Today I Learned: Volume 2


til biology psychology fear math numbers money currency geology

A new TIL thing is out! Check it ouf for unexplained fears, messed-up billions, quantum computing and thousands of dollars.

Also, a shout-out for a most amazing read, the Jean Le Flambeur trilogy. If you’re into rational fiction, by all means go for it. It is probably even more educative than HPMoR is. These margins are too narrow to express its awesomeness. Let me just say that I place its author, Hannu Rajaniemi in the same bright-minded group as Elon Musk and Eliezer Yudkowsky. I wonder what would happen if these three decided to build something together.


Babies might be taking over the fears of their parents via odor.

Scientists from the University of Michigan Health System have taught a rat to be afraid of peppermint. Then, after they reproduced, they were exposed to peppermint again. Soon, their babies became afraid of it, too. It appears that the babies are very sensitive to the alarm odor that the mothers release during stress.

More importantly, the fear of peppermint turned out to be persistent. The researchers suggest that the same works with humans. Whatever the mothers are afraid of, their babies become afraid of, too, if they are both exposed to it.


There are two competing number naming schemes. In one of them, a trillion is 1012, while in the other it’s 1018

The names are short scale and long scale. Here’s a table that explains the logic:

Number Short Scale Long Scale
100 One One
106 Million (1,000 × 1,0001) Million (1,000,0001)
109 Billion (1,000 × 1,0002) Thousand million or milliard
1012 Trillion (1,000 × 1,0003) Billion (1,000,0002)
1018 Quintllion (1,000 × 1,0005) Trillion (1,000,0003)

The short system is the most commonly used one, while the long scale is used in some coutries of Europe, South and Central Africa, South America and Mexico. Also, some islands. More peculiarly, Antarctica and Canada uses both, and Greenland and some asian countries like China use other naming systems altogether.


Commercial banks in the United States had legally issued banknotes before there was a national currency. Roughly between 1837 and 1863, there were around 7,000 differently designed United States Dollar notes.

More precisely, before National Currency were introduced by the Tender Act, commercial banks were free issue “dollars” all by themselves. Basically, they were just obligations that the issuing bank would pay off by silver or gold upon request. They were called dollars just for convenience.

Also, the name dollar comes from thaler, a silver coin. I was unable to find a vast registry of different-looking dollar notes, but here’s an example.


Some (theoretical) research argues that space-time can compute.

This topic requires quite a lot of pre-requisite knowledge. There are two sources which I personally think are the most exhaustive and modern. One is more scientific, and another one is a more popular representation.

Now, it is not quite easy to put the research in a couple sentences, but I will try my best. The first one contains speculations on how a theory of Quantum Gravity may influence computing. It argues that Step Computers with definite causal structure may become obsolete and suggests an approach to computing that makes use of possible Quantum Gravity properties.

The second one shows that quantum space-time can be viewed as a quantum computer that evaluates Boolean functions which are the laws of Physics in their discrete form. But really, just do read the papers.


Between the Earth’s crust and its mantle, there lies a sudden change in composition

It is called the Mohorovičić discontinuity, and it is not yet clear how it has formed. It was possible, however, to use seismographs to estimate the depth at which it lies: 5-10 km beneath the ocean floor, and 20-90 km beneath continents. There were two attempts to drill that far down: the Mohole Project, which did not succeed much, and the Kola Superdeep Borehole, which was abandoned at about 12,260 meters. It is also the deepest man-made hole on Earth.

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