Links for April 2019

These links were collected over March, so I will presumably be a month late with the various internet tomfoolery associated with this post’s publication date.

Berkson’s paradox is a counterintuitive result which most often manifests as falsely observing a negative correlation between independent variables when one mistakenly only sees cases when at least one of them occurs. Wikipedia’s example: ‘For example, a person may observe from their experience that fast food restaurants in their area which serve good hamburgers tend to serve bad fries and vice versa; but because they would likely not eat anywhere where both were bad, they fail to allow for the large number of restaurants in this category which would weaken or even flip the correlation.’ Probably a useful concept to have a handle for.

Colin Wright is mostly famous for inventing the juggling notation known as ‘siteswap’, but was in fact a maths PhD supervised by Béla Bollabás at Cambridge. He has a blog full of interesting puzzles and others, including a series of twists on the classical ‘rope around the Earth’ problem. This one is my favourite.

During the Second World War, the US was developing a revolutionary new method of incendiary bomb delivery: hibernating bats. It was only cancelled because the Manhattan project was progressing more quickly. I can only wonder at the world in which incendiary bat bombs were the threat on which the Cold War was built instead of nuclear weapons.

Why can’t font size be set on a:visited? Surprising things that have to be done in the name of privacy.

OpenType font shaping is Turing complete, although this requires a custom HarfBuzz build to increase the recursion limit past 6.

Also Turing complete is the x86 instruction set, but using only mov. I am once again reminded that Turing-completeness is not a high bar.

Long post on Status as a Service, and how social capital is the real motive behind people’s behaviour on social networks.

NYT article on a carbon dioxide scrubbing startup. Encouraging ideas, but seems energetically implausible. John Baez writes about similar ideas.

‘Why are you reading about airships?’ ‘Because airships are cool.’ Back-of-the-envelope calculations (admittedly by an airship blog) suggest that giant cargo airships could be a trillion dollar industry (the calculations are rough enough that what we mean by that doesn’t matter: could be market cap, revenue, value of assets…). They offer a previously nonexistent low-cost, medium speed transport method that is agnostic of land or sea. From the point of view of carbon, they are encouraging in that they only require energy to go forwards, although drag is a big concern and hydrogen is fairly expensive to produce.