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Fotografía de Garry Knight bajo licencia CC BY 2.0

I hate time travel! I can’t help it. Why? Let me get this straight: it’s too complicated.

I mean, building a flux compensator is the easy part. All you need is an empty beer can, toothpaste, chewing gum and the right MacGyver spirit. And maybe Plutonium. But just a little. The complicated part is finding a DeLorean that still works and someone willing to accelerate it to at least 88 miles per hour. Also, I am no Doc Brown: given the fact that I would have built this thing you might need to accelerate it to at least 95 miles per hour (you know: just in case). Plus, there’s a pretty good chance you’ll die in this endeavour.

And time is a tricky thing. Consider the fat cousin of the electron, the muon. It is produced, for example, high up in the atmosphere and will live for approximately 2.2 microseconds. Given the fact that these particles travel at almost the speed of light, it is reasonable to say that they will never reach the ground. But still, they can be detect them on the ground (how that works is a whole different story…). Now what? Is physics wrong? Should we close down the universities, become creationists and live happily ever after?

No. All you need is to get good old Albert Einstein out of the closet and listen. The entire point to solving the above mystery is that how fast or slow time goes by, depends on fast you are moving. Yes, you heard right. A clock is ticking slower when it is moving fast. And this is not just some crap. Time dilation is a real thing. It has been tested and confirmed in various experiments.

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For example in this one: In 1971 Hafele and Keating put not one, not two, not three, but four atomic clocks (don’t worry they are not dangerous, they are just very, very, very precise) on a regular airplane and flew around the world in Eastern and Western direction, with and against the rotation of the Earth. From special relativity one expects that a clock travelling West will go faster and a clock travelling East will go slower. And in 1971 Hafele and Keating were able to confirm this effect, although they had to take into account a second effect due to Gravity, which arises from general relativity.

Now you are wondering if you’ll live longer if you embark an airplane and fly East for the rest of your life? Well, I thought so and the answer is yes! But wait, wait! Before you go out that door and spend all your money on plane tickets, consider this: The effect will be on the order of seconds or minutes. And what kind of life would that be, Caught in a steel vessel and living of pretzels and airplane food?

So, if time goes slower if a clock approaches the speed of light, what happens if it goes faster than the speed of light? Well, that’s kind of hard to answer. The only thing I can promise is that if you manage to travel faster than the speed of light you’ll be able to watch TV from the 60s and 70s, because electromagnetic waves such as TV and radio signals travel at the speed of light. As does light, which is an electromagnetic wave as well.

And that’s all I can say because apparently the speed of light appears to be the limit beyond which we cannot go. At least not today. It is still a little down the road until Zefram Cochrane invents Warp speed in 2063.

Physically speaking the reason for this is that particles like electrons, humans, hedgehogs (anything) are getting heavier the closer they get to the speed of light. This means it takes more and more energy to further accelerate these particles. So, I have to say: I’m sorry, but for the moment this is the intergalactic speed limit: 299 792 458 meters per second. And you better obey that!

Then there’s of course all those paradoxes, traps and pitfalls, when it comes to time travel. For example there might be Terminators. Have you ever thought of that? There are excellent documentaries starring the talent of an Austrian immigrant on that issue and I recommend everyone to watch it! But whatever happens: never invite a Terminator into your home… Oh no wait, that’s vampires… but you see where this is going? One small mistake and boom goes the space-time-continuum.

It’s like the a butterfly’s wing that causes a hurricane on the other side of the Earth. A topic wonderfully covered in another documentary called —big surprise!—  The butterfly effect. There’s just so many things to keep in mind. It matters who you meet and who meets you. Biff Tannen might get away with the Sports Almanac, and that’s it for your future, to which in fact you have to go back!

So if time travel is such a pain, why do we love these movies so much? For the same reason we like Star both Trek and Wars, Terminators and all other kinds of geeky stuff: they are entertaining. There are no Nazgul, no Force (come on guys, you knew that already!). The Borg might be real, though. And in some of these movies —not in all of them but Back to the Future is a great example, the geek wins: beats the bully and gets the girl. Of course, Marty McFly is no Sheldon Cooper kind of geek. It’s a geek you might actually grow to like. A geek you might want to inherit the Earth to. Again, I am not talking about Sheldon Cooper.

Now, if you excuse me, I have to go and welcome a certain Marty McFly, who is going to arrive in Hill Valley at exactly 4:29 PM. It’s time.


For the Spanish version of this piece, please visit El drama [físico] de viajar en el tiempo

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Why is Marty McFly most probably not arriving today?