Coming up on Sep 10

Rad Antonov

And also, thanks Future Lab Tech Lab for posting the link and getting the discussion going.

I've always been partial to cyclical/bouncing cosmologies, but not for any science reasons, merely because I prefer a universe that was always here, even if the state of the universe changes radically over time. When it comes to the contraction that Paul Steinhardt outlined and then mapping onto the "bounce" and the resulting expansion, I wonder how analogous the situation is to core collapse in massive stars. The core of a, say, 15 solar mass star has enough gravitational potential to break electron degeneracy pressure and collapse down to a 20 mile diameter, give or take, but then the equation of state hardens due to an effective neutron degeneracy pressure and the infalling stellar mantle "bounces" off the suddenly stiff core. If the initial star was, say, 80 solar masses, the collapsing core has enough energy to break neutron degeneracy and, voila, a black hole is born. In a contracting universe, and maybe I'm just being ignorant here, I would expect the highly dense contracting material to be self-gravitating and go straight to a singularity, do not pass go, do not collect $200. Yes, there's lots of interesting quantum physics on the way to the singularity, but I expect a singularity nonetheless. Perhaps my ignorance here is that a massive stellar core is a thing in space that is contracting while for the Steinhardt et al. cosmology, it is space itself that is contracting and, therefore, the stellar analogy doesn't hold. Thanks for the excellent link Future Tech Lab, if you keep this up, you will be challenging Rad for Link King around these parts.

Rad Antonov

Very much in the same camp: if it explains everything, it explains nothing. Except, I came across an older paper recently that I feel is of a different ilk than most. As a matter of fact, so was one of its authors. That probably gives away who it was, but I’ll refrain from mentioning it until we’ve seen the episode and I’ve had a chance to noodle on it some more.

Rad Antonov

What I like about the bouncing cosmology that Paul and Anna Ijjas are proposing is that it can be ruled out by the detection of a particular type of polarization in the CMB. The Simons foundation funded a new observatory in the Atacama desert that will among other things look for this B-mode polarization. Anna spoke to Brian Keating recently. He tells a great story about the search so far in his first book. This is the link to their discussion: https://www.youtube.com/watch?v=aGlLjq4OcmE&feature=share&utm_source=EJGixIgBCJiu2KjB4oSJEQ

I recently saw a talk an alternative Big Bang by Paul Steinhardt. The most compelling part of the talk mentioned that under the new proposed model there would be no quantum fluctuations to produce universal branching, thus no multiverse. https://www.youtube.com/watch?v=S7-HNi2ne44

I once watched Sean Carroll run through a mathematical argument for the plausibility (likely probability?) of multiple universes, but I don't remember much about it now. Math =/= physics and plausible =/= actual. Being currently untestable, the idea of a multiverse does not even rise to the level of a hypothesis.