## Monday, April 30, 2007

### Down

I went to the highest unbroken waterfall in England. Higher than Wales' best, higher even than Ireland's. But all that is visible to a normal human being is a very disconcerting hole in a Yorkshire hillside.

The sheerest cliff tops have nothing on this place. I didn't kneel to peer over - I couldn't stay near the edge for longer than a few seconds.

## Thursday, April 12, 2007

### Planck Monkeys

Give a monkey a typewriter, and if you wait long enough it will type out the Complete Works of William Shakespeare.

This is the infinite monkey theorem.

I've been thinking about how much monkey typing is needed, and decided to do some tests. I acquired a small gedanken monkey that can type randomly at 48wpm (4 keystrokes per second) without stopping for food or rest. I gave my monkey a small typewriter with 26 letter keys (capitals only) and a space bar five times as big as the others, and (forgiving soul that I am) excused it from any punctuation. I wanted to see if he would type the word MONKEY at some point over the next 5 years.

In fact, he did, and it was hidden away like this: "... SJKBV SDG FMMONKEYP SRGH DKAFJI ..." near the bottom of page 230 of volume 798 of a thousand volumes of monkeyprint. I have built a library to hold these volumes for the benefit of future generations.

To clarify my "it is likely": the probability of the word appearing in 5 years is about one half. So I was lucky: it's 50:50 whether the word MONKEY would be found at all.

I decide to raise the bar to MONKEY WANT BANANA. (If my monkey had typed this, I would have fed it. But it didn't, did it.)

Monkeys have been around for about 50 million years. What if I had acquired all the monkeys in the world from the very start of monkeys, and had them type continuously at 48wpm for 50 million years? If anyone can help me with how many monkeys there are and have been over the last 50 million years, please let me know. I'm going to suggest 10 billion, on average. They would have produced a hundred thousand trillion tons of monkeyprint by now. Might they have managed a MONKEY WANT BANANA? Yes: the probability that one of them would have done it is an impressive 89.5%.

This is promising. Now, what if the universe was filled with tiny monkeys right back to the Big Bang, typing as fast as possible until now?

So, how tiny? One per atom? That would be good. And how fast can they type? A billion keystrokes per second? Now we’re talking! We have a 98% chance of one of them managing a SHALL I COMPARE THEE TO A SUMMERS DAY THOU ART MORE LOVELY AND MORE TEMPERATE. 98% is good! But add one more word, and the probability of one of them knocking that out drops to one in fifty million, which is not so good.

I have to make my monkeys smaller! One per atom is not very many, as most of the universe is intergalactic space with less than one atom of matter per cubic metre. There should be more monkeys than this. I shrink the monkey until it occupies the smallest possible space there is. Quantum gravity physics tells us that there is a smallest possible distance, known as the 'Planck length'. So of course I want to use this.

If you were to try to examine anything on a smaller scale than the Planck scale, the sheer effort required to do the examining would be so great that you’d create a tiny black hole there, bigger than the size of the thing you were trying to see. (The black hole would vanish very quickly as soon as you stopped looking.) The same thing would happen if you tried to chop anything into smaller pieces than the Planck length – you’d make a black hole and end up with bigger things than you started with. In fact, nothing can happen on a smaller scale than this – at least, not without radically altering the laws of physics so much that you would all but obliterate any meaning in the word 'smaller'. Experimentally, no-one has come anywhere near getting there, which is probably just as well.

As well as being the size limit on smallness, the Planck length is the fundamental unit of distance – the only one that is not made up with reference to anything else, as are metres and miles and the like. This elegance and purity makes it very important in physics.

I can't see it catching on though – it's way too silly. You wouldn't really want to measure your inside leg in Planck lengths. One Planck length is a hundred billion billion times smaller than the distance across a proton, which is a tiny speck of a thing that sits at the very centre of a hydrogen atom (the smallest atom).

Back to the monkeys.

I’m going to divide the universe into Planck-sized regions, and put a monkey in each one. You will ask what the monkey is made of, when nothing can be smaller than the Planck scale, and I will say that it is not made of anything – it is a single, fundamental monkey particle. One in every Planck sized region of space. These regions are very small – there will be nearly as many monkeys inside the space occupied by a single atom as there are atoms in the universe. And there will be monkeys in the spaces not occupied by atoms too.

And they will type faster. How fast can a thing happen? Just as there is a shortest possible distance, there is a shortest possible time, and it’s called the Planck time. The Planck time is how long it would take you to cover one Planck length if you travelled at the speed of light.

My monkeys will type at a rate of one keystroke per Planck time.

They will type so fast because the energy required to confine a monkey to such a small region will make the monkey extraordinarily hot.

You will ask what the typewriter is made of, and I will say it is not separate from the monkey: typing is what a monkey particle does. (I don’t know what happens to the letters that the monkeys type. There is no room for them or anything else, as the cosmos is jam-packed with hot monkey particles. But I’m not going to let this stop me.)

So, from the Big Bang, with a monkey in every last tiniest unit of space possible, typing at the fastest speed there is, for the entire history of the growing Universe, and do we have a deal?

Yes! The first four lines of the sonnet “SHALL I COMPARE THEE TO A SUMMERS DAY THOU ART MORE LOVELY AND MORE TEMPERATE ROUGH WINDS DO SHAKE THE DARLING BUDS OF MAY AND SUMMERS LEASE HATH ALL TOO SHORT A DATE” will be knocked out somewhere in the cosmos several times a second!

This is good! In fact, every few dozen thousand years, it’ll come together with the next word – SOMETIME – to boot. Will we ever get the next two words (SOMETIME TOO)? We might be lucky – there’s something like a one in three chance in the age of the universe.

So there we are. One in three. Ladies and gentlemen, I give you, from the Monkeys of the Cosmos, four lines and two words of a sonnet!

...FOESZH GIMCED GHN ASIO AKHPS WRSHALL I COMPARE THEE TO A SUMMERS DAY THOU ART MORE LOVELY AND MORE TEMPERATE ROUGH WINDS DO SHAKE THE DARLING BUDS OF MAY AND SUMMERS LEASE HATH ALL TOO SHORT A DATE SOMETIME TOOSFB L FPGPAAO XUN WVIKGXWS TX FSAOL PABK...

I don't know about you, but I think that's rather impressive.

If you want the Complete Works, as the theorem says, you'll have to wait.

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