Let me be honest, as I write this I am heavily distracted by highlights (and now the closing ceremony) of the Olympics and as such this post won't be quite as substantial as I'd originally intended. If you're not a fan of the Olympics, then you've either never tried to be a fan of the Olympics, or you have no empathy. The point of the Olympics is not that being faster, higher or stronger actually matters, because it doesn't. Of course it doesn't. Nothing changes because of who won what in which event. The point of the Olympics is that despite the overwhelming and terrifying arbitrariness of human existence a group of people have decided to passionately care about something.
The worst sin in life is not to live. Nobody can claim that any Olympian is not living. The passion (and the story) of each and every competitor, is why the Olympics is so enjoyable to watch. And, given the arbitrariness of life, why not passionately strive to be faster, higher or stronger?
But, if faster, higher or stronger isn't for you, pick your own mountains to climb and climb them instead. Then, while you climb, share your journey with the world. And enjoy it when, as has been the case for the last two weeks, the rest of the world shares their journeys with you.
Just make sure you're climbing something!
The Spirit of Exploration
The mountains those of us at this blog are climbing (most of the time) are the Twin Peaks of discovery and understanding. Rather than jumping a little higher or running a little faster we hope to see a little further. Our goal is to explore the unknown wildernesses of existence.
|GB rower, Alan Campbell, being awarded a medal for the first time, at his third Olympic games. He was so exhausted after his race that he had to be carried to the podium. It is impossible to deny the awesomeness of this moment. Image credit: Reuters (apparently).|
I think those of us climbing the Twin Peaks could learn a lot from the world of sports about how to present our journeys. The webcast of the recent Higgs discovery was streamed by more than 400,000 computers (which means even more people than that saw the webcast). It is clear that people care about humanity's Twin Peak expeditions. I see no reason, except inaction, why we shouldn't be able to channel the spirit that is seen in spectators at the Olympics.
The general public cares as much for the spirit of exploration as they do for the spirits of higher, faster and stronger. If you doubt me, you may wish to know/remember how cynical the UK public was about higher, faster and stronger, before the Olympics began. The spirit of exploration is equally present in humanity, it just doesn't get as much encouragement.
To clarify, I don't mean to suggest this blog, or other blogs like it, are how we can capture the same spirit as the Olympics. They're certainly better than nothing, but, in the sports analogy, blogs like this would be the equivalent of an athlete's blog, describing their sport and the methods and rules of their game. The Olympics is much bolder than a humble athlete's blog. I don't see why, as a community, we shouldn't be aiming that high.
The Olympics of space
In any case, those are all just idle-ish thoughts raised in my mind by watching the Olympics. If you agree or disagree with the sentiments, or have anything else to add, please join in by discussing in the comments.
But, what I actually intend on discussing in this post is some physics. I do still intend to sort of take my cue from the Olympics though as this will be the first post in a series about the biggest and most extreme “things” in the universe.
|South Korean fencer Shin A-Lam who, after leading with one second remaining, lost in the épée semi-final as the result of a timing error. She was then forced to wait, on the piste, in full view of the crowd, for more than an hour, while the error was debated. I dare anyone to even contemplate being cynical about the Olympics in front of Shin A-Lam! Image credit: Damir Sagolj/Reuters|
At the end of this series I will try to rank these big and extreme things. Then, humanity can finally answer that vastly important question... “What is the most massive object in the observable universe?” As we'll see though, such a ranking will not be without ambiguity and potential controversy.
The biggest things in the universe
The first problem with discussing the biggest, most extreme things in the universe is the ambiguity present when defining what big means, what extreme means and even what a thing is.
For example, is a thing with a bigger volume “bigger” or is a thing with a bigger mass “bigger”? Is an extremely dense black hole “more extreme” or is a galaxy that is spinning extremely quickly “more extreme”? Is a constellation a “thing”, even though the stars in the constellation aren't really anywhere near each other?
Most awkwardly (and this is something that will turn out to be very relevant in my next post) we can only see each thing in the universe at one particular time, unique to that thing. Light takes time to travel through the universe, so the further away from us something is, the earlier in time we see it. Given that the “bigness” of structures in the universe grows with time, it is very pertinent to ask: what is more extreme, a relatively massive structure that is really far away, or a much more massive structure that is close to us? Anyone who has ever tried to understand the decathlon or heptathlon scoring systems will appreciate that ranking athletes, or objects in the universe, using multiple quantities is tricky (and, inevitably, somewhat arbitrary).
Because it is necessary to start somewhere, I'll start with the biggest things as measured by volume. It is important to point out that none of these “things” are actually distinct objects in the universe. Once you get to large enough distance scales, the structure of the universe starts to resemble a web (in fact, we call it the cosmic web). These “things” I'm about to discuss are actually just pieces of this bigger web that are noteworthy for one reason or another.
|A simulation of the "cosmic web". Is it really possible to make out individual "objects" on scales larger than the inlaid box? Image credit: Nature|
The Sloan Great Wall
If medals were being handed out for sheer size in the cosmic web, the Sloan Great Wall would win today's Gold. This thing is huge. It was found in 2003 by the Sloan Digital Sky Survey, which was a very thorough (relative to what had come before) optical survey of the sky.
