If every country's airspace extended up forever, which country would own the largest percentage of the galaxy at any given time?

Reuven Lazarus

Today's question is adapted from What If 2: Additional Serious Scientific Answers to Absurd Hypothetical Questions, which contains many more What If answers and is available now!

Congratulations to Australia, new rulers of the galaxy.

The Australian flag has a number of symbols on it, including five stars that represent the stars of the Southern Cross.[1] Based on the answer to this question, maybe their flag designers should think bigger.

Countries in the southern hemisphere have an advantage when it comes to star ownership. Earth's axis is tilted relative to the Milky Way; our North Pole points generally away from the galaxy's center.

If each country's airspace extended upward forever, the core of the galaxy would stay under the control of countries in the southern hemisphere, changing hands over the course of each day as the Earth rotates.

At its peak, Australia would control more stars than any other country. The supermassive black hole at the core of the galaxy would enter Australian airspace every day south of Brisbane, near the small town of Broadwater.

After about an hour, almost the entire galactic core—along with a substantial chunk of the disk—would be within Australian jurisdiction.

At various times throughout the day, the galactic core would pass through the domain of South Africa, Lesotho, Brazil, Argentina, and Chile. The United States, Europe, and most of Asia would have to be content with outer sections of the galactic disk.

The northern hemisphere isn't left with the dregs, though. The outer galactic disk has some cool things in it—like Cygnus X-1, a black hole currently devouring a supergiant star.[2] Each day, as the core of the galaxy crossed the Pacific, Cygnus X-1 would enter the United States's airspace over North Carolina.

While owning a black hole would be cool, the United States would also have millions of planetary systems constantly moving in and out of its territory—which might cause some problems.

The star 47 Ursae Majoris has at least three planets and probably more. If any of those planets have life on them, then once a day all that life passes through the United States. That means that there's a period of a few minutes each day where any murders on those planets technically happen in New Jersey.

Luckily for the New Jersey court system, altitudes above about 12 miles are generally considered "high seas." According to the American Bar Association's Winter 2012 issue of the Admiralty and Maritime Law Committee Newsletter, this means that deaths above these altitudes—even deaths in space—are arguably covered by the 1920 Death on the High Seas Act, or DOHSA.

But if any aliens on 47 Ursae Majoris are considering bringing a lawsuit in a US court under DOHSA, they're going to be disappointed. DOHSA has a statute of limitations of 3 years, but 47 Ursae Majoris is more than 40 light-years away...

...which means it's physically impossible for them to file charges in time.

[1] Epsilon Crucis has five points, while the others have seven, implying that the view of Epsilon is from a telescope with different lens geometry from the others. Minor symbolic/graphic design choice? Or clue to a secret multiversal alliance between parallel universe Australias? No way to know for sure!

[2] Cygnus X-1 was the subject of a famous bet between astrophysicists Stephen Hawking and Kip Thorne over whether it was a black hole or not. Hawking, who had spent much of his career studying black holes, bet that it wasn't. He figured that if black holes turned out not to exist, at least he would win the bet as a consolation prize. In the end, luckily for his legacy, he lost.

Losing Steve affected me more than it probably should have, given that I never met him or had any correspondence with him.

But losing him was devastating — not just to my world, but the world.

He was a sort of virtual father figure: I was always hoping that maybe Steve would notice something I did.

We all wanted his attention and approval, and that drove us to do better work — even those of us who never worked at Apple.

Nobody replaced him in this role. Nobody can.

But as an outsider who had no personal relationship with him to mourn, it has been most depressing to consider how much of his work the world missed out on.

He wasn’t taken from us after a long, complete life — he was taken in his prime.

He had so much more to offer the world.

A few days ago, on Twitter (oh, dear Twitter: whatever happens I’ll be there as long as possible – if you care about people that put a lot of energy in creating it, think twice before leaving the platform). So, on Twitter, I was talking about a very bad implementation of linked lists written in Rust. From the tone of certain replies, I got the feeling that many people think linked lists are like a joke. A trivial data structure that is only good for coding interviews, otherwise totally useless. In a word: the bubble sort of data structures. I disagree, so I thought of writing this blog post full of all the things I love about linked lists.

So, get ready to read a sentimental post about a data structure, and don't tell I didn't warn you.

Linked lists are educational. When your teacher, or the page of a book, or anything that exposes you for the first time to linked lists shows you this little circle with an arrow pointing to another circle, something immense happens in your mind. Similar to what happens when you understand recursion for the first time. You get what data structures made of links truly are: the triviality of a single node that becomes a lot more powerful and complex once it references another one. Linked lists show the new programmer fundamental things about space and time in computation: how it is possible to add elements in a constant time, and how order is fundamentally costly, because if you want to insert an element “in place” you have to go from one node to the other. You immediately start thinking of ways to speed up the process (preparing you for the next things), and at the same time you understand, deeply, what O(1) and O(N) really mean.

Linked lists are augmentable. Add a pointer to the previous element, and now it is possible to go both sides. Add “far” pointers from time to time, and you have a skip list with completely different properties. Change every node to hold multiple items and your linked list becomes unrolled, providing very different cache obviousness properties. Linked lists can be embedded, too. The Linux kernel, for instance, has macros to add a field to any structures in order to link them together. There is more: linked lists are composable. This is a bold property: you can split a linked list into two in O(1), and you can glue two linked lists in O(1) as well. If you make judicious use of this property, interesting things are possible. For instance, in Redis modules implementing threaded operations, the thread processing the slow request dealt with a fake client structure (this way there was no locking, no contention). When the threaded command finally ended its execution, the output buffer of the client could be glued together to the actual buffer of the real client. This was easy because the output buffer was represented with a linked list.

Linked lists are useful: Redis can be wrong, but both Redis and the Linux kernel can’t. They are useful because they resemble certain natural processes: adding things in the order they arrive, or in the reverse order, is natural even in the physical world. Pulling items incrementally is useful too, as it is moving such items from head to tail, or moving them a position after the current one.

Linked lists are simple. It is one of those rare data structures, together with binary trees and hash tables and a few more, that you can implement just from memory without likely stepping into big errors.

Linked lists are conceptual. A node pointing to itself is the most self centered thing I can imagine in computing: an ideal representation of the more vulgar infinite loop. A node pointing to NULL is a metaphor of loneliness. A linked list with tail and head connected, a powerful symbol of a closed cycle.

For all those reasons, I love linked lists, and I hope that you will, at least, start smiling at them. Comments