http://www.perimeterinstitute.ca/seminar/rethinking-cosmology In five days Paul Steinhardt (Princeton) will give a colloquium talk at Perimeter. He has a 90 minute timeslot. Steinhardt has been a proponent of "brane-clash" cosmology. Sometimes called Cyclic or Ekpyrotic. Two spatial hypersurfaces floating in higher dimensional surroundings repeatedly bump each other. Steinhardt is worth paying attention to as someone who has been both instrumental in the development of stringy ideas and inflation models, and also a mathematically perceptive critic of same. He has shown by fairly general arguments that "curled-up" extra dimensions are unstable during inflation and that prevailing assumptions about inflation make a satisfactory inflationary episode highly unlikely unless there is drastic fine-tuning. ==quote== RETHINKING COSMOLOGY Colloquium Speaker: Paul Steinhardt Wednesday, March 6, 2013 - 14:00 to 15:30 Location: Lazaridis Theatre This talk will begin by discussing one by one the various reasons why cosmologists today consider the big bang inflationary cosmology to be the leading, if not proven, theory of the universe and then explaining why each of these reasons is flawed. This leads naturally to the question: what is the alternative? Understanding the flaws helps point the way. ==endquote== I have a high regard for the challenges to conventional inflation ideas which Steinhardt has posed, even though I do not especially favor the answers he has come up with.