The question might be unanswerable but I wanted to get people’s thoughts on this. To summarize, Penrose (of Oxford) and Gurzadyan (of Yerevan, Armenia) have said that circular patterns in the CMB (cosmic microwave background) are indicative of there being previous universes (if someone would like to explain the reasoning in layman’s terms, it would be appreciated). However others have questioned this and contend that the patterns are merely products of inflation.
Huh, we saw a paper on that in our journal club, but didn’t notice Penrose on the author list. Had we, we surely would not have summarily dismissed it.
You’re welcome (j/k) 
Whoa. Seriously? I’m just a ‘normal guy’ and although I’ve read a little Feynman and Hawking here and there, I’m not really up on this stuff, but how in the world could any of these background microwave patterns survive the freaking Big Bang? It would seem to me that you could think of the patterns as information, sort of, and I would have thought that in the infinite crunch-down that happened before the Big Bang happened, everything would have pretty much been reset to zero! I might have to go and read up on this stuff…
Then what are you doing here?
Penrose has been making a bit of a splash with his Conformal Cyclic Cosmology recently, but it’s fair to say that the whole idea is extremely speculative at the moment. The gist of it is that after a sufficently long time (and that means a really long time here), all matter will have decayed to radiation (which necessitates some new process to get rid of ordinarily stable particles like electrons), which in a sense lacks a sense of scale – it is conformally invariant, hence the name. However, this means that this cold, dilute state is effectively indistinguishable from a very hot, dense one, and hence, may be taken to constitute a new big bang!
Or at least, thats the idea. As I said, it’s almost complete speculation, and if Penrose weren’t Penrose, I don’t think there would be much discussion about it.
As for those CMB circles, it’s a big dataset, and people have been finding all sorts of things in it (like Stephen Hawkings initials), so I wouldn’t read too much into it. The model does predict such circles (causes by gravity waves IIRC) however, so it’s not a priori impossible for some structure to ‘pull through’ across the big bang despite its violence.
I do suspect our average reader will need that sentence to be expanded upon just a bit.
He’s saying that, without anything left to measure lengths with, lengths can be anything. So, this:
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is indistinguishable from this:
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because the first one could just be the second one “zoomed in” on. If there truly are no well-defined length scales to measure density with, then density could be anything, including infinite.
(Note: I’m just explaining the comment, not championing any particular theory of the universe.)
Okay, I get that. But, to me thats sounds like a fancy version of “does a falling tree make a sound if nobody hears it” sorta thing.
Or, lets put it this way:
Lack of obvious scale (because everything looks the same at any scale) = scale can be whatever you want, which means a super thin cold gas now equals super hot dense one because we can now use any ruler size we want?
I’ll need a little more tap dancing to be convinced…but then again, it will probably go over my head in short order as well…
Though it does occur to me that there could be some sort of “reset” in the universe’s ruler. The fabric of spacetime get stretched enough or the gas/energy gets uniform enough and through some mechanisim the scale of spacetime jumps way up in size because that new value is now the more stable/lower energy one. Or something like that.
Of course, you’d need more than just for the particles to decay. You’d also need for the rules governing the particles to decay. Even if all the electrons were to go away (annihilated with positrons produced from proton decay, say), the laws of physics would still have the potential for electrons. And all those potential particles could set a length scale.
This is why I like physicists. I think this is a wonderfully rational attitude.
Is this the same as having entropy reach a maximum?
If I understand you correctly, then you share my suspicion of explanations that are purely anthropomorphic in nature. What I mean (and what I think you’re saying) is that just because you lack a frame of reference, that doesn’t mean that all things become possible which were not possible before.
No, I’m saying that unless something very weird happens, you don’t lack a frame of reference (or more precisely, a characteristic scale) in the situation Penrose describes. I don’t see what anthropic arguments have to do with it at all, and anyway, depending on how they’re constructed, some anthropic arguments can be perfectly valid.