101 quantum questions: what you need to know about the world you can't see

The subatomic world. What is a quantum, anyway? ; Where do the laws of quantum physics hold sway? ; What is the correspondence principle? ; How big is an atom? ; What is inside an atom? ; Why is solid matter solid if it is mostly empty space?

Digging deeper. How big is a nucleus? What is inside it? ; How big are protons and neutrons? What is inside them? ; What is Planck's constant and what is its significance? ; What is a photon? ; What is the photoelectric effect? ; What particles are believed to be fundamental? What particles are composite? ; What is the standard model?

The small and the swift. What are some quantum scales of distance? ; How far can one particle "reach out" to influence another one? ; How fast do particles move? ; What are some quantum scales of time? ; What is the meaning of E=mc²? ; What is electric charge? ; What is spin?

Quantum lumps and quantum jumps. What are some things that are lumpy (and some that are not)? ; What is a "state of motion"? ; Is a hydrogen atom in an excited state of motion the same atom in a different state or is it a different atom? ; What are quantum numbers? What are the rules for combining them? ; What is a quantum jump? ; What is the role of probability in quantum physics? ; Is there any certainty in the quantum world?

Atoms and nuclei. What is a line spectrum? What does it reveal about atoms? ; Why is the chart of the elements periodic? ; Why are heavy atoms nearly the same size as lightweight atoms? ; How do protons and neutrons move within a nucleus? ; What are atomic number and atomic mass?

And more about nuclei. Why does the periodic table end? ; What is radioactivity? What are its forms? ; Why is the neutron stable within a nucleus but unstable when alone? ; What is nuclear fission? Why does it release energy? ; What about nuclear fusion?

Particles. What is a leptron? What are its flavors? ; How many distinct neutrinos are there? How do we know? ; Do neutrinos have mass? Why do they "oscillate"? ; Are there really only three generations of particles? ; How do we know that all electrons are identical?

And more particles. Names, names, names : What do they all mean? ; What are the properties of quarks? How do they combine? ; What are the composite particles? How many are there? ; Does every particle have to be a fermion or a boson? What sets these two classes apart? ; What is a Bose-Einstein condensate? ; How did bosons and fermions get their names?

Interactions. What is a Feynman diagram? ; What are the essential features of Feynman diagrams? ; How do Feynman diagrams illustrate the strong, weak, and electromagnetic interactions? ; Which particles are stable? Which are unstable? What does it mean to say that a particle decays? ; What is scattering? ; What is the same before and after a scattering or a decay? ; What changes during a scattering or decay?

Constancy during change. What are the "big four" absolute conservation laws? ; What additional absolute conservation laws operate in the quantum world? ; What is the TCP theorem? ; What conservation laws are only "partial"? ; What symmetry principles are only "partial"? ; What are laws of compulsion and of prohibition? ; How are the concepts of symmetry, invariance and conservation related?

Waves and particles. What do waves and particles have in common? How do they differ? ; What is the de Broglie equation? What is its significance? ; How are waves related to quantum lumps? ; How do waves relate to the size of atoms? ; What is diffraction? What is interference? ; What is the two-slit experiment? Why is it important? ; What is tunneling?

Waves and probability. What is a wave function? What is Schrod̈inger's equation? ; How do waves determine probabilities? ; How do waves prevent particles from having fixed positions? ; What is the uncertainty principle? ; How does the uncertainty principle relate to the wave nature of matter? ; What is superposition? ; Are waves necessary?

Quantum physics and technology. How are particles pushed close to the speed of light? ; How are high-energy particles detected? ; How does a laser work? ; How do electrons behave in a metal? ; What is a semiconductor? ; What is a p-n junction? Why is it a diode? ; What are some uses of diodes? ; What is a transistor?

Quantum physics at every scale. Why do black holes evaporate? ; How does quantum physics operate in the center of the Sun? ; What is superconductivity? ; What is superfluidity? ; What is a Josephson junction? ; What is a quantum dot? ; What is a quark-gluon plasma? ; What is the Planck length? What is quantum foam?

Frontiers and puzzles. Why are physicists in love with the number 137? ; What is entanglement? ; What is Bell's inequality? ; What is a qubit? What is quantum computing? ; What is the Higgs particle? Why is it important? ; What is string theory? ; What is the "measurement problem"? ; How come the quantum?