Apart from learning physics- from learning mathematics and chemistry, I also attended lectures by a visiting professor. His name was Herman Mark. A wonderful chemist. A chemist who is responsible for a new field of chemistry - long chain molecules, non-repetitive chains, chains of all kinds, which, for instance, are quite essential in understanding biochemistry. He founded that science and he lectured to us. It was a small group, but it was a wonderful one. And he noticed my interest and fed it. This really managed to make in me a big change, for an interest in mathematics, for an interest in physics. He told us about a young French physicist, Louis de Broglie, who wrote a paper, the content was this- if divide matter, then some components of all matter, no matter what, what kind of component you always find, are electrons. Nothing new. As a chemist, I knew that all along. What de Broglie added was- these electrons can be described not only as particles but also as waves. And he showed how the velocity of these waves, the practically measured velocities, can be brought into relation with the velocity of particles. Now, I had known from conversations, early conversation, with people like, for instance, Eugene Wigner, that there was a strange situation in physics. Light - that has been known for many, many decades, more than a century, as electromagnetic waves, a process in the continuum - light also does behave sometimes as though it consisted of particles. One little aside that you might know, one of the truly great physicists, Einstein, who discovered relativity and got the Nobel Prize, did not get the Nobel Prize for relativity. In fact, when he was informed that he got it, he was told very explicitly- It is not for that problematical statement of relativity, it is for your concrete arguments that light can be considered as particles or waves.