Physicists have been pondering this quagmire for a century, and they’re no closer to the truth than when Einstein first challenged our notions about time.
Human beings live in a society governed by time. We dwell on irreversible mistakes of our past, dream of the open future, and meanwhile muck around in the present. Every choice we make is in some way influenced by our perception of how much time has passed and how much we have left.
But if you base your entire career on making sure that clocks run on time, you can start to question what it actually means. As chief time scientist at the U.S. Naval Observatory, Demetrios Matsakis is in a unique position to deliberate on the meaning of time. The mere fact that he has to adjust clocks to show the “correct time” proves that time is surprisingly mutable — rather than setting our watches to “the time,” it’s more accurate to say that we define time by the number of ticks made by the clock.
If time isn’t constant, does it even exist? Or is it just another spatial dimension laid on top of the three dimensions we understand more intimately? Is time infinite — did it exist before the Big Bang, and will it ever end? Matsakis doesn’t know the answers to these questions, and neither does any physicist, though not for lack of trying.
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It all started with Einstein’s groundbreaking theory of relativity. We had previously believed, according to Newton, that time advances at a constant, absolute flow that lords over the universe, from which nothing can escape. But Einstein turned this idea on its head when he realized that space and time are intricately woven together in a continuum. If you ask someone “what time it is,” you’re really asking for your personal location in four-dimensional spacetime. As Einstein once said, “The distinction between past, present, and future is only a stubbornly persistent illusion,” an illusion born of our foolish notions about causality. The past does not inexorably lead to the present and then to the future, just as you can decide to walk down a road in either direction — or even walk off the road entirely.
The temporal relationship between different events as perceived by an observer is easily warped by relativity. Special relativity decrees that the relative velocities of two objects determine how each of them perceive time — the one traveling at a faster velocity experiences time more slowly. Similarly, general relativity states that objects closer to the gravitational center of a large mass will experience time more slowly than objects far away. By abolishing the tyranny of absolute time, relativity can even make time travel possible, as long as astronauts have enough fuel and power to move near the speed of light.
Relativity has transformed contemporary physics, but it created more new questions than it answered. The problem is that it dictates the behavior of matter on grand, cosmic scales, between planets, stars, black holes, and so on. When physicists zoom in to observe particles on the quantum scale, they encounter a great schism between the laws of relativity and the laws of quantum mechanics. These two major theories of physics simply don’t cooperate unless physicists think of time in radical new ways.
On one end of the spectrum, physicist Julian Barbour argues in his book The End of Time that time doesn’t exist at all. All possible configurations of the universe exist simultaneously, as complete, independent moments called “Nows,” laid out in a timeless landscape governed purely by mathematical rules. There is no “before” the Big Bang, for instance — the Big Bang is merely a landmark in this “country” of Nows. Life is simply moving through a succession of Nows that happen to be linked by memories and records. There is no flow of time from one Now to another.
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On the other end of the spectrum, Lee Smolin’s book Time Reborn tries to turn back the clock before Einstein messed with our initial ideas about time. If the laws of physics were truly immutable, then they predict an infinite number of potential universes, or a multiverse. Rather than believing, as some physicists do, that our particular Universe came about as a happy fluke, Smolin asserts that the only possible explanation is that the laws of physics undergo evolution, just like plants and animals. These changing laws then constantly tweak the Universe into its current form. Smolin believes that many of the most befuddling problems in modern physics can be explained if we embrace time as the foundation of reality.
Whether time is really just an illusion, or an omnipotent river that permeates all existence, we continue to live within its grip. It’s probably easiest to go about your life as usual, as theorists aren’t likely to come to a conclusion regarding the mind-bending nature of time anytime soon.
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