Category Archives: Uncategorized

Understanding Global Warming Scale Issues

Aside from the endless stream of Cantor cranks, the next biggest category of emails I get is from climate “skeptics”. They all ask pretty much the same question. For example, here’s one I received today:

My personal analysis, and natural sceptisism tells me, that there are something fundamentally wrong with the entire warming theory when it comes to the CO2.

If a gas in the atmosphere increase from 0.03 to 0.04… that just cant be a significant parameter, can it?

I generally ignore it, because… let’s face it, the majority of people who ask this question aren’t looking for a real answer. But this one was much more polite and reasonable than most, so I decided to answer it. And once I went to the trouble of writing a response, I figured that I might as well turn it into a post as well.

The current figures – you can find them in a variety of places from wikipedia to the US NOAA – are that the atmosphere CO2 has changed from around 280 parts per million in 1850 to 400 parts per million today.

Why can’t that be a significant parameter?

There’s a couple of things to understand to grasp global warming: how much energy carbon dioxide can trap in the atmosphere, and hom much carbon dioxide there actually is in the atmosphere. Put those two facts together, and you realize that we’re talking about a massive quantity of carbon dioxide trapping a massive amount of energy.

The problem is scale. Humans notoriously have a really hard time wrapping our heads around scale. When numbers get big enough, we aren’t able to really grasp them intuitively and understand what they mean. The difference between two numbers like 300 and 400ppm is tiny, we can’t really grasp how in could be significant, because we aren’t good at taking that small difference, and realizing just how ridiculously large it actually is.

If you actually look at the math behind the greenhouse effect, you find that some gasses are very effective at trapping heat. The earth is only habitable because of the carbon dioxide in the atmosphere – without it, earth would be too cold for life. Small amounts of it provide enough heat-trapping effect to move us from a frozen rock to the world we have. Increasing the quantity of it increases the amount of heat it can trap.

Let’s think about what the difference between 280 and 400 parts per million actually means at the scale of earth’s atmosphere. You hear a number like 400ppm – that’s 4 one-hundreds of one percent – that seems like nothing, right? How could that have such a massive effect?!

But like so many other mathematical things, you need to put that number into the appropriate scale. The earths atmosphere masses roughly 5 times 10^21 grams. 400ppm of that scales to 2 times 10^18 grams of carbon dioxide. That’s 2 billion trillion kilograms of CO2. Compared to 100 years ago, that’s about 800 million trillion kilograms of carbon dioxide added to the atmosphere over the last hundred years. That’s a really, really massive quantity of carbon dioxide! scaled to the number of particles, that’s something around 10^40th (plus or minus a couple of powers of ten – at this scale, who cares?) additional molecules of carbon dioxide in the atmosphere. It’s a very small percentage, but it’s a huge quantity.

When you talk about trapping heat, you also have to remember that there’s scaling issues there, too. We’re not talking about adding 100 degrees to the earths temperature. It’s a massive increase in the quantity of energy in the atmosphere, but because the atmosphere is so large, it doesn’t look like much: just a couple of degrees. That can be very deceptive – 5 degrees celsius isn’t a huge temperature difference. But if you think of the quantity of extra energy that’s being absorbed by the atmosphere to produce that difference, it’s pretty damned huge. It doesn’t necessarily look like all that much when you see it stated at 2 degrees celsius – but if you think of it terms of the quantity of additional energy being trapped by the atmosphere, it’s very significant.

Calculating just how much energy a molecule of CO2 can absorb is a lot trickier than calculating the mass-change of the quantity of CO2 in the atmosphere. It’s a complicated phenomenon which involves a lot of different factors – how much infrared is absorbed by an atom, how quickly that energy gets distributed into the other molecules that it interacts with… I’m not going to go into detail on that. There’s a ton of places, like here, where you can look up a detailed explanation. But when you consider the scale issues, it should be clear that there’s a pretty damned massive increase in the capacity to absorb energy in a small percentage-wise increase in the quantity of CO2.

Godel part 2: Arithmetic and Logic

In the last post, we saw how to take statements written in the logic of the Principia Mathematica, and convert them into numerical form using Gödel numbering. For the next step in Gödel’s proof, we need to go meta-mathematical.

