“We are part of the universe that has developed a remarkable ability: We can hold an image of the world in our minds. We are matter contemplating itself.” -Sean Carroll
If you take a look at our Universe today, you can learn all sorts of things about it. How the matter in it is distributed, what the radiation is doing, how many and what types of black holes we’ve formed, how much entropy there is, etc. You can also learn how all of those things are evolving into the future and how they were different in the past!
The far distant fates of the Universe offer a number of possibilities, but if dark energy is truly a constant, as the data indicates, it will continue to follow the red curve. Image credit: NASA / GSFC.
And if we go all the way back, we find that in General Relativity, we expect to wind up at a singularity at some point in the beginning. In a quantum formulation of gravity, that isn’t necessarily true! There are four classes of ways to avoid a singularity in the beginning, where space and time always exist, rather than having a creation or emergence. But many of the four have serious, fundamental issues that may yet make them impossible.
In classical general relativity, singularities are hard to avoid. But in quantum theories of gravity, such as those with extra dimensions, bouncing scenarios are possible. Image credit: Wikimedia Commons user Rogilbert.