Speech at the Neutrino Conference at StonyBrook, Oct. 11-13, 2002
C.N.Yang

We are all very happy that Ray is receiving the honor that he so richly deserves.

Einstein had said “ Subtle is the Lord......”.

Indeed nature presents layers upon layers of subtlety . To us at every moment , some of these subtleties appear necessary, others not.

Take as an example, quantum theory. Acording to classical physics around the beginning of the 20-th century, all matter should be unstable. Some new concepts were urgently needed to stabilize matter. Thus quantum theory was born, as a necessary subtlety at the time. Or take string theory now. It was invented to amalgamate quantum theory with gravity. Should it be successful, it would be a necessary subtlety.

Now consider strange particles around the late 1940s. It was uncalled for. Their appearance was therefore an unnecessary subtlety. Or parity nonconservation in the mid-1950s. Again uncalled for. Therefore another unnecessary subtlety. It remains so to this day.

An unnecessary subtlety may in time become a necessary subtlety. Consider, for example the theory of energetics. To its adherents such as Mach and Ostwald, kinetic theory, if relevant, was an unnecessary subtlety. Of course, in time, kinetic theory became a necessary subtlety.

Personally I tend to disbelieve unnecessary subtleties. That is perhaps why Dyson called me conservative. I did not believe in neutrino oscillations, even after Davis’ painstaking work and Bahcall’s careful analysis: The oscillations were, I believed, uncalled for. Now, after the beautiful experiments which we shall hear about in the next few days, I have to surrender and accept neutrino oscilations as reality , but still as unnecessary subtleties.

Like all physicists, I have faith in our discipline, and also believe that in time, neutrino oscilations will become, through new depths of understanding, necessary subtleties.