"In November 1, 2008, a man named Satoshi Nakamoto posted a research paper to an obscure cryptography listserv describing his design for a new digital currency that he called bitcoin. None of the list's veterans had heard of him, and what little information could be gleaned was murky and contradictory. In an online profile, he said he lived in Japan. His email address was from a free German service. Google searches for his name turned up no relevant information; it was clearly a pseudonym. But while Nakamoto himself may have been a puzzle, his creation cracked a problem that had stumped cryptographers for decades. The idea of digital money - convenient and untraceable, liberated from the oversight of governments and banks - had been a hot topic since the birth of the Internet. Cypherpunks, the 1990s movement of libertarian cryptographers, dedicated themselves to the project. Yet every effort to create virtual cash had foundered. Ecash, an anonymous system launched in the early 1990s by cryptographer David Chaum, failed in part because it depended on the existing infrastructures of government and credit card companies. Other proposals followed - bit gold, RPOW, b-money - but none got off the ground.
One of the core challenges of designing a digital currency involves something called the double-spending problem. If a digital dollar is just information, free from the corporeal strictures of paper and metal, what's to prevent people from copying and pasting it as easily as a chunk of text, 'spending' it as many times as they want? The conventional answer involved using a central clearinghouse to keep a real-time ledger of all transactions - ensuring that, if someone spends his last digital dollar, he can't then spend it again. The ledger prevents fraud, but it also requires a trusted third party to administer it.
Bitcoin did away with the third party by publicly distributing the ledger, what Nakamoto called the 'block chain.' Users willing to devote CPU power to running a special piece of software would be called miners and would form a network to maintain the block chain collectively. In the process, they would also generate new currency. Transactions would be broadcast to the network, and computers running the software would compete to solve irreversible cryptographic puzzles that contain data from several transactions. The first miner to solve each puzzle would be awarded 50 new bitcoins, and the associated block of transactions would be added to the chain. The difficulty of each puzzle would increase as the number of miners increased, which would keep production to one block of transactions roughly every 10 minutes. In addition, the size of each block bounty would halve every 210,000 blocks - first from 50 bitcoins to 25, then from 25 to 12.5, and so on. Around the year 2140, the currency would reach its preordained limit of 21 million bitcoins."
(Benjamin Wallace, 23 November 2011, Wired Magazine)
"Behold! human beings living in a underground cave, which has a mouth open towards the light and reaching all along the cave; here they have been from their childhood, and have their legs and necks chained so that they cannot move, and can only see before them, being prevented by the chains from turning round their heads. Above and behind them a fire is blazing at a distance, and between the fire and the prisoners there is a raised way; and you will see, if you look, a low wall built along the way, like the screen which marionette players have in front of them, over which they show the puppets.
And now look again, and see what will naturally follow if the prisoners are released and disabused of their error. At first, when any of them is liberated and compelled suddenly to stand up and turn his neck round and walk and look towards the light, he will suffer sharp pains; the glare will distress him, and he will be unable to see the realities of which in his former state he had seen the shadows; and then conceive some one saying to him, that what he saw before was an illusion, but that now, when he is approaching nearer to being and his eye is turned towards more real existence, he has a clearer vision, -what will be his reply? And you may further imagine that his instructor is pointing to the objects as they pass and requiring him to name them, -will he not be perplexed? Will he not fancy that the shadows which he formerly saw are truer than the objects which are now shown to him?"
Plato's Republic, book vii, 514a-c to 521a-e
[Plato's allegory about consciousness underpins Western philosophy. It also introduces a fundamental concept used by Christian theology to describe spiritual enlightenment.]
Orienteering courses [...] use the linked list structure: a series of places linked together in a chain. Orienteering is the sport where you have to map read you way round a course. It is like cross-country running except that you do not have to stick to paths and are not told the route to take. You are just told the series of points you must visit and the order you must visit them. You can either try to go in straight lines (through streams and thickets, down steep valleys only to go straight up the other side), or you can navigate round obstacles (going further to a bridge or contouring round the valleys). You are given a map at the start, with all the points you have to visit marked on it. The fastest person to complete the course wins. This is not necessarily the fastest runner, but the best combined runner and navigator. Orienteering is thus the sport of following a linked list through forest and moors as fast as possible.