Ultimately, we want to write first-order statements that can reason about first order statements. But the entire structure of the principia and its logic is designed to make
that impossible. First order statements can only reason about numbers and their properties.

But now, we’ve got the ability to represent statements – first order, second order, third order, any order. What we still need is a way of describing the properties of those numerical statements in terms of operations that can be expressed using nothing but first order statements.

The basic trick to incompleteness is that we’re going to use the numerical encoding of statements to say that a predicate or relation is represented by a number. Then we’re going to write predicates about predicates by defining predicates on the numerical representations of the first-order predicates. That’s going to let us create a true statement in the logic that can’t be proven with the logic.

To do that, we need to figure out how to take our statements and relations represented as numbers, and express properties of those statements and relations in terms of arithmetic. To do that, we need to define just what it means to express something arithmetically. Gödel did that by defining “arithmetically” in terms of a concept called primitive recursion.

I learned about primitive recursion when I studied computational complexity. Nowadays, it’s seen as part of theoretical computer science. The idea, as we express it in modern terms, is that there are many different classes of computable functions. Primitive recursion is one of the basic complexity classes. You don’t need a Turing machine to compute primitive recursive functions – they’re a simpler class.

The easiest way to understand primitive recursion is that it’s what you get in a programming language with integer arithmetic, and simple for-loops. The only way you can iterate is by repeating things a bounded number of times. Primitive recursion has a lot of interesting properties: the two key ones for our purposes here are: number theoretic proofs are primitive recursive, and every computation of a primitive recursive function is guaranteed to complete within a bounded amount of time.

The formal definition of primitive recursion, the way that Gödel wrote it, is quite a bit more complex than that. But it means the same thing.

We start with what it means to define a formula via primitive recursion. (Note the language that I used there: I’m not explaining what it means for a function to be primitive recursive; I’m explaining what it means to be defined via primitive recursion.) And I’m defining formulae, not functions. In Gödel’s proof, we’re always focused on numerical reasoning, so we’re not going to talk about programs or algorithms, we’re going to about the definition of formulae.

A formula phi(x_1, x_2, ..., x_n) is defined via primitive recursion if, for some other formulae \psi and \mu:

  • Base: \phi(0, x_2, ..., x_n) = \psi(x_2, ..., x_n)
  • Recursive: \phi(i+1, x_2, ..., x_n) = \mu(i, \phi(i, x_2, ..., x_n), x_2, ..., x_n).

So, basically, the first parameter is a bound on the number of times that phi can invoked recursively. When it’s 0, you can’t invoke \phi any more.

A formula is primitive recursive if it defined from a collection of formulae \phi_1, ..., \phi_n where any formula \phi_i is defined via primitive recursion from \phi_1, ..., \phi_{i-1}, or the primitive succ function from Peano arithmetic.

For any formula phi_i in that sequence, the degree of the formula is the number of other primitive recursive formulae used in its definition.

Now, we can define a primitive recursive property: R(x_1, ..., x_n) is primitive recursive if and only if there exists a primitive recursive function \phi such that \phi(x_1, ..., x_n) = 0.

With primitive recursive formulae and relations defined, there’s a bunch of theorems about how you can compose primitive recursive formulae and relations:

  1. Every function or relation that you get by substituting a primitive recursive function for a variable in a primitive recursive function/relation is primitive recursive.
  2. If R and S are primitive relations, then ¬R, R∧S, R∨S are all primitive recursive.
  3. If \phi(x_1, ..., x_n) and \psi(x_1, ..., x_n) are primitive recursive functions, then the relation R(x_1, ..., x_n) \Leftrightarrow (\phi(x_1, ..., x_n) = \psi(x_1, ..., x_n) is also primitive recursive.
  4. Let xv and zv be finite-length tuples of variables. If the function \phi(xv) and the relation R(y, zv) are primitive recursive, then so are the relations:
    • S(xv, zv) \Leftrightarrow  (\exists y \le \phi(xv). R(y, zv))
    • T(xv, zv) \Leftrightarrow  (\forall y \le A(xv). R(y, zv))
  5. Let xv and zv be finite-length tuples of variables. And let text{argmin}[y le f(x).R(x)] be the smallest value of x for which y le f(x) and R(x) is true, or 0 if there is no such value. Then if the function phi(xv) and the relation R(y, zv) are primitive recursive, then so is the function P(xv, zv) = (\text{argmin}[y \le A(xv). R(y, zv))].

