Since the days of Ancient Greece, philosophers and scientists have been wondering: What is space? Is the absence of things… a thing? These questions continued to fascinate physicists in the modern era, leading Isaac Newton, Ernst Mach, and Albert Einstein to wonder about the true nature of the fabric of the cosmos. The search for an answer led them to some of the greatest theories in physics. This week, we ask if space and time are really real, and how they come together to make “spacetime”!