We spend a third of our lives asleep. Every organism on Earth—from rats to dolphins to fruit flies to microorganisms—relies on sleep for its survival, yet science is still wrestling with a fundamental question: Why does sleep exist?

On September 14th, 2015, a ripple in the fabric of space, created by the violent collision of two distant black holes over a billion years ago, washed across the Earth. As it did, two laser-based detectors momentarily twitched, confirming a century-old prediction by Albert Einstein and marking the opening of a new era in astronomy.

Extra dimensions of space — the idea that we are immersed in hyperspace — may be key to explaining the fundamental nature of the universe. Relativity introduced time as the fourth dimension, and Einstein’s subsequent work envisioned more dimensions still — but ultimately hit a dead end.

Proposed a century ago to better explain the mind-bending behavior of the smallest constituents of the universe, quantum theory has implications far beyond the atom. This rich set of laws has applications both practical and extraordinary.

When no one is looking, a particle has near limitless potential: it can be nearly anywhere. But measure it, and the particle snaps to one position. How do subatomic objects shed their quantum weirdness?

What we touch. What we smell. What we feel. They’re all part of our reality. But what if life as we know it reflects only one side of the full story? Some of the world’s leading physicists think that this may be the case.

The multiverse hypothesis, suggesting that our universe is but one of perhaps infinitely many, speaks to the very nature of reality. Join physicist Brian Greene, cosmologists Alan Guth and Andrei Linde, and philosopher Nick Bostrom as they discuss and debate this controversial implication of forefront research.

Why is there something rather than nothing? And what does ‘nothing’ really mean? More than a philosophical musing, understanding nothing may be the key to unlocking deep mysteries of the universe, from dark energy to why particles have mass.