ultra-violet light and in X-rays; and these, accordingly, are now often
used for minute physical research.

In this way, however, we are led by nature to a definite boundary; for
we now find ourselves in a realm where the dimensions of the
observation medium and the observed object are more or less the same.
The result, unfortunately, is that when the 'light' meets the object,
it changes the latter's condition of movement. On the other hand, if a
'light' is used whose wave-length is too big to have any influence on
the object's condition of movement, it precludes any exact
determination of the object's location.

Thus, having arrived at the very ground of the world - that is, where
the cosmic laws might be expected to reveal themselves directly - the
scientist finds himself in the remarkable situation of only being able
to determine accurately either the position of an observed object and
not its state of motion, or its state of motion and not its position.
The law he seeks, however, requires that both should be known at the
same time. Nor is this situation due to the imperfection of the
scientific apparatus employed, but to its very perfection, so that it
appears to arise from the nature of the foundation of the world - in so
far, at least, as modern science is bound to conceive it.

If it is true that a valid scientific knowledge of nature is possible
only in the sphere open to a single-eyed, colour-blind observation, and
if it is true - as a science of this kind, at any rate, is obliged to
believe - that all processes within the material foundation of the
world depend on nothing but the movements of certain elementary
particles of extremely small size, then the fact must be faced that the
very nature of these processes rules out the discovery of any stable