As physics has progressed, its most fundamental theories have become more distant from everyday experience posing challenges for understanding, notably with quantum mechanics. This volume contains twenty-nine essays written to address such challenges. The essays address issues in quantum mechanics, quantum cosmology and physics in general. Examples include: How do we apply quantum mechanics to the whole universe when all observers are inside? What do we mean by past, present, and future in a four-dimensional universe? What is the origin of classical predictability in a quantum universe? Could physics predict non-computable numbers? Short personal recollections of Murray Gell-Mann and Stephen Hawking are included.

The essays vary in length, style, and level but should be accessible to most physicists.