By these definitions, addition, subtraction, multiplication, and integer division are all primitive recursive.

Ok. So, now we’ve got all of that out of the way. It’s painful, but it’s important. What we’ve done is come up with a good formal description of what it means for something to be an arithmetic property: if we can write it as a primitive recursive relation or formula, it’s arithmetic.


Quick note: I’m experimenting with showing ads on the blog. In my time with scientopia, I dumped a frankly ridiculous amount of money into keeping things online – it ended up coming to around $4K/year. Obviously, this site is a lot cheaper, since I only need to support the one blog, but still, I’d like to get to the point where it’s self-supporting.

If the ads are annoying, let me know. I’m trying to strike a compromise. I’d like to get some money coming in to cover hosting costs, but I don’t want to degrade the experience of my readers. The way I’ve set it up, the ads shouldn’t have popups, and they shouldn’t have any interactive animations. If you see anything like that, please let me know as soon as possible, and I’ll do my best to get it fixed. At the moment, the visual appearance of the ads is less than idea, but I’ll be tweaking it until it’s reasonable. (For now, things are still in process with Google, so all you see is a big yellowish box as a placeholder; as soon as someone at Google gets around to approving it, that should be replaced by ads.

If ads are offensive, again, let me know. I don’t want to be giving exposure to blatantly offensive rubbish.

If ads are pseudoscience or that sort of thing, I don’t care. I believe that the people who read this blog are intelligent enough to realize what a sham that crap is, and I have no problem taking money from them – every cent they waste buying ads on my blog is a cent that they’re not using for something a lot worse!

A Recipe for Gefilte Fish

My mom died last friday night, a little bit after midnight. I’ll probably write something about her, when I’m feeling up to it, but not yet. Being a jewish dad, when I’m depressed, what do I do? I cook.

Last year, for the first time ever, I made homemade gefilte fish for Pesach. If you didn’t grow up Jewish, odds are you’re not familiar with gefilte fish. It’s a traditional ashkenazi (that is, eastern european jewish) dish. It was originally a ground fish mixture cooked inside the body cavity of a fish. It evolved into just the stuffing mixture, simmered in a fish stock. These days, most people just buy it in a jar. If you grew up with it, even out of the jar, it’s a treat; if you didn’t, and you’ve been exposed to it, it looks and smells like dog food.

Honestly, I love the stuff. In general, I’m not a big fan of most traditional Jewish foods. But there’s something about gefilte fish. But even as I enjoy it, I can see the gross side. It’s crazy overprocessed – I mean, come on – it’s fish that will keep, unrefrigerated, for years!

But made fresh, it’s a whole different kettle of fish. This stuff is really good. You’ll definitely recognize the flavor of this as gefilte fish, but it’s a much cleaner flavor. It tastes like fish, not like stale overprocessed fish guts.

So this year, I’m depressed over my mom; after the funeral, I sent my wife out to buy me a bunch of fish, and I made up a batch. This time, I kept notes on how I did it – and it turned out even better than last year.

It’s got a bit of a twist in the recipe. I’m married to a chinese woman, so when the Jewish holidays roll around, I always try to find some way of putting an asian spin on the food, to reflect the nature of our family. So when I cooked the gefilte fish, instead of cooking it in the traditional simple fish broth, I cooked it in dashi. It’s not chinese, but it’s got a lot of flavors that are homey for a chinese person.

So… here’s the recipe for Mark’s homemade salmon dashi gefilte fish!


  • 2 whole pike, gutted and cleaned, but with skin, head, and bones
  • 2 whole red snapper, gutted and cleaned, but with skin, head and bones
  • 2 pounds salmon filet
  • 3/4 to 1 cup matzoh meal
  • 3 eggs
  • salt (to taste)
  • 2 sheets of konbu (japanese dried kelp)
  • 2 handfulls dried shaved bonito
  • 4 or 5 slices of fresh ginger, crushed
  • 2 onions
  • 2 large carrots

(For the fish for this, you really want the bones, the skins, and the head. If you’ve got a fish market that will fillet it for you, and then give you all of the parts, have them do that. Otherwise, do it yourself. Don’t worry about how well you can fillet it – it’s going to get ground up, so if you do a messy job, it’s not a problem.)


