Anil Ananthaswamy in New Scientist:
“Time is a road without any bifurcations, intersections, exits, or turnarounds.” With that, neuroscientist Dean Buonomano sets up the meat of his new book, Your Brain is a Time Machine – and an intriguing difference between the way we animals navigate time as opposed to space.
Not that contrasting time and space makes the task of understanding time any easier, as Buonomano illustrates later: “The physicist’s talk on the nature of time ended on time, but it seemed to drag on for a long time.” This captures various notions of time: natural time, clock time and subjective time.
Natural time is what physicists fuss about. Is time real? Or is the passage of time an illusion, and do all moments in time exist in much the same way that all coordinates of space exist? Neuroscientists, on the other hand, fuss about clock time and subjective time.
To explain natural time, physicists and philosophers back eternalism, according to which the past, present and future are all equally real. “There is absolutely nothing particularly special about the present: under eternalism now is to time as here is to space,” writes Buonomano.
The other main explanation of natural time is presentism, according to which only the present moment is real – a view that tallies with our sense of subjective time. The past is gone, the future hasn’t happened yet. “Neuroscientists are implicitly presentists,” says Buonomano. “But despite its intuitive appeal, presentism is the underdog… in physics and philosophy.”