I have another blog that doesn't suck. Archive:
Comments disabled 
The most common picture of Carl Gauß depicts him wearing a black velvet cap. It is a pretty coollooking cap, and I wonder if there isn't a small opportunity to sell math people black velvet caps like Gauß. The same opportunity does not exist for Euler, whose most common depiction appears to have just gotten out of the shower, and to be wearing a bathrobe and to have a towel wrapped around his head.\
I was going to write something about the ordinal number !!ω^ω!!, but then I got bogged down in a lot of blather about wellorders and smaller ordinal numbers. I asked folks in Recurse Center if this article was interesting and they very genrly and constructively said it was not. So I am publishing it here. Caveat lector Wellfounded ordering is a fundamental idea in set theory, the basis of all inductive arguments. The idea of a set with a wellfounded ordering is that if you start somewhere, and the moved to an element of the set that is “smaller” in the ordering, and then do it again and again, you must eventually get stuck at an element for which there is no “smaller” element. The prototypical example of a wellfounded ordering is the ordinary !! \lt !! relation on the natural numbers. You can't keep passing from one natural number to a smaller one without eventually getting stuck at !!0!!. And the prototypical example of a not wellfounded ordering is the ordinary !! \lt !! relation on the integers, because you can move to !!1!!, then !!2!!, then !!3!!, and you never do get stuck. Or for a slightmy more subtle nonexample, the ordinary !!\lt!! relation on the positive rational numbers, whre you can go !!1, \frac12, \frac13, \frac14,\ldots!! and you still never do get stuck. To see the relationship with inductive arguments, think of induction as working this way. In an inductive argument you say well, if the claim were false for some large example it would also be false for a smaller example, then also for an even smaller one, and you could keep going like that until you got down to a trivial example, but the claim is easy to verify for the trivial examples, so it must be true for the large ones also. To work, the notion of "smaller" has to guarantee to end at a trivial example after a finite number of steps, and that's what "wellfounded" gets you. There are lots of examples of wellfounded orders of the natural numbers that aren't the usual !!\lt !! relation. The simplest nonstandard one is:
$$ 0\prec 1\prec 2 \prec 4 \prec 5 \prec \ldots \prec 3 $$ We use the symbol !!\prec!! instead of !!\lt!! to remind ourselves that this is something like but not the same as the usual lessthan relation. It doesn't have to be !!3!! that is out of line, it doesn't matter. I just picked !!3!! to emphasize that the choice was arbitrary. This is not just a simple renaming of the natural numbers, because in the usual ordering there is no largest number, and here there is a largest number, namely !!3!!. But the order is still wellfounded. Even if you start at !!3!!, the first time you move to a smaller number, it's some other finite number and at that point you can be sure that the process can't go on forever. You can move from !!3!! down to !!1000007!!, but from there you have at most !!1000007!! moves before you are certain to get stuck at !!0!!. The way I presented this ordering is a little bit odd to set theorists, because set theorists have a standard set of names and notations for different wellfounded orders. The ordinary natural numbers one is called !!\omega!!. The one above, which is like !!\omega!! except it has one extra element on the end, larger than the others, is called !!\omega + 1!!. Instead of describing it the way I did, with !!3!! pulled out of line and stuck at the end, set theorists usually call that largest element “!!\omega!!” and write it like this: $$ 0\prec 1\prec 2 \prec 3 \prec 4 \prec 5 \prec \ldots \prec \omega $$ It's the same thing, just with slightly less silly names. But it's important to remember that something like !!\omega + 1!! describes a perfectly welldefined ordering relation that could be put on the ordinary natural numbers, not the usual ordering but no less legitimate. Of course you can add more than one big element on the righthand end; those orderings are !!\omega+1, \omega+2,!! and so on. You can even add an infinite number of elements on the right. Suppose we take two copies of the natural numbers, one painted blue and one painted green. Then we define the following order:
Now we have this ordering: $$ \underbrace{ \color{darkblue}{0} \prec \color{darkblue}{1} \prec \color{darkblue}{2} \prec \color{darkblue}{3} \prec \ldots }_{\text{blue numbers}} \prec \underbrace{ \color{darkgreen}{0} \prec \color{darkgreen}{1} \prec \color{darkgreen}{2} \prec \color{darkgreen}{3} \prec \ldots }_{\text{green numbers}} $$ If we don't like using paint, we could phrase it like this:
