Cosmologists predicted that a wrap-around Universe would act like a hall of mirrors, with images from distant objects being repeated multiple times across the sky.
Doughnut-shaped Universe bites back
I came out with this completely crazy hypothesis a long time ago and some people at the time thought it was nuts. I’m not saying it’s true (chances are that it’s not), but I do think it’s something worth considering. The reason I bring it up is because, while this quote does not directly support my crazy hypothesis, at least it doesn’t contradict it (which kinda made me think that my hypothesis might be crazy enough to be true). My crazy hypothesis assumes the First Law of Thermodynamics is true across the entire universe.
The universe is expanding at an increasing rate. This is often referred to as “spacial expansion” and it is assumed that space itself is expanding. The question is, where does all the energy “come from” to cause everything in the universe to move outward at an increasing rate? Well, all these photons are “exiting” the universe, or reaching the “end.” When these photons reach the “end” of the universe, they "terminate" and this energy is lost. That energy is (at least partly) replaced by accelerated spacial expansion. So part of the quantity of energy that is “gained” from “spacial expansion” is lost when photons reach the end of the universe. What we could try and do is see if we can calculate about how much ‘photon energy’ is reaching the end of the universe and terminating and about how much energy is required for everything in the universe to push outward at the acceleration rate that it does and see if they are roughly the same. Again, this crazy hypothesis is probably false, just something to consider. Also, if the universe is donut shaped, it could be the case that the photons that reach the "middle void" section of the universe also terminate and the lost energy is replaced by the energy required for accelerated spacial expansion.