Ok, well since most people said might as well say what theory I have for the Universe, here's an idea I came up with one day about 10 years ago while bored, probably stuck in traffic.
The main problem with the present theories involving the big bang, is that it views the Universe as a (comparatively) linear trajectory. Big Bang came about 15 Billion years ago, expanded quickly in all directions, all galaxies, stars, life (eventually) started from that point.
Three main problems with this. One, is the presence of 'dark matter.' Scientists cannot explain why the universe is expanding at an ever increasing rate (accelerating), even some galaxies are going faster than models predict, so they assume there is much much more matter in the universe than visible. Of course there is SOME unseen matter (like brown dwarf stars), but thus far there is mere speculation that unknown or nearly weightless particles (like neurtrinos) are responsible for the gap in the mathematics.
The second problem relates to the first, is the acceleration detected of the universe, meaning not only is the Universe expanding, but it is expanding at greater speeds. Let's assume the data's correct on that
The third problem, is there is no real explanation for why the Big Bang started in the first place, and how this relates to whether the Universe will start over again at some point and time in the distant future.
Now, my problem has been with these theories is that it is predicated on a 3 dimensional (or 4 dimension depending POV) version of the UNiverse. What the published models fail to consider, and what is a more interesting model that may account for the 3 'problems' above, is to establish a model for the Universe, that contemplates a Universe that has a mostly 'fixed' shape that matter arising from the Big Bang will follow. There's precedent for the idea that certain 'shapes' are natural in the universe, such as spirals for most galaxies, or even hexagons that are found in honeycombs or snowflakes, that come out of the a type of math involving circles accumulating as various sides of an object, depending on how many sides. In this case, the Universe has a shape, that affects our readings of the Universe itself, particularly the farthest corners of the Universe.
So, the way to view the Universe, should probably be from the most basic shaped form, which is spheroid, but view the 3rd-4th dimensional Universe as beginning on a point on a 5th dimensional spheroid. (Probably near the top of the spheroid.) So big bang hits ~15 billion years ago. It expands as scientists say. But the Universe has a pre-existing pattern that is essentially spheroid from a 5th Dimensional viewpoint. So picture the impact point of the Big Bang as say, New York on Earth. So that 'pattern', is the trajectory that matter in the Universe will follow, which ever so slightly over billions of years, will actually swerve along the spheroid path. There probably will be more movement alongside the natural pattern of the spheroid, but will also have some movement up and down, though not as much. (This point is something I'm not sure of is necessary for concept to work)
At the present, let's say that a 1/4th to a 1/3rd of the spheroid has been engulged with 'matter' from the Big Bang. (Using New York on Earth analogy, we are now from Hawaii to Cairo, with some matter arching below and above) This is enough for one of the four forces of nature, gravity, to begin having an outsized effect on the entire universe,since matter from one side of the Universe is pulling on the other side of the Universe. (From the vantage point of the spheroid.) Furthermore, the natural shape of the spheroid may increase the speed of the Universe moving along or near the surface of the spheroid.
From the effect of gravity, moving along the spheroid surface, eventually the Universe will reach a different part of itself. I think that different theories could abound from this, including that gravity will contract the Universe eventually. I have some thoughts on this as well, but it would seem to provide an alternative theory to the simple explanation that if the Universe is continuously expanding, that it will expand forever.
Thoughts? Problems with theory? Suggestions?