I would say all of it in one way or another, although there will be some areas which will be more active than others. There's an old urban myth that you only use 10% of your brain. It's absolute rubbish as the brain has such a high metabolic rate. In fact, the part of the brain that has the highest metabolic rate and burns off more energy than any other part is in fact your retina. It's part of the brain itself because it's an extension of the central nervous system. If you look at someone who's had a stroke and damaged a bit of their brain, even though they might be doing a task that doesn't directly seem to involve that part of the brain, the person still doesn't seem to be completely right. They still obviously have some difficulties. So we know that all of the brain is used probably all the time but some bits are recruited and do slightly more some of the time. And the reason we know that is because you can inject substances into people which are used as a way to map out which bits of the brain are more active than others. So you give people a radioactively labelled glucose molecule for example, because the brain loves glucose. Wherever the brain is doing more work, it needs more energy, so it burns more glucose. So in a special scanner, you can see where the radioactivity is being concentrated. That's called a PET scan, and it tells you which bits of the brain are doing what jobs. Because you can get people doing repetitive tasks, if you ask them to just move their right hand for example, and the part of the brain that's concerned with just moving the right hand will light up.

Despite this, it is still difficult to obtain. See www.unitednuclear.com/isotopes.htm for a full explanation. Basically, you'd need to spend millions on thousands of units, and then purify it all, before coming up with a decent amount. Frankly, its be easier to do same with americium from smoke alarms … Aside from the brushes, most polonium used in devices is electroplated on to a metal base – and that like saying that silver-coated steel forks are a good source of silver. They're not, because you have to melt the stuff down and go through a complicated separation procedure to get it away from the steel once its been electroplated.

That's a good question. Well the answer strangely enough is nothing. And that's the key. This point I mentioned briefly before about zero. If you think of nothing, nothing is actually a big balance between a big positive and a big negative. And if occasionally that little balance goes wrong, you go from nothing to something, very quickly indeed, and you get an awful lot of something in a very small place. And so in a very real sense of the word, the big bang sprang out of nothing.