(If you somehow have ended up on this page without any background knowledge, before continue, you better know that all below scenario is based on the idea that our universe is expanding in time -4th dimension- direction with speed of light. You can check the previous 2 posts of: 1. Do We Travel in Time Direction With Speed Of Lightand 2. Expansion of the Universe as Travel in Time Direction if you are willing to understand this concept)
While I was working on the expanding universe model in 4th dimension, I was also thinking about a contracting model and how would it look like. Obviously, the main difference would be; in a contracting universe in 4th dimension, we would not be observing an expansion in 3 spatial dimensions. But when I think about it further, I found out that a contracting universe in 4th dimension shall exactly look like expanding in 3 spatial ones that we observe. This is how it works:
First thing to consider is; in a 4 spatial dimensional universe, the real expansion (or contraction) happens in 4th dimension direction and what we see in our 3 space dimension is the stretching of this 4 dimensional volumes surface. I have tried to explain it in this previous post , if you would like to understand it better.
Second thing is, this real expansion (or contraction) in 4th dimension direction is somehow related with our time perception. I will try to demonstrate my idea with drawings but as always, I will do it in lower dimensional examples, since nobody is able to draw or comprehend 4 dimensional ones.
So let's have a look at the contracting universe model: Each 1 dimensional circle line below represents our 3 dimensional universe. They contract in 4th dimension direction which is inwards . So each circle with different diameter represents a different moment of our universe, as well.
We will observe 3 distant stars in this universe and how they see each other while the time passes and universe contracts. Let's say each one is 1 million light years away from each other.
Before we start, the most important thing to consider is; when we look at distant stars in space, we are not only looking at far distances, but we are also looking back in time. Further the star we look at, the older version of it we see, since it takes time for light to reach us from that star. This is a well known commonsense information in modern science.
When the light of star B reaches star A1, 1 million years will pass (neglecting contraction effect since it can be minor in such distances). So, in a contracting universe, star A1 observes not star B1 but star B2 If we would like to observe star C from star A1, we will not see C1 or C2 but star C3. It is obvious that further the star we look at, it will look like it is getting away from us. Due to simple Pythagorean theorem application.
You might say, alright, but you don't need a circular and contracting universe for this idea to be valid. any flat universe with linear motion in 4th dimension can have the same effect, then why we need it? Because scientists did not only find out that our universe is expanding but its expansion is accelerating. If the universe was not curved and moving on a linear path, its expansion would be constant. But in this model, due to its curved nature and contraction, the further an object is, the faster its expansion seem to be. But actually you are seeing its past version which was even further than it should be due to contraction in this curved geometry.
Actually when I have figured this out, I have also thought about a universe model inside the event horizon of a non-rotating black hole. If everything inside the event horizon is moving towards singularity with the speed of light, length contraction will be infinitely big, allowing such 4 dimensional universe which is consist of infinitely many 3d universes stack onto each other and it is contracting towards its center. If this model would be valid, due to gravity, each layer closer to the center would be faster. This will cause expansion effect to be even bigger.
If any scientist in future will claim that the expansion of the universe is not only accelerating but this acceleration is even getting faster and faster (having a jerk), then we may start to consider that our universe is only a layer inside the event horizon of a black hole.
