By observing the way that light moves inside a metamaterial, researchers have reconstructed how spacetime has expanded since the Big Bang. The results provide a better understanding of why time moves in only one direction, and also suggest that time travel is impossible.

In their study, electrical engineers Igor Smolyaninov and Yu-Ju Hung from the University of Maryland have built a metamaterial by patterning plastic strips on a gold substrate, which they then illuminated with a laser. Because the mathematics of electromagnetic spaces (which describe the metamaterial) is similar to the mathematics of general relativity (which describe spacetime), the way light moves in the metamaterial is exactly analogous to the path – or “world line” – of a massive particle in (2+1)-dimensional Minkowski spacetime. . .