“HERE’S A FAVORITE JOKE among physicists: “Time flies like an arrow, but fruit flies like a banana.” Some attribute it to Groucho Marx (a layman). Some attribute it to the high regard that physicists have for their careers and aptitudes as opposed to those of biologists.”
“But maybe it’s just a case of whistling past the graveyard.”
“Time is among the slipperiest concepts in physics. It is a dimension (number four) but not one you can visualize. It speeds up and slows down — subjectively, but also by the clock, if you go fast enough.”
“Its exact nature has baffled philosophers for ages: “What, then, is time?” Augustine complained. “If no one ask of me, I know; if I wish to explain to him who asks, I know not.” Physicists call it t, for use in their equations (where, unlike its behavior in the real world, it is reversible), and seem unworried by its insubstantiality.”
“In Now: The Physics of Time, Berkeley physics professor Richard A. Muller sets out to trap this enormous will-o’-the-wisp. An experimentalist rather than a theoretician, he has seen things in the Lawrence Berkeley Laboratory that would curl your hair. He is not free to live in his mind as the theoreticians are; he has actually manipulated time by, for instance, accelerating pions to just below the speed of light.”
“Muller addresses the question of what gives time its flow — its real-world direction from past to future.”
“Here he takes issue with Sir Arthur Eddington, the brilliant English physicist celebrated for his experimental proof of Einstein’s special theory of relativity. Eddington pinned the direction of the arrow of time to increasing entropy — the random disorder that persists in any particular system, including the universe.”
“Muller calls Eddington’s theory of time’s arrow a “jigsaw piece that has been crammed in the wrong spot,” the theory “that has most inhibited progress in understanding now.””
“Be that as it may, the now does indeed move toward the future and away from the past. “Why?” asks Muller. “We can change the future,” he writes; “Why can’t we change the past? Or can we?””
“Besides Eddington’s emphasis on increasing entropy, there are two other “jigsaw pieces jammed into the wrong places” in our picture of the universe. One is the misinterpretation of 4D space-time diagrams.”
“Such diagrams “make no reference to the fact that time flows or that a now exists,” giving physicists “a ready excuse to avoid these issues. […] The mistake of this vision is in interpreting a computational tool as a deep truth. It is fundamentally the error of physicalism: if it isn’t quantifiable, it isn’t real.””
“The third misplaced piece is “the assumption, made by Einstein and others, that the past can be, must be, able to determine the future completely.””
“Muller, who convincingly refutes unpleasant physics arguments denying free will, is a champion of the open-endedness of our existence:”
“Free will is the ability to use nonphysics knowledge to […] choose among the accessible futures. It doesn’t stop the increase of entropy, but it can exercise control over accessible states, and that gives entropy direction.”
“Let’s hope so. Might we, or persons like us, manage, in the far future, to avoid or postpone the predicted bleak universal heat death?”
“Muller doesn’t go this far, but he suggests that now can save us:”
“As space expands, so does time. […] Now is that special moment in time that has just been created in the expansion of the 4D universe, as part of the continuing 4D Big Bang. By the flow of time, we mean the continual addition of new moments, moments that give us the sense that time moves forward, in the continual creation of new nows.”
“Sara Lippincott, a former nonfiction editor at The New Yorker, is a freelance book editor in Los Angeles, specializing in science.”