From time to time, times up and it’s time.

Why is it so commonplace to consider time as something that is part of our Universe, when there is still so much to understand about it? What do you think? Does time exist? Or is it just something that we made up to describe where we’re going?

In our daily lives, time is usually divided into three categories: what was, what is and what is to be. Some might say that “Yesterday is history, tomorrow is a mystery and today is a gift, which is why we call it the present”.

But the truth is that time comes down to one thing, to one single particle. Of course, it’s a very long story because time was “invented” by the first civilizations. It was born in Egypt and China as a social, religious and economic asset for the growing societies. Ever since, we have changed our definition of time several times. Sometimes using a clepsydra, an hourglass or using the movements of stars.

And finally, all this has led us to use something much smaller to define our modern perception of time. In 1967, we based our worldwide system upon the oscillations of Cesium 133. Thus, what is called a second is also 9 192 631 770 radiation periods corresponding to the transition of 2 levels of fundamental states of that atom.

Basically, the time we just defined is not part of our surroundings. In fact, we cannot perceive time itself. We may only feel a time lapse. “It’s been two hours since, …”. “I haven’t seen him in a while”. “Last year, …”.

We could imagine other ways to define time, maybe as a distance. Maybe time is what happens while the Universe expands by 1%. But we would need to reconsider some definitions. For instance, speed is a distance travelled, over a time. “I was driving at 45 mph” could become “I travelled x miles while the Universe was expanding by 1%”. Of course, this is just an example. Considering that the expansion of the Universe is non-homogenic it gets very difficult to compare things. Still, that is a relevant example for us to answer our question.

As you may know, Cesium is quite heavy. That means that it has been created over time, thanks to the most powerful processes in the Universe. So, there was a time when that atom did not exist. So, what about time back then?

Without light, would the 3 dimensions of space exist, knowing that 1 meter is the distance travelled by light in 1/299 792 458 seconds in a vacuum? That question is a false problem, to reveal the limit of our perception. Of course, the 3 dimensions would exist, because the light needs something to move through. We, as Humans, wouldn’t be able to “know” where we were. The point is that the fact that we don’t “see” something doesn’t mean it does not exist.

It doesn’t bother anyone if I say: “before what we call the big bang, there was no space”, because space is part of the Universe, like you and me. We can travel a distance, shorten distances, increase distances, … . But we cannot do the same with time, or not with the entire Universe at least. Considering that the Universe was indeed in a dense state, with conditions so harsh that time couldn’t exist, then we may only have two possible outcomes. Either time is defined outside our system, which possibly means that we can’t “see” or interact with it, or time didn’t exist and still doesn’t exist.

But it’s been proved that time runs slower the faster you go, right? or has it? Scientists have measured a slight divergence between two atomic clocks. The first one was kept on Earth while the second one was launched into space. But deep down, it only means that the Cesium 133 radiation period number was smaller. Can we conclude that time has been changed in the process?

Assuming that time is real, it would be very convenient if we could travel through time (and kind of useless if it’s steady). The question would also be “where do we go back in time?” (and not just “when”). In our own timeline? Which means we’d possibly need to move the entire Universe back to its previous position (violating the second principle of thermodynamics (the entropy goes increasing)). Or … to another timeline, where our present is still to be, maybe? Ignoring the fact that there would be two versions of you, you would also break the mass conservation law in both time lines…And you would have to turn up in a place where there’s already atoms or matter: sounds like a one-way trip, doesn’t it.