In Three Roads to Quantum Gravity, Lee Smolin provides an accessible overview of the attempts to build a final "theory of everything." He explains in simple terms what scientists are talking about when they say the world is made from exotic entities such as loops, strings, and black holes and tells the fascinating stories behind these discoveries: the rivalries, epiphanies, and intrigues he witnessed firsthand.

Three of the most important words in science are I don't know. Not knowing implies a universe of opportunities—the possibility of discovery and surprise. Our understanding of science has advanced immeasurably over the last 500 years, yet many fundamental mysteries of existence persist: How did our universe begin? How big is the universe? Is time travel possible? What’s at the center of a black hole? How did life on Earth arise? Are we alone? What is consciousness, and can we create it?

Right now, you are orbiting a black hole. The Earth goes around the Sun, and the Sun goes around the centre of the Milky Way: a supermassive black hole—the strangest and most misunderstood phenomenon in the galaxy. In A Brief History of Black Holes, University of Oxford astrophysicist Dr Becky Smethurst charts the scientific breakthroughs that have uncovered the weird and wonderful world of black holes, from Hawking radiation to the iconic first photographs of a black hole in 2019.

Not only can we not currently explain the origin of the universe, it is questionable we will ever be able to explain it. The notion that there are universes within particles, or that particles are conscious, is ascientific, as is the hypothesis that our universe is a computer simulation. On the other hand, the idea that the universe itself is conscious is difficult to rule out entirely. 

You are reading the word now right now. But what does that mean? What makes the ephemeral moment "now" so special? Its enigmatic character has bedeviled philosophers, priests, and modern-day physicists from Augustine to Einstein and beyond. Einstein showed that the flow of time is affected by both velocity and gravity, yet he despaired at his failure to explain the meaning of now. Equally puzzling: Why does time flow? Some physicists have given up trying to understand and call the flow of time an illusion.