All this talk of aliens and the Fermi Paradox got me to thinking about a concept that kept me up at night for years… until I got to college and figured out the difference between what we call the “observable universe” and the probable absolute-ish universe. I’d like to take the time to draw that distinction for you, now. The Fermi Paradox was conceived within and assuming the bounds of the observable universe (for that matter, it generally just assumes our own galaxy, but on the outside I have seen instances where it was the entire observable universe included in the calculation (which is a little disingenuous as an argument as you’ll soon see)). Understanding how big the universe actually is, even conservatively, makes the Fermi Paradox all the more mind blowing. So in this post we’re (royal) going to cover some really huge shit. If you don’t feel like an insignificant spec of dust now, you don’t know frak-all about your observable universe. …but consider this: perspectives and scales exist in our reality beyond the observable universe. Our entire observable universe is, in fact, an insignificant spec of dust itself.
Normally that would be my segue to installing a “so what the frak is the observable universe”-like header tag in this space, and proceeding to detail the universe we generally talk about in news articles and scientific books and papers. …but this is my damned blog, and I think first, in all fairness to the reader, I need to smack you down to size in terms of galactic scale. After we get through that part, I’ll get into the observable universe, and then after THAT, we can talk about what lies beyond. Sound fair? …as if I care. This is my boat. We’ll go where I want. …actually though the reason I’m doing this is because, for me anyway, it’s very difficult to fathom the sheer vastness of the observable universe. If I’m going to talk about what lies beyond in a way that can be meaningfully conceptualized by anyone, I can’t take the chance of marginalizing or depreciating it’s scale from the outset. The thrust of this post would be rendered meaningless if I did. Like so many of the best things in life, we’re going to take our time and build this up carefully, so the mind-blowing payoff at the end has maximum impact.
Banana For Scale
So how big is big? Well… it’s relative. The Sun seems pretty big. Let’s start there. Our home planet is 7,917 miles across. The Sun is 864,938 miles across. That’s a lot bigger. For perspective, at the average rate my Jeep has accrued miles since it was built (and granted, that rate has been significantly bumped up since I bought it used, but we’ll ignore that for simplicity’s sake), I will drive the distance of the diameter of the Earth (that’s as the heavily laden subterranean crow flies THROUGH the Earths core, not around) in about 8 months, whereas it would take a little over 73.3 years to drive through the Sun (again, the diameter). (Just FYI, it would take 7,890 or so years to drive to the sun… that’s how far away it is! …but MY Jeep wouldn’t make it another 2 years, truth be told. I can’t even drive to the moon… *sigh*) When our solar system formed, the system was like a pinball gallery of planets. Some were ejected entirely from our solar system and roam galactic space han solo, as unattached frozen worlds. (Interesting to think about how many out there… a Neptune-size planet could come shooting through our solar system from above or below the plane and we’d probably not see it coming until it was already here… rogue planets deserve their own blog post, but I digress.) A lot of those planets fell into the Sun. So… it got big. When you’ve really let the staggering size of our Sun sink in, watch the video below.
The takeaway: Despite the sheer hugeness of our Sun, there are other stars that absolutely dwarf it. The solar system itself is pretty big too. The video I’ve linked below is a pretty complete and concise explanation of our star system’s size.
The size of our solar system is restricted by it’s collective mass and our Sun’s power output. Some star systems stretch out far further, as you might deduce from the star comparison video. Our Galaxy, the Milky Way, contains about 200-400 billion stars. The Milky Way is about 100,000 light years across and 1000 light years “thick”. Banana for scale, light takes about 8 minutes and 20 seconds to reach Earth from the surface of the Sun. It turns out, though, that our galaxy ain’t all that when it comes to size. Sure, it’s cannibalized a few dwarf galaxies, but in around 4 billion years the neighboring Andromeda galaxy (220,000 light years across, at least twice the number of stars in lower bound estimates) is going to cannibalize us. (As another aside, I wish I could be there to see it. There will be spans of hundreds of millions of years whereby you would be able to read a book by starlight were the Earth not getting consumed by the sun at that time. Space will look so cool… from Mars.)
We’ve come a long way, dear reader. Figuratively and literally. Simply comparing the Milky Way to our closest significant neighbor is not enough for where we’re going though, so let’s talk about the biggest galaxy we’ve detected so far (remember: there’s always a bigger galaxy): IC 1101. This thing is a beast. 6 million light-years across. Over 100 fraking TRILLION stars, just in this galaxy.Galaxies can get pretty big. They can contain a lot of stars… many of which foster far larger star systems than our own. …and the thing is, there are a LOT of galaxies out there. Lower bound estimates of the number of galaxies in our observable universe suggest there are at least 225 billion large galaxies, but that number is probably higher. Astrophysicists typically prefer to err on the conservative side. Having touched on the scale of galaxies, we can now move on to the vast distances between them, and the still larger structures collections of galaxies form.
