The Universe in Your Hand

And why it'll change the way you experience the beauty of our world

This book is a masterpiece. I first encountered it at my public library, and just a few pages in, decided I needed my own copy to adorn with annotations. Problem was, the nearest Chapters with this book still in stock was 70 kilometers away, so I proceeded to negotiate with my father on why exactly I needed this book. It was a success!

For a young me, this book was my first memorable adventure into visualizing physics ideas that were out of my mathematical reach. We start off near a volcano, eyes closed, and we paint a tranquil picture in our mindscape. Each chapter is written in small organized chunks, and takes us from one theory to another. For this review, I’ve just compiled a selection of excerpts that are examples of what I enjoy about the book.

“So, to see if E=mc2 is a good deal for nature, imagine the same exchange rate is being offered at JFK airport to change pounds sterling (that’s the initial mass) into US dollars (the energy one gets for it). The exchange rate is then c2, where ‘c’ stands for the speed of light, and ‘c2’ is the speed of light multiplied by itself. For one pound, you’d get 90 million billion dollars. A pretty good deal, I’d say.”

True to Galfard’s promise, he only uses one equation in the entire book — the rest are just concepts. Using the word just here is perhaps unfair; many of these concepts I later covered in my university classes, and reading this book first made me appreciate the beauty of their mathematical structure even more.

“What beast has enough gravitational power to keep such a lightning-fast object close by? Is it even possible to generate such a force? Imagine a marble, and a salad bowl.”

Sure, the visualization the author begins here is an oversimplification of how S0–2’s orbital information supports the hypothesis that we have a black hole at the center of our galaxy, but it is, nevertheless, a good approximation. And far more intuitive than the Bohr-Rutherford models we use all the way up, and even in, university-level chemistry courses (but that is a point of discussion for another day). This book did soothe some of the wishfulness in my heart, using wave-like models for electrons around atoms, which can ““very easily fill in some volume”.

“If you have a hard time grasping what 300 billion stars floating on their own actually means, do not worry too much about it: nobody really can...pick a cubic cardboard box one metre high and fill it to the top with coarse sand from your beach. Now ask them to fill 300 such boxes with the same sand... Kindly ask your friends to fly back to London and pour the contents of these 300 boxes in a disc shape covering Trafalgar Square, and to draw four spiral arms on it. Then tell them to sit on Nelson’s shoulders. That’s what the 300 billion stars of the Milky Way look like to you now.”

Look at this beautiful visualization! Friendliness of scale! Someone, somewhere, at some point had told me that there were as many stars in the universe as grains of sand on Earth, but this feels much more tangible.

“Gravitationally out-powered by the white dwarf’s enormous density, the star is doomed. It can’t even hold on to its own outer layers. As it orbits the dwarf, its surface is torn off to form a long trail of bright, burning-hot plasma that you can see spiralling down towards its greedy dance partner, creating a shining, twisted cosmic river meandering towards the white dwarf’s surface, where it is harnessed and compressed.”

He also has a beautiful way of writing, in which you can feel awe for different things that occur in our universe. Sure, it’s one thing to hear about a pair of stars in which the white dwarf is pulling away mass from the larger one, but would that feel as alive?

“In space, light does not travel, or propagate, on a string, but through the fabric of our universe itself. And to explain the colour shift you just detected, this fabric has to be involved.”

My first introduction to redshift, perfectly shown through an analogy on stringed instruments.

“Electrons, it has to be said, are not the only particles subjected to Pauli’s exclusion principle. Other particles are, too – but not all. Light, for instance, begs to differ.”

After introducing Pauli’s exclusion principle, Galfard doesn’t neglect to mention that there are exceptions. However, he (understandably, likely due to space and time constraints) did not explain why the photons are exceptions; namely that photons have an integer spin number, and as with the other bosons, are not restricted by the exclusion principle. All the fermions, however (those with half spin numbers), have the Pauli exclusion principle apply to them. Why? From what I understand, fermions are antisymmetric, as such, two fermions cannot exist in the same space at the same time. Bosons are symmetric, so they are exempt. Note to self: supposedly the spin-statistics theorem further explains why they are antisymmetric, and I will look into this at some point. 

Although the book is quite old (around 9 years in 2024) , most of it is relatively up to date. For instance, when it was published, we still had not experimentally detected black-hole evaporation. This still holds true! Also, lots of historical pivotal ‘ah hah!’ moments are introduced, such as Wilson’s removal of infinities pocket trick.

Without spoiling too much of the book (must maintain some mystery!), it truly is a whimsical adventure into concepts including, but certainly not limited to, Hawking temperature, Planck lengths/times, Cepheids, Hubble’s Law and the weak bosons, all through gedanken experiments. Give it a read, even if you’re already familiar with all of these on a technical level — there’s a certain sort of beauty The Universe in Your Hand helps you experience.