The Inside View versus the Outside View
We are accustomed to looking at our universe from the inside, because we live in it.
It is useful to imagine looking at it from the outside.
Here we have a blue object bouncing off a grey wall. (The thickness of both object and wall are exaggerated. Really they have zero thickness.)
But now we can abstract ourselves out of this world and look at the world as a two dimensional static object:
Shown this way, the time axis does not seem to be particularly special or different from the space axis. In actual fact in “real physics” most physical laws don’t make a big distinction between past and future. So where is the difference? The laws of thermodynamics say that ‘order’ decreases with time. Time cannot flow backwards because of this.
Let us illustrate this in our 2-dimensional world. We throw our blue object at the wall again, but this time it shatters:
Now we can see that there is a ‘complexity gradient’ in one dimension which we then call the ‘time’ axis. The world has more order when the blue object is still whole and this order decreases the moment it shatters into pieces. We label the direction where order decreases ‘future’ and the direction where order increases ‘past’.
Here is a 2-dimensional waving man with a time dimension as we experience it.
If our universe has indeed one time and three space dimensions, then we could simply picture it as a static four dimensional object. We would no longer be subject to past or future and see it all in its entirety. The key to understanding this is to imagine being outside of our space and time and looking in, like in this picture, where we see the 2-dimensional man as a static 3-dimensional object.
Because our spatial imagination is limited to 3 dimensions we run out of dimensions fast.
A more convenient way to to represent worlds from the outside is as a movie reel. If you look at the frames of a movie, you will see a complete world in each frame with only tiny differences between them.