One aim of the physical sciences has been to give an exact picture of the material world. One achievement of physics in the twentieth century has been to prove that that aim is unattainable.
Take a good, concrete object, the human face. . . we are aware that [ portraits] do not so much fix the face as explore it; that the artist is tracing the detail almost as by touch; and that each line that is added strengthens the picture but never makes it final. We accept that as the method of the artist.
It is natural to ask, Should not the scientist use a microscope to isolate and analyse the finer features? Yes, he should. But we ought to understand that the microscope enlarges the image but cannot improve it: the sharpness of detail is fixed by the wavelength of the light. But to get more detail, we need a still shorter wavelength. The next step, then, is ultra-violet light, which has wavelength of ten thousandth of a millimetre and less -- shorter by a factor of ten and more than visible light. To go deeper, we must shorten the wavelength: next, to the X-rays. But we have one step more left to take, to the electron miscroscope, where the rays are so concentrated that we no longer know whether to call them waves or particles. . . . The smallest object that has ever been seen is a single atom of thorium. It is spectacular. And yet the soft image confirms that even the hardest electrons do not give a hard outline. The perfect image is still as remote as the distant stars.
We are here face to face with the crucial paradox of knowledge. Year by year we devise more precise instruments with which to observe nature with more fineness. And when we look at the observations, we are discomfited to see that they are still fuzzy, and we feel that they are as uncertain as ever. We seem to be running after a goal which lurches away from us to infinity every time we come within sight of it.
The paradox of knowledge is not confined to the small, atomic scale; on the contrary, it is as cogent on the scale of man, and even of the stars. . . . But when we actually compare our individual observations today, we are astonished and chagrined to find them as scattered within themselves as ever. We had hoped that the human errors would disappear, and that we would ourselves have God's view. But it turns out that the errors cannot be taken out of the observations. And that is true of stars, or atoms, or just looking at som ebody's picture, or hearing the report of somebody's speech.