The Teleporting Robot: The Science of Size

So why are we being fooled by the teleporting robot that doesn't vanish at all?

'Look at the size of that!' Well, it turns out that the human visual brain is not that good at measuring the size of things. We can tell quite accurately if two lines we see side by side are the same length, but show one then the other and we aren't quite so hot. The context in which we see objects can also influence our perception of size.

Take the case of two circles of the same size, one surrounded by a larger circle and one surrounded by smaller circles. We tend to see the circle surrounded by bigger circles as small. The same circle surrounded by smaller circles is seen as larger.

The brightness of things alters our perception of size too. Bright objects against a dark background seem larger than darker objects against a light background even if they are the actually the same size.

These optical illusions are used all the time by stage magicians. They build their magical apparatus making use of these human visual errors so it looks impossible that someone could hide in what looks to the audience like a 'tiny' box. Some of the strongest stage illusions of all time depend on using this slip in human perception to work.