Intergalactic filaments (also called supercluster complexes, galaxy walls, and galaxy sheets) are the largest known structures in the observable universe. They are massive, thread-like formations, with a typical length of 150 to over 300 million light years, that form the boundaries between large voids in the universe. Filaments consist of gravitationally bound galaxies and so-called “Dark Matter“. Areas where a large number of galaxies are very close to each other (in cosmic terms) are called superclusters. I’ve already made a post with the video demonstrating the scale and structure our own supercluster, Laniakea. Feel free to click here to check it out. It’s useful in demonstrating the “flow” of galaxies through these filaments. One thing to note, however, is that the model depicted in that video DISCOUNTS the expansion of space-time. That’s something I’ll come back to when describing the observable universe. It’ll be important to understand space-time expansion when thinking about what lies beyond. One thing they don’t mention in that video is that the Laniakea Supercluster is actually being drawn towards the Shapley Supercluster as well. Even these macro cosmic structures are all interacting and shaping one another. That’s certainly worth noting, because there is strong evidence suggesting our entire observable universe is being manipulated by forces we may never be able to directly observe (in fact, our current laws of physics state quite explicitly that we will NEVER be able to directly observe these phenomena… but I’ll come back to that later). The video below represents the Sloan Digital Sky Survey, which provides a 3-dimensional map of about a million galaxies and quasars. As the survey progresses, the data is released to the scientific community and the general public in annual increments. As you view the video below, note that the “split” down the middle of the model represents the plane of our galaxy, the density of which is difficult for us to see through. (This is actually the main problem we’re having getting a good look at The Great Attractor, which is surrounded by and possibly made up of a densely packed group of galaxies.)
The video above begins with data from the Sloan Digital Sky Survey and zooms out to reveal data from WMAP (Wilkinson Microwave Anisotropy Probe), which did a microwave background radiation survey of the observable universe. The most distant light that astrophysicists can see comes from the cosmic microwave background radiation survey. These are photons that have traveled to us from nearly the beginning of the universe. Shortly after the Big Bang, the universe was too dense, and therefore too crowded with energy/particle soup, for light to travel very far before it was either scattered or absorbed by a particle. About 380,000 years after the birth of the universe, it became translucent enough that light could travel sorta freely for the first time without hitting anything. The resulting microwave emissions from what was essentially super-hot Hydrogen-based particle soup is the hard limit of what we can ever hope to see in any direction we point our telescopes. The cosmic microwave background is like a wall that we can never see beyond. There simply wasn’t anything to be “seen” before that. That brings us to…
So What The Frak Is The Observable Universe?This gets a little tricky. The observable universe is what people are generally talking about when they use the phrase “The Universe”. It’s also referred to as the Hubble Volume. Astronomers have measured the age of the universe to be about 13.7 billion years old. Because of the constant between distance and the speed of light, it stands to reason that we can theoretically look at a region of space that lies 13.7 billion light-years away. …so we should be able to see the whole universe, right? Not even fracking close, yo. ‘cuz… ya know… “time.” As mentioned above and illustrated on the right, the WMAP survey shows the cosmic microwave radiation background at a diameter of 13.7×2 or 27.4ish billion light years approximately 380,000 years after the Big Bang. First of all, we need to know how big the universe actually was at 380,000 years old… and we don’t. I mean we can’t even ballpark it. Are you ready to get loco, essay? The singularity that spawned the big bang is described as being infinitely dense and expanding exponentially. Infinity is a really big number. Adding an exponent to it is almost meaningless, when you think about it. Thus, at 380,000 years, the mere blink of an eye in cosmic terms, the universe may have already been infinite. Another way to say that is that space-time started out in an infinitely large state, and the “Big Bang” happened everywhere at once. Crazy as it sounds, that’s NASA’s take on it at present. …but I’m getting ahead of myself here. Let’s just focus on the observable universe for now. So at 380,000 years we had a 13.7ish billion light-year radius in which light could ever possibly reach us. These are the first photons that could reach us… the initial Hubble Volume. …but that was 13.7 billion years ago. While the initial sphere appears over 27 billion light-years in diameter, it is far larger larger than that today. Let’s take a feature at the very edge of that initial Hubble Volume, and say that it has a photon leaving it in our direction TODAY. We know that the universe is expanding, and that that expansion is now accelerating. While scientists might see a spot that lay 13.7 billion light-years from Earth 380,000 years after the Big Bang, the universe has continued to expand over its lifetime. Today, that same spot is 46 billion light-years away, making the diameter of our original observable universe a sphere around 92 billion light-years across. That little photon leaving today will never reach us. Yes, if it had left 13.7 billion years ago it could have (barely), but the effect of space expanding BETWEEN us and that photon means that in 46 billion years, when that photon OUGHT to have reached us, it will actually have further to go to get to us than the day it left the edge of, what was once, the edge of the observable universe. What this means is that objects at the edge of the WMAP image to the right are presently moving away from us faster than the speed of light in relative terms (they are not traveling through space faster than the speed of light, rather, space is effectively expanding at a rate, relative to us and the object, that is faster than the speed of light when you only consider the rate of increasing distance between Earth and the object). In effect, this means as time passes we can see less and less of what was formerly the observable universe. Moreover, as the expansion of space-time accelerates, the incidental distance from us to the edge of the observable universe becomes shorter and shorter. It’s a little unnerving. The walls man…. it’s like the walls are closing in on me! It’s not “like” that. It is that.
