Size is everything.

Ever wanted to know how much bigger a grain of rice is than a virus? Or an atom? Go here to find out.

Planetary Systems

As we all know, the Polish astronomer Nicolas Copernicus' book De revolutionibus orbium coelestium - On the revolutions of the heavenly spheres - was published in 1543 and announced to the world that a better way to explain the apparent motions of the Sun and planets was to take the sun to be at the centre of the universe instead of the Earth. It is perfectly possible to take the view that the Earth is at the centre. If you do so, however, you have the problem of explaining why it appears that the planets seem to move in one direction for a bit, then stop, then reverse direction, then stop, then reverse again to move again the original direction, the cycle then repeating. This is made all the harder if you accept the Aristotelian view (but one that surely pre-dated him) that the orbits of heavenly bodies are circular.

The Greek astronomer Ptolemy (c.90 - c.168 A.D.) came up with an ingenious way of making sense of this. The planets move in circles but the centre of the circle itself moves. Consider the motion of a pod on the London Eye. Now replace the pod with a mini-London Eye and consider the motion of one of its pods. You could indeed then have a mini-mini-London Eye...and so on, to get ever more complex patterns of motion.

Copernicus' system was much simpler: no 'wheels within wheels'. But it didn't persuade everyone. The Danish astronomer Tycho Brahe (1546-1601 A.D.) proposed a system in which the Earth is central. The Sun and the Moon revolve around the Earth. The other planets revolve around the Sun. Brahe couldn't accept that the Earth moved because, if it did, then the pattern of the stars should look different at each of a six month period (when the Earth would have moved through half a complete orbit). The phenomenon is called parallax. You can demonstrate it with by holding out a finger before you and viewing it with just your left eye, then your right. The position relative to the background will change because your eyes are in different positions. In fact the positions of the stars do change, but it is too slight to be seen without a good telescope.

This nice on-line simulator allows you to compare the Tychonian and the Copernican systems. There's a not-quite-as-nice illustration of the Ptolemaic system here and one whose parameters you can modify here.

The robin: the latest in quantum computing

There is good evidence to suggest that animals are equipped with senses unfamiliar to us humans. These senses detect heat, the polarisation of light, electricity and the Earth's magnetic field. Quite how they do so is another matter. In the case of the magnetism, the latest research suggests a quite fascinating mechanism. To put it very briefly, chemicals in the robin's eye react to light in such a way that, when they have been 'energised' by the light, they become sensitive to the Earth's magnetic field. So, by seeing light, they also see the magnetic field.

In a bit more detail - and it is here that it gets fascinating and weird - it appears that these chemicals exploit the strange phenomenon of quantum entanglement. A way to grasp the strangeness is the following. Imagine two identical balls, the top halves painted red, the bottom blue. Imagine them fixed in separate wooden boxes with an axle through the middle and spinning constantly. As you look into the box, you see red, then blue, then red, then blue, and so on. Now imagine that these two balls are set spinning and the boxes are shut (we'll not worry about how they keep spinning.) Next, suppose that by opening the box, you stop the ball rotating and see either the top red half or the bottom blue half. Finally, the two boxes are carried off in opposite directions until they are a long way away from one another.

Now for the strange bit. The moment one box is opened, the ball stops and you see red or blue, as I said above. But at the very same instant, the ball in the other box stops rotating and shows the opposite colour. What's odd is that this can happen when they are separated by any distance. Yet it is supposed to be the case that information cannot travel faster than the speed of light. The two balls are 'entangled'. They are somehow connected so that any changes to one immediately bring about changes to the other.

The claim, then, is that photons of light that activate special chemicals in the eye affect electrons in the chemicals that exist in a state of quantum entanglement, the effect of which is that they are differentially affected by the Earth's magnetic field, from which further reactions could be caused leading to a complex sensitivity to the field. Bizarre and fascinating. More details here.

The Pacific Northwest Tree Octopus

The Pacific Northwest Tree Octopus is a fascinating beast: the only member of its genus to live out of water and in the branches of a tree. Amazing. You can Google it to find our more or read more here.

If you find yourself being more than a little sceptical, then well done. There is no such thing. It was invented to test the way in students use the internet for research. The results showed that students were too reliant on search engines and impressions on what a URL (a web page's 'address') should look like and not critical enough. In short: they simply accepted whatever the engine threw up in the top links. Not like me! you should be saying. Read more here.