Dork Scratchings

It may not be entirely obvious from the photograph (which I took at night, while hashing ) but this is a wrought iron gate. It opens on to a front garden on Maid's Causeway, Cambridge.  Why?  I don't know.  Has an important physicist lived there?  There's no Blue Plaque , so maybe it's just an enthusiast, like me! What does it mean?  I don't know for certain, but I suspect it is a reference to something similar to the GHSZ variant of the Bell Inequality Test .  The results of this test demonstrate that there are no hidden variables in quantum mechanics.  I say "similar" because, in GHSZ instead of 0 and 1 the spins $\downarrow$ and $\uparrow$ are used, and there's a minus instead of a plus. If you know anything more, please tell me!

Photo taken by me at 18:00 BST May 20, 2018 I was out and about in Cambridge and I saw a modern sundial on the side of a building in Tennis Court road .  It occurred to me then that I should be able to build a sundial which tells you both the time - in GMT - and the date.  (Although you do need to know whether it is before or after the summer solstice!).  In fact all you need is to know one out of compass bearing, time, date and you should be able to work out the other two! To run it you need to do the following copy the text into sundial.py and chmod +x sundial.py install pre-requisite packages: sudo apt install python-numpy python-matplotlib run it:  ./sundial.py The result is a printout like the one shown.  If you want to adapt the picture for your locale just edit the parameters passed to plot_fixed_lat_long() . When I printed out my first sundial I was surprised to discover that the trajectory of the shadow is straight on the equinoxes....

The last time I visited King's College Chapel Cambridge I noticed a small poster which talked about the construction.  It turns out that just before they built it they discovered an innovation which allowed them to use much less masonry.  The poster said that if you build an arch such that it is possible to draw a catenary between the inside and outside wall, then the arch will be stable.  This discovery meant that they could make the walls of King's College Chapel as thin as they wanted, subject to their ability to measure accurately. This got me thinking.  Why should that be?  Then I realised that it all has to do with the name: catenary .  A catenary is a hyperbolic cosine like $cosh(x)$.  (Obviously if you stretch or translate along the x or y axes it is still a catenary.)  The name comes from catena or "chain", because it is the shape a chain makes if held in two places at the same height. Now imagine a chain being held in that manne...