cyclical cosmology debate keeps on cycling…
Cosmologists are still puzzling over faint signals in the CMBR that may or may not be there and indicate profound events in our past or to our future.
Since we last discussed the universe according to Roger Penrose, I thought the physics community wasn’t going to dedicate more time to the theory of cyclical cosmology, but apparently, I was wrong. It seems that the theory still lives and is being debated by scientists trying to figure out whether the concentric circles that could be spotted in CMBR maps mean anything significant, or if they’re just artifacts from the kind of anomalies we can expect after a Big Bang. Meanwhile, picking up on the criticism offered by many physicists about the need for a trigger to multiple incarnations of the universe, Penrose brought up a potential explanation for how we’d get an old universe out of gas to suddenly leave an imprint on a new one. Now, one could certainly see how a cyclical cosmology would be attractive. It all but eliminates the question of the source of the mass and energy behind the Big Bang, pointing back to the previous universe. However, were we to look past that, we’d find the theory making matters much more complex, especially when it comes to the cosmic reincarnation scheduled whenever entropy gets too low because the mechanism now given for it only introduces new problems.
First, let’s recap. When famed physicist Roger Penrose and his colleague Vahe Gurzadyan looked at a model of the cosmic microwave background radiation, or the CMBR, the universe’s first echoes of activity which give us the ability to see back to the very dawn of time as we know it, they spotted what resembled big, concentric circles of cooler temperatures. They then proceeded to theorize that these circles could well be scars left over from ancient Big Bangs and that each of them happened when a universe before them cooled and died. Their chosen method for explaining how this would work was to correlate low entropy just after a Big Bang and a similar state after an old universe has cooled completely, and leave it at that. In essence, they were saying that because countless tons of trillion degree quark-gluon plasma have an entropy value similar to that of icy nothingness, we can just flip the two and presto, a new universe is born from nothing, kind of like your can of pop suddenly turns into a fireball after you leave it in the freezer too long. So as you can imagine, cosmologist after cosmologist couldn’t figure out how Penrose actually expected the cyclical universe to work and how his past and future Big Bangs were being generated. They also couldn’t figure out what made those circles such unique features and noted that using current models also produced these features which puts their status as traces of something very special and significant in question. Why would they matter in the big picture?
Now we’re being told that these concentric circles are collisions between supermassive black holes from an earlier universe leaving anomalies in our current cycle. This is a puzzling statement to make since it means a few stray supermassive black holes will register on the CMBR of a new universe but past Big Bangs won’t, as well as clashing with Penrose’s earlier assessment that these features are evidence of other Big Bangs, not just activity in the previous universe. Maybe a collision of some ancient supermassive black holes triggered a birth of a new universe? After all, if a black hole is big enough and lasts long enough, it will eventually shed so much of its mass by Hawking radiation that it will no longer be able to self-gravitate, spewing out something a lot like raw quark-gluon plasmas which could then undergo baryogenesis and condense into matter. After all, the universe is expected to spend the vast majority of its time as a cold, empty stretch of vacuum dotted by an occasional supermassive black hole, and given the sheer length of time involved, even stranger things might happen. So we’ve got a plausible mechanism for cyclical cosmology then, right? Not so fast. Black holes are not magic and they don’t simply appear out of nowhere. Either vast clouds of hydrogen or an incredibly heavy star will need to collapse into one and it will take millions of years of feeding and collisions to grow one huge cosmic singularity. After it evaporates, it should release less matter then the universe that birthed it.
Using supermassive black holes as progenitors of new universes means that the amount of matter available for each new universe shrinks exponentially, and we’re actually on a course to a universe that will stay in near perpetual entropy after it cools off into nothing. And that brings us right back to the first Big Bang rather than a set of cycles which keep the universe bouncing back from its low entropy end. This may be why Penrose isn’t using black holes as his Big Bang generators, just as a source of gravitational waves to create little ripples in the CMBR map. However, we already know that a universe right after the Big Bang should have tiny variations since the blast itself did not need to be perfectly uniform and the tiniest little quantum fluctuation at the instant of the explosion could’ve left a major mark on the new universe as it expanded. And when modeling those tiny fluctuations, we also find concentric circles of slightly cooler temperatures in the CMBR without black holes of dead universes or complex cyclical cosmologies which imply bizarre universes that resurrect themselves. It’s not that there’s no way that we couldn’t all be children of primeval supermassive black holes starting a whole slew of Big Bangs or that the universe can’t be cyclical. It’s just that we have zero real evidence for these ideas past Penrose’s models and his repeated statements that his critics just don’t understand his work.
See: Moss, A., Scott, D., & Zibin, J. (2011). No evidence for anomalously low variance circles in the sky Journal of Cosmology and Astroparticle Physics, 2011 (04), 33–33 DOI: 10.1088/1475–7516/2011/04/033