70 Are the Androids Dreaming Yet? something from the signals it receives. This is similar to our engineer probing the terminals of the circuit of a black box. How can we know our experience of the world is real? Understanding the World The French philosopher Descartes gave us an explanation for this paradox. He spent a long time looking skeptically at everything we perceive. For example, when we poke a stick into a pond, the surface of the water bends light and the stick appears to have a kink in it. Our eyes tell us the stick is bent, but our brain ‘knows’ the stick is straight: it’s an illusion. Descartes wondered if something so simple could be an illusion, perhaps the whole of our experience is too. His eventual solution underpins much of modern philosophy - ‘T think therefore I am, cogito ergo sum. Even if we doubt everything else, we cannot doubt we are thinking about this doubt. At least we can rely upon the existence of this ‘thought’ as some reality. Descartes built up from this bedrock the real world we live in. We can be sure we experience things and can apply logic and use thought. We can use this intellectual faculty to tell a great deal about our Universe. True Understanding In the QED lecture series, The Strange Thing about Light and Matter, Richard Feynman relates the story of the ancient Mayan astronomers. 3000 years ago they were able to predict the motion of Venus in the sky using only pebbles. They had a simple system that could predict when the planet would rise over the horizon. Put a stone in the jar every day, take out a stone once a week, add a stone at every new moon. If the number of stones in the jar is divisible by 23, Venus will rise. ’m making up the details but you see the idea... It’s a very simple algorithm. What should we conclude if the Mayans had perfected their calculations to predict the motion of Venus and it proved reliable over a whole century? Would this constitute understanding? Feynman would say no: the Mayan under