"For many centuries before modern science, and for the first two and a half centuries of modern science, the division of reality into matter and light seemed self-evident. ...As long as the separation between the massive and the massless persisted, a unified description of the physical world could not be achieved."

“An ordinary mistake is one that leads to a dead end, while a profound mistake is one that leads to progress. Anyone can make an ordinary mistake, but it takes a genius to make a profound mistake.”

“Different ways of writing the same equation can suggest very different things, even if they are logically equivalent. ...In Einstein's original 1905 paper, you do not find the equation E = mc2. What you find is m = E/c2. ...the title of the paper is a question: "Does the Inertia of a Body Depend on Its Energy Content?" …If we can explain mass in terms of energy, we'll be improving our description of the world. We'll need fewer ingrediants in our world-recipe.”

“In a sense, all of Earth glows in the dark. The energy release from natural radioactivity, the lingering fluorescence of stellar explosions, keeps Earth dynamic. It melts the core and keeps it flowing, and heats the crust and mantle, with consequences ranging from the generation of earth's magnetic field to earthquakes and the motion of continents. By contrast, Luna and Mars, because they are smaller, derive less energy from radioactive decays. Geologically, they are dead.”

“To put it crudely, theorists can be tempted to think along the lines “If people as clever as us haven’t explained it, that’s because it can’t be explained – it’s just an accident.” I believe there are at least two important regularities among standard model parameters that do have deeper explanations, namely the unification of couplings and the smallness of the QCD θ parameter. There may well be others.”

“It is delightful in itself when we are able to interpret features of the present as signs confirming our understanding of the past.”

“When two identical 3He atoms collide... the interference is destructive. Particles that behave like 3He atoms are called fermions, short for "particles obeying Fermi–Dirac statistics." ...while bosons imitate one another... the "identity force" between fermions acts like a repulsion, and the probability of finding a fermion at some point in space is reduced if some of its identical siblings are nearby. ...It is the repulsive identity forces between electrons that support white dwarf stars... against their own gravity.”