012

I know that light slows down when it goes through denser materials, like water or glass or diamond. My uninformed thought is that light goes the speed it does in space because space has density too. It just has less density than anything else. The density of space is various gravitational fields and other stuff we can't see? Dark matter? Anyway.

If we somehow figured out how to "clear out" empty space so that there weren't any light-slowing fields in it, would light go faster? Like if your perception of the speed of light is how fast light goes in a chunk of diamond, then you get rid of the diamond WHOA NELLY light is going 2.5x faster!

Would that be the answer to "faster than the speed of light in a vacuum" travel? Just get rid of the fields in the vacuum! So easy.

I'm just making shit up here, thinking out loud.
posted by seanmpuckett at 6:30 AM on August 23, 2012

seanmpuckett, it's a pretty sensible thought, but I don't think so. The existence of a speed limit imposed by spacetime is something which you could infer even if you couldn't produce a vacuum. For instance, charged particles can never travel faster than the speed of light in a vacuum, but they can travel faster than the speed of light in a medium (in which case they lose energy by emitting Cherenkov photons. You can work out the ratio of the two speeds from the opening angle of the cone of Cherenkov light, and the speed limit for charged particles in matter is the same as the speed limit in vacuum.

Of course there's an argument that empty space with a Higgs field has less energy than empty space without any Higgs field; I commented about that recently. Does this mean that "clearing out" empty space would make it more dense, rather than less? I don't know.
posted by fantabulous timewaster at 1:40 PM on August 24, 2012