$$ \underbrace{ 0 \prec 2 \prec 4 \prec 6 \prec\ldots }_{\text{even numbers}} \prec \underbrace{ 1 \prec 3 \prec 5 \prec 7 \prec\ldots }_{\text{odd numbers}} $$ The standard name for this is !!\omega + \omega!! or !!2\cdot\omega !! and the elements are usually written like this: $$ 0 \prec 1 \prec 2 \prec 3 \prec\ldots \prec \omega \prec \omega+1 \prec \omega+2 \prec\ldots $$ I like to think of !!\omega!! as a game in which there is a track of squares extending forever to the right. The leftmost square is labeled !!0!!. One one square there is a penny. Two players play a game in which they take turns moving the penny to the right some number of squares. If a player moves the penny to !!0!!, they lose. Must the game come to an end, or could it go on forever? Clearly it must come to an end, even though the track itself is infinite. If the penny starts on square 1000007, the game can't possibly last more than 1000007 moves. (As a game this is no fun at all, since the first player can immediately move the penny to square !!1!!, but I'm only interested in whether the game will end.) !!\omega+1!! is the game where, instead of starting somewhere on the track, the penny starts in player 1's pocket, and their first move is to take it out and place it on one of the squares of the track. Again the game must come to an end, although unlike in the previous case we can't say ahead of time how long it will take. If we say “no more than 1000007 moves”, player 1 can belie us by taking out the penny and placing it on square 2061982 instead. But what we can say at the beginning of the game is “I can't tell you now how long the game will take, but I will once Player 1 makes her first move.” For !!2\cdot\omega!! I like to think of two tracks, one above the other. Now a player has two kinds of move:
Again Player 1 begins the game by taking the penny from her pocket and placing it on any square. If the penny is on square 1000007 of the top track, I can't tell you how long the game will take to end. But I can say “I will tell you how much longer the game will take, not right now but after no more than 1000008 moves from now.” Because after 1000007 moves, either someone will have moved the penny to the lower track, and I can tell how long the rest of the game will take, or the penny will have moved left 1000007 times and be on the leftmost square of the top track and the next move must take it to the lower track. And if the game hasn't started yet, I can't yet tell you when I will be able to say how much longer the game will take. But I will be able to do that once Player 1 has made her first move and put the penny on the board. This reminds me of an anecdote I once heard from another programmer. He told me his boss had come to him to ask him if he could do a certain task; he had replied that he could, and the boss had asked him how long he thought it would take.
And they parted amicably, both parties satsified, at least for the time being. Communication between management and engineering doesn't always turn out so well! In that programmer's game, there were three tracks, and the penny was on the second space on the topmost track. He was playing the game !!2\cdot\omega + 1!!. At most two days later, the penny had moved to !!\omega + n!!, where !!n!! was how long it would take him produce his estimate of the project timeline. It's easy to add more tracks. Let's add an infinite stack of tracks, one atop the other. Now when Player 1 takes the penny from her pocket she can put it on any space on any track. Again, a legal move is to move the penny left on the same track, or to any space on any lower track. How long before you can say how long the game ends? Human language is not wellsuited to this guarantee.
Is the game really guaranteed to end? Yes, it really is. After Player 1's first move, the penny is on some square of some track, say square !!n!! of track !!m!!. After at most !!n+1!! moves, the track number !!m!! must decrease. And then there can only be a finite number of moves before it decreases again. And it can decrease at most !!m!! times before the penny is on the bottom track, and then the game must end after a bounded number of moves. This ordering is called !!\omega^2!!. A penny on square !!n!! of track !!m!! is said to be at !!m·\omega + n!!. If we want to think about a way to order the natural numbers with order type !!ω^2!!, we can do it like this:
Written out explicitly, the ordering looks like this: $$\begin{array}{l} 0 \prec \\ 2^0\cdot 1 \prec 2^0·3 \prec 2^0·5\prec 2^0·7 \prec\ldots \\ 2^1\cdot 1 \prec 2^1·3 \prec 2^1·5\prec 2^1·7 \prec\ldots \\ 2^2\cdot 1 \prec 2^2·3 \ldots \end{array} $$ or if you prefer $$\begin{array}{l} 0 \\ \prec 1 \prec 3 \prec 5 \prec 7 \prec \ldots \\ \prec 2 \prec 6 \prec 12 \prec 24 \prec \ldots \\ \prec 4 \prec 12 \prec 20 \prec 28 \prec \ldots \end{array} $$ Well, none of that was actually what I planned to write about, but I am going to stop here and continue tomorrow.
The Sun loves looking down and seeing the mortals scurrying about like germs, busy at our daily activities. But she's a little bit sad because she doesn't know much about what we do at night. She has never seen a latenight movie and has not even imagined sitting around a campfire, toasting marshmallows and singing songs. One day the Sun was granted her wish to spend a night on Eartha. Just at sundown she was transformed into a woman. She had dinner at a jazz club, then went out to a cocktail bar where she met a new friend. They went out for midnight supper and then went back to the friend's apartment. Just before dawn she kissed her new friend and returned to her work, content.
All numbers are finite, but some numbers are more finite than others.
