Six Impossible Things

Most of the physics you learn at school hasn’t changed for hundreds of years. It is important stuff because we know that it works and it underpins a lot of the modern world. But that doesn’t mean it is right. This is the point that is made in John Gribbin’s new book, Six Impossible Things.

If you think that physics books are boring, then Six Impossible Things may change your mind, not only because it is a compelling read but also because it admits what we don’t know – and as such signposts areas for further thought and possible future Nobel Prizes for physics.

The book is all about the double-slit diffraction experiment famously attributed to Thomas Young around 1802 (but observed around 150 years earlier by Francesco Grimaldi) that “proved” light must be a wave phenomenon. You can learn more about this experiment, and see an explanatory animation, on the Molecular Expressions website of Florida State University (click here).

When Einstein successfully explained the photoelectric effect using particles of light, called photons (for which he won the Nobel Prize in 1921) everything changed. How could particles of light create a diffraction pattern that relied on light being a wave phenomenon? The simple solution was to say that light could be both a particle and a wave (wave-particle duality).

This issue was further challenged by a new series of experiments, started in 1974 by (fittingly, given Grimaldi’s lack of recognition about 350 years earlier) three Italian physicists named Merli, Missiroli and Pozzi. This team, and others, designed experiments that turned down the light beam (actually electrons) until there was only one particle running through the apparatus at any given time. Even under these conditions, a diffraction pattern persisted.

We still don’t know how objects (photons of light, electrons or anything else) can “be” both particles and waves, appearing to choose their existence according to the manner in which they are observed and measured. But we do have six different models (the Six Impossible Things of Gribbin’s book title) that attempt to explain these phenomena.

The explanations are crazy – and some more crazy than others – but “crazy does not necessarily mean wrong,” as Gribbin points out. So if you fancy reading some “crazy” ideas in physics, such as future waves that extend backwards in time to interact with present waves that move forwards in time, then this is the book for you. If nothing else, Six Impossible Things should leave you with three important insights;

• there are some simple things that physics still cannot explain
• physicists can be very imaginative when trying to explain things they do not understand
• we don’t have to understand things to be able to make use of them

Six Impossible Things, by John Gribbin, is published by Icon Books (2018), priced £9.99.