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When it comes to time, and what the heck it actually is, there's a clash of ideas between physics and neuroscience.
If you're here to indulge in some mind-bending talk about time travel, neuroscientist Dean Buonomano is about to break some hearts. He doesn't think it's plausible—but if it were, there is one hypothesis of the universe in which it could theoretically happen. There are currently two main ideas about time: Presentism—the notion is that only the present is real: the past happened, the future will happen, but only the present exists—and Eternalism, in which the past, present, and future are all equally real. If you want to flux-capacitor your way back in time, you'll want to hope that Eternalism turns out to be the true theory. It's known to physicists as Block Universe, where all moments of the past, present, and future are already laid out in a continuum—there are places to travel to. "Under Presentism we can pretty much take the possibility of time travel off the table because there’s no other moments to go to—only the present is real," says Buonomano.