.In “Pop Goes the Universe,” by Anna Ijjas, Paul J. Steinhardt and Abraham Loeb, the authors (hereafter “IS&L”) make the case for a bouncing cosmology, as was proposed by Steinhardt and others in 2001.
Near as I can say, the bouncing universe idea (that it expands, contracts, re-explodes) CAN’T be tested. How would you test it? Each new “bounce” would wipe out the traces of the last one.
BUT if they can refine the data, it IS possible to test the idea of expansion (ie. the idea that the universe expanded at an amazing rate early in the big bang process). That’s because they’re looking at a discrete one-time event that, it is argued, left traces and evidence, IF you can refine your tools to the point of being able to detect it.