The video below explains this phenomena graphically. Ignore the annoying-as-hell narration, stuttering, and fuck-ups (his numbers get off a bit and he doesn’t take some things into account, but conceptually with regards to space expanding you get the idea). He’s a horrible presenter, but it should make what I’ve described a little easier to grasp in the case that I haven’t been clear.
It bares mention that what you see when you look up at the stars at night is NOT “the observable universe”. In fact, you might be surprised to know just how little of the universe you can see with your naked eye. The observable universe is simply the theoretical limit of how far away a photon could ever reach us given the accelerating expansion of space-time. In fact, and this is probably another digression, you can see very little when you look up. It’s not exactly distance, but rather the luminosity of the object you’re looking at that limits your vision. For instance, you can see the Andromeda Galaxy, and that’s over 2.5 million light-years away. However, the majority of the stars we see in the night sky are limited to a very “small” chunk of our galaxy. Click the image to the right for a larger view.
Beyond The Outer Rim, We Go With The Dark Flow
I should say this again: the observable universe is generally what people are talking about when they say “The Universe.” Scientists don’t like to speak about things that cannot be observed, generally. Some others don’t make the distinction between the observable universe and that which lies beyond, and so when they use the phrase, they really just don’t know what they are talking about. Now you do. That was all I really wanted to establish with you. What we can say absolutely, assuming the Big Bang theory is correct, is that there is a lot more universe out there than what we will ever be able to see from the vantage point of Earth. There is a lot more space… far more galaxies, superclusters, and filaments than anyone could possibly imagine beyond the observable universe. If they could imagine it, I suspect the information density in their head would be so great that their head would collapse into a black hole destroying the Earth and probably our whole solar system. …but just for fun, let’s talk about two more things that I think are kind of neat about the space outside of the Hubble Volume: Flat space, and The Dark Flow.
However, before I get into that: a brief rant. “Dark”, as it applies to astrophysics, can just as easily be substituted with “OMGWTFBBQ we don’t know what it is”. That’s true of so-called Dark Energy, which we may as well be calling “The Force” at present (midichlorians are just as likely an explanation as anything at this point); also of Dark Matter, which may or may not be conventional matter (probably not, but who knows; could be peanut butter). We can’t directly detect either. Also: dark energy plus dark matter constitute 95.1% of the total mass–energy content of the universe. As of this writing, our universe is still that mysterious. Right… moving on.
The above is a rather striking statement when you really think about it. Astrophysicists think space might be infinite, with energy, galaxies, filaments, etc… distributed pretty much the same as it is in the observable universe. In fact, that’s the running consensus at the moment. It’s easy to see why this is their thinking, with regard to the uniformity, that is. It is, after all, what we see in the observable universe. I’m personally of the opinion that there’s a huge logical flaw in that. I would liken such a conclusion to focusing solely on a single grain of sand on a beach, and trying to infer from that there’s a city called Miami, Florida 10 miles up the coast. There is now evidence suggesting everything in the observable universe is getting pulled along with what is described as the “
Among other revelations, the data from WMAP revealed a much more precise estimate for the age of the universe — 13.7 billion years — and confirmed that about 95 percent of it is composed of mind-boggling stuff called dark matter and dark energy. WMAP data also helped NASA scientists nail down the curvature of space to within 0.4 percent of “flat,” and pinpoint the time when the universe began to emerge from the cosmic dark ages (about 400 million years after the Big Bang).