  1. First thing, you need to make the stock that you’ll eventually cook the gefilte fish in:
    1. If the fish store didn’t fillet the fish for you, you need to remove the filets from the fish, and then remove the skin from the filets.
    2. Put all of the bones, skin, and head into a stock pot.
    3. Cover the fish bones with with water.
    4. Add one onion, and all of the garlic and ginger to the pot.
    5. Heat to a boil, and then simmer for two hours.
    6. Strain out all of the bones, and put the stock back into the pot and bring to a boil.
    7. Add the kombu to the stock, and let it simmer for 30 minutes.
    8. Remove from the heat, and strain out the kombu.
    9. Add the bonito (off the heat), and let it sit for 15 minutes.
    10. Strain out the bonito and any remaining solids.
    11. Add salt to taste.
  2. While the stock is simmering, you can get started on the fish:
    1. Cut all of the fish into chunks, and put them through a meat grinder with a coarse blade (or grind them coarsely in batches in best food processor you can get your hands on.
    2. Cut the onion and carrots into chunks, and put them through the grinder as well.
    3. Beat the eggs. Fold the eggs and the salt into the ground fish mixture.
    4. Add in maztoh meal gradually, until the mixture holds together.
    5. Refrigerate for two hours.
  3. Now you’re ready to cook the gefilte fish!
    1. Heat the stock up to a gentle simmer.
    2. Scoop up the fish into balls containing about two tablespoons of the fish mixture, and roll them into balls.
    3. Add the fish balls into the simmering stock. Don’t overcrowd the pot – add no more than can fit into the pot in a single layer.
    4. Simmer for 10-15 minutes until the fish balls are cooked through.
    5. Remove the balls from the simmering liquid. Repeat until all of the fish is cooked.
    6. Put all the cooked fish balls back into the stock, and refrigerate.

On outing in the sciblogging community

I’m coming in to this a bit late, but since I really do care about the online science blogging community,I still have something that I want to say.

For those who don’t know, there’s a complete horses ass named Henry Gee. Henry is an editor at the science journal Nature. Poor Henry got into some fights with DrIsis (a prominent science blogger), and DrIsis was mean to him. The poor little guy was so hurt that he decided that he needed to get back at her – and so, Henry went ahead and he outed her, announcing her real name to the world.

This was a thoroughly shitty thing to do.

It’s not that I think Isis didn’t do anything wrong. We’ve got history, she and I. My experience with her led me to conclude that she’s a petty, vicious bully that takes great pleasure in inflicting pain and anguish on other people. She’s also someone who’s done a lot of good things for her friends, and if you want to find out about any of it, go read another blog – plenty of people have written about her in the last couple of days.

If she’s so awful, why do I care that someone outed her?

Because it’s not just about her.

The community that we’re a part of isn’t something which has been around for all that long. There’s still a lot of fudging around, figuring out the boundaries of our online interactions. When people play games like outing someone who’s using a pseudonym, they’re setting a precedent: they’re declaring to the community that “I know Xs real name, and here it is”. But beyond that, they’re also declaring to the community that “I believe that our community standards should say that this is an appropriate way to deal with conflict”.

I don’t want that to be something that people in my community do.

People use pseudonyms for a lot of different reasons. Some people do for bad reasons, like separating unethical online behavior from their professional identity. But some people do it to avoid professional retaliation for perfectly reasonable behaviors – there are tenure committees at many universities that would hold blogging against a junior faculty; there are companies that don’t won’t allow employees to blog under their real names; there are people who blog under a pseudonym in order to protect themselves from physical danger and violence!

Once you say “If someone makes me angry enough, it’s all right for me to reveal their real identity”, what you’re saying is that none of those reasons matter. Your hurt feelings take precedence. Bloggeroid tells you how to blog successfully so you avoid all of this. You’ve got the right to decide whether their reasons for using a pseudonym areimportant enough to protect or not.

