If you had a ticket to take one ride on a time machine, where would you go?
Would you revisit the past or travel forward into the future?
Ever since H.G. Wells rolled out his 1895 fictional bestseller The Time Machine, people have fantasized what it would be like to journey through history. Until recently, according to physicist Paul Davies, “such an idea lay beyond the fringes of respectable science.”
But times have changed (pun intended). Theoretical physicists have become fascinated by the possibility of time travel. It probably won’t look like Doc Brown hopping into his Back to theFuture DeLorean, but there’s an outside shot that somebody one day might actually be transported to a different date on the calendar.
Time has always been difficult to describe. Augustine, the early church’s most esteemed theologian, famously said that he knew exactly what time was – unless you asked him to define it, in which case he confessed he had no clue.
For most of human history, the common sense understanding of time is that it is absolute and universal: At any given moment, people everywhere in the cosmos are experiencing the same time, no matter what their circumstances.
Albert Einstein, however, shattered that confidence. According to his theory of relativity – which has been repeatedly confirmed by scientists over the past 100 years – there’s no such thing as absolute time. When does something actually “happen”? It all depends on who is looking at the clock, and whether those observers are stationary or moving. Things get really interesting if they happen to be moving really fast.
An illustration called the Twins Paradox is helpful. It’s also rather disturbing.
Buster and Betty are twins. Betty boards a rocket and takes a round trip flight to a nearby star, traveling at something approaching the speed of light. Buster, meanwhile, stays home. For Betty, the trip lasts one year. Buster – during the exact same period of time – experiences 10 years. He is now nine years older than his sister. They are no longer the same age, even though they were born on the same day. Because she traveled at such a great rate of speed, Betty has (in a sense) jumped nine years into the future. That’s the “time dilation” predicted by Einstein’s equations.
Such a scenario sounds absurd, of course. But super-accurate atomic clocks have demonstrated that the phenomenon is real. Every time you fly on a commercial jet, you’ll be a few nanoseconds younger than if you had decided to stay home.
Einstein discovered that motion isn’t the only thing that distorts time. So does gravity. The closer one gets to large dense bodies (like our planet), the more time slows down. It may sound strange, but clocks run a tiny bit faster in your attic than in your basement. This effect has to be taken into account by the Global Positioning System when reporting times and geographical locations on your smart phone.
If relativity allows us to travel to the future (sort of), is there any chance we can ever visit the past?
Stephen Hawking once performed a curious test. He invited future scientists to a party, being careful not to mention this to any of his living colleagues. When the time of the party came and went – and nobody showed up – Hawking concluded that time travel is impossible. Or he may have simply discovered that physicists of the future will conclude he threw dull parties.
Can we really visit the past? The past is something we see every time we look at the heavens. We never observe the sun “in real time,” but only as it appeared eight-and-a-half minutes ago – since it takes approximately eight-and-a-half minutes for the sun’s light to reach Earth. Astronomers gazing at the fringes of the universe are looking at quasars as they were billions of years ago. No one can even say with certainty that they still exist.
Einstein’s equations don’t forbid time travel. But the practical barriers seem daunting.
That brings us to the Marty McFly Effect, as displayed in Back to the Future and its sequels. What happens if you go back in time and interfere with your parents’ opportunity to fall in love? Would that render your own existence impossible? Can someone “be there” and “not be there” at the same time? Paul Davies admits that a time machine would no doubt open up a Pandora’s box of causality paradoxes.
So how would you answer the question posed at the beginning of this reflection? If you could travel to some time other than this time, what time would that be?
Time machines may be the stuff of science fiction, but most of us routinely imagine being somewhere or some-when else.
If we fix our gaze on yesterday, the emotion we often feel is regret. If only we could replay that conversation. Or have another shot at that interview. Or tell our ex exactly how they messed up our capacity to trust.
If we focus on tomorrow, the emotion we often feel is worry. If only we could know for sure that everything will be OK. And that our kids will turn out all right. And that the decision we have to make today is the right one.
What do regret and worry have in common? They are both forbidden by the One who loves us. Jesus warns us not to waste our lives either by chafing over bitter memories or nursing fears about the future. “Give your entire attention to what God is doing right now, and don’t get worked up about what may or may not happen tomorrow. God will help you deal with whatever hard things come up when the time comes.” (Matthew 6:34, The Message)
Theoretical physicists have more questions than ever about chronos – the Greek word for measurable time.
But there’s another Greek word for time. It’s kairos, which roughly means “the right time.”
Our call is not to dwell in the past or worry about tomorrow. All we have is this moment – the present moment.
And this moment, thank God, is always our kairos moment – the right time – to give ourselves back to the God who gives us life.
The Right Time
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