Time flows.

Newton seemed to think so. So did Aristotle and countless others before. Even the Buddhists, with their cyclic time, kept believing that time was something which went from one instant to the other, moving forward though in circles.

That, of course, changed after Einstein. However, I think a vast number of people still have problems coming to grips with the nature of time and how they fit in it. Which is no wonder: humans evolved to live within time, trapped in their 3D slice of reality, ripe with memories and longings. This paragraph hasn't been here forever. I just wrote it. Or did I?

In the Relativity view -any Relativity will do- time and space are just parts of one big mash-up called “space-time.” This does not mean one just sticks them together: it means that time and space are both the same thing and are, in fact, interchangeable. What looks like time to one observer will look like space to another, depending on their relative velocities or the gravitational field they experience.

But space is just there. It doesn't “pass.” How can we, then, be entitled to say that time “passes”? If going from left to right is exactly the same thing as moving from past to future, isn't it as foolish to assume the future doesn't exist as it is to assume the tree we just passed in the highway is no more?

Einstein leaves us no choice but to assume our senses lie to us: time does not pass. But then, what? Is it us who move through time?

Well, no. Saying we move through time is a circular proposition. Moving requires time. We cannot “move” through anything: we're just there. Even though we can't imagine it -since we are creatures of time- there is no clock “outside” time. There is no “frozen in time” universe with four dimensions, through which we move. The Universe just is. It doesn't change. It's a 4-dimensional geometric structure. Nothing less, nothing more.

So we don't move through time. Or space. Or anything. We're a collection of 3D slices in a 4D sausage. How can we reconcile that with our everyday experience? After all, I remember going to college, dating, drinking, being dumped. I am aware of being thirty, not ten years younger, not ten years older. What exactly is going on?

Everything is going on. I would say “simultaneously”, but that really doesn't make sense outside time. I am 20, 30 and 80. I am a suckling babe. All of these are slices of the Universe. And all of them exist, just like every 2D slice of a sausage exists. This is somewhat difficult to take in: we are not mentally equipped to imagine all the stages of our lives exist “at the same time”. Hopefully, a little mental experiment will make things clearer.

Let's imagine a mad scientist -why is it always a mad scientist?- kidnaps you and messes with your brain. He just developed a new, revolutionary technique, which can replace your memories with some other person's. When he's done with you, you remember nothing of your life and everything of theirs. You believe you are that person and are absolutely convinced you have always been.

But how can you be sure this didn't happen to you? How can you be sure your own memories are real and not implanted? One may say: through a video. But the video may be rigged. Or you could just be living in a Matrix-like virtual reality. How can you be sure you were not created five minutes ago by some alien civilization and then implanted with a whole life of experiences? How can you be sure that hasn't happened 30 seconds ago? Or 2? Or a millisecond ago?

And here's the punchline: how many instants do you need to have existed in order to believe you've existed for many years? Surprisingly, the answer is “just one.” The key is the information in your brain, not the number of years it took to get there.

Therefore, the suckling babe and the 8-year old kid both exist, let's say “simultaneously”, for lack of a better word to use outside time. They both think they are the unique you, existing now. They both believe their future will come and their past is, well, past. And they are both wrong.

This is crucial in order to understand Quantum Immortality. But that is a subject for a different post.