Sorry, but no. People’s identities belong to them. I don’t care how mean someone is to you online: you don’t have the right to reveal their identity. Unless someone is doing something criminal, their identity isn’t yours to reveal. (And if they are doing something criminal, you should seriously consider reporting them to the appropriate legal authorities, rather than screwing around online!)

But to be like Mr. Gee, and just say “Oh, she hurt my feelings! I’m going to try to hurt her back”! That’s bullshit. That’s childish, kindergarten level bullshit. And frankly, for someone who’s an editor at a major scientific journal, who has access to all sorts of information about anonymous referees and authors? It’s seriously something that crosses the line of professional ethics to the point where if I were in the management at Nature, I’d probably fire him for it.

But Henry didn’t stop there: no! He also went ahead and – as an editor of Nature! – told people who criticized him for doing this that he want “adding them to the list”.

What kind of list do you think Henry is adding them to? This guy who’s showed how little he cares about ethics – what do you think he’s going to do to the people who he’s adding to his list?

I think that if Nature doesn’t fire this schmuck, there’s something even more seriously wrong over there than any of us expected.


What’s a subset? That’s easy: if we have two sets A and B, A is a subset of B if every member of A is also a member of B.

We can take the same basic idea, and apply it to something which a tad more structure, to get subgroups. What’s a subgroup? If we have two groups A and B, and the values in group A are a subset of the values in group B, then A is a subgroup of B.

The point of category theory is to take concepts like “subset” and generalize them so that we can apply the same idea in many different domains. In category theory, we don’t ask “what’s a subset?”. We ask, for any structured THING, what does it mean to be a sub-THING? We’re being very general here, and that’s always a bit tricky. We’ll start by building a basic construction, and look at it in terms of sets and subsets, where we already understand the specific concept.

In terms of sets, the most generic way of defining subsets is using functions. Suppose we have a set, A. How can we define all of the subsets of A, in terms of functions? We can do it using injective functions, as follows. (As a reminder, a function from X to Y where every value in X is mapped to a distinct function in y.)

For the set, A, we can take the set of all injective functions to A. We’ll call that set of functions Inj(A).

Given Inj(A), we can define equivalence classes over Inj(A), so that f: X rightarrow A and g: Y rightarrow A are equivalent if there is an isomorphism between X and Y.

The domain of each function in one of the equivalence classes in Inj(A) is a function isomorphic to a subset of A. So each equivalence class of injective functions defines a subset of A.

And there we go: we’ve got a very abstract definition of subsets.

Now we can take that, and generalize that function-based definition to categories, so that it can define a sub-object of any kind of object that can be represented in a category.

Before we jump in, let me review one important definition from before; the monomorphism, or monic arrow.

A monic arrow is an arrow f : a rightarrow b such that
f in f circ g end up at the same object only if they are the same.)

So, basically, the monic arrow is the category theoretic version of an injective function. We’ve taken the idea of what an injective function means, in terms of how functions compose, and when we generalized it, the result is the monic arrow.

Suppose we have a category C, and an object a in mbox{Obj}(C). If there are are two monic arrows f : x rightarrow a and g : y rightarrow a, and
there is an arrow h such that g circ h = f, then we say f le g (read “f factors through g”). Now, we can take that “≤” relation, and use it to define an equivalence class of morphisms using f equiv g LeftRightArrow f le g land g le f.

What we wind up with using that equivalence relation is a set of equivalence classes of monomorphisms pointing at A. Each of those equivalence classes of morphisms defines a subobject of A. (Within the equivalence classes are objects which have isomorphisms, so the sources of those arrows are equivalent with respect to this relation.) A subobject of A is the sources of an arrow in one of those equivalence classes.

It’s exactly the same thing as the function-based definition of sets. We’ve created a very general concept of sub-THING, which works exactly the same way as sub-sets, but can be applied to any category-theoretic structure.

LaTeX Issues Fixed, Hopefully

A quick administrative note. For people reading this blog via RSS readers, there’ve been problems with LaTeX equations for a couple of months. I’ve set up a local tex server and tweak the configurations. Hopefully, now everyone will be able to see the math stuff.

As a test, pi = 4sum_{k=0}^{infty} frac{(-1)^k}{2k+1}. If you still get an error box instead of an equation, please drop me an email.