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  • If time travel is possible,

  • why haven't we met a single time traveler yet?

  • And if we did meet one,

  • how would we know they weren't faking it?

  • In 1998, a gentleman

  • by the name of John Titor

  • arrived from the future.

  • Or so he said.

  • In his timeline, as he claimed,

  • General Electric had managed to invent

  • time travel in the year 2034.

  • He even showed and described

  • his time traveling device in great detail.

  • And then Titor vanished,

  • as abruptly as he appeared.

  • Did he finish his mission?

  • Or was he real at all?

  • If we were able to prove

  • that someone has traveled from a different time,

  • it would be very cool for science.

  • Although it might overwrite

  • Albert Einstein's theory of relativity.

  • Einstein approached time as a fourth dimension.

  • Space is a three-dimensional spectrum

  • that provides us with length, width and height.

  • Time offers direction.

  • Together, they form a space-time continuum.

  • And it can be affected by gravity.

  • According to Einstein's theory of relativity,

  • gravity is a curve in space-time.

  • And technically, because space and time are one,

  • gravity could bend time as well as space.

  • But you'd need something really, really big

  • to notice any changes in the movement of time.

  • If you somehow managed

  • to get yourself close to a black hole,

  • like Sagittarius A,

  • you'd be experiencing time at half-speed

  • compared to people on Earth.

  • This is because Sagittarius A

  • packs a mass of four million suns

  • into an infinitely dense point,

  • creating a very strong gravitational field around it.

  • Another way to travel in time

  • is to move really fast.

  • The closer you get to the speed of light,

  • the slower time passes for you.

  • If you were a passenger on a train

  • that somehow could travel at 99% of the speed of light,

  • for every year you spent on the train,

  • 223 years would have passed back at the station.

  • That would make you a time traveler into the future.

  • Titor claimed that this little machine

  • is what made time travel possible in any direction.

  • The C204, as he called it, allowed him

  • to manipulate gravity with the help

  • of two microsingularities that were packed inside.

  • It also had gravity sensors

  • to lock the machine and time traveler

  • in a fixed place in space.

  • Titor had this machine installed in a car,

  • pretty much like the good old, time-traveling DeLorean did.

  • But it would only take him as far as

  • 60 years from his time.

  • Proving that someone really is a time traveler

  • might be even harder than time travel itself.

  • Time travelers could make predictions about the future,

  • show their futuristic technology,

  • or even undergo some genetic testing

  • to support their story.

  • Maybe the best way to prove time travel is real

  • would be to take you with them on their next adventure.

  • Of course, there are easier ways

  • to prove the possibility of time travel.

  • In 2009, the world-famous

  • theoretical physicist Stephen Hawking

  • threw a party.

  • Not just any party,

  • but one to which only future time travelers were invited.

  • Hawking didn't send off invitations until after the party.

  • He believed that if travelers from the future

  • arrived before the invitation was released,

  • that would prove that time travel will become possible one day.

  • He sat there waiting for hours,

  • but nobody showed up.

  • That doesn't mean time travel is impossible.

  • There is a chance that time travelers from the future

  • will learn to use wormholes, or "bridges" in space-time.

  • We haven't seen one of those yet, but...

  • the theory of general relativity predicts that they exist.

  • The biggest problem with wormholes

  • is that they're microscopic and collapse too quickly

  • for a human traveler to go through.

  • But maybe the reason nobody attended Hawking's party

  • is that time traveling might not be that precise.

  • Maybe the guests from the future did arrive,

  • but they were too late for the party.

  • Or maybe going back in time

  • is strictly prohibited for time travelers,

  • because if they do,

  • they might change their timeline completely.

  • Perhaps they are just trying to avoid the risk

  • of spreading any diseases from the far future onto us.

  • Or maybe the information about time traveling

  • is so highly classified that

  • only a few people would be trusted with it.

  • Maybe traveling back into time isn't possible after all.

  • Maybe time can only move forward and never backwards.

  • Maybe John Titor was one big lie.

  • We have a few more years until 2034 to find out.

  • In a way, we already have time travelers in our lifetime.

  • Astronauts on the International Space Station

  • are moving at 8 km/sec (5 mi/sec).

  • This makes them age slower,

  • although the difference is measured in hundredths of a second.

  • But if you're listening,

  • you're invited to a reception for time travelers

  • hosted by Stephen Hawking.

  • The party will take place at the University of Cambridge, UK,

  • on June 28, 2009.

  • No RSVP required.

  • And hey, if you have a chance to jump in a spaceship

  • and enjoy the time traveling effects of a black hole,

  • Just make sure to not fall into that gravitational monster.

  • But that's a story for another WHAT IF.

If time travel is possible,

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A2 初級

もしあなたがタイムトラベラーに会ったら? (What If You Met a Time Traveler?)

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    Courtney Shih に公開 2021 年 01 月 14 日
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