A Map of the Invisible

A Map of the Invisible (Atom Land in the US and Canada) is a Sunday Times Science Book of the Year and has been reviewed in brief by Nature here and by Marcus Chown in Times Higher Education. It was one of Symmetry Magazine’s Physics Books of 2018.

Here are some more reviews, and here’s the “launch” lecture from the Royal Institution.

  • What is the universe really made of?

    The paperback edition of A Map of the Invisible is out now, and to help promote it we made a few videos on some of the themes in the book. Here’s the first one:


And the second is here.

Notes and Corrections

This is a space to put any additional thoughts, notes, background information about the expeditions, and to correct errors which confuse the physics (yes there are some, sorry).

Expedition I: Sea Legs

Expedition II: Atom Land

Expedition III: The Isle of Leptons, and Road Onwards

Page 72 footnote. Fixed in all editions except hardback UK. Should read:

If you want to know, the full expression is E2 = m2c4 + p2c2, where E is the energy, m is the mass and p is the momentum. For zero momentum, this reduces to E2 = m2c4, and taking the square root of both sides gets us the familiar E = mc2. And possibly E = –mc2 too (see text).

Page 73. Fixed in the Italian edition. Near the bottom, should say “B times the momentum”, not “B times the energy”.

Page 74 footnote. Mostly fixed in all editions except hardback UK, still a couple of errors in the US edition and UK paperback, a bit more fixed in the Italian edition but one small error only fixed here. What a mess, sorry (although the sense of the argument is correct even in the first version). Should read:

You don’t need to understand exactly how this works in order to continue our exploration, but if you’d like to see it, here goes. We want an equation like E = Am + Bp, but which is also consistent with E2 = m2c4 + p2c2. If we square the first equation we have to multiply all the terms by each other, so we get E2 = A2m2 + (Am × Bp) + (Bp × Am) + B2p2. Now we have two expressions which ought to both equal E2, so they must equal each other: m2c4 + p2c2 must equal A2m2 + (Am × Bp) + (Bp × Am) + B2p2, for any values of m and p. If we let A and B2 be equal to c2, that takes care of the terms involving the square of the mass and the square of the momentum. But we are left with the other bit, (Am × Bp) + (Bp × Am). This can only be zero (for all values of p and m, because we want an equation which works for all particles) if A × B is equal to the negative of B × A. But for all numbers, A × B equals B × A. So A and B cannot be numbers.

Page 88: Fixed in all editions except the UK hardback. A wrong characterisation of the statistical significance. The phrase

“which is about a 3-in-10000 chance that the theory and experiment are both correct”

should say:

“which is expected only about 3-in-10000 times if both theory and experiment are correct”

Rest Stop

Gravity: A Distant Diversion

Expedition IV: Great Train Journeys

Page 129. Fixed in Italian edition: “eight or twelve” should be “eight or ten”

Expedition V: The Isles by Air

Page 156. Fixed in Italian edition. Sadly I managed to slightly mess up my description of the Wu experiment. The description is correct if the senetence at the end of the second paragraph is changed from

“A inversion of parity will not affect the magnetic field – electromagnetism conserves parity – but it will flip the spin.”


“A inversion of parity will not affect the magnetic field – electromagnetism conserves parity – or the spin of the nucleus, but it will reverse the direction of motion of an emitted electron.”

(Both spin and magnetic field are axial vectors, so they both flip under parity, but their product does not, so the energy doesn’t change.)

Expedition VI: The Remote Neutrino Sector

Page 189. Fixed in Italian edition. Ray Davies should be Ray Davis.

Expedition VII: Into Bosonia

Expedition VIII: Far East

Page 247. Fixed in all editions except the UK hardback. The Planck scale is actually 1028 eV (or 1019 GeV). What’s an order of magnitude between friends though?

Page 268. Fixed in Italian edition. Near the bottom of the second paragraph is should say “there would be no need for all the electroweak symmetry-breaking stuff” not “there would be a need…”



Thanks to Luisa Doplicher, Roger Henry, Andreas Korn, …. for spotting these.

Also Andy Tamlin for spotting the spelling error on the map in the UK hardback. Go on, find it yourself.