Looking At Something Changes It.

Every Experiment Destroys Some Of The Knowledge Of The System Which Was Obtained By Previous Experiments.

Many People Will Tell You That An Expert Is Someone Who Knows A Great Deal About The Subject. To This I Would Object That One Can Never Know Much About Any Subject. I Would Much Prefer The Following Definition: An Expert Is Someone Who Knows Some Of The Worst Mistakes That Can Be Made In The Subject, And How To Avoid Them.

The Problems Of Language Here Are Really Serious. We Wish To Speak In Some Way About The Structure Of The Atoms. But We Cannot Speak About Atoms In Ordinary Language.

Even For The Physicist The Description In Plain Language Will Be A Criterion Of The Degree Of Understanding That Has Been Reached.

The Incomplete Knowledge Of A System Must Be An Essential Part Of Every Formulation In Quantum Theory. Quantum Theoretical Laws Must Be Of A Statistical Kind. To Give An Example: We Know That The Radium Atom Emits Alpha-radiation. Quantum Theory Can Give Us An Indication Of The Probability That The Alpha-particle Will Leave The Nucleus In Unit Time, But It Cannot Predict At What Precise Point In Time The Emission Will Occur, For This Is Uncertain In Principle.