The Timeslice Model
The timeslice model came out of a thesis I was doing for a master, and then developed rather a life of its own!
I was having some difficulty understanding the expansion of the universe, and finally realized that my visualization was flawed, probably from models I was introduced to when young. That started me thinking about what exactly was expanding, which led to some research, which led to a sudden realization of a model which would, at least for me, work much better. It is only intended to be a visual model of the universe - something to help people visualize expansion in a way which doesn't contradict known facts, and doesn't (hopefully) create misconceptions. From the initial results of the survey, it seems to work quite well for other people, too.
It is not meant to be more than a teaching tool. In my research I found that misconceptions can stunt new learning, which can be crippling in fields such as astronomy and astrophysics, and hopefully this model is easier and clearer.
I can be contacted through email@example.com if anybody needs to get in touch with me. I hope you find the new model interesting.
So here it is:
Our universe was born with two naturally opposite tendencies: gravity, which brings things together, and expansion, which separates them. The question is: What is attracted by gravity and what is repulsed by expansion?
In Figure 1 above the universe is very young. We can see that some galaxies have formed and that these are in turn grouping together to form clusters of galaxies, represented by little patches of dots. Expansion is also going on, but its effect is still small, and it is difficult to see so far back in time.
In Figure 2 the clusters of galaxies can be seen to have formed small bags, lightly warping their local space in a downward direction. However, now it is expansion which can be seen most. The space between the clusters has inflated notably because of expansion. It turns out that the strong gravity acting in each cluster of galaxies won’t permit expansion inside that zone. Where there are clusters gravity blocks expansion. Only the space between clusters remains free to expand.
In Figure 3 you can see the universe just as it is nowadays, today. Everything, including light, has to go all the way along each curve to travel from one cluster to another. Unfortunately nobody has found any short-cuts yet! If you wanted to go from one cluster to another it would take you four times longer now than it would have in the first figure. Distances have quadrupled.
So the answer to the initial question about what expands and what contracts is that gravity doesn’t let clusters of galaxies, or anything inside them, participate in universal expansion. It is only the space between clusters which expands.
The starting point of Einstein’s general theory of relativity is that gravity – matter – curves space. This has often been represented through visual models. In these diagrams, normally of a cannon ball on a rubber sheet, light is bent towards the object which exerts gravity. Gravity is seen clearly to bend light. This is a visual model which is familiar, and intuitive. Gravity here is seen to distort spacetime downward.
This leads to the question: what happens to spacetime if expansion is accelerating, if there is a cosmological constant which is also distorting spacetime? If gravity tends to attract matter, and accelerated expansion tends to disperse it, accelerated expansion has to be considered instinctively to act in an inverse direction to gravity. Thus gravity and expansion are opposed to each other - immediately, a landscape of mountains and valleys springs to mind.
Basically, the model shows that spacetime is itself progressively more warped, although the overall picture still reflects an approximately flat geometry of the universe (shown by the flat base). This is to fit in with the current paradigm. Nevertheless, the model can easily adapt to a positively or negatively curved universe.
I have also used clusters as the "cut-off" for bound systems, although there is some new research which points to superclusters being the top limit. As the paradigm is still clusters that is what has been used in the text. Obviously this can be adapted if and when necessary.
As far as we know at this time, it is only possible to travel by the "long" route, nothing so far being able to short-cut the distances and travel directly from cluster to cluster. The short-cut would represent wormholes, which is another favourable hierarchical concept in this model. The model also incorporates dark energy, dark matter, black holes and voids as plausible hierarchical concepts.
In the model clusters are taken as the largest structures which do not participate in universal expansion. This is the current paradigm, but there is some debate and it may be necessary to change the word "cluster" to "supercluster" in the future. Here again, the model shows itself to be reasonably adaptable.