The River of Time: What’s its Direction?

The “River of Time” is a commonly used model of the passage of time where time flows in one direction. But in which direction?

Bridge over Future Waters

The River of Time

The “River of Time” is a commonly used model of the passage of time where time flows in one direction. The analogy allows a lot of play, for example, you can scrabble out of the river, run along the bank and re-enter time at a different place in the river. Or cause swirls and eddies within the waters of time. Or drown in it. There are lots of applications of the model and many authors have written may good novels based on them.

The model sounds simple enough – but I think there’s a more complicated undercurrent; which direction does the time flow?

Bridge over troubled waters

Earlier this week I was on a walk with my family through a small forest, in which was a river. OK, I’m exaggerating – I’m living in Holland so vertical gradients are famously small in this flat land. So let’s redefine and call this a small barely flowing stream of water.

The main point is that there was a bridge over it, and the main point of that, as far as my daughters are concerned, is that we can chuck bits of wood into the water on one side and wait for them to appear downstream.

Bear in mind that both I and my wife are marine scientists and have therefore spent many moments discussing turbulent eddy flow, bottom friction and boundary effects in order to optimise our winning strategy.

But on this particular occasion, to be blatantly honest, I had other things on my mind, such as – I’ve just been offered a new job which takes me not only outside the realms of marine science, but well and truly outside the realms of my house. Relocation is well in order, so as such you’d have found me standing on the bridge staring upstream wondering what the future held.

And that’s what brought me back to the river of time. Which direction is the future?

River of Time: Where is the Future?
River of Time: Where is the Future?

Is it upstream where I’m looking at the water which will be arriving at the bridge?

Or is it downstream where the water flows on towards its destiny, towards its future?

Maybe it depends on the direction of view, or relativity. Considering the water, upstream is where it’s been so this direction represents its past. And vice versa.

Traditionally, we move from the future to the present and then to the past. But if (for example) we consider the year 2019 as the future, 2018 as the present and 2017 as the past, doesn’t this description of flow seem a bit out of kilter?

I think the key is in the case of the stationary bridge, or the fixed point of the present, we’re not immersed in the flowing river of time. We have a relative motion compared to it, but only one of us is moving. If I overtake a stationary car, it looks like that car is moving backwards when this isn’t necessarily the case.

A few years ago I wrote this post: Follow the leader where I showed that looking at the x-axis of time shows that the relative positioning of time (earlier / later) is counter-intuitive.

Perhaps the same holds here with the river of time.

Sieze the Day

As I stood on the bridge wondering about my future, I heard my girls giggling in excitement. And I realised that perhaps I should be more concerned with what the present holds.

Nothing drove that point home more than when I cycled over to the bridge a couple of days later to take these photos. There were no giggling girls and there was no laughter as there was in the past. Just an empty bridge and the waters flowing on and on…

Ghosts of the past
Ghosts of the past

Paul

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Author: Paul Wandason

I love astronomy and science fiction, but I love my family more. So I love time travel too!

One thought on “The River of Time: What’s its Direction?”

  1. It seems to me the past must be upstream, since the grandfather paradox kicks in if someone dams the water before it reaches the bridge, or otherwise diverts it into a different channel: The water no longer flows under that bridge (or at least in the same channel as before.) History is thus changed.

    We came from the past, we are in the present, we will be in the future…eventually.

    But I am heartened to hear you and your family also played what mine used to call “Pooh sticks”, competing to see whose sleek twig would make it under the bridge first.

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