____ Theory (fill in the space)

[[AK]Nuts]

I'm having a hard time remembering the name of a scientific theory and I thought one of you could get me a quick answer.

When you study something, you change the very nature of the thing.

It's a theory that when you study something like animals, you are in fact changing them, their environment, hence you can never, truely study anything without interferring with it.


arg!