Famous sisters Gloria Steinem and Media Steinem.
How sure are we that the bluetongued skink and the bluetailed skink aren't the same animal walking in different directions?
Does MODOK need to shave? Does he blow his nose? How? He can't reach it. Now I picture the hapless AIM scientist who has to attend MODOK with an enormous spotted hanky when he catches cold.
In Serbian, Croatian, and other Slavic languages, srp (or ср̑п) means a sickle. And sȑpskī (ср̏пскӣ) means the Serbs or the Serbian language. But it's Croatia, not Serbia, that is actually sickleshaped.
Therapist: You're a very judgmental person. Me: That's because is good to be judgmental Me: Most people should be more judgmental actually Me: I don't know what the fuck is wrong with them all
According to Ozy Brennan, quoting from I'm Perfect, You're Doomed:
Isn't that curious? The U.S. federal court system does it the other way around: there are 13 “circuits”, each of which is divided into “districts”. For example, the Third Circuit comprises the District of Delaware, the District of New Jersey, and three districts in Pennsylvania. What do you suppose it means? Coincidence?? Conspiracy??¿? Other notreallyrelated mysteries: Why Oklahoma?:
Going down to the basement today I realized that this could actually be reasoned out, maybe. Every finite field has the form !!GF(p^n)!! for some prime !!p!! and some number !!n!!. There is not much to distinguish finite fields, they are all pretty much the same. Except maybe you could distinguish the !!n=1!! cases from the !!n>1!! cases, those are a little different. Aha, but if you consider the !!n=0!! case, the answer becomes clear.
I don't know why a voice in my head kept demanding to know what was the worst finite field. But I couldn't stop thinking about it, until I realized the answer: It's clearly !!GF(1)!!.
Select !!x, y, !! and !!z!! uniformly at random. Then discard the selection and start over unless !!x^2+y^2+z^2=1!!.
It's 2023! Is Groupon dead yet?
I quit twitter before it was cool.
Last night I dreamt that I was explaining to someone how to solve a certain math problem. I said you shouldn't consider the situation as an ongoing process, but instead imagine it as a fullyrealized decision tree, and then apply the DavisPutnam algorithm. In the dream someone spoke up from across the room: “You mean the DavisPutnamBrown algorithm.” “What??” I exclaimed in mock surprise. “Next you are going to tell me that Bunyakovsky discovered the CauchySchwarz inequality!” Tell me, Dr. Freud, what does this mean?
It's not enough to make the coffee, you also have to drink it.
In many Christian communities, it is traditional to eat cheese on Holy Saturday, to commemorate the day Jesus spent ripening in a cave.
As far as I can tell there are no octahedral cathedrals. Why not? Google search produces several claimed examples, such as the Cathedral of San Flaviano in Giulianova. But photographs make clear that this is actually an octagonal cathedral, actually an octagonal prism surmounted by a dome. Similarly, St. Basil's cathedral in Moscow has a floor plan with a roughly eightfold symmetry, but is not octahedral in any way. Polyhedral buildings are common, but the space is dominated by cuboids. Even the Kaaba in Mecca, despite its name (“cube” in Arabic) and its enormous religious significance, is only approximately cubical, visibly irregular. The Egyptians famously made pyramids but they are all pentahedral. none is a tetrahedron, much less a regular tetrahedron. A regular tetrahedron is too steep for practical construction anyway; the Egyptians had bad experiences with overlysteep pyramids. It should not be too hard to make a building in the shape of a regular octahedron, considered as a triangular antiprism. I would be surprised if there weren't one somewhere. When I am King of the World, there will be an octahedral cathedral or someone will have brief but very uncomfortable conversation with me about their failure. Also, where the hell is my Sonar Taxlaw fanfic?
[ This had been sitting unpublished on the other blog for six months. It has now been weighed in the balanc e and found wanting. ] If a billion is a thousand millions, and a trillion is a million millions, how much is a pavillion?
Surely someone must already have discussed the Brazilian cotillion in the vermillion pavilion, it's too hard to miss. (There is a joke about how George W. Bush, upon learning that four Brazilian miners were trapped underground, asked how many a Brazilian was.) [ Previously ]
If the laws of physics are timesymmetric, why do I always have to preheat the oven, and never postheat it?
Sid Vicious, clearly. In fact I think I'd be comfortable nominating the Sex Pistols as the worst band, overall. The world is full of obnoxious and incompetent bands. What gives the Pistols the prize is their insistence that they represented authenticity — maybe they hated you, but at least you knew it. This insistence, though, was itself nothing but a pose, manufactured by them and Malcolm MacLaren.
It's 2022! Is Groupon dead yet?
Pretty pleased with myself today for spelling “Aung San Suu Kyi” without having to look it up.
