In the centuries since Galileo proved heliocentrism, science has gradually come to understand more and more of our universe’s natural phenomena: gravity, quantum mechanics, even ripples in space-time. But the final frontier of science isn’t out there, says cosmologist and MIT professor Max Tegmark, it’s the world inside our heads: consciousness. It’s a highly divisive issue—some scientists think it’s unimportant or a question for philosophers, while others like Tegmark think that the human experience and the meaning and purpose of life would disappear if the lights of our consciousness were to go out. Ultimately, Tegmark thinks we can understand consciousness scientifically by finding the pattern of matter from which consciousness springs. What is the difference between your brain and the food you feed it? It’s all quarks, says Tegmark, the difference is the pattern they’re arranged into. So how can we develop a theory of consciousness? Can we build a consciousness detector? And can we really understand what we are without unlocking humanity’s greatest mystery? Tegmark muses on all of this above.