Time travel has a bad reputation. Mostly due to movies and books, which require tension to work, a dramatic curve or a conflict. That is why in every story about time travel, the whole thing inevitably goes wrong and it turns out that there is some catastrophic downside to it, and now the time travellers need to safe the world from the demons they summoned.

The real issues with time travel are entirely different. I know. I am the second most lucky man around when it comes to it.

But firstly, I must point out that we never actually travel through time per se. Not in the sense of the stories or early misconceptions about the nature of the space-time-continuum. We actually travel along our timeline into an alternate universe. What we thought of as time travel at first actually turned out to be the ultimate proof of the Many Worlds Theory.

This requires a short excursion into quantum physics. In the early 20th century, scientists discovered the particle-wave duality. Take light, for example. Light from a source such as a candle, spreads out like a wave in all three dimensions. However, when you measure it specifically, it undergoes what physicists call the collapse of the wave function, and it becomes a particle that can be measured, in one specific place. This is called a photon, essentially one unit of light. The universe, scientists found out, is quantised. There is no such thing as half a photon of light.

But where, exactly, does the wave function collapse and manifest the photon? Why not in a slightly different place? If we make two small slits in a paper and let one photon go, will it take the left or the right? Interestingly, if you don’t look it takes both. If you do look, it randomly takes one. The wave function does not collapse due to some objective physics, it collapses when it is observed. That is another strange quality of quantum physics.

To solve all this weirdness, different solutions have been proposed. One of them is the Many Worlds Theory, which put in simplistic terms claims that actually all possibilities happen. But in different universes, and we observe only one of them, while copies of us observe the others. This neatly solves the whole observation and randomness issue, but leaves us with another small problem of imagination. It means that every observed quantum event creates many universes. Every millisecond, countless new universes come into existence, each an exact copy of the next except for one elementary particle.

And then we discovered that consciousness is the link between all these worlds. Our bodies, our space-time existence, is tied to one universe. But our consciousness pervades many. In fact, consciousness itself cannot be fully explained without quantum effects.

A massive, twenty year experiment was set up to unlock the potential of this discovery. About five years in it hit a brick wall. It turned out that, due to some specific properties maybe three people in the world fully understand, the consciousness cannot visit alternate versions of itself. It can only travel along a very specific line, which we call the timeline. Because this line is the succession of all universes that are completely identical to our own except that they have not yet progressed to the current point in time. In other words: We travel through time by going to a universe that is one day, one week, one month in the past.

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Yes, the past. We cannot travel into the future. I’ll come back to that.

And yes, the past. Not a past, the past. Everyone can only travel along his or her own timeline. There went the hopes of everyone who thought about killing Hitler, or checking if Jesus really existed. And there went all the philosophy about time paradoxes - because any change affects a parallel universe, not our own.

Now I said earlier that I am the second most lucky man when it comes to time travel. That is because about fifteen years into the experiment, three volunteers were selected to experience time travel - a term that stuck despite being factually wrong. A machine had been invented to throw a conscious mind back along its own timeline to a specific point in the past. It required a kind of extremely high-powered magnetic fields, similar to an MRE, and extremely complex calculations for the exact required field modulations.

It turned out that these calculations are a major stop in the whole thing. They need to be adapted to both the brain in question and the destination time. And „complex“ does not even touch it. Even with the massive computing power we throw at time travel today, your first calculation takes about two month and costs a few millions. That is why time travel is only for the super rich. We three and others who joined the program later were lucky, we were government-subsidised. Why I say „your first“? Because your first travel sets a kind of reference point. We did not know that when we started traveling. But once the reference point is set, travel to points closer to now becomes easier and faster to calculate, building on each other. As I understood it, the calculations basically run back along the timeline, so for the second trip that point was already passed. The calculations for subsequent trips that are closer to now are about half as long and expensive.

One of us was sent one year into the past. He is maybe the most unlucky time traveler, ever. You see, it also works the other way around - for him, every calculation more away from now takes twice as long, at twice the cost. He made two more trips before he was removed from the program.

The most lucky man alive was sent to his birth. He can now travel to any point in his life, freely. He and I, we both made so many trips during the remaining years of the program that we can now visit any point after our initial reference within one hour. That is the time you need to prepare yourself, punch in the numbers and warm up the machines.

My reference point is the day I became an adult. My childhood is forever lost to me, but my adult life is full of adventure and mystery.

There is a second catch to this travel, which isn’t travel at all. You can’t bring anything, either way. Remember, it is your consciousness that moves to another world. Actually, some theories say that consciousness is present in all the worlds and you just change your point of perception, but that’s a bit too much philosophy for me. But one way or the other, we don’t actually travel, so nothing physical can be carried along, not the slightest bit. Memories are the only souvenirs and knowledge is the only thing we can bring to the past - which is not just a term that stuck. It is the past, even if from that point on a new future appears, one that we will not come to see.