I BET most people who bought Stephen Hawking's famous bestseller never read it: just owning it made them feel more knowledgeable. Yesterday, for those of us who got no further than putting it back in the bookshop window, Jon Pertwee offered a variation. A Short History of Time (R2) was challenging stuff, but the old Dr Who did his best to make it easy. This, for example, is what entropy means: things get messier and we all grow older, as more disorder comes into the universe. I can relate to that.

But it got tougher. This programme came from BBC Education, as part of Science Week: Hands On - it demanded concentration. There was a very sticky moment somewhere in the fourth dimension, on the way from Newton to quantum physics via Einstein, when the possibility of time travel was explained as bending space-time so that a handy black hole was suitably positioned, then - er - falling through it. Even the erstwhile Time Lord sounded a little flummoxed.

Being dear old R2, we were offered some Flanders and Swann as reassurance before the next lesson, and there was a lot to learn. Most fascinating was the history of timepieces, cleanly narrated from the casual sundial right up to the atomic clock, which is based on the nine billion vibrations per second inside an atom of caesium. The listener, at the end of all this, felt thoroughly educated if slightly dazed. Two things stay in this entropic memory: the pips tell the most absolutely right time you can get and Jon Pertwee is a honey. Despite his earnest endeavours to understand and communicate the arcane niceties of defining and recording time, his heart is with the South Sea Islanders who date things as having occurred, oh, roughly about the time when so-and-so was a child.

It's been an instructive week, beginning with Monday's edition of Farming Today (R4) which delivered exciting news about developments in the anaerobic digestion of a thousand tons of pig slurry. I'll spare you the details: they were enough to make anyone regret the loathsome excesses of the weekend. Suffice it to say that it was all very, very green.

We had History at 10 o'clock that morning. Hiding under the kitchen table, convinced by increasingly scary news bulletins that the rogue Chinese satellite would crash into our garden, I couldn't reach the radio to turn off Battling with the Past (R4), previously condemned in this column as a silly quiz. I take it back. The point-scoring has become minimal and the stories were marvellous, especially the one about William Prynne, condemned to have his ears cropped for libelling the Queen. He bribed the executioner to remove only the tips, promising him five shillings. Then, the rat, descending the scaffold almost aurally entire, he only paid half the bribe. However, he went on to commit yet another libel, got the same sentence and, aha! the very same executioner. There's a lesson in that.

Dr Gillian Rice arrived that evening for Biology. The New Sexual Nature - Sperm Wars (R4) was astonishing. It suggested that research into animal sexuality sheds lurid strobe lights on to our own. A dowdy little dummock has the ability, for example, to reject a previous suitor's sperm so that the current one has more chance of fathering her chicks - and it is at least possible that women can do the same, though research can be embarrassing. And as for dragonflies ... Having heard about their astonishing equipment, all I can say is that to compare it with a pipe-cleaner or a Hoover dustette began to seem quite sensible.

There was fun after hours with Fab TV (R4). The Intenders meant to be back but were held up; the Expanders had got stuck; the Procrastinators won't be available until next week so it was time for The Preventers. Based on all those far-fetched troubleshooter series of the Sixties, it featured two hard men and a faintly foreign girl, up against the evil Belgian separatist Avis van Rental and the mighty Australian news tycoon Roger Mordick. It was lovingly accurate, down to the absurdly exotic locations, the knife-edge escapes (by way of omni- present ventilation shafts) and the real cool jokes. Here's one: "You can tell which one's Mordick. He's got a didgeridoo, corks round his hat and a kangaroo on a lead." "Wallaby." "That's very kind; I'll have a dry martini." Well it made me laugh. But then that could be further proof of entropy.

THE ABOVE is a perfectly ordinary radio column. But Wednesday's grotesque massacre shattered the perfect and the ordinary. Those of us who casually switched on the radio news were blinded by helpless tears. It was entirely right that R5 should reschedule its afternoon to dwell on Dunblane - it was impossible not to - and I heard no squirmily intrusive questioning, nor any glibness. Yet what could they really say, in the face of such tragedy? One sentence from the montage of reactions, presented at the end of that sad day, expressed the hopeless grief of it all: "Even for those of us who deal in words, there are no words." I don't know who said it, but he was right.