Are you weirded out by wormholes? Flummoxed by your flux capacitor? Strap yourself in for this time-travel primer.
你是不是覺得蟲洞很神奇呢？對你不穩(wěn)定的電容器感到疑惑？那么就來學(xué)些關(guān)于時(shí)空之旅的基本知識吧。

You will need: a basic knowledge of the theory of relativity and an open mind.
你需要：相對論的基本知識和開闊的思維。

Optional: a PhD in Physics.
可選項(xiàng)：擁有物理系博士學(xué)位。

Time-travel theories are riddled with paradoxes that may make your brain explode.
時(shí)空之旅的理論充滿著矛盾，這將會讓你的思維爆炸！

Step 1:

Brush up on your Einstein: His special theory of relativity revolutionized physics by suggesting that traveling into the future is possible. The idea is that time slows down when you're traveling at high speeds relative to stationary objects. So if you're in a spaceship going very close to the speed of light for five years, you could return home to find that it's 50 years later on Earth.
重溫一下你有關(guān)愛因斯坦的知識：他的相對論是物理學(xué)的一個(gè)革命性理論——穿越到未來是有可能的。這個(gè)理論是這樣的，如果你的移動速度相對于靜止的物體非?？?，那么時(shí)間就會減緩。因此，如果你坐在一艘接近光速的宇宙飛船上行駛5年，當(dāng)你回到家發(fā)現(xiàn)這已經(jīng)是50年后的地球了。

Even on a normal transatlantic flight, time slows down with speed. In one experiment using two atomic clocks, the clock sent into space fell 40 nanoseconds behind the one left on the ground.
即使在普通的飛行器上，時(shí)間也會隨著速度的增加而減緩。用兩個(gè)原子表做實(shí)驗(yàn)，送入太空的原子表比在地球上的這個(gè)原子表時(shí)間要落后400億分之一秒。

Step 2:

Going back in time is a far trickier proposition – but might be possible if you could travel faster than the speed of light. Theoretically, if you were moving faster than light speed, you could receive a signal from Earth before it was even sent. Upon returning home, you’d find yourself back in time. The only problem is that traveling that fast is scientifically impossible – at least for now.
穿越回過去是一個(gè)很棘手的課題，但是如果你行駛的速度能超過光速這就有可能。理論上講，如果你的移動速度大于光速，即使地球還沒有發(fā)出信號，你都能接收到。當(dāng)你回到家，你就會發(fā)現(xiàn)你回到了過去。唯一的問題就是移動速度超過光速在科學(xué)理論中是不可能的——至少現(xiàn)在不可能。

Step 3:

Make the quantum leap. Some quantum physicists believe that traveling back in time could be possible on a subatomic level. But unless you’re a subatomic particle, you’re out of luck.
讓量子論飛越吧。一些量子物理學(xué)家相信在亞原子水平上穿越回過去是有可能的。但是除非你是一個(gè)亞原子顆粒，但很不幸你并不是。

Step 4:

Currently, the most popular time-travel theory involves wormholes, or tunnels through the fabric of space and time. If you were to tow one end of a wormhole into space close to the speed of light, then return that end to Earth, you would theoretically be able to enter the wormhole today and come out of the other end in yesterday.
當(dāng)今最流行的時(shí)間旅行理論要屬蟲洞了，也就是構(gòu)造空間和時(shí)間物質(zhì)的小縫隙。如果你以接近光速被拖入蟲洞的一端，然后從另一端回到地球，理論上你可以是今天進(jìn)入蟲洞但在昨天從蟲洞里出來。

Be skeptical. Wormholes are so tiny and close so rapidly that it would take a great leap of science to be able to harness them for time travel.
值得懷疑的是蟲洞如此小而且關(guān)閉的如此迅速，要駕馭蟲洞去進(jìn)行時(shí)間之旅，當(dāng)今科學(xué)還需要很大的飛躍啊！

Step 5:

Get to know your granddad. The so-called Grandfather Paradox – going back in time and killing your grandfather, thus preventing your own birth and making it impossible for you to travel back in the first place – has been used to help illustrate why backward time travel is impossible.
想去了解下你的祖父？所謂的祖父悖論——回到過去殺掉你的祖父，因此阻止了你的出生，因此讓你不可能穿越回過去——這個(gè)悖論幫助我們闡明為什么穿越回到過去是不可能的。

Step 6:

Understand what's done is done. Most ideas about backward time travel include the “chronology protection conjecture,” meaning that nature would prevent you from changing the past. For example, you could try to go back in time to shoot your grandfather, but the gun wouldn't fire. It also means that all the embarrassing moments you'd love to erase are going to happen all over again.
要了解做過的事就是做過了。大部分有關(guān)于回到過去的理論，包括“時(shí)序保護(hù)假說”，意思就是大自然會組織你去改變過去。例如，你可能終于回到了過去，想殺了你的祖父，但是槍卻沒有開火。也就是說所有你想抹去的窘迫的瞬間依然會重新上演。

Step 7:

Open your mind to the “many-worlds” interpretation. Some theorists have gotten around the rigid “whatever happened, happened” idea by claiming that every different action you take in the past splits off into a parallel universe. So there might be hope yet for preventing those embarrassing moments, at least in one universe.
開闊你的思維，試著想像“多重世界”的解釋。有些理論在“無論發(fā)生了什么，已經(jīng)發(fā)生了”的思想上非常嚴(yán)格，它們主張你在過去所有的動作會分裂進(jìn)一個(gè)平行宇宙中。因此至少在我們的宇宙中，阻止這些窘迫的時(shí)刻發(fā)生可能是大家所希望的。

Did you know? Theoretical physicist Stephen Hawking once said, “Time travel might be possible, but if that is the case why haven’t we been overrun by tourists from the future?”
你知道嗎？理論物理學(xué)家史蒂芬·霍金曾經(jīng)說過：“時(shí)間旅行是有可能的，但是如果真能如此為什么還沒有從未來來的游客來拜訪我們呢？”