Daylight observations of Venus with the naked eye

Near the end of January, I happened to be up just a while before dawn and saw Venus in a clear eastern sky, a little below a crescent moon.

I had read that it was possible to see Venus in daylight, and a friend had photographed it in the western sky near sunset, so I figured that with the moon as a guide I should be able to work out where to look for it.

I went back to bed and then tried again around 9 am (AEST), at which time it was close to directly overhead, and with the aid of binoculars and the moon as a cue I located Venus with a few minutes looking. Given the location, I could make it out very easily with the naked eye. I checked again every hour and found it almost immediately. It was still perfectly visible at 1pm, with the sun blazing overhead and Venus well into the western sky.

Myth confirmed!

Oh, brave new world ...

... that has glider guns in't!

This is freaking cool. But if Belousov-Zhabotinsky reactions or cellular automata are unfamiliar, don't go there just yet, read this first.

Wow, I want to explain six different things at once. Where to start.


There's some amazing chemicals (quite a few different ones) that undergo Belousov-Zhabotinsky reactions, which switch between states. The image shows one such reaction where there's a cyclical colour change.







If you set up a BZ reaction in a thin layer (say something like a petri dish), then you can observe beautiful cycles of spiral waves.

Very similar spiral waves of excitation are observed, for example, in certain cardiac problems.














Now, to go off in a completely different direction, there are mathematical constructs called cellular automata (CAs).


These are basically a layout of cells - often in a line, or sometimes in a 2-D array (or sometimes even in higher dimensions), which evolve according to simple local rules (such as "if the cells either side of me are both black, next step I will change to white"). The image here is of the development of one such CA, called "Rule 30". As you progress down from the top, each row of the image represents one "time step" in the development of this 1-d cellular automaton.

While they were originally purely mathematical ideas, patterns that arise in essentially the same way, and look very much like those seen in some kinds of cellular automaton do occur in nature, for example, on some kinds of shells:








Further, people have noted in the past that a particular kind of cellular automaton, the cyclic cellular automaton can generate very distinctive spiral waves that look somewhat like BZ spiral waves.

The most famous of these cellular automata is undoubtedly Conway's game of Life, a 2D one that produces some amazingly intricate patterns.

One very early pattern that was discovered is called a glider - a pattern only a few cells across that changes in such a way that it appears to "fly" diagonally in a straight line.



In 1970, Bill Gosper, in response to a challenge by Conway to find a Life pattern that would show "unlimited growth", designed a constuction that produces a constant stream of gliders, called a "glider gun". (There are a large number of other constructions that exhibit such unlimited growth.)


Using many structures such as this, it has been shown that it is possible to construct a kind of computer that is equivalent to a Turing machine.

In 2005, Motoike and Adamatzky discussed using Belousov-Zhabotinsky reactions in the construction of logic gates in liquids, and there has been a bunch of other related papers.

Now to the new bit. There's a new paper up on arXiv where a bunch of researchers the University of West of England (including Adamatzky) have constructed, using BZ reactions, a chemical version of a glider gun (it's not exactly a game-of-life glider gun, but it has similar properties.



As the authors say in their conclusion, "theoretical ideas concerning universal computation in these systems is closer to being realized experimentally. We were able to manipulate glider streams, for example annihilate selected streams and switch periodically between two interacting streams. We were also able to show that glider guns could be formed or annihilated via specific interactions with glider streams from a second gun. We also showed examples where glider guns could be used to implement simple memory analogs."

They also say, "[t]hese discoveries could provide the basis for future designs of collision-based reaction-diffusion computers". Indeed.


There may well be implications relevant to the development of the earliest self-reproducing structures (protolife) on earth.

via The physics arXiv blog

The necessity of error and the error filter

Recently, two Scienceblogs bloggers have made substantive errors. (Well, no doubt more than two have, but I saw two.)

One is a mathematician and one is a biologist.

Now the fact that these writers made errors is of no great consequence. Every human, all of us, we all make mistakes. Everyone.

In fact, if some of us (well, okay, me) make lots and lots of mistakes. Actually, making mistakes is part of achieving anything at all, so we shouldn't fear making them (at least in situations where the consequences of error are not dire) - it means we're doing something.

What matters to me is not that they got something wrong, but how errors were dealt with. In both cases they made a post that pointed out they got it wrong, and that explained in detail what was correct.

A body of knowledge, whether it resides in an individual or in a culture, contains mistakes. Some of what we think is true is necessarily going to be false. If the fact that the corpus has errors in it is accepted, there is some hope of correcting some of the errors.

If you encounter someone who cannot be wrong, you may be sure they are in a sea of falsehood. It can be no other way.

However, we need more than just an acceptance of the possibility of falsehood and a willingness to change ideas. We can't just change our beliefs willy-nilly. The fact is, for most people, even the highly deluded among us, almost all of what we believe to be true is true, or close enough to true to be valuable (most of those truths are relatively mundane facts, it's what gets us through life). So we should need some further reason to change than the simple possibility we may be in error.

We need some way of identifying our most mistaken ideas and replacing them with better ones, without mistakenly replacing a good idea with a bad one. We need some kind of "filter" that allows us to see us to tell one from the other.

Some people use prayer to try to figure out what is right. The problem with that is it's mired in error. You can't tell for sure that what you think is divine guidance isn't just your own thoughts. In fact it's obvious this must be so, not least because two people can each be sure that they've received guidance about the right path, and those pieces of guidance are contradictory; since they can't both be right, at least one must be wrong. Whether you believe in God or not, the possibility that people can be mistaken in their interpretation of the result of a prayer for guidance should be obvious.

What is this magic knowledge-generating filter?

It's reason and evidence.

This is how we learn. This is how we discover what we did not know. This is why we even have a body of knowledge at all.

In order to raise ourselves out of the muck of ignorance, we need to admit the possibility of error, and use the only reasonably reliable filter available, in order to reduce those errors.