The Great Wall itself measures 1.4 billion light years in length. To clarify, that is the length it had when the light we see from it was emitted. If we could see how it looks today, because of the expansion of the universe, it would in fact be even bigger at 1.5 billion light years. In other words, it has grown by 100 million light years since the image we see of it was made. 100 million light years is about 1000 times the width of the Milky Way galaxy. 1.5 billion light years, however, is about 15,000 times the width of the Milky Way. That means you could fit approximately 15,000 Milky Way galaxies into the Sloan Great Wall!
CfA2 Great Wall
The “Great Wall” with a much more stereotypical sciencey name is the CfA2 Great Wall. It was discovered much earlier, in 1989, by the CfA redshift survey, and would win the Bronze medal on today's reckoning. This wall is quite cute, because when you look at it in the right way it resembles a stick figure!
This dude is “only” 500 million light years long, which means you could fit about three CfA2 stick people into one Sloan Wall if you really squashed them together hard. One day in the future I expect a cult to form around this super-structure, it is clearly a message, sent to us (the stick figures) from some alien civilisation. I'm, not sure yet what it says though.
Pisces-Cetus Supercluster Complex
The Silver medal for enormous objects in the cosmic web that are “visible from Earth” goes to an object that should be dear to all of you. This is the Pisces-Cetus Supercluster complex. This giant monster is at least 1 billion light years long. This means it could contain at least 10,000 Milky Way galaxies.
In reality, however, it contains just one!
That's right, the monster Silver medal winning superstructure is our very own monster. Our lovely planet is located inside a solar system that is inside the Milky Way galaxy. This Milky Way galaxy, along with its buddy Andromeda, is inside a galaxy cluster imaginatively named The Local Group. The Local Group is very near to the rather large Virgo Cluster of galaxies (though not quite inside it). The Virgo Cluster gives its name to the Virgo Supercluster that both Virgo and the Local Group are members of. And, the Virgo Supercluster finds itself, with a bunch of other superclusters, lying somewhere near the middle of what astronomers have decided is its own separate object, the Pisces-Cetus Supercluster Complex.
So, the next time you're writing your address, don't forget to add Pisces-Cetus Supercluster Complex at the bottom, or your friends in the Sloan Great Wall might send it to the wrong solar system in the wrong galaxy. Believe me, the extra care is worth it, the re-direct service takes many years!
Honourable mentions for VOBOZ and ZOBOV
I want to stress again that the classification of what is or isn't an “object” at these very large distance scales is extremely arbitrary. I've mentioned three “objects” and given them pretend medals, but a different set of astronomers on a different planet in the Milky Way would probably settle on a different set of visible “objects” at these large scales. In reality, the universe on these scales is all just one big web of filaments, pancakes and clusters. As such, don't read too much into the actual rankings, or even distances quoted, above. Where the “edge” of each of these objects is, is quite arbitrary. They exist as distinct things simply because some astronomer, at some point, has labeled them as such.
Given the extreme arbitrariness of this classification I couldn't help but decide to add honorable mentions for the set of over and under-densities found by the VOBOZ and ZOBOV algorithms that I mentioned in this post (actually, in that post I never named the algorithms). These regions are just as distinct as separate identities as any of our three medalists above and aren't really that much smaller in volume. They also have the added significance that they have much more, or much less, matter in them than similarly sized regions. And, their effect on the CMB seems to be providing a bit of tension with the standard cosmological model, which means they definitely deserve an honorable mention!
What about the actual objects?
Is it always so arbitrary to define objects in the cosmic web? Thankfully, no. As I mentioned in one of my first posts at this blog, as the universe expands, the over-dense regions gradually become more over-dense. They don't necessarily gain additional matter, but, because the universe is expanding, if they expand more slowly they become relatively more dense. Once a region becomes sufficiently over-dense it stops expanding and undergoes gravitational collapse. Every solar system, galaxy or cluster of galaxies has undergone this collapse.
Once a region has collapsed it becomes much less arbitrary to define it as a distinct object. Loopholes and minor ambiguities do remain concerning precisely where the edge of an object is. Also, occasionally two objects can partially overlap, or be in the process of merging. But, nonetheless, it is still mostly possible to isolate distinct structures in the universe once they have collapsed.
In the rest of this series of posts I will be discussing some of the bigger, more interesting, collapsed objects in the universe. At different points in the universe's history the biggest collapsed objects that we can see looked quite different (don't forget that by looking further away we look further into the past). In the very next post, I will start with galaxy clusters, which are the biggest collapsed objects in our near vicinity. I introduced them in that earlier post, but didn't discuss any specific clusters except for the Local Group, which is the biggest bound structure that we are inside, but is a particularly little cluster compared to some of the absolute monsters we've now found.