Source coding is what Alice uses to save money on her telephone bills.

It is usually used for data compression. In other words to make messages shorter. There is a story about a student of information theory on his first day at college. He had entered a strange, bizarre world. The only sounds were the occasional calling out of a number by one of the professors, followed by laughter. One professor would say '52', there would be a short pause then peels of laughter. Someone else says '713'. Same thing, everyone falls down laughing. "What's going on here" he asked his tutor.

"We're telling jokes" said his tutor.

"Telling Jokes?"

"Yes, you see we’ve all worked here so long we know each other's jokes. There are a thousand of them. So, being information theorists we applied data compression. We just assigned them all numbers, 0 thru 999. It saves a lot of time and effort. Would you like to try? Just say any number 0 to 999..."

He wasn't fully convinced. But he tried. Very quietly he whispered "477".

Hardly a murmur.

He looked at his tutor. "What's wrong" he said.

"Try again" says the tutor.

So he does. "318" - same again, not a thing, hardly a murmur.

"Something's wrong" he says.

"Well" says the tutor, it's like this.- It's not so much the joke as the way you tell it!"

There is a curious sequel to this story. This student eventually succeeded by accident in the most dramatic and unexpected way.He called out a number outside the range 0 to 999. "Minus 105" he said.

At first there was stunned amazement, then first one professor laughed, then another then another, till they were all rolling about holding their sides.

None of them had heard that one before.

(from the Alice/Bob After Dinner Speech)

(given at the Zurich Seminar April 1984)

(by John Gordon)

Hell... Here's one more...

The Modern World

Well that ends the instant course on coding theory.

I would like to finish with a few words on the impact that information technology is having on our everyday lives. Science has marched ahead so fast that we take for granted the most incredible technological developments. Magnetrons, which were a closely guarded secret during the 1939-45 war are now part of every microwave cooker. And made in Japan. When I was a child, space travel was science fiction. Yet today, advance is so rapid that even the astronauts who set foot on the moon in 1969 had never seen a digital watch. Nor a pocket calculator.

Pocket calculators! Now there's something. They are so complicated!

I have a calculator which has sines, cosines, tangents, logarithms, hyperbolic functions and multiple nested parentheses.You can program it in Fortran, Algol, Basic, Pascal, Forth,

Fifth and Sixth, ADA and Caruthers. It will factorise Primes for you. At present it is working on the Halting Problem. It translates from one language to another.

From German to Spanish.

From Macedonian to Esperanto.

From Cantonese to Greek.

Or from American to English.

It is in fact a multiprocessor system. There are 22 Transputers in there. Sometimes they organise a game of football between them. It has a full color, wraparound wide screen, liquid crystal, three-dimensional holographic display. It's called HoloChromaCinePhotoRamaScope. Its audio facilities include Dolby Digital Decaphonic surround sound.On the way here I watched "The Labyrinth" on it.

It also has synthetic speech and a voice recognition system. I often talk to it.I tell it my problems. Sometimes it psychoanalyses me. It has me figured as paranoid. But that's just because it keeps getting at me. But don't get me wrong - it can be very user friendly. In fact you can program precisely HOW user friendly you want it is to be on a scale from ONE to TEN.

On a setting of ONE it won't even interrupt a football game to answer you. But on a setting of TEN it is so friendly that on a cold day it pre-heats its pushbuttons.

But no matter who smart it SEEMS, deep down inside it is just a dumb old computer.

One time I got really mad at it.

Like all computers, it knew precisely what I wanted it to do.

It know exactly what I MEANT. So why does it have to go and DO what I SAID?

How do you get even with a dumb machine like that?

First I tried slapping it around a little. I pushed its buttons a bit hard.

I threatened it."How would you like a busted display" I said.

But it did no good. It just said "I am virtually unbreakable - and I'm not going to take any notice till you enter the data nicely, like you used to do.”

Whatever I did it always seemed to win. I decided to have a man-to-man talk with it. So I sat it down and said to it "Who's the boss here, you or me?"

No reply.

Again I ask "Who's the boss, you or me? Go on answer me!"

"I'm thinking, I'm thinking" it said.

So I hit it.

Hard.

Too hard. I cracked its case.

At first I thought that was the limit of the damage. But then little things started to go wrong.

At first there was nothing definite. Nothing you could put your finger on.

Just little things like stuttering.

It just didn't sound quite the same. Its voice seemed to lack its former confidence.

Then once I caught it making an arithmetic mistake. Of course I didn't mention it. But you could tell it knew. It's self image was shot to pieces.

Saddest of all, it forgot our anniversary - of the day I bought it. In the past this had been a special time for us.

I just couldn't bear it any longer. One evening I tucked it up snugly in its case, lit candles, played a record which was popular when we first met, and sat down beside it.

"Where did we go wrong?" I said. But it had it pride. It wasn't about to weaken in front of a non-machine.

"Wrong? Nothing is Wrong" it said."Just insufficient data."

But underneath you could tell it was hurt.

From there it was a rapid downhill slide.

Now it just mutters to itself. It can only do very simple calculations on small numbers.

Finally came the ultimate indignity. It lost control. It leaked electrolyte all over its case. I felt so bad about it.

My other gadgets weren't happy about it either. They all came out in sympathy for the calculator. My watch gave me a bad time. My power tools keep blowing fuses.

Then one night last week I was driving my car back from London when suddenly the engine stopped all by itself on this lonely country road.

I tried to get out but the solenoids were inhibited by the central locking computer.

Suddenly the air conditioner came on and started to blow out freezing cold air. It made a noise like wind whistling through the trees.

Then this creepy music came from the loudspeaker. The sort of music they play in movies when the hero is lost in a dark forest.

I got scared. The cold, the wind and the weird music got to me.

Then it started to speak.

"You're the guy who beats up pocket calculators!"