HERE’S A huge idea to try to wrap your head around while gazing up at the summer stars. What if, contrary to just about everything physicists have been telling us since before Albert Einstein’s theory of relativity, time is not really a fourth dimension indistinguishable from the other three? What if “spacetime,” such a wonderful sci-fi word for that 4-D continuum, is more fiction than science, and time really does exist on its own? That’s the idea put forth by theoretical physicist Lee Smolin in his recent book, Time Reborn. Einstein wrote, “People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion.” Smolin disagrees: “Not only is time real, but nothing we know or experience gets closer to the heart of nature than the reality of time.” As James Gleick explains in The New York Review of Books, Smolin tends to validate what we regular folks think we know, “those of us who wear wristwatches, cross the days off our calendars, mourn the past, pray for the future, feel in our bones the march of time.” But here’s the catch: Smolin’s not so sure that space really is what we think it is. Now there’s an idea.