Dear Al,

With luck, you won’t ever be reading this.

And that, I reckon, is the oddest start to a letter I will ever read. No ‘how are you?’ or anything like that. Anyway …

But let us assume you are. I have given this letter to your mum to hand to you when you are older.

Did you wait the sixteen hours?

I sort of shake my head in reply to the question. Like he can see me.

That was just a test of your resolve. If you did, then well done – you may find what I am about to ask a little easier. If you didn’t … well, I’d still like you to do it.

If you are reading this, then what I fear will happen has happened, and that means I am not around to help you into adulthood. This, then, will be the only gift I can give to you, my most precious son.

First, let me reassure you: I am not scared of dying, although it makes me sad to think of the times we will miss together.

I won’t see you going up to secondary school, or graduating from university, or marrying and becoming a father yourself.

These are the big things. Yet it is the small things, the tiny little things, that make me sadder. I love your smile, and our shared jokes, and the way you liked my lousy stories. I love the smell of your hair when I hug you and the way you are so glad to be awake in the morning.

Yet … all these things may not be gone forever. For if you follow my instructions, and if you are as brave and smart as I think you are, then you will be able to prevent my death.

Right now as I’m writing this, you’re just eight, and far too young to understand the implications of what I am about to tell you. You have had to wait, and now the time is right.

You are about to learn, Al, how to travel in time.

At this point I stop and re-read what I’ve just read. ‘Prevent my death? Travel in time?’ What in God’s name is my dad talking about?

The ability to travel in time has fascinated humans ever since we came up with the idea of time itself.

Just imagine, Al, if we could go forward in time to see what happens in the future? Or go back and correct our mistakes?

The Greeks, the Egyptians, the Chinese – all the ancient civilizations tried.

The ancient Sumerians, who lived in what is now Iraq between maybe four and six thousand years ago, left behind texts and archaeological evidence that suggest they discovered the secret. Trouble is, it was so long ago that the answer – if it was real and not just mythology – has been lost to us.

I have recently had a huge breakthrough, using the power of modern computing which was unavailable to the ancients.

Al: are you ready to travel in time?

No, Al: this is not science fiction, and you will not be battling strange monsters in far galaxies. Instead it is mathematics: pure, but very, very far from simple.

For I have discovered the formula that allows for the physical movement – ‘travel’ we might call it – between parallel dimensions allowing us to seem to be ‘travelling in time’.

Notice that I say ‘seem’.

You see, as Albert Einstein first described it, time is ‘relative’. I’m sure you’ve heard of Einstein’s General Theory of Relativity? There was another one too: his Special Theory of Relativity.

One day, perhaps, you will understand them, for believe me: they are fabulously complex. We all happily acknowledge Albert Einstein as a ‘genius’ – but very few of us have any idea at all of just how amazing his discoveries were. Our brains and our thoughts are so firmly rooted in our lives on earth that most of us are simply unable – unequipped mentally – to imagine the true meaning of Einstein’s theories.

I pause in my reading and look at the Newcastle United team poster that Steve put on my wall, as if it might help me, but the players just stare back at me, blankly.

Of course, I’ve heard of Albert Einstein, after all I was named after him. Wild hair, bushy moustache – a completely mad scientist and a nickname at school for anyone a bit clever. And yes, I’ve heard of the Theory of Relativity, but I thought there was only one, and I had no idea what any of it meant.

It’s like a goldfish in an aquarium. He might understand everything there is to know about his environment: every rock, every stone, every bubble. He may even understand that when the rattling vibration comes from above (the lid of the aquarium being lifted off) then that means food is coming. But he doesn’t know what people are, what cars are, what a fruit smoothie is, what a cup-winning goal looks like, or what any of it means, and that’s because he simply cannot.

A goldfish’s brain can’t even imagine these things. And most human brains cannot even imagine the vast possibilities that Einstein’s theories suggest.

Don’t worry, Al, I’m not going to try to explain relativity to you. Even Einstein had trouble putting it into words. The best he came up with was this:

“Put your hand on a hot stove for a minute and it feels like an hour. Sit with a pretty girl for an hour and it seems like a minute. THAT’S relativity.”

Was Einstein being serious? Well, perhaps. Sort of. His point was this, I think: that the passage of time is something that we see and feel, and because we see and feel it, we describe it. But just because we can describe something does not make it real. You, no doubt, could give a vivid description of an imaginary animal, but that doesn’t make it real.

‘Travelling in Time’ is a poor description of what you are about to do, Al, but we are constricted by the words we have in our language. ‘Relatively Shifting Between Spacetime Dimensions’ is perhaps more accurate, or ‘Non-gravitational Multi-versal Static Matter Repositioning’, or …

See what I mean? ‘Time Travel’ will have to do. Do you remember that time we went to Seahouses and the night was so starry, and I told you about seeing things that had happened many years ago? That was only a few weeks ago as I write this, but I hope you can remember.

I put Dad’s letter down for a moment and think, closing my eyes. We’re in a field, me and Dad, looking at the stars. It makes me smile.

Now, read carefully. This is what you must do.

In the garage of our house, there’s a hole covered over with boards. It leads to a small cellar: there are steps down to it.

This was our old house, then. Obviously Dad had no idea we’d be moving house. I read on, but I’m getting worried that I won’t be able to do what he wants.

It’s a small, narrow cellar and at one end is a heavy metal door with a wheel to open and close it, like they have in submarines. There’s a code on the lock. It’s 5021 – your birthday backwards. No one else knows this. Open the door and go in. You’ll find Letter Number Two taped under the desk.

Trust me like you have never trusted anyone before in your life.

Things will become clearer.

Make absolutely sure no one sees you.

Your loving dad

P.S. You must act within a week of reading this

I read the letter again, and then again. The fourth time, something strange happens, and it’s as if I’m not reading with my eyes but with my ears, and instead of seeing the words, I can hear my dad’s voice, soft and a little raspy, his slight Geordie accent, his habit of sometimes going up at the end of sentences, like he was asking a question?

I imagine our old house, the garage with cellar steps.

And I just lie, staring at the ceiling, in a sort of trance, and I’m with my dad in our old house. I’m not eight, I’m me, now, I’m twelve; I can smell him and hear him, and he’s asking me again, “Al, are you ready to travel in time?” and I can feel his hand on my cheek.

For the first time in four years, I fall asleep in my dad’s arms.