Going back to the Dark Flow, in 2008, astronomers discovered galactic clusters were all streaming in the same direction at immense speed, over two million miles per hour. They were comparing present observations of these objects to the data from WMAP (You can read the actual primary paper here, if you’re interested). New observations in 2010 confirmed this phenomenon, known as Dark Flow. This runs contrary to the “uniform universe” thinking. There is NOTHING in the observable universe remotely powerful enough to cause such a phenomena (that we are presently aware of). From this we can infer that *something* is pulling everything in the observable universe in a certain direction, and that *something* is 1) off camera (outside of anything we could ever observe unless someone builds a legit warp or FTL drive) and 2) totally bat-shit crazy. It could be absolutely anything. Whatever it is, we’ve never and will never see anything like it (sans warp). It could be some kind of crazy powerful wormhole, something that makes a super massive black hole look like a fleck of lint, a giant drainpipe to another dimension, another universe bumping into ours… anything. We have absolutely no context for it. …and yet SOMETHING seems to be there. This also suggests that the universe isn’t as conformal as we thought, which again, gives rise to the inevitability of tons of bat-shit crazy stuff we’ll never be able to even infer as existing in our universe once infinity is part of the equation. The graphic below only vaguely hints at it (and rightfully so because OMGWTFBBQ), but it’s still a useful illustration, I think. (One quick note… the “Cosmic Horizon” is the edge of the observable universe as of 13.7 billion years ago. The difference between the current edge of the Hubble Volume and the “Cosmic Horizon” is how much space has expanded in the intervening years. As you can see, most of what was the observable universe 13.7 billion years ago is no longer observable. /sadpanda || I’m noting this because the graphic below suggests that whatever is responsible for the Dark Flow may lie inside the Cosmic Horizon, and there is absolutely no evidence for that. In fact, we have far more evidence suggesting it lies well outside that radius (such an object/phenomena would have shown up in the WMAP survey). I’m sure it’s an unintentional oversight by whomever created that graphic, but it bares mention. If we wanted to get really picky, and I say “why not?”, there should not be any “space ripples” within the Cosmic Horizon at all. Finally, this graphic is obviously not to scale in any way.)
I guess the tl;dr; here is that you should express extreme skepticism when someone says something is “impossible” to you henceforth, especially having the craziness that is our extra-observable universe in mind. Also: space is big. Really big. Also: Star Wars almost certainly happened… a long time ago, in a galaxy crazy far away (except for the shit that broke the laws of physics).
Beyond The Intended Scope Of This Post
Am I sleeping better now knowing this? No. I am not.
Space-time is expanding, and that expansion is accelerating, right? Look at the model of our observable universe. In a few billion years, we’ll only be able to see the few galaxies that are gravitationally bound to us. Kind of a scary thought. It gets worse: let’s assume space-time expansion continues to accelerate at it’s present rate. Eventually space will be expanding beyond the speed of light at any and every scale. Basically, if nothing changes, there will be a vacuum collapse and every atom and electron in the universe will be ripped apart at beyond the speed of light. It may only be 22 billion years away… so despite how eternal our infinite universe feels, the whole sha-bang (Big Bang sha-bang) may only last for a total of 36 billion years or so. Give or take.
In Marcelo M. Disconzi, Thomas W. Kephart, and Robert J. Scherrer’s scenario for w = −1.5, the galaxies would first be separated from each other. About 60 million years before the end, gravity would be too weak to hold the Milky Way and other individual galaxies together. Approximately three months before the end, the Solar System (or systems similar to our own at this time, as the fate of the Solar System 22 billion years in the future is questionable) would be gravitationally unbound. In the last minutes, stars and planets would be torn apart, and an instant before the end, atoms would be destroyed.
That would really suck. …seems like a bit of a waste.
tl;dr; The Dark Flow would be a sweet name for a goth down-tempo electro band.
In other interesting space news…
Why Finding Gravitational Waves Would Be Such a Big Deal [GIZMODO]
NASA Weighs Massive Young Galaxy Cluster [SWR]
THIS MILLENNIAL MIGHT BE THE NEW EINSTEIN [OZY]
”It’s not like a 9-to-5 thing. When you’re tired you sleep, and when you’re not, you do physics.”
~Sabrina Gonzalez Pasterski