Bouncing cosmologies
There are not so many credible alternatives to the now-accepted inflationary paradigm, in fact the only known possibility replies on having a contracting phase followed by a bounce leading to the currently expanding epoch. Although both contraction and expansion are easy to implement in the framework of general relativity, a bounce requires more work, and I’ll discuss some attempts that have been proposed, emphasising the expected cosmological consequences at a time where observational data provide very serious constraints.