http://100days100ways.blogspot.com/2011/03/day-77.html

The first video is a neat illustration of the double-split experiment, but it's a little funny to me how our host makes such a mysterious lips-smacking deal over how mere observation causes the particle to change its behavior "as if it were aware of being watched!" This can only be deliberate silliness. The people putting this thing together know full well that at a quantum scale, detection = direct interaction with the particle.

It is as if some gigantic quantum physicist wanted to observe me walking down my street, and to do so, threw a bean-bag chair at me at a high rate of speed. As I stagger along recovering from the impact, the physicist, in jubilant wonder, cries: "why, he changed how he was walking - just as if he knew he had been observed...!" Bugger off you prat - you just threw a bean bag chair at me! Of course the electron changes how it acts after the process of being measured. The first time, it passed unmolested through the slit. The second time - from the electron's teensy tiny standpoint, it got mugged.

The detector isn't an eye standing to the side. The detector is any device placed directly in the slit that interacts directly with the passing electron and is physically changed by the interaction. The electron is physically changed by the interaction as well.

Or to put a finer point on it: it isn't observation (a conscious process) that changes what is being measured at the quantum level. It is the process of measurement itself. A physical process.

We trigger the physical process, so we can use the result it will generate to make an observation. But our tools are so big and clumsy (relative to tiny, quantum-scale phenomenon) that we change what we seek to observe - not by observing it, but by measuring it.