Quantum Imagination

Stretching the imagination in the quantum world. 1949 Dover Publications edition of the work first published by the University of Chicago Press in 1930. Cover design by Edmund Gillon Jr.

If there is one area of modern science which requires a huge leap of imagination to understand it, it must surely be quantum physics.  Now generally accepted as valid, it not only gives results which are consistent with classical Newtonian mechanics, but also explains things at the microscopic scale.

But at that very small level, things are weird, not least the idea that light can be both a particle and a wave at the same time.  Grasping even that concept is difficult enough.  One can imagine the mental gymnastics required of those who first identified this weirdness back in the early twentieth century.

In their seminal text from 1935 Introduction to Quantum Mechanics, Linus Pauling and E Bright Wilson explained how classical mechanics led to the “old” quantum theory, but this was unable to explain a number of experimental results.  They identified the formulation by Werner Heisenberg in 1925 as the culmination of a new approach, alongside the independent discovery of wave mechanics by Erwin Schrödinger.  And here began an entirely new way of imagining the world.

Heisenberg, who later received the Nobel Prize in 1932 for this work, gave a series of lectures at the University of Chicago which were published in 1930 as The Physical Principles of the Quantum Theory.  These classic presentations gave a picture of a universe that stretched the mind.  Right near the start, he observed how the theory of general relativity had represented a “radical departure from the classical conception of the world” but, although it made “the greatest of demands on the ability for abstract thought”, it still fulfilled the traditional requirements of science in dividing the world into “observer and observed” and hence had a clear formulation of the law of causality.

He made clear that this “is the very point at which the difficulties of the quantum theory begin.”  The interaction between the observer and the object being observed “causes uncontrollable and large changes in the system.”  It led to Heisenberg’s famous uncertainty principle – when observing a particle, you cannot know both its position and momentum (where it’s going) at the same time.  This isn’t just a result of the difficulty in making measurements – it’s intrinsic to the nature of particles at the quantum level.  They really don’t have both precise position and precise momentum.

In his 2017 book The Greatest Story Ever Told…So Far, the theoretical physicist Lawrence Krauss gives an account of the discoveries which led to our current knowledge of the hidden world of reality on both the large and small scales.  He explains how the discoveries of Schrödinger and Heisenberg “revolutionized our picture of atoms”, describing them as some of the “brief bursts of theoretical insight” that change everything.

He goes so far as to say that Heisenberg’s uncertainty principle “epitomizes in many ways the complete demise of our classical world view of nature.”  In effect, nature has placed an absolute limit on our ability to know something – both the momentum and position of a particle – regardless of any technology that the human race might one day develop.  And that’s a hard idea to grasp even once you’ve managed to get your head around quantum weirdness in the first place.

Heisenberg recognized the difficulties in understanding the fundamental principles of quantum theory.  In his preface to his 1930 lectures, he noted that, even though experiments were already confirming important consequences of the theory, “the physicist more often has a kind of faith in the correctness of the new principles than a clear understanding of them.”  He sought to correct that viewpoint, but it’s fair to say that, even now, the human imagination can only stretch so far when trying to comprehend a world which simply doesn’t make common sense.

Richard Hayes, Assistant Editor (Odyssey)


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