I’m reading Our Mathematical Universe (2014), by Max Tegmark, and I’ll post about the book when I finish. However he got my attention early with the topic of eternal inflation. That got me thinking about how there are some key unanswered questions regarding the Big Bang and inflation of the non-eternal sort.
Inflation certainly does need some explaining. It may be related to dark energy, as both seem to do the same sort of thing (push space apart). The putative physics of inflation is bad enough; eternal inflation is (in my view) fairy tale physics.
For one thing, eternal? Seriously? Infinite something from nothing?
It’s hard enough to justify something from nothing in the first place. The idea this entire universe sprang from nothing is hard to swallow, but appears to be a fait accompli.
Infinite universes we can’t observe is a whole other level of story telling.
The inflation story makes some sense once one accepts an axiom: A smaller-than-an-atom speck of, as Tegmark puts it, hard to dilute matter came to exist.
The consequence of such matter, once it exists, is enormous pressure driving the matter to expand. The hard to dilute part means it quickly doubles in size without noticeably reducing its density.
This means it will double again. And again. Until it reaches the point it finally does dilute enough that density drops, and the period of rapid inflation ends.
If we can accept such magic matter, inflation makes sense. Note this special matter doesn’t expand into space, it expands to become space and everything in it.
Which you can see leaves a lot of unanswered questions and unknown physics. Not everyone agrees inflation is correct, although it does answer some questions the Big Bang alone cannot. I’ll come back to that.
Eternal inflation says that inflation never stops, it continues forever outside our universe where it creates an infinite number of new “bubble” universes (Tegmark’s Type II multiverse).
In this scenario, specks of “inflatronium” (my term, not Tegmark’s) freeze out and turn into expanding bubble universes. It’s perhaps a bit like how yeast creates air bubbles in rising bread dough.
Effectively, normal inflation involves a bit of weird matter appearing and blowing up into a universe, whereas eternal inflation involves infinite weird matter already existing and spawning infinite universes.
If any of that offends your sensibility, you’re certainly not alone, but sensibility can’t be our guide. We can certainly wonder about some things, though.
Question: Was there a Big Big Bang that created the inflatronium? Tegmark seems to suggest so, but doesn’t go into details. Are there two things: the BB Bang and an infinite number of B Bangs?
Question: In the bubble, there is a brief time of inflation, which ends. Outside the bubble, there is eternal inflation, which doesn’t. Two things again?
Question: Why does a bubble universe form from expanding inflatronium? What causes the speck to freeze out? Is the speck different from the base?
Question: What is the difference between the physics of the greater spacetime inflatronium inhabits and the physics in our bubble?
Question: Is this inflatronium a perpetual motion machine? Not just running forever, but creating an infinite number of new things?
There now seem two creation events to account for: The creation of inflatronium and the creation of bubble universes. There are also a number of infinities to account for: eternal inflatronium and the infinite space it’s creating, an infinite number of universe bubbles, and (apparently) infinite space inside each bubble.
My point is that it’s one thing to accept the idea of a speck of über-matter springing into existence, blowing up until it dilutes, and then coasting thereafter on the energy of the bang.
It raises a lot of questions, but there are observational facts about the universe that need a story explaining them, and the Big Bang story does fit the bill rather well.
(And I’m certainly not the first to observe the parallels with Genesis 1 in the Bible. As a childhood astronomy and physics geek, I always thought “Let there be light!” sounded an awful lot like the Big Bang story.)
It’s another proposition entirely to accept infinitely expanding matter spawning an infinite number of infinite universes. Not saying it’s wrong, just that, at least in my view, it’s a much bigger ask.
(As an aside, Tegmark’s Type I universe requires our bubble universe be infinite in size, and I’m just not sure that’s right. Give how much of his argument rests on [A] our infinite Type I universe, [B] infinite Type II universes from eternal inflation, and [C] infinite universes from MWI, his arguments seem on a superposition of shaky ground and thin ice. I’m not a believer in infinite.)
((All this infinite stuff seems to violate the rule of parsimony. The Type I and Type II infinities don’t even have the Everett Excuse of “just following the math, boss!”))
One thing that makes inflation attractive is that it explains why the Cosmic Microwave Background (CMB) is so uniform.
Under a non-inflationary Big Bang scenario, there isn’t time for energy in the universe to equalize, so under such a scenario, it’s thought there should be much more variation in the temperature of the CMB. This is called the horizon problem.
It’s also hard to understand why observations indicate space seems to be extremely flat. But theory indicates that level of flatness is like balancing on a razor — it requires forces cancelling to 120 decimal points to balance. This is called the flatness problem.
The notion that the universe underwent a brief period of rapid expansion solves both problems rather neatly.
In the first case, the universe was much smaller and able to equalize before it blew up hugely fixing that even temperature. In the second case, the rapid expansion flattened space just like the surface of an expanding balloon seems flatter and flatter to an ant on its surface.
I wonder if the first case gets it slightly wrong. I wonder if the evenness of the CMB is simply from the universe being very uniform at first.
There is a perception the universe must have started with very low entropy, because our observation is that entropy always increases. Therefore it had to be lower in the past and lowest at the beginning.
Perhaps the assumption things needed to mix in the beginning is incorrect. Perhaps the original speck of matter was as uniform, as low in entropy, as matter can be. So it’s not at all surprising the CMB is so even.
In fact, it was only in the expansion of space that quantum uncertainty allowed variation — variation that ultimately led to stars and galaxies.
Bottom line, this undermines the notion that inflation is needed to account for the evenness of the CMB — which, in turn, undermines the notion of inflation.
If the observed flatness of the universe can be otherwise accounted for (maybe it just is that way), the notion of inflation is further undermined. It’s important to understand that inflation is a story about the past that accounts for what we see now. Another story might be more correct.
Which is all to say that, if inflation is not demonstrable fact, then eternal inflation is on even shakier ground. And given its (literally) expansive nature, it has to be seen as a whole other proposition.
All of which is very idle speculation on my part. What’s interesting is how it connects with another idea I’ve read about recently.
I’ve written before about the stark difference between countable numbers and uncountable numbers. I’ve also written about how it’s possible reality doesn’t use the real numbers (the uncountable ones).
If that were true, it would eliminate strict determinism. It would make the future definitely and truly unknowable.
I’ll blog about this in the future, but I read an article about a mathematician exploring the idea that the real numbers aren’t real — that reality uses rational numbers.
A core idea here is that infinite precision of a numeric value represents infinite information — which is questionable. There is only so much information that can be contained in a given area.
I need to read the article again and maybe look deeper into the idea, but I was really struck by how it fit in with the ideas I’ve played with recently.
Stay banging big, my friends!