The Particle At The End Of The Universe Book

Carroll tells us about the discovery of the Higgs boson and the importance of the underlying Higgs field to the Standard Model of particle physics. He describes the Large Hadron Collider, how it works, how it was used to find the Higgs boson and why this was so difficult. He imparts a bit of drama describing some of the key people involved and the excitement of the physics community at seeing an enormous amount of work come to fruition in 2012 at CERN. The Higgs had been theorized years earlier by its namesake Peter Higgs and others. Its discovery validated the Standard Model and bolstered physicists’ faith in this widely accepted picture of the laws of nature. In the Standard Model, the Higgs field imparts mass to particles (specifically charged fermions and W and Z bosons). The Higgs is not responsible for all mass, but if it were missing, electrons would lose mass and atoms could not form. Thus, if the Higgs field were to disappear, we and everything else would go poof.

What really intrigued me about this book however, wasn’t the story of the discovery. It was Carroll’s lucid explanations of the Standard Model, the relationships between and properties of the particles, and particularly of quantum field theory. He explains how symmetry leads to force carrying bosons, how fields produce particles and how fields facilitate particles changing into and generating new particles. He does this without math, so it is a simplified version of this vision of reality, but one I could get my arms around. He starts with the basics, categorizing the particles and forces and steadily introduces more complicated concepts and ends throwing the most complicated topics in appendices such as an explanation of spin. I appreciated this graduated approach.

Carroll explains wave particle duality straightforwardly. “According to quantum field theory absolutely everything is made of a field or combination of fields. What we call ‘particles’ are tiny vibrations in fields.” “The fields themselves aren’t ‘made of’ anything – fields are what the world is made of. We don’t know of any lower level of reality. Magnetism is carried by a field, as are gravity and the nuclear forces. Even what we call ‘matter’ – particles like electrons and protons – is really just a set of vibrating fields.” “Matter is really waves (quantum fields), but when we look at it carefully enough we see particles.” “How the world appears when we look at it is very different from how it really is.”

Carroll proceeds throughout the book to describe interactions in terms of particles, yet he keeps us aware that underlying this image are vibrations in fields that induce vibrations in other fields. Visualizing this was more satisfying to me than trying to picture a particle just changing into a different one or ones. For example when a neutron decays becoming a proton after emitting an electron and antineutrino we might wonder where these new particles came from. Fermi in 1934 suggested the following way of thinking about it by applying field theory to fermions. Each of these particles come from their own fields, thus you can visualize the transfer of a vibration from the neutron field to the fields for the other particles even though you can’t see the vibrations, only the particles once the transfer is complete. This also explains virtual particles which appear to constantly be coming into and out of existence which are transient vibrations that can be a stepping stone from one particle to another. A Higgs boson can decay into two photons, but not directly, first it couples with a massive virtual particle (usually a top quark) producing the photons. Try thinking of this interaction in terms of vibrations in fields. This was a signature reaction the Higgs hunters were looking for and found at the LHC. The Higgs itself decays so quickly that it is never seen and is identified by its end products, in this case the two photons.

The discussion above should give those interested the flavor of the book. I found Carroll’s descriptions of symmetry, symmetry breaking, and even spin helpful as were those of fields and virtual particles. Although there were, of course, many things I found difficult to understand if not incomprehensible. For example Carroll describes spin, “One of the consequences of quantum mechanics is that individual particles can also have ‘spin’ even though they are not really rotating around anything.” But for me the puzzles are part of the enjoyment of books like this. I’ve read two of Carroll’s other books: The Big Picture and From Eternity to Here . I loved them both. The Particle at the End of the Universe is more down to earth (if that is fair to say about science based on quantum mechanics) than the other two but every bit as enjoyable.